Replies

1. 
   Gabe | May 31, 2002 02:30am | #1

   Kraft paper does not a vb make......

   Probably the worst claim to being a vb on the market.

   Gabe

1. 
   UncleDunc | May 31, 2002 02:59am | #2

   If carefully sealed at the joints, 3/4" plywood is a pretty good vapor barrier. I did a quick web search and found references for 1/4" and 1/2" plywood with perm ratings at or below 1. You could also use a vapor retardant paint on the warm side of the plywood.

2. 
   Dave1981 | May 31, 2002 03:14am | #3

   I wrote message number two and deleted it but I mentioned using krafted faced insulation for a vapor barrier. Apperently some people did not think this was good enough. After thinking more about the topic, you can put all the plastic over the insulation you want, any moisture that hits the insulation will make it soggy and it will most likely fall into the crawl space.

   What about running a plastic vapor barrier first, leaving it loose so that it sags in between the joist bays. Then run the kraft face insulation over the top. You would still be able to glue the sub floor without the worry of the insulation deteriorating. 

1. 
   UncleDunc | May 31, 2002 04:08am | #4

   I think wolf's point is that if you lay plastic over the joists and then glue the plywood down, you've glued the plywood to the plastic, not to the joists. I suppose you could glue the plastic to the joists and then glue the plywood to the plastic, but that's not going to do much good unless the plastic has the same physical properties as wood.

   Or maybe you're thinking of the glue just as a sealant?

3. 
   Matthew | May 31, 2002 04:55am | #5

   I had a simular situation. I built over a garage slab. I ended up using ridgid foam insulation and then a vapor barrier and then plywood (no glue). However, I recently read that you can put the vapor barrier down first, then the joists, then you can use fiberglass insulation and glue the plywood to the joists. Seemed odd to me to put the vapor barrier on that side, but I did see two sources that recommended it.

4. 
   dabonds | May 31, 2002 04:16pm | #6

   If you read my last posting please ignore it. I was tired last night. I have the same situation in my 100 year old house and can recommend another method of achieving both your insulation and vapor barrier requirements. If you can get into the crawl space after the floor is installed by far the easiest way to insulate would be to spray in insulating foam. Much easier than laying on your back an stapling up fiberglass and it is a very good vapor barrier. You can do it yourself by ordering the foam from FOMO. Makes the floors quieter too. (http://www.fomo.com/products/largekits.html)