I apologize if this has been covered already...I searched but couldn't find what I needed so..

I have a 850 sq/ft home located in Kenora Ontario P9N0E7 Canada. We just went through a bitterly cold 8 week period... my oil bill was awful...and the electric bill about the same. For me it was a kick in the pants to make some changes to the building; starting with an improvement to the roof insulation (going from R40 to R80).

Next is the harder one.

The walls are 2x6 with batt insulation and like all homes up here have 6 mil poly on the inside (right behind the drywall). My plan is to strip off the vinyl siding and add either 2/3/or 4 inches of rigid foam (blue) or similar.

I have read on the site that consideration must be given to allowing the wall to "dry" either in or out, since IN is currently blocked by the 6 mil poly I assume that it must dry outwards. That will probably limit the amount of foam I can put on the exterior but I don't know how to determine what the practicle limit is (2/3 or 4 inches).

I know I will have to fur out the doors and windows and add a rain screen behind the vinyl siding before I put it up again. Will Tyvek (or similar) be adequate on the exterior of the foam under the strapping (that will be used to attach the siding to?

Thanks

do a youtube search into passive house retrofit, I have been watching videos all day, the whole concept of a passive house is verry interestring, you'll find all sorts of details as to what to use and how to go about it, in the end you'll have to make a chouse of what you are most confortable with

A 2x6 wall with R20 batts vinyls siding wood sheathing & siding and half-inch gypsum wallboard performs at about R14 whole-wall, after thermal bridging of the studs is factored in.

If you added 2" of Type II EPS (1.5lbs/cubic foot density, R4.2/inch @ 75F/24C, R4.5/inch @ 40F/4.4C- increasing as temps go lower). A 2" it would have about 1.5 perms of drying capacity toward the exterior, which is plenty, and it would bring your whole-wall R up to about R23 during the winter.  If 3" you'd be down to 1 perm and R27-R28 whole wall (cutting your wall losses in half) which is starting to get pretty tight from a vapor permeance point of view but still OK under vinyl siding, which is inherently back-ventilated, and doesn't retain moisture (like masonry or fiber-cement can.)  If you want to go even higher R with exterior foam you'd  have to drop back to Type-I EPS (1lb nominal density) which can be a bit of a pain to deal with in a wall assembly since it's easily damaged.

Alternatively you could use rigid rock wool board (Roxul ComfortBoard), which is nearly the same R/inch as EPS, but more than an order of magnitude higher vapor permeance. It's more expensive than EPS, but it's also completely fireproof, and there are no thickness limits from a vapor permeance point of view. You can get it as thick as 3" (R12), which is probably the practical limit from an installation- ease point of view.

At about R20 whole-wall the windows usually dominate the heat loss figures, so beyond the first 3" of  exterior insulation you'll probably be getting more performance per loony out of something like low-E exterior storm windows on north, east and west sides (preserving the full solar gain of the south facing windows.)  A tight low-T storm window drops the U-factor of a U-0.35 window to about U0.28-U0.30.  It will bring a U0.30 window down near triple-pane sealed window performance.

The low-E Larson storm windows sold through the blue & orange box stores are pretty good if you upgrade to the Silver or Gold series- the low end Bronze versions leak more air than you'd like in a high-performance house.  A quick web search determined that the blue box store carries Larson. The Larson dealer finder has a dozen or so hits of mostly the blue box store in the Toronto/Hamilton area- nothing close to Kenora, but you can probably still order them through the box-store even if they don't normally stock them.

THANKS a million.... that was exactly the info I needed

To be absolutely clear, EPS is the only rigid foam sufficiently vapor permeable to even consider here. With XPS you'd be limited to about 1" (R5), even 1.5" would be below 1-perm, and all polyiso products have facers rated at less than 1 perm.

Rigid rock-wool is the better way to go since you have the interior side poly. It's considerably more expensive than EPS, and you have to play around a bit with the strapping screws to end up with a flat-looking wall since it's slightly compressible, but it'll be much more moisture resilient than a 3" EPS solution.

Thanks again...that is exactly the clarity I was looking for. I will be looking for 3" EPS foam.

As a follow-up; if I may,

the house is build on a slope. The roadside (west) has about 12 inches of wood framed wall above grade and another 36" or so below grade. The sides (north and south) having increasingly more above grade wall resulting in 48" of wood framed wall above the grade at the lake side (east ). The crawlspace is about 50" in places but uneven with a concrete floor poured over the granite.

There is a stepped concrete pony wall (is that the right desc for a small 12" wall extending above the grade beam that the wood framed wall sits upon? It is stepped in places so 12" here and 24 there)) that sits on the grade beam which in turn sits on granite.

I want to insulate the lower wall (heated crawlspace) as well.

For the wood framed sections above and below grade I am curious if the same 3 inches of EPS will work.

I propose to provide protection for that foam (with vertical vinyl siding above grade and pressure treated plywood below grade)....          or

since EPS absorbs water from the soil should I use XPS below grade?

Problem I see and I'm near sighted :) is that any of the below grade wall that's wood framed will run into a problem with water vapour permeability if I use XPS, if I use EPS I don't know how to protect it from soil moisture,

The worst will be the west side which has about 36" of wood framed wall below grade (it is currently covered in pressure treated plywood) .

The ground is a sandy loam and well drained.

I need a better picture- are you intending to insulate a framed wall below grade on the inteior side of the granite foundation?

It's a commonly held belief that EPS absorbs moisture more than XPS, where in fact the opposite is true. EPS has better closed-cell structure and fewer broken cells than XPS, but it also has interstitial spaces between the bead structures. When you submerge EPS and XPS, the EPS will initially take on moisture more rapidly, but that effectively stops when the interstitial spaces are filled. But when the tide goes out it releases the moisture just as rapidly. Both EPS and XPS take a 7-10% hit in R value when submerged in liquid water for long periods, but the EPS drys orders of magnitued faster. In dry soil there isn't really a problem with either, but note, EPS is widely used in marine applications for everything from lobster pot buoys to dock floats, and XPS is not.

If you put 3" of Type-II (1.5lbs per cubic foot nominal density) against foundation wall you're golden. At 3" it runs about 1perm, which is a minimalist class-II vapor retarder. If you then put a framed wall with batts or whatever on the conditioned space side, as long as you don't put up an interior-side vapor barrier like poly, the susceptible wood tracks the moisture levels of the interior air, and not the ground moisture. With R15 Roxul in a 2x4 wall 3" of EPS is PLENTY to be protective of the studs, and would also be sufficient to keep frost from accumulating over the winter on the section that might be above-grade. Kenora is essentially equivalent to a US zone 7 climate, and R10 would even be protective of wood sheathing on a 2x4 studwall in an above grade wall. With 3" of EPS you'd be averaging above R13.5 during the winter months that count form a moisture accumulation point of view, despite only rating R12.6 in an ASTM C 518 test. (Even that would be over R10, and meet code.) See: http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_7_sec002_par025.htm

Rigid polyiso is something to be careful about below grade, because unlike EPS and XPS, it WILL wick water. You can't bury it under slabs, but you can still use it effectively for insulating basements, as long as you take care to keep the exposed cut edges off the slab. (I put 3" of iso on my poured concrete basement walls, but it stops 4-6" from the slab, due to a history of spring thaws where the water table is sometimes above the slab. If it were EPS it would be fine even if it extended below the slab down to the footing.)

No sorry..exterior only.

The stud bays on the below grade walls already have  R20 batts in them (pink) with 6 mil poly and then drywall.

---I will be using 3 inch EPS to the footings.---

Taking the 3" EPS all the way down to the footings is the right way to go as long as you have a good capillary break (metal flashing or EPDM sill gasket) between the top of the foundation and the foundation sills. With the interior poly any liquid moisture that finds it's way to the footing will wick up the concrete, putting the foundation sill at risk, since it can't dry toward the interior through the poly.

Using a rigid rock wool product designed for exterior below grade insulation (eg, Roxul DrainBoard: http://www.roxul.com/files/RX-NA_EN/pdf/Sell%20Sheets/DrainBoard.pdf ) for the above-grade concrede down to about a foot below grade (with clean stone backfill) allows the foundation to dry toward the exterior.

Another tried & true common method for dealing with it is to stop the interior poly about knee-height above the slab, to allow footing moisture to dry toward the interior rather than saturating the foundation wall all the way up to the foundation sill.