floor insulation...

[Kris]

another question, before i get moving along.....i have read a bit on here about insulation and a little on the net....but i wasnt sure what to do just yet....

what i was thinking of doing was framing my 12 x 14 floor, putting some thin plywood on, then flip it over and insulate it with r-20...and then lay my 3/4 inch plywood floor on top..

i have heard some people recommend a vapor barrier.
i saw one guys cabin used little vents on the crawl space side of the floor, for airflow...
also..some people mentioned laying plastic over the crawl space ground....
my neighbor's cabin has no vapor barrier in the floor..he claims it breathes better.......

i will be about 2 feet off the ground..my area is fairly dry over-all.....and i plan on skirting the cabin...

i am open for suggestion....
thanks for your comments...

k.

[MountainDon]

Plastic on the ground with rock or gravel to protect it is a good idea.

Plastic vapor barrier is usually not required in a floor.

Venting is good.


One thing I don't like about installing the insulation before finishing the walls and roof is the danger of rain getting it wet before getting the structure dried in. 

[scooterw]

  I also had the same question about a floor vapor barrier.  I was planning on adding R30 unfaced insulation in 2x10 joists with 3/4 adventech on top....   I just read on another forum 
(http://www.asktooltalk.com/questions/faq/insulation/cabin_floor.php)  I should use paper or foil backed insulation with the paper/foil on top facing the floor for to create a vapor barrier for the floor?     I also was thinking that plastic wouldn't be good as a vapor barrier under the floor....    thought's on the paper/foil backed insulation?       could/should I just add tar paper under the floor over the insulation or get faced insulation?   
                         I'm confused and just want to do the correct steps...   thanks, Scott
btw.... this forum is awesome and has helped me alot w/my Victoria setup       

[markert2523]

Sounds like the floor would be a little heavy to be hefting around but I see the merits of your plan.  I insulated and sheathed the floor of my 12x16 after the fact and it was a lot of time on my back.  Maybe you could save a little weight by only installing the floor joists needed to tack in the plywood and then flip it and install the others.  Although you could have racking problems doing it that way.  In any case, I recommend installing the insulation before the 3/4 subfloor.

[boltpost]

Are you installing the floor insulation from the top? (walking side) if so, what is holding the insulation in, and not falling to the ground.
and
I wanted to spray foam the floor and use sheet foam, thoughts on this.
thanks
boltpost

[MountainDon]

I wanted to spray foam the floor and use sheet foam, thoughts on this.

That confuses me. spray and sheet 

[MushCreek]

It's a little more work, but how about just nailing small cleats at the bottom of your joists, then drop in plywood strips. This would provide backing for the insulation without either having to flip the whole assembly over, or work on your back in the dirt. I agree, though- the trick is keeping the insulation dry until you get the house dried in. I wonder if you could leave out some of the floor sheathing so you could blow cellulose in their after drying in the house.

[boltpost]

MountainDon :

I wanted to use a Flash & Fill / Flash & Batt  from http://www.sprayfoamdirect.com/home-owners/flash-a-fill--flash-a-batt for the floor.  As the web site states : spray foam insulation can be combined with other insulations to make a powerful hybrid method that gets similar results as doing all closed cell foam but with less cost. It's a great way to get the benefits of closed cell spray foam and save money on insulation at the same time.

Thoughts ?

[Danfish]

I recall either the Journal of Light Construction or Fine Homebuilding had an article on this approach sometime last year.  Sounded good, but with the high cost of foam and the extra labor of two step install...wonder if total economics works out.

[PEG688]

Flash and batt works very well! 

  Flash / spray and then sheet foam would not work , the spray gets on 'things'  and does not end up perfectly flat so attempting to cut rigid foam to fit would be impossible.

  Spaying / sealing the rim is popular , combined with batt insulation in the joist bays.    Worth doing,  IMO,  for comfort factor , cuts down drafts to near zero.   

G/L PEG

[boltpost]

THANK YOU for you insights and comments