I did not see a specific forum for insulation and i could use some solid advice on insulation , it is a new build "cottage"and have made some mistakes . i used 1/2 inch ply on the exterior walls and then just put house wrap on it to weather the winter . i have the windows installed and i have heard i should have used foam sheets and diagonal bracing instead of the 1/2 plywood . is it still possible to install the foam and what thickness . and noew the real problem is to use sray foam on the interior walls and basement walls and of course ceiling . it is a loft 12 12 pitch 2by 10  and main 2by 6 walls  and the basement is concrete and 2by 4 stud walls. is it really a better product than say roxul at r24 and r31 - i have asked a sprayer and he quotes all you need is 4 inches and its at its peak insulation value and its the product to use . it will pay it back . i need good solid advice on this , value is all i want  thanks

Posted By kellytheaker on 21 Feb 2013 09:29 PM
I did not see a specific forum for insulation and i could use some solid advice on insulation , it is a new build "cottage"and have made some mistakes . i used 1/2 inch ply on the exterior walls and then just put house wrap on it to weather the winter . i have the windows installed and i have heard i should have used foam sheets and diagonal bracing instead of the 1/2 plywood . is it still possible to install the foam and what thickness . and noew the real problem is to use sray foam on the interior walls and basement walls and of course ceiling . it is a loft 12 12 pitch 2by 10  and main 2by 6 walls  and the basement is concrete and 2by 4 stud walls. is it really a better product than say roxul at r24 and r31 - i have asked a sprayer and he quotes all you need is 4 inches and its at its peak insulation value and its the product to use . it will pay it back . i need good solid advice on this , value is all i want  thanks

It's certainly possible and desirable to put rigid foam on the exterior of the sheathing & housewrap.  How thick and what type depends on both the local climate and the stackup of the rest of the wall.

For the abover grade walls, the 4" of closed cell spray foam will be more air tight than Roxul unless you caulk every stud to the sheathing with acoustic sealant caulk, use air-tight techniques on the gypsum and foam-seal the electrical penetrations through all framing, including studs & plates, which is a lot of detailing, but cheap stuff.  But the closed cell foam @ 4" will underperform a full cavity fill, due the the more severe thermal bridging (you only have 4" of stud rather than 5.5" at ~R1/inch.)  Using open cell foam that fills up the cavity completely would be more air-tight and have a comparable "whole-wall" R value even though the center cavity value would only be ~R20,  since the R4 of stud-bridging increases to R5.5 when the cavity is completely filled.

If the studs are 16" on center the "framing fraction" will usually come in around 25% of the entire wall space.  If they are 24" on center it will be more like 20%. 

At a 25% framing fraction if you include the R value of both the wallboard gypsum and the polywood  the 4" of closed cell foam the wall would have a whole-wall average R of R12.

With a full cavity fill of open cell foam it comes in at R13.

At a 20% framing fraction the 4" of closed cell comes in a hair under R14, about the same as a full fill of (much cheaper) open cell foam.

If you add 1" of EPS to the exterior it adds R4 to those numbers, if you add 2" it adds R8. (Eg: 20% framing fraction is R14, with an inch of EPS it becomes R18, if you add two inches it's R22. etc.)  With other insulation it's similar- XPS adds R5/inch, and with polyiso it adds R6/inch (a bit less, if it's a VERY cold climate- derate polyiso to R5.5/inch at +5F/-15C or below if that is your average binned-hourly mid-winter temperature.)

But be careful about going with polyiso with vapor-barrier foil facers, unless you put on enough that you can keep the interior side vapor-open, so that it has a path to drying.  The amount of foam necessary to do that is highly local-climate dependent.  In the US there are prescribed minimum R-values for the exterior insulation to be able to avoid interior vapor retarders, which are specific to each US climate zone embedded in IRC code. These are minimums- there are no maximums, but if you use foil faced polyiso (which allows NO drying to the exterior), it is usually better to overshoot the minimum by 50% or more.  With EPS or XPS the absolute minimum is still fine, but anything over R10 with EPS should be treated as if it were impermeable.  With EPS you can go to about R16 or so before it becomes too vapor-tight.

There are many useful tips on how to install exterior rigid foam on this blog piece, with many of the relevant details found only in embedded links.  Since your windows are already installed yours will be by definition an "innie" window setup.  They have full detail drawings available to members in some of those links, but if you know how to flash a window it's usually not very difficult to handle 1-1.5". At 2"+ there is a bit more to it, but still not a rocket-science project to design.

Thanks the stud walls in the basement- 2+4 are 16Inch centres , and upstairs 2+6 walls are 16 in centres . as well as the roof - cathedral 2+10 16 inch centres .do you prefer closed cell insulation vs the batts ,and do you vent the roof from the soffit to ridge with foam or put it straight on the plywood . Yes i can flash a window , but these windows came with a nice brick mould on them and nail fin and they are in but if an inch of foam makes that big of a dif i should be considering butting it in o the brick mould , is the foam that impressive on say the ceiling vs batts , southern ontario is the spot

i could not link to your first site

Posted By kellytheaker on 22 Feb 2013 04:32 PM
i could not link to your first site

http://www.buildingscience.com/documents/guides-and-manuals/irc-faqs/irc-faq-insulating-sheathing-vapor-retarder-requirements/files/FAQ%20Vapor%20Retarders_2011.pdf

cut and paste?

Posted By kellytheaker on 22 Feb 2013 04:20 PM
Thanks the stud walls in the basement- 2+4 are 16Inch centres , and upstairs 2+6 walls are 16 in centres . as well as the roof - cathedral 2+10 16 inch centres .do you prefer closed cell insulation vs the batts ,and do you vent the roof from the soffit to ridge with foam or put it straight on the plywood . Yes i can flash a window , but these windows came with a nice brick mould on them and nail fin and they are in but if an inch of foam makes that big of a dif i should be considering butting it in o the brick mould , is the foam that impressive on say the ceiling vs batts , southern ontario is the spot

From a thermal performance point of view an inch of exterior foam buys you more performance than a full cavity fill of closed cell foam, since you get the full-R of the exterior foam, whereas the framing robs high-R cavity fill of it's performance potential. But there is still the moisture factors to consider.

In a Toronto/Windsor climate you would need R7.5 or more on the exterior of the 2x6 wall to be able to skip interior vapor retarders.  But if you put an inch of EPS or XPS on the exterior, and a flash-inch of closed cell foam on the interior, then compressed an unfaced R19 or low-density R22 batt into the remaining 4.5" of space the sheathing could still dry in both directions, and would not accumulate much wintertime moisture.

In the basement ideally you would have rigid foam between the stud edges and the foundation, and no interior vapor retarder.  If the studwall is already up, use an inch of closed cell directly on the concrete sealing it to the studs, and unfaced low density R11s compressed in the remaining  2.5" (or split R19s). The stud edge next to the concrete it still somewhat susceptible, but the foam will protect both the studs and the gypsum from both ground moisture and wintertime moisture loading, and still allows the concrete to dry toward the interior, which is at least partially protective of the stud edge next to the concrete.

With only 2x10s in the cathedralized roof you have to go unvented or you'll be woefully below code min.  The most optimal approach would be 2" of closed cell foam applied directly under the roof deck and high density "cathedral ceiling" R30 fiberglass batts, or R30 Roxul the remaing space. That would get you to about R42 (code is R50 in Ontario), which is still pretty good for that climate. Do NOT use interior poly or the assembly will trap moisture.  As a sanity check on this approach see:

http://www.buildingscience.com/docu...of-systems

See tables 3 & 4 p.11 and look at the column for 2" ccSPF + spray fiberglass. Your climate is most similar to the 5A-Chicago, but with the lower R value your roof deck is even more protected than the assembly simulated, since it will be ever so slightly warmer on average.

Closed cell spray foam isn't the greenest stuff, since it's blown with HFCs that have a VERY  high greenhouse gas potential. Any amount over the first inch or two will have a net lifecycle greenhouse gas footprint larger than the energy use it offsets(!).  The exception that may be available in your area would be a water-blown product from Icynene: MD-R-200 (and NOT MD-C-200, which is blown with HFC245fa).  It's still expensive stuff, and only R5.2/inch compared to other closed cell foam (not that it makes a measurable difference when it is used between studs & rafters), but it has less than 1/1000 the greenhouse gas potential.  If that's what you use it's better to use 3" on the roof deck, since it is also somewhat more vapor permeable than HFC blown foam.  For the 2x6 studwall 2" of MD-R-200 + R23 Roxul is a better fit, but below grade an inch is fine.

thanks again for the education