I think this is going to be an interesting thread

You are not crazy but as far as I know, if you plan to place foam insulation, it will not help to place more than 4" thick, in other words, if you use 2x6 you are covered.
The bigger heat loos/gain is thru the attic. You need to make sure to place R-50 or higher in the ceiling and use energy efficient trusses and maybe is better to put the money in the best windows you can purchase. I know of a person that used 2 fixed windows together in some areas (they had to place silica for condensation between them and make sure that the windows were spotless in between)

If you are not goinf to use sprayed foam, then you could consider using 2x8 studs (or 2x6 for an R-23)
Good luck.

Before you go to all the expense of 2x10 exterior walls,
you might want to take a look at SIPs panel construction.

Or even 2x6 plates with staggered 2x4 studs on 1 foot centers.
This has the effect of eliminating the thermal bridging effect of the studs.

Also look into the cost of Isynene foam insulation.

I just can't fathom the cost of 2x10 exterior walls.

Pooh Bear

At least thirty years ago, someone up in Fairbanks, AK did something similar to what you are thinking of doing. There was a write up on it in one of the papers up there. Fairbanks sees 40 below routinely, and it can get even colder.

I recall the story quoting the owner as saying he felt that if some insulation was good, a whole lot more should be even better. I don't remember how thick his walls were, but I do recall someone saying they were thick enough that looking out one of the few narrow windows reminded him of gun slits in a fortress.

The owner was forced to put a furnance in to comply with the local codes, but he said he did not need to run it. The house stayed warm enough from the "living heat" of the stove, the occupants, etc.

I thought the story was interesting at the time, but I don't know if I could stand not having large windows in a house. For me, that would be the deal breaker.

I think the additional depth would look good. It's only 4".

But it seems to me that you would be better off going with more mainstream building practices. Why not just get a SIP kit or use ICFs and use passive solar techniques, geothermal, etc.?

I don't think your crazy, but there are some other ways to get a very tight and insulated home:

My suggestions are:

1. ICF home with R-50 in the attic and meticulous air sealing in the attic.
2. A super insulated home using 9.25 inch I joists as the exterior wall framing, blown cellulose and the same attic and air sealing in #1. This will probably have many issues with inspectors though. This method is detailed in several construction journals, and most use electric baseboard heaters due to the low btus needed to heat the space.
3. 2x6 walls, blown cellulose and the attic from #1. But also add 1 inch of XPS onto the sheathing before installing siding.

Most window manufacturers can accomodate the 2x6 plus 1 inch of XPS, but the other methods will require your trim carpenter to extend jambs.

I second bdpeck, with the added comment that 2x10's ain't cheap, and you actually don't want them due to the lack thermal barriers. Staggered 2x4 studs can accomplish the same thing re depth and provide thermal breaks, but double-studding is also expensive. Do a careful price comparison [apples to apples], and I suspect you'll find ICF giving equal or better R-value with a LOT less effort.

Window depth in ultra-thick walls can be made somewhat more appealing by setting the windows in the exterior as is standard for more shallow walls, but the bucks cover the full width and the interior depth is finished as though it were wall [that sounds funny because it IS wall, just wall that is right-angles to the window assembly, which is going to require extreme care in waterproofing techniques]. Interior sill depth is usually just sufficient for plants on the lower sill (design with waterproof trays that fit neatly) and a set of roll-down window quilts attached to the top. When using window-quilts, a box valance is recommended for both improved insulative value and to permit a more usual window treatment of drapes, etc.

I've never made particular notice of the wall depth at the entry door, but windows can be well done, or way out.. and too far out isn't comfortable to live with.

I strongly suggest you read beforethearchitect.com/ especially his section on lighting and window placement. You can literally make a house a misery by doing the wrong thing.

As far as window depth is concerned, take a look at, oh, Versailles or even some colonial structures here, like Mt. Vernon or Monticello. Those walls are deep, and to my mind, the window depths are beautiful.

"Most window manufacturers can accomodate the 2x6 plus 1 inch of XPS, but the other methods will require your trim carpenter to extend jambs."

Is there a product that's equivalent to XPS that isn't as flammable?

Terry

I'm pretty sure that XPS isn't any more flammable than plywood. The fumes from it being burned are worse than from wood, that's true.

I think there are some rigid board fiberglass or other material, but I'm not sure if it's less flammable or not.

Search for rigid insulation and see what you can find. And check the MSDS (I think that's the right acronym?) Data Sheets for the flammability rating.

Your biggest problem will be finding a HVAC sub that will know how to properly size and design the system.

Not crazy, but as others have essentially said, you are trying to re-invent the wheel. There are newer techniques and processes that will get you extremely good efficiency without going to the expense and trouble of what you are proposing.

I didn't read the other replies so maybe someone mentioned the same thing--our old house was a super insulted house with 12" walls. However, this was done with two stud walls built with 2x4s instead of with 2 x 10s and the walls were spaced so that there would be two layers of 6" fiberglass insulation bats. The 2x4s on each wall were staggered so that there was always at least 6" of insulation between a stud and an inside wall. Scroll down to STC-55 in the link for a picture of the framing---ours was set up for 6" fiberglass batts of insulation instead of the 3-3/4" shown in that picture. I loved the extra deep window sills, as did our cat. The house was warm and quite. In our new house we did 2x6 studs with extra thick styrofoam on the outside, and I think that works almost as well as 12" thick walls, and it cost less.

Here is a link that might be useful: 12

ralph

you didn't mention what you will be doing with windows & doors. The biggest losses are there, around the weatherstipping and through the glass, not through walls. Adding exrta attic insulation makes a lot of sense since heat rises. You don't have to go crazy with wall thicknees to have a super insulated house. You should make sure all knooks and crannies are caulked from the inside of the house - that will help too.

Here is one pitfall - with a tight house you have to bring in fresh air periodically (check the HVAC forum for info on this). Look into HRV's or ERV's.

You also have to be very careful with damp basements if you have one. A tight damp house is a great environment for mould. Get a humidistat (20 bucks) and measure the humidity in the basement (it might look dry, but still have a lot of trapped moisture). If the humidity is above 50 to 55%, get a dehumidifer.

Good luck.

I don't think you're crazy; but there are so many modern systems that can do this significantly easier, and perhaps even cheaper, that I question why you're going down this path.

If you want a 'super insulated' home
what about SIPs??
osb sandwiches foam, minimal
loss of ins value due to little use of framing members,
and imo the best building system to date.

Granted you are not in my climate, but I met a
friend here years ago who lived in Michigan, He was
a SIPs builder and it performed as well there as here,
so I feel comfortable in recommending it to you as well.

SIPs panels are being used in our hurricane recovery areas,
as prefered systems due to high wind requirements, strength
and the energy efficiency savings.
With SIPs as well as ICF as Rbadger noted, adhering to load calculations is a must for not only an efficient home, but a healthy one. Less tonnage of hvac is one benefit with these better building systems.

Don't expect the hvac industry to provide you a 'free' load calc.
The more tons of hvac they can sell you the more their profit. And sadly, many companies either don't use the proper input values ..
ie SIP or ICF true values & air leakage reduction values,
and the load calc is not 'true'.
* reread this when you see the same symbol below...

Rbadger does unbiased load calcs, and can also do a duct design & layout..( I think he does the latter two..).
Unbiased is the key word in that statement. You should at
some point 'talk' with him.

There may be a hvac co in your area that does the true calcs. But be prepared to shop around. With SIPs in my area we are achieving 750 sq ft per ton..although I hate rule of thumb sizing,,it is a term you will hear alot as
you shop hvac co's. Rule of thumb is at best a guess.

* see above

For fast quotes- many hvac co's use them..around here
the ones who haven't chosen educate themselves use
400 to 500 sq ft per ton. Steer away from these hvac co's.
Be prepared to shop.

Also SIPs panels come in different insulation values, this differece is due to thickness of foam 4", 6" and possibly
8". panels come as blanks, meaning that window and door openings are not cut, or precut, but there is little room
for error in precuts.

If this is a system you may be interested in ...I'll email
the retired SIPs builder and ask him to chime in.

Windows..they can be trimmed out, additional cost, but for me it is not the way it looks that is as important at this stage. Buying a better window is important.
The windows and doors are the weak spot of any wall.

Look for a NFRC sticker on the window brands that you are
shopping. NFRC is an independent (see how I keep comming back to an independent source of info..beware of sites
selling you products) company that tests & rates all
windows worth buying. You'll find that the common numbers
to shop for are on this sticker..Solar Heat Gain Coefficients (SHGC) and U-factors.
.4 SHGC or LESS is the best buy, invest in Low e glass
as it will keep heat in the house in the cold months.
I see a lot of .35 SHGC windows around here, of course
the Low e install is in my climate, your Low e will
be located on a different glass surface as per your climate.

The important thing is to buy a window that will not transfer heat or cold from the outside to the inside.
Metal windows condensate and cause a LOT of moisture/mold
issues that take years to show the total depth of damage.
The only way that metal windows don't have some degree of
condensation is if they have a wood frame to the interior.
Metal transfers heat/cold and is a good conductor..wood is a poor conductor.

Oberon is the window expert here that is happy to share his
expertiese & years of experience.

Best of luck and enjoy your learning experience.
Keep in mind the house as a system..not individual
componets. Everything has to work together, not against
each other to achieve a healthy house.