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Typical Air Infiltration Rates?

 
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Old 02-26-2019, 09:21 PM   #41
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Re: Typical Air Infiltration Rates?


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Originally Posted by duburban View Post
Nice job. How did you air seal your double stud walls?

Until recently the double stud was a no-brainer but Iím seeing efficiency in a 2x6 wall with exolation. Add air barriers mid wall assembly is a major effort.


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We built the exterior walls normally as load bearing. Acoustical sealant mud sills to foundation and acoustical sealant on any other joint on the exterior as well. He kept the 1st floor framing, so we taped the mud sill to the foundation with some special siga tape I believe. We used CDX plywood as sheathing. Used 3m all weather tape (8067 I think) to air seal the sheathing. Went over it with a 475 product. Maybe intello Mento. It was black. taped it as well. cut the rafters flush and ran 5/8 cdx on the roof and taped sidwall sheathing to zipwall. roof got covered with 2 layers of 2" poly iso. All joints taped. We built the eaves and rake over hangs and screwed them to the house with the tops flush with the top of the poly iso. Ran 2x's on the flat parallel with rafters and screwed them through the foam. Ran them out onto the eave overhangs which helped give the eaves support and then redecked the whole thing with 5/8" CDX, roof paper, and asphalt shingles. Best way hands down IMO to do a roof(other than the asphalt). you can replace the roof indefinitely and not screw with your air barrier at all. Plus, its vented.

Interior of the double walls was caulked to the sublfoor and we used an intello smart vapor reatarder on the interior and taped the joints and top and bottom after it was insulated. 12" thick walls. IMO I would go heavier than R60 on the roof.

In the future I would recommend strapping the interior walls after dense pack. The walls do tend to sag/bulge and it is a hassle when hanging board. Most hangers still don't get that the walls need to be rolled right before hanging. The strapping really helps with that on roof assemblies. The only issue is that it makes for some custom jamb widths with windows and doors. But if you've got 12"-16" walls already it's probably not an issue. Actually as I'm typing this I remember when we were doing siding or something some of the exterior sheathing had pushed off the house from the densepack. Not sure what had happened, but it was nailed properly. I think it was from getting wet too much and the nails just lost their hold. We screwed it back in and taped the screw holes. Like I said though, still haven't found the perfect way to go. Double walls are pretty nice though. The second wall is built inside where its dry.
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Old 02-27-2019, 09:49 AM   #42
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Re: Typical Air Infiltration Rates?


Nice assembly. Solitex mento is the exterior membrane. Leaving the eaves off and wrapping the whole building is great but certainly an added step which is hard to stomach.

My little projects budget is ever decreasing so Iím looking at trusses. Iím trying to scheme up a detail where the ceiling seals to top plate which seals to exterior air barrier...




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Old 02-27-2019, 11:12 AM   #43
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Re: Typical Air Infiltration Rates?


In my house I ran the rafter tails through, but trying to air seal that is just not plausible.(although I did end up at .9 ACH) Thatís why we did it the other way on my dadís. There is definitely added cost to it all. And I donít feel like I have comfortably figured it all out yet.
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Old 02-27-2019, 11:14 AM   #44
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Re: Typical Air Infiltration Rates?


Quote:
Originally Posted by duburban View Post
Nice assembly. Solitex mento is the exterior membrane. Leaving the eaves off and wrapping the whole building is great but certainly an added step which is hard to stomach.

My little projects budget is ever decreasing so Iím looking at trusses. Iím trying to scheme up a detail where the ceiling seals to top plate which seals to exterior air barrier...




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I think thatís what golden view does or did. For a ranch it wouldnít be a bad way to go.
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Old 02-27-2019, 11:56 AM   #45
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Re: Typical Air Infiltration Rates?


[QUOTE=duburban;
My little projects budget is ever decreasing so Iím looking at trusses. Iím trying to scheme up a detail where the ceiling seals to top plate which seals to exterior air barrier...

[/QUOTE]

If you're in an area that straps ceilings, you can run a piece of 3/4" osb over the top plate extending into the inside a few inches, then grace vicor over the top of that and seal to your exterior sheathing. Your drywall then can act as the air barrier for the ceiling when sealed to the drywall. Using truss screws like Strong Drive SDWC or Fastenmaster's FrameFAST makes this connection a little easier to detail as opposed to truss clips.
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Old 02-27-2019, 07:31 PM   #46
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Re: Typical Air Infiltration Rates?


I really believe in air sealing outside of the insulation area. With what youíre talking about with a ranch it isnít as big a deal using the ceiling drywall as an air barrier. I like running a blower door after the dried in stage prior to insulation to check for air leaks. Itís a good time to do it and easy to fix problems. It also keeps cold air from infiltrating into your insulation and killing your r value. That said, I wouldnít totally bail on air sealing the interior as well to keep moisture from the inside migrating into the walls excessively.

I guess Iím saying I would run the air barrier in a ranch just like we did at my fathers. Insulate the rafter bay and the roof above it and then have attic space be technically conditioned. No worries with HVAC systems and ducts. Iíd still probably insulate the ceiling bays with batts too. Thatís about the only place Iíll use fiberglass batts is in interior partition walls.
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Old 02-28-2019, 07:53 PM   #47
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Re: Typical Air Infiltration Rates?


Quote:
Originally Posted by Philament View Post
If you're in an area that straps ceilings, you can run a piece of 3/4" osb over the top plate extending into the inside a few inches, then grace vicor over the top of that and seal to your exterior sheathing. Your drywall then can act as the air barrier for the ceiling when sealed to the drywall. Using truss screws like Strong Drive SDWC or Fastenmaster's FrameFAST makes this connection a little easier to detail as opposed to truss clips.


Thatís exactly what I was thinking. Iíll post my detail when itís drawn.


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Old 03-01-2019, 11:20 AM   #48
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Re: Typical Air Infiltration Rates?


You guys have an interesting discussion going here. For the most part,I've been able to follow along. One thing I recall,Martin Holiday who weighs in on Green Building Adviser and author of Musings of an Energy Nerd advocates that for the most part,every climate zone should have continuous rigid foam over all the exterior wall area to prevent thermal bridging.The R value needed will depend on your zone. I do not see that in Joe's double stud wall.

For those who have been long subscribers to FHB mag. you may remember Joe wrote a how to article depicting his own office energy retrofit.......years later,he wrote another follow up explaining the errors and problems created in that design.
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Old 03-01-2019, 02:18 PM   #49
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Re: Typical Air Infiltration Rates?


The double wall deals with thermal bridging because the 2 walls are separate. Foam over the exterior is a good method for a remodel or someone who wants to maximize interior
space with a given footprint.
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Old 03-01-2019, 06:04 PM   #50
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Re: Typical Air Infiltration Rates?


Quote:
Originally Posted by Morning Wood View Post
The double wall deals with thermal bridging because the 2 walls are separate. Foam over the exterior is a good method for a remodel or someone who wants to maximize interior
space with a given footprint.
Yes & no - depending on the style of double wall it can reduce it a lot but there generally is still areas you will have issues.

Given a preference I think most noted above would go with foam (or ROXUL) on the exterior rather than super thick walls on the inside. Though they will probably preface it like I do with an "it depends"

As for the article mentioned - one key is if you are truly going for high performance, 2 layers of foam on the exterior with the seams offset as all things expand & contract

Drywall ceiling as an air barrier - it is for everyone just mostly overlooked / done as an afterthought. Most interesting one is done by an Archi (sorry can't recall at the moment - Steve...) but he installs the drywall ceiling before the interior walls or rough in work is done ensuring that it is a true barrier especially as he does a blower door test after it is up

As for trusses & adding in eaves later while wrapping Vycor up & around or inside - it isn't to difficult as you can order the trusses without the tails (or go raised heel) & then you can create the overhang with almost any look you are going for (regular soffit, beadboard, etc...) The added benefit is you can really tie the structure together with sheathing instead of needing blocking / ties, etc... I wrote about some of that here: http://thehtrc.com/2013/common-sense...wall-sheathing
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Old 03-01-2019, 06:24 PM   #51
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Re: Typical Air Infiltration Rates?


Iím running into a slight issue with wanting deep overhang + applied eves on this little project. I may have to mock it up and jump on it or talk to a real engineer.

I wanted to post this product that I saw at my local supplier recently. Itís a solution for thermal bridging around Windows.

I would imagine that windows could be done better in double stud walls. They all seem to have continuous bucks from inside to out.




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Old 03-01-2019, 06:27 PM   #52
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Re: Typical Air Infiltration Rates?


I did the factory tour at https://bensonwood.com and they are serious about the plywood air barrier on ceilings.

Iím thinking that the ceilings of my little house will be truss bottom chord, 1/2Ē air sealed to walls, strapping (chase for wiring and electrical boxes, drywall.

Light fixtures will be surface mount LED so they donít penetrate the ply air barrier.


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Old 03-01-2019, 07:11 PM   #53
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Re: Typical Air Infiltration Rates?


Sean,are talking about the barn retrofit article in FHB ? Also,Durban,did you see the article on Benson in the current issue of JLC ?
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Old 03-01-2019, 07:27 PM   #54
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Re: Typical Air Infiltration Rates?


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Sean,are talking about the barn retrofit article in FHB ? Also,Durban,did you see the article on Benson in the current issue of JLC ?


I havenít, Iíll see what I can find on the JLC website.


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Old 03-02-2019, 07:23 AM   #55
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Re: Typical Air Infiltration Rates?


FJN I think you are right about FHB, but also have heard him discuss it in person

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