Best way to superinsulate?

Started by jimgranite, January 22, 2007, 11:12:14 PM

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My wife and I have more or less decided on the size and shape of house we want ( 2 story, about 26 x 38) and the fact that we want it to be well-insulated and heated with wood (electric heaters for backup).  But I'm having a tough time figuring out the best way to get walls that are R-30, more or less, with the least work.  
We want a lot of pine panelling and very little drywall, so that would seem to rule out rigid foam panels, at least on the interior, since they have to be covered with drywall for fire resistance.
We are considering having the shell built with sips and a trussed roof, then finished by us.  I have a feeling, though, that the cheapest option may work out to be standard framing with a deeper wall cavity-- either double 2x4 or 2x6 built out with furring strips-- and then insulated with fiberglass or cellulose.  
Any thoughts?


Welcome to the forum.  John has mentioned adding a bit of foam to the outside to bring levels up and insulate the stud also.  

More opinions should pop in here soon. :)



The following site mentions a way to add insulation to a 2x4 wall:

The forum discusses the Money Wall. Otherwise I suggest spray foam. It may cost the most but will give you the most bang for the buck.  8-)

Just my 2 cents .....


Welcome aboard!  
We want a lot of pine panelling and very little drywall, so that would seem to rule out rigid foam panels, at least on the interior, since they have to be covered with drywall for fire resistance.
If you use foam on the inside and must have drywall for fire code, that doesn't mean you can't place your pine over the drywall. No need to get fancy on the joints either, just sorta smooth with no big lumps.

Regarding using foam on the exterior, I'm not an expert, but is there a potential problem with sealing the outside like that and ending up with moisture buildup in the wall if you also have a vapor barrier under the inside wall/drywall,panelling?? Or what am I missing in my thinking?

Oh, where are you?


QuoteBut I'm having a tough time figuring out the best way to get walls that are R-30, more or less, with the least work.  

Well of course one of the "easiest" ways is straw bales.  :)


QuoteBut I'm having a tough time figuring out the best way to get walls that are R-30, more or less, with the least work.
2x6 framing with fibreglass = R-19
add 1 inch blue styrofoam @ R-5  = total R-24, not too bad, use 2 " foam = total R-29

But even more important than a high R factor is properly sealing the building as it is built. Stopping hidden air infiltration is worth several R-value points.

Then you'll need to ensure a fresh air intake to guel the wood burner.


   Saw a "superinsulated home" being built years ago in Minnesota.

  The builder used 2" X 8"s for sill and top plate.  Also framed around windows and
doors with 2" X 8"s.  Alternated 2" X 4"s 24" on center.  Then added 1" foam insulation
on the exterior.  Sheathed corners with 1/2" plywood - then covered with 1/2" foam.
Also, used steel strapping in an "X" pattern for strength.  Ceiling insulation was 24".

 They were also using triple glazed windows, storm doors, insulated wood foundations,
and were all electric homes.  

  You can use store bought, off the shelf doors and windows.  Just extended windows
jambs on the inside.  Door jambs on the outside - Otherwise extensions will be butted
against hinges.

  You may also want to investigate using a heat exchanger for ventilation.   Also humidity
sometimes becomes a problem.

  Also, using an aluminum foil radiant barrier for house wrap and under roof sheathing
seems to have some benefits.


i built my home 32 x 92 and used  2 x 12 for the top plate, thus my walls are  11.25 inches thick studded on the inside and outside with 2 x 4 s.  stuffed the whole thing full of fiberglass for r 40 and the ceiling is r 60 with 15 inches of fiberglass
it is cool in summer and warmin winter
is in north carolina and total energy bill with teen is about 1500 dollars a year  gas hot  h20, gas cook, and gas furnace and  2 ton ac a bit of over kill likely but  we like our big space and we like to be comfy


Go underground??  See Mike Oehler's book.

High thermal mass/heavy duty south exposure for three seasons/awnings or pergola in the summer works in moderate climates.  Not my favorite, I think, because I have glare issues if all the light comes from one direction.  But some acquaintances have one, and have loved their house for over 20 years.  For sure, it will hold a reasonable temperature for a couple of cold cloudy days--I house-sat for them for a while one winter.

There is something in Germany called Passivhaus.  No outside heating.

This link might be to their home page, I was actually looking at a FAQ page:

Quote1) Can a house really stay warm without a heating system?

- Passive houses that have been tested and are already occupied have conclusively proven: Even in our middle European climate, houses can be built with such low heating energy requirements that minimal additional heat added to incoming fresh air, is sufficient to keep the house warm and comfortable in winter. Measurements in passive home subdivisions have proven that energy requirements for heating can be accurately predicted, and that even with a great variety of occupants, calculated consumption agrees with average actual consumption.

3) Can you open windows in a passive house?

- Of course, occupants may open windows whenever they want; however, they won't have to. A passive house is continuously supplied with fresh air via the ventilating system. This has advantages: Unlike window ventilation, fine filters in the ventilating system keep out dirt and pollen. Air quality within the house is always excellent, even when occupants are away and/or windows are never opened. Of course, as with all houses, if windows are left open in winter for longer periods, the inside air temperature will decrease noticeably, and energy consumption for heating will increase.

Here's a link to a house built in the U.S. to passivhaus specs.  4-page .pdf file.

I think I'd rather have a non-load-bearing straw bale house than that one, though.   :)

But I don't mind serious temperature swings--I turn off the heat most nights in this dreadfully underinsulated and leaky travel trailer--dogs, cats, and a couple of heavy comforters help.  I'd probably find myself sleeping outside 10 months of the year.

PAHS and AGS both claim that they can give you annual heating and cooling--Passive Annual Heat Storage or Annuallized Geo-Solar.

Out in left field--with IIRC really nice sets of links:


Aha!  Some good ideas here.  We have actually considered strawbale and researched it pretty thouroughly.  However, we live in Indiana and have a fair amount of rainfall and humidity, and ultimately, strawbale is just best for dry climates.  It also looks like a considerable amount of extra labor-- 3 coats of plaster inside and out, plus all the detailing necessary to keep the bales dry.  


I have praised the value of Icynene so much on here you all probably think I work for them! Not the case at all, just a firm believer and here is why.
If I remember correctly, the R value of Icynene is only 3.7 so for a standard 2 X 4 wall you max out with 3.5" of Icynene or approximately 13. This is not that high but, what I like is that I have a totally sealed wall or ceiling. No air can leak in through this stuff and that makes all the difference.
We've discussed the issue of vent vs no vent attic a couple of times also and I am on the side of non venting but, that is due to the type construction I am using or more correctly the layout, floor plan I designed.
Yes, it is expensive but, for new construction, I think it's worth it.
Okie Bob


As mentioned earlier, insulating the framing and airsealing are of as much importance as the total R-value of the assembly.

Icynene (or any foam) has a max R-value between 3.5 and 4. Not much different than hi-density fiberglass. However the Icynene particularly is very good at air sealing.

I'm currently designing a super-insulated house for wood and electric heat that will also have noise concerns (they are in a flight path for jets). Similar to what pauls mentions in his project above, we are building a double stud 8" frame wall (2x8 top and bottom plates with 2 staggered 2x4 @ 24" walls on each side [offset 12"]). We can have one layer of R-21 and one of R-13 fiberglass with no conduction through the studs. At the rim joists and sills we will spray Icyene for a few inches of insulation but mostly for air sealing. We will also get a bid from a local BIBS installer as they can just mesh the whole place and then pump in fiberglass with a latex binder to fill up all the cavities to the desired density. This may not be much more expensive than batts, but will likely be a lot less expensive than doing all Icynene.

For the roof we will do R-38 hi-density fiberglass in 2x12 rafters (for cathedral ceilings) with 1" of Thermax on the bottom for extra R-value and sound isolation.

There are other techniques in the book I coauthored, "Superinsulated Design and Construction" (some of which are only cost effective in very cold climates).


My brother-in-law built a huge 6,000+ sq ft house in Fairbanks with 16 in walls, double 2x6 with gaps between.  All stuffed with fiberglass batts and then sealed with plastic sheeting.  This was in the early 80s and they did not seal as well as he would do it now.  He is still living there, I visited in Dec.  

He does not build that way now, still adding on to his B&B, (he is always building), and he now uses 2X6, flashcoating with foam, (he has his own foam truck), and then two layers of two inch foam sealing all the way around each piece of foam with sprayed foam so that it is VERY tight.  He feels that this is at least as efficeint as the 16 inch walls.

Another builder in this area builds a 2x4 wall with osb exterior sheeting.  He  then attaches two layers of foam to the outside and then uses 1 by or 2 by strapping, (I'm not sure which), to hold the foam against the osb and on which the exterior siding is attached.  So far I like that the best and am going to explore it more.  


If you really loved straw bale, the book "Serious Straw Bale" is for northerners.

(and people who say it can't be used in the south are often referring to the Burritt Mansion--now Museum--in Huntsville Alabama.  Plenty water damage in the ceiling there.  Could be why the walls deteriorated.)


I'm not heading for 16" thick walls here but I'm thinking 2x6 walls with fiberglass bats combined with outside 1" or 2" foam. I just hate the look of older homes than have been "upgraded" with foam on the outside covered by vinyl siding leaving with windows with that indented look.This must mean the windows/doors need to be installed protruding outside farther so the foam doesn't leave the windows sink in. Presumable I would have to fir the windows flush to the inside wall due to the extra wall depth?


   Instead of exterior foam, we are considering a radiant barrier.  Check out the Double Bubble
Foil/Foil Insulation.


I saw a home under construction by a small local custom builder over the weekend. [Albuquerque, New Mexico] Framed with 2x8 plates like John mentioned, with double, inside/outside 2x4's on 16" centers. They spray foam at all the joints and spaces where there's a possibility of air in/exfiltration as well as the hard to get to nooks and crannies. Then when the interior walls are up they blow insulation into the wall cavities. The chief himself was there checking things out and said that method shows much better results when thermographed as compared to f-glass batts.  The ceiling gets R-40 worth of blown in cellulose. They also run all the heat/cool ducting and seal the joints with mastic instead of cuct tape and cover them all with insulation. They install a heat exchanger air exchange system along with 90%+ furnace and a 20 SEER A/C.


MountainDon: That should be an excellent system - good combination of practical and cost-effective strategies.

Bayviewps: Radiant barriers make sense as a secondary attic insulation in cooling climates (reduces the AC load), however, they have been generally oversold and do not live up to advertised projections in heating climates. I would not suggest it as a replacement for exterior foam wall insulation.


I am thinking  wet-spray cellulose is the way to go.  I was quoted a price of 62 cents a square foot for a 2x4 wall, 75 for 2x6.  Its fire-proof and blocks airflow better that fiberglass.  I even took a hunk of old cellulose out of our attic to test-- still fireproof.

Now I have to decide between a double wall with 8 in. of cellulose, or 2x 6 wall, cellulose, then 1 1/2 in. of rigid foam on the outside.  Can new construction windows be installed outside the foam?  Or would they have to be inset as mentioned above?


  Thanks for the input.  They are really pushing the radiant barrier here in Dallas. . . Of course, we get more summer heat than, winter cold.


 Can new construction windows be installed outside the foam?[/quote]

I thinking with Jim on this. If you install windows on the exterior sheathing and than add say 2" of foam, you're left with windows "sunk in" compared to the surrounding siding. Does framing in the rough window openings with 2x8 in 2x6 walls make any sense? The extra 2"  thickness protruding to the outside would allow for 2" of foam and leave the windows looking normal when siding is installed? Just a thought.


This is my question as well.  I looked through all of my framing books to find an answer and none existed in them.  I assume there is a standard method...  Just need to know what it is.


Here is a quick sketch on how I would suggest building an exterior foam insulated superwall.

This is for horizontal lap siding. You may need to adjust for other siding types.

Thinking about the housewrap a bit more, I think I would put it up over the foam and then hold it down with the 1/2" spacers that provide the rain screen for the siding. (The spacing depends on the support needed for the siding you choose.) This housewrap would lap over the top of the head flashing to drain any moisture from the cavity. This cavity should also be open at the bottom of the wall and this vented opening can be wrapped in screen if you have problems with insects.


I like the drawing John.  I hesitate to ask for the free info, but how would you do one with 2x4 walls, no interior batting but 4 inches of foam on the outside?  There is a builder here using that method, I haven't been able to see how he does it.  


No interior batting? You mean no stud insulation. An exposed framing system? Like an old whitewashed cabin?