Hey what do you think about an A-Frame cabin, like a 2 bedroom. I was reading somewhere that A-Frames are the least expensive houses to build, and easy.

I wonder if the windows on the front and back might work for a passive solar design.

What do you guys think of that in a New England climate?

I see also the department of agriculture released plans for an A frame house and other vacation homes in 1978 (click)

I'm going to buy that.

A-frames :

Are they funky-cool or what?

Can they be made an an affordable passive solar dwelling?

Tell me what you think :)

Thanks,
Craig

p.s. Here is the example pictured above in detail (click)

Passive solar rules of thumb call for glazed area of ~7% of the square footage of the structure, major insulation upgrading, and significant thermal mass to keep from overheating. Which means you'd be adding both insulation and a lot of concrete/stone to a standard cabin design. But there's no hard rule on this ratio. The PassivHaus super-insulation approach can easily be applied to an A-frame.  Super-insulated you need to carefully design in the amount of glazed areas and overhangs to control it.

This would be relatively easy to pull off in southern New England, but is still possible without breaking the bank in the 8000HDD+ climes of northern ME/NH/VT.  A-frames are structurally simple, making them easy to insulate and build to a very-tight specification.  If you prefer the plank & raftered look on the interior, look into using fiber-faced iso board on the exterior of the roof deck under the roofing, which has the advantage of making an excellent thermal break at the rafters with superb air tightness. (Hunter, Atlas and others make ventilated nailer deck variations for the outer layers, if that's a concern.)  You'd likely need at least 6" (~R40) of iso to get it to PassivHaus levels in this sort of climate.  Insulating the floor  and end-walls to a high-R would also be necessary.  Alternatively using 10-12"-thick EPS SIPs for the roof may be easier/cheaper than raftered w/iso on the exterior.

Bottom line- any form factor can be made into a passive solar structure if you pay close attention to insulation, air-tightness, and blocking thermal bridging by structural/other elements. But a cabin built to a 1978 spec probably isn't gonna cut it without extensive modification for higher-R.

Thank you for the thought provoking reply Dana :) You certainly know what you are talking about.

I'm still trying to understand all of this and have been reading a lot.

Do you design passive solar houses?

From what I was reading it looked like a New England Saltbox plan would be better suited to passive solar with big windows facing south and an angled roof that reaches the ground on the north side (kind of like an A-frame), like this :



I saw it in this video about "Zero Energy Design" :

http://www.youtube.com/watch?v=lzGaLw__kdk

http://www.zeroenergydesign.com/Architecture.htm

Have you heard of that?

Have a nice day :)
Craig

I don't design passive solar houses (but I could).   The fundamentals of heat loss & solar gain are pretty straightforward- it's the careful  implementation that's more difficult. ALL houses are passive solar houses- some are just better thought out than others.

But key to having a large solar-fraction is ultra-low loss, which means high insulation values. You can't really make up for higher losses with more glazed area, since the heat loss on non-sunny days (or nights) exceed your solar uptake & storage capacity. The PassivHaus approach is passive solar by virtue of balancing the glazing for it's direction to the sun, ultra-low heat loss (==high-R values), and providing sufficient thermal mass to keep the diurnal temperature swings low.  Salt-box architecture approach allow you higher amounts of S-facing glazing, but with with a low enough heat loss on the rest of it, that isn't necessary OR desirable. 

The "Saskatchewan Conservation House" passive & active-solar superinsulated house built in Regina back the 1970s  was a roughly salt-box form factor, and it tended to overheat (the active solar never ran since it was never needed, and was eventually dismantled). 

The PassivHaus Institute is a direct descendant of that design effort, and their passive solar & heat gain/loss modeling methods are about as good as it gets.  The form factors of their designs aren't  necessarily radical or obvious to the untrained eye, and you need not be restricted to something with a large amount of south-facing glass.



(The evacuated tube active solar collectors below the overhang on the Saskatchewan Conservation House were eventually pulled since they weren't necessary!)

You can definitely get there with an A-frame, with the gable end facing south.  You'll likely need to limit the N-end glazing a bit to lower the heat loss, but super-insulating the simple & flat roof area is dead-easy compared to more complex designs.  Designing it with sufficient S-end overhangs on the roof (and likely just above the windows given the high peak of an A-frame's roof structure) to limit overheating in the shoulder seasons & summer will be necessary.  You may need operable exterior shades as well.

Some PassivHaus designs retain a bit of salt-boxy-character though eg:






Others, not so much:

Thanks again Dana :) You have given me a lot of keywords to Google with.

I've re-read this entire page and am in the process of reading David Wright's "Passive Solar Primer" book. I'll have to study this PassivHaus information too :)

It seems like you find the A-frame agreeable, that's cool because my daughter Chloe and I both think it's a funky cool structure :)

It will be our first house :)

If you are bored sometime and would like to scribble some rough plans for a small 2-bedroom passive solar A-Frame, that could be built for like $25,000 in central Maine's climate, that would be great :)

I wonder too if it would just be smart to copy the "Saskatchewan Conservation House", do they distribute the blueprints and plans for that one? I bet Maine and Saskatchewan have similar climate.

In the meantime I will refer to this thread and study PassisHaus :)

have fun!
Craig

p.s. Here is Chloe :

I found a free A-Frame cabin plan on the internet if anyone is interested :

http://www.pdfgarageplans.com/blog/wp-content/uploads/2009/02/36-a-frame-house-plans.pdf

[quote]
Quote: Sent Fri, 22 January 2010 06:06 PM by spystyle

Hi Dana :)

I don't know if you saw my reply to your post in my "A frame" thread.

I really appreciate your input and have even contacted the creators of Saskatchewan conservative house, one of them wrote back to me and says he sells the original drawings for building that house.

I thought more about the small A-frame, could it be made passive solar by simply making the walls 100 R-value, glazed on the South side, and a big thermal mass for the floor?

If that is true I wonder what is the least expensive way to achieve non-toxic R-value? I know things like "Earthships" are well insulated but tires are toxic. I wonder what is very affordable with super R-value. I don't mind if the walls are 5 feet thick :)

I'd like to figure out a way to build small affordable passive solar houses :) Small but livable, like apartments.

Do you have a website for your designs?

Thanks!
Craig
[/quote]


[quote]
Quote: Sent Fri, 22 January 2010 06:39 PM by Dana1

I don't design houses (I'm an engineer, not an architect).

You don't typically need anything like R100 walls to go PassivHaus in New England. R30 would be a minimum, but R50-R70 makes it easier. The key is to minimize glazed area, and provide thermal breaks on all structural timbers, since that will dominate the heat loss by quite a bit.

Double-wall or Larsen truss construction with blown cellulose makes arbitrarily high R-values possible, but it takes a 12-15" thick wall to get to R50-60. 4x8 sheets of 3" iso board designed for roofing run ~$55/ea, and are R20 per layer- you can get to R60 in only 3 layers. Don't go thinner than 6" on the roof.

Don't forget you'll need at least R30-40 under/on the foundation too. EPS is the cheapest way to go there. Put the EPS on the exterior, keeping the thermal mass of the concrete walls & slab on the interior.

It's worth buying the PassivHaus software to tweak your design- you'll save a lot more in materials up front than the cost of the software, and you'll be able to figure the right price/performance for your budget.

There are people designing EXTREMELY tiny houses out there (under 100 square feet), which would be trivial to turn into totally passively heated structures.

dana
[/quote]

Craig;

I always thought A frames were cool back in the 70's, I have designed a few myself. But from a floor usage standpoint
they are not very practical, I put then into the same category as octagon and dome homes. All of those and log cabins are really cool and if you plan to stay in the home until you die would be OK, but if you plan to resell in the future, you have probably limited the potential buyers to about 1% .
Now you got me thinking about bell bottoms, leisure suits and when I still had hair :)

Some A-frames are clearly worse than others.  Tiny 1-storys can be made more practical using the upper portion as a storage loft/mini-attic, cutting down on the awkwardness of trying to build in closets.  Utilizing the extra depth of cabinets build onto the roof-wall using drawer slides can also make it work better.  They're not nearly as difficult to work with than geodesic or ferro-concrete/foam domes, etc. (You have at least SOME flat wall space, and the sloped-side is at least straight.)  They're no worst than head-bonker 2nd storys of many cape cod style houses, but yeah, you have to lay it out to accommodate the slope, which is a limiting factor. 

I have friends in central MA who live comfortably as a 4 person familly in a 2-story A-frame with a full walk-out basement- it has it's charms.  The front half has an open loft-space used as an office/study above the living room, and the sleeping quarters are split between the first & second floors in the back, leaving the built-out basement as recreation & shop space.  It works, and works well.  Shrinking it by a whole story it might feel very cramped due to the head-bonk & upper cabinet factors.

But to their credit, A-frames shed snow better than conventional designs, and ice dams are unheard of, both of which are issues in parts of ME.

We have a 28 ft by 32 ft by 28 high Aframe summer cabin with a half loft. Beautiful in the summer but impossible to heat in the winter. All the heat goes right up to the peak and stays there. I've thought of using a plastic sheet to divide off the peak area in the winter - otherwise very difficult to stay warm on the main floor.

Good Luck

I think they are no fun to shingle.