# Insulating basement slab with radiant heat.



## CENTERLINE MV (Jan 9, 2011)

Does anybody out there have a good solution for insulating the edges of a radiant slab where there will be garage door openings? I'm putting down 2" polystyrene under the slab and around the perimeter of the foundation walls. But, what about the edge of the slab in the door openings? I have a 25' opening and a 9' opening. Is there a good way to insulate this edge without having any exposed insulation in the doorway? 

I was considering installing 2" of foam and having 2" of concrete over it to at least buffer the thermal loss, but I'm concerned the concrete will crack since there's likely heavy equipment that'll be coming through the doors (skid steers).


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## donerightwyo (Oct 10, 2011)

I would just use a piece of expansion as a thermal break. I would be nervous about the 2" breaking out as well.


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## CENTERLINE MV (Jan 9, 2011)

I was also thinking a custom made I-beam that sits to the height of the floor with rigid foam secured in the web. That way it's super strong, has almost no thermal break, and the machines can run over it all day long.


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## Golden view (Feb 16, 2012)

I've always been amazed this detail is never really addressed, but I've built a few super insulated homes in Alaska and none seemed to have much of an issue arise from essentially have a heated slab edge out in the cold. They always burned fuel close to the calculated rate.

The edge at the door would always get foam cut at a 45 degree angle and held just below grade. I'm more worried about the top of the slab that's exposed.

My only simple thought to make it better is to not form the slab straight across at the door to have less exposed surface area. With OHDs mounted inside and a thick wall, you might have 12"+ of exposed concrete the length of the door.


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## CENTERLINE MV (Jan 9, 2011)




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## Texas Wax (Jan 16, 2012)

My understanding is that a thermal break/expansion jiont in those areas are a good solution. The thermal mass of the slab, insulated under retains a large amount of heat and easily offsets a minimal heat loss. Putting a conducting material such as steel or running concrete to concrete is less effective. Allowing the heat to easily travel outside the building envelope, creating a more significant heat loss.


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## CENTERLINE MV (Jan 9, 2011)

Texas Wax said:


> My understanding is that a thermal break/expansion jiont in those areas are a good solution. The thermal mass of the slab, insulated under retains a large amount of heat and easily offsets a minimal heat loss. Putting a conducting material such as steel or running concrete to concrete is less effective. Allowing the heat to easily travel outside the building envelope, creating a more significant heat loss.


Yes, but if the steel is insulated as illustrated in my drawing, there is no significant thermal break.


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## Golden view (Feb 16, 2012)

CENTERLINE MV said:


> Yes, but if the steel is insulated as illustrated in my drawing, there is no significant thermal break.


A lot of heat escapes through the flange in that scenario.


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## Philament (Dec 9, 2014)

What's the cross-section of the foundation look like at the garage door? 
Are you pouring and apron in front of the garage or gravel ramp?
Have you poured the slab inside already?


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## CENTERLINE MV (Jan 9, 2011)

Golden view said:


> A lot of heat escapes through the flange in that scenario.


I'm thinking about keeping the flange in the conditioned space and pouring a slab outside of the door. The edge of the flange will basically be where the garage door lands. Also, the flange is only 1/4" thick and maybe 2-3" wide so I don't think much of a heat sink regardless.


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## CENTERLINE MV (Jan 9, 2011)

Philament said:


> What's the cross-section of the foundation look like at the garage door?
> Are you pouring and apron in front of the garage or gravel ramp?
> Have you poured the slab inside already?


I'll make a sketchup drawing of what I'm thinking & post up l8r... Stay tuned!


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## Morning Wood (Jan 12, 2008)

The radiant can be nice for keeping ice away from the garage door seal. I don't really see the problem with your I-beam other than it rotting out over time. Maybe use stainless😄


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## CENTERLINE MV (Jan 9, 2011)




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## TimNJ (Sep 7, 2005)

I don't like the "I" beam idea.
With you up in MA. bringing in equipment with road salt will spell future disaster for that steel.


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## CENTERLINE MV (Jan 9, 2011)

TimNJ said:


> I don't like the "I" beam idea.
> With you up in MA. bringing in equipment with road salt will spell future disaster for that steel.


Here on the Vineyard 95% of our roads are dirt roads & very little salt is used (We're also in gardening zone 7a and rarely see snow & ice---except the past week lol). The garage bays open up to a mechanics shop for power equipment. The large openings are for getting machinery, mowers, etc... in to the mechanic. I plan on priming the beam with automotive primer and spraying with a durable finish. If he's gotta spray it once a year for maintenance then so be it.


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## rustyjames (Aug 28, 2008)

I would just leave a 1/2" gap between the slab and apron, backer rod, sealant and be done with it :thumbsup:


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## Morning Wood (Jan 12, 2008)

Again, stainless.


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## Golden view (Feb 16, 2012)

I'm not convinced any of these ideas have a ROI period better than the life of the structure.


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## Golden view (Feb 16, 2012)

This


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## CENTERLINE MV (Jan 9, 2011)

Golden view said:


> This


I like the idea, but with EPS beveled like that, I'm afraid the concrete would crack from a machine driving over that spot.

I also like the idea of stainless, but I'm sure that would be wicked expensive.

The 1/2" gap with backer rod & sika sealant is probably the most cost-effective route for R.O.I.


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