Exterior insulation for gable side of home
When adding exterior insulation to a home, should the insulation extend all the way to the top of the gable if the attic is a non-conditioned, soffit and ridge vented attic? The wall has a 13′ cathedral ceiling on the interior side and I intended to insulate to this level, plus about 6-8″, following the pitch of of the cathedral.
I see no point in insulating just this small portion when the rest of the attic will not be insulated based on cost. I would have to used 2×6’s ripped to the proper depth of the 4″ of foam to cover this top portion. My only concern is the weight of the 2×6’s versus foam and furring, and the rain screen details in this area to prevent bugs. I would assume the bug screening would still go near the soffits since I wouldn’t want bugs camping out between the 2×6’s.
Any help or other suggestions would be appreciated. I think the cost difference to do the remainder of the wall in foam would be in the 1-2 hundred dollar range.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Michael, if there's an un-conditioned attic, then there's no need for exterior insulation above the height of ceiling insulation. But the furring strips need to be held off the sheathing to remain in the same plane. You could try cutting strips of foam to stack up under the furring. You might have enough off-cuts from doing the walls to avoid buying too much extra foam. I would install the insect screen at the very top of this ventilated air space.
The other consideration is the continuity of your WRB. Will you have house wrap or a peel and stick membrane covering the wall sheathing? This material should continue all the way up the gable end to the underside of the roof. Unless you're using the face of the foam as your WRB, then I think you're stuck extending the foam all the way up.
Michael,
Mark's answer is a good one. Note that it may be easier, for a variety of reasons, to just continue the foam all the way to the rakes rather than come up with shims and transition details.
Who knows: The attic may become conditioned space in the future. Either way will work, as long as you think through the water-management details carefully.
Mark/Martin,
谢谢你的好的建议。我可能会结束up going foam to the rakes for ease. The guy who built the house decided he didn't need a WRB on this side of the house, yet the garage next to it has some. I haven't quite figured out how this guy passed inspections.
I highly doubt I would make the attic a conditioned space as I don't intend on having much up there and it is pre-engineered trusses over an odd T shaped cathedral building. This makes it pretty busy up there. I currently have flex ducted AC tubing up there, but have strongly considered switching to a new system as my evaporator just died to formicary corrosion, and people are gouging for an R410A charge.