Is This A Feasible Way To Insulate A Basement Floor? - Insulation - Page 2 - DIY Chatroom Home Improvement Forum

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Old 12-11-2011, 04:31 PM   #16
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We had this exact process done in the basement of our walkout ranch (1850 sf)

We had to dig for new footings and the basement bathroom pipes, so it "made sense" to jackhammer the entire basement and install hydronic radiant. It is the nicest area in the house during the winter, and so much more comfortable than any finished basement I've been in.

But, we had great contractors who knew what they were doing, installed a 5 zone system and included dampers in the the upper level ducts so the basement hydronic is balanced seasonally with the upstairs. Then there is perimeter insulation for the absolutely necessary thermal break, and gravel/ foam underneath it all. Insulating from the ground is absolutely necessary or the heat goes into the ground rather than into the floor. We left steel trowel (smooth) finished concrete for the floor, no staining although we considered it. Just deciding where to place the control joints so they looked, and functioned, correctly required a meeting of the minds.

We even added a zone to the upstairs master bath because warming the floor up there while we had access to the subfloor made sense.

It was a HUGE project. Just getting rid of the concrete required a small bobcat in and out of our basement door for a while. We had a nearby area we could dump the concrete, otherwise it would have been $ for another process to haul it away.

This was in 1997-8, the system still works fine.

My impression is that the systems have come a long way since, but knowledgeable local contractors seem indispensable. If you go DIY, be prepared for a lot of heavy work. We are v experienced DIY'ers, but this was not the place for our skills - too much heavy equipment and man hours for that.

Have fun down there.


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Old 12-11-2011, 07:34 PM   #17
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CarlsonRower -

You are just like 95% of the people around grossly over-rate the amount or even the need to insulate the floor area more than i minimal airspace.

Even if it is -10F, outside the temperature of a soil and slab in place is in the range of 55F and is constant. If you condition the space and cool, insulation of the floor reduces the thermal benefits of the floor in the winter. Most people assume the soil at the floor level varies closelt with the exterior temperature. - By the way, the theoretical required frost depth is not necessarily related to the theoretical frost level.

A little insulation may help if it is not carpeted.

I do not have an exact answer regarding the suitablity of the 2" new concrete, except that the successful jobs I have seen usually are thicker than 2", have wire reinforcement and are poured over a slip barrier the prevent any cracks in the old slab from telegraphing through.

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Old 12-11-2011, 07:45 PM   #18
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In case my comments added to confusion about insulating under the floor, the purpose of the insulation is to provide a thermal break between the
("55 degree") soil and the new floor. The soil should stay cold, while the floor needs to warm up. Unless there is a thermal break (we used 2 inch rigid EPS) the heat will be wasted in warming the soil, rather than the concrete floor. As I understood it at the time, there have been many disputes when the thermal break was inadequate and the floor underperformed.


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