Guys,
I’ve come across numerous articles recently about the proper way to finish basements and I’ve been designing them accordingly (I’m an architect & not a builder). I find most builders know little about the newer methods and still want to do it the old (wrong) way, with fiberglass batts & vapor barriers. I’m trying to educate them, but they think I’m crazy & read too much……go figure.
The question has to do with the floor construction. A recent article by Andy Engel (a FHB contributer) noted that he uses 1″ rigid EPS over the slab, then 2 layers of 1/2″ plywood over that. He notes that it has the compressive strength to support the subfloor without sleepers. I used to spec 1 1/2″ rigid insulation between 2×4 PT sleepers, but I think it’s best to eliminate the sleepers.
Does 1 1/2″ or 2″ rigid insulation work without sleepers, or is this a problem with the compressive strength of the EPS insulation? Is the thicker insulation pose any problems with the longer conc. screws necessary to attach the subfloor to the slab?
THanks in advance,
Brad964C4
Replies
Greetings Brad,
As a first time poster Welcome to Breaktime.
This post, in response to your question, will bump the thread through the 'recent discussion' listing again which will increase it's viewing.
Perhaps it will catch someone's attention that can help you with advice.
Cheers
every court needs a jester
Brad:
I don't really know the answers to your Qs but can tell you that rigid EPS foam comes in different compressive strength ratings. Anyway from maybe 5 to 30 PSI, and when you convert that to PSF, you can see that the right product can provide some respectable support.
BTW - Andy Engel is a regular contributor here at BT. You can post the Q directly to him if you can figure out what his user name. Try doing a search. Then do a post and beside the "To:" box click "Others" and type in Andy's user name.
Matt,Thanks...will look into the EPS specs & will try & contact him directly
In this area we usually put the foam under the slab. Seems the foam has sufficient compressive strength so support 4 in. concrete + other loads. Also put poly over the foam.
Brands I have used are Dow Styrofoam, and Celfort.
I have no experience with this, but apparently Dow Corning
makes a grade of pink foam insulation that is 25 p.s.i.
spec'd for "below grade." I suppose this is denser than the
normal foam.http://store.dunnlum.com/builderwire20/common/store/itemdetails.aspx?categoryid=223&itemid=16312
First, Your link is for Foamular , by Owens Corning (Pink Board) , not by Dow Chemical(Blue Board). But you are right, and both Owens Corning and Dow Chemical make EXPS that has PSI rating higher than that . Check out their websites, look for Architects or Builders specification information .
http://www.dow.com/styrofoam/na/pro-us/products/highload_100.htm http://www.foamular.com.au/pdf/foamular_physical_properties.pdf
I always get these guys confused.Doesn't Dow make a formulation with borate in it?
That's what I'd want for below grade.
That I don't know for sure, but I believe not.
I know someone here knows a source for borate treated faom but cannot remember who it is.
There was another thread a month or so ago about EXPS foam being used under slabs and the borate foam was mentioned.
bump
every court needs a jester
Brad,
I've followed Andy's method using EPS but I recommend that you use XPS instead. The EPS was pretty good but there was some deflection in the corners of the room. At http://www.buildingscience.com it says that you can use up to 1" XPS on top of the slab (and I think 2" XPS on the walls, but I don't recall) and still get the benefits of limited vapor transfer through the foam. The XPS has plenty of compressive strength.
Billy
I've been thinking about this floor system myself,,,,,,, the foam + the plywood +the finish floor,,,,,, and I keep wondering. How do you handle the stairs?? The first rise loses 2+ inches, seems like a trip hazard. Do you replace the staircase? Or maybe leave out the foam system at the landing and transition to the the added hieght in stages??
Harry
I think it would mean building a new set of steps.
The compressive strength of EPS is related to the density. I chose to use 2 Lb density borate treated EPS under my shop slab that has a 25 PSI/3,600 Lb/Ft² capacity (which is higher than the soil). I ordered it from Premier/Insulfoam. It works like Balsa wood with standard tools. Hand-held hot knives are a little slow. Note that the R-value lowers as the density increases.
Most EPS in home centers is .5 to .65Lb/Ft³, but is borate treated in our area. I don't recall the compressive strength but any of the manufacturers can tell you.