# High R-Value Wall Assemblies



## TLP (Jun 17, 2013)

http://www.buildingscience.com/doctypes/enclosures-that-work/etw-high-r-value-enclosure-assemblie

From what I gather from published models a standard fiberglass or cellulose filled wall bounded by drywall and a cladding, convective air and moisture loop can cause degradation of the whole wall r-value even if the envelop is sealed and the blower door shows it good. The cavity of the wall is ‘two dimensional” and the flow through the wall one dimensional or “hygrothermal”. Fiberglass batt, and both blown and sprayed cellulose are air permeable materials allowing possible air paths between the interior and exterior as well as convective looping in the insulation. Although densepack cellulose has less air permeance it does not control air leakage. Rain leakage into the enclosure is the leading cause of premature building enclosure failure. Air need not leak straight through an assembly to cause moisture problems; it can also leak from the inside, through the wall, and back to the inside; or it can leak from the outside, through the wall, and back to the outside. Condensation within the studspace is possible if this type of airflow occurs, depending on the weather conditions. This insulation design is highly moisture vapor permable and difficult to control by a vapor barrier. It can cause mold and mildew and other health issues. If you vapor seal both sides if this cavity with no ventilation it can reduce the cellulose ability to dry, this material otherwise has good drying ability. This wall system is difficult to air seal adequately and prone to air leakage related condensation and energy losses. 2x 4 on 16 oc has more interfaces and cavities compared to 2 x 6 so it’s efficiency is lower. 

A spray foam filled wall high density foam (2.0 pcf) ranges between R-5.5-R-6.5 per inch for the aged R-value, and low density foam (0.5pcf) has an R-value of approximately R-3.6/inch…. Since high density foam is generally installed short of the cavity to avoid trimming, the installed insulation R-value is approximately R-30 (using R-6/inch). Low density is generally installed deliberately overflowing the cavity and trimmed off resulting in an R-value of approximately R-21. The R-value of the high density spray foam wall decreases from an installed R-value of R-30 to approximately R-20, a decrease of R-10 because of thermal bridging. The low density spray foam wall decreases from an installed insulation R-value of 21 to a whole wall R-value of approximately R-16. Air Leakage – Both low density and high density foam form an air barrier decreasing thermal losses through air leakage. Air leakage is still common under the bottom plate and at the rim joist if these areas are not detailed correctly. Air leakage is significantly minimized by installing spray foam insulation in the studspace since both low density and high density spray foam act as an air barrier. This increases the durability of the wall system considerably over standard construction. High density (2.0 pcf) foam forms a vapor control layer reducing vapor movement through the enclosure, minimizing the potential for wintertime vapor condensation and summertime inward vapor drive. Low density foam allows moisture vapor movement through the foam so other methods of vapor control such as poly, kraft paper, or vapor barrier paint may be required based on the geographic location. Both of the spray foam walls dry relatively slowly if water enters the enclosure, since they do not experience convective looping and air movement similar to air permeable insulations. Spray foam does not provide any buffering capacity or redistribution. Foam is relatively moisture tolerant and will be able to dry given enough time. Ventilation behind vapor impermeable claddings and interior components (e.g. kitchen cabinets) can encourage drying. The primary durability risks associated with these wall assemblies involve moisture damage related to rain water penetration. Both air leakage and vapor diffusion durability is significantly increased with spray foam but some vapor control may be necessary with low density spray foam in cold climates. Spray foam significantly reduces risks of poor air tightness detailing of the exterior sheathing or interior drywall. 

It may be possible to use spray foam insulation in combination with another insulation strategy to maximize the R-value gained with the spray foam insulation.

Begs the question what combination, cellulose and foam (low or high) and what does the wall assy look like?

PS: If anyone has a more up to date design guide please post it.


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## TLP (Jun 17, 2013)

So let’s see if I can simplify the above with respect to a hybrid foam (SPF)-cellulose design. It’s one thing to build an R-Value wall and another to sustain it.

If you were to SPF (high density) the envelop prior to insulation for air leakage, drywall, and pass the door test you have only solved part of the issue. If the drywall is not sealed inside moist air can enter the wall cavity build mold and mildew, get cooled or heated by a convective loop, drastically reduce r-value. Increase HVAC loads. If you cut the high density foam shy of the lower/upper sill you leave air pockets decreasing the r-value by 1/3, however in addition to hd foam being a good air barrier it also does a good job at minimizing moisture drive through the wall assy. Low density foam does not leave any gaps but, does less at air sealing and moisture drive. If you use low density foam poly, kraft paper, or vapor barrier paint may be require if there is a lot of moisture in your local. One danger of using foam compared to air permeable cellulose or fiberglass is it does not dry as fast if subjected to moisture, and if there is a convective loop air and moisture will degrade r-value significantly, therefore venting behind cladding might be a good idea. Nice thing about foam is it doesn’t distribute moisture or air well, compared to air permeable insulation. If you install batting in this wall cavity surrounded by three SPF surfaces and do not cut the insulation close to the foamed upper/lower sill you still have the potential for a convective loop path. A method to close this loop if air enters the cavity makes sense. If you use 2x4 framing the risk multiples. If you use a 100% foam filled wall depending on the density of foam will determine how much vapor sealing is needed. If moist air enters the cavity it won’t convect but, will take longer to dry which can promote mold and mildew and r-value reduction unless there is a ventilation system.


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## Joasis (Mar 28, 2006)

There are coming code issues with spray foam. I don't know how valid the point will be until we have years of experience with the product, but lawyers are lining up for the class action suits coming due to off-gassing, and fire departments are getting involved over the toxicity of the product when burning....

New energy codes are coming on that will require r-20+ in a few years, and the HERS ratings are in place...plus the blow door tests we do now....so where do we go? 

As an ICF builder, this topic only concerns me as far as the roof assemblies go, and if I can use a LiteDeck or Insuldeck form, then concrete is my choice. 

When we build with basically organic materials, or combinations of materials that are not permanent in nature, there will be no perfect answer.....but the university studies in our area confirm that the most effective way to insulate any wall is to prevent air movement in total. A wall built with sheetrock and OSB, and sealed with caulking, no insulation, is just as good as a wall with fiberglass built in the traditional manner. 

From our continuing education classes, it appears the house wrap guys are all over this, on the moisture issues as well as air barriers, but to me, it seem they are promoting their own product with biased research. You want an effective wall? Try and ICF with 2-1/2 inches of 2lb. density EPS, 6 inches of concrete for the thermal mass, and another 2-1/2 inches of EPS, sheet rocked, and sealed windows. About as every efficient as it gets short of underground.


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## Golden view (Feb 16, 2012)

All the rage in Alaska is the REMOTE wall. Here's a link to the manual: REMOTE manual

It puts the dew point completely outside all wood elements, and the wall can dry to the inside of the structure. We're approaching 10 years of testing.

This, or ICF with 4.5" foam on the outside to keep the thermal mass above freezing.

For traditional wood frame with fiberglass, we treat the vapor retarder detailing as if we are building a swimming pool to hold water.


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## Golden view (Feb 16, 2012)

There are many advantages to those who want to frame with wood. You can do 2x4, you can run HVAC and plumbing in exterior walls, you don't have to be concerned with advanced framing. The R11 fiberglass is "Bonus" and does little. You can just put it in full width bays for ease of installation.


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## TLP (Jun 17, 2013)

Thanks for the very good responses. Give me some time to study them and respond.


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## TLP (Jun 17, 2013)

Golden view said:


> All the rage in Alaska is the REMOTE wall. Here's a link to the manual: REMOTE manual
> 
> It puts the dew point completely outside all wood elements, and the wall can dry to the inside of the structure. We're approaching 10 years of testing.
> 
> ...


REMOTE WALL – Hard to debate 10 years of testing. Should work well in Zones 4-6 and where there is high humidity. 

From what I gather, provides thick foam wall mass envelop air and vapor seal, moisture wall cavity drive control or interior-exterior wall moisture, pressure, and temp differences, by keeping the exterior wall insulated (warmer) and from collecting cold or hot moisture, pushing the dew point from the wall cavity to outward framing. The inner wall cavity needs no insulation and is made available for mechanicals (HVAC, HRV, ETC) better if 2 x 6s are used and no need to worry about the hazards of exterior wall freezing,. Or you can use 2 x 4 framing to cut cost since insulation is not needed. 

This design is not affected by systems penetrations (electrical, plumbing, etc), also does not trap in wall cavity moisture potentially degrading r-value drastically from wet insulation, has a low thermal bridging (exterior-to-interior ratio is 58-to-42, with 42% on the warm side that test show won’t reach it’s dew point—more than double the 20% recommended by the ASHRAE standards) and air movement (convective loops). If wetting occurs wall will dry to inside warmer air.

Risk of workmanship error and detailing labor time reductions. For example, exterior transitions such as cantilevers and large bay windows can be time consuming to seal and insulate properly. The REMOTE system simplifies the detailing in these areas by attending to them on the exterior where they can be readily incorporated into the continuous thermal envelop provided by ridged foam. Another example, properly sealing the number of holes for heating, plumbing and electrical conduits and the number of different contractors cutting these holes makes it virtually impossible to get a perfect seal REMOTE solves. Contractor can use well known conventional 2 x 4 framing to keep cost down. Foam detail training might be an up-front investment. 

REMOTE allows more space for insulation in the roof of a structure and eliminates the need for constructing the 'second' roof. This modification allows for more cost effective construction and a higher R-value where it is most needed–in the ceiling

The best time to do a blower door test when the foam board, exterior membrane, ceiling vapor barrier, windows and doors are all in place and the ceiling has been sheetrocked. Ideally any plumbing and wiring penetrations will also be in place. The speciﬁc locations of air leaks can be easily identiﬁed and remedied.

At the end of the manual it said they were going to conduct more test on loosely installed batts but I can not find it.?

I this what you are finding on cost?

The cost of the REMOTE wall system is somewhat higher than the conventional system, but apples-to-apples comparisons are difficult to make. In this study, including labor, we compute the REMOTE wall to cost about $0.85 more per square foot of heated space (including the garage) than the conventional approach. Other estimates, that exclude labor, put the cost premium at about $0.30 per SF of heated space. For a 2,500 SF house, the REMOTE premium would be about $1,500 (assuming the labor costs to equal the materials cost) to $2,125 (based on the $0.85 per SF premium) over the conventional wall system. CCHRC is continuing to research ways to reduce this cost; but this cost seems worth the benefits of a healthy, durable home.

Sounds like you got to watch sizing your HVAC too thier model was off,

There remain questions about the fuel-usage rates observed in this study. The REMOTE home appears to be using fuel at a rate almost twice what was predicted by the AK Warm analysis (which was very low). This rate is not overly excessive compared to other highly rated homes; but is higher than was expected for such a well built home. Given the insulation values and the air tightness results, this is unlikely to be an envelope issue. The best explanation to-date is that the boiler is oversized and the standby and stack losses are using the extra fuel as compared to the predicted rate. 


Are you doing a blower door test prior to rocking the walls, if so what ACH? 

Did it take a while to get subs up to speed? 

Are you building to the manual detail if so how are you blocking your trusses, what method to join wall and attic insulation? I like the deeper variation of an energy heel truss to gain more attic insulation (attached)

Also, I read on this thread: http://www.contractortalk.com/newreply.php?do=newreply&p=1878991



Golden view said:


> When there is little solar gain, and heat flow only happens in one direction, thermal mass is not a factor until the power goes out, then it keeps things warm longer.
> 
> In Fairbanks, we are doing some of the most cutting edge building research for cold climates. See CCHRC.org.
> 
> ...


What software ru using and does it take into account moisture infiltration air flow or fluid dynamics? I'm looking at REM most widely used: I'm surprised that ICF Quadlock roof w/o needing 2 more inches of foam doesn't perform better in your model considering all the issues with the air and moisture standard fiberglass, cellulose, and foam on wood options that are "cheaper" have. It is also hard to verify and vapor seal don't you agree unless to blower door test.


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## Morning Wood (Jan 12, 2008)

How do you guys feel about double stud walls in new construction. They seem to be hard to beat. I just met a young guy who is quality control and design for an insulation company who will be insulating my new addition with cellulose. He claimed to have the 2nd tightest house in the world. .09 air changes, 50 CFM at ACH 50. No foam in his house at all.


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## Morning Wood (Jan 12, 2008)

By the way. I've been waiting a long time for a thread like this on this site. Albeit, what you guys are talking about is not entirely in laymens' terms.


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## Golden view (Feb 16, 2012)

Morning Wood said:


> By the way. I've been waiting a long time for a thread like this on this site. Albeit, what you guys are talking about is not entirely in laymens' terms.


This is getting a few steps above my level too. Sorry TLP, I may get back in more detail after I process this some more.

Double wall is fairly common in Fairbanks. I did a double wall house with 2x6 R-21, vapor barrier, then 2x4 R11. 

All the wires and everything were in the 2x4 wall. No detailing the vapor barrier around boxes and such. You have to frame the walls twice, so if they are complex it can be a pain, but the 2x4 wall can be built without headers or jacks so it is faster.

It ended up being more like 1.0 ACH50 but I know many of the problem areas. 1100 sf house with a lot of penetrations and I'm now convinced the subfloor leaked some, because the main difference between that and the previous one with better air tightness was the previous one had a poured gypcrete floor.

After that I did 2x6 W/R-21 and wrapped with 1.5" EPS. Also common in Fairbanks. I'm convinced this performed better. Of course with double wall you can go about as thick as you want.


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## Morning Wood (Jan 12, 2008)

I haven't gotten the final numbers on my house yet. But, I haven't insulated yet, and I'm at 1 ach50. I haven't gotten the volume quite dialed in yet either so my numbers could be off. The house is 3k sq ft. kind of embarrassing.


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## Golden view (Feb 16, 2012)

It is interesting that the fuel estimate was so far off. I've long felt that oil fired boilers are problematic when over-sized, but the smallest input rating we can get is about 65,000 BTU/hour. There are many inneficiencies in the standard practices we still use. For example, in a 1500 square foot home I built last year, the boiler is in the 600 sf heated garage. It is a direct vent boiler. At -40 degrees (f or C), the garage stays at about 75 from jacket and pipe losses from the boiler. The garage heating zone has never come on.

Another not-so scientific bit of information comes from another common scenario I've encountered. Made up numbers but they accurately represent the average outcome: A home with a boiler burns on average 1000 gallons per year. Combustion efficiency is steady every year at 80%. The homeowners replace the boiler with oil fired direct vented heaters that run at 86% efficiency. Their fuel usage goes down to 600 gallons.


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## Golden view (Feb 16, 2012)

This got me thinking. I've contacted some of my recent clients to see how their fuel usage is compared to the model I did with AKWarm. My own house, the first I ever built, was fairly accurate.


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## hdavis (Feb 14, 2012)

I'm assuming it's due to direct vent.


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## Golden view (Feb 16, 2012)

hdavis said:


> I'm assuming it's due to direct vent.


What is? A few topics were covered.


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## Morning Wood (Jan 12, 2008)

Golden view, what do you guys do for air sealing? And what kind of tightness do you shoot for in your general homes?


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## hdavis (Feb 14, 2012)

Golden view said:


> A home with a boiler burns on average 1000 gallons per year. Combustion efficiency is steady every year at 80%. The homeowners replace the boiler with oil fired direct vented heaters that run at 86% efficiency. Their fuel usage goes down to 600 gallons.



That's the one.


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## Terrorron (Nov 7, 2008)

This is also a topic that I'd been waiting to see appear on these boards.

About a year ago, I dropped my renovating contacts and went back into the world of residential insulation...something that I had experienced great success with in the past.

I am in Edmonton, Alberta. 

The thermometer here currently reads -32C. 

Up here in the "Great White North" we are taking a hard look at the options available to create a "better mousetrap" with respect to exterior envelopes.
One of the builders that I am doing quite a lot of work with (Landmark Homes) is moving to building ALL of their houses exterior envelopes as "pre-fab" sections, insulated with 2lb foam in a temperature controlled (factory) environment. As for the post-erection aspect, I install ceiling vapor barrier and remediate deficiencies in the envelope due to mechanical trades. This makes for a VERY TIGHT envelope as they also use all of the latest advantages (HRV system, neoprene gasket electrical boxes and HDF attic access boxes). The plate poly is installed *on top of the interior walls, *(prior to roof installation) so the vapour barrier is 100% continuous throughout. We shoot all of the windows with a 2" deep bead of low expansion P/U foam and insulate the remainder of the cavity with fiberglass. Rim joist areas, cantilevers and the "bonus room" floor are "shot on site" with 2lb foam, after erection of the structure, but once we have been in and sealed the ceiling, so that heat (for curing) can be assured. 
They are also actively investigating (experimenting with) supplemental techniques over the 2lb system. 
The latest "experimental" house I did for them involved R80 (double layer R40 Batts) in the main floor "bumpout" areas, 2lb 2 x 6 walls with the "Spider" system to fill the remaining cavity, PLUS an additional 2" of HDF on the exterior with acrylic stucco over this! 2 lb foam in the ceilings shot to R 30 plus an additional R50 of loosefill cellulose blown on top of the foam. 
18" truss heels  
These folks are taking it seriously.

On the other hand, most of the others are "standard spec"; R20 fiberglass batts and "superseal" poly specs on the outside walls/ceilings. R 40 cellulose blown attics. Tightness of the envelope varies from "adequate" to "leaky", this mostly pendant on the diligence of the framer when installing the plate poly during construction.

Buyer beware. You can only work with what you are given.

Fiberglass batt will never go away...it's too cheap of a solution and it works. The beauty of it is that when the lumber shrinks, the inherent compression in the batts will still FILL the stud cavities; the same CAN NOT be said for "shot on site" 2 lb houses when framed with dimensional lumber. 
Landmark uses LSL/LVL in all of the "critical" areas on their "shop built" exterior sections to ameliorate this problem.

No, I do not work for them. I'm not here to "pimp their stuff". These are observations as to the evolutions happening in this particular market.
EDIT IN: EVERYTHING here is high efficiency, direct vented. It's been this way for 10 years now. After all? We're "Dirty Alberta"...polluting the entire continent with our tarsands projects and we need the carbon credits.
1/2 lb foam is a joke and Should BE outlawed...


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## Golden view (Feb 16, 2012)

Golden view said:


> What is? A few topics were covered.


I think so too.


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## Golden view (Feb 16, 2012)

Morning Wood said:


> Golden view, what do you guys do for air sealing? And what kind of tightness do you shoot for in your general homes?


I shoot for 1 ACH50. I can do better but my clients are looking for economical homes and 100 year payback upgrades don't fly. I have colleagues that get those clients. 

My average project on a budget has little more than good practices: 6 mil poly on walls and ceilings, all joints lapped over framing with tremco (acoustical sealant, Black Death) including to subfloor, vapor tight electrical boxes, all penetrations detailed in some way. Often run through solid foam blocking at penetrations. Windows sealed to framing with can foam.

Edit: oh yeah, and usually a single roof penetration. The plumbing vent. DV boilers.


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