Is 3/4 foam under Advantec sufficient for a floating garage shop floor?

[James W Glenn]

I want to lay down a wood floor in my 24'x24' garage. It has a reasonably clean slab, 7 years old, and the house plans called for a vapor barrier under the concrete. My goals are a comfortable and safe work surface and moisture control. I live on the eastern Shore of Maryland some 300 yards from the Chesapeake and with the high humidity the existing slab is frequently wet with condensation. My rough plan is to lay out a vapor barrier then float Advantec over 3/4 ridged green foam from Lowes. I was also considering using strips of 3/4 pressure treated plywood as floating sleepers, with the idea of still being able to drive a vehicle into the shop if necessary. An added challenge is that the shop is presently full of piled full of tools and shop stuff, that will stay in the garage and have to be moved at least twice during the installation.
I would appreciate any feed back about the feasibility of this plan. Thanks, Woody

[Jim Andrew]

The R value for the blue Dow board is at most 6 r factors per inch. If you don't already have the material bought, a better plan would be to use 1 1/2" thick foam, between treated 2x2's or 2x4's, on the 19 3/16" spacing, look on your tape measure, it is marked the same as the 16" centers, only you use 5 boards in 8' instead of 6. If you are really scrimping, you could use treated decking which is 1" thick, and 1" foam board. Be sure to use Dow board or Foamular, closed cell styrofoam. I am sure you would get a little insulation value from the 3/4" foam, but more insulation is better. And using plywood for the sleepers is risky, as plywood can delaminate.

[Jim Falsetti]

Woody, if you have not done so already, please take a look at buildingscience dot com to see what they have learned about how to put wood floors over concrete slabs.

Jim

[Kevin Gagne]

I used the DRIcore system and am very happy with it. There is space under it for airflow. The room was much warmer once I put it down. Fairly easy to install since they are 2' panels and lock together.

[Larry Edgerton]

Woody, if you have not done so already, please take a look at buildingscience dot com to see what they have learned about how to put wood floors over concrete slabs.

Jim

I second that. I have his "Building in Cold Climates" book that I use as a guide and have consulted them on a couple of projects.

[James W Glenn]

Thanks for the Buildingscience link. I will defiantly go through some more of the 167 search results that I found there. Today's thinking is to install "Delta-PL" under the whole floating structure to control moisture and mold issues. The "Plywood sleepers" will reinforce the Advantech edges and the 3/4 foam will provide additional insulation and continuous support for the Advantech. I think I can keep the cost to around $2.50 a sq-ft.

[Jim Falsetti]

Woody - George Bregar provide an excellent summary on his Delta FL install (http://www.sawmillcreek.org/showthread.php?128924-Delta-FL-Installation-Experience).

I installed Delta FL over a new slab (2012) and then put a floating laminated prefab floor over the Delta FL. The space is conditioned with a heat pump. Seems to work fine. Regarding parking the car on the Delta FL, if you call their tech support people, they can tell you the maximum recommended loading.

Jim

[Kevin Gagne]

If you use DRIcore you can do everything with one stop since it is all integrated into the panel. http://dricore.com/en/pdf/2004-fall-FAQ.pdf

[Don Jarvie]

I wouldn't plan on putting a car in if your install a floor. The weight of the car will crush the floor unless you use sleepers every 6 inches or so.

You could if you use the plywood sleepers and plywood over them but the sleepers will have to be fairly wide to handle the weight.

Just my 2 cents.

[Alex Stace]

dricore is nice for true wet situation but provides no insulation and seem to require edge airflow gaps as well.

I am considering the same general idea, 2" foamboard topped with a layer or two of OZB subfloor, with no sleepers, as it is totally continually supported there should be no weight carrying issues. will have a continuos non penetrated vapor barrier below as well.

[Darren Almeida]

I put down a vapor barrier, PT 2x4 sleepers (wide side down) 16" OC, 1.5" rigid foam between the sleepers, and then 3/4" advantek on top of it. Love it. Comfortable on the feet and knees, huge insulation improvement, and way easier to heat the space now.

[Jim Andrew]

I have to ponder the difference in Woody's location on the edge of Chesapeake bay and my location on the edge of the great American desert. Can't imagine the need of ventilating my slab to avoid problems here.

[Kevin Jenness]

When I added to and finished off my shop I laid down a 6 mil poly vapor barrier, 1" polyiso foam with sleepers 16" o.c. and 3/4" Advantec.For supporting a car I might go down to 12" o.c. sleepers or up to 1" Advantec. It works well for heat control and comfort. More thickness is better- I found a good deal on used 1" foam board so that's what I used, on the walls as well between drywall and framing. The foam came from a big box roof teardown at about 1/2 the cost of new material- look on Craigslist for similar stuff.