Getting ready to pour a 22 x 26 foot monolithic footing and slab for a carriage house garage/apartment at my house. The garage space will have radiant tubing installed in the slab for occasional use. This may in the future become a heated shop space. Here are the questions.
1. I am planning to use foamboard under the whole slab. What thickness or R value should I use? What is typical?
2. We are also planning to place foam board on the exterior of the footings for the entirety of the perimeter. What thickness or R value? What is typical? We plan to run it up level with the top of the slab.
The project is in Detroit so the temperatures can run down to below zero.
Replies
I used 2" rigid (pink or blue) 150. Some codes dictate 250 for garage slabs. Same around the perimeter, although 150 will be sufficient for that. Since the greatest heat loss is through the perimeter, it wouldn't hurt to go with 4" there. Just double up the 2".
Since you say "occasional use" you should definately go with insulating under the entire slab. Some installers recommend only partial so you can use the earth as a heat sink, although you'll see some controversy about that.
Here's a good link for you:
http://www.radiantpanelassociation.org/i4a/pages/index.cfm?pageid=1
Go to the public bulletin board.
DT, you can save a bunch on the foam if you use beadboard instead of the blue or pink stuff.
You can go with a Type II R10 board for about $11 a sheet, Type IX (2 pound) is about $14 a sheet recently. http://www.r-control.com/eps_foam/default.asp
Call the local manufacturer (looks like Grand Rapids) and find out where you can get it locally, or you may have to order it directly. No one stocks the stuff except for Type I which is NOT suitable for your use.
Joe H
Why wouldn't I want the IX product? For that matter why not the I product? Water Vapor Permeance?
Thanks for the help!
The difference is the density of the foam & it's crush resistance. Type I is not adequate for under slab use, Type IX is probably more than you need for a home garage. The difference that matters is the price? 20 sheets Type II @ $11 = $220. 20 sheets Type IX @ $14 = $280.
It's not much in the overall scheme of things, but eventually all those $60 extras add up to something. If there's no advantage to using the higher density stuff, why spend the money?
Joe H