Hey everyone...I have a few questions regarding cellulose insulation. I have it in the ceiling joists of my house. It is up to/slightly over the joists. Is this high enough? I went up and loosened it all up and loosly pushed it back into where the rafter bays meet the ceiling joists. Should I have loosened it all up? Some of it was very packed in spots. I had clumps of it that needed to be physically broken apart. seems to me that is would insulate better if loose yet filling all voids. I'm not sure when it was installed but my house was built in 1925. When was cellulose introduced. There also is a very thin layer of what appears to be rockwool on the bottom of the ceiling joist against the ceiling. I'm sure that isn't doing anything. I am redoing the ceilings with sheetrock throughout as I can't stand plaster/laths. Can I shovel off the cellulose as I do each room's ceiling and insulate with fiberglass and then replace the cellolose over the fiberglass? I have seen this method in new homes that I have built(I am a carpenter). My only fear is that the fiberglass will get compressed and lose r value. Also if I do this should the vapor barrier go up or down or should I not use the batts with barrier? Thanks for any help.

Jason

Yes, the cellulose will insulate better if it is not compressed. I don't know how much is "enough" because I don't know what region your house is in. Yes, you can shovel up the cellulose and re-use it over the fiberglass,,,it won't compress the fiberglass enough to matter much. The vapor retarder should go on the winter warm side of the assembly, that's down in the cold regions. Whether you even need a vapor retarder depends on the amount of attic ventilation you have compared to the attic floor area, but determining the exact amount of ventilation in square inches of net free area is not easy in an existing house.

Sounds like I am on the right track. My upstairs is cold in the heating months(I live in Vermont) which seems weird to me as heat rises. I guess it is because I only have one forced air duct upstairs. I'd say my attic is about 27 feet by 18 or 20 feet and the ridge height off the tops of the joists is 5 feet(gambrel roof). I have one 12"x12" vent in each gable. There is a vapor barrier on the rockwool insulation underneath. Not sure that it is needed though. Another question is that I have blown-in cellulose in the walls. I believe that they are 2x4. I'm guessing that the cellulose will settle in the wall just like the attic leaving voids near the tops? Do my plans of padding out the studs to 2x6 and installing fiberglass instead make sense. I am planning on tearing all the plaster out anyways. I am guessing vapor barrier on the inside of the walls. And how much would be too much cellulose over the fiberglass in the attic. Is there such thing. I am just thinking that when I remove it from the walls I will have a lot of free insulation to use up there. Thanks so much for the reply.

J

OK, your attic is about 540 square feet floor area, and you have about one square foot of net free ventilation, assuming the louvers have 50% net free area. That's somewhat less ventilation than the current building code requires. Without a vapor retarder in your ceiling assembly, you would need 3.6 square feet of net free area, but don't panic, there are hundreds of thousands and maybe millions of houses which have ventilation similar to yours and which function with no problems. You are not required to bring your house up to current codes.

For your walls, if you use R-19 or R-21 fiberglass, you should have a vapor retarder on the inside face of the wall, right behind your wallboard. Most insulation comes with a vapor retarder as part of it...the side with the stapling flange is the vapor retarder side.

If you place fiberglass insulation in your ceiling, I think you should use a vapor retarder, because that reduces the ventilation requirement to 1.8 square feet, which is much closer to what you have. If you were buying all the attic insulation, then there would be a point beyond which the return on investment would be so small as to make it uneconomical, but your cellulose is essentially free, so pile it on to your heart's content. Just dont pack it in down where the roof meets the ceiling...taper it off before that point, so that the roof plane remains as cold as possible as far down as possible.

Yes, I would say you're on the right track.

I've done a little more research and I've found out that the walls/lower roof(gamrel) are 2x4 and filled with cellulose. My upstairs is very cold in the winter. Would fiberglass insulation be better and is it worth padding out the wall to handle 2x6 high density fiberglass. It bothers me that the upstairs is so cold. Also another question is my upstairs bathroom floor is very cold. there is a drop ceiling below but it seems like it has more to do than just that. It is a small shed dormer. Could it be that where the rafters meet the wall there is air getting in? Seem to me I need to take all the cellulose out and pad out the walls, seal any drafts, and re-insulate with fiberglass. Where would I start? I am guessing the upstairs would be first. I'm getting a wood stove and new chimney for it this summer so that should help.
Well thanks for any help,
J