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Topic 3 – Install Bracing or Sheathing and Erect Exterior Walls

In order to provide lateral strength to a wall, a form of sheathing or bracing must be applied. This provides the rigidity required to withstand pressures from the wind and prevent the wall from racking. In most cases, sheathing is applied to exterior walls, although bracing is also acceptable and may be required in some circumstances such as:

– No wall sheathing is applied; out-buildings such as garages and sheds may have the exterior finish applied directly to the framing
– Wall sheathing consists of rigid insulation or composition board which lacks the strength to act as bracing/structural sheathing
– Wall sheathing is horizontally applied boards, such as shiplap

Types of Wall Bracing

Wall bracing comes in a few different forms:

– Cut-in Bracing – These are blocks that are cut to fit between the stud spaces, usually made from 1 ½” stock. The blocks are fitted snugly at an angle from bottom to top plate
– Let-in Bracing – a continuous piece of lumber, usually 1×4, is installed in notches that have been cut in to the studs to allow the board to sit flush. There are also metal T braces that can be installed in its place. Ideally, let-in bracing is installed at 45° from bottom to top plate
– Knee Bracing – This is used if the brace is interrupted by an opening. Simply a let-in brace that returns on itself

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When installing bracing, a number of guidelines should be followed:

– Brace as close to 45° as possible
– Brace at least one end of every wall
– Brace must contact top and bottom plates, fastened with 2 – 63 mm nails
– Knee braces must meet at exterior corners

Types of Wall Sheathing

There are four most common forms of wall sheathing used:

– Lumber – Usually ¾” (1×6 – 1×10), which can be square or shiplap. Due to cost, it no longer used by most. It can be applied diagonally or horizontally. If applied horizontally, bracing is required underneath as it does not provide the lateral strength required.
– Composition Board – Generally refers to asphalt-impregnated fibreboard such as buffalo board or gypsum board. Both types may provide the required rigidity (see 9.23.10.22 in the NBC)
– Rigid Insulation – Can be used in lieu of sheathing but does not provide the required rigidity and wall must be braced underneath. Used when a higher R-value is desired without using larger framing members. Sheets can be either square or shiplapped.
– Plywood and Panel Products – Nearly all new homes are sheathed with plywood or OSB. It is a very strong and cost-effective way to provide the lateral support required.

Installation of Sheathing

– Wall must be straight and square before sheathing
– Snap a chalk line 48” up to guide the top edges of sheets
– Start sheathing on same end as layout was started
– Straighten bowed studs as you go to centers
– Stagger vertical joints in sheathing and provide 1/8” gap between courses
– Insulate any voids that may be covered or enclosed by sheathing
– Openings can be cut out using either a router or circular saw
  • Routers are fast and accurate, but wear out quickly

Calculating Sheathing Quantities

In order to calculate sheet quantities, the total wall area is required. The total wall area is calculating by multiplying the perimeter of the building by the wall height. We then divide the total wall area by the area of a sheet (usually 32 SF) and round up to the nearest sheet:

 

Total Wall Area=Perimeter x Wall Height

 

# Sheets=Total Wall Area ÷32

For example, we will use a house that is 36’ x 40’ with 8’ walls to find the number of sheets required (no waste):

 

Total Wall Area=2(36′+40′)=2 × 76′=152′

 

# sheets=(152′x 8′) ÷ 32 SF= 1216 SF ÷ 32 SF= 38 Sheets

 

***Try the following:

  • Calculate the amount of sheets required for a building 29’-6” x 38’-0” with 9’ high walls.

Erecting Exterior Walls

After sheathing is applied and all opening cut out, the wall can be erected

– Remove all nails that were placed to hold the wall straight and square
– Install blocks at floors edge to prevent wall from slipping down
– Place blocking underneath the top plate to allow hand placement
– Attach studs approx. 16” down from the top plate at end studs to allow quick bracing after wall is stood

After walls are stood, the bottom plate is nailed into place on the chalk line, and the wall is braced. Walls should be braced at least 6’ up and the wall plumbed.

If the floor was installed level, and the walls sheathed straight and square, the corners should be plumb when tied together. After all the walls are erected and corners are tied in, the wall is straightened using a string line and braces. The braces added during erection may need to be removed during this process but should be replaced as the wall is straightened.

Review Questions

  1. What two important steps must be taken before the wall sheathing is applied?
  2. What minimum thickness of plywood wall sheathing is required with supports at 24” O.C.?
  3. What are the nailing requirements for plywood sheathing on exterior walls?
  4. What is the reason for allowing clearance between courses of sheathing?
  5. According to the NBC, when is diagonal bracing required in an exterior wall?
  6. True or False:
  1. The bottom row of sheathing is usually installed before the top
  2. Plywood sheathing should be butted tight between rows
  3. The windows should be cut out before the walls are stood
  4. When panel type sheathing is applied horizontally, the vertical joints should be staggered.
  1. Calculate the amount sheets required for a building 28’-3” x 39’-0 with 10’ high walls and sheeted with 4’ x 8’ x ½” sheathing.
  2. Calculate the number of 4’ x 8’ x 3/8” sheets required for the following structure:

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  • L-shaped building with 9’ walls
  • 3 walk-in doors (18 SF each)
  • 12 windows (150 SF total)
  • Add 5% for waste
  1. What must be done prior to standing walls?

 

Answers:

  1. Ensure wall is straight and square, fill voids that will be covered by sheathing with insulation
  2. 7.5 mm (9.23.17.2)
  3. 150 mm (6”) along edges and 300 mm (12”) along intermediate supports (9.23.3.5-B)
  4. Allows for any expansion that may take place
  5. When there is no exterior sheathing, or exterior sheathing is insufficient for bracing (9.23.10.2)
    1. True
    2. False
    3. True
    4. True
  6. 42.03 or 43 sheets
  7. 48 sheets
  8. Remove nails placed for squaring, add blocks at floor edge, place blocks underneath to grab wall, have braces and nailers ready

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Carpentry Refresher Program Manual Copyright © by Saskatchewan Indian Institute of Technologies-Trades and Industrial is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.