I'm building a new home and currently looking at two ways to insulate the home. The house has 2x6 framing with 1.5" pink codeboard (R 7.5) over the OSB plywood. I'm in Ontario Canada. Option 1: Walltite Eco @ 2" to all walls and R12 batts. R20 Walltite Eco to all headers. R32 Walltite Eco to all overhangs. R12 Walltite Eco in the basement. R50 blown fibreglass to the attic. Option 2: R20 Walltite Eco to all walls and headers. R32 Walltite Eco to all overhangs. R12 Walltite Eco in the basement. R50 blown fibreglass to the attic. There is minimal cost difference between the two but the contractor said that the fibreglass does help to cut down on noise transmission from the outside. Does anybody have an opinion on which way to go? Am I better off going all foam or flash and batt?

We no longer use fiberglass here in Minneapolis, as it can lose nearly 50% of its R-value when subjected to sub-zero temperatures. It is cellulose in the attic and 2# foam in the walls - or some combination thereof. The exterior is usually an XPS sheeting product above an R-5 to prevent the dreaded "thermal bridging" of typical stud construction.

We may get sub zero temps but thats usually with a wind chill added on. I do have the R 7.5 board on the outside for thermal bridging but don't know which way to go for the wall cavity. The difference between all foam or flash and batt on the walls is only $700 more for all foam. Is the R20 sprayed better than 2" sprayed plus R12 batt? BASF rates Walltite ECO at a R value of 10.5 for 2" so the flash and batt would be R 22, but is this as good as R20 in foam. Also with just having the foam will I notice more outside noise?

Wind chill is an arbitrary number produced to increase weatherperson drama and only important if you are personally exposed to it. It has no bearing on heat load analysis.

As for Bat & Flash, it appears to be an unproven technology the performance of which is highly dependent on the applicator. It requires a careful and accurate application of close cell (2#) foam to a depth specific to the climate. There is also the question of cellulose settling, moisture retention etc.

I believe the 2# foam to be the best overall performer and long-term investment for the majority of home in cold dominant climates. I use it my own and could personally verify its installation depth with a 16 penny nail. I paid for a high performance product and got what I paid for. As you research the various options you get a lot of opinion but unless my the indispensable Dana1 will come out, measure specify and inspect the final product I will only have confidence in 2# foam for R-value, permeability, sound attenuation and structural integrity

I don't disagree with all foam being a good solution, but I think that taped exterior rigid foam + cellulose + interior air barrier/vapor retarder (of some class) is also quite good.

jonr;

I defer to your obvious expertise in structural details, but still wonder if the layman can get the best system without some personal experience or independent consultation? Local code officials notwithstanding.

I guess what I'm looking for is the best system for the long term. I don't plan on building and moving again so this should be my last house. I would rather pay the upfront costs now than regret it latter. As for the building envelope I will have taped Tyvek, shiplapped Owens Corning codeboard at 1.5" (R 7.5), osb, and a 2x6 wall. I'm looking at getting R20 in the walls. From what I've read the all foam approach is probably the best option. I already have 4" of foam under the basement slab and will have R12 sprayed on the foundation walls, and plan on putting R50 in the attic as well. I just want to make sure I do this right and it looks like all foam is the better choice.

Though I design and install HVAC systems (mostly radiant) for a living, my last large project was a renovation of my own home in which I used 2# foam.

One of the deciding factors was the 4" balloon frame walls. The previous owner had furred out the already small upper level bedrooms to 6" to accommodate enough fiberglass to meet the MN energy code. I didn't think it was the best use of space nor a good way to seal up a balloon frame farmhouse circa 1921. For me the choice was obvious, including 6-7 inches of foam under the hot roof.

I would consider 2x4 stud walls with foam.

http://www.advancedenergy.org/build...r_2x6.html

Posted By dlunn on 06 Jun 2011 11:43 AM
We may get sub zero temps but thats usually with a wind chill added on. I do have the R 7.5 board on the outside for thermal bridging but don't know which way to go for the wall cavity. The difference between all foam or flash and batt on the walls is only $700 more for all foam. Is the R20 sprayed better than 2" sprayed plus R12 batt? BASF rates Walltite ECO at a R value of 10.5 for 2" so the flash and batt would be R 22, but is this as good as R20 in foam. Also with just having the foam will I notice more outside noise?

Even at -10C the hit in performance for low-density fiberglass in a cold side up configuration is still well into double-digits from it's 20C or 25C ratings.  At -10C it's almost down a third.  At -20C it's about half.  In a heating-dominated climate you'll do much better to use either high-density blown-in-mesh fiberglass (1.8lbs density Optima or Spider), or open-blown cellulose at similar density.  Low density fiberglass also loses some R at the temperature extremes too, but not nearly as dramatically as in attics.

You may be over-rating your batt R values in the flash'n'batt.  Mid density batts only perform at their rated value only when not installed. Compressed into their standard stud-bays they go up in R/inch, but down in overall value, losing ~3%-  an R13 batt in a 2x4 studall wall is really only a bit over R12.5.  Low density batts are even worse- an R22 batt is only R19 when stuffed in a 2x6 bay, and an R19 batt is really only R18, when installed per the manufacturers recommendations!  For proper de-rating for compressing into flash'n'batt see:  http://numsum.com/spreadsheet/show/21111  When dealing with a low

Figure on no more than R4/ inch for any compressed-thickness of batt, but R5.25/inch for filling the same space with foam. Of course the batt should always be under tension, and filling the entire space, whereas trimming closed cell foam flush with the studs is extremely difficult, so count on it being a 1/4-1/2 shy of the full depth.  In center cavity R value it's about a wash, but even if it were full-up the thermal bridging of the studs negates most of the potential improvement anyway.  No matter what you fill the cavity with, you're only looking at ~R14-R15 for the studwall section, before adding the R value of the exterior foam, due to the thermal bridging impact of the studs, headers, plates, firestops, etc.

At even R4/inch or higher the thermal bridging of the studs DOMINATES the heat transfer of the whole-wall, you're as a rule better off using flash'n'fill (for the air-sealing) and spending the foam-difference on thicker exterior foam, since without the thermal bridging you'll get the full R out of it.  The fiber layer sees a lower temperature difference, and loses less R with outside temp, and the sheathing stays that warmer, for fewer condensing hours.

At 2" BASF Walltite ECO is 0.7 perms, which is low enough to limit the moisture diffusion from the interior reaching the wood anyway, even if you DIDN'T keep it warmer with the exterior foam. Do NOT use interior poly or kraft facers, and use R15 or higher batts that will fully compress into any unevenness in the foam surface. Gaps on either side of the fiber layer cut into performance considerably due to free-convection.  Sprayed cellulose (any density) or high-density blown fiberglass would be better, since it conforms to all anomalies. 

In fact in the warmer southern & southeastern parts of Ontario R10 on the exterior and a full cavity fill of blown/sprayed cellulose would work, even without an interior vapor barrier. See: http://www.buildingscience.com/documents/guides-and-manuals/irc-faqs/irc-faq-insulating-sheathing-vapor-retarder-requirements

The real question is if there's any up-cost for going R10 on the exterior with a flash'n'batt  studwall vs. R7.5 on the exterior & full-foam studs.  I'm betting it's a wash, but the higher-R exterior foam buys you a lot more performance than anything you could do at R20+ center-cavity the stud bays.  The studwall you've described will come in at ~ R22 whole-wall, but putting a half-inch foam on the exterior brings it close to R25, or about a 10% improvement, for about the same money.  (In fact, if you went with 4" of exterior foam and R20 batts/blown in the cavities you'd be well over R30, a much more substantial boost in performance.)

Dana, I am always impressed both with your general knowledge of the subject and your dexterity, but you spend a lot of time coming to the same conclusion. Air infiltration is not addressed in most comparisons and the most important factor in heat loads once a reasonable R value in attained (in fact nearly any R value). Thus the argument for foam and most especially in retrofit work (not the case here I understand).

Please address the 2x4 vs. 2x6 argument as it has been poorly handled in the past and with much the same argument and outcome as this one

x

I'd like to see more hard figures regarding air infiltration. Less is always better, but once you have a tight house, going to very tight may not be worth the expense. Going from $60/year* in infiltrated air heating/cooling expense to $30 isn't worth much effort. Also, minimizing pressure differentials might be much more cost effective than producing a tighter house - no pressure differential equals no infiltration, even with a leaky house.
* - the figure I calculated with a real house

Building air tight (sub 1.5 ACH/50) is pretty cheap & easy for new construction, if often difficult in retrofits. It also doesn't take spray foam to get there- a well defined primary air-barrier in the plan, and ample use of acoustic-sealants and other caulks does a world of good. The ease & economics of achieving it is why Canadian R-2000 spec is for <1.5ACH/50

It takes a bit more attention to detail to meet the PassiveHouse spec of < 0.6 ACH/50 and isn't worth chasing unless you're really taking it to the full PassiveHouse extreme.

The 2x4 vs. 2x6 construction comparison/argument is basically this: 2x4 16" o.c. construction has about the same board-feet of lumber and structural capacity as 2x6, 25" o.c. construction (and this is without going to OVE or advanced-framing technique.) The differences in cost for a fiber cavity -fill insulation are small, but the difference in whole-wall R value is significant due to the lower fraction of framing area and higher R of the thermal shorts of the framing. It boils down to ~ R10 whole-wall-R (thermal bridging included) in the 2x4 case as compared to R14 for 2x6. You can go with a lower k-value fill such as R6/inch foam for the cavity but it doesn't affect the cavity fill since it does nothing to block the thermal bridging of the low-R studs (R3-3.5 in the 2x4 case R5ish in the 2x6 case). High performance stick-built is all about reducing and breaking the thermal bridging of the structural wood.

Take the 2x6 24" o.c. case:

With 5"(R30) in 2lb foam center-cavity but never hit R20 for a whole-wall R with 20% of the area bridged by R5 studs headers plates band joists etc, the heat loss/gain through the wall is dominated by the thermal bridging of the studs. But with a R20 fiber fill in the cavity and an inch of iso or 2lb foam (R6) on the exterior you're at R20, out performing the foam-filled cavity (no-exterior foam) solution with only A QUARTER of the foam volume.

In much of Ontario only R6 would not be sufficient to protect the sheathing from interior moisture drives in winter with only latex paint as the interior vapor retarder, but R10 would be in places like Windsor/Toronto, at which point you'd be at R24 and still with LESS FOAM than a 5" all-foam cavity fill.

In Thunder Bay or Sault St. Marie you'd need to bump it up to ~ R15 or so, bringing the the whole wall R up to ~ R30 ish, using only 20% more foam than a 5" all-foam cavity fill.

Or, you could keep it at R20 and use code-prescribed interior poly, protecting it from winter moisture drives, at the expense of overall drying capacity.

Rigid iso (polyisocyanurate) roofing insulation is pretty cheap stuff, and R5.6/inch when derated for temps below -10C. The standard fiber-faced 4x8' sheets x 3" thickness run ~$55 f.o.b. the distributor's yard, and would have a derated R of ~ R17, or about 10 cents/R/square foot (or ~ $1/R/square-meter). The installed price of R6/inch 2lb foam at a buck a board foot is 17cents/R/foot. Use of rigid iso "outsulation" is becoming a preferred method of getting R30- R40 walls with cellulose-filled 2x6 construction in my neighborhood. No way does it cost anywhere near 7 cents/foot to deliver, install and air-seal rigid iso. Some of the mid-density R5/inch closed cell foams can come close to that, adding a tiny bit of thickness to the overall assembly, and making air-sealing much easier.

Posted By BadgerBoilerMN on 06 Jun 2011 05:09 PM
Dana, I am always impressed both with your general knowledge of the subject and your dexterity, but you spend a lot of time coming to the same conclusion. Air infiltration is not addressed in most comparisons and the most important factor in heat loads once a reasonable R value in attained (in fact nearly any R value). Thus the argument for foam and most especially in retrofit work (not the case here I understand).

Please address the 2x4 vs. 2x6 argument as it has been poorly handled in the past and with much the same argument and outcome as this one

The facts & physics don't change just 'cuz someone else is asking, eh?

Like "...nearly any R value" air sealing gets a lot less relevant when you get it down to 2 ACH/50, but given that a lot of existing stock is 10+ ACH/50, hell yes it's important.  But 3lb cellulose can be nearly as tight as foam, usually at a lower installed price, but foam may be the better option in many retrofits for it's vapor retardency.  New construction can be built much tighter at minimal cost, but until codes call for blower door verification and minimum standards, the typical numbers are still 5+.

But stick-built thermal bridging issue doesn't go away with wishful thinking, what it takes to keep the average winter temps of susceptible wood above the dew points of interior air changes only with local climate, thermal mass only reduces energy use signficantly when it's fully inside the insulation, water only runs downhill, and cloudless skies are usually blue in the middle of the day.  Facts oft-repeated may sound like a broken record, but the mere assertion of the facts is often met with skepticism unless presenting the long(er)-version of the birth certificate (and even then some skeptics will remain.) 

heheeehee

The dumber I am, the smarter you get!

I got snookered again, eh?

Standard wall detail loses 60% of energy through conduction. Cut 1" thick foam strips 1.5 inches wide and attach to the inside and outside of all framing. This stops most of the bridging and per study improves total thermal performance of the wall by more than 54%. It is easy to do and very low cost. It also allows for a cavity that is an extra 2 inches deep for insulation infill. It does require use of longer nails or screws when attaching sheating.

This is a lot cheaper than external sheeting and just as effective.

Brian

You lose some air sealing and fill insulation such as fiberglass or cellulose will not be as effective as continuous rigid foam.
Even so, maybe someone should sell 60 psi XPS edged 2x6s (of which 2x4 is wood).

Posted By zehboss on 22 Jun 2011 05:47 AM
Standard wall detail loses 60% of energy through conduction. Cut 1" thick foam strips 1.5 inches wide and attach to the inside and outside of all framing. This stops most of the bridging and per study improves total thermal performance of the wall by more than 54%. It is easy to do and very low cost. It also allows for a cavity that is an extra 2 inches deep for insulation infill. It does require use of longer nails or screws when attaching sheating.

This is a lot cheaper than external sheeting and just as effective.

Brian

Stud strip-foam + fiber fill may be as-effective as exterior foam sheathing from a strictly thermal point of view, but for moisture control at the structural sheathing point of view, not so much (particularly in this cool/cold Ontario climate).

Over reliance on the permanent integrity of low-perm interior vapor retarders in cold climates isn't always the best strategy. Every inch of exterior foam on 2x4 construction is roughly equivalent to moving ~2 climate zones warmer from awintertime moisture accumulation in the structural sheathing point of view.  In US zones 3 & 4, even the warm edge of zone 5 the strip approach can work just fine in conjunction with rainscreened siding.  In zones 6 & above you're counting on a low-perm vapor retarder to be installed perfectly and remain so over time, or you'd have to build with gypsum/fiberboard structural sheathing rather than OSB/ply, in conjunction with rainscreened siding.  Exterior foam is a more resiliant approach in cold climates, since it's tolerant of minor air leakage from the interior.

Most of Ontario is roughly equivalent to US zones 6-8 (with the exception of the southern stretches along Lake Erie & Lake Ontario which are more like zone 5).  A stud-strip approach there is higher risk if low-cost air-permeable stud insulation is used, even when build to code with interior poly vapor barrier, 10mm rainscreen on the siding.  Sometimes the cost of more foam is worth it.  More than mere thermal performance it buys resiliance when applied to the right layer of the stackup.

Thermablok sells stud-edge aerogel insulation strips for exactly this sort of application, but unless you're buying miles of it I suspect it's not cost-competitive with cut down XPS (yet).

A well-insulated house is a bit like dressing for the weather. A wool pullover will keep you warm if the wind is not blowing and it is not raining. On a windy, rainy day, wearing a nylon shell over your wool sweater helps keep you reasonably dry and warm. A house is similar.