Despite the fact that the construction of most decks requires a building permit and that compliance with the Building Code¹ is mandatory, Canadian building codes don’t actually address deck requirements particularly well². These codes often need to be interpreted to apply their building-centric rules to decks. One area where there is lack of clarity is around the attachment of decks to houses. The importance of this detail cannot be overstated. The vast majority of deck collapses are the result of a failure occurring where the deck meets the house.

Ledger boards are frequently used as this attachment point. A ledger board is a piece of dimensional lumber, like a 2″x8″, that is attached securely to the structure of the home. On a wood-frame home, it is commonly secured to the rim joist of the house with bolts or screws (or to the foundation wall). This is shown in Figure 1. On a solid masonry home, proper fasteners may also be used to secure the ledger board to the masonry wall. Done properly, this is a structurally-sound solution.

 

A problem arises, however, when decks are supported on wood-frame, brick (masonry) veneer³ houses. Unlike solid masonry walls, masonry veneer is not intended to be load-bearing, it is simply a cladding, like vinyl or wood siding, albeit somewhat heavier. If you were to remove the brick veneer from one of these houses, the structure of the house would be unaffected. It is generally accepted in the building community that ledger boards should not be attached to this non-structural cladding.

A common practice in the case of masonry veneer walls, however, is to secure the ledger board to the rim joist of the house as shown in Figure 2, either with a threaded rod (as shown), or with carriage bolts or lag screws. The bolt or screw ostensibly secures the ledger board to the rim joist, not to the brick veneer. Deck builders who install ledger boards this way claim that they are not securing the ledger to the brick veneer, they are installing the screws or bolts to the rim joist through the brick veneer.

 

The problem with this logic can easily be demonstrated with a thought experiment. Imagine the same installation, but with the brick magically and suddenly removed. Everything else is the same. The same length of bolt, and the same distance between the ledger board and the rim joist. This is shown in Figure 3.

 

The concern is quite evident. If lag screws were used, those lag screws would be cantilevered (sticking out) out from the sheathing a distance of 4” to 5” with the load of nearly half the deck on the outer end. It is plain to see that the lag screws could not support the load of the deck in this configuration and would bend downward⁴. In the case of threaded rods or carriage bolts (with washers and nuts), the problem is even worse since there is nothing to stop the rotation of the bolt at either the ledger board or the rim joist. The bolts would rotate down, and also likely bend as well. Would you trust your family’s safety to a deck supported as shown in Figure 3?

What stops this from happening in the real world? The presence of the masonry veneer, of course. The bolt/screw is either installed tight inside the hole in the masonry veneer, or the bolt/screw deflects under the load of the deck until it rests on the masonry veneer. The masonry veneer is the only thing stopping the bolt or lag screw from deflecting any further. At that point, all gravity (vertical) loads from the ledger board are transferred from the bolt to the masonry veneer, not the rim joist⁵.

Gravity loads are not the only concern. Decks are subjected to a variety of lateral loads ranging from wind loads to the dynamic loads of people moving about on the deck. Look again at Figure 3. What is stopping the deck from moving towards the home if there is no brick veneer? Nothing. Therefore it is the brick veneer that is taking the lateral load in that direction.

As can be easily seen, while the rim joist can resist lateral loads away from the wall of the house, it is the brick veneer that takes up the gravity loads as well as the lateral loads both towards and parallel to the house wall.

There are other complicating factors with this type of installation. For example, when tightening the bolts or screws, if the installer is not careful, there is the risk of over-tightening, which can place enough pressure on the masonry veneer to crack it and cause it to bow inward. Also, the introduction of holes in the wall increases the risk of wood rot in the long term. Both of these result in localized weakening of the masonry veneer and the wood structure respectively.

As noted, brick veneer is not a load-bearing element of a home. For this reason, many Chief Building Officials⁶ (“CBOs”) in Ontario (and perhaps other areas of Canada) prohibit the practice of bolting through the brick veneer. The Toronto Area Chief Building Officials Committee (“TACBOC”) publishes standard construction details to demonstrate how to achieve minimum Ontario Building Code compliance in a variety of applications, including the construction of decks. With respect to attaching decks to a brick veneer home, the TACBOC detail does not include a ledger board. Instead, the TACBOC detail recommends that two or more beams extend through the wall to be supported at the house end by the wood studs and by blocking installed below the beams⁷. Although not a TACBOC detail, another option is for the deck to be built free-standing, with a beam (supported by posts) running along the wall instead of a ledger board.

 

Some Ontario CBOs do, however, permit the “bolt-through” approach; not explicitly endorsing it, but approving decks designed and constructed this way. Unfortunately, it seems that while the Building Code itself is the same throughout the province, the application of the OBC is not. It is our hope that in future, not only will deck construction requirements become more explicit (prescriptive) in the Building Code, but that the requirements of the Building Code become more uniform across the province, if not the country⁸.

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1. The focus of this article is on the Ontario Building Code, and the state of these issues in Ontario, however similar issues are likely to exist in other provinces. In the US, the International Residential Code is more explicit about prohibiting loads on brick veneer walls. The American Wood Council also publishes DCA 6, a prescriptive guide for deck construction in accordance with the 2015 IRC. ↩︎
2. An exception to this is the excellent Supplementary Standard SB-7 of the OBC, which sets out specific standards and details for guards. ↩︎
3. All brick is masonry, but not all masonry is brick. The terms are used interchangeably in this article. ↩︎
4. For example, a deck with a ten-foot span in Orangeville, Ontario would create a factored load of 545 lb. if the bolts were installed every 16 inches. In fact, while this load will bend a 1/2″ screw, the even greater effect is likely the lever action of the load on the wood of the rim joist, which will result in a bending moment of 238 ft-lb and will put a downward load on the outer face of the rim joist of 1900 lb. and an equivalent upwards load at the inner face of the rim joist. This exceeds the compressive strength of No.1/2 SPF lumber at both faces. In English, the load of the deck is sufficient for the screws to crush the rim joist and tear out. ↩︎
5. In fact, depending in the degree of looseness where the lag screw or bolt passes through the masonry veneer, the bolt or screw may impose an uplift load on the rim joist as a result of the gravity load on the other end. ↩︎
6. One might just as well refer to to the municipality or the building department. Ultimately, however, the responsibility lies with the municipality’s Chief Building Official. ↩︎
7. A configuration that the author has not seen in the field at any time in the last 35 years. ↩︎
8. The just-announced 2024 Ontario Building Code, once implemented, will increase harmonization between the OBC and the National Building Code. More than 1,700 technical variations between the two codes are being eliminated. The 2024 OBC consists of the 2020 National Building Code and the 2024 Ontario Amendment, outlining the differences. Perhaps one day, the OBC and NBC can evolve to the point that there is no need for the Amendment. ↩︎