Replies

1. 
   splintergroupie | Jun 22, 2006 08:03am | #1

   You can press-fit it between the rafters and then run a bead of expanding foam around the perimeter. It holds the sheet foam in place and eliminates air leakage, too.

1. 
   yojimbo | Jun 23, 2006 01:14am | #4

   sweet, thanks for the info.  I was unable to locate this kind of info from any internet searches. 

1. 
   splintergroupie | Jun 23, 2006 04:04am | #5

   Glad to help. I was trying to remember today whether i had the best luck foaming 'up' or foaming 'down' - i remember one direction gave me more control over the bead, but i'll be darned if i remember which it was, so experiment. The gun mentioned would make foaming easier, but i hit a great sale on Great Stuff expanding foam so i used that. The cans are easy to maneuver in tight spaces.

2. 
   Snowmon | Jun 22, 2006 05:33pm | #2

   "If so how is the rigid insulation held in place so that it does not fall?"

   I use screws with fender washers on them, or I run bits of strapping across the face of the framing.  In the second case, shims can be added to brace it tight as needed.

   Then I inject foam around the perimeter.  When the foam sets up, I remove the screws or strapping, and fill any holes with a shot of foam.  Keep in mind that the rigid foam needs the be braced fairly well, or the expanding foam will tend to push the edges away from the sheathing.  This may not be much af an issue in tour case, since you are not filling the cavity level with the framing.

   A proper foam gun is a good investment if you are doing much of this sort of work.

   Best to leave an adequate gap on all sides of the rigid foam to allow for easy spray foaming.  I have a Pageris gun which has a needle point tip, so I can get by with a 1/8 gap (or even less).  For straw foam, you would want enough gap to get the straw in there.

   "Don't put your faith in governments, which are made by men; put your faith in individuals, who are made by God."

3. 
   BryanSayer | Jun 22, 2006 06:35pm | #3

   I don't know if these would work for 4" foam or not, but if your rafter bays are a consistent standard size, someone makes a metal/wire "rod" that is just held in place by pressure. You bend the rod slightly to put it in place. I think Simpson or Tyco makes them.

1. 
   DaveRicheson | Jun 23, 2006 04:40pm | #6

   Just buy a couple of length of grid hanging wire from an accoustical suppl y house. The heavey gauge stuff used to hang commercial ceiling grid is the same stuff others sell, cut to 14 5/8" and 22 5/8" lengths for f/g batt installation. Unit cost per piece is about 1/3 if you cut them yourself vs. purchasing packages of precuts. You also get to adjust your cuts to match the stud or rafter bas that are just a little over size.

    

   Dave

4. 
   cmcguire1 | Jun 23, 2006 05:07pm | #7

   Did this recently in my kitchen addition.
   Held the foam in with toenails tacked into the rafters, then pulled them after foam sets.
   I cut the foam for a loose fit (about 1/4" gap each side) to make room for gunning in expandable foam.
   Trim with a utility knife the next day-the ones with a long snap off blade work well here-flex the blade flat for a clean cut.
   Quick and easy.
   Good luck.
   C