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Old 04-23-2011, 07:49 PM   #1
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Knee wall w/ soffit vents no ridge vent -- seal soffit vents?


I have an issue that is very concerning to me and would truly appreciate expert advice --

My home is a 1899 foursquare with a copper architectural shingle roof. The roof is approx. 10-15 years old. All work described here was done by the prior owner who is an architect.

The attic is finished and has three knee wall areas -- one across the entire back and corners, and one at each of the front corners of the house.

The soffits have been vented with 3" round vents. However, the roof is not vented. Batt insulation fills the entire void between the roof/framing and the sheetrock ceilings.

Batt insulation also runs down the knee walls.

There are random-width floorboards across the entire attic space, including in the knee walls. In some places the floorboards cover the soffit bays so that they don't seem to provide much ventilation.

In some places there is loose (cellulose?) insulation between the floorboards and the plaster ceiling below.

My question, finally, is how should I insulate and ventilate (or not) this space? I had two insulation contractors recommend two different approaches: One contractor would seal the soffit vents and insulate the roof in the knee wall area with rigid foam, where the roof is not currently insulated. The other contractor would dense-pack insulation under the attic floor where the knee walls meet the floor and leave the soffit vents alone.

I know the correct thing to do would be to tear off the roof or the sheetrock ceilings and install baffles and ridge vents, but that is almost certainly cost-prohibitive. Is one of the other approaches recommended by these contractors the way to go?

In addition, I just discovered a bath vent open to one of the front corner knee wall areas. Does this need to be vented through the roof or could I direct the vent to a sofit (there happens to be good access to a large rectangular soffit vent -- presumably installed for that purpose at one point in time).

Thank you in advance for your help

By the way, I am located in Maryland if that makes a difference.


Last edited by tblaz; 04-23-2011 at 07:53 PM. Reason: edited to note geographic location
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Old 04-24-2011, 04:12 PM   #2
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Knee wall w/ soffit vents no ridge vent -- seal soffit vents?


The soffits have been vented with 3" round vents. However, the roof is not vented. Batt insulation fills the entire void between the roof/framing and the sheetrock ceilings. ---------------------------- 3” are hardly enough to reach the 9NFVA per foot of soffit, unless spaced tight to each other continuously. They have very limited NFVA because of the metal and screen; http://www.lomanco.com/ProductPAGES/CirkVents.html
The math; http://www.airvent.com/homeowner/pro...it-specs.shtml
You could add static vents (turtle-back) close to the ridge on all sides. Continuous venting close to the fascia board is best, though most 4-squares have limited soffit depth.

Batt insulation also runs down the knee walls. --------- as it should if it is high density, which I doubt; The "biggest loser" in fiberglass insulation.... up-grade and add a house wrap to prevent wind-washing.

There are random-width floorboards across the entire attic space, including in the knee walls. In some places the floorboards cover the soffit bays so that they don't seem to provide much ventilation. ----- need 1” minimum, 2” is better.

In some places there is loose (cellulose?) insulation between the floorboards and the plaster ceiling below. ------- want to seal the floor cavity under the wall; http://www.buildingscience.com/docum...archterm=insul
http://www.homeenergy.org/archive/he...95/950309.html

My question, finally, is how should I insulate and ventilate (or not) this space? I had two insulation contractors recommend two different approaches: One contractor would seal the soffit vents and insulate the roof in the knee wall area with rigid foam, where the roof is not currently insulated. The other contractor would dense-pack insulation under the attic floor where the knee walls meet the floor and leave the soffit vents alone.----------- foam is good as it air seals any wiring/plumbing holes (though you can DIY here). Foaming the rafters through-out would be best (if money is there), then plug the soffit vents (still need upper attic vents if already insulated ceiling to Code; Find; http://publicecodes.citation.com/ico...001_par001.htm
Use Zone; http://publicecodes.citation.com/ico..._11_sec002.htm

If only foaming ceiling, need to isolate it from attics at ends for fire; 4.2.1.2; http://building.dow.com/ee/pdf/ESR-2142.pdf

How thick is the insulation on the sloped ceiling?

Gary

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