Slab insulation

Constantin

I think the architect needs to go back to statics school and figure out what the actual psi load is in the floor below, acounting for the spread of the load, the strength of the rebar and the concrete, etc. In other words, you'd need to reach some impressive local pressures before the concrete would deflect enough to crush the foam.

A relatively inexpensive way to "tighten up" the concrete in a corset is to put in #4-60 rebar, elevated to sit in the middle of the concrete slab. Treat re-entrant corners carefully with 4' of rebar on a 45° tangent to the corner to prevent a crack from propagating into the slab. A structural engineer can give you guidance on the spacing for the rebar, we used 14" and 16" in the foundation walls.

Our basement slab has developed a few hairline cracks. However, it was only reinforced with the usual wire mesh mess. Rebar on proper stools would have put the mesh we're it's needed. Underneath, we have 12" of compacted gravel and 2" of foam. As hot rod pointed out, proper compaction is key.

Wayco Wayne_2

Where can I get

engineering ratings for 2" extruded polystyrene. I have an architech who is worried it isn't strong enough under the slab. Heaviest thing in the room will be a refrigerator, or me if I keep eating those supply house donuts. WW

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Unknown

I got cars and trucks on it

Did a 6 cars garage and vechicles are sitting inside with no cracks or settlement from installation back in 1999.... Make sure u packed the hell out of the gravel.... Any toppings, concrete or balck top is only as good as the subbase...

Couderay

Foam insulation

Helped a buddy three years ago, spring time, install radiant heat in a shop with 2 inch foam over a foot of compacted sub base. Parks several cranes in there at a time with nothing more than a few hairline cracks in the concrete. Don't know how long it will last but so far so good.They just bought a 175 ton crane and it sits in there now when not being used.Years ago worked at a junk yard that had the same set up,and they ran W18 Case end loaders thru the shop with cars on them to drop off and be taken apart in the winter time.15 years has gone by system still chugging along. As stated above a GOOD sub base and a high bag mix on the concrete should not lead to any problems

Weezbo

It is unfortunate that is the case here as well.

about the only thing they will agree to is, rebar tied in 2' squares over wire mesh with fiberglass entrained and that is only the "Brave one" *~/:) the rest seem to want the crete sitting on the compacted ground with extra wide slopped and very deep footings with no insulation beneath the footing part of the monolithic pour....

when you put rail road track that comes above the concrete , to roll large yellow iron knick knacks in, i can see leaving the insulation off beneath them...

Unknown

thanks,Joe

Thanks , Joe, for proving its can be done... Some years ago, the local fire dept somehow got rich and built a huge addition with drive thru bays. I questioned about having the radiant floor heat instead on 1200 degrees overheaded radiant tubings setup... Nope, the mr know nothing engineering its can't be done due to the weight of the engines, ladder trucks, etc. Now they are spenting ton of money on electric fans blowing the risen heat blanket down and the floor still ice cold...

Ragu_5

Wayne...

I saw a spec sheet from Dow a long time ago; the standard 2" foam that is stocked in lumberyards is rated at 20 PSI. They make foam up to 100 PSI, but is is special order.

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ed_25

donuts

your supply house has free donuts. Mine can't even get an order right!

hr

Foam has different psi ratings

the typical board you buy at insulation wholesalers is Dow or Owens Corning 250, meaning 25 psi load.

This info is available at their websites.

Some home centers have cheaper 15 psi stuff, beware.

Dow makes a 40,60, 80, and 100 psi foam "Hi-Load" available. It's used on some roofing applications and under airport runways.

I had to use some 60 psi under a heavy equipment shop recently.

Keep in mind the subgrade and compaction of that. To use hi load foam on a subgrade that is not to spec is a waste of money.

On all commercial shop slabs around here the structural engineers require a compaction test. You might be surprised how often a sub grade fails this test and compaction equipment has to be used to meet the spec

Rebar or remesh doesn't substitue for in-adequate sub grade compaction

hot rod

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hr

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