Ventilation 2021 IRC CH.8

[MFlores1]

I am having trouble with my third-party reviewer in this area. Am I wrong in insisting on a calculation for the attic areas, not in the thermal envelope of a home with spray foam added to the roof deck? The areas in question are the garage and the patio, since we are in climate zone 2 the exceptions do not apply, and the builder must comply with the 1/150 rule.

 

[Energystar]

I assume you are talking about a vented attic vs. unvented. The exception in R806.2 does apply in CZ 2. You can use 1/300 with the right amount of upper and lower ventilation. The garage area should be included. I suppose the patio area would depend on whether it is enclosed.

 

[MFlores1]

The home is a Spray foam roof deck with blown insulation for the walls, the areas in question are the garage and the patio, no ventilation was installed till I noticed the homes with no ventilation.

 

[Energystar]

The enclosed attic over the garage should be ventilated.

 

[classicT]

Trying to follow you @MFlores1...

Are you indicating that the primary attic space above the dwelling, plus the patio cover and garage are all constructed as unvented attic spaces?

If so, the gable end walls of the attic, plus the ceiling of the attic could be insulated to bring the entire attic space into the building thermal envelope. This process would be atypical though. It is more common to insulate the wall line of the primary dwelling space through the attic space and leave the garage and patio cover area as conventionally vented attic spaces.

It would not be permissible to spray insulate the roof of the garage and patio, but leave the conditioned attic space without all sides insulated - in this case, the ceiling and any gable end walls of the connected attic space over the garage and patio area.

 

[classicT]

It would not be permissible to spray insulate the roof of the garage and patio, but leave the conditioned attic space without all sides insulated - in this case, the ceiling and any gable end walls of the connected attic space over the garage and patio area.

See R806.5 #1 -

2018 IRC R806.5 Unvented Attic and Unvented Enclosed Rafter Assemblies​

Unvented attics and unvented enclosed roof framing assemblies created by ceilings that are applied directly to the underside of the roof framing members and structural roof sheathing applied directly to the top of the roof framing members/rafters, shall be permitted where all the following conditions are met:

1. The unvented attic space is completely within the building thermal envelope.
2. continues... {omitted for clarity}

 

[bill1952]

The enclosed attic over the garage should be ventilated.

Even if the thermal barrier is the roof deck? Though I'm a little confused by the description that says the foamed roof decks are not a part of the thermal barrier. I'd assume the foam would be a vapor barrier - closed cell? - and not sure exterior - warm and moist - air inside the vapor barrier is a good idea.

But this is building science thinking, not code.

 

[steveray]

I'm a little confused by the description that says the foamed roof decks are not a part of the thermal barrier

THIS^^^^^^

 

[classicT]

THIS^^^^^^

I think I understood the issue.

The attic spaces above the garage and patio are likely unconditioned and exist outside the thermal boundary of the home. However, the builder may have assumed that by insulating the roof deck, they would be exempt from venting these attic spaces.

This would be an error. Ideally, if located outside the thermal boundary, the roof deck would not be insulated. However, if they spray insulated the roof deck of these areas, but did not insulate the gable end walls nor the ceilings, then this would be unconditioned attic space and require ventilation.

 

[bill1952]

No concern about attic being cooler and the warm moist air entering the attic condensing? The spray foam will definitely keep it a little cooler.

I'll assume no ducts in attic.