Attic ventilation and insulation

[Daox]

I'm not trying to put down a vapor or wind barrier. I was thinking of putting down a sheet of something over the fiberglass insulation so that the cellulose doesn't crush it down. However, after being up in the attic quite a bit this weekend, I don't think thats really going to be necessary. The amount of cellulose I'm putting in will weight roughly 1.5 lbs per sq ft. I don't think that'll crush the fiberglass much and it won't be worth the trouble of putting something down to seperate the two.

[davidbr13]

Daox, in the highlighted area, I would try first using some of the foam channels to get air from the new soffit vents into the attic area. Then fill the rest of the volume between the channels and the interior with spray-in foam (probably need an insulation contractor to come spray it in, but it only takes a few minutes once they get going). That'll have the added benefit of sealing all the air leaks. This can be done from the inside without having to compromise the roof, though you do have to remove the ceiling drywall over the highlighted area temporarily.

If you want added insulation in the area, then at the same time you could add furring strips to the bottom of the rafters to give you extra space, then slip in more insulation before reinstalling the drywall. Of course this "lowers" the ceiling in that area, so it's a bit of a trade-off.

[Daox]

This is what I ended up doing with the first half of the attic. The bottom of the angled area has about 1.5"-2" of rockwool in it (~R-3 per inch). I slid in two sheets of 1" thick polyiso insulation above it (R-6.5 per inch). This will give me a combined total of roughly R-18. Nothing amazing, but that is about as best as I can do with the hard access to the area. Using the foam boards also allowed me to leave a 1" gap above the foam as an air passage for venting. They also extend far enough up to act as a dam for when the cellulose is blown in.

When winter does decide to come around, I'll measure the wall temp and see how cold it gets. I have one of those IR temperature guns. If need be, I'll add another sheet or two of foam board on the inside of the wall and drywall over it.

Next on the list is adding in the cellulose. That'll really pump up the r-value. I'm planning on blowing in roughly 12" of cellulose over the existing rockwool and fiberglass. This should get the r-value for the rest of the attic up to about 60-65.


Insulation diagram.




Fitting and cutting the foam boards.




Installed foam boards.

[davidbr13]

That looks like a pretty good way to go. I've been at it, too, insulating over the garage, making a cover for the attic stairway, and adding a radiant barrier on the most sunlit side of the roof, a little at a time. It'll be interesting this coming winter and summer to see how much it helps. It certainly can't hurt.

Another easy area to insulate is plugging up the fireplace opening when not in use. We don't use ours, and it generated a considerable draft all the time, even with the damper and doors shut tight. A couple of foam boards glued together and a nice looking fabric cover fixed that problem, and looks good at the same time.

[Daox]

I finally got back to this project last night (*grumble* too many other fires to put out lately). At the last update, I had installed the foam board on one side of the attic. I also have added vented soffits since then. So, that one side is completely done.

Last night I did the other side of the attic with the wife. We got most of it done, but are going to need one more piece of foam board to finish up. I also still need to add the vented soffit, but we'll wait for next year now that its getting cold out.

Now, we're finally ready to blow in the cellulose! I'm excited about this part. I just have to check out the local stores. Theres two different brands out there. The Greenfiber that the big chains carry, and another one (I forget the name) that a local store carries. The price is significant enough to warrant looking into, but I'm not sure of the quantity of the packages. Unfortunately, I haven't been able to find a good way to measure the two. One measures theirs in weight, where the other measures theirs in cubic feet of coverage.

[Daox]

Well, I finally found out the two cellulose packs are the same weight. One is $4 and one is $6.50 though. Quite a big difference in price when you are buying 50 packs ($200 vs $325).

However, now I'm waiting on my cousin. He just bought a truck that needs new brakes. Once he is done fixing it, we'll pickup the cellulose with his truck and a trailer. That'll save me a delivery charge.

[toyobug]

how are you going to blow it in?

[Daox]

It should be quite easy with a blowing machine. I've seen it done, never done it myself though. You just have one person filling up the hopper and the other blowing it all in. Here are a couple pics I found on Google.

[toyobug]

i take it that most rental stores have thos available?

[Daox]

When I buy my bags of insulation I get the blower for X hours (based upon number of bags bought) of free rental time.