How and Why to Insulate the Edge of a Concrete Floor Slab

[@wigram3799]

Hi Matthew, I wanted to attached a diagram, but not sure how. I'm keen to use an insulated slab if we chose concrete over cross laminated timber flooring. The poly up the exterior foundation seems like a weak link. My thought was you could do a 110mm wide concrete ring foundation as was standard before the ChCh earthquake, Then fit 50mm poly up the inside of that ring foundation so it sits proud by 50mm, brace as required and use this as the boxing for the concrete slab inside. I was thinking you would make the edges of the slab deeper, and use poly pods in a grid with thinner poly under all the toughs so there is no direct connection between slab and dirt. the inner slab is self supporting, and the 140mm timber framing sits on the edge of the inner slab (outside 50mm over the poly), the brick work and cavity are above the ring foundation. No ties between the ring and floor slab - the ring foundation only holds the bricks up. Roof and walls all supported by slab. Thoughts on this idea? (if you can figure out what I'm talking about without a diagram :-)

[@user-up2kz6ws6m]

Another interesting thing, is by just isolating the edges and down 60 cm you will only loose 15% heat even if the floor isn't insulated. Insulating the edges alone can actually be sufficient,. Big factories Apply this practice

[@bpdp379]

How would you recommend the transition from a heated slab to a driveway apron?

[@habenarohank]

If I add Pex tubing (with out insulating under the slab but around the outside perimeter) in the slab and heat it for free in the fall with evacuated solar tubes would the ground retain the heat (heat sink) or would the heat loss be absorbed down? From my understanding the R value of the ground will keep the heat under the slab

[@philgwellington6036]

Thanks Mathew, Just what I was looking for. NZ seems a bit behind in smart construction practice.

[@tutnallman]

the ground is relatively warm. edge insulation is a must but why not develop a thermal coupling with the subsoil. as you say a house on top keeps it warm. in uk I would say that the subsoil is 12-15 degrees C. with a heated slab (UFH) this would become a huge heat store. my initial evidence for this came from a neighbour who built an extension with a concrete slab on 100mm polystyrene. the old tiled floor of the existing house is warmer than the new floor and much more pleasant to walk on. Discuss:

[@eceaey2064]

Hi, imagine a building without any floor (just soil) and that the walls and foundation of the building is partly made of mud and dirt (old building 1700). What would your advice be on insulating the floor and including the mud walls?

[@AKwildernessfarm]

There’s the “slabless” method. Level the floor with well draining rock, then lay down a vapor barrier, followed by EPS foam board insulation, and lastly subfloor. If you wanted a natural dirt floor, you could burry the foam board insulation and have a few inches of compacted soil on top. The mud walls could be constructed by applying adobe or cob on foam board with wire mesh.

[@michaelbluejay]

Simply adding rigid insulation to the exterior slab walls puts the structure at risk for hidden termites if special precautions aren't taken. The termites tunnel behind the insulation and you never see them. Google it.

[@studdruppo]

Insulated concrete slab foundation. A fix for termites. kzbin.info/www/bejne/h4SmlnuDZsxparc

[@AnonAnders]

Excellent point.. any idea how to insulate the edge of the slab? My house is so hot from the heat leaking through the baseboard area. Walls are cold, floor 3 inches away from wall are cold but next to and baseboard are hot

[@jacobjackson6513]

why don't they just insulate the top of the slab ?

[@zteaxon7787]

This

[@andreycham4797]

those who design houses like this in you country, do they even graduate a high school? Why would they put insulation under the slab where soil itself works as a insulator and no insulation where you have ambient cold temperature?

[@johnwhite2576]

condensation and comfort

[@lilysmith3004]

I sincerely hope that's an ironic comment

[@dareisnogod5711]

Your "solutions" leave much to be desired. I've seen better & longer presentations; you could too by checking around.