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Small unvented soffit area

The front elevation of my home contains a gable roof area that protrudes less than two feet from the main front wall. There is of course a very small and isolated soffit area on each side of the gable in this 2 foot protusion, that is purely for design as it contains no soffit vents. The gable contains a ridge vent (as does the rest of the attic) and a gable vent. The attic area above this gable area is common the the rest of the house attic, which has functioning soffit vents and baffles.
One side of this protrustion exists next to the front door and frequently this very small area of roof suffers from ice damming. The ceiling in this room is a 12 foot flat ceiling in the center of the room, with short slopes dropping to the 10' plate line on the sides. Therefore, there is a very short run of "cathedralized" ceiling leading to the flat attic above. This cathedralized area is against the roof deck and contains R-30 batts with no baffles since there were no eave vents to baffle.
Obviously there is air leakage leading to the ice dam problem, as well as an inferior level of insulation in the flat attic area (amazing that attic areas that are difficult to get to are often under-insulated compared to easily accessable areas!) I can take care of the air sealing and adding additional insulation in the flat attic.
My question is this: Since these very small soffits are non functioning, can I dense pack that soffit area along with the roof side slopes? Some of the R30 batts in the sloped area have been damaged by critters in the attic previously, so removal of the remaining batts will not be too difficult.

Asked by Chris Brown
Posted Nov 29, 2012 11:39 AM ET


3 Answers

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You can't use cellulose insulation for an unvented insulated sloped ceiling. For more information on your options, see How to Build an Insulated Cathedral Ceiling.

I suggest that you remove the drywall on these sloped areas so that you have good access to the rafter bays. The best way to insulate an unvented sloped ceiling is with closed-cell spray foam. Be sure to include at least the code-minimum level of insulation.

For more information on ice dams, see Prevent Ice Dams With Air Sealing and Insulation.

Answered by Martin Holladay
Posted Nov 29, 2012 12:40 PM ET


Martin, your bias is showing....I never mentioned cellulose! But, I get your point about dense packing the non vented slope area. The question remains about these small soffit areas. As they are non functional, should they be insulated, or left as is?
Thanks, Chris

Answered by Chris Brown
Posted Nov 29, 2012 1:51 PM ET


Here in New England, "dense packing" always refers to cellulose -- but I suppose it's also possible to install blown-in fiberglass at a higher-than-average density. Either way, that approach won't work without ventilation channels.

Concerning the soffit area: whether it is vented or not is of little importance. What matters most is that you have a clear thermal boundary between the interior of your house and the attic. This boundary needs to be as airtight as possible, and needs to have a continuous layer of insulation that (at least) meets the minimum requirements established by code.

Answered by Martin Holladay
Posted Nov 29, 2012 2:24 PM ET

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