Replies

1. 
   dIrishInMe | Jul 25, 2005 05:47am | #1

   It depends on where you live.  I'm building some slab on grade houses right now and installed a 2' strip of rigid foam around the perimeter only.  This is what is required by NC code.  This is pretty much what is done with basements too, although if the basement slab is, say 6' below grade, obviously, the need for insulation is greatly diminished - unless you live in Alaska ;-)

   Re installing rigid insulation on top of the slab, you would end up with a much more "user friendly" floor.  The added expense would have to be taken into consideration though.  I'd estimate roughly $1000 per 1000 sq feet for materials only. 

   Whatever you do, don't forget the poly under the slab though.  It is essential and keeps moisture from coming up through the concrete.
    

   Matt
1. 
   _fred_ | Jul 25, 2005 05:58am | #3

   "Whatever you do, don't forget the poly under the slab though.  It is essential and keeps moisture from coming up through the concrete." 

   That leads me to another question. I was looking at some laminate flooring recently and it specified  a vapour barrier on top of concrete, below the underlay. would that be redundant? or is it a good idea?

   PS what do you mean by user friendly? do you mean that it will create a buffer from hard concrete?

   Edited 7/24/2005 11:01 pm ET by 1fred

1. 
   dIrishInMe | Jul 25, 2005 01:11pm | #4

   In this case redundant is OK.  The laminate manufacturer (nor some homeowners) have no way of knowing if there is a VB under the slab.  So, if there is, VB on top of the slab is a cheap insurance policy.

   User Friendly =  hard and potentially cold concrete and damp concrete converted to a soft stepping wood floor.  For example, a hard concrete floor makes one's feet tired after a number of hours, and the dull thud sound that your kid's head makes when he trips and falls is rather disconcerting.

   The extra layers will cost a bit of sometimes valuable head room though.   Matt

2. 
   MikeSmith | Jul 25, 2005 05:47am | #2

   most builders do not insulate basement slabs.... think it's a waste of time and money

   we always insulate basement slabs with 2" EPS, treated with borates ( PerformGuard ), under the slab on top of a 12" crushed stone bed ( high water tables ) with internal drains to daylight  or to a sump

   Mike Smith Rhode Island : Design / Build / Repair / Restore
1. 
   jimz | Jul 25, 2005 09:49pm | #5

   Mike:I know that you're located in the northeast.  So when you insulate your slab homes, is the 2" foam board:

   1) totally covering the floor or just 2 ft in from the perimeter?

   2) covered with poly before pouring?

   Rookie

1. 
   MikeSmith | Jul 25, 2005 11:18pm | #6

   it's under the whole floor...

   we used to use the 6 mil poly.. but our studies show that the eps will retard vapor.... and the 2" thickness is strong enough to withstand abuse during the pour..

   assuming it's installed on well graded and compacted gravel baseMike Smith Rhode Island : Design / Build / Repair / Restore

1. 
   bigman | Aug 18, 2005 04:27am | #7

   Hello Mike, I live in Montville CT and am about to pour in the next 2 weeks, and I wanted to know if you tape the seams of the EPS boards and do you use wire mesh or fibermesh in your basement slabs?

   Thank you, Bigman (Dave)

    

1. 
   MikeSmith | Aug 18, 2005 05:15am | #8

   big... we use 2" EPS  and under slabs we order 2 lb/cf density..

    we get it from Branch River Foam in Smithfield, RI... 2"   ( and 2lb. density ) is strong enough to pour on and walk on without breaking up ..

    we don't tape the joints.. but we do put about one inch of sand  on top to give it some protection and absorb some of the bleed water...

   we use 12" of  3/4" stone under our slabs with a 4" perf-pipe  around the border  either leading to daylight or a sump.. this pipe system also has risers to provide for future  radon mitigation if needed..

    the foam goes right on top of the well graded  stone

   we use  4" of 3000 #  3/4" stone mix with no WWM or fibermesh..

    watch the jobsite water adds and pour  a stiff mix with just enough water to work  Mike Smith Rhode Island : Design / Build / Repair / Restore

2. 
   bigman | Aug 25, 2005 01:30am | #9

   Hey Mike, I spoke with Ed at Branch River Foam and he said that I dont need the 2" 2lb foam board, to use the 2" 1lb. he said it was just as rugged and that it was being used under slabs at the "Big Dig" without any breakage problems. I need 3600 Sq Ft and  with the 2"  1lb at .17/board ft vs 2" 2lb at .35/bf  I could use the $1260.00 elsewhere in my project. Are there any particular reasons you use the 2lb? and do you think I should use poly under the foam, over the gravel?

   Thanks

3. 
   maggie2142 | Aug 25, 2005 03:42am | #10

   I used 2 1/2" thick, R-10, 1# EPS foam from Branch River under 6" concrete for a radiant floor heated airplane hangar I did recently in New Hampshire.  About 3,000 sq. ft.  Handling the one pound  foam was no problem, and it was half as much as the two pound.  The 4x16 foot panels go down quickly with fewer edges to contend with than the typical 4x8.  The issue is not with the load bearing with the concrete placed and cured, it is the durability when your concrete guys are working on it.  I think the 1# is plenty durable, and your concrete men can't be a rougher bunch than mine!

   Put 6 mil poly under the foam to keep the water out of the foam.  1# EPS with borates is a much better deal than the standard 2# XPS foam. 

4. 
   joeh | Aug 25, 2005 03:47am | #11

   I used Rcontrol type II I think they call it. It's one pound, about half the price.

   Same advice from the salesman, it's the guys walking on it that will do the damage.

   Joe H

5. 
   MikeSmith | Aug 25, 2005 04:13am | #12

   well, bigman... there you go... consensus says.. save your money..

   ask your concrete guys to have mercy....

   i was used to the higher compressive strengths of Foam-ul-R & Styro -SM, so when i switched over to EPS, i was looking for more of the same..

    i forget what the compressive strength of the  1 lb/cf  is..

   i do think the 2" board is strong enough for the walking by the placement guys  as long as there are no voids under the foam.. and they are careful on the edgesMike Smith Rhode Island : Design / Build / Repair / Restore

6. 
   DonNH | Aug 25, 2005 04:43am | #13

   Funny how there can be big differences of opinion on some of these topics.  I just poured a garage floor, using 2" of 1# EPS on the advice of a friend who also is a manufacturer of the stuff (and gave me a good deal).

   Over on the Doityourself.com forum under garages, the topic came up, I mentioned what I had used, and got a couple very adamant responses that I should have used the XPS, due to its higher strength, higher R-value, and lower water absorption.

   It's too early to tell with mine - it's only been 3 weeks and I've yet to put any serious weight on it, as I'm building walls right now.  Seems like the EPS should be adequate, however.

   Don

7. 
   MikeSmith | Aug 25, 2005 06:12am | #14

   yeah, well, i used to be a big advocate of XPS... not any more..

    EPS for me...Mike Smith Rhode Island : Design / Build / Repair / Restore

8. 
   BillHartmann | Aug 25, 2005 05:58pm | #16

   I ran across the numbers at one time.IIRC even the 1 lb stuff is good for 7 psi, that works out to 1000 lb/sq ft.And with concrete you have 100% contact.The only problem with the lighter weight stuff is possible damage befor/during the pour.

9. 
   DonNH | Aug 25, 2005 07:48pm | #17

   Bill,

   I think the number I saw for the 1# was 10 psi.  However, I believe I also saw a note that that value is based on 10% compression, which would be .200" for a 2" thick base.  That's a lot of movement for concrete.  I think though that with good compaction underneath, a well poured and cured slab with some reinforcing, that I'd always have the load spread out enough that I'd never come close to that kind of pressure & deflection.

   Don

    

10. 
    moltenmetal | Aug 25, 2005 05:44pm | #15

    Just poured my garage/shop and basement with 2" of 1.5# EPS under both.  6 mil poly on top of the foam as a VB because the EPS is somewhat permeable and the VB should be on the warm side.  Seams in the poly were well overlapped but not taped.  WWM in the basement with a few 1/2" bars thrown in to hold it up against the abuse of the concrete finishers' feet, and 1/2" bars 12" OC for my shop.  I sawed pieces of backer brick from a chimney we demo'd to use as chairs- lots of bearing area and nice and smooth so it didn't tear the poly. 

    So you can split the difference and go with 1.5#.  I bought it at a good price from Amvic when I bought my ICFs. It's plenty durable enough to survive the pour.  Just make sure your stone base is very well levelled.