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Insulating kneewall with no soffits

The articles I've read talk about air flow coming from the soffits. My house doesn't have soffits. The only air flow is from the roof vents. Do i insulate the roof and make the space conditioned space or insulate the knee wall and floor leaving the space as unconditioned?

Asked by user-7114034
Posted Jul 11, 2018 6:28 PM ET
Edited Jul 12, 2018 6:56 AM ET

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1.

User 7114034,
First of all, can you tell us your name? (I'm Martin.)

Does your house lack soffits or does your house lack soffit vents? Plenty of homes have soffits without soffit vents.

The soffit is the horizontal board or "ceiling" under a roof overhang. If your house has soffits, you can hire a carpenter to install soffit vents in your soffits.

If you house lacks soffits, you have no roof overhang, and the water from your roof dribbles down your siding every time it rains. There are a few houses like that.

If you want either (a) a vented attic, or (b) a vented insulated roof assembly (a vented cathedral ceiling), you need soffit vents.

If soffit vents are impossible, you will end up with either (a) an unvented attic, or (b) an unvented insulated roof assembly. Both of these are possible, but they have to be detailed correctly.

For more information on these issues, see these three articles:

“How to Build an Insulated Cathedral Ceiling”

“All About Attic Venting”

Answered by Martin Holladay
Posted Jul 12, 2018 6:28 AM ET

2.

Hi Martin, I'm Ellie.
I don't have soffits as I have no roof overhang but i have roof vents.
"Two ways to insulate attic knee walls" article doesn't mention what to do with the sides of the triangular area e.g. one method mentions what to do with the sloped roof and the other method mentions what to do with the floor and knee wall.
"If you plan to insulate a kneewall and the attic floor behind the kneewall, protect the insulation with an adjacent air barrier. The air barrier should have no leaks, especially in the areas where the floor meets the wall and the wall meets the roof." I don't understand what this means. Is the poly on the triangular inside area behind the knee wall? Or is the poly on the bedroom side of the knee wall?
If I have roof vents, what do I do? Have them closed off? I'm about to get new shingles, do I tell the roofers not to install new roof vents?

Answered by user-7114034
Posted Jul 12, 2018 8:30 PM ET

3.

Ellie,
It sounds like you have a Cape Cod house (1 1/2 stories), but I'm not sure.

In a typical Cape, there are attics on the second floor (these are the triangular attics behind the kneewalls) as well as a third-floor attic above the horizontal ceiling on the second floor. Which type of attic are you talking about?

For the vented approach to work, you need a way for air to enter near the bottom of your roof. These could be wall vents in the second-floor attic, in theory -- although this wouldn't be as good as soffit vents. But this is just one component of a venting system. You would also need baffles in the sloped ceiling section to allow air to pass between the top of the insulation and the underside of the roof sheathing. This air could then escape through the ridge vents.

If you have these baffles in the sloped ceiling, you can go ahead and insert wall vents in the triangular attic behind the kneewall, to admit outdoor air to your second-floor attic.

Q. "Is the poly on the triangular inside area behind the knee wall? Or is the poly on the bedroom side of the knee wall?"

A. The air barrier I am talking about is on the attic side of the kneewall. Polyethylene would be a bad choice to use as an air barrier (because it would become a wrong-side vapor barrier). The article you quoted from includes better options for an air barrier at this location: rigid foam or housewrap, for example.

Q. "If I have roof vents, what do I do? Have them closed off?"

A. If you have (or intend to install) all of the components of a vented roof assembly, keep the ridge vent. If you lack (or are unable to achieve) all of the components of a vented roof assembly, you will have to convert your roof assembly into an unvented roof assembly, as described in the articles I linked to.

Answered by Martin Holladay
Posted Jul 13, 2018 4:22 AM ET

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