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"envelope home" design

Last Post 28 Jul 2010 01:34 PM by Alton. 15 Replies.

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bearfan

New Member

Posts:4

22 Jul 2010 06:04 AM
I built one of these designs in the 80's for my parents, and knowing what i know now(which isn't a whole lot more), this design keeps rattling around in my head. It worked exceptionally well, and would have been a lot more efficient if there was a HRV because of poor air quality, and at the minimum should have had some type of humidity control. Electric baseboard heat in W.C. IL> and the heat bills were $45 p/m, and was regulated by a stat in each room. It was an easy build, and added costs for the design I believe were somewhere around 10-15% more, but energy saviings made up for it. No furnace or A/c, and the house never got over 68 degrees in summer with NO window treatments. It woulld get real warm though with a lot of people, and would have to open windows to the air space to cool it down. Anybody here have any experiences with this design, or studied it/built one?????

wes

Advanced Member

Posts:810

22 Jul 2010 08:11 AM
I have been interested in this idea for many years, though I have no personal experience in building a home using it. Enertia Buildings Systems uses this idea in all their homes. You can check out their website for more info.

Wes Shelby<br>Design Systems Group<br>Murray KY<br>[email protected]

bearfan

New Member

Posts:4

22 Jul 2010 08:56 AM
It's an efficient design. I like the Enertia design also, but they are in N.C., and I'm in IL. I imagine that I could find a mill in WI to do it, but their design would cost to use it from Enertia, and the mill too. We had a pit formed up with the concrete foundation that was 8'x10', and filled with river rock for a heat sink, and had tile over the joists in the "sun room". When I scrutinize the idea now, I don't think that it did much. A major problem was in the sun room, the casement windows on the front(South side) would sweat pretty bad and freeze in the winter. The French doors going into the living area had a leak in the glass seal and discolored the glass, and the Anderson rep said it was from the daily drastic temp changes, and wasn't covered for replacement. The air space was insulated but also had a ridge vent, and I think if the whole air space was air tight there wouldn't have been any problems. The exterior walls were 2x6, but just fg batts, and if I would do it again I would make the walls R 30? and use 2x4 insulated interior walls and put the HRV on the interior ceiling, which is in the airspace. The design could be heated with solar thermal fairly well with a DHW as backup, and to pass occ permit. It was a breeze to frame, and the roof wasn't insulated or drywalled, which I would do now. I was a young framer and fairly inexperienced then, with no experience fom my parents, and it went pretty fast. I would like to see somebody here make suggestions for wall designs, both exterior and interior for a 20'x48' with or without a walkout basement. Anyone have any suggestions for a N. IL. area???

Dana1

Senior Member

Posts:6991

22 Jul 2010 11:40 AM
This sort of design might work in relatively temperate mixed heating/cooling climates like NC with average annual temps in the 55-60F range (with similar subsoil temps), but really wouldn't cut it much in the upper midwest or most of New England, or hot humid places like the the gulf states. They're relying on the thermal mass of the cellulose & lignin of the wood (and to a lesser degree, some phase-change of other wood materials) and earth-coupleing to even out the temperatures on the diurnal cycles, and mess around with solar gain & night-time air convection cooling to moderate the average temps within the outer envelope. In colder climates there simply isn't enough solar gain during the winter to cover the load at modest Rs, and the subsoil is too cold to use as a heat buffer without insulation. That's not to say you can't get a lot out of passive solar, thermal mass, or nighttime cooling strategies in N. IL- you can, but you need higher R than the Enertia designs deliver. R30 clear walls are something of a minimum to make passive heating/cooling handle a large fraction of the load though. (The Urbana Passivehouse works, but with R60 clear-wall R values and very careful glazing design. In hot humid climates the humidity of night air ventilation would turn the envelope space into a festering mold pit, and the nighttime air temps aren't low enough to really buy you much sensible cooling. Even as far inland as Memphis TN the summertime daily averages are ~80F, with dew points typically in the high 60s/low 70s, compared to NC's mid-high 70s and more moderate dew points. In Houston or Lake Charles, fuggedaboudit- way too sticky in summer to invite humid night air halfway into the R, raising the RH into the 80%+ range. It could work well in much of California though, where diurnal temp swings are high, but nighttime air is cool & dry, and the winter heat loads are modest. But high-R, managed solar gain & modest thermal mass with nightime ventilation for cooling may still work better.

Bob I

Veteran Member

Posts:1435

22 Jul 2010 12:55 PM
Don Booth owner of Community Bulders in Canterbury, NH built quite a few of these in the area & wrote two books about them. I believe they still work pretty well, although there have been some moisture issues & various relatively minor problems. This was before we knew much about "air sealing", and the walls were of course Fiberglass batts. I always looked at them as a type of superinsulation with the air space forming a huge, insulated buffer. I don't know how to calculate the R value of 18" of warm or tempered air, continually in motion due to convective currents surrounding the living space, but I'm sure it is considerable. There were issues raised about fire & how it could engulf the house - so they developed a type of fire shutter in response to that. His overall goal was to build good, inexpensive homes using passive solar heat, which these were. With our current knowledge of insulation, air sealing, moisture control etc someone may be able to overcome all of the issues. Probably now we'd be able to build a house that would function as well without the envelope for an equivilant cost. Don also built double stud wall designs & was one of the first in the area to concentrate on passive solar & superinsulation, starting in the 70's. There was a company I ran into at a trade show in Boston two years ago selling new precut envelope house kits - maybe they would turn up on a google search.

Bob Irving<br>RH Irving Homebuilders<br>Certified Passive House Consultant

Dana1

Senior Member

Posts:6991

22 Jul 2010 05:28 PM
Posted By Bob I on 22 Jul 2010 12:55 PM Don Booth owner of Community Bulders in Canterbury, NH built quite a few of these in the area & wrote two books about them. I believe they still work pretty well, although there have been some moisture issues & various relatively minor problems. This was before we knew much about "air sealing", and the walls were of course Fiberglass batts. I always looked at them as a type of superinsulation with the air space forming a huge, insulated buffer. I don't know how to calculate the R value of 18" of warm or tempered air, continually in motion due to convective currents surrounding the living space, but I'm sure it is considerable. There were issues raised about fire & how it could engulf the house - so they developed a type of fire shutter in response to that. His overall goal was to build good, inexpensive homes using passive solar heat, which these were. With our current knowledge of insulation, air sealing, moisture control etc someone may be able to overcome all of the issues. Probably now we'd be able to build a house that would function as well without the envelope for an equivilant cost. Don also built double stud wall designs & was one of the first in the area to concentrate on passive solar & superinsulation, starting in the 70's. There was a company I ran into at a trade show in Boston two years ago selling new precut envelope house kits - maybe they would turn up on a google search. An essential (IMHO) difference between Don Booth's version of an envelope house and the Enertia design is that Booth insulates the walls (R19 minimum on the outer envelope, somewhat thinner on the inner shell), whereas Enertia utilizes only heavy timber and a calculated thermal lag. I'd be curious to compare the cost & performance of a Booth NH design to this no-insulation Enertia house built in northern central MA: http://enertia.com/ProjectHub/t...fault.aspx With R19+ on the outer shell and say R13-ish inner shell on Booth's design, we're talking a significant steady-state R, quite independent of the solar gain/nighttime loss aspects. It's functionally similar in many ways to the Enertia, but R30 in a single-shell design is also going to perform dramatically better than "typical" stick built homes in NH. Given the complexity of the design the double-shell approach it's likely to have a higher price/performance compared to superinsulated single-shell passive solar designs such as the PassiveHouse methodology. Double-studwalls & Larsen trusses add complexity too, but you can buy a heluva lot of cellulose for the cost of the gazillion board-feet of timber that go into an Enertia design, and filling the inter-envelope cavity with insulation is almost certainly going to be more effective than designing the outer shell to be lossy enough to drive a convection loop. (We've learned a lot, and the modeling has gotten a lot better since the late 1970s.) And you can't really cheat mother nature on relative humidity & dew point- ventilating inside the thermal boundary with outdoor air when the outdoor dew points are over 60F isn't very healthy, for humans, or for wood based building materials. Lots of exposed heavy timber is sure aethetically pleasant to look at though. More envelope house stuff: http://www.motherearthnews.com/Gree...House.aspx A fundamental premise of the envelope house concept is/was that a heating & coolings systems are necessary, and the exterior shell becomes that "system". By contrast, the superinsulation school starts with the premise that it's possible to slow heat transfer in either direction to the point that heating systems (even large passive convectors) aren't necessary, and that with sufficient cleverness using well-placed optimally sized windows, high R (on all 6 sides of the cube) and supertight construction, temps can be controlled by primarily by adjusting the ventilation rate, winter AND summer. Both have issues with humidity control in hot humid climates, but the costs of dehumidification of a tight superinsulated house are quite modest compared to cooling & heating an overventilated, underinsulated house. I'm personaly drawn more toward the super-insulation camp, and away from massive glazing & heat storage approaches on the grounds that it's conceptually simpler, easier to design for, and probably cheaper to build in most cases.

bearfan

New Member

Posts:4

23 Jul 2010 10:10 AM
Thank you for the informative responses. I always wondered about this design, and I thought that it worked well. But the design did not do the whole job because it didn't deal with the humidity issues. I always thought with the amont of moisture buildup on the windows in the sun space that there would be some mold/mildew issues and possible rot problems in the exteriior walls. I also thought that there was redundancy in the wrong places too. As much as I would like to refine this idea/design, I must accept the obvious fact that it did not thoroughly complete the requirements of the walls in dealing with moisture, and if the moisture issues were properly dealt with, the energy costs and use would have matched or exceded a conventionally built house. I had wondered that if the exterior walls and roof could be air-tight, that with a 2x4 interior insulated wall, the "living area" could be more easily climate controlled. With todays knowledge of super-insulated walls and testing data, the interior insulated wall and the sun space are wasted resources that could be better utilized in the exterior walls and foundation. I sincerely appreciate the info provided by the responses. I guess that I must accept the facts and take my biased thoughts of the design out of the equation. As much as I want it to work will not make it so, similar to trying to teach calculus to a sparrow. Thanks again.

Dana1

Senior Member

Posts:6991

23 Jul 2010 05:32 PM
Posted By bearfan on 23 Jul 2010 10:10 AM Thank you for the informative responses. I always wondered about this design, and I thought that it worked well. But the design did not do the whole job because it didn't deal with the humidity issues. I always thought with the amont of moisture buildup on the windows in the sun space that there would be some mold/mildew issues and possible rot problems in the exteriior walls. I also thought that there was redundancy in the wrong places too. As much as I would like to refine this idea/design, I must accept the obvious fact that it did not thoroughly complete the requirements of the walls in dealing with moisture, and if the moisture issues were properly dealt with, the energy costs and use would have matched or exceded a conventionally built house. I had wondered that if the exterior walls and roof could be air-tight, that with a 2x4 interior insulated wall, the "living area" could be more easily climate controlled. With todays knowledge of super-insulated wall asnd testing data, the interior insulated wall and the sun space are wasted resources that could be better utilized in the exterior walls and foundation. I sincerely appreciate the info provided by the responses. I guess that I must accept the facts and take my biased thoughts of the design out of the equation. As much as I want it to work will not make it so, similar to trying to teach calculus to a sparrow. Thanks again. With some real R value (unlike the Enertia) it could indeed be made to work reasonably in IL with some air & vapor sealing + humidity control. Sun spaces are very nice to have in winter, and limiting the full conditioning to the smaller area of the inner space can make what is otherwise a small house seem much larger, with the additional floor space of the inter-shell room, with the heating/cooling costs of a well-insulated smaller house. Mechanical dehumidification of the sun space need not be unduly complicated or expensive to operate either, as long as ventilation rates are sufficiently low (air-tight is good.) The concept has merit, but may prove to be something of a luxury when all cost/benefits are hammered out relative to other approaches. I remain unconvinced that Enertia's no-insulation, only heavy-wood approach works really well (or is cost effective) in the upper midwest though. The R19 outer envelope R13 inner shell approach used in the NH examples would likely work in IL, or even with higher-Rs if the ratios were similar. With the sunspace more than half-way into the total R, it would likely stay above freezing even at 0F with no sun, and be quite pleasant to hang out in on sunny mid-winter days. There's also value to the aesthetic aspects of a home too, and the look & feel of envelope homes seem pretty nice. It's not exactly "living" hanging out in dark thick-walled foam cubes, eh? But the PassiveHouse approach can also have a nice look & feel inside & out, even in a cube with a peaked roof . (Do check out their series of videos explaining details of their design & construction methods.)

wes

Advanced Member

Posts:810

24 Jul 2010 09:10 AM
As I remember the concept, the end walls were thicker and almost windowless. The north wall was doubled with an air space and the south wall was the 'sunspace'. Dana, critique this idea. ICF walls for the end walls. 6" SIPS outer walls, and 4" inner walls on the north, and 4" inner walls on the south. 6" SIPS for the outer roof panels, and an additonal R19 on the ceiling of the inner house.

Wes Shelby<br>Design Systems Group<br>Murray KY<br>[email protected]

Bob I

Veteran Member

Posts:1435

24 Jul 2010 10:15 AM
The other feature of the envelope houses I've seen is a crawl space with dirt floor. An insulated, well sealed crawl space plus an HRV (and good foundation drainage) would likely take care of the major humidity issues. Since the windows were concentrated on the south, good seasonal cross ventilation was almost impossible.

Bob Irving<br>RH Irving Homebuilders<br>Certified Passive House Consultant

bearfan

New Member

Posts:4

24 Jul 2010 02:03 PM
Yes, the walls were single on the East and West, and we put one window in the East end, and the garage was on the West end. It had a full basement also. The cross ventilation was excellent, even with the double set of windows in the back(North) side. THE biggest drawback was moisture, and that could be dealt with very esily now. I must admit, I had FINALLY come to the conclusion that this design maybe was very feasible, but you folks have put a glimmer of hope back into my head. HA ha ha. I imagine that there is some type of ratio of the sun space to the overall area of the house to make the air currents more active. I had thought that with attention to detail and air sealing, couple with the fact that the sun space would also be conditioned, wall penetrations would not be as critical on the interior walls. The PERSIST wall method would work, and that with maybe steel stud interior wall framing, the ability to put mechanical equipment in the sun space would be positives. But, the sunspace, even though it could function as a 3 season area, is sacrificed just for the thermal efects. The added building costs for this would offset HVAC requirements, but due to various codes and governing bodies, dedicated systems would still have to be used, even though they could be the least expensive choices. Way to go folks, you've gone and given me hope again. LOL

Dana1

Senior Member

Posts:6991

27 Jul 2010 12:24 PM
Posted By wes on 24 Jul 2010 09:10 AM As I remember the concept, the end walls were thicker and almost windowless. The north wall was doubled with an air space and the south wall was the 'sunspace'. Dana, critique this idea. ICF walls for the end walls. 6" SIPS outer walls, and 4" inner walls on the north, and 4" inner walls on the south. 6" SIPS for the outer roof panels, and an additonal R19 on the ceiling of the inner house. Not sufficient detail to say for sure, but a one flaw might be that with 6" SIPs on the N side of the envelope it might not be lossy enough to drive a strong enough thermosiphon. Many 1970s/1980s sunspace house w/storage designs used 500-1000W blowers to move air into/out-of thermal storage in rocks. The envelope design is one way of moving that heat around without use of power, but it DOES still require energy to move that air- that motive energy is just now in the form of heat loss. Without the heat loss, the air doesn't move much. The more R you put into the outer envelope, the weaker the force. Ca. 1980 16" o.c. R19 batt insulated walls have a clear wall R of ~ R17, whereas a 6" EPS SIP will be ~R25- a significant increase.

buck3647

New Member

Posts:85

27 Jul 2010 12:52 PM
Foam Dome design. Currently my company has completed a 30 ft in diameter monolithic concrete dome in Inverness, Florida. Applied to the exterior is 3 inches of 3LB closed cell foam. The intent is to not only waterproof the concrete but also eliminate heat or cool thus maintaining the interior at a relatively fixed temperature with humidity being more of a concern, easily eliminated by use of circulation either mechanically or manually. Ductless split systems are ideal for module designs. By building in modules energy use is dramtically reduced, each module having its own power source. Now evaluating the feasibility of encapsulating a mobile home in closed cell roofing foam in an attempt to put mobile homes off the grid. www.safedomes.com D Pressler
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Alton

Veteran Member

Posts:2164

28 Jul 2010 08:47 AM
D Pressler, What did you use to protect the polyurethane foam from UV? Did you use acrylic paint?

Residential Designer & Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period . 334 826-3979

buck3647

New Member

Posts:85

28 Jul 2010 11:26 AM
Yes several layers of acrylic sealer to build up to a 30 mil thickness. Initially a stucco type of material was to be trowled on but once the contractor saw it was closed cell foam not open cell he had no idea how to seal it so in order to not destroy the foam I had an acrylic sealer applied. I am now in the process of having a stucco type material applied. My goal is to be able to spray residential roofs on the exterior.

Alton

Veteran Member

Posts:2164

28 Jul 2010 01:34 PM
For future jobs you might want to considered spraying on glass fiber reinforced concrete to protect the polyurethane permanently. See http://strataus.com/us/ for an example.

Residential Designer & Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period . 334 826-3979