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. :)
John
The following site mentions a way to add insulation to a 2x4 wall:
http://forums.taunton.com/tp-breaktime/messages/?msg=84574.1
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!
Quote
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.
http://images.google.com/images?q=straw+bale+house :)
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.
http://www.sunwindows.com/Services/Installation_windows_02.html#Step%204
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.
http://www.radiantbarrier.com/
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:
http://www.passiv.de/
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.
http://www.naima.org/pages/resources/library/pdf/RP064.PDF
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.
http://www.greenershelter.com/index.php?pg=2
Out in left field--with IIRC really nice sets of links:
http://www.midcoast.com/~bo/PAHSgreenhouse.html
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.)
http://www.amazon.com/exec/obidos/ASIN/1890132640
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.
http://www.radiantbarrier.com/
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?
John:
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.
(https://i56.photobucket.com/albums/g166/jraabe/exteriorfoamwall.jpg)
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?
No interior insulation, but 4 inches of foam insulation on the outside. The inside studs are open leaving room for plumbing and wiring and air movement if needed. I haven't had a chance to go look at the house under construction but I guess he has built several that way. Some friends currently own one and LOVE it.
I guess I need to explain that the studs are not exposed, he does have interior drywall and a finished wall.
Doesn't make any sense to me to spend money on expensive exterior foam and then not put the inexpensive insulation in the cavities you will be closing up anyway.
I'll talk to the builder, but remember, this is a real cold climate. Not as bad as Fairbanks, but it was -39 a couple weeks ago.
The complete foam wrap eliminates the problem with wood transferring heat and also the problems that are associated with settling or moving batts over time, Just a little bit of incomplete insulation along the edge of a stud will cause a lot of thermal transfer.
I notice in my little cabin that I am building that there was a huge amount of heat loss at the top and bottom plate. I neglected to put in a foam insulating pad at that point. Of course I caulked that up. But foam on the outside would have extended above and below the plates.
You are right about the expense however, don't know if it's worth it.
Quotethis is a real cold climate.
All the more reason for more insulation. :-/ Leaving the cavities empty is a puzzler to me. :-?
One of the goals of these foam-on-the-outside schemes is to eliminate thermal bridging by the wood studs. But I wonder if there ends up being almost as much or more thermal bridging due to all the nails through the foam. Steel conducts heat 400 times better than wood, so a single large nail (large enough to go through 4" of foam) conducts about as much heat as a twelve inch length of 2x lumber. If the nail spacing through the strapping and foam is closer than that, I don't think you're gaining much.
One possible reason for not filling the cavities behind the foam is to avoid condensation inside the wall. In cold humid climates, the added batt insulation might cool the inner foam surface enough to cause condensation there. And a thick layer of foam would act as a vapor barrier keeping the wall from drying out. I think this would definitely be a concern in Juneau. I'm not familiar with the climate in the Fairbanks area though.
Excellent point Bartholemew. If there were batts in the cavity, there would almost surely be a soaking wet layer right on the sheathing.
That is a little bit of what I fear with the 1 inch foam all around the exterior. I worry about it with the 4 inches of foam as well. Where exactly does the condensed moisture end up, and how does it dissipate after condensing?
With the 6 inch fiberglass batt, I know that it does condense somewhere in there, but at least it has a chance to dry out a little after
Quote#1... eliminate thermal bridging by the wood studs.
#2.....is to avoid condensation inside the wall.
Bartholomew, both points are very well made. Wish I had thought of the first, and I've forgotten about the second. I've been in a warm/hot low humidity climatetoo long. (OK winters are cool to cold, but it's still pretty dry.
Re #2: How about applying the foam board to the interior side of the studs and covering over with drywall? :-/ Install fiberglass in the framing cavities as usual. That would place the super vapor barrier characteristics of foam on the warm side. (Could be a problem with the pipes in the framed wall?) If that works, then...
Re #1: Run 1x furring strips horizontally on the inside every 16 inches and securing the foam to them. Drywall on top. Of course that would really puzzle someone coming along later trying to find studs to secure something to. ;D
I think I still prefer more or less conventional framing and sealing the bejeebers out of it before installing fiberglass in the cavities. I especially like the staggered interior/exterior 2x framing method if one is concerned about thermal breaking the studs.
If going with conventional framing, it might be possible to work out something with foam covering the top and bottom plate areas (thermal break) on the exterior and using the added thickness as some sort of an architectural detail. :-? Depends on the exterior materials. Easy to do with stucco. Around here the builders use a lot of foam like that (covered with housewrap or felt and chicken wire) for raised borders around windows, doors or wherever to help break up the monotony of flat stucco areas.
Yes, an exterior (or interior) layer of foam is a wonderful conductive break in the framing. Such foam sheathing is doing its best work where it covers the solid wood (you can see this in the calcs on my diagram above where 1" of foam doubles the R-value of the framing.)
The cost effectiveness of the foam does go down pretty fast as you add more inches. And since it is so much less expensive, the cost effectiveness of fluffiness such as BIBS or fiberglass stays quite high - at least until the cavities are fully filled and you have to build new ones ;).
You always want to max out the most cost effective measures first. This makes both economic and resource utilization sense.
PS - 1. Any wall with 1" + of foam (plus batt) will be too well insulated to ever reach the condensation (dew) point on the moist interior. 2. The surface area that nails contribute to conduction is negligible. They are anchored into wood with an R-value of 1/inch. 3. Where you really see conduction take off is when people build with steel framing. There you get some real bridging and the nails or screws are part of that inside to outside heatflow freeway. Steel buidings (if heated) have lots of problems with condensation and corrossion unless they are fully foam sheathed.
True John, the remaining wood does provide a bit of a thermal break. However, the nail is drawing heat from not just the small cross-sectional area of it's tip but also from the sides (think of a cone on its side with its base on the inner wall surface and the nail sticking into the point). An analogy is a bridge across a river. The people living right next to the bridge might use it the most but it also serves the surrounding area. Likewise, the nail acts as a heat conductance bridge across the foam for a fairly large area of inner wall surface. How large is the question. In this thermal image, you can see the largish blobs where heat is conducting away through the drywall nails.
(http://www.maverickinspection.com/big%20wall.bmp)
Simplifying now, suppose each nail provides a thermal bridge for a rectangular area of inner wall surface which is the width of the stud and 3" up and down from the nail. Well, if the siding is horizontal lap siding with 6" exposure then there is a nail every 6" and virtually all the heat transfering through the studs can bypass the foam.
The added foam does provide more insulation between the studs. However, it seems to be sold/justified mainly on the basis that it reduces thermal bridging. I believe that the thermal bridging effect is much less than most people assume. As a result, it
might make more sense to spend the money elsewhere... upgrade from 2x4 to 2x6, BIBS or cellulose in place of batts, icynene, etc. What I'd really like to see is actual whole wall test results from Oak Ridge National Labs or similar impartial organization.
--------------------------
On the condensation issue, I'm talking about the surface of the foam, not the inside wall surface. In martyv's example, suppose that R-19 of fiberglass is added behind the R-20 foam. The inner surface of the foam will then be roughly halfway between the outside and the inside temps. Given high enough indoor humidity and cold temps outside, there can easily be condensation inside the wall.
http://www.buildingscience.ca/bsd-106-understanding-vapor-barriers
Quote...in cold and very cold regions the thickness of the foam sheathing should be determined by hygro-thermal analysis so that the interior surface of the foam sheathing remains above the dew point temperature of the interior air ...
The hygro-thermal analysis is done using software such as WUFI from ORNL (free to download and fairly easy to use). Probably worth doing if you are building in an extreme climate or doing something beyond the tried-and-true for your area....
http://www.ornl.gov/sci/btc/apps/moisture/index.html
Coastal Contractor, November 2006, did an article on foam sheathing which said that 1" xps would likely work for every U.S. area south of Long Island. I guess they were just thinking of the Eastern seaboard. The article is posted at the Journal of Light Construction website ( jlconline.com ) but I'm not sure if you need a JLC subscription to access it. I subscribe to the online version and have access to their 20 year archive of JLC articles--a good deal.
As far as thermally-leaky fasteners, I think a weighted average of material conductivity based on contribution to wall area might be appropriate--at least that's what they use for computing the R loss from framing members. When I calculated for 10d nails (8x16 pattern like for fastening strapping), I'm getting about 4.4 compared with R5 for non-perforated 1" xps. Using stainless-steel 10d nails, I'm getting about 4.6. Don't use aluminum nails: it drops to R3. I'm not an engineer and pretty new to this so I could be doing it wrong; however, it seem like the building science experts are probably aware of fastener conductivity and still use external foam in many of their model wall designs. ;)
If it's 70 degrees inside and 20 below zero outside, and the moisture is moving from the warmth to the cold, it would seem that it needs to condense somewhere. It certainly isn't 70 degees only 1/4 inch into the foam from the -20 degree exterior air.
Since the foam is a vapor barrier it would seem to trap the moisture just inside the foam, would it ever be cool enough to codense right there? I would think so.
In fact the place it might be most likely to condense would be along the studs because they would be cooler.
And after it condenses it would run down the inside of the wall I suppose.
I am not a thermal engineer, but I am certainly interested in this question for practical reasons.
Hopefully the interior vapor barrier keeps the RH in the insulated area low enough that the moisture never reaches it's dew point or that the dew point occurs somewhere in the foam where there is no humidity or problem. Not a scientist either - learned some of this in pilot training though.
If the moisture stays in the heated area and doesn't reach it's dew point there will be no condensation.
QuoteAs far as thermally-leaky fasteners, I think a weighted average of material conductivity based on contribution to wall area might be appropriate
I'm not entirely sure. Doesn't that approach basically make the simplifying assumption that heat will only flow in a straight line from inside to out (or vice versa) instead of following the path of least resistance? That assumption might not affect the results too much when all the materials are of roughly similar conductivity. But when they differ by three orders of magnitude, the result could be overestimating the actual r-value by quite a bit.
Nonetheless, if there are 17 10d nails per stud (i.e. for 6" exposure siding) and the studs are 16" OC, I calculate the combined r-value as 3.62. If instead I assume the foam is fitted in between 2x lumber, I get 3.64 for the combination. That suggests that upsizing the studs and fitting the foam between them would be just as effective. You'd also get additional benefit from having an extra 2" of wood providing a thermal break for the nails.
Another possible option might be to use plastic nails. But I don't know if they are approved for siding use.
QuoteHopefully the interior vapor barrier...
You do have to make sure you don't effectively end up with vapor barriers on both sides, since some foam has fairly low permeability and there is 4 inches of it. But that's what the WUFI software is for.
I guess that is where some of the new methods run into problems -- things happen in places they never used to.
OK, first on condensation.
You have to have airflow to have problems with condensation. If the dew point is reached inside your wall insulation, foam sheathing or wood framing it will condense moisture only if air leaks are bringing fresh moisture there. While there can be "vapor pressure" through a material such as framing, such condensation is trivial. Over 95% of the moisture transport in real houses is through the air leaks in the structure itself. Airflows from a warm moist interior reaching a cold surface (most often the inside of the wall sheathing or siding) will drop their moisture there. This only becomes a problem when the transport of the airflow is sufficient to overwhelm the ability of the materials themselves to absorb that moisture. Wood framing, sheathing and siding can hold lots of water before it becomes a problem.
Framing lumber, for instance, might rise in moisture content seasonally from 15% to 45% absorbing scores of gallons of water transported by small air leaks. Then this will dry out in the summer. There will be no surface moisture at any time during this entire yearly cycle. Steel framing and vinyl siding holds much less water and manifest moisture (real water) problems much faster. These buildings are much more likely to have mold issues.
On conduction through fasteners. It is based on an area weighted calculation of total assembly R-value. Steve044 is doing the right calculation. The R-value calculation is a representation of the "line of least resistance". Lower R-values do pump heat faster than higher R-values. Nothing more magic than that is going on. It is why moisture problems show up first on the surface of the windows where the R-value is 1 to 3 rather than the 14 to 21 you have in the wall.
Themography can show small differences in heat conduction and can thus make these differences visible. The windows in such a photo are off the chart until the sensitivity is dialed way down.
Is Fibre Brace sheathing better than wood in regard to increasing insulation?
Here is a very good technical article on building with insulated sheathing. Included many details such as how to handle windows and doors, housewrap, structural bracing, etc. These are folks who do their homework (Building Science Corp (http://www.buildingscience.ca/).)
(https://i56.photobucket.com/albums/g166/jraabe/wall.jpg)
http://www.buildingscience.ca/documents/reports/rr-0501-guide-to-insulating-sheathing/?topic=/doctypes/researchreport
Thanks John! I guess that's why you're the architect and we're... :-? well, we're not. ;D So one should take extra time and care to stop the air in/exfiltration above all else.
Absolutely! Airsealing is the big key to controlling moisture.
RE: On the question (youngins) of composite (fiber) sheathing. I don't know that particular product (there are many brands made locally from waste wood products). Most fiberboard sheathings are only slightly better than OSB or plywood at insulation (check the R-value. Solid wood is about R-1 per inch) and far worse at structural integrity for bracing and worse at nail holding for siding. They are cheaper and may be code approved if you are in low wind areas. These are sometimes sold as an "insulation" product but this is used as a marketing term and the supplier hopes you don't understand R-values.
I call out structural sheathing (OSB or plywood) in my plans but lots of builders use fiberboard ("punkboard" :-?) sheathings too.
Did you know:
John wrote a book "Superinsulated Design and Construction." 1987 I think.
ISBN 0-442-26051-2 It's out of print - available on Amazon from serveral used book sellers. This book is an investment.
http://www.amazon.com/Superinsulated-Design-Construction-Building-Energy-Efficient/dp/0442260512/sr=11-1/qid=1170628674/ref=sr_11_1/002-5259018-9563210
Is the composite sheathing what we used to call black board?
Because, strangely enough, it was black.
Either nobody's using it any more or it gets covered up by tyvek.
QuoteHere is a very good technical article on building with insulated sheathing. Included many details such as how to handle windows and doors, housewrap, structural bracing, etc. These are folks who do their homework (Building Science Corp (http://www.buildingscience.ca/).)
That is an
excellent, very informative article. Thanks a lot John! :)
QuoteIs the composite sheathing what we used to call black board?
Because, strangely enough, it was black.
Either nobody's using it any more or it gets covered up by tyvek.
If what you're talking about is a kind of fibrous material it's still in use around here by some builders. They may use OSB at the corners and fill in the spaces in between with the black stuff. I can't for the life of me remember the name, but there's a stack of it at Home Depot. The houses in my neighborhood have a lot of it in them. (22 years old) Currently it costs more than OSB so I don't understand why anyone would use it.
Fibre Brace -
Rob LeMay used it on his - http://www.countryplans.com/lemay.html
Its cheaper than OSB and claims to be better at sealing moisture. - Is this true?
Quote
Its cheaper than OSB and claims to be better at sealing moisture. - Is this true?
It looks a lot like the stuff down at the Home Depots here, but without looking at it again I'm not sure. As far as moisture resistance, since reading the article posted by John on superinsulation I don't think that's a factor. The resistance to moisture is going to be built into the wall using a housewrap or foam board or combo thereof. How it is achieved depends on your location with regards to climate, humidity, rainfall, temperatures, etc. The black material I'm familiar with definitely does not have the same structural strength of OSB or plywood. A nail driven into it can easily be wiggled back and forth and be pulled out by hand. A nail in OSB will bend before deforming the hole if you wiggle it .
QuoteIt looks a lot like the stuff down at the Home Depots here
Same stuff at Home Depot here in North Texas. I priced it against plywood (not sure now if it was OSB) for wall sheathing - the FibreBrace was like $7 and the wood was like $14.
There is a nice looking pamphlet in front of the FibeBrace touting how much better it is against its wood counterpart. If I find it I will post back. Anyway, I believe that is what Rob indicated he used for the initial sheathing. I would be curious as to what, if any, other material he put on before the siding.
I am considering using it on the playhouse to see how it actually performs.
Who knows, I might be going back and ripping it out later - but I guess nothing ventured is nothing learned.
The $14 must be plywood (CDX ?) Here the OSB is currently $6.39. Last time I looked the black board was more than the OSB. Code here won't let you use the black stuff at corners, so I figure that indicates a strength deficiency. IMO.
After mulling over fasteners some more, I realized that the bottleneck in heat flow would be the surface area of fastener in contact with wood. I then realized that John said exactly that a couple days ago but I just misunderstood what he meant....sorry John, I will try to read more carefully in the future. Anyway, I calculated that 17 nails with 1.5" of bite would have a combined 12 square inches of surface area. Based on that, the R-value of externally-applied foam would be reduced by only a negligible 1%.
Martyv, it doesn't really answer the question, but the Building Science Corp "Designs that Work" house for Juneau also uses external foam with no cavity insulation. Unfortunately, they don't explain why they chose not to fill the cavities. But it could be that the Fairbanks builder has just modified that design. Yes, yet another link to the Building Science site...lots of good reading there...http://www.buildingscience.ca/documents/primers/bsp-035-designs-that-work-very-cold-climate-juneau-ak/section-2-the-basic-very-cold-climate-house/
(http://www.buildingscience.ca/documents/primers/bsp-035-designs-that-work-very-cold-climate-juneau-ak/section-2-the-basic-very-cold-climate-house/2006-11-15.0689020850)
Steve, there is a paper discussing R-value calculations and thermal breaks at http://www.esim.ca/2001/documents/proceedings/Session7-1.pdf. They say that the area-weighted average of U-values will always overpredict the R-value as it doesn't account for heat flowing sideways within the wall. For wood framing, the error is small. But, when the wall contains metal or other highly conductive components, then the error can be quite large. They got an R-value 86% too big when using that method to calculate the R-value for a wall using 2x6 metal studs.
Question. On the sketch above I'm seeing house wrap on the wall sheathing with the blue foam outside of that. I thought the wrap was supposed to be as close to the cold side as possible which would put it between the foam and the final exterior siding?
Actually looking at John's post on 2/2 the wrap seems to be outside the foam.
Looking at and reading the Buliding Science website, http://www.buildingscience.ca , the layer of housewrap is placed on the exterior side of the studs as a drainage plane on the outside. The foam layers go over the housewrap. They recommend a semi-permeable latex paint over drywall on the interior wall to allow the inner space of the wall to"breath" or transfer any humidity out to the warm side. They also point out that sealing the top and bottom plates is very important, otherwise all your best insulating is for naught. Another interesting thing I noted was their recommendation to use non-paper faced drywall in the hot-humid climate areas. To reduce possibility for mold I surmise.
"They also point out that sealing the top and bottom plates is very important, otherwise all your best insulating is for naught."
This is one of the reasons I am considering exterior insulboard. On my last cabin I had the whole interior spray foamed. Then I went inside at -30 degrees with it still unfinished and heated with an electric unit heater. I was blown away by the amount of heat loss, (cold air infiltration), at the top and bottom plates and even where king studs were side by side with cripples etc. All that would be taken care of by exterior insulation.
After all that...I just got a good deal on a load of three sided logs...so now I will build another inefficientt log cabin. But I sure like log cabins.
If I had to deal with -30 (F) temperatures (although by -30 C it's already durned cold--the scales are the same at -40) I think I'd do some heavy duty insulation--or have planned for the thermal mass of the building to be self-heating. Not sure that "both" works well.
My log room at the barn--still doorless--can stay below freezing all of a sunny day when the outside temperature is up into the high 40s. And it has south-facing windows. Small but there. But I expect if I could ever get it up to a reasonable temperature, it would stay there for a good while. Maybe after the door--and the last of the windows--is in. But since there's no insulation below ground there it will probably always be cold in winter.
Around here older log cabins often have something on the order of clapboards on the outside, plaster, even wallpaper over very thin boards on the inside, that would work to still use the structure but conceal insulation.
I don't think the location of the housewrap is critical when you are using exterior foam. The foam itself is a weather barrier and air barrier. I would put it over the foam and under any spacers for the siding. It provides both an infiltration barrier and UV protection for the foam.
If it is not exposed for long and it is easier to wrap the wall prior to the foam then that should work just as well.
If you have siding and furring over exterior foam, why have a drainage plane (house wrap or paper) against the sheathing? ... or anywhere? Isn't the foam closed-cell?
Some recommend embossed wraps, or multi-layered papers, etc, to assure drainage .... at what point does the drainage plane against the sheathing allow so much air to move around that it defeats some of the effectiveness of the exterior insulation?
A closed cell foam installed over sheathing is going to do a good job of insulating the framing and providing an air barrier to infiltration. A drainage plane over this is primarily to break the capillary action of water from wet siding. This could be wood spacers, dimpled housewrap such as some of the newer products, or wavy old 30# asphalt building paper. It doesn't really need to be more than one of these.
These all allow a bit of airflow behind the siding but this is to the outside of any insulation. It probably does sacrifice some of the insulating value of the siding. (Small as it is.)
Just FYI, the references to http://www.buildingscience.ca is now http://www.buildingscience.com.
here is an example link previously referenced in this thread. BTW, I do know this thread is dead but I thought this would save others time because there is some really good information referenced in this thread.
http://www.buildingscience.com/documents/reports/rr-0501-guide-to-insulating-sheathing
Quote from: MountainDon on January 24, 2007, 11:30:35 PM
Welcome aboard! 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.
I want to put 2 inches of blue styrofoam on the inside of my roof rafter fiberglass insulation. There are no building codes in my area. Can I safely nail 3/4 inch T&G pine directly over the styrofoam without drywall first?
Thanks,
Dave
On ours I put 1-1/2" of foam beneath the rafters, fiberglass between the rafters, then screwed osb to the rafters through the foam and then attached T&G to the osb. It's been there at least 25 years. I reshingled last year and pulled some sheets of roof sheathing with damge from waiting too long to reshingle. Everything underneath was fine... In VA.
I see osb was $6.39 in '07, ah those were the days, I think I paid around 5 bucks a sheet when we did ours.
Thanks Don_P,
The OSB is a great idea. I'll probably wait until the price drops below the current $30 per sheet. I still have to insulate with fiberglass under the main floor. I'll do that first and see how much warmer it stays in the cold weather..
Dave