By Jon Eake
We hear a lot about a House-as-a-System but often get broadsided by various trades wreaking havoc on each other - or on the house or on the homeowner - all while "simply doing their job."
Roofers are considered responsible for the performance of the roof, yet we now have ample demonstration that inadequate insulation in the attic or, more importantly, hot air leakage from the house are the primary causes of ice dams, ice cycles and leakage from the roof.
So an electrician who installs a recessed light fixture that is not of an airtight variety and is not installed in an airtight manner can sabotage the roofer's work and reputation. A heating or ventilation contractor who runs ductwork through the attic can be well meaning, but if hot air leaks out of those ducts, or if the insulation is inadequate over the ductwork (and R-5 is totally inadequate), the roofer is hit with ice and failure again. I have heard of roofers who refuse to shingle roofs that have heating ducts in the attic because they know they will be called back for something they have no control over.
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Mechanical Systems vs. Structural Safety
Here's an example of the performance-based building code in action. There have recently been reports of a rash of houses in Quebec with rotten roof decks caused by bathroom exhaust fans ducted through the attic to flush-mounted soffit grills pointing vertically down. The builders swear they have met code in that they have exhausted to the outdoors and claim there is no specific requirement other than to exhaust outdoors - while anyone who understands that hot air rises knows that the majority of the moisture in that bathroom exhaust air stream will simply rise back up into the attic through the soffits right next to the exhaust grill. These are roof failures that the installers of the exhaust fans say are not their problem. Lowes Hardware even indicates on its Web site that this is the preferred installation.
I and others have always taught "better building practices" as stating that exhaust hoods in the soffit area must be far enough below ventilated soffits to assure dispersal of the moisture before it can re-enter the attic - generally 18 inches or more below the soffit. When I contacted CMHC and HRAI they were both a bit thrown off to discover that, when pressed to cite code, there was no such specification in the code. So I went to the IRC codes centre to see how the new performance code deals with this question.
In the 2005 NBC, 9.32.3.11 Ducts, Sentence (2) states: "Exhaust ducts shall not discharge into heated or unheated enclosed spaces." This provision doesn't indicate whether this discharge is direct or indirect, but in the case at hand it is obvious by the physics of rising hot air as well as the directly correlated roof decking rot right above this exhaust, that this duct is "discharging into an unheated enclosed space." But the builders insist they met code by "discharging outside the envelope."
Following the logic of the new code a little further, this code requirement is attributed to two intent statements: "Health - indoor conditions" and "Structural Safety". The second of these intent statements in the code reads:
OS2 Structural Safety
To limit the probability of failure to completely remove water vapour from buildings, which could lead to condensation, which could lead to the deterioration of building elements, which could lead to structural failure, which could lead to harm to persons.
ADAIRE CHOWN of the codes centre in Ottawa concludes: "If one exhausts immediately below vented soffit, there is obviously nothing to keep the humid air from re-entering the attic. This arrangement would not meet the 'intent' of the requirement."
Consequently, a consumer wanting warranty redress for the roof damage can, in fact, use the code to support his claim because the "intent" of the code provision to prevent moisture saturation and rot of the roof deck is violated with this exhaust arrangement. Here, roof deck condensation is inevitable, not accidental.
