Insulation, Radiant and Vapor Barriers - How to insulate between I-Joists?

The floor above my garage is I-joists 16" OC, and I had intended to install 16" R-19 batts of kraft-faced fiberglass. Unfortunately, the 16" batts are only 15" wide, and because the plywood of the joists is only 3/8" or so, I'm ending up with 1/2" gaps on either side. And since the heat is coming from above, the vapor barrier has to go UP where we can't reach to staple it. What's the best way to do this?

Thanks!

Blow in cellulose. It is far superior to fiberglass and will fill everything.

Cover the ceiling with 5/8" sheet rock.

Put the vapor barrier where you need it for your average climate.

Dick

Like said Use cellulose it will fill in for that 1/2"
Also the cellulose wont burn are melt in a fire like fiberglass will.

You said the heat is coming from above. Insulation will do nothing for radiant

Airman -

I believe the space above is a living space since it is referred to as a "floor above the garage". Probably the reason for I joists instead of trusses.

Dick

Yes, the room above the garage will be heated, and the garage itself will also be insulated, although unheated. I live in Virginia, so we have significant humidity issues both summer and winter, but have to pick one or the other, and I've been putting the vapor barrier on the conditioned side. (To be truthful, I *want* leakage of heat into the garage, as I'm only discluding it from my HVAC for fire code reasons. But I don't want to make the rooms above the garage uncomfortable in the process.)

I'm familiar with blowing insulation into attic spaces, but how do you blow into inaccessible sealed cavities? Once the drywall is up, I'd be unable to blow, but without the drywall up, nothing would be there to hold it in. I could staple plastic under the beams, but then the vapor barrier is on the wrong side. In either case, it would be very difficult to get a consistant thickness without gaps.

Would it actually be better if I used reflectix vice fiberglass in this situation? As reflectix is only 5/8" thick, I could staple it to the 2/3 flanges on the joists and not have any gaps. The reflectix website said it was roughly equivilent to R16.8 for under-floor applications IIRC, but R19 is required in my area in crawl spaces, so I'd have to supplement it, too.

16-in. o.c. wood I-joist floors require a 16-in. commercial batt instead of the 15-in. wide batt designed to fit between thicker, solid-sawn joists.

regards,
Vic

If you put the 5/8 drywall up first you need it for fire code. you can cut a small hole in it in each joist space and run the blower hose in the joist space and blow the insulation in it that way. Small patch over the holes and you wont know it. If you have just the sub floor on top put the poly down over the sub floor then the new floor Or cut strips of poly and staple it to the floor up in the joist first then the drywall then blow the insulation.

ED;)

16-in. o.c. wood I-joist floors require a 16-in. commercial batt instead of the 15-in. wide batt designed to fit between thicker, solid-sawn joists.

regards,
Vic

Given our situation, I think this is the easiest solution! I'm using cellulose in a couple spots in the house where the plumbing is just too complex to be able to fit glass bats, but it's just going to be too much trouble to fill in these I-joists, especially when I know we could simply friction-fit glass in the whole thing in an evening. Hopefully I can find a supplier without too much trouble.

Thanks, all!

Yes, the room above the garage will be heated, and the garage itself will also be insulated, although unheated. I live in Virginia, so we have significant humidity issues both summer and winter, but have to pick one or the other, and I've been putting the vapor barrier on the conditioned side. (To be truthful, I *want* leakage of heat into the garage, as I'm only discluding it from my HVAC for fire code reasons. But I don't want to make the rooms above the garage uncomfortable in the process.)

I'm familiar with blowing insulation into attic spaces, but how do you blow into inaccessible sealed cavities? Once the drywall is up, I'd be unable to blow, but without the drywall up, nothing would be there to hold it in. I could staple plastic under the beams, but then the vapor barrier is on the wrong side. In either case, it would be very difficult to get a consistant thickness without gaps.

Would it actually be better if I used reflectix vice fiberglass in this situation? As reflectix is only 5/8" thick, I could staple it to the 2/3 flanges on the joists and not have any gaps. The reflectix website said it was roughly equivilent to R16.8 for under-floor applications IIRC, but R19 is required in my area in crawl spaces, so I'd have to supplement it, too.

VA does not have RH problems in the winter. I know your at the cost but its still dry.