Please help out a newbie...


Old 01-05-06, 05:58 AM
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Join Date: Jan 2006
Location: USA
Posts: 2
Please help out a newbie...


I need some help with insulation installation. I have a 150 (1849) year old home with no insulation in the attic. This is the type of attic that you can open a door and walk right up there. It is almost another room (we want to convert it into a room later on in life) and we use it now for storage so just putting insulation on the floor is not an option. We want to put it on the roof but I have some questions on this. My wife and I went to the local Home Depot and Lowes and talked to some people but we got mixed answers.

The first question is what R rating should I use for the Philadelphia area? The reason I ask this is when I was looking at a chart in Lowes, it says R-49, but when I went to Home Depot, they said the most should be R-38. What is the correct R rating?

The other question I have is this (and I will try to explain this well)…We have an attic fan to help with ventilation and to get the hot air out in the summertime. The guy at home depot said that I need to block this in the winter with something so moisture will not leak out. He mentioned that I could use faced (brown bag or foil looking stuff) insulation if I block the vent but I need to use unfaced if I keep it unblocked because the facing holds in the moisture. Now, that makes no sense to me. If it holds it in, why would I want to keep the facing on? It seems backwards to me. What is the correct way to do this? I would like to be able to use facing on it if I could because I go up there a good amount and I would like the protection incase I bump into the installation while I am up there.

Oh, and to help (hurt) matters, the previous owners must have had insulation up there before be got the house because I can see the staples and the little ripped paper from the facing, obviously from a previous try at this. They did not have the attic fan at the time, we had that installed as soon as we moved in.

I really hope this makes sense and someone can help me out, I want to tackle this project this weekend if possible

Thanks for all your help!!!!
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Old 01-05-06, 06:04 PM
Join Date: Jan 2006
Posts: 143

Pennsylvania energy code mandates R-38 attic insulation for Philadelphia and adjacent counties. You can put in more if you wish. R-38 is required and should be sufficient.

It will not be possible to put R-38 into your rafters rather than your floors if you plan to finish the attic space later. The reason is simple: R-38 insulation requires a cavity depth of at least 12" in order to fit the insulation. If you plan to cover the rafters in the future with drywall, it cannot extend below your existing rafter edges. Unless you have 12" deep rafters or thicker, R-38 simply will not fit into your rafter spaces.

If you choose to insulate your rafter rather than the floor, you will also need to insulate your attic's gable end walls if any. These walls will require at minimum an R-16 insulation depth. This again poses a problem because standard wall studs will only be 4" deep. This is not enough to allow for R-16 insulation even if using dense pack fiberglass which will provide up to R-15 for 2x4 walls. Unless your gable end walls are at least 2x6s, you won't be able to meet energy code with existing 2x4 walls.

If you choose to insulate your rafters rather than the attic floor, you will need to close off the attic fan in winter. Otherwise your heat will simply rise through the uninsulated attic floor below and flow right out this hole in your roof and would be the same as insulating the attic floor but keeping the windows open in the room below.

If you insulate the attic rafters, it is a building code requirement to have a vapor retarder on the warm-in-winter side of the insulation (toward the attic not the siding or the roof) for the insulation in your gable walls and rafters. This vapor retarder is there to keep gaseous water vapor inside the room and to keep it from moving into rafter and wall cavity spaces where it can contact cooler surfaces and condense as liquid water causing water damage.

If you choose to insulate your attic rafters rather than the floor, you will also need to install rafter vents from the open eaves to the ridge vent and if you do not have both type vents, must install them.

The bottom line here is that installing insulation in your attic rafters will be far more costly than simply adding insulation to the attic floor. You will need to extend the depth of the rafters to provide a deep enough cavity for the required insulation depth. You will likely also need to do this for your gables walls as well.

Insulating the attic rafters will also be less energy efficient because by insulating the rafters rather than floor, you end up heating the attic space just as you do now. Any heat that rises through the attic floor will not be trapped at that level, but will continue up into the attic.

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