polystyrene under basement pad

billybarty · 09-30-2008, 11:47 PM

I am building a wood basement with a concrete floor and am wondering about insulating under it. I have a concrete footing with tamped gravel under the floor. My plan is to lay poly over the gravel and then 1" extruded polystyrene and then 3 inches of concrete. Are there any concerns I should have as far as condensation happening on top of the insulation and wrecking the concrete?

yesitsconcrete · 10-01-2008, 07:54 AM

i wouldn't bother as ambient earth temp's about 65f,,, insulation only affects the transfer rate of heat to cold. poly & 4"'d be my choice.

billybarty · 10-01-2008, 09:04 PM

I never mentioned that its a walkout so the front of the basement floor should be a lot colder than the back. Frost level here is about 8 feet and can get very cold.

yesitsconcrete · 10-02-2008, 06:05 AM

sandbagger !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

frost protection makes lotsa sense, then,,, on the footer's face & up the backside.

now, anything else you'd like to throw into the pot ? ? ?

billybarty · 10-02-2008, 02:15 PM

Yeah, I have some questions about sheeting and insulation but I'll put it in the construction forum. Thanks for the advice. And just to be clear, if I lay poly over top of the gravel and then put 1" polystyrene and then the concrete there won't be a condensation problem?

**Termite** · 10-02-2008, 03:16 PM

I'd put the vapor barrier on the "warm" side of the insulation. That would be right under the concrete. I doubt you'll have any trouble either way though.

RippySkippy · 10-02-2008, 05:16 PM

My basement has (top down) 4" concrete, radiant heat, 2.5" Owens Corning Formular 250, and I don't recall the thickness..but plastic. It's the driest basement I've ever had...and no, there's no condensation that I'm aware of.

On a side note...not all foam is rated for under slab installation, make sure to use the right product.

09-30-2008, 11:47 PM	#1
billybarty Member Join Date: Feb 2008 Posts: 60	polystyrene under basement pad I am building a wood basement with a concrete floor and am wondering about insulating under it. I have a concrete footing with tamped gravel under the floor. My plan is to lay poly over the gravel and then 1" extruded polystyrene and then 3 inches of concrete. Are there any concerns I should have as far as condensation happening on top of the insulation and wrecking the concrete?

10-01-2008, 07:54 AM	#2
yesitsconcrete Member Join Date: May 2008 Posts: 567	polystyrene under basement pad i wouldn't bother as ambient earth temp's about 65f,,, insulation only affects the transfer rate of heat to cold. poly & 4"'d be my choice.

10-01-2008, 09:04 PM	#3
billybarty Member Join Date: Feb 2008 Posts: 60	polystyrene under basement pad I never mentioned that its a walkout so the front of the basement floor should be a lot colder than the back. Frost level here is about 8 feet and can get very cold.

10-02-2008, 06:05 AM	#4
yesitsconcrete Member Join Date: May 2008 Posts: 567	polystyrene under basement pad sandbagger !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! frost protection makes lotsa sense, then,,, on the footer's face & up the backside. now, anything else you'd like to throw into the pot ? ? ?

10-02-2008, 02:15 PM	#5
billybarty Member Join Date: Feb 2008 Posts: 60	polystyrene under basement pad Yeah, I have some questions about sheeting and insulation but I'll put it in the construction forum. Thanks for the advice. And just to be clear, if I lay poly over top of the gravel and then put 1" polystyrene and then the concrete there won't be a condensation problem?

polystyrene under basement pad