Replies

1. 
   Guest_ | Sep 16, 2000 03:14am | #1

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   Am I getting this right? You're gonna have a true cathedral ceiling, so you wanna have space for insulation and vent chutes between the rafters. Your model energy code undoubtedly calls for R-30, so you're gonna need the depth of a 2x10 for the chutes and R-30C. You won't find R-30C at the big boxes. Don't know where the R-19 reference came from.

   You could hang the 2x4's with nail plates, but recognize that they must carry the weight of the ceiling material (if the rafters are 16" O.C., 1/2" sheetrock should do). A nail gun would come in handy for this approach, and you'll be amazed how heavy it becomes after a few hours of overhead nailing.

   Good luck, Steve

1. 
   Guest_ | Sep 16, 2000 04:26pm | #2

   *Why can't you just add a layer of foam insulation under the drywall, am I missing something?

1. 
   Guest_ | Sep 17, 2000 01:30am | #3

   *I'm thinking along with Steve here, but maybe you don't have a cathedral ceiling-what are the ceiling joists/collar ties? Where are you located? You have a ridge vent, but do you have soffit vents leading up to the ridge?

1. 
   Guest_ | Sep 18, 2000 10:55pm | #4

   *I guess I am still wondering why adding a layer of foam insulation is a bad idea, if not the best idea. Oh well, I have a lot of questions.

1. 
   Guest_ | Sep 19, 2000 12:16am | #5

   *Qtrmeg:How thick would this foam need to be - say to give an additional R-15?

2. 
   Guest_ | Sep 19, 2000 12:48am | #6

   *If you dont have ceiling joists it would seem like you'd have to have collar ties on those rafters. If having a vaulted or cathederal ceiling isnt a huge thing to you, you might consider installing ceiling joists. It's easy, it solves all the insulation problems and makes installing the drywall alot easier (easier = cheaper if you're hiring someone). Unless you put in a raised floor you'll probably still have a high ceiling.JonC

3. 
   Guest_ | Sep 19, 2000 12:53am | #7

   *If high density styrene, 3" thick assuming you can get the edges tight and sealed somehow.The 2" board I've used a few times is R-10.

4. 
   Guest_ | Sep 20, 2000 01:00pm | #9

   *Oh geez, polyiso 2" = r14? Add to r19 in 2x6 for >r30. Like I said, am I missing something? You can price the job both ways, but I would rather go with the foam if it were my house.

2. 
   berniekwan | Sep 20, 2000 01:00pm | #8

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   I am contemplating converting a garage to a family room. The garage is not insulated. It is constructed with 2 I 4s walls and 2 I 6 rafters. The roof is pitched 6/12. The roof decking is of 1 I 12 pine board with a ridge vent. I was told that in order to properly insulate the room to R-19 or higher, I would need to sister 2 I 10s to the rafters to provide for proper ventilation behind the insulation. Could I attached 2 I 4s to each rafter to build them up to 2 I 10s using nail-on metal plates? Any suggestions? Thanks