Anyone use Concrete blankets under the slab for insulation?

[HetrickElectric]

A local gentleman told me that he uses the big concrete blankets under his slabs instead of the 2" foam. Then he puts down the 6" x 6" wire and zip ties his water lines to that for radiant heat setups. He said it works great, eliminates the need of a vapor and is much less expensive.

Any thoughts?

 

[walrus]

A local gentleman told me that he uses the big concrete blankets under his slabs instead of the 2" foam. Then he puts down the 6" x 6" wire and zip ties his water lines to that for radiant heat setups. He said it works great, eliminates the need of a vapor and is much less expensive.

Any thoughts?

Are you talking about the black construction type blankets? They're full of fiberglass, once wet they'd be useless as insulation

 

[PAToyota]

First concern would be settling as a concrete blanket has no compressive strength. Second, as Walrus mentions, compressed by the weight of the concrete above and damp they aren't going to have much in the way of insulating qualities either.

 

[HetrickElectric]

That was my thoughts on the situation as well. He seemed to be really satisfied with how the projects he did with them turned out though.

 

[tdkkart]

I suspect he's happy because he's unloading some blankets that he bought and can't use or get rid of.

 

[hidollartoys]

I believe that "r" value of slab insulation is less inportant than isolating the slab from earth contact. While 2" of foam would be better, any type of temperature break barrier would provide some insulating capacity since heat is also lost through conduction. I also believe that if a truly insulated slab was the point, then slab parameter insulation would be required as discussed in the IRC under frost protection for slab on grade. Any slab on grade will also lose a large amount of heat from the edges either exposed or at/below grade.

 

[walrus]

I also believe that if a truly insulated slab was the point, then slab parameter insulation would be required as discussed in the IRC under frost protection for slab on grade. Any slab on grade will also lose a large amount of heat from the edges either exposed or at/below grade.

From what I've heard you'd be better off using more insulation on the edges of the slab and less in the middle. In Maine you also should extend the insulation out past the slab and I would definitely do the edges

 

[brad d]

you can get SM foam form roofing places used for pretty cheap (its used under tar flat roofs) Or you can go to a door/ garage door place and pick up the window cut outs from them and use it under your bad.. also cheap and works so I have been told.

I used the 3" used SM foam from the roofers.. but i have a structural pad with piles under it
(3" might be a bit thick)

 

[badgerboiler]

Blankets are not insulation. Cheaper is not better. Perimeter insulation is more critical because of frost. Many large commercial systems are designed without the benefit of sub-slab insulation. It is about response time and ROI.

For smaller shop (under say 10,000 sq.ft.) it makes sense to use closed cell polystyrene (rated for compression) to R10 for cold climates. We shoot the PEX right down to the CPS and pour concrete.

 

[badgerboiler]

Closed Cell Polystyrene is the standard for in-slab radiant floors (2" R10 is common in cold climates). Blankets are not insulation. If your friend is satisfied it is because the soil has a natural resistance to heat transfer.

Perimeter insulation is the most critical because of frost.

Some commercial systems (generally over (10,000 sq.ft.) are often designed without the benefit of sub-floor insulation, but this can hamper response time and add to fuel cost. It is an ROI thing, but rest assured if you don't invest you won't get a return.