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Old 05-17-2011, 10:00 AM   #1
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Correcting insulation

This past November I moved into a Cape Cod style home. The second story has a knee wall on the south side of the house that I can access. The knee wall is completely insulated - floor, walls, and rafters. The insulation in the rafters is unfaced and right up against the wood board sheathing. Our inspector told us we might want to think about remedying this situation, but wasn't clear about how.

The house has soffits but no soffit vents, so do I need to pull down this insulation? There are gable vents and two roof vents - I can see up into the roof section through an opening in the ceiling (when I take down a light fixture) and there is not insulation between the rafters up there - only on the celing.

I also cannot access the knee wall on the north side of the house, so I have no way of knowing if things are installed improperly in that area.

Without soffit vents, should I bother taking down the insulation or installing baffles behind them? For what it's worth, the wood sheathing I can see appears to be in decent condition.

Is this the sort of situation that's worth going through the trouble of creating access on the other side of the house in order to see how things are installed over there?

Thanks for any input on this. Our house is in the northeast.
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Old 05-18-2011, 09:32 PM   #2
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I'd install an access to any attic over 30sq.ft., as per Code. Just to see if everything is A-ok.
The small attic behind the knee wall should have gable end vents if unable to tie the attics together via the insulated sloped ceiling, as should the attic above the sloped ceiling. That top ceiling needs your min. R-value for your area, as does the attic floor behind the knee-wall; find your zone-
Find the R-value with your zone;

Air block under the wall, and install housewrap on the attic side over the batts;
You need an air-space above the rafter insulation , is it drywall already
Knee-wall attic rafters shouldn't be insulated, only the floor.
Air seal first;

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Old 05-23-2011, 04:32 AM   #3
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Often roofs leak, often condensation forms on the inside of a roof and mold grows and wood rots.
In the recent past the best way to deal with this was to allow air to blow though and help dry the roof timbers and sheathing.

More recently we have come to understand that the passing wind that causes an area of low pressure to the lee of a home, does indeed pull air through the roof, but it also strips the warm air from our homes.

With the move to saving power the emphasis has changed to making homes air tight and to understanding the reasons why condensation forms on/in timber.

If you move the waterproof sheet insulation to a position two inches below the sheathing then any water that comes through the roof will run down and may disappear outside without causing any damage, more likely it will make the walls wet and cause damage there.

By filling the spaces between the rafters with a closed cell insulation like polystyrene and then adding another three inches of polystyrene below the rafters, you isolate
the inside comfort zone of the room from the cold air outside, this makes heating the room a lot cheaper (can be 90% cheaper depending where you live and how thick the insulation is)

The major problem with American light weight homes is that more than 1/8th of the surface is connected to the outside cold air and about the same is connected to the inside warm air, this vast amount of wood provides an express route out for our expensive air, wood is a very good conductor of heat, compared to polystyrene.

Insulating roofs, walls, ceilings and floors with 7 or more inches of polystyrene can save you a fortune on your heating and cooling bills.
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attic , baffle , cape , insulation , rafter

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