This site serves as a reference point for the Canadian construction industry, with free resources on engineered wood products (ewp). Trusses, I-joists and more are addressed here. Designers, engineers, builders and municipal officials now have a one-stop shop for this information, whether on site or in the office.
You must read the disclaimer before using this site. You must also check for variations within the applicable provincial/territorial building code, from the referenced NBCC content.
Our content is divided into 2 sections:
Our poster-size EWP Regulations Summary (below)
The below discussion of ewp regulations is based on NBCC 2015, the 2014 TPIC, CSA O86-14, and the 2015 Wood Design Manual. Caution is advised , as section numbers in provincial codes can differ from those in the NBCC, despite the content being largely identical. Significantly, section 9.23.13 of NBCC 2015 does not exist in the 2012 Ontario Building Code, which shifts subsequent sections of the OBC down in number.
This page presents the information on a large canvas in order to communicate spacial relationships between ideas. Peruse the info by zooming in on different areas.
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WHY THESE PUBLICATIONS HAVE AUTHORITY There are various sources of authority in Canadian ewp construction, both within and supplementary to the provincial adaptation of the National Building Code of Canada. Part 9 construction must conform to either Part 9 itself; to "good engineering practice such as provided in the CWC, 'Engineering Guide for Wood Frame Construction'"; or to Part 41 . 2 This is as per section 9.4.1.1. 3 - For joist and beam products, Part 9 itself contains some degree of information. The Engineering Guide expands on it, but some topics remain unresolved. For these we will consult other sources of good engineering practice. Of particular note is manufacturer's literature4 . For some brands such as Nordic joist, this precludes literature released by APA - The Engineered Wood Association. Manufacturers who have had their product certified by APA's Performance-Rated I-Joist program will defer certain product details to APA literature, or include near-identical copies of APA content in their own literature5 . - For trusses , Part 9 itself explicitly defers discussion of design to the TPIC's Truss Design Procedures and Specifications for Light Metal Plate Connected Wood Trusses6 . This is stated in section 9.23.14.11(6). Certain details are still dealt with in Part 9, as well as the Engineering Guide. Part 4 contains few details beyond loading, with respect to actual ewp design solutions. Instead it specifies in section 4.3.1.1 that the design basis of Part 4 structures is CSA Standard O86. This standard contains some details of ewp, but it also states, in section 3.3.2, that "new or special systems of design" that it does not cover may be used, provided the design is based on adequate engineering principles. The products we are discussing are examples of such systems and the same resources that we will apply to Part 9 as "good engineering practice" will at times come into play for Part 4 structures. This includes documents from the TPIC and CWC, as well as manufacturer and APA literature. The commonly-known requirement that Limit States Design (LSD) be used for structural engineering in Canada is dictated by section 4.1.3 of the code. In this section the overal process of load analysis in building design is described, and LSD is exclusively referenced. This has been the case in all versions of the code since 1985, after several years of the Canadian construction industry transitioning to LSD in practice. USE OF LIMIT STATES DESIGN IN CANADA Regarding DL , Part 4 says in section 4.1.4 that DL includes the self-weight of structural members as well as the weight of various permanent fixtures, of which a few examples are listed. No actual quantities are given. In this sense Part 4 is even less specific about minimum specified DL than Part 9. We do have access to base predictions of what the weight of DL fixtures will be, by way of the quantities that apply to Part 9. In discussing Part 9 loads we concluded that floor DL should be 10-15 psf, and for roof DL we used quantities found in section 5.3.1 of the TPIC standard. On top of the base floor DL , 4.1.4 says to add at least 1 kPa (21 psf) for the weight of partitions. In practice, it is often obvious that the actual DL that a Part 4 floor will experience will exceed this minimum, so a job-specific DL will be predicted by adding the known weight of each component of the floor composition plus the 21 psf partitions. Equally frequently, a value will be given explicitly in the structural plan. For roof DL , 5.3.1 of the TPIC lists 12 psf (5 psf TC DL + 7 psf BC DL) for Part 4 sloped roofs1 , or 10 psf if the roof has no ceiling2 . The question of LL is answered directly by section 4.1.5, which lays out values to be used for typical, uniformly-distributed LL as well as stating that a concentrated Live Load check must be performed, using the values in Table 4.1.5.9. In the popular CSBuild software, this check is not carried out, and each member must be run through the companion software for individual members, CSBeam, with the option to perform the check enabled. For the uniform LL, Table 4.1.5.3 lists the specified LL to use for different types of roof/floor area. The entries in the table for residential areas are of particular interest. As mentioned in our discussion of Part 9 loads, consultation of Part 4 is actually required to establish Part 9 floor specified LL. It is here that we find the typical residential LL value of 40 psf, listed for all residential areas falling within the scope of NBCC Division A sections 1.3.3.2 and 1.3.3.3 (1.1.2.2/1.1.2.4 in OBC), ie. Part 4 and Part 9 areas respectively.3 . The item "Attics" in the table is also of interest. For Part 4 structures, roofs are required to be designed for bottom chord LL . It is here that we see the value of 10 psf to be used. Note that the item "Roofs" and corresponding value 1.0 kPa can typically be ignored for sloped roofs1 , as its footnote refers to section 4.1.5.5 which says that only the greater of SL or roof LL must be used for roofs without pedestrian traffic. In virtually any context, sloped roof SL will be greater than this value of 1.0 kPa. As for SL , section 4.1.6 gives a more complex formula than that shown in Part 9. Note that the formula is meant to be applied individually to every square foot of roof where the result will differ from the general result at typical areas of the roof; so the implementation of increased loading for snow drift is incorporated right into the formula. The variable Ca takes on higher values in areas where drift will occur. 1 For flat roofs see the separate section.2 The use of 12 or 10 psf total DL for sloped roofs includes joist roofs in common practice, despite being separated into loads for the TC ie. "top chord" and BC ie. "bottom chord" as if only applying to trusses.3 An exception is listed for work areas within live/work units, where 2.4 kPa must be used.PART 4 LOADS 1 When Part 4 is used for a Part 9 structure, the option is given to maintain the loads and deflection and vibration limits of Part 9.2 After these 3 options are listed, it is stated that the latter two options are not valid if the loads specified in these locations for a structure such as that being built exceed 2.4 kPa, unless walls and footings are also designed as such.3 Regarding trusses, section 9.23.14.11 re-states the option to use Part 4, and then seems to adjust the previous presentation of "good engineering practice" as an alternative to Part 9, implying in sentence (6) that both adherence to Part 9 as well as the ability to justify truss design procedures via 3rd party descriptions, is required. An example is then given of a 3rd party source: the TPIC's Truss Design Procedures and Specifications for Light Metal Plate Connected Wood Trusses. 4 The Engineering Guide actually directs the reader, in section 6.3.3.1, to the relevant Product Evaluation Report, which will often in turn direct the reader to product literature. This is the case with Reports issued by the CCMC.5 Even non-members will often have very similar details to those of APA, as a result of the industry-wide process by which standards have been established. This similarity among competing products means it may at times be safe to take inspiration from an APA detail, knowingits sound engineering basis, for a solution involving a non-APA product. APA also issues literature on certain technical topics without specifying that it applies only to APA-rated joists. 6 The version of the TPIC standard which applies to NBCC 2015 construction is TPIC 2014. There are newer versions but they will only be in effect for NBCC 2020. This has been confirmed by representatives for the TPIC, despite the statement in the foreword of the standardsaying that previous versions are obsolete. SELECTION OF BUILDING CODE SECTION Division B Section 3.1.2.1 of the NBCC specifies different building "occupancies" - for example Residential. EWP, and combustible material in general, is permitted as a building's primary material when dictated by Division B Section 3.2.2, which makes reference to the occupancy, number of stories and a few other criteria. Eligible buildings fall under B(2) (Treatment occupancies), B(3) (Care occupancies), C (Residential), D (Business and Personal Services) and E (Mercantile). Prior to NBCC 2015, provincial codes had begun to allow buildings up to 6 stories (5 EWP floors and an EWP roof), as exemplified by a well-known January 2015 amendment to the OBC 2012. Section 3.2.2 of NBCC 2015 now reflects this progression. A permissible wood building might need to conform to the rules of Part 9 or Part 4. Division A Sections 1 1.3.3.2 and 1.3.3.3 specify which buildings are Part 4 and which are Part 9, based on the aforementioned occupancy, whether or not a building exceeds 3 stories or has a largest story exceeding 600m 2 , and a few other criteria 2 . Whether a building is residential or commercial in nature does not guarantee which building code Part applies. We note, though, that Part 9 never applies to "Assembly Occupancies" which, according to the definition in Division A section 1.4.1.2, include restaurants and schools. We often incorrectly say that Part 9 applies solely to "residential" and Part 4 solely to "commercial". This colloquialism can cause a bit of confusion. For example, in the settings dialog for the CSBeam software, the interpretation is partly correct in that it recognizes that Part 4 structures can be residential. A building type of Residential or Commercial is first chosen, and then the Importance Category options change accordingly with Part 9 and Part 4 appearing as options when Residential has been chosen. However, a selection of Commercial likewise changes the options, with actual Importance Categories as defined in Part 4 appearing. This seems to assume that all commercial buildings are Part 4. It should be further noted that even with residential buildings which are truly Part 9 in nature, Part 4 must be consulted as certain topics in Part 9 refer to Part 4. This results from Part 9 topics being united by their relevance to small residential buildings, while Part 4 is aimed at structural issues in general which can apply to all buildings. Additionally, section 5.2.1 of the TPIC standard dictates that trusses with span greater than 40' must be designed as per Part 4. Likewise, Part 3 contains information relevant to EWP design despite never being a project's officially-designated Part from a structural standpoint. After the above-mentioned building occupancy definitions in 3.1.2.1 and combustible construction rules in 3.2.2, the remainder of Part 3 contains general requirements for ensuring fire safety and general safety in designs. It is for this reason that the Ontario Building Code Matrix includes the option of "Part 3" under the list of project classifications, alongside Part 9 and Part 11 (Renovation). This classification concerns factors of interest to municipal officials, but the actual Part regarding structural information will always be either 9 or 4, and designers are correct to display Part 9 or Part 4 on their EWP layouts. 1 In certain provincial adaptations including the Ontario Building Code, these section numbers are different. 2 We also note that the CWC's Engineering Guide For Wood Construction states in the Foreword that only for Live loads up to 2.4 kPa (48 psf) should the Guide or Part 9 be used; however section 4.2.3.1 contradictingly says that Live loads should follow section 4.1.5 of the code, which offers loads greater than 2.4 kPa for many building areas of which one or more is sure to appear in every commercial building. Since we know certain commercial buildings are permissible in Part 9, this limit of 2.4 kPa seems to refer to only the area of floor in question, not the floor system as a whole. LOADS AT FLAT AND ALMOST-FLAT ROOFS INCLUDING BALCONIES We first note that in addition to using the loads we will discuss here, roof truss designers are required by section 6.4.4.7/7.3.2.4 of the TPIC standard to reduce material capacities by 25% and avoid using the modified formula found in section 6.5.13.5 of CSA O86-14, whenever a truss has a pitch less than 2/12 for more than 50% of its top chord. Flat roof loading is a specific case of the general loading rules in Parts 9 and 4, and to obtain specified loads we will look at specific details of those Parts or the materials they refer to. In our discussions of both Part 9 and Part 4 roofs, we drew DL values from section 5.3.1 of the TPIC standard. When a roof is flat, the TC DL increases to 10 psf for both Parts, bringing the total when combined with BC DL to 17 psf (or 15 psf for Part 4 roofs with no ceiling)1 . The SL and LL values of flat roofs without pedestrian traffic are unchanged from those of sloped roofs, for both Part 9 and Part 4. For Part 9 flat roofs with pedestrian traffic, only the greater of SL or 1.9 kPa (40 psf) must be applied as per section 9.4.2.3, provided that the rooftop area in question serves only one dwelling unit. When more than one unit is served (public spaces), both SL and LL must be applied. The LL will be as per Table 4.1.5.3, with the applicable item likely to be "Balconies". Part 4 flat roofs with pedestrian traffic must be designed for the greatest of the following as per section 4.1.5.5: the SL, whichever LL value in Table 4.1.5.3 would best represent the pedestrian traffic (probably "Balconies"), and the most appropriate sub-value in Table 4.1.5.3 under "Assembly areas" (probably the first one listed, which gives the general value of 4.8 kPa). Caution is advised of the fact that this applies to only the roof itself ie. the top surface of the members that support it, and as such it is in addition to the bottom chord LL which will already have been applied if the roof is made with trusses (see our main discussion of Part 4 loads). 1 The use of 17 or 15 psf total DL for flat roofs includes joist roofs in common practice, despite being separated into loads for the TC ie. "top chord" and BC ie. "bottom chord" as if only applying to trusses.DRIFT LOAD Part 9 does not require designing for drift load, as is commonly known. As mentioned in the our discussion of Part 4 Loads, the implementation of drift load is built into the SL equation. Typically the structural plan for a project will provide gradient diagrams which do the math for the designer, to show the decline of the calculated SL as distance to an obstruction increases. USE OF 100 PSF AT PUBLIC CORRIDORS AND STAIRWAYS The common belief is that 100 psf should be used at all public corridors. Table 4.1.5.3, which as mentioned in our discussion of Part 4 loads is the main listing of Live Loads in the code, confirms this for corridors that are considered Assembly Areas; however for more general corridors it indicates that, for those that are above the first storey of a building and not more than 1200 mm wide, section 4.1.5.4 should be consulted. 4.1.5.4 in turn states that these corridors can be designed for the specified LL of the building type they serve. When such corridors are in a residential setting, this means that 40 psf LL applies. While a stairway could be considered part of a corridor, it is more conservative to consider it an "exit" of which it meets the definition in Division A section 1.4.1.2. Table 4.1.5.3 requires that both exits considered Assembly Areas as well as more general exits, 100 psf should be used. This should logically be applied across both landings of staircases and the stairs themselves. FLOOR DEFLECTION CRITERIA Typical floor deflection criteria originates to a surprising degree in simple best practices as opposed to official directives in the code. The L/360 LL deflection used in the design of Part 9 floors is part of Part 9 itself, in section 9.4.3.1. However for TL deflection we must look elsewhere. The Engineering Guide for Wood Frame Construction gives no numeric limit for TL deflection, only reiterating in section 6.1.2 that LL deflection can't exceed L/360, and adding in 6.6 that for beams, an absolute limit of 15mm should be added and TL should be used in place of LL when concrete topping is present. The CWC's The Span Book only repeats the L/360 LL and 15mm absolute limits, while adding that LL limits can be relaxed when there is no ceiling (actually only true of roof members and ceiling joists as per Table 9.4.3.1 of the code). Two more 3rd party sources are relevant: the CSA 086, and the CWC's The Wood Design Manual which outlines design methodologies that apply 086. We also have the option of using Part 4, but as our discussion of Part 4 deflections will show, it actually refers the reader to CSA 086. In CSA 086 we find in section 5.4.2 a general deflection limit for structural members of L/180, with sections 15.2.4, 15.3.4 and 16.3.5 all referring back to this number--but it does not say whether this refers to LL or TL deflection. However, section 2 of The Wood Design Manual which discusses "Bending Members", lists a roof/floor TL deflection limit of L/180 and indicates that this comes from the aforementioned CSA limit. Table D-1 in NBC 2015 Structural Commentary D also refers to this CSA limit as a TL limit1 . We can garner from all this that the actual worst-case TL deflection allowed by code-authorized sources is as high as L/180, with L/240 being a common industry practice. With respect to Part 4 deflections , the relevant sections 4.1.3.4 and 4.1.3.5 both point the reader to Appendix A, the corresponding sections of which in turn pointing to the aforementioned NBC 2015 Structural Commentary D. They also point to section 4.3, the general-purpose section on requirements to be met external to the code itself, which for wood construction equates to CSA 086. But as discussed, the only limit these sources offer is the TL limit of L/180. So there is even less of an official limitation on deflections in Part 4 than in Part 9. Of course a Part 4 structure has a structural plan which should specify deflection limits as per the project engineer. 1 See footnote (5) of this table.ROOF DEFLECTION CRITERIA INCLUDING FLAT ROOFS, JOIST ROOFS AND BALCONIES For Part 9 truss roofs , section 9.23.14.11 indicates that the deflection to be checked is that of the entire truss span when loaded with ceiling load + 1.33SL for 1 hour, and gives limits in a table. Sentence (6) of this section then states that truss design procedures must be justifiable via 3rd party descriptions, offering as an example the TPIC's Truss Design Procedures and Specifications for Light Metal Plate Connected Wood Trusses. In Table 6.6.2 of this standard, the row for "Bottom chord truss joint or panel" shows verification of the tabulated values in the code1 , but without mention of the 1 hour time span on the deflection resistance or the optional L/180 limit for those non-plaster/gypsum ceilings with a span less than 4.3 m, and with an extra limit of L/180 given for when no ceiling is present. Limits are also given in the other table rows for specific parts of the truss. Note that often design software programs do not simply check the deflection of Part 9 trusses when loaded with the 1.33SL + ceiling load mentioned above, but in fact run through all load combinations for Ultimate Limit States (of which Load Case 3 will always be a worse-case than 1.33SL + DL), checking predicted deflection for each one. This can be seen in the results dialog box shown in Mitek's Engineering program, when a truss is run. A truss roof will also have a measurable horizontal deflection . This is not mentioned in Part 9 of the code, but Table 6.6.2 of the TPIC standard contains an absolute limit of 1" on horizontal deflection. For joist roofs , the stated deflection limits for Part 9 are set in Table 9.4.3.1 of the code, and require the joist model under consideration to be loaded with all non-DL (this may include LL, SL or both as mentioned in our discussion of flat roof loads). The L/360 limit listed here for rafter and joist roofs with a gypsum ceiling (virtually all roofs that joist designers encounter) is commonly known and used by joist designers for roofs. A notable exception listed is balconies and decks serving single dwelling units, which need only meet L/240. Beyond these stated limits, we must also note the two other possible origins of Part 9-compliant practices beyond Part 9 itself: Part 4, which as discussed below reveals little; and "good engineering practice". As explained in our discussion of floor deflection, the only authority on good engineering practice offering a further deflection limit is CSA 086, which gives in section 5.4.2 a general limit for any structural member of L/180. Section 2 of The Wood Design Manual and Table D-1 in NBC 2015 Structural Commentary D2 both imply that this limit is for Total Load, and design software programs typically provide a setting for the TL joist roof deflection limit, as they do with floors. For Part 4 structures there is the L/180 TL limit explained in our discussion of floor deflection criteria. In addition, for truss roofs the table in the TPIC standard used for Part 9 roof deflection also contains limits for Part 4. The truss model being compared to these limits is to be considered with several factored load combinations applied, as the "Loading Used" shown atop the Part 4 column is VL+DL (VL refers to the non-DL portions of the combinations for Serviceability Limit States shown in Table 5.1.3.23 ). The exception is the row for "Bottom chord truss joint or panel" ie. the deflection of the truss as a whole, where each value listed is indicated as requiring the truss model to only include DL or VL. This expectation that designers model the truss in three different ways is the reason truss design programs provide settings categories for LL deflection limits, DL limits and TL limits, as seen in the Deflection dialog box of Mitek's Engineering program. The horizontal deflection of a Part 4 truss roof should not exceed the 1" limit found in Table 6.6.2 of the TPIC standard. For Part 4 joist roofs , the structural plan for the project usually also provides explicit deflection limits from the engineer. 1 The table actually presents these limits as applying to a truss loaded with 1.33SL + 0.5LL + DL. DL can be interpreted as ceiling load. The code presumably leaves out mention of the LL since it no longer requires trusses to be loaded with LL.2 See footnote (5) of this table.3 Not to be confused with the more commonly-discussed combinations for Ultimate Limit States which are in Table 5.1.3.1RULES REGARDING TRUSS PLATES Rules regarding the materials used and physical properties of truss plates can be found in CSA O86 section 16.4, while rules regarding the measuring of truss joint strengths where plates are used can be found in section 12.8. The latter is applicable to the establishment of published design strengths for plates, as well as the selection of plates in the design of individual trusses (usually plate selection is done by software and hidden from the designer). Being part of CSA O86 these contents directly apply to Part 4 construction. For Part 9 construction the TPIC section "Joint Design Procedures" is a duplication (and expansion) of the information in CSA O86. The latter of the sections mentioned above is also given authority for Part 9 by section B sentence 1.6.4.2 of the Engineering Guide for Wood Frame Construction. TRUSS BRACING (PERMANENT AND TEMPORARY) Under Part 9 , bracing of entire trusses and of members within them is outlined in section 6.7.5 of the TPIC standard, which references a publication called “Building Component Safety Information” by the American groups the Truss Plate Institute and the Structural Building Components Association. Section 9.23.14.11(3) and (4) of the code add a requirement for long webs. Section 9.7 of the CWC's Wood Design Manual contains largely a reprinting of the information in the TPIC standard. Neither Part 4 itself nor CSA O86 deal with truss/member bracing, so the same sources should be sought as with Part 9. BASIC MINIMUM BEARING LENGTH OF BEAMS There is a commonly-stated rule that the code requires beams to have at least 3 1/2" of bearing length (except, obviously, where the calculated bearing length required is greater than this). In reality, this applies more specifically to beams falling under Part 9, supporting floors (including those also supporting roof, we can assume). Additionally, the statement of this rule--in section 9.23.8.1--adds that beams sized using the code's span tables are an exception, as these tables have their own bearing requirements in their footnotes. For Part 9 beams supporting roof but not floor, Part 9 gives no base minimum lengths, but for beams sized using the tables minimums are given in the footnotes. Without explicit minimums for beams supporting roofs in general, we note the option to consult Part 4 as mentioned in our discussion of Part 9 loads. However Part 4 does not give explicit minimum lengths either, for floor beams nor roof beams. No minimum bearing lengths can be found in CSA O86 either. So it seems that the 3 1/2" minimum bearing length for Part 9 beams carrying floor is the only such minimum in the code. USE OF MID-SPAN BRIDGING AND BLOCKING The use of blocking or bridging at mid or mid and third spans, sometimes accompanied by a requirement for a strap or drywall ceiling below, may be needed to satisfy the requirements of the CCMC vibration check (see the separate section USE OF THE CCMC VIBRATION CHECK). USE OF BLOCKING UNDER NON-LOADBEARING WALLS The use of blocking under non-loadbearing walls running parallel to the joist direction, is as per NBCC section 9.23.9.8(1) and (2), and manufacturers' details. For Part 4 structures these details should be treated as a minimum standard by the project engineer. MAXIMUM SPACINGS BASED ON ROOF/FLOOR SHEATHING USED 1 since Part 4 structures must account for wind load and often seismic load. See the section LATERAL SUPPORT COMPONENTS for more information.For Part 9 floors , Tables 9.23.15.5.A and 9.23.15.5.B give minimum sheathing types for various common floor spacings. Plywood and OSB products may conform to either the CSA standard specific to the type being used (e.g. O151 for Canadian softwood plywood), or to CAN/CSA standard O325.0 Construction Sheathing. Table A applies to sheathing conforming to a type-specific standard, and table B applies to that conforming to O325.0. Therefore the standards-compliance of the sheathing in use must be known before the allowable product-spacing combinations can be known. Also note that while it is commonly believed that the maximum spacing depends only on the thickness, for the most part these tables contain entries for the grades of sheathing defined in the standards, and only after the appropriate grade has been looked up do the thicknesses appear as sub-entries of the grade (and only in Table A, as O325.0 defines only grades, with manufacturers free to make products meeting a certain grade with any thickness provided they meet the performance criteria). For Part 9 roofs , Tables 9.23.16.7.A and 9.23.16.7.B serve a similar purpose to those used for floors. On a Part 4 structure a cost-cutting measure like the use of a greater-than-normal spacing is unlikely to happen; nevertheless with a little digging we can verify that the allowable product-spacing combinations are the same as those for Part 9. We first note that Part 4 itself says nothing about sheathing, however every Part 4 structure contains floor and/or roof systems considered diaphragms transferring lateral loads1 , so we consult the information in CSA O86 section 11 Lateral-load-resisting systems, which we will apply to floors and roofs including those not acting as diaphragms as a conservative measure. Subsection 11.2.1 states that diaphragms are to be made using sheathing panels discussed in section 9 Structural panels, which in turn refers to the type-specific standards and all-encompassing standard (O325.0) that we mentioned for Part 9 sheathing. These standards are used more narrowly than in Part 9: the only OSB standard listed is O325.0, and the only plywood standards listed are the type-specific kinds. However, section 11.2.2 then adds that the type-specific OSB standard O437.0 may also be used. In addition, the section's shear strength tables refer to panels using only thicknesses like type-specific standards, with a supplementary table listing equivalent O325.0 grades and no mention made of which apply to OSB and which to plywood. This implies O325.0-compliant plywood can also be used. All this to say that the same set of sheathing types can be used as for Part 9 applications, and therefore the same product-specific maximum spacings apply. . FASTENING OF FLOOR/ROOF SHEATHING For Part 9 floors and roofs that are not expected to act as diaphragms1 , section 9.23.3.5 gives sheathing fastener minimum lengths and maximum spacings in a table. For sheathing thicknesses up to 3/4", 51 mm (2") nails or 45 mm (1 3/4") screws/ring-thread nails are to be used, spaced maximum 300 mm (11.8") and 150 mm (5.9") along panel edges. The table also permits the use of staples, and gives lengths and spacings. Sentence (4) of the section gives a minimum diameter of 3.2" for floor sheathing screws. We now turn to Part 9 floors and roofs that are expected to act as diaphragms, and Part 4 structures for which we will apply the approach for diaphragms to all floors and roofs as a conservative measure. A diaphragm's sheathing must follow CSA O86 section 11 Lateral-load-resisting systems. In subsection 11.5.3.4 we see the same 300 mm (11.8") spacing of sheathing nails not along panel edges, as specified for Part 9. We are then to consult Table 11.5.2 for spacing of edge nails and nail sizes. Nail lengths are not given explicitly but can be gathered by adding the supplied panel thickness and nail penetration for each table row. In general longer nails must be used than in Part 9. For 7/16" (11 mm) sheathing, the table indicates that 1 5/16" (38 mm + 11 mm) nails can in fact be used, and for 1/2" sheathing 2" nails are ok. But for sheathing thicker than this longer nails are needed. Regarding spacing of edge nails, we note that the minimum is 150 mm as with Part 9, but optional smaller spacings with higher shear strengths are also listed. Finally, we note that for each table row there is a specified nail diameter, not mentioned in Part 92 . Screws are not mentioned anywhere in this section. It seems that sheathing cannot be screwed on a Part 4 structure. 1 A Part 9 floor or roof may or may not be expected to act as a diaphragm to transfer lateral loads to shearwalls, as explained in the section LATERAL SUPPORT COMPONENTS.2 As mentioned in the notes to the table, Section A.11.5.1 describes a modification factor for thinner nails.NAILING OF JOISTS TO PLATE For this topic, please first read the section LATERAL SUPPORT COMPONENTS. As explained there, a joist that is part of a floor/roof that must act as a diaphragm or laterally support the wall below, might have different or additional fastening requirements. For Part 9 construction, Table 9.23.3.4 in the code specifies nailing of joists to a plate, but does not specify whether it applies to engineered joists or just conventional lumber. Manufacturer publications seem to assume it only applies to conventional lumber, as they tend to specify smaller 2 ½” wire or spiral nails, one driven from each side of the joist. This of course does not apply to joists with high uplift, for which the designer of the floor system should specify a connection. For Part 4 construction, CSA section 15.2.5.1 states that nailed connections should be designed in accordance with section 12.9, “Nails and spikes”. That section deals with the design of a nailed connection from scratch. When a joist reaction is similar to that of a typical Part 9 joist, it might be appropriate to draw upon the solution found in manufacturer’s literature (typically two 2 ½” wire or spiral nails, one driven from each side of the joist), with the assumption that for such reactions this connection has been designed in a way that respects CSA section 12.9. For greater reactions the project engineer should be consulted. NAILING OF EWP BEAMS TO PLATE OR POST In general fastening of beams should be dealt with on a case-by-case basis. Even for Part 9 construction, Table 9.23.3.4 in the code does not contain a specification for beams. Manufacturer’s literature can be consulted, although in some cases it will only show solutions involving special hardware like post caps or details involving end-nailing through king posts, without touching on toenailing. Consideration should be given to whether the beam is part of a floor/roof that must act as a diaphragm or laterally support the wall below. NAILING OF RIMBOARD TO PLATE For this topic, please first read the section LATERAL SUPPORT COMPONENTS. As explained there, a rimboard that is part of a floor/roof that must act as a diaphragm or laterally support the wall below, might have different or additional fastening requirements. For floors/roofs not acting in this way, we see that for both Part 9 and Part 4 construction, we find nothing in the chain of documents with authority until we come to manufacturer’s literature (or APA literature where appropriate). Consult the appropriate proprietary document. Typically 2 1/2" toenails at 6" on centre will be specified. END-NAILING OF JOISTS THROUGH RIMBOARD For this topic, please first read the section LATERAL SUPPORT COMPONENTS. As explained there, a joist that is part of a floor/roof that must act as a diaphragm or laterally support the wall below, might have different or additional fastening requirements. For Part 9 construction, Table 9.23.3.4 in the code specifies that three 101 mm nails should be used for end-nailing of joists through a rimboard, but does not specify whether it applies to engineered joists or just conventional lumber. Manufacturer publications seem to assume it only applies to conventional lumber, as they tend to specify smaller 2 ½” wire or spiral nails, and only one through each flange. For Part 4 construction, CSA section 15.2.5.1 states that nailed connections should be designed in accordance with section 12.9, “Nails and spikes”. That section deals with the design of a nailed connection from scratch. When a joist reaction is similar to that of a typical Part 9 joist, it might be appropriate to draw upon the solution found in manufacturer’s literature (typically two 2 ½” wire or spiral nails, one through each flange), with the assumption that for such reactions this connection has been designed in a way that respects CSA section 12.9. For greater reactions the project engineer should be consulted. NAILING OF TRUSSES TO PLATE For this topic, please first read the section LATERAL SUPPORT COMPONENTS. As explained there, a truss that is part of a floor/roof that must act as a diaphragm or laterally support the wall below, might have different or additional fastening requirements. For Part 9 construction, Table 9.23.3.4 in the code specifies that two 82 mm nails should be used at each truss-to-plate connection. Higher loads, whether downward, uplift or horizontal, will necessitate a more thorough design, and clause 5.9 in section B of the Engineering Guide for Wood Frame Construction gives a bit of commentary in that regard. Design software should alert designers to such further connection requirements. For Part 4 construction, neither the code nor CSA O86 offer specific instructions for nailing of a truss to a plate, so this situation should be seen as a nailed connection that must be designed like any other, as per CSA section 12.9 “Nails and spikes”. With that being said, design software might automate this design or the project engineer may end up specifying the same connection detail as would be used for Part 9. NAILING OF BRIDGING AND BLOCKING Bridging and blocking are used for vibration control, and blocking is used in several more ways. In all cases, manufactuer's literature may have details for the most basic requirements. Blocking is also used under offset loadbearing walls and non-loadbearing walls, and in several other situations discussed in the section LATERAL SUPPORT COMPONENTS. The usages dealt with in that section often have special connection requirements as indicated there. This has to do with the role of a floor or roof in laterally supporting a wall below, or in acting as a diaphragm. DESIGN AND MANUFACTURING OF HANGERS The sources we will site here all refer to hangers as "joist hangers"; it can be assumed that these sources also apply to hangers for beam products and trusses. As section B sentence 6.3.2.2 of the Engineering Guide for Wood Frame Construction states, hangers used in Part 9 structures must be designed as per CSA O86, the same as those used in Part 4 structures. Section 14.5 in that standard details the requirements of hanger design. USE OF HANGERS The sources we will site here all deal with joist hangers. For truss hangers, in the absense of official rulings, the responsible use of CSA O86-approved hangers can be looked upon as "good engineering practice" (Part 9) or "new or special systems of design" (Part 4). For Part 9 structures, section B sentence 6.3.2.2 of the Engineering Guide for Wood Frame Construction permits the use of hangers in joist floor systems, provided the hanger is at least 50% of the joist depth and has been designed as per CSA O86. For capacities, designers should consult the manufacturer's catalogue. For Part 4 structures, hangers are permitted by virtue of CSA O86 section 15.2.5.2 for joists and 15.3.5.1 for structural composite lumber. Both of these sections make reference to section 12.10, which contains details governing use. For capacities, designers should consult the manufacturer's catalogue. USE OF THE CCMC VIBRATION CHECK For traditional solid-sawn joists, a methodology for checking vibration exists in section A-9.23.4.2 of the National Building Code of Canada. In the Part 4 Building Code Structural Commentary D, the methodology from A-9.23.4.2 is recommended while also recommending the Applied Technology Council's "Design Guide 1, Minimizing Floor Vibration". For pre-engineered i-joists, CSA 086 section 5.4.5 indicates that a modified approach is needed, but the only sources recommended are the aforementioned Part 4 Commentary and the Wood Design Manual, which simply points to A-9.23.4.2 in section 2 "Bending Members" and actually describes it in section 11. It seems that neither the code nor the CWC wish to specify an official process for checking vibration. As such the process described in the CCMC document "Development of Design Procedures for Vibration-Controlled Spans Using Engineered Wood Members" has become the technique of choice for predicting vibration. It is used by many Canadian joist manufacturers for span tables and design software settings, and is recommended alongside the old solid-sawn process in section 7.6 of The CWC's The Span Book. LATERAL SUPPORT COMPONENTS (RIMBOARD, BLOCKING, ETC.) For mid-span bridging and blocking used for vibration control, see the sections USE OF MID-SPAN BRIDGING AND BLOCKING and NAILING OF BRIDGING AND BLOCKING. For blocking under non-loadbearing walls, see the section USE OF BLOCKING UNDER NON-LOADBEARING WALLS. For bracing of truss webs, see the section TRUSS BRACING. NBCC section 9.23.9.3 states that joist bottoms must be restrained from twisting at their ends. For I-joists, section 2.4 of the CWC's Wood Design Manual refines the requirement by stating "Top and bottom flanges must be laterally restrained against rotation". Joist manufacturers' literature prescribe solutions to accomplish this, beyond the simple techniques like toenailing that the code suggests. This has lead to various requirements placed on users of I-joists, involving the use of components like rimboard and blocking, installed according to specific details. Literature has also addressed the lateral restraint implications of joist mid bearings, and of rimboards where walls run parallel to joists. The solutions prescribed for these situations have one complication in common: they are subject to change based on one or both of the two conditions that we will discuss next. In other words, there is no universal detail for these situations. The first condition is that the wall on which floor joists bear may or may not be dependant on the joists for its own lateral support. This mainly occurs with foundation walls. The second condition is that the floor may or may not be considered a diaphragm that must transfer lateral loads to shearwalls. Part 9 wind and earthquake bracing is covered in section 9.23.13 of the NBCC, but some provinces like Ontario choose not to enforce this section by not including it in their provincial codes. Where this section is enforced, it involves in the simplest case a procedure involving the composition, dimensions and locations of "braced wall bands" which are selected stretches of loadbearing wall within a structure. Section C of the CWC's Engineering Guide for Wood Frame Construction offers a similar, alternate procedure for this simple case. While these procedures do not involve explicitly designing diaphragms and shearwalls, certain details of Part 9 floor design in section B of the Engineering Guide, specific to floors that are diaphragms, should now be followed. For structures that demand greater analysis1 , the full Diaphragm and Shearwall subsections within part B of the Engineering Guide are to be followed. These sections include still further floor installation details. Finally we have the greatest degree of required diaphragm/shearwall analysis, which is for Part 4 structures. These require full engineering of these elements, which might require untold floor installation details. The sections that follow attempt to reveal the criteria for lateral support-related situations, in light of both the conditions we've discussed wherever applicable. Note that beams should play the same role in lateral support measures as the joists that surround them, but details are not available for beams in many of the situations we will discuss. Wherever we refer to lateral support solutions for/using joists, it should be assumed that they apply to beams as well. 1 Figure C1 in the Engineering Guide plots the maximum spacing between braced wall bands for which its procedure/the NBCC procedure can be used, for which the Diaphragm and Shearwall subsections of section B can be used, and for which Part 4 should be used; all as functions of a few variables of the structure and site. Section 9.23.13 of the code instead lists only the ranges of these variables for which its contents apply, and later in its braced wall panel specifications the max spacing is shown. FURTHER TRUSS DESIGN INFORMATION For more specific issues in the design of trusses, further reading might be necessary beyond the passages we've referenced elsewhere on this site. For Part 9 trusses, of the documents we've discussed only the TPIC standard contains detailed analysis of truss design. The Engineering Guide for Wood Frame Construction even reiterates, in section B sentence 1.6.4.1, the code requirement that the TPIC be the standard to which trusses are designed and fabricated. When it comes to the design of individual members within trusses, like chords and webs, sound engineering principles of solid sawn lumber design1 should be followed, the source of which is CSA O86. Section 6.5.13 contains some details specific to truss members. Individual members are usually analyzed by design software. For Part 4 trusses, the TPIC standard is a good source of reliable design techniques. As with Part 9 trusses CSA O86 governs individual member design. 1 And of structural composite lumber or glulam design, in cases where these products are used in trusses.FURTHER DESIGN INFORMATION FOR JOIST, BEAM, RIMBOARD & HANGER PRODUCTS Topics not covered on this site have been omitted because they concern engineering questions with answers that are dependent on the material properties of the product involved. Therefore for these topics manufacturers' literature should be consulted. Joist manufacturers literature, for example, will contain detailed rules regarding the placement of holes and notches and the construction of cantilevers, including brick-cantilevers. JOIST CLOSURE AT PERPENDICULAR SIDE At the ends of a joist span (where the joists sit on a dropped bearing, or at the end of the overhang if joists are cantilevered), the typical solution is to install a rimboard through which joists are end-nailed. This serves to support vertical load from above, as well as satisfying the above-mentioned requirement for lateral restraint. An alternative shown in the literature details of most joist manufacturers, is to install solid blocking between joists in lieu of a rimboard (this option obviously has a different vertical load transfer capacity, and is not usually offered for cantilevers1 ). If another joist span approaches and bears on the same dropped member from the opposite side, the two spans will share a single row of blocking where they butt up to each other. With both these solutions, it is important to note that when the floor must laterally support the wall below, a different solution could be needed as per the building designer or the prescriptive design standard used. Section 6.5.1 of the Engineering Guide for Wood Frame Construction makes this requirement official, and section 9.1.1 adds that whatever solution is prescribed is to follow Part 4 of the code. An example of a regional solution to this problem is the Alberta Housing Industry Technical Committee publication "Guidelines for Lateral Bracing of Residential Concrete Foundation Walls". This document contains details for laterally-braced foundation walls, which 1) only support the use of rimboard, not blocking, at the foundation wall, 2) require special nailing and/or connectors at both the foundation wall and the opposite end of the joist when it sits on a beam, and 3) in certain cases require a conventional lumber rim or 1 1/4" thick rimboard at the foundation wall. Likewise when the floor is considered a diaphragm, the ability of the single-rim solution to transfer shear forces may not be sufficient unless refined in some way. Section 10.4 of the Engineering Guide for Wood Frame Construction and section 8.2 of the CWC's Wood Design Manual2 both describe certain shear forces and the special nailing and framing anchors required at the rim to counter these forces. For diaphragm-to-shearwall forces, the APA document "Shear Transfer at Engineered Wood Floors" describes how APA Rimboard is not by itself a sufficient solution. Recommendations are made to add a piece of lumber where the rimboard meets the plate or a shear transfer plate on the exterior side, to accomodate further nailing. To connect a shear wall above to a shear wall below, further details are shown which include doubling of the rimboard. In general a single rimboard or joist blocking where joists are perpendicular to bearing, requires further analysis when laterally supporting a wall below, or when part of a diaphragm/shearwall system. When the blocking we've described is missing in one or more joist space, or when a short section of rimboard has been cut out, it may or may not be structurally acceptable. Designers may be asked to approve such a site condition in order to appease a building inspector. It might also be desirable to move a piece of blocking a short distance away from the bearing, for retrofit or in order to allow the passage of mechanical. For cases where there is no load bearing wall above, manufacturers may offer a general-purpose detail approving these situations. For all other cases, an engineer must assess the situation. 1 A third option is typically offered for cantilevered joists, involving 3/4" wood structural panel in place of rimboard.2 Figure 8.4 seems to show a cantilevered joist, but presumably would apply to any joist running perpendicular to the wall.SUPPORT OF CANTILEVERED JOISTS ABOVE BEARING For closure of the floor cavity at the end of the cantilever, see the section JOIST CLOSURE AT PERPENDICULAR SIDE. In the same way that joists must be restrained from rotating at their ends, section 2.4 of the CWC's Wood Design Manual states that "I-joist bottom flange bracing is required where the joist is cantilevered". In manufacturer and APA literature this is accomplished using blocking, typically shown within an overall cantilever detail that also specifies components like cantilever reinforcement gussets. Some manufacturers such as Nordic release details showing alternate forms of blocking besides solid blocking, so that the overhang is not cut off from the rest of the floor cavity. The section JOIST CLOSURE AT PERPENDICULAR SIDE explains that rimboard or blocking along joist ends, installed typically, may not suffice when the wall below requires the joists to provide it with lateral support, or is a shearwall requiring the joists to act as a shearwall. In these cases, the blocking details for cantilevered joists may likewise fail to suffice. In such cases the project engineer must specify the connection. JOIST LATERAL SUPPORT AT A MID-SPAN BEARING The NBCC does not make mention of mid-span bearings as it does end bearings. The literature of most joist manufacturers specifies that joists can be simply toenailed when there is no load-bearing wall above, while solid blocking must be added when a wall is present. When the bearing is a shearwall, sections 6.5.2 and 9.5 of the Engineering Guide for Wood Frame Construction state that the connection must be sufficient to transfer forces between the wall and diaphragm. The connection should be specified by the project engineer. JOISTS BEARING ON BOTTOM FLANGE OF A STEEL BEAM Most manufacturers issue details for the case where a joist is bevel cut in order to fit between the flanges of a steel beam, where it bears on the bottom flange instead of sitting in a hanger. These details respect and reiterate the common engineering principle of not bevel-cutting an I-joist past the edge of its bearing. Blocking is typically shown, next to or within an allowed short distance (say, 6") from the beam. This satisfies the NBCC requirement that joist ends be restrained against rotation. A manufacturer may or may not allow an occasional piece of blocking to be omitted for, say, the passage of mechanical. On details where no nailer plate is installed on the steel beam flange, glue is typically required between the joist and flange, as well as a strap underneath the blocking. It is important to note that when the beam is part of a shearwall and the floor a diaphragm, the ability of these details to transfer shear forces may not be sufficient as explained in section 10.4 of the Engineering Guide for Wood Frame Construction. The connection should be specified by the project engineer. JOIST CLOSURE AT PARALLEL SIDE Along the edges of a floor system parallel to the joist direction, common sense says that a single, typically-fastened rimboard is not a very secure base when there is a load-bearing wall above. For parallel edges of floor or roof systems without a wall above, this is less of a concern. In practice the most common measures used to address this stability issue are to use a double rimboard; install blocking (often cut-offs) at regular intervals along a single rimboard, either sistered to it or perpendicular running to the adjacent joist; or to install squash blocks at regular intervals. Our goal here will be to identify the more official, mandated requirements for parallel side closure. For a given structure there are several considerations to be made. Perhaps the consideration with the most widespread implications is how to interpret section 9.23.11.2 of the NBCC, which states that "The bottom plate in exterior walls shall not project more than one-third the plate width over the support." It is not stated precisely what the "support" is. In a common installation where the floor framing is joists, on which sits sheathing, on which in turn sits the wall plate, the support could be taken to mean the rim material. If so, then even a double 1 1/8" rimboard would not provide 2/3 the width of a 2x6 bottom plate. This has not historically been a point of contention in the inspection of parallel rim, but it could become one. In 2016 there was a notable case in Carleton Place, Ontario where framers were required to change their rim installation detail on the grounds of plate support. The engineered joist industry should begin to consider new details for parallel rim, or the NBCC ammended, in anticipation of possible future conflicts over this issue. Possible details involve pony walls in place of rimboard, the placement of squash blocks on the inside edge of the rimboard lining up with the studs above, or an engineering analysis of the role played by the floor sheathing, in creating a composite effect with the rimboard whereby the load could be demonstrated to transfer through over a region 2/3 the width of the plate. Another consideration is whether the floor must laterally support the wall below. Section 6.5.1 of the Engineering Guide for Wood Frame Construction makes this requirement official, and section 9.1.1 adds that whatever solution is prescribed is to follow Part 4 of the code. An example of a regional solution to this problem is the Alberta Housing Industry Technical Committee publication "Guidelines for Lateral Bracing of Residential Concrete Foundation Walls". This document contains details for laterally-braced foundation walls which utilize solid blocking on the parallel side, connecting the rimboard to adjacent joists. Certain details of the structure determine the spacing of the blocking and whether it must be installed in the first, first and second, or first three joist spaces. Special fastenings are also specified and in one case 1 1/4" thick rimboard. It should also be discerned whether the floor is considered a diaphragm. For such floors, section 10.4 of the Engineering Guide for Wood Frame Construction and section 8.2 of the CWC's Wood Design Manual both describe certain shear forces and the special nailing and framing anchors required at the rim to counter these forces. For the specific case of parallel rim, the Engineering Guide adds in Figure 6.5 that blocking should be installed between the rim and first joist (although it does not specify the spacing). The APA document "Shear Transfer at Engineered Wood Floors" prescribes the addition of a piece of lumber where an APA rimboard meets the plate, or a shear transfer plate on the exterior side, to accomodate extra nailing for diaphragm-to-shearwall forces. To connect a shear wall above to a shear wall below, further details are shown which include doubling of the rimboard or blocking at 4' on centre. A provincial code may mandate details like double rimboard or blocking, even when the considerations we've discussed would not deem it legally necessary. For any case where blocking is to be used along a parallel rim but connection details have not been specified, the APA document TT-078C "Suggested Blocking Details For Started Joists Of Engineered Lumber" is a good resource. While use of these values is a common practice originating in industry and academic work, it has become part of code. Within Part 9 itself we find section 9.4.2 Specified Loads. It provides a direct answer to the question of SL , giving the formula S = Cb ∙ Ss + Sr in 9.4.2.2. However no mention is made of LL or floor/roof DL. With regard to "good engineering practice" section 4.2 of the Engineering Guide for Wood Frame Construction reaffirms the SL equation above. Regarding floor DL , 4.2.1.2, 6.3.2.4 and 6.3.3.3 say that the weight of partitions can be ignored for residential construction, and all relevant tables assume 10 psf (a commonly-stated alternative to 15 psf). Regarding LL , section 4.2.3.1 says to follow section 4.1.5 of the code. There are other publications that would qualify as good engineering practice. Table 1 in the CWC's The Span Book shows 40 psf floor LL and 10 psf floor DL . There is also CSA Standard 086 and CWC's The Wood Design Manual which outlines design methodologies that apply 086, but these publications, in sections 5.2.3 and 1.2 respectively, simply point to the code for determination of specified loads. The TPIC standard, meanwhile, reaffirms in section 5.2.1 the SL calculation above, and in section 5.3.1 gives us our 10 psf roof DL (3 psf TC DL + 7 psf BC DL) 1 . The third option is to follow Part 4. For roof loads this would give more conservative values than those established here. Regarding floor DL, consulting Part 4 will reveal no specific loads, so it seems that the references to 10 psf in the above engineering documents, as well as the many references to 15 psf in publications and common industry wisdom, are the most official directives available on DL. As such 10 psf can be used if necessary in cases where actual loads cannot be proven to be higher, but note that using 15 psf is by far the most common and expected practice in Canada. Regarding floor LL, Part 4 will provide official code affirmation of the use of 40 psf noted in the engineering documents mentioned. 1 The use of 10 psf total DL for sloped roofs includes joist roofs in common practice, despite being separated into loads for the TC ie. "top chord" and BC ie. "bottom chord" as if only applying to trusses. PART 9 LOADS FOR FLOORS AND SLOPED ROOFS Copyright 2017 Justin Poirier. All rights reserved.
