wall system
Last Post 30 Apr 2018 10:57 PM by Dana1. 13 Replies.
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garretttpeUser is Offline
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15 Apr 2018 10:49 AM
Good morning All I am looing at building a house n central VA my plan is this Paint, 5/8 sheetrock, 2x4 studs,3 inch CS foam, 2 inch blue board, 1/2 inch advantech, house wrap, CertainTeed vinyl siding.. does this sound ok? thaks al
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19 Apr 2018 03:58 AM
Okay, haven't seen the term "blue board" used in a while. XPS foam board.
You'll wind up with a nominal R-Value of 28 or so up front. However, as the XPS offgasses, you'll lose R-Value over time. Dropping you down to 24-25..
I'd look at standard EPS. Sure, the R-Value is lower, but it doesn't decrease.

Also, no OSB/Plywood?

You CAN do this sort of thing, I've seen it done on small dormers and the like.. But I wouldn't do it on a ground floor. You lose a bunch of lateral/racking resistance. You also lose most of your nailing surface on the exterior of the house.
And you'd have to tape it VERY well to prevent water infiltration.
If you decide to go ahead this way, apply it in 2x1" layers and offset seams (which should be sealed on both layers).
And I'd be using foam-friendly construction adhesive to seal the first layer to the studs and the second layer to the first (of course screwing everything down into the studs).

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19 Apr 2018 03:58 AM
Okay, haven't seen the term "blue board" used in a while. XPS foam board.
You'll wind up with a nominal R-Value of 28 or so up front. However, as the XPS offgasses, you'll lose R-Value over time. Dropping you down to 24-25..
I'd look at standard EPS. Sure, the R-Value is lower, but it doesn't decrease.

Also, no OSB/Plywood?

You CAN do this sort of thing, I've seen it done on small dormers and the like.. But I wouldn't do it on a ground floor. You lose a bunch of lateral/racking resistance. You also lose most of your nailing surface on the exterior of the house.
And you'd have to tape it VERY well to prevent water infiltration.
If you decide to go ahead this way, apply it in 2x1" layers and offset seams (which should be sealed on both layers).
And I'd be using foam-friendly construction adhesive to seal the first layer to the studs and the second layer to the first (of course screwing everything down into the studs).

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19 Apr 2018 08:09 PM
Closed cell foam between framing is a waste of expensive foam. A full-fill of half pound open cell foam and an "extra" quarter inch of continuous EPS would outperform it a fraction of the cost. The 3" thermal bridge of the framing (about 25% of the face area of a typical wall) is only R3.6 and conducting most of the heat when you have R18-R20 at center cavity. With a full cavity fill the thermal bridge is 3.5" and about R4.2 a very real improvement in the performance of the framing fraction, almost enough to compensate for the much lower R at centercavity. For a more detailed explanation (with some of the arithmetic detailed) see:

http://www.finehomebuilding.com/membership/pdf/184243/021269086NRGnerd.pdf

To cut to the chase, see the table on p3 (PDF pagination). Using 3" of closed cell foam buys only R0.8 in whole-wall R over a full-fill R13. A quarter inch of continuous EPS buys you a full R1, a quarter inch of polyiso about R1.5.

XPS is blown with HFC134a, a very powerful greenhouse gas, more than 1000x CO2. While it's LTTR is R5/inch, don't expect more than R4.5/inch after 20 years, or more than R4.2/inch after 50 (no matter what the "lifetime warranty" says.)

Polyisocyanurate is blown with hydrocarbons (usually a variant of pentane) which is only ~7x CO2. While there is some long term degradation from it's labeled R6/inch to R7/inch (depending on manufacturer and density), and some cold-climate temperature derating, in your stackup and location it will always perform at R5/inch or better. See the curves in this bit o' marketing fluff from Dow (touting the superiority of their Thermax branded polyiso):

http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_098a/0901b8038098a015.pdf?filepath=styrofoam/pdfs/noreg/179-00263.pdf&fromPage=GetDoc

The generic polyiso curve with the severe temperature derating dip is well aged 2lb fiber faced goods. Lighter density foil faced polyiso sheathing (any vendor's ) will outperform that. Note, the temperature is the mean temp through the foam, not the cold side of the foam. With R13 open cell cavity fill and 3" of exerior polyiso the mean temp through the polyiso at Lynchburg's +17F outside design temp (https://articles.extension.org/sites/default/files/7.%20Outdoor_Design_Conditions_508.pdf ) and an indoor temp of +70F would be about 32F, where even 3" of aged 2lb roofing iso would deliver R14 or so, and anybody's foil faced iso would be delivering more than R15. Dow is claiming R20 or so at that temp, if you look at the graph on page 3.

Fresh XPS would be R16-ish at that temp, but aged XPS would be about the same as generic foil faced polyiso when it's +17F out, but would underperform aged generic polyiso the other 99% of the time.

The greenest foam is foam that has been reclaimed from building demolition, since no new polymer or blowing agent is being used. Reclaimed roofing polyiso would still outperform aged XPS for most of the season in central VA in your stackup, if falling a hint shy the 1% of the hours it's below +17F outside. Roofing polyiso is often reclaimed in demolition & re-roofing, and nearly-perfect condtition goods are still only about 1/3 the cost of virgin-stock goods. Many salvage materials vendors and dedicated foam reclaimer advertise in venues such as this:

https://lynchburg.craigslist.org/search/sss?query=rigid+insulation





[edited to add] I see that I mis-interpreted the stackup a bit- there's only 2" of foam outside the 1/2 inch advantech OSB, so adjust accordingly. That drops the mean temp through the foam at +17F to about 23-24F, not that it makes a whole lot of difference. Even 2" well-aged roofing iso would perform at about R9 at that temp, and better than even XPS at at the mean average January outdoor temp of ~38F, which would put the mean temp through the foam at about 50F.

https://weatherspark.com/m/19627/1/Average-Weather-in-January-in-West-Lynchburg-Virginia-United-States#Sections-Temperature

Bottom line: Save the high R/inch foam budget for the continuous foam sheathing, not the cavity fill, and use polyiso, not XPS on the exterior. A full 3.5" of open cell foam will be less than half the cost of 3" closed cell. The 2" of reclaimed roofing polyiso would cost less than half the cost of 2" of XPS, and outperforms it enough to more than make up for the lower performance open cell cavity fill. Even 2" of brand new Thermax wouldn't be a huge up-charge from 2" XPS, and a much bigger uptick in performance.
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25 Apr 2018 04:17 PM
thank you all for the response, my schedule has been nuts since I posted, I didn't want anyone to think I was ungrateful by not responding with a thank you sooner. If i get this correct I should use open cell foam cavity fill, NO XPS (blue board, I live in northern Maine and that is what everyone calls it......lol) and 2-3 inches of Polyiso on the outside, I still like the idea of using Advantech which is extremely water resistant in order to have a 100 percent nailer for the siding and house wrap is ok. Am I correct? and i will for sure be looking at reclaimed insulation.

I live in Northern Maine and have a ICF house footer to rafter( 2nd one built in the county at that time i was told) with closed cell foam in the attic, I am heating 1600 total space using under 250 gallons of heating oil per year to include my hot water.. so only thing I know is closed cell foam and blue board under concerete floor due to radiant heat, I want to build my next house myself and this site is teaching me so much.

now I am thinking about 2x6 walls with open sell foam cavity filled and 2 inch NON XPS on the outside
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25 Apr 2018 08:41 PM
For central VA 2" of any type of foam on the exterior of a 2x6/R20 open cell wall would beat code minimum requirements with some margin.

To be structural the Advantech needs to be nailed directly to the studs directly, not through 2" of foam. The moment-arm of the additional 2" isn't likely to meet spec on racking resistance against the wind. It's fine to put the foam on the exterior of the structural sheathing with the foam strapped to the wall with 1x4 furring through screwed to the studs 24" o.c. with pancake head timber screws (eg Fastenmaster HeadLok) with at least 1.5" of screw penetration of the studs, and mount the siding to the furring. The housewrap can go either between the foam & sheathing, or on the exterior side of the foam, depending on where you mount the windows. If the exterior glass is roughly co-planar with the sheathing it's called an "innie" mount, and the housewrap goes between the foam & sheathing ( crinkly types such as Tyvek Drainwrap preferred), with the window flashing properly lapped to the housewrap. If the glass is roughly co-planar with the siding it''s referred to as an "outie" mount, which will need window bucks that extend to the exterior side of the foam, and the housewrap & flashing directs water to the exterior side of the foam, behind the siding.

Putting the foam on the exterior side of the structural sheathing puts all of the structural wood in a warmer, better protected location. It's really preferable to putting the OSB on the exterior side of the foam. If you really prefer to have the continuous nailer, take a look at Huber ZIP-R, which can be structural even at 1.5" thickness if using their fastener spacing specs. ZIP-R is half-inch Huber ZIP (which has a spray-applied WRB, no housewrap needed if you use their tape & methods on the seams.) I believe at 2" or higher it will need shear panels or let in bracing on the studs for structural rigidity- consult with the state/county for the racking load requirements & with Huber for load capacities of the thicker ZIP-R. http://www.huberwood.com/assets/user/library/ZIP_System_R-Sheathing_-_Product_Data_Sheet_(R3-12)_v1.pdf

ZIP-R can be pretty pricey compared to used roofing iso + furring + housewrap using OSB or CDX structural sheathing, but it goes up a lot quicker. In high labor cost areas like mine (MA) ZIP sheathing (if not ZIP-R) seems to be winning in the marketplace over housewrap + OSB despite the higher material cost.

If you were to build the same house in Arastook County ME, that's US climate zone 7, which would need a minimum of R15 continuous insulation on the exterior of a 2x6 /R20 wall to have sufficient dew point control with just latex paint as the interior vapor retarder. The rest of ME is zone 6, which needs at least R10 on the exterior. No matter what foam you use, it's going to take more than 2" for zone 7. In zone 6 using 2" polyiso would just make it, after temperature derating for climate and stackup, but it would take 2.5" if EPS. See:

https://up.codes/viewer/wyoming/irc-2015/chapter/7/wall-covering#R702.7.1

From a total thermal performance point of view a 2x4/R13 open cell wall with 2" of exterior polyiso meets IRC code minimum, if that's your goal:

https://up.codes/viewer/utah/irc-2015/chapter/11/re-energy-efficiency#N1102.1.2

garretttpeUser is Offline
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28 Apr 2018 04:00 AM
Thank you
I actually live less than 15 min from the HUBER plant, I am in Fort Fairfield Maine, (Aroostook, not Arastook....LOL) and the plant is in Easton Main, I used their engineered sheathing with a rubber like coating on my roof of my garage.

thank you very much for you advice, I will dissect it so I can get a good understanding of the window placments and the racking issue. I still need to grasp an INNIE vs OUTIE window
Larry
garretttpeUser is Offline
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28 Apr 2018 04:00 AM
Thank you
I actually live less than 15 min from the HUBER plant, I am in Fort Fairfield Maine, (Aroostook, not Arastook....LOL) and the plant is in Easton Main, I used their engineered sheathing with a rubber like coating on my roof of my garage.

thank you very much for you advice, I will dissect it so I can get a good understanding of the window placments and the racking issue. I still need to grasp an INNIE vs OUTIE window
Larry
garretttpeUser is Offline
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28 Apr 2018 04:00 AM
Thank you
I actually live less than 15 min from the HUBER plant, I am in Fort Fairfield Maine, (Aroostook, not Arastook....LOL) and the plant is in Easton Main, I used their engineered sheathing with a rubber like coating on my roof of my garage.

thank you very much for you advice, I will dissect it so I can get a good understanding of the window placments and the racking issue. I still need to grasp an INNIE vs OUTIE window
Larry
garretttpeUser is Offline
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28 Apr 2018 04:00 AM
Thank you
I actually live less than 15 min from the HUBER plant, I am in Fort Fairfield Maine, (Aroostook, not Arastook....LOL) and the plant is in Easton Main, I used their engineered sheathing with a rubber like coating on my roof of my garage.

thank you very much for you advice, I will dissect it so I can get a good understanding of the window placments and the racking issue. I still need to grasp an INNIE vs OUTIE window
Larry
garretttpeUser is Offline
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28 Apr 2018 04:00 AM
Thank you
I actually live less than 15 min from the HUBER plant, I am in Fort Fairfield Maine, (Aroostook, not Arastook....LOL) and the plant is in Easton Main, I used their engineered sheathing with a rubber like coating on my roof of my garage.

thank you very much for you advice, I will dissect it so I can get a good understanding of the window placments and the racking issue. I still need to grasp an INNIE vs OUTIE window
Larry
garretttpeUser is Offline
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28 Apr 2018 04:01 AM
Thank you
I actually live less than 15 min from the HUBER plant, I am in Fort Fairfield Maine, (Aroostook, not Arastook....LOL) and the plant is in Easton Main, I used their engineered sheathing with a rubber like coating on the roof of my garage.

thank you very much for you advice, I will dissect it so I can get a good understanding of the window placments and the racking issue. I still need to grasp an INNIE vs OUTIE window
Larry
garretttpeUser is Offline
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28 Apr 2018 04:01 AM
Thank you
I actually live less than 15 min from the HUBER plant, I am in Fort Fairfield Maine, (Aroostook, not Arastook....LOL) and the plant is in Easton Main, I used their engineered sheathing with a rubber like coating on the roof of my garage.

thank you very much for you advice, I will dissect it so I can get a good understanding of the window placments and the racking issue. I still need to grasp an INNIE vs OUTIE window
Larry
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30 Apr 2018 10:57 PM
Posted By garretttpe on 28 Apr 2018 04:00 AM
Thank you
I actually live less than 15 min from the HUBER plant, I am in Fort Fairfield Maine, (Aroostook, not Arastook....LOL) and the plant is in Easton Main, I used their engineered sheathing with a rubber like coating on my roof of my garage.

thank you very much for you advice, I will dissect it so I can get a good understanding of the window placments and the racking issue. I still need to grasp an INNIE vs OUTIE window
Larry


Innie vs. outie issues are covered fairly well here:

http://www.greenbuildingadvisor.com/blogs/dept/musings/innie-windows-or-outie-windows
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