# Double stud wall construction-anybody seen it/done it?



## Badfish740 (Oct 7, 2010)

Since researching superinsulated home building techniques has developed into somewhat of a hobby I ran across a new (to me) method that seems pretty straightforward-the double stud wall:

Double stud wall with spray foam

R-35 or so walls sound pretty good to me.  The interesting thing is that they only use 2" of spray foam (to keep the cost down I'd imagine) and fill the rest with cellulose.  I wonder what a wall full of spray foam would be rated at (and what it would cost).


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## dougstove (Oct 7, 2010)

In my area most of the better contractors are doing double wall 2 x 4",  more or less as described in the building science article.


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## lukem (Oct 7, 2010)

Closed cell foam R value is about 50% higher than cellulose.


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## Badfish740 (Oct 7, 2010)

lukem said:
			
		

> Closed cell foam R value is about 50% higher than cellulose.



Wow-so it would probably be safe to say that R-45/R-50 would be possible will all closed cell foam.


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## Burn-1 (Oct 7, 2010)

The modified Larsen Truss is also a great way to make a larger insulation cavity. 

Superinsulated home using Larsen Truss

The 2,000 SF house in the article above only needs 4/5 of a cord for a winter in Western Massachusetts.


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## Reggie Dunlap (Oct 7, 2010)

That's a good way to build walls, but very expensive. In a mild climate like NJ I'm not sure it's worth the expense. The first inch of urethane foam does 90% of the insulating, every additional inch helps to a point of diminishing returns, somewhere around 2-3 inches in walls. I'd concentrate on making the walls airtight with minimal foam and putting the savings into roof insulation.

There are less expensive ways of creating a thermal break so the framing members don't conduct heat outside:
-Install 3/4" strapping on the inside of a 2x4 or 2x6 wall and fill the entire cavity with foam and/or cellulose. 
-Install rigid foam on the exterior of the wall with siding installed over the foam.

Depending on wall thickness you may need extension jambs on doors and windows if your framing isn't l isn't 6 9/16" deep.


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## btuser (Oct 8, 2010)

You only lose about 10% through the walls.  It's not worth the money.  There's an argument that your wasting money when it comes to 2x4 vs 2x6.  The whole point was to have 2x6 walls 24" on center but everyone builds 16" on center so you're gaining very little.


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## nate379 (Oct 8, 2010)

Most houses around here are built with at least 2x6 walls and if not that, then 2x8.  I have even seen some up toward the interior with double 2x6 and 2x8 walls.


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## vvvv (Oct 8, 2010)

cheaper & better to use 2" solid foam [r-10 minimum] on exterior & fill walls with whatever.


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## northernontario (Oct 8, 2010)

My sister is currently building a straw-bale wall house using a larson truss wall setup... Truss' are the load-bearing component, bales are in-fill, then plaster over top of it all.  Easily R40+ in the walls.  

Combined with an insulated concrete floor, insulated concrete foundation, well insulated attic (I believe she's doing atleast R50), designed for south-facing solar gain... it's gonna be a toasty little house!  

Of course, spray-foam has an aged R-value of ~R6... so on a 2x6 stud wall (5.5" depth) you're looking at roughly R33 in the walls.  But the huge advantage to sprayfoam is that it seals all air movement... so you achieve a true insulative value... doesn't matter if the wind is blowing or not.  The problem with fiberglass batts is air can move through them... so if you haven't sealed off all air movement, their insulative value drops.  

And yes, you have to remember that insulation follows the laws of diminishing returns.


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## vvvv (Oct 8, 2010)

northernontario said:
			
		

> My sister is currently building a straw-bale wall house using a larson truss wall setup... Truss' are the load-bearing component, bales are in-fill, then plaster over top of it all.  Easily R40+ in the walls.
> 
> Combined with an insulated concrete floor, insulated concrete foundation, well insulated attic (I believe she's doing atleast R50), designed for south-facing solar gain... it's gonna be a toasty little house!
> 
> ...


wood expands & contracts with humidity, so will the sprayfoam develop cracks eventually?


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## Badfish740 (Oct 8, 2010)

Reggie Dunlap said:
			
		

> That's a good way to build walls, but very expensive. In a mild climate like NJ I'm not sure it's worth the expense. The first inch of urethane foam does 90% of the insulating, every additional inch helps to a point of diminishing returns, somewhere around 2-3 inches in walls. I'd concentrate on making the walls airtight with minimal foam and putting the savings into roof insulation.
> 
> There are less expensive ways of creating a thermal break so the framing members don't conduct heat outside:
> -Install 3/4" strapping on the inside of a 2x4 or 2x6 wall and fill the entire cavity with foam and/or cellulose.
> ...



Good points-thanks.  I will take issue with one of them though-NJ's climate is indeed mild compared to Vermont...if you're talking about winter   I'm really less concerned about about _losing_ heat in the winter than I am with _gaining_ heat in the summer.  Our summers are humid and nasty and it seems like we get more 90+ days every year.  The home we're planning is not going to be huge (just under 3000 sq/ft) and I plan on heating with a gasification boiler.  In terms of property, a woodlot capable of producing at least a cord per year will be a requirement, so a supply of free fuel + the efficiency of a gasifier (DHW needs will be mostly taken care of by flat plate solar collectors) = heating cost isn't that big of a concern.  Sure, I don't want to be burning 5 cords a year like I am now, but if I could get down to three for a house that size I think I'd be happy.  Anyway, back to our brutal summers.  Right now in our 1960s era ranch with fiberglass in the walls and ceiling and a fair amount of air leakage, air conditioning will add anywhere from $100-150 a month on top of our normal electric bill.  That's not with keeping the house at 68 degrees either-we're lucky if it gets down to 74.  The point is that I would love to be able to keep the house at 68 in the summer and not spend hundreds per month on electricity.  I'd have to find some way to run the numbers, but I'm betting that R-40 or so walls would help with that a great deal.  I'd also love to either install photovoltaics during construction or later down the road, and super-insulating the house along with other cost savers such as LED lighting and no resistance heating loads (wood heat and hot water + propane for cooking and clothes drying) would probably allow me to have a negative electric bill for the life of the home.  Upfront costs would be certainly be higher, but if we stay in the home 30 years (or more) the payoff would be huge.


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## btuser (Oct 8, 2010)

Sprayfoam sticks like glue.  It would take a large earthquake.  Eliminating the thermal bridging in conventional structures is a serious upgrade with the double-wall construction.  I'd say maybe 10 grand for an average house for the walls, then you're looking at jamb/trim extentions.  

I bet we'll see this as a retro-fit to McMansions in the future.  You'll lose some square footage but what's the big deal in a house 3x bigger than you need?


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## vvvv (Oct 8, 2010)

btuser said:
			
		

> Sprayfoam sticks like glue.  It would take a large earthquake.


equake is sudden impact. wood expand/contract by humidity involves many cycles of little impact. if foam gets rigid, it should crack where its "glued" to the wood.........ithink


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## Badfish740 (Oct 8, 2010)

btuser said:
			
		

> Sprayfoam sticks like glue.  It would take a large earthquake.  Eliminating the thermal bridging in conventional structures is a serious upgrade with the double-wall construction.  I'd say maybe 10 grand for an average house for the walls, then you're looking at jamb/trim extentions.



I should add that we'll be DIYing it.  Another reason we're looking at double stud construction vs. something like SIPs is because double stud is more labor, but no more complicated than conventional framing.  We're going for a rustic look so jamb and trim extensions will hopefully be rough sawn lumber from trees on-site.  Plus, let's say that we stay in this home 30 years (hopefully more) and that electricity rates DON'T go up :lol: yeah right...but let's assume that to make the math easy.  Last year I spent about $1800 on electricity.  $1800 x 30 years = $54,000-remember, this number is not adjusted for inflation, rate hikes, or anything else.  When you factor in rebates, tax credits, etc...that _might_ cover the extra cost of double stud walls, LED lighting, and photovoltaics, but when you also factor in the power that would be sold back to the grid over that time AND the sale of the SRECs over the life of the system (currently trading around $600/Mwh and only showing signs of going up) the home could possibly pay for itself in 30 years.


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## Reggie Dunlap (Oct 8, 2010)

If your set on eliminating the thermal bridging it's going to be easier and cheaper to sheath the exterior in rigid foam. In your climate I don't think any method of eliminating bridging is going to add up to much savings over the long term. 

Another option is to build standard 2x6 walls, install one inch of spray foam against the plywood sheathing and put fiberglass batts in the remainder of the stud bay. That would give you an airtight wall and accomplish 99% of what the double wall would, at a fraction of the cost.


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## btuser (Oct 8, 2010)

~*~vvv~*~ said:
			
		

> btuser said:
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There's no way for the wood to swell when its encased in foam.


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## Reggie Dunlap (Oct 8, 2010)

Foam can crack if it's installed improperly. I've seen it happen when they mixed the chemicals wrong and when it was applied in temps that were too cold. Both times the cracks showed up with a day or so. I always wait at least a week before covering the foam up just to make sure.

Other than that foam is pretty rugged. Seasonal movement of framing members doesn't cause any problems.


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## vvvv (Oct 8, 2010)

btuser said:
			
		

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encased is front, back,sides, top,& bottom?


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## semipro (Oct 8, 2010)

Some foam is more flexible than others.  The canned type sold for use around windows and doors is more flexible than the regular type.


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## GaryGary (Oct 9, 2010)

Hi,
Here is a nicely done home that uses double stud walls and cellulose:
http://www.builditsolar.com/Projects/SolarHomes/MAZeroEnergy/MAZeroEnergy.htm

Some more double stud wall material here:
http://www.builditsolar.com/Projects/SolarHomes/constructionps.htm#Double

If you want the lowest cost way to get wall R values up in the mid 20's with not thermal bridging, I think the horizontally strapped or Mooney wall is a good way to go:
http://www.builditsolar.com/Projects/SolarHomes/constructionps.htm#Stick
The first "gimmie shelter" example is very good, and the Mooney wall entry is quite detailed.


The Larsen Truss is another not so expensive way to get high R values with minimal thermal bridging:
http://www.builditsolar.com/Projects/SolarHomes/LarsenTruss/LarsenTruss.htm

You can use my Home Heat Loss calculator to play with heat loss from each componetnt (walls, ceilings, windows, infiltration) separately -- just plug in the degrees days for an area near you and enter the R values for the kind of construction you are interested in.  It will give the loss through each component and the cost of the energy you are using for each component -- you can play around with improving each component independently.  With respect, statements like only 10% of the heat goes out the walls are kind of misleading in that they assume some typical construction of the other components.  
It literally only takes 5 easy minutes to see the actual heat loss and dollar numbers for your the house construction you are interested in in your area.
http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm
The calculator is free -- if you have any trouble with the inputs, drop me an email.

When you do the wall R values, bear in mind that the the thermal bridging of the studs in conventional walls cuts the R value by a fair bit.  A wall insulated with R 19 insulation ends up more like R15.  The whole wall calculator will give you actual R values for all the common wall constructions that include thermal bridging.
http://www.ornl.gov/sci/roofs+walls/AWT/InteractiveCalculators/rvalueinfo.htm

I'm personally not convinced that the spray foam is needed as a component of a double stud wall.  Many many double stud walls have been built with just dense pack cellulose insulation, and I've not heard bad things about these.  The foam (especially if closed cell) is nice, but substantially increases the cost of the wall.  If you put a few bucks into being careful not to build in water vapor and condensation problems, its probably not needed.


Gary


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## benjamin (Oct 9, 2010)

Gary's a hard act to follow, well done!

The foam article seemed very leery of moisture issues.  I don't like to hear that everything has to be detailed just right or you'll end up with problems.  

Two vapor barriers (inside and outside) is not a good idea.  Does the magic of spray foam change this?  Reggie Dunlap may be right here, exterior foam has a pretty good record despite being less than ideal regarding the "2/3 rule" (vapor barrier on the inside third of the wall), that's assuming there is no interior vapor barrier.


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## StackedLumber (Oct 9, 2010)

We've had great success w/ the "flash and batt" way of insulating w/ 2 inches of spray foam that gave us 7.1-8.1 R value per inch and then stuffed the rest of the cavity w/ R-19 batts.  We did have one spot that did crack and we ended up cleaning it out and giving it a second application of foam.  Not sure what caused it to crack, but my guess would have been the temperature b/c it was pretty cold when we sprayed.

Also, the rigidity of the spray foam is amazing, way more than the stuff from a can.


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## precaud (Oct 9, 2010)

Hi Gary, I'm glad to see you here at the Hearth.com forums. Just in case folks didn't put 2+2 together, builditsolar.com is Gary's website. And in my opinion he has done more to make DIY solar building accessible to more people than just about anyone. The solar air heaters I built onto the side of my home are a combination of one of Gary's designs, Nick Pine's concepts, and early work done in the Taos, NM area using low-mass passive solar collectors. If you're thinking of adding solar of any type to your home, spend some time perusing Gary's website, it's the best resource there is.

Sorry to blow your cover Gary, but you deserve the thanks and respect!


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## nate379 (Oct 9, 2010)

Had I been around when my house was built (I bought a "model" home) I would have paid extra to have 1/2" "R Board" put on the sheathing before the siding went up.  My walls are R21, but the R board would help "decouple" the studs.  Right now sometimes when the frost is just right or it's very cold like (-30*) there is enough heat transfer from the studs that it will show where they are on the siding even!

Some of the other houses that were built they put a thin foam between the sheathing and studs.  I don't really like that idea because the OSB to stud should be tight against each other for a good shear wall.  With the foam the OSB is floating on the studs a bit.


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## vvvv (Oct 9, 2010)

NATE379 said:
			
		

> Had I been around when my house was built (I bought a "model" home) I would have paid extra to have 1/2" "R Board" put on the sheathing before the siding went up.  My walls are R21, but the R board would help "decouple" the studs.  Right now sometimes when the frost is just right or it's very cold like (-30*) there is enough heat transfer from the studs that it will show where they are on the siding even!
> 
> Some of the other houses that were built they put a thin foam between the sheathing and studs.  I don't really like that idea because the OSB to stud should be tight against each other for a good shear wall.  With the foam the OSB is floating on the studs a bit.


Buildingscience.com specified r-10 minimum for exterior foamboards so to avoid condensation from interior air penetration into wall cavity. alaska may be more due to colder weather?


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## GaryGary (Oct 9, 2010)

precaud said:
			
		

> Hi Gary, I'm glad to see you here at the Hearth.com forums. Just in case folks didn't put 2+2 together, builditsolar.com is Gary's website. And in my opinion he has done more to make DIY solar building accessible to more people than just about anyone. The solar air heaters I built onto the side of my home are a combination of one of Gary's designs, Nick Pine's concepts, and early work done in the Taos, NM area using low-mass passive solar collectors. If you're thinking of adding solar of any type to your home, spend some time perusing Gary's website, it's the best resource there is.
> 
> Sorry to blow your cover Gary, but you deserve the thanks and respect!



Hi -- thanks for the kind words!

I'm always looking for good projects to add to the collection, so if you (or anyone) has one, please send it in.
You live in a great place for solar.

Gary


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## vvvv (Oct 9, 2010)

GaryGary said:
			
		

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i posted a window foam panel, elastic scheme on your site but could only manage to post it as a response to another project. its ugly foam but the concept is very easy to use. here's the blog i did if u wanna grab it or comment..........great site u have.
http://czarcar-foamwindowinsulation.blogspot.com/


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## Wallyworld (Oct 9, 2010)

Here is what I did on my new shop, 2 inches of closed cell over the studs, plywood over the foam. R19 fiberglass inside the 2 by 6 studs


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## btuser (Oct 9, 2010)

I like the PT plywood on the bottom.


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## jotul8e2 (Oct 13, 2010)

btuser said:
			
		

> You only lose about 10% through the walls.  It's not worth the money.  There's an argument that your wasting money when it comes to 2x4 vs 2x6.  The whole point was to have 2x6 walls 24" on center but everyone builds 16" on center so you're gaining very little.



Re: 10% loss through walls.  I've heard that a lot and I am ... skeptical.  Yes, I know heat rises.  I would like to see some actual data on this - can anyone point me to some?  In any event, the elephant in the room is always windows and (to a lesser extent) doors.  The very best windows on the market have insulating values of r 2 or so, and very few have coatings to reflect ir back into the house, so even more heat is lost to direct radiation through the glass.  I think the heat losses through conventional windows and doors are far higher than most people suspect - again, I'd like to see some data if anyone knows of any.

I built my house (southern Missouri) with 2X6 walls on 24" centers, r19 batts, with standard chipboard sheeting and an overlay of 1" foam panels.  I estimated the extra cost of the 2 X 6 walls to be something less than $400 - more expensive studs, but fewer of them.  Keep in mind you only use them on the outside walls.  With the drywall, insulation, sheeting, foam, and exterior siding, I must have just a bit less than r 30 at the cavities.  I also chose smaller and fewer windows.  We can see out, but I have no 16' atrium windows or anything silly like that.  The attic is r 60 - 70.

We have 2600 sq. ft. over a full walkout (but unfinished) basement, are all electric, and on a well so I pay to pump my water.  I also have a 2200 sq. ft. shop which I air condition (humidity control).  My total consumption last year was just under 13000 kw.  By far most of that was in the summer months as I heat with wood all but 8 weeks or so in the winter and spring.

Back to windows:  I have just recently got to work on doing something about the widows.  I have put up single cell thermal blinds in all but two windows.  We shall see.  For a more significant effect I may add insulating, close fitting drapes.

We could do better, but as pointed out in some other posts the return on investment gets pretty poor pretty quick.


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## Seasoned Oak (Oct 16, 2010)

jotul8e2 said:
			
		

> btuser said:
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I googled this and got percentages all over the map. THe wall loss was in the range of 25 to as much as 50%. Some sites had more being lost through walls than the roof,perhaps cuz there may be more wall area than roof. After reading all this id say insulate them both well and dont worry about the %


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## midwestcoast (Oct 16, 2010)

You won't get a good rule of thumb on what %age of heat is lost through walls, windows, doors....  There are just way too many variables: 
Tightness of envelope
Design & shape of the house (2-story has nearly 2X the wall area as a ranch, large square house has much lower wall area to floorspace ratio than a small rectangular one...)
Amount, type & install quality of wall & attic insulation
#, size & quality of windows & doors
Foundation insulation
It goes on & on, but here's the way I look at it; The better insulated your attic & the higher quality windows & doors, the more heat (%age wise) you'll loose through the walls and vice versa.  You won't have a highly efficient envelope unless all parts are tight & well insulated. I really don't see 4" of fiberglass batts as a well insulated wall for modern construction, especially with the poor instalation practises that are nearly universal. 
Doors & windows (if they seal properly) don't loose as much heat as many think since they're typically a very small %age of wall area. The payback on window replacement is often very long (aesthetics & functionality notwithstanding) & I've never seen it calculated-out by a window company as a way to entice customers.
Oh, and I just gotta say it: Heat doesn't rise, hot air rises


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## ihookem (Oct 16, 2010)

I built 2 exact houses and lived in the first for 4 years. The second house I spent just one winter in. Both were 2x6 walls. The first was blown in cellulose ,the second is 4-41/2 " of closed cell foam. The foam was 1500 more than cellulose. The first house with cellulose walls didn't let any airflow through that I could tell by putting my hand over all the outlets on the outside walls, I could not feel any cold air coming in through the outlets even at 40 mph winds. This was a "true" r-18 wall plus r-6 for 1" foam plus r-2 for the brick to equal a "true" r 26 wall.  Batts of r 19 is not a real r 19 if the wall has air leaks. My new house has with 4-4 1/2" of closed cell foam. This makes r 28 plus r 1 for the osb sheathing plus r 2 for the brick, equalling an r 31 wall. I don't think I can tell the difference in heat loss but my first winter with foam was an easy winter. If I did it again I think I would spray 1" closed cell and fill the rest with cellulose to save about 1,000 dollars. Also, weather you get foamed walls or not make sure you foam the floor trusses in the basement and between the roof trusses and make sure they spray up the bottom of the roof sheathing a few feet. This stops the chance of draft going into the attic and stops ice back damming.


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## Seasoned Oak (Nov 21, 2010)

I would think the best combination is Standard levels of Insulation combined with Solar and Wood heat. Once you go over a certain amount in the walls and roof you will just lose it all through the windows and doors.


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## GaryGary (Nov 22, 2010)

trump said:
			
		

> I would think the best combination is Standard levels of Insulation combined with Solar and Wood heat. Once you go over a certain amount in the walls and roof you will just lose it all through the windows and doors.




If you are in a cold climate, I'd respectfully disagree a bit.

I'm a pretty dyed in the wool solar heating fan and get a good fraction of my heat from solar collectors, and I've consulted with a lot of people who have put solar heating in.   My conclusion is that if you have the luxury of building a new house that putting your money first into a very good thermal envelope, and then into solar is the way to go.  I think that the standard level of insulation, infiltration sealing, windows ... is not good enough, and you can see codes changing around the country now to require higher levels.   A home with a good thermal envelope can be heated effectively with solar and without an excessively large collector array.   I think the Passive House Institute is pretty close to the right ball park on their homes - maybe just a bit over the top.

For retrofits, its harder.  Our house is insulated to the code of Montana in 1995 -- R19 walls, R38 ceilings, double glazed low-e windows.  We have worked fairly hard at improving this with more attic insulation, more sealing, crawl space insulation, inside insulating window treatments.    This has all made a significant difference, but even with the thermal envelope improvements we have made, the 240 sqft of solar collector we have only provides about 30% of our space heating.  Our total heating bill with envelope improvements and solar is down to a bit less than half what it was when we move in.   If I were able to start from scratch on the house, I could cut the heat loss in half, and then the 240 sqft of solar would provide 60% of our space heating.

It would be interesting to hear what other peoples experiences have been.

Gary


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## Seasoned Oak (Nov 22, 2010)

The author of this thread did not address windows and doors.My point is if your going to go to extreme lengths on the walls and ceilings without doing the same with windows and doors your heat will indeed escape there.
Yes a super insulated home can be heated with very little heat,but at what cost. At some point you will never recover your initial investment. Windows with performance to match 12" walls are not cheap and probably its not practical to even try it with a retrofit.


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## precaud (Nov 22, 2010)

trump said:
			
		

> My point is if your going to go to extreme lengths on the walls and ceilings without doing the same with windows and doors your heat will indeed escape there.


More accurately, your heat loss through the windows and doors will be the same whether the walls are treated or not.



> Yes a super insulated home can be heated with very little heat, but at what cost. At some point you will never recover your initial investment.



Actually, at some point you WILL recover your cost - when you sell the home. And it will be accelerated by the cost of heating fuel increasing. The chances of both of these things happening is very good...


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## Seasoned Oak (Nov 22, 2010)

Precaud wrote
Actually, at some point you WILL recover your cost - when you sell the home. And it will be accelerated by the cost of heating fuel increasing. The chances of both of these things happening is very good...[/quote]
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With a huge % of the countries homes UNDER WATER people are lucky to recover the cost of a regular home. My heating cost is $750 for the year for a 3000SF home in central PA,and 400 SF of my wall area in a 100 year old home has no insulation at all. Yes i will probably get around to it soon but what will i save $50 a year? hardly worth taking a day off work to do it.  Im a big believer in insulation but there is a cost benefit to consider.


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## precaud (Nov 22, 2010)

Gary,

Absolutely no question, retrofits are harder to make efficient. And that's unfortunately what most of us have to deal with. I think we can get them pretty efficient, but with larger day-to-night temperature swings than a properly-designed thermal envelope would have. 

I'm going into this winter with 160 sq ft of solar (plus two sets of another 32 or so sq ft of windows that give 1/2 day of direct gain each) - that's a bit more than double what I had last year - heating 1150-1200 sq ft with 9 ft ceilings, R48 average in the ceiling, uninsulated but massive walls, full basement under heated on weekdays only, but never at night. The 6.3 ratio of floor area to glazing area is on the low side, but I felt it would be necessary for the solar to carry the entire daytime heat load during the coldest part of the year. Last year I used a tad over 1.5 cords of wood to supplement the solar upstairs; I'm interested to see how much less is needed this year. Comfort levels are WAY up already - by 4pm it's 79F in the house, diminishing to 67 at 5am. This is with no wood heat and lows in the upper teens/low 20's. We'll see how it fares in January, when we see the season's coldest temps.


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## precaud (Nov 22, 2010)

trump said:
			
		

> With a huge % of the countries homes UNDER WATER people are lucky to recover the cost of a regular home. My heating cost is $750 for the year for a 3000SF home in central PA,and 400 SF of my wall area in a 100 year old home has no insulation at all. Yes i will probably get around to it soon but what will i save $50 a year? hardly worth taking a day off work to do it.  Im a big believer in insulation but there is a cost benefit to consider.



I think you're confusing the issue by generalizing it so much. Under-water homeowners aren't going to put any money into efficiency, so there's no reason to even bring them into the picture.

I can only think of maybe $30-$40 that I've spent on insulation that has not added to definitely reducing heat loss and raising comfort levels. They were experiments that didn't make any difference. Unfortunately I'm at a place now where the next step that will make a significant difference (insulating the walls on the exterior), if I am to take it, will cost a bunch. Unless a windfall of unexpected proportions comes my way, it probably won't happen.

[Sigh.]


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## benjamin (Nov 22, 2010)

The homes that are underwater aren't because they spent too much money on insulation.  Insulation is a tiny fraction of the cost of even a modest new home, and in most cases the extra insulation in a new home has a payback in a few years on energy costs, plus there is a comfort factor.  There are still new homes built with no insulation under or around the foundation, even with finished basements.  Really? most people aren't storing their cider barrel and potatoes down there anymore.  

Obviously if you're heating an existing home with coal, free wood, or sawdust (thanks Kenny!) then it's not going to pay to get extreme triple glazed windows or do superinsulation.  On the other hand if you start looking at what people pay for wood boiler systems, heat pumps or even standard HVAC then the insulation starts to look like a bargain.  

I see lots of old homes with little or no insulation because "it won't pay off", but when gas or oil hits a certain price they will pay to do it, and they will pay a lot more than if they had done it thirty years ago,  not to mention the heat wasted and comfort missed in the meantime.  

Then again... since in a few years we'll all be living in vacuum canister apartments with Gary's incredible solar collectors, maybe we shouldn't sweat the small stuff?!?


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## precaud (Nov 22, 2010)

My major point is: it's a mistake to view "payoff" only in money-out-of-pocket terms. Increased comfort level, less work expended on preparing firewood, increased value to a future purchaser of the home; these (and other things) are all real, tangible payoffs.


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## midwestcoast (Nov 22, 2010)

jotul8e2 said:
			
		

> Back to windows:  I have just recently got to work on doing something about the widows.  I have put up single cell thermal blinds in all but two windows.  We shall see.  For a more significant effect I may add insulating, close fitting drapes.
> 
> We could do better, but as pointed out in some other posts the return on investment gets pretty poor pretty quick.



Sounds like you have a very efficient home there. nice job!  There are many examples of indoor removable storm windows on the builditsolar.com site. Should get you another R-1 all day long, not just night.


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## Seasoned Oak (Nov 22, 2010)

precaud said:
			
		

> My major point is: it's a mistake to view "payoff" only in money-out-of-pocket terms. Increased comfort level, less work expended on preparing firewood, increased value to a future purchaser of the home; these (and other things) are all real, tangible payoffs.



I do agree with every word. I rehab old houses for a living and i insulate as thorough as possible. The last house i did was done so well it never went below 50 in winter even with the heat turned off. That said,there are still other factors at play.When doing my house the biggest savings by far were had through changing from a liquid fuel to a solid fuel heat. I saved the entire cost of the furnace the very first year. I also save about 20% annually by enclosing a south facing porch making a passive solar collector out of it for very lo -cost. Finally i will add insulation to the mixture which has the lowest payback per $ spent in my case. Obviously if you want to keep your electric or oil or other expensive heating sources than insulation may be your highest payback upgrade,for your particular situation. Each case is different. Dont get me wrong,im not discounting the value of insulation. I know from experience in the absence of a changeout of heating fuel sources insulation can make all the difference. In my case though the cost of 12" walls and triple pane windows would be way more than i will pay for heating fuel for the rest of my life.


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## precaud (Nov 22, 2010)

Well it's clear you understand the game, trump. The key is to identify the highest payoff vs cost scenarios and execute them. And each house has to be evaluated and optimized carefully.


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## jimbom (Dec 19, 2010)

Hi,   I built 12" double stud walls when we built our retirement home in 1990.  We have a 50 x 40 foot home with ample glass east/south  and minimal glass west/north.  In the Ozarks, heat and coolth cost about the same so insulation saves money in both seasons.  

I had the lumber yard rip my 2 x 6 studs into 2 x 3 studs. They did it at no cost.  The framers had to erect one extra exterior stud wall, which they did in a flash.  From that point forward, labor costs were the same as conventional construction.  The walls are 12inch.  It is fiberglass batt construction with Tyvex house wrap.  I paid very careful attention to airtight features.  The cost difference between 12" and 6" batts in 1990 was minimal.  Double stud made the electrical wiring go very quickly, but since I did the electrical, no dollar savings were realized.

The ceiling has two foot of fiber glass blown in.  The trusses are 2' deep at the bearing point.  Deep trusses were less expensive for my application because it permitted more 2 x 4 chords where 2 x 6 would have been required.  I was the general contractor on the house and did much of the mechanical and electrical work myself.  Before the ceiling insulation, I carefully and completely foamed up all the potential air leaks.  All places where wires and pipes penetrated top plates were foamed closed.  The access hatch to the attic is in the front porch ceiling so no air leaks around that penetration.  Air vents were foamed carefully.  The house is truly air tight.  Because of this, I have outside air intake for the basement mechanical, the dryer and the fireplace.  Make up air for the stove exhaust and bathrooms comes from the basement under a generous gap in the basement stairs door.

At the time I built, energy prices were relatively low, and people questioned the wisdom of my actions.  No building code would have recommended this level of insulation for our climate at that time.  They still don't.  I am conversant with diminishing returns with regard to insulation.  I am a registered professional engineer with degrees in mechanical and civil engineering.  I worked in horizontal and vertical construction for 20 years before retiring.  So I was able to quantify the returns versus investment increments.  I my house, the most expensive part of 12 inch walls was the loss of 90 square foot of interior floor space at $50/square foot.  I included this in my investment cost.  The Law of Diminishing Returns should really be the Suggestion of Diminishing Returns.  Because each situation has unique aspects that should be considered.  It is not a simple 'insulation around the pipe' problem.

At the time of construction, I anticipated solar heat in the future so I designed and installed a simple warm water radiant floor.  It uses conventional pea gravel concrete, ASTM D3309 polybutylene pipe, and inexpensive site built copper pipe manifolds.  We heat the house with one 35,000 BTU/hour gas 40 gallon hot water heater which also provides our domestic hot water.  It is air conditioned with one 18,000BTU/hour central air conditioning unit.  Savings from having no furnace and a 1.5 ton air conditioner were not included in my calculations, but would reduce the original investment.  We raised two boys here and had few hot water problems.  We have replaced the hot water heater twice or three times, but are still on the original AC unit.  The polybutylene pipe has been no problem and will likely last fifty more years at the temperatures I need.

Because my energy costs over the years were so low, solar heat was never high on the to do list.  Then I saw Gary Reysa's BuildItSolar site and was inspired to complete the original solar concept.  Gary is an exceptional man and probably has given more freely of himself to make our country energy independent than anyone in the USA.  I have never met the man but he has my respect.

Since my annual costs are so low, I cannot justify many dollars for solar.  So, I have been picking up components off the internet and Craiglist postings for the last two years.  If you wait long enough, everything you need will come up for sale cheap.  For example, I bought 500 square foot of tempered glass for a dollar a square foot.  I bought 500 square foot of used freezer panels for $100.  Right there, I have the back, insulation and cover for my water panel.  My panel will not have tubing, rather the water will just run down the freezer panel surface similar to a Thompson system.  I have also obtained a 1000 gallon steel water tank for $200 and an unbelievable amount of cheap structural steel for the panel structure.  My panel will be site built 40 x 12 foot.  This will require a well made structure to accommodate wind loads.  I have  all the major components for very little money.  Another $1000 or so will see it to completion.

This has been way to much information.  However, my madness has a point.  You just cannot isolate a twelve inch double stud wall from the rest of the variables.  The climate, energy costs, all investment costs, all energy savings, and all the other elements of the structure should be considered if you want an accurate guess of the utility of a tight house envelope.

Sorry for the long post, but thanks for having this site.  I am learning a lot from the posts on here and hope to be able to contribute a little on the wood side when I become more knowledgeable about my wood stove and my wood lot.  Thanks, Jim


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## nate379 (Jan 8, 2011)

The problem I see with that though is you loose most of the shear strength the plywood provides.



			
				Wallyworld said:
			
		

> Here is what I did on my new shop, 2 inches of closed cell over the studs, plywood over the foam. R19 fiberglass inside the 2 by 6 studs


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## Wallyworld (Jan 8, 2011)

The inside walls are screwed OSB so doubt thats a factor. I should have screwed the outside plywood also. It was done with a nailer, 3 1/2 nails and way more nails than normal but I see your point and thought of that. I think if if was screwed and maybe even construction adhesive so you had a sandwiched wall it would be no issue. I'll tell you as far being comfortable inside it rules, I use solar  and a wood stove to heat the space. Haven't had a fire in 2 weeks and the temps inside are still in the 50s.It was 2f yesterday morning.


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## btuser (Jan 8, 2011)

JimboM:

How do you heat the house and get hot water from the same water heater?

I'm in the same boat when it comes to solar.  I just scrounged a brand new controller, but I've been looking for a tank for a long time.


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## jimbom (Jan 9, 2011)

btuser said:
			
		

> JimboM:
> 
> How do you heat the house and get hot water from the same water heater?



Good question.  What I am about to write is not condoned by any building code that I know of.  Any public health officials skip this comment.  Same for any water treatment operators.

The floor loop is tapped directly into the bottom and top of the water heater.  The floor loop water is pumped through the water heater as needed.  The water that heats the floor could be giving a shower in the next instant.  The hot water tank temperature is set to medium temperature on the dial.  Nothing extremely hot or anything out of the ordinary.

Do not do this at home unless you are comfortable with the methods to keep pathogens from growing in fresh water.  Not to recommend anyone do this, but the key is to keep the water in the floor loop circulating at all times.  My judgment was this would prevent health hazard from the water.  We have been doing it since 1990/91 and no trouble to date.  This includes when the floor is drawing no water from the tank.

There are a lot of smart people on this forum and I know the arguments against this.  I agree with those and do not recommend this type of system for use in any application.


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## jimbom (Jan 9, 2011)

btuser said:
			
		

> JimboM:
> I'm in the same boat when it comes to solar.  I just scrounged a brand new controller, but I've been looking for a tank for a long time.



I found a propane tank on the cheap.  The safeties, fill point, and other hardware had been removed.  It was in good shape, had two coats of paint on the exterior and no apparent rust.  

As a bonus, when I called the number in the ad, I recognized the voice.  Our kids had played baseball together all the way through high school and we know each other very well.  He had obtained three neutered tanks from a propane company in some sort of barter deal.  I was the first to respond to his ad and he steered me to the best tank and loaned me a trailer from his business to take it home on.  It weighs 900 pounds.  I used the Ozark forklift to get it off the trailer.  All you need is a tie down strap and a tree.  You tie the tank to the tree and drive the trailer from under the tank.  

Now that I know propane tanks become excess, I might start with propane companies to find a tank.  Also, good would be areas where they are currently installing natural gas systems.  When we did that here in 1992, almost everyone switched.  The local propane guy still has ~1000 tanks out on his farm.  Will not let go of a single one.  They show up on Google earth.  Do not know what he is thinking.  Must have something to do with taxes or liability or something not apparent to a layman. 

I on the other hand do not yet have a controller.  Such is the life of comshaw artists. Between honey-do jobs today, I was looking at thermistors and thermocouples on the net.  They are very reasonable.  My thinking is I will put those in when I put things together and then monitor with hand held meters until I can figure out the best operating scheme.  Then I will know better what I need my control system to do.  Meantime, I will be the controller.


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## GaryGary (Jan 9, 2011)

Hi,
One inexpensive way to build a tank for solar systems is to use a plywood box that is framed with 2 by lumber and lined with EPDM rubber roofing membrane.  For non-pressurized drain back system this works well.  The design may seem a little goofy, but this design goes back to the 70's, and has a very good track record.  I've heard from people who are just changing out their original EPDM liner for tanks that were installed back in the 80's.  Tanks up to 800 or so gallons are easy to do in this way.
One nice thing about these tanks is that the when the EPDM liner does go out it can be replaced and you are then good for another couple decades.  They also work out for spaces with limited access, as they can be passed through the access in pieces and assembled in place.

The tanks need to be insulated, and the best place to put the insulation is inside the plywood before the EPDM goes in.  At least the first layer of insulation needs to be the polyiso type of rigid foam board insulation -- most lumber yards carry polyiso, but may not know it by that name -- ordinary Styrofoam won't take the temperatures.  The insulation turns out to be the most expensive part of the tank.

For solar space heating applications, you can just pump the hot water right out of the tank, around your floor loop, and right back into the tank -- no heat exchanger normally needed.  For heating domestic hot water, you do need a heat exchanger to transfer the heat stored in the tank to the potable hot water -- I use a 300 ft coil of 1 inch PEX for this -- it serves as both a pre-heater and a heat exchanger.   Using a smaller coil of copper pipe is also common.

These are the details on my 180 gallon tank:
http://www.builditsolar.com/Experimental/PEXColDHW/TankConstruction.htm

Another scheme is to use multiple 50 gallon plastic drums for heat storage -- there are some temperature limits, but a number of people have successfully done this.  The JC-SolarHomes website has a lot of info on this scheme. 

On the controller front, you can still get the Goldline GL30 for about $90 if you look around, and John Canivan at JC-Solarhomes makes a kit differential controller.  Might also Google "Shem controller" -- this is a China imitation of the Steca type controller.  I was given one to try, and its been working on my space heating system for all of this season with no problems -- not sure what they cost, but I think fairly cheap. 


Gary


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## Trouthead (Jan 12, 2011)

I built and have lived in a double walled house since 1980.  I would never build a house any other way, but I would change some ways  of doing it.  I used 2x4 studes with fiberglass batts vertically in the outer and inner walls, and fiberglass batts horizontally in the inner wall.  For sure in the future I would spray foam the outer stud wall and then most likely  use either blown in fiberglass or cellulose. My ceiling has R-65 worth of cellulose, and my roof trusses have a kicker built into them to set the roof above the outer walls and allow better insulating out over the walls.  I am not sure I would do that any differently other than  up it to R-75.  I used 6 mil plastic as a vapor barrier through the whole house, and if I did it again I would take better care with it.

My house was the first one to  use Tyvek in my area, and I would probably not change that.  Non expanding foam was not around in 1980, so I stuffed fiberglass around the windows  and doors for windproofing, certainly better ways of doing that now.  My windows are triple pane on the north and double on the south  and east.  My crawl space was insulated on the outside of the foundation walls, but a few years back I had the inside walls and header of the crawlspace sprayed with 4 inchs of foam.  My crawl space now stays 59 degrees all winter.  It used to get down to 38.  I also blew the vents shut, and then need to put a dehumidifier  in.  My humidity now stays at 35%.  The end result of the crawlspace work was I now have higher  radon than I would like and will do  a radon mitigation in the crawlspace this spring.

I wish windows were better.  Even the best are like big holes in the wall.  Some of the european windows look good but they are hugely expensive.  My non carpetted floors are still colder than I would  like.  I have thought about spraying foam on the under side of the floor, but would do it in sections to make sure I still keep the crawlspace warm with waste heat from the floor.

I used wood and electrical baseboard heat until this year when I switched to a gas heating stove.  Still don't have the first gas bill, but the electric bill was 462 KwH worth it for the month  of December.


I don't know were the point of diminishing returns is with insulation, but 30 years later  I think I am under that point, and would build the next one with  MORE insulation.

It  also is very quiet.

I live in Wyoming so it is very cold in the winter and hot in the summer.  Right now it is -7 degrees, last summer we had days upon days of the high 90s.  The whole hose until last summer was cooled with a 16000 BTU window unit.


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## pybyr (Jan 12, 2011)

One technique that I've seen (and used in rennovating my kitchen) is to run 1x3 strapping horizontally, nailed to 6" vertical studs on the inside of the wall structure, on 18 inch centers.  

You reduce "thermal bridging" immensely, but with far less material and labor than the double stud wall- and it is simple to weave into rennovations of an existing structure if you are opening up the walls on the inside.


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## GaryGary (Jan 12, 2011)

pybyr said:
			
		

> One technique that I've seen (and used in rennovating my kitchen) is to run 1x3 strapping horizontally, nailed to 6" vertical studs on the inside of the wall structure, on 18 inch centers.
> 
> You reduce "thermal bridging" immensely, but with far less material and labor than the double stud wall- and it is simple to weave into rennovations of an existing structure if you are opening up the walls on the inside.




Some detailed info on these horizontally strapped walls:
http://www.builditsolar.com/Projects/Conservation/MooneyWall/MooneyWall.htm


And, a couple more detailed descriptions of strapped walls in new construction here:
http://www.builditsolar.com/Projects/SolarHomes/constructionps.htm#Stick
The "Gimmie Shelter" links.

This does seem like a good way to go, and it can be used on retrofits and new construction.

Gary


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