# For passive solar, which is better construction?



## cc-rider (Jul 29, 2003)

If I had these two options, which is better if my goal is to make a passive solar home? (Or as passive as I can!)

Dry stack cement block, coated inside and out, and then a 2X4 framed and insulated interior wall attached to the interior, and some sort of wood facade on the outside. Holes in the blocks would be filled with stone or sand.

Or a wall constructed of a sandwich of 2x4 framed wall with fiberglass on each side and 3" of blown cellulose in the middle? This wall would have board and batten on the outside, drywall or wood on the inside.

I'm assuming the cement block wall has more thermal mass, but less insulation. By putting a wood facade over the exterior, does that ruin the ability to absorb heat?

The triple-wall has more insulation, but less thermal mass. 

Should either it be built on a slab for thermal mass, or a basement?

I also just read recently that an attached sunroom on a slab wasn't a good idea. I couldn't understand why, but I think it was that the slab absorbed the heat and wouldn't let the heat into the rest of the house??!?!!?

My goal is a small house (under 1400), if that makes a difference. I was thinking a 24X24 with attached sunroom on the south, but now I'm confused.

Any help would be appreciated! I keep changing my mind as to what I want to do! Whatever it is will have to be something that can be done by myself (130# of the weaker sex), and cheaply priced. I'd love SIPs or something like that, but can't afford it.

Chris - in REALLY COLD Ohio.


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## wy_white_wolf (Oct 14, 2004)

Since the block is on the outside of your insulation it does not add thermal mass. The insulation will stop it from radiating heat to the interior.


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## OntarioMan (Feb 11, 2007)

If the block wall is the "structural" component of the building - you could use a "Larsen Truss" to super-insulate the exterior. Low tech and comparatively low cost.

The flanges are 2x4 or 2x6 ripped in half - the webs are 3/8 ply/OSB - the exterior would be covered with 1/2 ply/OSB. Advantage of this truss system is that depth of the truss can be easily modified - depending on how much insulation you'd like to use.


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## cc-rider (Jul 29, 2003)

OntarioMan said:


> If the block wall is the "structural" component of the building - you could use a "Larsen Truss" to super-insulate the exterior. Low tech and comparatively low cost.
> 
> The flanges are 2x4 or 2x6 ripped in half - the webs are 3/8 ply/OSB - the exterior would be covered with 1/2 ply/OSB. Advantage of this truss system is that depth of the truss can be easily modified - depending on how much insulation you'd like to use.


Is the Larsen Truss not structural?? It's only purpose is to add insulation (which I'm assuming now....thanks to White Wolf.....should be on the OUTSIDE of the house?) If the insulation is on the outside, does that keep it from collecting the heat in the winter from the sun?? (I guess it isn't a collector as much as it is a storage thing, huh?) 

Could you just use the Larson Truss as the only thing on the wall....making it a foot thick, or so, and blow it full of cellulose? (It'd have to be structural then, though).

Is there a "passive solar for REAL dummies" book available?

CC


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## Explorer (Dec 2, 2003)

Google 'Larsen Truss' yields 153,000 hits. Lots for you to study.
I just looked at one and it seemed interesting.

http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/97/970308.html


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## OntarioMan (Feb 11, 2007)

The Larsen-Truss is not structural, and yes, it is added to the outside of the building to super-insulate. 

The Larsen-Truss wall is not thermal storage nor is it a solar collector - it is simply insulation to isolate the interior of the building from the exterior. Not only does the Larsen-Truss allow you to add large amounts of insulation, but because of its design, it conducts very little heat through the wood - only the webs are in direct contact with both the interior and the exterior.

The concrete block wall in the structure would be an example of thermal storage because of its mass. A window or solar collector placed in the wall would be examples of solar heat sources.

The purpose of my post was to show that there are ways to super-insulate without using "high-tech" materials such as SIPs - especially when the insulating wall itself is not structural - as in your proposed design which used a concrete block wall.



cc-rider said:


> Is the Larsen Truss not structural?? It's only purpose is to add insulation (which I'm assuming now....thanks to White Wolf.....should be on the OUTSIDE of the house?) If the insulation is on the outside, does that keep it from collecting the heat in the winter from the sun?? (I guess it isn't a collector as much as it is a storage thing, huh?)
> 
> Could you just use the Larson Truss as the only thing on the wall....making it a foot thick, or so, and blow it full of cellulose? (It'd have to be structural then, though).
> 
> ...


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## Countrybumpkin (May 12, 2002)

Now, why couldn't one take that Larson framing system. meaning cutting a 2x6 in half, and nailing them to the inner and outer edges of, say, a 2x12, meaning using the 2x12 as the top and bottom plates. Should then be as strong as a normal framed wall, and one could run electric, etc w/o cutting holes. And, whole inside could be filled w/ the insulation one needs.


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## cc-rider (Jul 29, 2003)

Countrybumpkin said:


> Now, why couldn't one take that Larson framing system. meaning cutting a 2x6 in half, and nailing them to the inner and outer edges of, say, a 2x12, meaning using the 2x12 as the top and bottom plates. Should then be as strong as a normal framed wall, and one could run electric, etc w/o cutting holes. And, whole inside could be filled w/ the insulation one needs.


I've thought about something similar using 2x8 for top and bottom plates, and using 2X4's staggered 24" on center with even ones being on the inside face and odd numbered ones being on the outside face, so you could weave the insulation between them and not have any thermal bridging except for the top and bottom plates. (Does that make sense?? I can't describe it).

Do you think the Larson truss uses those OSB plates more than just the top and bottom? From the picture, it looked like they might be spaced up and down the studs.

So, CBumpkin, do you think that if you used 2X12's instead of the OSB plates, it would be strong enough to be structural? Hmmmmm.....so many options...... by the way....nice to chat with you again! They've moved my office to Lima, hate the commute!  I'd rather be spending time with the chickens!  (You don't have a rooster I could borrow for a couple weeks this spring, do you?!?!?)


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## Countrybumpkin (May 12, 2002)

Hello-CC-hope you get that house started-if you need a hand, we'll be out there to help! I have a banty rooster you can borrow-he's rarin' to go!LOL


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## cc-rider (Jul 29, 2003)

Countrybumpkin said:


> Hello-CC-hope you get that house started-if you need a hand, we'll be out there to help! I have a banty rooster you can borrow-he's rarin' to go!LOL


I HAD (had being the operative word) 2 buff orpington roosters this past summer, along with 4 more hens, but the neighbor's dogs came over and killed every one of them. I had raised them from day-olds, and they were about 4 months old at that point. I was so mad!!!! I went out to that land I bought in the country and built a chicken palace for the 4 older hens that I still had in town and moved them out there. 

The dog warden gave me enough money to replace 4 of the hens, but I never did find any roosters. I might have to buy some day-olds again and start over, or just get a different breed. In the meantime, I thought it would be fun to hatch some eggs.  I've got one hen that is broody, but I also have an incubator that I've never even taken out of the box! 

What's your next project? I've got a barn going up.... framework is done, overhang soffits..... then the storm hit and the steel hasn't gone on yet. Sigh. Poor tractor has sat outside all winter! Goal for this summer is to get a cabin built so I can move out there! I'm tired of driving out there every day to check on the chickies. That's why I've been scouring through all the passive solar stuff and asking a bazillion questions! Sounds like you know a lot about solar....

CC


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## Countrybumpkin (May 12, 2002)

I'm still learning about the solar-but we are trying to go off grid-a little at a time! Again, if you need a hand, just yell!


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## Explorer (Dec 2, 2003)

OntarioMan said:


> The Larsen-Truss is not structural,


Why do you say this? I see no structural difference between this wall and a regular exterior house wall made of 2x4's or 2x3's. Isn't the sheathing that makes both structural?


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## MELOC (Sep 26, 2005)

half of the new construction is sheathed with styrofoam insulation. i would think the stud wall itself is structural.

i would focus more on well placed windows with thermal shutters and internal air circulation if passive solar was a concern.


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## OntarioMan (Feb 11, 2007)

In the diagram I posted, the Larsen-Truss is not part of a structure that carries a load - other than its own weight - which is traditionally how a Larsen-Truss is used. When something does not carry a load, it is commonly referred to as "non structural". The sheathing on the truss no doubt makes the truss system stronger - although still not a structural component.

Could it be made to carry a load? I suppose anything could be made to carry a load if properly designed/built. Aside from a minimal amount of web material and the fact that most Larsen-Truss construction is done on the jobsite - the Larsen-Truss is similar to engineered wood beam/truss construction.

I have seen engineered wood beam/truss used as wall studs.












Explorer said:


> Why do you say this? I see no structural difference between this wall and a regular exterior house wall made of 2x4's or 2x3's. Isn't the sheathing that makes both structural?


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## Explorer (Dec 2, 2003)

MELOC said:


> half of the new construction is sheathed with styrofoam insulation. i would think the stud wall itself is structural.


This is the first I have heard about this technique. Is it code where you are? I don't believe it would be permitted here. Do they use some sort of a brace to get shearing support?

A larsen truss with sheathing would be similar to a torsion panel, but not quite. A torsion panel need sheathing on both sides. I use torsion panels (homemade) for all the shelving in my workshop. Unsupported shelves 8" long with heavy tools and material like bolts. I have not had and bowing in the 4 years they have been in use. I have also used torsion panels, homemade, for a roof with roofing shingles on one side using logs, 4' center to center, as rafters. Again, no problems


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## SolarGary (Sep 8, 2005)

cc-rider said:


> If I had these two options, which is better if my goal is to make a passive solar home? (Or as passive as I can!)
> 
> Dry stack cement block, coated inside and out, and then a 2X4 framed and insulated interior wall attached to the interior, and some sort of wood facade on the outside. Holes in the blocks would be filled with stone or sand.
> 
> ...


Hi Cris,
If you use the dry stack block method, you want to put the insulation on the outside of the blocks. The thermal mass of the blocks is not at all effective if you put the insulation inside of it. The most common way to do this is using the extruded polystyrene rigid foam insulation board (the pink or blue stuff). But, the details are important -- you have to have a way to keep water away from the insulation. 
The idea of having lots of thermal mass inside the insulation is that the thermal mass reduces the daily temperature swing. If you have a house with solar passive gain (e.g. south facing windows), then without thermal mass, the house will overheat fairly early in the day causing you to open doors and windows to vent the heat. If the house has sufficient thermal mass, the sun warms the mass, and the house warms more slowly and does not overheat -- after the sun goes down, the thermal mass gives up heat, and keeps the house warmer through the night. Thermal mass is most effective if the sun can shine directly on it during the sunny part of the day -- this is one reason why concrete slab floors are popular for solar passive houses.

--
The wide plate coupled with the staggered 2X4's is a good way to go for high insulation value. I think you would be better off to fill the whole cavity with cellulose. 
The Larsen truss also provides very good insulation levels, but is fairly labor and material intensive.

There are other ways to do it -- you might just take a look on this page -- it catalogs every form of energy efficient construction I've been able to find:
http://www.builditsolar.com/Projects/SolarHomes/constructionps.htm#Larsen

Ones I like:
The "Gimme Shelter" method -- good insulation value at very little extra cost.
In my mind, this might be the best all around money/Rvalue compromise.
SIPs are good -- high insulation value and good sealing (maybe expensive).
Straw Bale -- especially if you (and friends) can provide the labor.
The "Earth Sheltered Houses" book by Rob Roy is a very good book if you want to go with the dry stack.
Note also the "Van Geet" home -- a really nice dry stack house
The ICF's with the insulation on the inside are good, but probably expensive.

You might also want to have a look at the pages on designing passive solar homes -- you want to get the glazed area, thermal mass, insulation, and summer overheat protection all in the right mix.
http://www.builditsolar.com/Projects/SolarHomes/solarhomes.htm

On the attached sunroom:
There are two ways to do an attached sunroom:
1) Maximum house heating scheme: In this scheme, you want to minimize thermal mass in the sunspace (this is where you heard the slab is bad). This way the sunspace heats up very quickly when the sun gets on (no slab to slowly warm up). As soon as the temperature near the top of the sunspace gets to 80F or so, you transfer this heat to the house. All day long the sunspace produces heat (lots of heat), and you transfer it to the house all day long. As soon as the sun is not on the sunspace, it will cool quickly, because it has little thermal mass. At this point you close off the sunspace and let it get cold -- it will get quite cold, since it has no thermal mass of its own to keep it warm. You can't grow plants in this kind of sunspace in mid-winter -- they will freeze, but you get max house heating. 
2) Plant growing sunspace scheme: In this design, you include thermal mass in the sunspace itself, and you should also include some means to insulate the sunspace windows at night to reduce heat loss. This kind of sunspace will heat up more slowly, and will provide some (but less) heat to the house. But, you will be able to grow plants in it, and it will not usually require heating to keep the temperature above freezing at night.

1) and 2) represent the extremes -- you can build something in the middle with some mass -- this might be used as a plant season extender, but not support plants in the coldest months.
Sunspace info here:
http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm
I like the book by Andrew Shapiro -- it covers both types of sunspaces, and tells you how to design one for your climate. The book is out of print, but available cheap on Amazon.com used books. 


I think your plan for a something like 1400 sf home with attached sunspace is a good one. There is no getting away from the fact that more square footage adds to both the initial cost and to the ongoing heating costs. Having the sunspace gives you some extra "bonus" square footage that also provides heat to the house -- a win-win.

Gary


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## MELOC (Sep 26, 2005)

Explorer said:


> This is the first I have heard about this technique. Is it code where you are? I don't believe it would be permitted here. Do they use some sort of a brace to get shearing support?
> 
> A larsen truss with sheathing would be similar to a torsion panel, but not quite. A torsion panel need sheathing on both sides. I use torsion panels (homemade) for all the shelving in my workshop. Unsupported shelves 8" long with heavy tools and material like bolts. I have not had and bowing in the 4 years they have been in use. I have also used torsion panels, homemade, for a roof with roofing shingles on one side using logs, 4' center to center, as rafters. Again, no problems



maybe i have some misconceptions or maybe i have seen some crappy jobs. i did hear a buddy talking about sheathing just the bottom floor on some jobs.

i don't think it would be code anywhere, so maybe my statement was an exaggeration. 

i'm sure cc will build a structurally sound house. i think the focus should be on getting the passive solar inside the house and to circulate the heat, and not to worry about heating the exterior walls. i would think you would want any thermal bank on the inside of the insulation if you wish to use the thermal bank. 

but hen what do i know after stating such an exaggeration like i did above.


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## MELOC (Sep 26, 2005)

i am having some vague memories of the mention of a thin metal diaonal bracing and the use of thermoply. i can't be sure. but that is thread drift.


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## SolarGary (Sep 8, 2005)

cc-rider said:


> Is there a "passive solar for REAL dummies" book available?
> 
> CC


This is a good one on the basics:
http://www.builditsolar.com/Projects/SolarHomes/PasSolEnergyBk/PSEbook.htm
And its free!! 

Gary


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## cc-rider (Jul 29, 2003)

Thanks for all the links! I spent a TON of time last night looking over some of those, and I'll probably print off the entire book mentioned above (easier to read in the bathtub that way!) 

Thanks so much! I think I'm definately starting to "get it". 

Chris


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