Replies

1. 
   BlueStone | Jul 30, 2007 04:24pm | #1

   There are differences of course when insulating walls vs. ceilings vs. wood floors vs cconcrete floors The obvious reason is heat entrapment and or escape. And the fact that heat rises.

   But normally when we talk about insulating a slab we really mean moisture problem avoidance and not heat issues. When we talk about the top of a slab we mean moisture control and foot comfort.

   IMO polystyrene foam up to 2 inches and 5/8 plywood would be the right choice. The poly for moisture and the plywood for foot comfort.

   If you have MFG recommendations for the thickness for their product in your weather zone/region you would do well to stick to that.

   I think the two layers of 1/2 inch plywood is overkill / over expense and simply a choice.

   Good luck

    

    

    

1. 
   skippy | Jul 31, 2007 12:14am | #3

   I do not have a vapor barrier under the slab does this change how you would handle putting foam insulation down? Would you secure the 5/8 ply through the rigid foam to the floor with tapcons etc.?Thanks
   Skippy

1. 
   BlueStone | Jul 31, 2007 12:39am | #4

   Try any good construction quality moisture cured adhesive. Just ask at your local builder supply or check 3M products for adhesive.  I think they have some of those.

   After the insulation is down I would, but many people may not, attach the plywood. Any wood can bow or bend.  Like nailing, do one edge or end, then the center then the other edge so the plywood will flatten out.  Leave some breathing room at the walls, at least 1/16 inch on each side of the room.

   Good luck

    

1. 
   skippy | Jul 31, 2007 04:59pm | #5

   Little confused- use the adhesive to attach the ply to the insulation? Any point in adhering the insulation to the concrete?Skippy

1. 
   BlueStone | Jul 31, 2007 05:19pm | #6

   Sorry about that, you can use the adhesive on both sides - floor and plywood -

   On the underside it helps keep air pockets from forming when placing heavy objects on the floor and helps prevent any sideways movement.

   On the topside it helps keep the plywood firm against the poly and also helps prevent sideways movement.

   It's about like what we do when applying floor sheathing to joists. We glue and screw (or nail).  We want everything tight and nonmoving except as a whole unit.

2. 
   NRTRob | Jul 31, 2007 05:39pm | #7

   "Foot comfort" is a heat issue. If the panel surface is colder than room temperature, it is reducing overall comfort (not just foot) as well as pulling heat from the room, into the ground.Insulation slows down the rate of transfer, which allows the surface temperature to rise further, increasing overall comfort as well as reducing that downward heat transfer.Heat doesn't rise, after all. Only hot air does. Any cold surface will draw heat from a room via radiation or conduction with anything it touches.Not trying to jump on you, just a few observations. Even in non-radiant applications, insulating slabs or slab floors can have dramatic comfort effects on more than just the feet, and it will save energy and money.-------------------------------------
   -=Northeast Radiant Technology=-
   Radiant Design, Consultation, Parts Supply
   http://www.NRTradiant.com

1. 
   skippy | Jul 31, 2007 05:51pm | #8

   The two things I can't seem to get any consensus on are- the use of a vapor barrier on the floor and how much (depth) insulation to use on floor. The floor does not have a vapor barrier or insulation below and I am not going to use radiant heat in floor.In the end I want a comfortable space to live in that does not have mold issues.What I read is inconsistent and what I get on this forum and over at JCL is all over the map. I would be interested in your take.
   Skippy

1. 
   NRTRob | Jul 31, 2007 05:59pm | #9

   I would follow building science's advice. But I would do that because I am not a vapor barrier expert.As for insulation, I would go for 2" of rigid foam under nearly any residential slab in a real winter climate.-------------------------------------
   -=Northeast Radiant Technology=-
   Radiant Design, Consultation, Parts Supply
   http://www.NRTradiant.com

2. 
   BflatBlue | Jul 31, 2007 09:30pm | #10

   The basement systems franchises offer an interlocking 12 by 12 (I think) plastic subfloor.  It is raised of the slab using a grid pattern so that there is airflow between the slab and the floor.  Once this is installed, you go ahead and put your floor on top of this.  Maybe your rigid insulation too.  You'd have to check with the franchise to see their recommendations.  I think the main site is basementsystems.com and then look for a franchise in your area.  I like this idea better than the subfloor panels you get at Lowe's, mostly because those are particle board glued to the plastic.  Those panels would also give you the ventilation though, and should address your concerns about mold.

2. 
   Danno | Jul 30, 2007 06:23pm | #2

   If moisture avoidance is your main concern (as the second poster mentioned), maybe you could just put down something like "Dry-core" panels (interlocking OSB squares 2' on an edge that have plastic with built in water channels on the bottom).