Replies

1. Expert Member
   Dana Dorsett | Sep 10, 2013 05:29pm | #1

   The better bang per buck on balloon framed antiques is to dense pack the wall cavities with cellulose and NOT gut the rooms unless the old plaster & lath is in such terrible shape that it can't be saved. Dense packing will reduce the air leakage on the walls by something like 98%, and it'll be done in a few days rather than a few years (and in most of MA it's subsidized. (Check out your subsidy availability/options at masssave.com .)

   If you decide to strip the old plaster in any room at some later date, dense-packed cellulose stays in place- you can strip the wall and it'll still hang there, and won't need to be redone. And the sooner you add insulation the better- it's very cost effective even un-subsidized if you're heating with oil.

   Then, re-point and repair any degradation to the foundation, and use 2" closed-cell polyurethane and intumescent paint on the walls, sealing & insulating all the way up & over the foundation sill & band joist. If it's a dirt floor it's worth digging in 4" of clean gravel and putting 2" of EPS covered by a 2" rat-slab (or a full-thickness slab) at some later point, but the really significant losses are conduction and air leakage at the foundation walls, not the basement floor.

   If any single large zone is open enough, it's also worth looking at installing a ductless air source heat pump (mini-split , multi-split), which will pay for itself in well under 5 years at the recent 5-year averages for both electricity and heating oil. This is a more complicated call than air sealing and insulation, but no less worthwhile, at $3.50-4 oil.

   A flash-foam seal with open-blow cellulose is one way to deal with the attic. You can usually air seal fine using far less foam by spot-sealing though- you don't need anything like 500-1000 board feet of foam that I see some people adding. Cutting up rigid foam to block the big holes, sealed in place with a FrothPak kit or can foam is just fine. When you think you have it all, a blower door test will show you where the other 200 square inches of leak are. You have to use sheet metal to air seal around flues & chimneys, and isolate the chimneys & flues from the cellulose with a wrap of R15 rock wool batt bound with wire to keep it from opening up over time or heat.

2. 
   user-1115477 | Sep 10, 2013 06:36pm | #2

   Brian,
   Simply insulating the x4 wall cavities might get you through this winter only costing you your arm, but I think you are going to also lose your leg by next winter if you don't add at least 2" of rigid foam to the outside.

3. 
   bac478 | Sep 10, 2013 11:39pm | #3

   Thanks Dana. The plaster upstairs is in pretty tough shape and some was previously torn out in the stairwell and replaced with very shoddy drywall work. I already have about 200 sheets of drywall in the garage from a local hardware store liquidation.
   I am very familiar with mass save and all the available rebates, they will be out at the house in early October so I can take advantage of those rebates.
   I have read a lot of the guides and articles over at the building science corp. website so I am familiar with the ccSPF method for fieldstone/brick foundations. I am reluctant to use it because of the freeze thaw damage that is already present in the bricks. It seems like the bricks will be wetter and colder if they are sealed and insulated with ccSPF on the interior and that it will make the freeze/thaw worse. Is this a valid concern?
   Reason I suggested a flash coat of foam in the attic is I figured I could rock the ceilings first and then have the foam guy come and do the open walls and attic at the same time so it would be cost effective. Maybe it isn't necessary and some sealant and can foam would work alright. Is something like airtight drywall recommended for a scenario like this or is it ineffective? Seems like it is pretty complicated and not favored anymore. If not how else could I maintain air barrier continuity?
   The oil furnace is natural draft, I acquired a power venter for very cheap but haven't installed yet. At what point do I have to start worrying about backdrafting down the chimney as a source of makeup air? My goal was to get the house tight and insulated enough to heat/cool with a couple mini-splits year round but it seems like the investment is pretty substantial to get to that point. Is it cost effective to pursue that level of insulation and sealing?

4. Expert Member
   Dana Dorsett | Sep 12, 2013 03:06pm | #4

   You'll have a hell of a time making that place tight enough to be concerned about back-drafting & makeup air for the boiler on a 2-story chimney. If the chimney is currently lined with terra cotta you may not be able to vent the power-drafted furnace into it without spending some real money on a liner, which may not be worth it if the plan is to move on to a heat pump solution in anything like a decade or less. By the time you get the house tight enough to really matter from a safety point of view the heat loads will likely be within range of a ductless solution. (It might already be- you'd be surprised, but it might take a 4 ton Mitsubishi Hyper Heat to get there before insulating.)

   Air sealing with a flash of closed cell foam for both walls and attic is expensive and unnecessary. Blowing the cavities with cellulose takes care of nearly all of the wall-leakage, and is also worth it on R-value. Doing the insulation even before you gut the interior is usually possible, and it'll still stand up just fine when you strip the old plaster, as was the case on a recent deep energy retrofit on an 1890 vintage house I was involved with in Worcester: http://worcestermag.com/2013/04/08/1890-worcester-home-undergoes-deep-energy-retrofit-201984871/10919 . It's pretty common to peel back the interior OR exterior of even the less-dense 2-hole method cellulose and have the stuff hang there like it was installed yesterday:

   http://www.buildingscience.com/documents/insights/bsi-043-dont-be-dense/

   Something to watch out for is clapboards nailed directly to the studs without benefit of sheathing, in which case you can't dense pack OR simply foam the cavities. Most homes that vintage used wide-plank sheathing, usually with an asphalt or rosin-paper between the sheathing & clapboards. Before doing anything there, investigate the stackup.

   Air tight drywall on the ceiling works just fine without the $1-2000 in closed cell foam. Using open cell foam to seal the attic floor also works just fine, and would meet code in a vented attic with cellulose on top as the topside thermal barrier, but it's possible to do it all with air-tight gypsum & caulk, if need be.

   Drainage of the foundation on the exterior is the most important aspect for protecting it from freeze/thaw damage. Yes, insulating the foundation will keep it colder, but not substantially wetter. Brick saturated enough to sustain freeze/thaw damage is universally at drainage issue. Insulating won't increase the number of freeze thaw cycles, only the month(s) at which it occurs. Field stone drains pretty well all by itself, but any brick that's below-grade can have issues if not well drained, with good management of surface water. Usually (depending on the mix) the mortar can be protected from efflorescence degradation with a sacrificial parge of lime mortar on the interior prior to insulating, but to avoid freeze thaw spalling you simply must keep it dry enough. If the above grade exterior mortar on the brick is in good shape, dig down to the fieldstone in a few places to inspect the condition on the exterior, which sees as many freeze/thaws as the interior, the brick foundation being at most ~R1 when saturated to those levels.

5. 
   bac478 | Sep 12, 2013 05:39pm | #5

   Thanks again Dana, keep the information coming, I am trying to learn as much as I can.

   This might be a dumb question, but why wouldn't I be able to insulate if the clapboards are nailed directly to the studs? Is it just because water will get into the cavity and soak a sensitive insulation? There is vinyl siding on the exterior but I don't know what is underneath, I will have to take a look.

   What about open-cell in the wall cavities? From what I have been able to read it looks like it is about the same cost as dense pack cellulose but it is a better air barrier. I don't think there would be a vapor problem with that kind of assembly either since open-cell is vapor permeable.

   The methods I have seen for insulating the basement with closed cell foam typically use the exterior side of the foam as the drainage plane. Seems like this would make the brick wetter since water isn't being diverted away to the exterior before it gets to the brick. Instead, it is being allowed to moisten the brick which can no longer dry to the interior because of the impermeable foam. It seems like this would make the spalling worse. I think there is a BSC paper about the dangers of insulation brick on the interior that is susceptible to freeze thaw. The above grade brick looks fin and from what I can tell, the spalling is limited to bricks on the interior wythe.

6. Expert Member
   Dana Dorsett | Sep 12, 2013 06:57pm | #6

   If you sprayed foam on the backsides of the clapboards they would retain rain & dew moisture. In the first season or so the paint would start to peel, and within a decade they would be done from rot, fallling off from rusted out nails, etc. Clapboards need the micro-gap behind them as both a capillary break to keep moisture from migrating inward (which it would, with open cell foam, not so much with closed cell) and to allow at least a modest amount of drying toward the exterior. Most homes built in 1890 will have some layers if impermeable lead paint trapping the moisture in the wood if it can't dry to the un-painted back side, and it simply can't dry toward the cavity through open cell foam in winter.

   With a cellulose fill it would soak up that moisture, and would quickly become saturated.

   But with just the micro-gap between clapboard & sheating, most assemblies do just fine post-insulation, though some may still experience paint-failure, the clapboards themselves usually survive to be re-painted (preferably with a semi-permeable latex.)

   Unlike open cell foam, cellulose can actually be protective of the exterior sheathing by sharing the wintertime moisture burden. Dense-packing in new construction can be as expensive as open cell foam, but from a retrofit point of view half-pound pours have significant blow-out and void problems, and are more expensive. Only in a full-gut situation is open cell comparable on cost/risk to cellulose, but at $3.50/gallon oil there is a serious cost to waiting if you're rehabbing a room at at time, and the cost of open cell foam to do one room at at a time is probably at least 2x as expensive as doing the whole house at once. You need to be spraying at least a couple thousand board feet at a time for it to be worth tying up a truck & crew for the afternoon. A 10 x 15' section of full dimension 2x4 wall at a 20% framing fraction and a window or two is ~400 board feet of foam- they'd have to charge you extra to pay for their road time, as well as the set up and break down time costs. A cellulose crew could dense pack the whole place in under two days, and save you 300 gallons of oil or more in the first season, and you could rehab the place in comfort, at your leisure.

   In US zones 6-8 climates there's a very real risk of freeze thaw spalling on the EXTERIOR side of ABOVE GRADE walls when insulating on the interior. In zones 4 & 5 that's usually only an issue on brick faces with chronic rain-wetting, zero roof overhangs, or poorly routed roof drainage, etc.. Deep below grade freeze/thaw spalling on the exterior is rare (it simply doesn't cycle temperature that quickly or often.) To have freeze thaw spalling on the interior face requires both high moisture content in the brick (from either rain wetting or ground moisture wicking a well as repeated deep cycling between freezing and thawing. Insulating the interior evens-up the temperature of the brick, and lowers range of the daily temperature cycles it experiences- it won't make the problem worse, but the solution is still managing the bulk-water moisture. If there's freeze thaw spalling on the interior, it's likely to be there on the exterior, usually just above & just below grade where the moisture content is still high, and the temperature cycling deep.

   It could be that you just have softer more susceptible brick, and that the degradation isn't really from freeze thaw, but mechanical pressures. In a 50-55F basement even through R1 of masonry it takes fairly cold outdoor temperatures to actually freeze the interior side face of the brick. (What's your zip code, for weather/climate data purposes.)

7. 
   bac478 | Sep 13, 2013 08:00am | #7

   So since the wood cladding is covered in impermeable paint on all sides but the back, it can only dry to the interior. Adding a water sensitive insulation like cellulose would cause that moisture to be absorbed by the cellulose and it would saturate and mold. Adding open cell would limit drying aside from diffusion through the material and would cause the boards to stay wetter longer. Closed cell would eliminate drying completely and the boards would rot. So if I have clapboards nailed to the studs I have to leave an air hap behind them to facilitate drying and redistribution at the interior surface. do I have all that right? The dense pack cellulose is sounding pretty attractive at this point since I could do the whole house in one shot and get at least a little bit of insulation in the walls before the coming winter.

   The more I think about it, the brick is an interesting case. I meant to take some pictures this morning so you could see what is going on in the basement, but I will do my best to explain. The house is built on a slope from front to rear so I have a walkout basement with the door at the back. The rear wall consists of poured concrete about a foot up from the slab with a regular wood framed wall above it. The rest is a couple feet of fieldstone at the bottom with brick the rest of the way up like I had described earlier. There is a decent looking slab poured at two different heights in the basement, but there is a big hole in part of it (maybe 5' x 5') under the stairs. The basement is very leaky in every way possible. There are 3 windows that are nowhere near airtight, one of them isn't even attached currently, so I have a 1.5' x 2.5' screened hole just above grade that needs to be fixed. There are bricks with spalling randomly throughout the interior wall. Some of them are so bad they are literally half gone leaving a hole to through to the next wythe. There is even a brick that was left sitting on the slab in the basement that has completely disintegrated. I haven't look closely, but I don't think there is any spalling at all on the exterior above-grade surface of the brick. Some is painted red, although I don't know what kind of paint was used (I understand latex is the way to go). Interestingly there was a section of the house that was clearly added on not too long after initial construction. I say that because it uses the same style of building with plaster and lathe walls, fieldstone and brick foundation, etc. It is clear where the old brick well meets the added brick wall because they look different. What is interesting is that none of the bricks in the added section are showing any signs of spalling at all. To me this means that the bricks used to build the "initial" house are of poor quality, at least by today's standard.
   It makes sense that insulating the interior of the foundation would even the temperature and could even prevent some cycling. Would exterior drainage be required to prevent further deterioration of the brick, or would the ccSPF suffice as a draining plane?

   I will try to take some pictures this weekend. Area code is 01301

   Do you have a case study or pictures or anything like that for the Worcester project you worked on? I followed the link but there wasn't a whole lot of info available there.

   thanks again for your help.

8. Expert Member
   Dana Dorsett | Sep 13, 2013 11:59am | #8

   You understand the issues of clapboards nailed directly to studs sans-sheathing correctly. The only addition I'd make is that the hazard to the clapboards themselves is independent of the permeability of the paint, only that paint failure and rot will be more rapid with low-perm paint. The rot progress is slower if the clapboards were unpainted or only stained, but eventual failure is just as certain.

   Even 1/4" of air gap is sufficient to be protective, if you need to build out something between the gutted studs.

   Whatever the cause, if you have bricks in the foundation so far-gone that they're completely crumbling & disappearing you really need to take care of the foundation issues on a priority basis. I suspect the real problem is the structural capactiy/quality of the original brick, not a freeze/thaw issue. (The climate in Greenfield isn't particularly severe from a freeze/thaw severity point of view. The 99% outside design temp is only -2F, and the January binned hourly mean temp is in the low 20s.) You may be able to stabilize it with a few poured footings and lally columns, then replace the failing brick with poured concrete or CMU or simply jack the house up a fraction of an inch for replacing the foundation sections that are failing, but a foundation in that rough a shape can't be just parged and foamed-over. Seek professional advice from a foundation repair company. (About 25 years ago I helped a friend stabilize the foundation on an 1889 house undergoing a full-gut rehab in north Cambridge, leveling up the floors in the process. Jacking up the house to deal with it isn't as drastic or difficult as it might sound.)

   The Worcester DER on Crompton Street was done under National Grid's Deep Energy Retrofit program, and Building Science Corp was the primary consultant on it, but SFAIK the project hasn't shown up on the BSC or Nat'l Grid websites. The basic methodologies weren't too different from their usual:

   http://www.nrel.gov/docs/fy12osti/53684.pdf

   https://www1.nationalgridus.com/DERCaseStudy

   The details in brief are:

   Against my advice the owner removed the pre-existing cellulose in the walls, and used closed cell foam in the wall cavities on the theory (newbie paranoia? :-) ) that it was necessary to meet the higher air-tightness thresholds needed for an increased subsidy. It would have made no financial sense to do it that way, and probably didn't even break even (assuming it was needed at all) with the subsidy boost. ( I was pushing that he at least back off to open cell, which would have been as-tight or tighter than the more expensive closed cell solution, with only a very modest hit in overall thermal performance.) But the place did test at 464cfm/50 - pretty damned tight for a 3-story house + full basement, and the bulk of the leakage at that point was identified as poor air sealing on the basement door, which was rectified but not re-tested.

   It was balloon-framed full dimension 2x4s with wide pine plank sheathing. It ended up getting wrapped in the crinkly type Tyvek (detailed as an air barrier) with 3-3.5" of reclaimed roofing iso lapped by a 1" layer of foil faced iso on the exterior, with 1x furring on to which fiber cement siding was added. The roof got 6" of reclaimed iso above the roof deck (with weatherproof membrane between the iso and roof) and 5.5-6" of closed cell (again, against my advice- would have gone open cell there after the dense-pack in netting quotes were sky high ) between the rafters. The 1980s U0.6 replacement windows and remaining original window bits were yarded out, and new U0.18 double-hung Paradigms went in, the antique doors were replaced with R5 doors.

   Two inches of closed cell polyurethane went on the foundation walls and band joist, and 2" of XPS went under the slab (it had previously been dirt). BSC had originally recommended spraying closed cell polyurethane on the floor, was pushing for 3" of EPS on environmental & cost grounds, the owner opted for XPS after BSC vaguely referred to "issues" with closed cell poly urethane in under-slab applications (something that I never got the full scoop on.)

   Each of the three apartments are heated & cooled with a single 1.5 ton Mitsubishi mini-split, two of which are fairly oversized for the loads, but only somewhat oversized for the cooling load on the top floor which gets more sun on both the east and west facing windows. Temperature balancing between rooms is partially achieved via exhaust-only registers for the ERVs on the doored off rooms, with supply-only in the common areas with the mini-split heads. That approach works fairly well on the lower two units, but the mid-summer AM solar gains on the top floor sometimes has (fairly minor) comfort issues the doors to the common area are closed during the hours of peak gain.

   Hot water is supplied by separate condensing Rinnai tankless units mounted in the basement common-area.

   Overall performance has been pretty good- it's even hard to see the heating & cooling loads in the power bill which is predominantly the plug-loads, with large month-to-month variation. So far all of the tenants have been students at Holy Cross University, which is less than a half-mile from that house.

   With the DER subsidy from National Grid the project came in at about what he'd budgeted for doing a much less extensive rehab. At various points he blamed ME for making it a bigger project, (OK, guilty...! :-) ) but now that it's done he's happy with the result. (During the process he wasn't always so sure, but kept the blame-game good-natured.) My role was primarily advisory- I found him the subsidy money, the cheap reclaimed form (saved over ten grand on that part), and technically vetted the thermal envelope design details, and the HVAC proposals. He has since applied some of what he learned on the DER project to the expansion/remodeling on his own home. In the process of vetting the HVAC stuff I learned more about ductless air source heat pumps than I'd been exposed to previously, and have applied that elsewhere too. (That technology has come a long way in the last 10-15 years!)

9. 
   bac478 | Sep 13, 2013 11:48pm | #9

   Here are some pictures of the foundation interior.

   http://s1162.photobucket.com/user/bac478/library/House

   The spalling pattern is kind of odd and randomly distributed.

   There is also a picture of the wall cavity. I looked through the cracks in the boards and there is definitely something besides vinyl on the other side. It almost looks like brown paper, but I couldn't really tell looking through an 1/8" gap.

   What does it look like is going on in the foundation and in the wall? From what I can tell it looks like it would be alright to insulate the cavities. They seem dry and protected to the exterior.

10. 
    bac478 | Sep 14, 2013 07:37pm | #10

    I peeled up a couple layers outside. From what I can tell there is vinyl siding, then about 1/2" of foil faced polyiso then construction paper, and then the original wood siding. Should be safe to insulate I think. At least there is a little bit of polyiso on the outside.

11. Expert Member
    Dana Dorsett | Sep 16, 2013 10:47am | #11

    The half inch iso makes it LESS safe to insulate, but not impossible.

    The foil facer on the iso and it's thickness (or rather lack thereof) are an issue. Foil is an extreme class-I vapor retarder- a true vapor barrier, which eliminates any meaningful drying toward the exterior. But with only ~R3 on the exterior of the old siding/sheathing, when you insulate the cavities with open cell foam or fiber, the average winter temperature of the siding will be below the dew point of healthy-normal interior conditioned space air. When that happens the old sheathing/siding will accumulate moisture over the winter, and give it back up in the spring, and without interior side vapor retarders the amount of moisture will be substantial- enough to sometimes create mold hazard conditions.

    In a zone 5 climate for full-dimension 2x4 framing you'd need twice that exterior R-value to keep the wood warm enough to avoid that issue, with 3.5" 2x4s it takes at least R5 to meet code:

    http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_7_sec002_par025.htm

    In this situation you have a few options, in the preferred order, from a moisture resiliance point of view:

    a. Re-side and add more exterior foam. If you're planning to re-side the place within the next couple of years, this is the way to go- you can insulate now, add foam later with minimal risk. But putting it off a decade or more is risky.

    b. Dense pack it with cellulose, and use a "smart" vapor retarder such as Certainteed MemBrain, or Intello Plus on the interior. As long as you get to the rehabbing the interior within a a couple of years this too should be OK. Smart vapor retarders have variable vapor permeance- when the air next to the vapor retarder is dry, under 35% relative humidity (as the interior air will likely be in winter) it behaves as a class-II vapor retarder. But when the air next to the vapor retarder is much over 40% RH (as the cavity-air will be in spring, when the cellulose and sheathing are releasing their accumulated winter moisture) it becomes fairly vapor-open, and the drying rate is only limited by the vapor retardency of your interior paint (standard latex is typically 3-5 perms.) That way any accumulated moisture dries fast, about 4-5x as fast as it was gained.

    c. Gut the interior and add a flash thickness of at least 1/2"of CLOSED CELL foam, then fiber. Unless the full-gut happens all at once this is going to be expensive on foam (small jobs cost more), and expensive on heating fuel used over the seasons prior to full insulation. But the closed cell foam is 1-2perms, vapor retardent enough to limit moisture accumulation in the sheathing, yet vapor open enough for it to dry at reasonable rates in the spring, and the temperature of interior surface of the foam will average above the dew point of the conditioned space air, limiting the amount of moisture that the cellulose needs to buffer.

    d. Dense pack it with cellulose and paint the interior with "vapor barrier" latex. This is cheap, but limits both the moisture accumulation rate and drying rate pretty severely. Moisture getting by the window flashing, may take a VERY long time to dry, but at least with cellulose that moisture will be redistributed with minimal damage, not concentrating in the structural wood.

12. Expert Member
    Dana Dorsett | Sep 16, 2013 10:58am | #12

    Forgot to mention:

    Yes the brick damage does have the appearance of freeze/thaw damage. The bricks probably vary in both hardeness & porosity (common), but it looks repairable. Have a pro assess it on a site visit though. Once repaired, insulating will limit the number & depth of freeze thaw cycles it sees in a year, but limiting the ground moisture &eave drip-edge splash-back on the exterior is still a priority.

13. 
    bac478 | Sep 18, 2013 09:56pm | #13

    I did a little more reading and understand this vapor stuff a little better now. I went out and actually measured the polyiso and came up with 3/4". That should give me just under R5 on the exterior if it was brand new insulation. This still isn't really enough to keep the interior side of the sheathing warm enough to prevent water vapor from condensing most of the time. However, there are two things that I think help the situation. First, the polyiso is installed over the old siding which should leave a relatively substantial intermittent gap behind the foil face since the insulation is flat and the siding isn't. Second, there is building paper installed between the insulation and the siding which provides another slight air gap. The IRC and other sources allow a class III retarder on the interior as long as the exterior side of the sheathing is vented. There are some problems however. First I don't know for sure what the old wall construction consists of. From the pictures of the interior and what I saw on the exterior, it looks like there is painted wood siding over some board sheathing. Is painted siding over board sheathing considered vented? Seems like similar assemblies have been insulated in the cavity with no problems for quite some time, right? With these things considered would it be safe to insulate?

    On a related note, is there a preferred caulking for air sealing? What about a foam?

14. Expert Member
    Dana Dorsett | Sep 19, 2013 05:23pm | #14

    R5 is enough to meet code with 3.5" cavity depths, a bit thin for full-dimension 2x4s, but I wouldn't sweat that with dense-packed cellulose (but I WOULD sweat it with fiberglass or open cell foam.) Even R4 - R4.5 is a heluva lot better than R2.8 - R3. But cellulose can buffer a lot if you keep it air retardent enough to keep convective transfer between interior & exterior to a minimum. Putting up a smart vapor retarder on the interior as you rehab the place is still going to be worth it when skating a bit below code on the insulating sheathing, to not rely TOO much on the capacity of the cellulose.

    With the micro gaps and the lateral channels of the old painted clapboards you get a bit of capillary break, but no real drying toward the exterior. If it's leaded paint on the old clapboards the sheathing won't dry into the oddly shaped cavity anyway. It's still the R-value of the foam that matters most, and you're a bit shy, but not 3-alarm-no-way-Jose shy of code on that. With 3/4" goods I'd go ahead do it, with the aforementioned caveats.

    Air sealing with acoustic sealant type caulk is tried & true, as are 1-part can foams and 2-part polyurethane kits. When you have a lot of air sealing with big gaps it's sometimes worth springing for a 12 board-foot FrothPak kit, which is a 1.75lb density polyurethane. Both of the big box-store chains usually carry it, but check local inventory before heading out:

    http://www.homedepot.com/p/FROTH-PAK-12-Foam-Sealant-Kit-308900/202892533#.Ujtptj9dA9k

    http://www.lowes.com/pd_144279-236-157802_0__

15. 
    bac478 | Jun 18, 2014 04:39pm | #15

    I'm bringing this one back because I have a couple more questions.
    1) the foil face on the iso is a vapor barrier. The intello is a vapor retarder sometimes. It is not good to have vapor retarders on both sides of the wall. I understand that the intello should open up when risky conditions arise. Is there a case where this arrangement could cause problems? I can't see why, but if I installed the intello and then installed more exterior foam later could there be an issue. essentially the intello becomes unnecessary and seems like it would actually decrease drying potential of the wall.
    2) to install cellulose behind intello 475 recommends horizontal battens. This makes my wiring easier. However, it seems like being limited to only using shallow boxes might cause problems especially where multiple switches, outlets, etc reside in one box. What are the usual solutions? Cut and tape the intello?
    3) I have been taking a look at mineral wool. I have read about the pros and cons. It would be a little cheaper and easier to deal with than cellulose. I have seen more arguments for cellulose than mineral wool but they go both ways. Moisture adsorption and air permeance seem to be the significant differences. I understand convective loops. What I don't know is whether or not I want my insulation to hold a lot of moisture. I understand the buffer effect but it still seems counterintuitive from an engineering perspective. Seems like every other wet part of a building uses moisture resistant materials.

16. GBA Editor
    Martin Holladay | Jun 18, 2014 04:54pm | #16

    Brian,
    The Intello membrane is a smart vapor retarder. If you are installing it on the interior side of your wall assembly, it will perform well.

    I'm not sure where you intend to install the foil-faced polyiso, but if you are installing it on the exterior side of the wall assembly, make sure that it is thick enough to keep the interior side of the rigid foam above the dew point in winter, and everything will be fine.

    If you want to use the Intello membrane as an air barrier, and you want to run wiring in a service chase on the interior side of the Intello, you can make the service chase as thick as you want to accommodate any size electrical boxes you want to install. If the horizontal 2x4s aren't deep enough, you can add 1x4s on top of the 2x4s. Not cheap, but effective.

    Either cellulose or mineral wool can work well in this type of wall, as long as the insulation is installed conscientiously. Use whichever insulation material you prefer.

17. Expert Member
    Dana Dorsett | Jun 18, 2014 05:38pm | #17

    Mineral wool does not have the moisture buffering capacity of cellulose, and the moisture content of the structural wood would peak much higher. Mineral wool does not have tighter air-permeance than cellulose at typical densities. Dense-packed fiberglass does if you take it to 2.2lbs/cubic foot or higher, but not enough to help the moisture migration issues. Whenever you are marginal on exterior-R for dew point control it's generally safer to use cellulose, taking advantage of it's moisture buffering capacity.

    Like MemBrain, Intello becomes quite vapor open when the moisture level of the entrained air next to it in in the fiber layer exceeds 50% RH- more than 10 perms, but it fairly vapor tight when the proximate air is under 30% RH (under 1-perm). So when it's warm enough that the sheathing and cellulose on the exterior side of the assembly are giving up their wintertime accumulation, the air next to the Intello become high RH, making it vapor open. Under those conditions the drying rate toward the interior is limited by the vapor retardency of the finish paint (typically 3-5 perms.)

    Then, when the sheathing cools off and begins adsorbing moisture from the cavity air, the Intello becomes fairly vapor tight, slowing the rate of moisture transfer from the conditioned space into the cavity. This material behavior makes it something of a "moisture diode", since moisture is able to leave at a much faster rate than it enters.

18. 
    user-1061844 | Jun 18, 2014 10:35pm | #18

    Brian, we at http://www.foursevenfive.com recommend service cavities with ProClima's INTELLO Plus" because it assure the best dense packed results - horizontal pockets are created by the counter battens of the service cavity. it has the benefit that you can run wiring there without having to drill through studs and you can add some additional insulation there as well.
    Using battens that are deep enough for deep electrical boxes, can be tricky, as attaching 2x4 on edge takes much more skill/effort then 2x2's or the like.
    If you have a need for a single deeper box, you can use an INSTAABOX or Lessco box" to create the required additional depth in a service cavity (sse image)

    You could use these installation boxes as well, if a service cavity is not feasible - do note that dense packing becomes trickier/requires more staples and deviates from our recommendations (it is shown on the INTELLO product page in the video) - or you can indeed use batt insulation, without a service cavity - but do remember that you should airseal each electrical penetration and for every electrical box there would
    - 1 cable that would pass out through the INTELLO, sealed with Proclima TESCON tape or a KAFLEX gasket
    - 1 wire coming back in through the INSTAABOX.

    For best blowerdoor results and renovation effectiveness (air-sealing is the first priority as it is the most cost effective element you can implement) - you should try to minimize the number of penetrations. Since in renovations there are complications no matter what, because of floor joist, interior walls and other interruptions in your airbarrier - so pay attention to those connections as well (various solutions from ProClima for that are available) to make your airtight layer as continuous as possible

    
19. 
    bac478 | Jun 19, 2014 07:23am | #19

    I know that intello and majpell can be used to hold back dense pack cellulose during installation. The price point on both these products is high ($0.43/sqft for intello and $0.33/sqft for majpell) compared to Membrain ($0.13/sqft). Can Membrain be used while dense packing or will it stretch, tear through staples, or something like that? I couldn't find anything from the mfg because they push blown-in fiberglass instead of cellulose. Is there any installation data for DP cellulose +Membrain?