edge insulation on slab for radiant heat

crankcase · 10-02-2010, 10:00 AM

OK I screwed up, but so did the contractor too. I have a "engineered floating slab" for my detached garage. It's a 4" floating slab with beveled edge that goes down to 16" wide thickened edge around the perimeter about 12" deep. So kinda like a little footing. I laid 4 loops of pex for radiant heating on top of a 7 layer foil, bubble and aluminum faced insulation blanket before the concrete was poured. The day of the pour (after the pour) the contractor told me that we probably shouldn't have run the tubing down in the thick edge part, only where the floor was 4" thick. The tubing was spaced 6" apart for maybe 24" along the outside edge, then 12-14" spacing along the rest of the slab.
Their is 1 course of block then the walls are set un top of that. Originally the contractor was going to use the split block to match the house, but since the slab was now done and my tubing was "wrong", he suggested that we use smooth block then run foamboard tight against the outside of the block to a depth of 48" around the perimeter, then run a horizontal piece of foam, 10" below grade, kinda like a sideways off set "T". Run some flashing over the exposed foam so it don't look too bad. Alright I says let do that, we'll go with the smooth block then. Well aparently the workers didn't get the message and when I get home from work the next day I have my split face block in place, it looks nice but now how am I going to run my foam board tight against it for insulation?
I need to insulate it somehow cause my block will just radiate the heat off of the tubing, but what I don't get is it would radiate anyhow even if I kept the tubing away from the thick edge. I filled the blocks that weren't core filled with the j bolts with foam beads, but that's not going to do too much.
I'm almost thinking of spray foam and painting it up against the block, and still foam board below grade, Then I have the front side with an apron, anything here would really look like hell. I'm in Minnesota and this garage will have 2 zones for heating, garage space won't be too warm, but there is some office, living quarters that need to be kept warmer thru the winter.

**Gary in WA** · 10-03-2010, 12:52 AM

Sounds like you have had some problems. Check with your local B.D. about the foam all the way up or not, also covering the foam against insects and rodents. I wish you had done a search here on radiant barriers under slabs before the pour: http://www.healthyheating.com/Page%2...o_bldg_sys.htm

http://www.greenbuildingadvisor.com/...cience-podcast

Find your foam thickness here: http://www.energycodes.gov/support/slab_faq.stm

Under the living area, a vapor barrier is required. I hope he air sealed it: http://www.100khouse.com/2009/06/24/...b-air-sealing/

If no vapor barrier plastic, at least: http://www.nrmca.org/aboutconcrete/cips/29p.pdf

Add more than the minimum required amount of glazing (operable) for ventilation if no gravel, v.b., to help clear the moisture rising with the heat drawing from the capillary water under the slab. Be sure to use a poly sill sealer under the p.t. bottom plate for a capillary/thermal break. Choose your cavity insulation carefully as now you are heating those stud bays from below. Even double layer the sill sealer. Have you given any thought to a rain-screen, does your area permit it? http://www.greenhomebuilding.com/pdf/RainScreen.pdf

http://www.nchh.org/Portals/0/Contents/Article0440.pdf

Gary

crankcase · 10-03-2010, 03:42 PM

Thanks for the links Gary, very informative stuff. I want to clairify that the insulation under the slab is more substantial that aluminum faced bubblewrap.
It's basically a concrete blanket used for curing concrete in cold weather. Here's a link to a similar product:
http://www.pregis.com/LinkClick.aspx...id=519&mid=688

We just built a new home and the builder used the same stuff in the basement and we are heating that with a 15KW off peak boiler. Builder said he has been using this for a few years now, feedback from clients was positive. I was hesitant at first, I guess I'll let you know if I'm a believer...It is wrapped and stiched in a heavy tarp which he claims doubles as a vapor barrier. Any seamed were overlapped at least 6" and taped with foil duct tape.

The structure is already up and here is a cross section of what I have:

yellow is the blanket/vapor barier insulation
red circles denotes pex tubing loops
white circles = rebar
that's supposed to be 1 coarse of 6x8 split face hollow concrete block. core filled with polystrene beads
1 layer sill seal
2x6 PT plate
2x4 bottom plate
not shown is 1 layer of housewrap under vinyl siding
Green denotes proposed foam board insulation drawn at 2" thickness. I was leaning towards Thermax foil sided 1" , vertical is 48", horizontal is 24"

crankcase · 10-03-2010, 03:53 PM

lets try this a little easier on the eyes.

**Gary in WA** · 10-04-2010, 04:40 PM

http://docs.google.com/viewer?a=v&q=...3V4gVambxIzD3A

http://www.inspectapedia.com/Energy/...urate_Slab.htm

http://docs.google.com/viewer?a=v&q=...4EyM707m0gPdXQ

Be sure to install flashing over the board on the foundation. Some areas require 6” down to check for termites…for others reading. I'd slope the "T" for draining liquid water.

Gary

shumakerscott · 10-06-2010, 12:49 AM

Here is a wealth of information. I used it as a guide when I did my floor.
http://www.radiantdesigninstitute.com/

dorf dude...