DIY Home Improvement, Remodeling & Repair Forum > DIY Home Improvement > Roofing and Siding > Insulate open rafter roof




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Old 01-24-2012, 01:10 AM  
Jaxx
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I'd like to add my questions to this discussion since it is related.

I own a semi flat roof home with open beam ceiling. On top of the rafters sit 2" insulboards with tar and gravel on top.

My ultimate plan is to insulate and then to cover the ceilings with sheet rock and install recessed LED lights.

The rafters show different amounts of sag which causes a problem putting up sheet rock.
The area between the rafters above the wall is poorly insulated. I saw a few areas where I can even look into the house from the ouside through gaps in this area (See area on attached Pic 1 and Pic 2).

I thought about putting up rows of 2x4's perpendicular to the rafters at 16 " spacing. This would tie all the rafters together and would form a solid, level base for sheet rock.

Question 1: Is this a sound solution to counter the different amounts of sag?

Next I read about "vapor barriers vs vent" topic and the condensation issues this could generate of not done right.

Question 2: Looking at the pictures I attached to this post, what would be best practice to get this done with a good (best?) rate of insulation? Could you explain what I need to watch out for in my case to make sure no problems arise?

Thanks a lot for all your support. This is a great forum and I just signed up and this is my first post!!



pic-1.jpg   pic-2.jpg   pic-3.jpg   pic-4.jpg   pic-5.jpg  

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Old 01-24-2012, 11:15 AM  
nealtw
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You won't want to put vents in this area becuase you would lose the effect of the foam on the outside so I think your only option is spray foam on the inside.
If the ceiling has drywall on it now, I'm not sure but that may want to come out first.
As for trueing the ceiling, there are lots of ways you could do that and your way should work fine. If the beams are at 24" on center I would measure up on each end 2 1/2 inches and chauc line and just attach 2x4s to the side of them to the line, sag gone.



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Old 01-26-2012, 01:03 AM  
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There is currently no drywall on the ceiling. I want to put dry wall up though.

Is there any way to prevent moisture from building up in the scenario I was planning on doing (see first post)?

Thanks

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Old 01-26-2012, 01:05 AM  
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There is currently no dry wall on the ceiling. I was planning on putting dry wall up though.

Is there any way to prevent moisture from building up in the scenario I am planning on doing (see first post)?

Thanks

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Old 01-26-2012, 03:17 PM  
nealtw
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I am in a wet zone and when we insulate something like this we have to leave a space above the insulation with vents on lower and higher end. We put a vapour bearier between the insulation and drywall. The proplem you have is the foam on the outside is a vapour bearier. Here you would have to use a foam inside so there would be no cavity for air. This may not the same for all zones.

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Old 01-27-2012, 03:20 AM  
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I think neal's suggestion about your sagging 4x's would be your fastest, cheapest route. Personally I would stay away from running the 2x's perpendicular. Only because the 2x4's are just going to follow the the shape of the existing beams ,and depending on how bad they are sagging this could mean a lot of shimming in order to get your 2x4's to plane. As for the 2x4's tying the rafters together, the roof sheathing is already handling that. Its difficult to tell from the photos, the exact spacing on your rafters. It looks to me like those are more than 24" o.c., looks more like 32" o.c. If it is over 24" o.c., add a 2x6 rafter in center of each bay, then do like neil suggested and scab 2x's along side the existing beams.

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Old 01-27-2012, 09:06 PM  
Jaxx
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ok, let's assume I go neal's route and attach them to the side of the 5 inch rafters. This would still mean that the beams I need to attach the drywall to are 24" o.c. That's a bit much, isn't it? Should I THEN run 4x2's perpendicular 16" o.c.?

Also, how expensive would foam insulation be?

Could I just not insulate the space above the drywall? Would I get condensation issues by blocking off the space between the rafters more or less without ventilation (I would also have the recessed LED lights in the ceiling that generate some heat)?

Thanks guys!

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Old 01-29-2012, 06:15 PM  
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I measured the rafter spacing and actually they are 30 inch o.c. Considering this, could you give me any advice on my questions in the above post?

Thanks a lot!

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Old 01-29-2012, 09:33 PM  
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To bad,5/8 drywall would have been fine with 24" on center. I would cut a 2x6 rafters the same measurements as the beam and notch each end 1" on the bottom, one for each cavity and add the 2x4, to the side of each beam and you will have something like 15" on center. I don't really have the answer on insultation but I think the bottom of the cavity looks like it has no insulation now.

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Old 01-29-2012, 10:16 PM  
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Hey Neal,

I don't fully understand how the 2x6 would be attached in combination with the 2x4's, in the scenario you described. Could you sketch it? I assume this concept would still take into consideration the sag of the rafters?

What do you think about putting 2x4's on the side of the rafters (from the ridge down to the wall) to create a straight surface on the bottom (this is pretty much what you proposed initially, correct?), but then attaching 2x4's perpendicular along the bottom. These could then be 16 or 24 inch o.c.

Thanks a lor for your support!



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