I am planning on building my own home, and was planning on a Cape Cod style home for several reasons - closer to the ground so I could do most work myself without elaborate ladders or scaffolding, and I could leave the upper level unfinished for now if need be (master bedroom on main level). But then I think the roof (even SIPS) with dormer windows would not be as efficient as a separate attic where you could really pile on the insulation and not have any dormer window breaks in the envelope. How much do you think style of a home plays into its ability to be (at a reasonable price) super insulated?

It does play into it, certainly. For a "cape" you have these options: open spray cellulose is the least expensive "good" insulation (not including fiberglass batts which are IMO, junque), but to use it on a cape you'd need something like a "raised heel attic truss" or a "super truss". Doable, but limits your floor space & room layout. You can also use a combination of spray foam and dense packed cellulose if you build a "hot" roof with deep TJI common rafters (TJI's minimize thermal bridging), or build your own roof with 2x10's and "hang" 2x4 rafters below for the depth. You can eliminate the spray foam by venting the sheathing. So it can be done, but adds depth to the roof, complexity and cost.

For DIY, consider a small ranch, oriented correctly to solar south. OVE walls with outsulation. Energy heel scissor truss with 24" over hangs, a walkable roof ~5:12 pitch KISS helps when you are building yourself. a cape is harder- but not impossible to air seal and insulate well. Cheers, ERic

Naturally, a slab-on-ground ranch is the most intrinsically energy efficient design.

Having a flat ceiling with no recessed lighting and a vented attic provides an opportunity for good air sealing and inexpensive insulation like celluose that can be piled up to R-60 (about 17") or so with some care in selecting the sheetrock to support it.

A simple retangular shape offers the opportunity for good air sealing and minimal thermal bridging (in stick homes) associated with each corner in the design that requires extra studs.

I agree, a boxy shape that allows easy use of cellulose. Once you factor in everything, dirt (ie, underground or more ground contact) tends not to be the most cost effect insulation. Most PassiveHaus designs are consistent with these principles.

A rectangular ranch style with ICF walls and insulated slab that has hydronic radiant floor heating. Minimize the windows on all walls except the wall that faces the equator. Size the windows in the equator wall to provide the appropriate amount of passive solar heating given the house heat loss. Size the roof overhang so as to provide full sun Winter and full shade in Summer. We like to use 6/12 attic trusses with energy heels to maximize ceiling R-value and provision for future living space options (or maximize resale value). We prefer a simple flat 9 to 10' ceiling over cathedral/vaulted ceiling (i.e., less ceiling area to lose heat).

Posted By sailawayrb on 08 Oct 2013 10:00 PM
A rectangular ranch style with ICF walls and insulated slab that has hydronic radiant floor heating.
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In my case of getting a new house built, changing from wood stud walls to ICF would have cost an extra $25,000. For about the same amount (http://www.residentialenergylaboratory.com/costs.html) including tax and utility rebates/credits, I could add extra insulation to the walls, ceiling, crawl space walls and floor, and add solar PV and solar domestic hot water and get close to net-zero source energy. I chose the later option, and am comfortable with that choice.

In looking at the PassiveHaus designs, I'm surprised at how little use they make of overhangs. My guess is that this isn't an oversight - these designs are thoroughly analyzed. Perhaps summers aren't hot enough in their respective locations.

direct south sun, unlike west sun, is high enough in summer so much of the light bounces off the glass.

I've always regarded multiple story houses as a less expensive path to green than a ranch on a slab. In cooling oriented climates, a two-story cuts the heat load on the roof in half. In the north, a ranch with a finished basement doubles the floor space without doubling energy use. Solutions like cool roofs and FPSF abound of course. But in either case, spending the same amount on attic insulation gets you twice as much in a multistory.

I would agree Todd that once you exceed about 2000 SF, going to a multi-story house is certainly a less expensive path to get additional SF with minimal additional energy inefficiency. In fact, if you are building on a small suburban lot, a multi-story house may be required just to get 2000 SF.

However, if you truly want to be green and maximize energy efficiency, you first try to build the smallest possible house that you can make work for your living situation. Heat loss is equal to the exposed building assembly area times the building assembly U-factor times the delta temp. So significantly reducing the total building assembly area (i.e., reducing the wall area in addition to the ceiling area) is much easier to accomplish than significantly reducing the building assembly U-factor. Once you have minimized the total building assembly area, you can than apply the resulting cost savings to minimize the building assembly U-factor (i.e., maximize the building assembly R-value) by adding more insulation.

Fifty years ago the average house area was less than 1000 SF. Makes one wonder if housing SF expectations have perhaps gotten out of hand. Modern housing architecture is certainly impressive to behold, but often excessive and ineffective use of windows along with wasted showoff space adversely effects energy efficiency. A simple ranch style home is pretty hard to beat for energy efficiency if you can make it work for your building location and your living situation. I am not convinced that people are a lot happier today with their larger housing and required work situation to support it than they were 50 years ago.

Aesthetics is always an area where one has to balance the visual appeal of the home with the green appeal. Some people focus completely on green and throw aesthetics out the window. Which is fine if the neighbors don't get mad and they plan on living there until they die. But if they have to sell a home that looks visually unappealing, even though efficient, it might be a very difficult sell.

I know many homes that were super energy efficient but they would not win any architectural awards. Some might even find them "ugly" at times. We are emotional beings and aesthetics do matter. If they didn't, then women wouldn't make themselves attractive to men, car manufacturers wouldn't make visually appealing cars, etc. It would be a bland world but it's not.

With that being said, sure, a box is the easiest and least expensive design to make energy efficient.

Sailor - I agree that we totally over build as far as size is concerned. Some of this is just the peacock approach but some comes from jurisdictions that want a minimum size for tax purposes. There is also the resale value. A small house has no value up here even if it is well built.

Todd - right on. The more space between one set of footings and one roof the cheaper it is to build. The closer to square the higher ratio of floor space to outside wall. That's why the Yankees built salt boxes. But that also brings us to Bear's comment. Plug ugly is still plug ugly if painted green.