Insulation behind gable with cedar shingle siding


  #1  
Old 11-28-14, 12:28 PM
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Insulation behind gable with cedar shingle siding

I'm on the tail-end of restoring the exterior upper south portion of my very old house. I mostly just have to install new cedar shingles on the decorative gable extension where I've pulled off old decaying shingles. I have all the shingles primed and painted and ready to go.

The portion of the gable with shingles is built-out from the 2x4 framed house structure by about 18". The face of this extension has spaced out 1x4's as nailers for the shingles. When we pulled off the old shingles we found that the sheathing on the house behind the gable extension does not extend all the way to the roof, so we could see inside the walls. The insulation put into the walls when whoever finished the attic (1970's?) had fallen apart in the exposed areas and most of it had fallen down onto the soffits below, so we were looking directly at the back of drywall. The insulation used was something that had black tar paper on both sides and softish fiberglass looking stuff inside. We pulled off a few of the 1x4 nailers so we could reach in and clean up all the old junk. Then we hand-filled the bays (I wasn't going to rent a blower for such a small area) from the top with loose cellulose and rockwool to try to fill the voids down in the bays where there was still some of that old insulation. Once filled enough that we could reasonably finagle fiberglass batt insulation we finished the rest up to the roof with R-19 carefully cut to friction fit. Each piece is tucked in ~12" behind the sheathing at the bottom and ~3.5" behind the top chord at the top, and has maybe 12-24" of exposed middle.

So here are my questions: Should I take any additional measures to seal/insulate and make sure my insulation stays in place? Should I add anything before I put new shingles up (weather barrier or something)? I'm pretty sure putting the shingles up right against the 1x4's is the right thing to do, and I don't think I'd want to put plastic or anything impermeable in the gable. I do worry a bit about the fiberglass staying in place long term.

BTW, the underside shingles were in pretty good shape so we kept them in place. I added some 1.5" 18ga SS staples places where then needed tightening up and then we cleaned them up and primed and painted them twice. Now they feel extremely solid!

Thanks!
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  #2  
Old 11-29-14, 06:06 AM
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I would have removed the old 1X's and installed 1/2 CDX plywood, then covered with 30 LB. felt.
I'd also get rid of that style window that's in there now.
That has to be #1 when it come to troublesome, air leaking windows.
 
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Old 11-30-14, 12:40 AM
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The window can be dealt with any time. I just need to get my siding buttoned up now. From reading a number of articles and forum threads online, many advise not installing shingles directly against continuous sheathing/weather barrier, and instead suggest installing furring strips over top of the sheating/barrier then putting your cedar shingles on. This lets the shingles breath from both sides.

Actually, I would have first wanted to do what you suggest, which is re-sheath with plywood, then I read what I mentioned above. This has left me a little unsure, which is why I'm posting this here I hope to hear some critical thought on whatever methods anyone suggests.
 
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Old 11-30-14, 07:58 AM
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I'll also add that I made an 'interior storm' for that window years ago - zero leaks
 
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Old 12-03-14, 01:27 AM
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Hi Joe,

In your mind what do I gain by replacing the shingle nailers?

Any comments on how to treat the exposed fiberglass (if at all)?
 
  #6  
Old 12-03-14, 02:33 AM
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I'm slow at absorbing what you will be putting back together. I like the strapping behind the shingles, but I would think an air barrier to protect the back (exterior) of the insulation would be desirable. Actually, that is where I would like to see the cdx.

On the gable ends I would be seeing, inside to out, drywall, insulation, cdx, house wrap, then the large air gap with the strapping and 2 layers of shingles. The shingles will shed the rain and snow and be able to dry, but the gable wall needs the air barrier to protect the insulation. I also like the cdx as opposed to just the house wrap to add support and keep the critters out. Just house wrap will billow in and out with the wind and pump air through the gable walls.

Bud
 
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Old 12-03-14, 09:58 AM
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There is a product called "CedarBreather" that you could use behind the shingles. I think it's intended for cedar roofs, but I see no reason why it wouldn't be effective for exterior walls as well.
 
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Old 12-03-14, 12:49 PM
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Bud,
I'd be very happy having the sheathing extend to completely cover the fiberglass, but that would mean removing all the strips and cutting complicated shapes to fit into the space which is already a bit difficult to work in, then putting all the 1x4's back.

I like keeping the 1x4's and not putting anything continuous there because I'm seeing this space as attic space, and I want it to have ventilation. I won't go as far as installing ugly vents right on the front of my house. I think the shingles, installed with 1/8 - 1/4" spacing, will provide just the right amount of distributed ventilation.

The question is will it be too much ventilation and do I have air blasting through like Bud said. Fiberglass needs fairly still air to be effective.

Ply, house wrap - is there a middle ground? Something really stiff and heavy but that can still be worked like fabric? I was thinking about 1/4" foam because I could rough shape it really easily and bend & saw it into place, then staple it against the fiberglass, but I don't feel like it'd hold well. Anything waterproof like foam would have to be installed with plenty of gaps so moisture could escape.

Air movement is at worst an occasional loss of efficiency for the fiberglass - my biggest fear is the insulation slumping and coming out of place over time. What if I made 3/8 x 1.5" strips and stapled them in to hold the insulation in?
 
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Old 12-03-14, 12:54 PM
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Any some progress photos, because people like pictures
The original 120yr old underside shingles that we decided to keep look brilliant with a coat of primer and 2 coats of paint. The new shingles and trim for the face of the gable are in my basement, primed and painted, waiting for me to make some final decisions about insulation and sheathing.
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Old 12-03-14, 02:10 PM
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House wrap would be fine if you can get it in there and if stapled up tight it would serve to hold the fg in place. Given that this is protected by the shingled wall in front it should not get a lot of direct wind. And the shingles should vent fine.

A key component of the wall assembly wiil be a good air sealing job on the inside.

BTW, those shingles now look better than brand new .

Bud
 
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Old 12-04-14, 02:07 AM
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My neighbors probably think I'm crazy - up on planks and ladders stripping all my siding down to bare wood. But everything is coming out looking brand new when I'm done

Maybe house wrap held in with the edges wrapped around strips of wood that are stapled down - staples directly in fabric material always seems to tear out. It might work.
 
  #12  
Old 12-04-14, 04:08 AM
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There are three components of a wall assembly, air barrier, weather barrier (rain), and thermal barrier. Although the house wrap helps to slow air flow, it is the weather barrier and those staple holes will have little effect especially with the depth of that cavity (they would normally just get a piece of tape), rain will never get there. The other property the house wrap has to have is the ability to dry to the outside. The drywall or sheathing (when used) becomes the air barrier.

The outboard layer of shingles you are redoing becomes a decorative rain coat, a very nice looking one.

In my trade the "in and out" weatherization companies always weigh every step against its cost. But as your pride in your project is showing through, it illustrates the beneficial side of doing a really good job, even if it is beyond what is required. Every home I have worked on has something few can see that I can remember going the extra mile and that has always made me proud.

Bud
 
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Old 03-06-15, 08:27 PM
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I thought I'd follow up on this thread with some photos. I did end up sealing the exterior side of the wall with a house wrap. I was able reach trough the nailer strips and install the housewrap using 3/8" thick furring strips and an air powered 1/4" stapler. I originally thought it wasn't going to work out too well but I have to say the final product is extremely robust.

I had to pick out warm days to finish my shingling. It was a very slow install process, mostly because there's so little field to just 'go to town on' and so many edge pieces to cut.. Every cut got primed. Everything was installed with 1.5" long 7/16" stainless staples. Small triangle pieces got 'glued' with polyurethane caulk and also stapled with my 1/4" stapler.

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Old 03-06-15, 08:35 PM
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Another few warm (meaning 35 degrees) days let me put in the decorative edging. These were all 4" wide pieces that I cut on the table saw just for this. In addition to the staples, each piece got 'glued' in place using polyurethane caulk. Building on top of other shingles the 1.5" staples didn't really get much to bite into so I wanted to adhere the shingles as well. Polyurethane caulk is super sticky, will never turn brittle, can fill a large gap, and can be used in cold temperatures, so this was ideal for my project.

When it gets warm enough I'll do a final coat of paint.

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