I have read in the articles and forum posts here about the importance of slab edge insulation to reduce heating loss in a cold weather. In our shop we put 2” XPS on the inside of the foundation wall to make an insulated break along the edges of the planned 5” thick slab. But I’m not sure how one is supposed to treat the edges of the slab at the 12’ overhead door where the slab edge will actually be outside the building envelope meeting the packed gravel drive/park area. I sort of understand forming out the area with 2x4 to contain the slab (no direct experience yet, but I plan to learn!). But I'm not sure how – or if – it is reasonable to try to insulate the doorway edge.

I saw this slab edge product on-line, do you have any comments on it?
http://www.energyedgeforms.com/index.htm

Or a DYI idea: Form out the edge with some high quality ‘plastic’ lumber people use on decks (no rotting). Put XPS on the inside of the formed area. Place the concrete and never remove the plastic/insulated 'form'. Bring gravel up to it, compact and call it done. Would that work? Any advice or comments are welcome. We plan to do all of the prep (stone, VP, 2’ perimeter rigid insulation, rebar) and then hire out the actual pour for the 30x50 slab. If it works, I attached a photo of the door opening with a yellow box representing the slab edge.

Any advice or comments are welcome. We plan to do all of the prep (stone, VP, insulation/basic forming, rebar) and then hire out the actual pour for the 30x50 slab. I attached a photo of the door opening with a yellow box representing the slab edge.

Thanks

The slab edge system in the link is only R7. 2" thick t & g XPS comes in 2' wide sections by a number of different lengths (8',10',12'), and 'on edge at the door would deliver R10 down to about the same depth as your interior insulation. (or you could double-layer your 1" goods.) A few plastic ties to anchor it into the slab won't hurt, but depending on how you treat/pave the exterior, may not be essential- the XPS will tend to stick to the concrete, but can be peeled off with a wrecking bar if it isn't anchored. (Simply trapping it will suffice if you're hard-paving the exterior.)

Staking cheaper standard lumber as backing for the pour,( and pulling it later) would probably be cheaper/stiffer and more robust than PVC or composite decking. If you're concerned about protecting the insulation from damage after the fact, rigid fiber-cement board (Hardi or similar) shored up with timbers for the pour and left in place for the backfill would probably work better than Trex, etc. By itself composite decking is way too flexible to use as concrete forms without a lot of support. Well-compacted backfill would probably do it, but compacting the gravel will tend to push the form inward rather than leaving straight line.

BTW: Does the interior slab edge insulation extend up above the foundation sill to provide at least some thermal break all the way around the perimeter, or is it just thermally isolaining the slab from the foundation? (Even 3" of sub-R2 foundation around the bottom of the wall can become a measurable fraction of the heat loss in a well-insulated building.)

Thanks for your input, as always, it is very helpful.

If I understand you correctly and take into account our site, it seems to me the proposed solution would be:
- attach 2’ x 12’ and 2” thick XPS to exterior block, supported by lumber as needed 
- XPS serves as form as well as slab-edge insulation, lumber taken off after pour
- protect exterior XPS with cement board (gravel parking, no paving)

This makes ‘construction’ sense and seems doable. But let me ask about a concern I have. Termites!

Termites were in part the reason why I chose to use the rigid insulation on the interior of the building foundation wall rather than exterior. I could be wrong, but I thought the risk might be less with the interior XPS application. Also, the framer used untreated lumber & no gasket between block and lumber for vertical framing around the 12x12 door (this only for the door framing, not for the sill which is treated with good quality gasket underneath).

I plan to treat the lumber with Timbor – but I’m not sure how well that protects, especially since the metal siding/trim is already on. And for that matter I don’t have an accurate picture on what the real risk is from termites, and how rigid insulation may impact that risk. Am I building a well insulated structure that will require extensive reframing 15 yrs down the line? I hope not.

I’ve attached a close-up of the framing (from the interior) to show my area of concern. A small piece of XPS in the corner is not yet installed but I will add it. The top of slab will be two inches below the top of the interior XPS around the entire perimeter of the building.

How much increased risk is there from termites if I have an exterior piece XPS (2’ wide, 2” thick) down in the ground and extending up to the top of slab (to provide a form and insulation)?

With the termite issue in mind, do you have any other comments/advice on construction?

Thanks!

babybldr;

you can buy Perform Guard® EPS  a termite resistant expanded polystyrene insulation for all types of construction.

cmkavala, Thanks for the tip on borate treated rigid insulation. I guess I should have thought of that one on my own … but I’ve kind of had only the XPS on my brain. To tell you the truth I didn’t really realize that termites might be such a problem, and I’m still not sure where we stand on that. I will definitely try to get the treated rigid insulation for the slab edge applications and use the concrete form idea suggested by Dana1 above. I’m not sure where to buy the treated insulation (didn’t see it at the big-box store) so I’ll work on that next. Thanks!

BabyBldr;

Termites don't eat the foam for food, but they will nest in it. Mice will do the same.     the following links shows some locations, not all foam mfg.'s have the capability to add borate. You won't have any luck at the Home Depot,  nor would I expect that they would even know what you are talking about

http://www.foam-control.com/contact/contact.asp

http://www.energysystemsinc.com/perform.htm

http://www.achfoam.com/TermiteResistantEPS.aspx

Using a strip of copper flashing between the foundation & foam, extending all the way to the foundation sill can be a termite-toxic deterrent as well.

Maybe a little late for your conversation but I just came across this question… The EnergyEdge material referenced in the first comment by BabyBldr is a product designed exactly for these applications. (Our system has been detailed into use below overhead door to create a thermal break there.) It is a concrete edge form, and does contain R10, insulation. (2lb, ACH below grade approved EPS 2-5/16” thick, this is the same material Chris referred to with borax to deter insects, i.e. termites!) The forms stay in place, replacing the requirement for perimeter wood forms. They are supported on the interior by our braces that also properly support interior perimeter re-bar. Our system saves natural resources and reduces construction waste; eliminates chemical release compounds and form stripping and recovery labor. We meet IRC2006 code required slab edge insulation and are a critical… normally missing… element in the buildings thermal envelope. Our system improves the performance of building and mechanical systems, especially ICF, SIP walls and Radiant Floor Slabs.

We are in the process of being distributed through the CertainTeed network across the United States and Canada. See your local sales rep and ask… we are new with them so do not take “I don’t know about it” for an answer. Go to our web site at www.EnergyEdgeForm.com or CertainTeed’s foundation division web site. I also placed our product information on this web site on our material. Or, you can give drop us an Email… use [email protected]. Thanks for the interest!

PS... I tried to attach a photo but could not... If anyone knows how to insert a photo, let me know and I will do so.

This is how we eliminate heat-loss at the slab edge http://www.viking-house.ie/passive-house-foundations.html

This is how we eliminate heat-loss at the slab edge

Impressive engineering work. Do those EPS elements get cut on-site?

The EPS manufacturer delivers them to site pre cut!

Do they custom cut each job off your electronic files via direct submission or is this something that has been worked out over time?

For example, if you have a special job that changes some details of the elements; thicker or thinner or whatever, do you alert them to that or does it just get fed into the cutter and out it comes?

We usually send them a dimensioned drawing showing what shapes we need.

Are these suited to North America, or do we like to build them too big?