Commentary on Part 9 National Building Code of Canada: 1990

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CHIVES

Commentary on Part

9 National Building Code

of Canada

1990

The attached pages identify errata to the Commentary on Part 9 of the National Building Code of Canada 1990. They are included to facilitate use of the

Commentary. Errata are identified by an

e

in the mar- gin nearest the change.

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Commentary on Part 9

Table 1

Summary of occupancies covered in Part 9

* _{Group C classification permitted only if the home is set up as a dwelling unit for not more than ten people,}

who must be ambulatory. Otherwise the building is classified as Group B (see Table 2). Examples Houses, Hotels,

Dormitories, Boarding or lodging houses, Motels, Apartments, Children's custodial homes, Convalescent homes* Banks, Barber shops, Dental offices, Medical offices, Offices, Tool rental, Appliance service Department stores, Mercantile stores, Supermarkets, Shops Warehouses, Workshops, Salesrooms, Factories, Planing mills, Repair garages, Laboratories, Service stations Creameries, Factories, Laboratories, Storage garages, Salesrooms,

Warehouses, Storage rooms, Workshops

Description of use Sleeping rooms

for persons who are not detained involuntarily or who do not need care or treatment Transaction of business or for personal or professional services Display of merchandise or sale of retail goods Making, repairing or storing goods or materials (combustible content >50 kg/m2 or 1200 MJ/m2) Same as above but with low fire load (combustible content <50 kg/m2 or 1200 MJ/m2) Occupancy Residential Business and Personal Services Mercantile Medium Hazard Industrial Low Hazard Industrial Designation Group C Group D Group E Group F, Division 2 Group F, Division 3 Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays

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e

Building Area (1.1.3.2.)

Deflections (9.4.3.)

Ceiling finishes less prone to cracking, such as tiled ceilings, can accept larger deflections without dam-

e age. An increased deflection of 1 1 x 0 of the span is

therefore permitted for ceiling joists, provided they do not also serve as floor joists in other than bed- rooms.

Figure 10. Lines of equal vertical stress

caused by surface loads

Load - 100 kPa Load - 100 kPa

t t t t t t t t t t t ? ? ? ? ? ? ?

(a) Actual distribution of load (b) Load distribution assumed in Section 9.4

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Commentary on Part 9

Figure 24. Permitted reduction in required width

Door permitted to encroach 50 rnrn

required width

Figure 28. Minimum window clearances if not protected with wired glass or glass block

Figure 26. Protection of exit windows

Scope (9. I

0. I

.)

no minimum

A ,Jdistance requlred

(a) Exposing window ~n same plane as exlt wlndow

'1.2 m min. if 1,314h separation

exit window IS

not wired glass or glass block

(b) Exposing wlndow at an angle to window in exit

exit stalrs

a

Building occupancies regulated in Part 9 are based on "major occupancy" classifications as discussed in Section 9.1 of the Commentary. They can have subsidiary occupancies that differ from the principal occupancies. Where a subsidiary occupancy is used for assembly or high hazard industrial uses (Table 21, it is regulated in Part 3 (Subsections 3.3.2. and 3.3.5.) even though the major occupancy is within the scope of Part 9.

Closures in Fire Separations

(9. I

0. I

3.)

Frames for solid core wood doors can be either wood (38 mm thick, unrated) or steel (20 minute rating). Most doors in fire separations are required to be self-closing and equipped with a latch to hold them closed under fire conditions. The only excep- tion is for doors in corridors that serve suites in Group D occupancies (9.10.1 3.10.). Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays

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Where a duct passes completely through a rated fire separation, it provides a potential passageway for fire and hot gasses. To maintain the integrity of the separation, a fire damper is usually required in the plane of the separation (9.1 0.1 3.1 3.). This device is also required to have a fire protection rating. It is normally held in the open position by a fusible link, and is installed so that it will stay in place if the duct collapses. In some cases, however, ducts can penetrate a fire separation without appreciably affecting its performance, and no damper is necessary. For example, exhaust ducts penetrating the fire separation around a vertical shaft are not required to have dampers if the shaft is exhausted in a way and the ducts are terminated in a way that makes it unlikely that smoke or fire entering the shaft via one duct will be drawn into a duct leading to another fire

e compartment[Figure40(9.10.13.13.)].

Compartmentation (9.1 0.9. to

9.1 0.1 3.)

If a mezzanine is not considered to add to the storey height of the building (Figures 6 and

7),

its floor assembly is not required to be designed as a fire separation. Such mezzanines are also allowed to inter- connect with the adjacent space without the special compensation measures previously mentioned. If, on the other hand, the mezzanine is considered to add to the storey height, the mezzanine must be enclosed by fire separations with a fire resistance

e rating at least equal to that of the other floors (Figure 45) unless the special compensating mea- sures described in Subsection 3.2.8. are taken. In other locations, the prime objective may not be to contain a hazard, but to protect the space from fires originating elsewhere. Public corridors and exit stairways, for instance, are required to be isolated by

e fire separations to prevent the entry of fire so that they will remain tenable while the building is being evacuated.

Figure 45. Compartmenting of storeys

Third Storey Second Storey First Storey

I

Group D

45 mln fire 45 min fire separation separation above and below mezzanine

(9.10.8.1 .)

Figure 49. Soffit protection over common attic spaces

unless space between roof sheath~ng and top wall

/' ', plates 1s flre stopped f ~ r e

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Commentary on Part 9

Separation of Residential

Suites (9.1 0.9.1

4.)

As may be seen in Table 7, dwelling units are required to be separated from each other (and from other parts of the building) by a 45 minute fire separation if the dwelling unit contains one storey, and 1

e hour if the dwelling unit contains 2 storeys or more. Most dwelling units in semi-detached and row 6 houses, therefore, have to have at least a 1 hour fire separation, even bungalows, since most contain a basement storey.

Fire Stopping (9.1 0.1 5.)

In small spaces, such as stud, joist and furring spaces, fire stopping usually consists of the same material as the framing and furring. In larger spaces, such as attics and soffits, sheet material is generally used (12.7 mm gypsum wallboard, 12 mm plywood or waferboard, 6 mm asbestos board or

e 0.38 mm sheet steel). A double layer of board lumber is also permitted if the joints are staggered between layers. Fire stops can be pierced by piping, wiring or ducts, provided the openings around the penetrations are tight-fitting or sealed with a fire- resisting material. Such measures not only reduce the risk of fire spread but reduce the amount of air leakage into concealed spaces that might cause con- densation problems in winter.

Figure 58 (a). Maximum window areas for

different limiting distances for groups C, D and F-3 occupancies

0

Figure 57. Measurement of limiting distance

I 1 I

2 0 3 0 4 0 5 0 6 0 7 0 8 0

D~stance to property l ~ n e (m)

(a) with no interior fire separation

Hatched areas show areas where limiting distances "d" apply Lot lines or assumed lines ,between buildings I Lot Line (b) with interior fire separation Copyright © NRC 1941 - 2019 World Rights Reserved © CNRC 1941-2019 Droits réservés pour tous pays

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Figure 58 (b). Maximum window areas for different limiting distances for groups E and F-2 occupancies

1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0

D~slance to property llne (rnl

Smoke Alarms (9.1 0.1 8.)

Construction Camps (9.1 0.20.)

The low cost of such systems invites their use beyond the minimum requirements specified in

e Subsection 9.10.18., particularly if battery-operated units are used. Alarms to protect the living area (statistically the most dangerous area of the house) as well as the basement by supplemental alarms would appear to be economically justified on the basis of reduced fire damage alone.

Fire Fighting (9.1 0.1 9.)

While the requirements for such access in Part 9 are written in very general terms, those in Part 3 are very specific. A user of Part 9 who wishes more pre- cise direction on the design of access routes should

e consult the requirements in Part 3 (3.2.5.).

Although construction camp buildings are in general required to conform to the same spatial separations as other buildings, they need not be spaced Inore than 10 m apart (9.10.20.5.). In some camp designs, the various buildings are interconnected by a series of enclosed walkways to permit workers to go from one building to another without going outdoors. To reduce the possibility of fire spreading by means of these walkways, a fire separation is required where they join each building (45 minute) (9.10.20.4.). Such walkways are also required to have a low flame spread rating (25 over 90% of the walls and ceiling) to reduce the risk of fire spread (9.10.20.6.). e

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-

Commentary on Part

9

Figure 65. Cross section through wallflloor junctions sound abs materl orbi~ ial

/

\ I vibration break

Section 9.1

4 Drainage

Although a variety of materials are permitted to be used for sub-surface drainage, the most common material until inore recent years has been clay tile

e pipe. This pipe is normally 300 mm long and 100 mm in diameter, with individual pieces spaced about 6 to 10 mm apart to allow the entry of water. The top half of these joints is protected with asphalt paper or polyethylene film before the tiles are covered with crushed rock or coarse granular fill (Figure 72). This reduces the possibility of soil being washed into the piping (9.14.3.3.).

In recent years, lightweight polyethylene drainage pipe has replaced clay tile as the most popular choice of drainage pipe. The concentric grooves on the pipe allow it to bend so that it can be shipped in long coils and installed in one piece around the perimeter. Slots in the pipe allow the water to enter the pipe. Like clay tiles, it must be laid on a firm base and covered with about 150 mm of crushed

e _{rock or granular fill (9.14.3.3.(4)). The crushed rock}

increases the water collecting area around the pipe, and keeps the soil from contact with the pipe surface. Silty soil, however, can find its way into the piping and can eventually block the drainage. Although it is not required by the Code, some builders cover the crushed rock with a filter fabric to keep soil from entering the pipe.

Section 9.1

5 Footings and

Foundations

Footing sizes, for example, are based on soil with a bearing capacity of 75 kPa (1500 ib/ft2). This is a e fairly conservative load and is easily carried by most soils. Loose sand and loose gravel, however, have a bearing capacity of only 50 kPa and require footings that are 50% larger than those shown in Table 9.15.3.A. Soft clay has an allowable bearing pressure of only 40 kPa and footings must be almost twice as large as the listed sizes. (The identification of soil types is discussed in Section 9.4 under the heading e

"soil bearing capacity.") Foundations on soils with these lower bearing capacities are therefore required to be designed either in conformance with Section 9.4 or the more rigorous design procedures in Part 4. Not all soil types are allowed for in Section 9.4. e

Filled ground, for example, is not covered. Such soil can be extremely variable and requires very careful assessment in foundation design. Conditions such as this, which are not covered in Sections 9.4 or 9.15, must be designed in conformance with Section 4.2.

Section 9.1 7

Columns

(25) CAN/CGSB-7.2-M88, Adjustable Columns, Canadian General e

Standards Board, Ottawa, 1988.

Seismic Considerations

(9.20.1.2.)

Part 9 does not require degrees of reinforcing. It merely specifies that a minimal amount be provided, depending on the height of the building and the seismic zone it is in. The reinforcing is expressed as a proportion of the cross-sectioned area of the wall (0.2%). It is required to be distributed so that not less than 1 / 3 of the required steel area is installed either e

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Figure 102. Individual rod type masonry ties 25 rnrn

v

/

/- 900 mrn rnax

,

'

spacing

Rain Leakage (9.20.1 3.)

Foamed plastic insulation is commonly attached directly to the masonry surface by means of a water- proof adhesive or by mortar. In such cases, sheathing paper cannot be used between the insulation and the masonry, and the insulation itself must therefore be able to resist the passage of moisture over the

e entire surface (9.20.13.10.(3)).

Section

9.21 Chimneys and Flues

e (31) CSA 8139, Installation Code for Oil Burning Equipment, Canadian Standards Association, Rexdale, Ontario, 1991.

e ( 3 3 CAN/CGA B149.1-M91, Installation Code for Natural Gas Burning Appliances and Equipment, Canadian Gas Association, Don Mills, Ontario, 1991.

e (33) CAN3-B365, Installation Code for Solid-Fuel Burning Appliances and Equipment, Canadian Standards Association, Rexdale, Ontario, 1991.

e (34) ULC S629-M1987, Standard for 650°C Factory-Built Chimneys, Underwriters' Laboratories of Canada, Scarborough, Ontario, 1987.

Floor Joist Spans (9.23.9.)

Example 1: A living room floor is required to support 50 mm of concrete topping. The required distance to be spanned is 4.0 m. The joists are No.1 spruce-pine-fir. Only cross bridging is to be used. Find the size and spacing required for the floor joists if the concrete topping load is 1.2 kPa. 1. Design live load for living room = 1.9 kPa

(Table 4.1.6.A.)

2. Extra load due to concrete topping = 1.2 kPa Total = 3.1 kPa

3. From Table A-1, to span 4.0 m with No. 1 SPF e

with cross bridging requires 38 x 235 mm (2 x

10) spaced 400 mm O.C. for ordinary weight floors (4.1 7 m allowable span).

Figure 120. Maximum size notches and holes in studs and plates before repair is required

u

Load bearing studs

- a+b =

40 rnrn rnin. e

- 40 rnrn rnin.

+

Non-load bearlng studs

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Commentary on Part

9

Figure 124. Joist supported on steel beam e (from Canadian Wood Frame House Construction,

CMHC, NHA 5031, Ottawa, 1988)

Wall Plates (9.23.1 1 .)

Where wide openings are to be bridged by lintels, or if a reduced ceiling height is used, there may not be sufficient room above the lintel to provide the usual doubled plate. In such cases, only one top plate may be extended across the lintel to provide a suitable tie. The top plate must, of course, be supported through- out its length by the lintel. If there is no room to allow the top plates to extend across the framing, the wall plates may be terminated at the lintel, provided a metal strap or wood tie is provided across each

e end of the lintel [Figure 129 (9.23.1 1.3.(4))].

General Installation

e

Requirements (9.24.3.)

e

Fire Separations (9.24.2.4. and

9.24.3.2.)

Materials (9.25.3.)

Of the various foamed plastics used for residential insulation, cellular or foamed polystyrene is the most common. The standard to which it is required to be made recognizes four grades or types

(9.25.3.1.). "Type 1" is the least dense. It is the most permeable to moisture, and is more water absorbent than other grades. Because of this, it is not permitted to be used in contact with the ground or as roof insulation in so-called "inverted roofs." (Inverted roofs are constructed so that the main waterproofing membrane is beneath the insulation to protect it

e from extremes in temperature.) The product standard for the installation of polystyrene insulation requires the insulation to be face marked to indicate its type, as well as the manufacturer's name or trade- mark and the standard to which it is produced.

Installation of Insulation

(9.25.4.)

(4@ ASTM C516-80, Specification for Vermiculite Loose Fill Thermal Insulation, American Society for Testing and Materials, Philadelphia, 1990.

Calculation of Dew Point

Temperatures

The temperature drop at any point in an assembly varies with the thermal resistance to that point. If, for example, a wall has a total thermal resistance of, say, 3.0 RSI, and the total resistance from the interior to the point is 1.0, then the temperature drop to that point is 1/3 of the total drop through the wall. If the

outside design temperature is -30°C (based on the January 2 1/2% temperature), then the outside air

temperature to be assumed for purposes of this calculation is -20°C, or 10" above the January design

temperature (as permitted in Article 9.25.5.2.). The e

total temperature drop across the wall is 40". The temperature at the air/vapour barrier would be 20°C (inside air) minus 1 / 3 x 40, or 6.7"C.

Foamed Plastic Insulation

(9.25.6.3.)

Where foamed plastic insulation is applied to a masonry wall, no additional vapour barrier is necessary, provided the foamed plastic has adequate resistance to water vapour flow (permeance of less than 230 ng/(Pa.s-m2)). Most common foamed or e

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Commentary on Part

9

Figure 138. Flashing wood siding to roof shingles

I

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Figure 140. Flashing wood siding to built- up roofing 50 mm clearance

e

above loof

5-

ts 150 mm min.

-

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Commentary on Part

9

Figure 145. Wood shingle roofs

eave protection

max. width min. width

roof deck

/'

Grits

in approx. 6 mm

adjacent space between courses shingles

Reinforcing (9.28.4.)

Stucco wall reinforcing is normally attached to the wood framing with galvanized roofing nails or sta- ples that penetrate at least 25 mm into the framing. Although it is preferable to attach the reinforcing back to the framing to reduce the risk of stucco cracks, direct attachment to waferboard, strand- board, plywood or lumber sheathing is also permitted if the sheathing is thick enough to provide adequate nail strength to support the weight of the

e stucco [at least 12.5 mm (9.27.5.1.(2))]. There is usually little or no advantage to be gained, however, in such direct attachment.

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Floor Drains (9.31.4.4.)

House basements are subject to periodic water leaks as a result of flooding conditions or severe storms. These are also required to have floor drains unless it is not possible to drain the water to a sewer, ditch or

e

dry well without the use of pumps.

Exhaust fans were specified for electrically heated houses in the 1980 edition of the NBC, to reduce the incidence of excessive humidity levels in these houses. However with the continuing emphasis on reduced air leakage and the development of more efficient fuel burning systems, health concerns became paramount. These concerns led to the cur- rent requirements for mechanical ventilation in all dwelling units regardless of the type of heating sys-

e

tems used (9.32.3.1.).

e

Capacity (9.32.3.1. and

9.32.3.2.)

Simple Exhaust Systems

(9.32.3.)

e

(59) Chimney Safety Tests Users Manual (2nd Edition), Canadian Housing Information Centre, Canada Mortgage and Housing Corpora tion, Ottawa, Ontario, 1988.

Stoves and Space Heaters

Burning Solid Fuel (9.33.1.2.)

e

(64) ULC S627- M1984, Space Heaters for Use with Solid Fuel, Underwriters' Laboratories of Canada, Scarborough, 1984.

Section

9.35 Garages and Carports

Carports have different degrees of enclosure, rang- ing from being entirely open, to being totally enclosed except for the doorway. Since certain requirements apply only to garages and not to carports, it is important to make a distinction between the two. Garages, for example, are required to have certain features to prevent them from exposing the remainder of the building to exhaust fumes but carports are not (9.10.9.16. and 9.10.13.15.). For the purpose of applying these requirements, therefore, a parking structure is considered to be a garage if more than 60% of its perimeter wall area is enclosed

(9.35.2.1 .).