[Kempfe]

Hi. I am insulating someones attic with rigid insulation boards stuck between the rafters. It's hard to cut them perfectly so to seal I will use expanding foam. It's a big attic and it would take perhaps 100 cans of expanding foam which is a big waste and too expensive. Can anyone recommend how to get expanding foam in larger quantities/containers? Also, what tape do you recommend to tape over 2 pieces of insulation spanning the 2x4 rafters as well. The boards are stuck pretty well but I do want to tape also for a better moisture barrier. Thanks alot in advance for your suggestions.

 

[SprayFinish]

You can buy gallon size 2 part foam, but this is a little different than the cans of "Great Stuff" or whatever other brands they have. With this you have to do a 50/50 mix of both parts A & B for the reaction to occur. I believe you can get 5 gallon drums as well. If you want something in comparison to the canned stuff then look for 2 part polyurethane foam in a 2lb density.

I'm not saying I have used this for your application, but you asked for large amounts of foam and this is what I got.

 

[Morning Wood]

You could get something like a 20 lb propane tank of foam that attaches to a gun. That is what I'd be using. It isn't 2 part and I believe it is low expansion closed cell.
Besides that, I'm a little concerned about you stuffing insulation into bays and creating a hot roof. Did you leave an air space between foam and sheathing? How much foam are you putting up?

 

[Golden view]

Not that I have encountered a situation to insulate like you propose, but I think I could do a 2000sf attic with 12 cans and a pro gun (hilti, great stuff pro, etc). Maybe 6. Yield is 1000 lineal feet with a small bead. You'd go mad trying to do that with the crappy disposable cans.

Maybe work on your measuring and cutting technique

 

[Kempfe]

thanks

good call. I just purchased a gun and I am ordering the 30oz great stuff pro cans. And yes, it's a vented roof so there is air flow behind the insulation. Any suggestions on the tape? Thanks again.

 

[pappagor]

foam the joint the tape will not last more then a few years

 

[madmax718]

This sounds like a wacky job. Spanning over a 2x4 rafter? Im afraid to see a roof using 2x4 rafters.

Also, I wouldnt recommend stuffing the rafter area with rigid foam. If your trying to make a conditioned space in the attic, why not just go straight across with the rigid foam. The most you'd loose is 2-3 inches, still provide full gable venting/ridge venting/etc.

 

[jandersoncont]

Fomo Products, maker of Handi-Foam, makes an ideal foam for your job. It comes in a 24lb tank, with a hose that runs to an applicator. You can also get an adapter to adapt the hose to one of their guns. (I highly recommend the gun)
The part number - P40540 (I260 40 Series One Component Cylinder Foam)
If you want to use the gun, you'll need this Adapter for gun foam
And the gun. (get the cheapest one, especially if this is a one time thing. Also remember, one regular can of the foam is the equivalent of about 3 cans of straw foam, since you can control it much better. Increased control = less waste.

Hope that helps!