Replies

1. 
   moltenmetal | Nov 24, 2004 04:30am | #1

   In a cold, mostly-heating climate, vapour barrier goes on the warm side.  In this case it's under the subfloor, above the insulation.  If the place is already built, that's very tough to achieve- and even if it's new construction, installation of flooring may punch your vapour barrier into a swiss cheese and render it useless. 

   Below should be air barrier but no vapour barrier otherwise you may have condensation/mold/rot problems. 

   You're probably best off to use a self-sealing type of insulation like spray foam (icynene or urethane etc.)- it will act as its own vapour barrier as well as sealing all the places where warm, moist air may want to leak out through defects in your vapour barrier.  It's that leaking air which will make its way into your insulated cavity to find a cold place and result in condensation- as well as sucking heating dollars out of your house.

   As far as providing a barrier to pests, somebody's probably got a neat solution to this but I don't...

2. 
   RobArnold | Dec 03, 2004 03:57am | #2

   Another idea is just to take some extruded polystyrene and rip it to fit between the joists.  then get some spray foam (great stuff of a gun you can buy cans for) and fill the gaps.  This will seal from the weather and keep it air tight, while saving the cost of icynene.

    

   Rob

3. 
   KylefromKy | Dec 06, 2004 08:12am | #3

   If you have good access to the bottoms of the joists you might be able to staple hardware cloth to them to keep rodents out, although they can't live in polystyrene as easily as in fiberglass.

1. 
   rez | Dec 06, 2004 08:58am | #4

   To eliminate the possibility of a moisture collection in the bays I was hoping to hear someone say they used tyvex house wrap secured to the bottoms of the floor joists. 

1. 
   Luka | Dec 06, 2004 02:07pm | #5

   Vapor barrior, shmaper barrior...I'm still reeling from the revelation that floors are not walls.I mean, it turned my whole world on edge.:)

   The person you offend today, may have been your best friend tomorrow

4. 
   UniqueSheds | Dec 06, 2004 02:50pm | #6

   I would suggest you add some 1/4" ply as your final layer.  An open bay such as you describe will only become a hotel and highway for the mice.  They will get in and tunnel through all the insulation and will eventually find a small hole and gain access to the interior walls and enter the house.

   I recently worked on a similar situation and because the access was so limited, just a 1' crawl space in some areas, I attached the ply with a palm nailer.

   -Mark

    

1. 
   PenobscotMan | Dec 06, 2004 10:02pm | #9

   Do you mean PW on the bottom, under the insulation?? 

   And how much insulation should there be?  I (and Bookworm also, probably) have 2X10 joist bays that could be filled with something.  That would be easy to with FG (which everyone on BT hates), but I don't see how to do it with foam sheets which are only 2" or so.

1. 
   UniqueSheds | Dec 06, 2004 10:07pm | #10

   What I mean is that by having some plywood attached to the floor joists, from underneath, you then prevent any critters from gaining access to the insulation, whether it is fiberglass, rigid, or whatever.

   -Mark 

2. 
   bookworm | Dec 09, 2004 02:39am | #15

   Thanks U.S. for your response:

   But the 1/4 inch ply.... or osb as someone else suggest... doesn't this create-- if not a vapor lock within the floor... at least a solid surface for any moisture in the floor to drip on to and rot/ or mold.  Do you vent the ply?  Do you strap then vent to create gap between insulation and ply?  In horror I have recently crawled under a house (ripe with the smell of mold) to find plastic underneath.  This I know is wrong... but now I've got the fear.... of mold.

   Bookworm

5. 
   johnnyd | Dec 06, 2004 03:22pm | #7

   Do you have enough room under there place FG batts and then  nail sheets of OSB up?  Palm nailer would work good for that.

   I've had good results with building a floor system (this was 20X24) out of joists, nailing OSB to the bottom as system was built in sections and slid onto the beams.  Then filled joist cavities with FB batts from the top, and finished with 3/4" T&G plywood subfloor.

   No vapor barrier, but if I was to do it again, I would pour cellulose into the cavities and drap 6 mil poly over the joist/insulaiton system before the ply.

6. 
   xMikeSmith | Dec 06, 2004 05:05pm | #8

   protecting the pipes : wrap w/ heat tape, build a foam column around it , and enclose it with plywood ..

   for the floor.. install 3/8 plywood .. leave  a slot so you can insert a cellulose blowing hose nozzle

   slide the  nozzle to the end of each bay and blow until you hear the pitch change and the flow stops..

   slide it back and repeat.. all the way to the slot.. reverse and blow the other side

   use a plywood gasket to blow the slot area

    cover the slot and you're done..

    fiberglass sucks .. and the rodents love it.. they don't like the  boric acid in cellulose

   Mike Smith   Rhode Island : Design / Build / Repair / Restore

1. 
   CapnMac | Dec 06, 2004 11:05pm | #12

   Wouldn't it be as easy to do a blow-in cellulose like retrofit?  2" hole every 4' or so through the ply, fill till the pitch changes, or it blows out the other holes . . .

   Peppermint oil is supposed to be a good specific for keeping the mice out.  The number I remember is that a mouse only needs a 1/2" hole to get in.Occupational hazard of my occupation not being around (sorry Bubba)

1. 
   xMikeSmith | Dec 07, 2004 12:21am | #13

   we find the slot easier..

   and i agree.. the plywood is not going to keep the mice out.. they have to WANT to stay out.. which the cellulose doesMike Smith   Rhode Island : Design / Build / Repair / Restore

1. 
   CapnMac | Dec 07, 2004 02:17am | #14

   which the cellulose does

   Which rates a "Huzzah³!" in my book--the trick of it being those finicky bits around pipes & wires & the like.Occupational hazard of my occupation not being around (sorry Bubba)

7. 
   TimmyH76 | Dec 06, 2004 10:33pm | #11

   Spray Foam...its the way to go...Just started using it for everything I can..works great.... fast..a little pricey but our clients love the final product