# Knee wall w/ soffit vents no ridge vent -- seal soffit vents?



## Gary in WA (Mar 11, 2009)

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/products/intakeSoffit-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; http://www.diychatroom.com/f98/biggest-loser-fiberglass-insulation-90438/ 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/docu...llation-of-cavity-insulation?searchterm=insul
http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/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/icod/irc/2009/icod_irc_2009_11_sec001_par001.htm
Use Zone; http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_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


----------

