Insulation, Radiant and Vapor Barriers - What type of insulation?

I would like to insulate between the floor joists of a raised sunroom/conservatory. I am hoping to use cut foam boards between the joists and as a single horizontal layer underneath. A few questions:

1. Is this type of installation recommended?
2. What type of insulation board should I use (there are many options at Lowes/Home Depot)?
3. Do I need spray insulation as well to fill the gaps?
4. Any tips on installing?

Thanks in advance.

Hi 105 and welcome to the forum. So, what is underneath this room? Rodents can and will go right through foam board, I just did a job this summer where the big ones had moved their colony. We moved them out and did a final cover in OSB. If it is over a protected space you are probably OK.

Foam board works great but comes in thin to thick. Depending upon your exposure you may need thick. Cutting to fit is a tedious job, but caulking will fill the small gaps. Can foam works when it is warm enough, but is a pain as you can't easily start and stop to fill as you go.

A quick and simple approach would be to fill with unfaced fiberglass, cover with 2 inches of rigid, and then if necessary cover again with 7/16" OSB. Minimal cutting, great R-value, and easily done.

I use the pink or blue, or the foil faced if I can have it face an air gap. If all of this is inside, then you will need a fire rated covering like sheetrock. If outside, check, but the OSB should be acceptable.

enjoy,
Bud

Bud,

Thanks for your response.

The underneath is exposed to the outdoors. Right now the gaps between the joists isarefilled with fiberglass and covered with plywood/osb. There is evidence of rodents in the insulation as well as moisture collection. Was not aware that rodents eat through foam!

I am looking to improve the insulation and heard foam insulation to fill the gaps would help. If I did that, and then covered with plywood/osb, do you think that would improve the R-value?

Thanks

Yes they had a ball building tunnels and nests. We trapped over twenty of them before we were satisfied we weren't boxing some inside. These were not mice, so the lady of the house wanted to be absolutely certain nothing was left inside. I won't repeat her exact words:madhell:.

In NY, your vapor barrier should be on the warm side of the insulation, which would typically be just under the flooring. If you use rigid, it is essentially a VB, but when used on the outside, it must be thick enough that the inside surface does not get cold enough to cause condensation. With the underneath exposed to the weather, you should have, in my estimation at least R-38 and some would suggest as high as R-50. You are not going to want to put in that much foam.

What are your joists? 2x10's 8's or what, so we can see how much a combination of fiberglass and rigid can give you.

Were you planning on removing the old fiberglass or cleaning it up and adding to it?

Bud

Yes - rodents are a pain. At least snakes only leave their skins behind...

The joists are 2x10s. The bottom of the joists is 3' off ground level.

If I put rigid (by that I believe you mean rigid foam insulation) flat underneath the joists, and seal the joints, will that still allow rodents to penetrate?

Hi again, I'm always puzzled how issues that have been around for so many years still don't have a single simple solution.
You mentioned you have already seen signs of moisture, so don't want to repeat that. Here's my suggestion, assuming you are starting with empty cavities. Cut and fit 2" foil faced Polyisocyanurate, it's the one the big boxes usually sell with the foil face and has a bit higher r-value. Caulk or foam in place to get a good air seal. That leaves 7.5" to fill with unfaced fiberglass insulation, fill it 100%. Then cover with 7/16" OSB. No vapor barrier on the outside. On the outside, finish everything so rodents and insects can't find a place to seek access. On the upper/inside, seal all air paths, wiring, other, so no direct air paths exist. The tiny amount of moisture that can pass through the 2x10 bridging can also pass through the OSB to the outside. The above combination will bring you up to about an R-40 with the added benefits of being totally air sealed and having one radiant barrier, so you should be in pretty good shape.

Happy insulating
Bud

Bud - thanks for your advice. Will let you know how the install goes.

Bud - found this at HD.

Product Information Error Page (http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100322376)

They did not have 2" foil faced Polyisocyanurate, so will this suffice? Do it fit it with the foil facing downwards?

Thanks

Yes, foil facing down as the fiberglass acts as an air gap. The radiant barrier effect works best with a gap, although no one really wants to put a number on it's actual benefits, like an r-value. I suspect it is more than most will admit, especially in a closed space where it won't be subject to dust and contamination.

Also, your link just went to an error page.

Bud

Hears how we build in Pa. First the crawl space has to have cross ventilation. If its built on a small block wall to support the plate and floor there needs to be grills in the block wall for cross ventilation. If there is a foundation with cross ventilation and screens in those vents the all you need to do is ripp 1 1/2 strips of treated 1 bys and tack nail them to the bottom inside joist as a small ledger. Now take some Styrofoam 1' thick cut them the 14 1/2" wide and drop those 8'x14 1/2" into the long joist bays. Now you can get some "R" 30 insul faced or un faced and drop the right on top of the foam. The faced HAS to be at the sub floor "HEATED SIDE" and not on the foam. If its unfaced then a 6ml ploy vapor barrier again on top of the floor joist. If its a raised floor and no walls to protect the floor The use treated plywood os OSB to the bottom of the joist, Again now you va flop the insulation id from the top and the BARRIER is on the top of the floor joist WARM side. The perfect way if you have to work from below is get a insul company and spray foam every thing from below and shave off the excess that Hung below joist and again bottom cap the joist with treaded ply or OSB to keep the mice out either or a vapor barrier is the best way and on the warm side. If unsul get 5% of mostiure in it, the insul will lose 95% of its insul properties