Insulating area behind a knee wall?

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Old 04-21-01, 08:46 PM
MostlyCranky's Avatar
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I had some problems with ice damns this past winter and want to resolve the issue now. I have a finished 2nd floor cape style house. I have soffit vents and a ridge vent, but did not have rafter vents running down to the soffit, instead they stopped part way down the rafter behind an insulated knee wall. I think this is the problem. I am adding rafter vents down to the soffits, and my question is can I insulate the rafters in this storage area behind the knee wall?

Would this cause more problems? Seems to me that insulating this area would help keep down the ice damns, as well as make it more comfortable.
 
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Old 04-27-01, 04:15 PM
zalyx1
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Cranky,

I am currently faced with the same circumstances. Same type of house. I have been asking around , including this site. The most common answer I get is to insulate as well as vent down to the soffits . This supposedly keeps a more even temperature from top of roof down to soffits thus decreasing the chances of ice damns. I beleive you want to keep the temps. within about 20 degrees from top to bottom.
It seems reasonable to me, but I am not even close to being a professional. Just passing along informaton I have heard ,hope it helps. Would still like a few more opinions (from qualified people) myself.

Good luck, Bill
 
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Old 05-11-01, 03:40 PM
Insulman
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from my experience in these situations the storage areas are the main culprit... they generally have minimal insulation in the floor area which is above heated living space..thus heat loss from below melts the snow above so additional insulation on those floor areas is probably the fix.. of course you want those storage areas so that causes another problem. One person I know built up the floor and insulated and then reinstalled another deck above...but this is costly.. also a tremendous amount of heat loss from the living space on the 2nd or 3rd floor leading to the storage areas is usually occuring at the entry doors to said storage areas.. You can usually install insulation on the back sides to help reduce heat loss...Also much heat is lost from the kneewall area you might consider installing unfaced insulation like R-7 horizontially by stapling it to the visable studs
 
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Old 05-15-01, 06:16 PM
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Well, after some rather extensive research I have learned there are two accepted methods to insulating kneewall storage areas.

1. It is not acceptable to insulate both the kneewall and the rafters in the storage area. One or the other, not both. If the kneewall is insulated, adding more insulation in the floor is warranted, as well as weather-stripping and insulating the access doors. Supplementing the kneewall insulation is also a good step. Unfortunately this leaves the storage area cold or hot depending on the season.

2. The other way to do it is to remove the insulation from the kneewall completely. Install/extend air channels and R19 faced in the rafters, then top it off with wallboard or hardboard. An acceptable practice that adds a bit more insulation is to substitute R19 faced for unfaced, then add one inch R5 rigid foam panels across the rafters. Add a vapor barrier and finish with wallboard, etc. More expensive to do it this way as you are now heating the storage area, but solves the problem of getting a more temperate climate in the storage area. Also should keep the roof temperature consistent in the winter.

Thanks to all for responses.
 
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Old 05-15-01, 06:56 PM
Insulman
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Hi Cranky....


your secound solution to removing the kneewall insulation and then installing Insulation to the rafters of the storage areas sounds resonable.. but adding air baffles under the insulation won't really do any good unless you have soffit venting on the outside for air to breath from the outside up those channels and then exhaust through the roof vents in the attic area above the living space of the 2nd floor... If you chose to go that route instead of drywall in the ceiling of the attic space since it is for storage only you could consider using unfaced insulation followed by your 1 or 2 inch rigid foamboad then covered with a paper commonly known as FSK which is a reinforced foil material which has a 25-50 flame and smoke spread and should pass and codes in your areas.. the approximate cost of FSK material should be around 35 to 40 cents per square foot it comes in long rolls and should be easier to install than drywall.. by using nails with washers on them and nailing into the rafters above..also dont forget if you remove the kneewall insulation you will also need to install insulation on any outside walls which may be in your attic spaces....

but before going to all that expense you also might see if anyone in your area does the spray in expanding Foam insulation.. In this area it is used by spraying this expanding foam directly to the underside of the roof deck..

supposedly if the product is completely filling all voids under the roof deck so as not to have air between the insulation and the deck then air baffles are not necessary..

If you cant find anyone who does this in your area but have an interest email me back and I am sure I can find a manufacturer who will probably have someone doing this method of insualtion in your area..

Good luck

 
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