Hi, I am currently an Owner/Builder and am trying to come up with an insulation strategy for insulating a new home..... I purchased a victorian style home from a gentleman who is unable to finish it. The house is currently framed, sheathed, wrapped and has 1" of rigid foam on the exterior. The roof and soffits (continuous vented aluminum) are also complete. The inside is completely devoid of anything other than the framing.... No mechanicals at all. This a rendering of the home:
http://imgur.com/r3xgr.jpg
http://imgur.com/ut81q.jpg
The walls I plan to have air sealed with a scratch coat of closed cell foam, then use batt insulation (2x6 framing). The attic, however, I'm not sure what to do with. We intend to eventually frame out the third floor, so I'm hesitant to insulate it using conventional techniques. Would an unvented attic be the way to go here? I was thinking of just having 3-4 or so inches of cloced cell foam sprayed into the rafters, so when the time comes to finish it, I wouldn't have to redo anything. Is this appropriate for a southern Wisconsin climate? Any thoughts? -Kyle

What type of foam board is on the exterior? Does it have poly or foil facers?  (Brand name might be useful here.)

Flash & batt works, but in your climate you'll still need to use air-tight methods on the interior wallboard and vapor-retardent latex paint to limit wintertime moisture accumulation in the studs. Wet-sprayed fiber insulation (with water-activated adhesives) will outperform batts for the cavity insulation.  Batts are impossible to install perfectly- even less so over less-than perfect surfaces like your flash of closed-cell foam, but sprayed insulation makes it's own perfect fit around everything, limiting internal convection currents, leaving no voids or compressions. Going with spray cellulose would also give the structure a hygric buffer, wicking any condensation or incidental minor bulk water incursions away from the wood, protecting it.  New-school super-fine sprayed fiberglass works well too (much better than the coarser-fiber stuff), with similar R/inch as cellulose, but no hygric buffering.

Going unvented attic with 4" of cc foam on the rafters, with the rest of the cavity filled with better quality spray fiberglass (eg JM Spider) also works. (See RR-1001 for confirmation that it will keep the roof deck dry enough for your roofing material type- you can probably get away with 2" of ccSPF, the rest spray fiberglass in southern WI if you have dark shingles.)  Code in southern WI calls for R38 min, but R50 would be cost-effective if the bulk of the R is in fiber rather than foam. (4" of cc foam is only ~R24.)  At only 3" Spider is rated as the (code required) ignition barrier for the foam, if you wanted to leave it open. (But it'll perform better from an insulation point of view if you have an interior-side air-barrier.  A layer of interior gypsum and vapor retardent latex would be a good idea, but don't use highly vapor retardent goods like poly on the interior if you're going  with 2" or more on the SPF.)

You don't say how deep the rafters are, but if they're 2x8s, 2" of ccSPF would give you R12, and the remaining 5.25" would be worth ~ R21 if done in Spider or at 1.8lbs/ft³ density, for a total R31-33.  If you went with 4" ccSPF you'd be at R24, and the remaining 3.25" of space filled with Spider would bring you up to the code minimum ~R38.  If they're 2x10s you can cheap out, put in 2"  (R12) of foam, fill the remaining 7.25" with 1.8lb Spider and get R39-R40.  If they're 2x12s you can hit R50 with 2" foam, 9.25" Spider.  (Be sure to specify 1.8lb minimum nominal density for the  since the lower density 1lb Spider is lower R and allows much more air movement within the layer which could lead to more air-transported moisture condensing on the rafters.)

You can probably use a foam/cellulose combi in the rafters as well, but it has a slightly lower R per inch than 1.8lb Spider, you'd just squeak code minimum with 2x10s with only 2" of foam, but with 2x12s  you'd hit ~ R46-R47.  Resistance to convection is still very good with cellulose- far better than batts.  (One of JM's marketing lines is to harp that it's "as good as cellulose" on convection losses, but their data that proves it is at densities somewhat higher than 1.8lbs.  At 4lb density Spider is slightly better than 4lb cellulose on air flow, but higher R.  But that's higher than any standard installation density for either.)

Thank you for the generous amount of information. The foam is not foil faced, and to be honest, quite weathered. It is now yellow in color (from pink) and you can almost rub powder off with your bare hands. The siding person mentioned I should probably wrap it again, since, he doesn't think tape will stick. Will there be any issues with having the rigid foam between two layers of housewrap?

I've scratched batt insulation of the list and it looks like air sealing with CC then filling the rest with some other blown or sprayed material will be the best of both worlds from cost/performance perspective.

The rafters are 2x10, 16" OC. It sounds like you are saying 2" of CC with 7.25" of spider will get me to code compliance. The attic will likely remain unfinished for several years, then framed in with some of the ceiling being shared with the rafters. At that point I could look at supplementing?

FYI: The shingles are are a medium brown color, and the decking I believe is likely standard felt/OSB.

Posted By beckkl on 02 Jun 2010 04:49 PM
Thank you for the generous amount of information. The foam is not foil faced, and to be honest, quite weathered. It is now yellow in color (from pink) and you can almost rub powder off with your bare hands. The siding person mentioned I should probably wrap it again, since, he doesn't think tape will stick. Will there be any issues with having the rigid foam between two layers of housewrap?

I've scratched batt insulation of the list and it looks like air sealing with CC then filling the rest with some other blown or sprayed material will be the best of both worlds from cost/performance perspective.

The rafters are 2x10, 16" OC. It sounds like you are saying 2" of CC with 7.25" of spider will get me to code compliance. The attic will likely remain unfinished for several years, then framed in with some of the ceiling being shared with the rafters. At that point I could look at supplementing?

FYI: The shingles are are a medium brown color, and the decking I believe is likely standard felt/OSB.

If it was pink it was probably Corning's version of XPS, which will be vapor-permeable enough to allow the assembly to dry.  You can use latex primer on it anywhere you want tape to stick.  Taping the seams & caulking the edges turns it into an air-barrier, but wrapping it with housewrap or felt doesn't hurt- both are highly permeable. 

In the damp climate of WI I'd highly recommend building-in at a 3/8" rainscreen gap between the siding & housewrap/felt too, which keeps the structure even drier by allowing the drain-plane to dry quickly.  There are commercially available mesh products for establishing the gap, but moisture resistant furring through-screwed into the studs, mounting the siding to the furring also works.  That little bit of dead-space adds some R, but it's primary benefit is to keep both the siding and the wall assembly much drier.  By relieving the pressure, even wind-driven rain has a hard time soaking the housewrap, and with an air layer to dry into the housewrap and the back side of the siding never stay wet for long.  (Ten millimeter rainscreen is now required by code for new construction everywhere in Canada.  It arguably should be in the US too, anywhere it rains more than 15-20"/year, since it adds a lot of weather resiliency to the structure for low additional cost, but SFAIK it hasn't made it into code here yet.)  The concept isn't new, and has been used in commercial construction and with residential stucco siding for a long time, but has not been commonly used with other siding materials until recently. It's essential when using reservoir claddings that wick water in, like stucco, brick, or stone, but it makes a real difference with all siding materials.

Yes, 2" ccSPF +  either 7.25" 1.8lb-density Spider or  spray-cellulose gets you to code, unless your town exceeds the state code for the heating-degree-days you get.  (Colder areas of northern WI are required to install R49-min- the state of WI calls it out by the very local climate, not a single statewide number the way it is in some other states.)   With cellulose you'd still be required to put 1/2" interior gypsum as an ignition barrier for the foam, but not with Spider.

A decade or two down the road, putting panelized iso above the roof deck when it's time to re-shingle can bring the R up considerably.  Several iso & EPS manufacturers make both vented & unvented panels with OSB nailer deck pre-applied to the rigid foam panel. (That's my own long term strategy for dealing with mere 6" rafters in the cathedral-ceiling attic rooms in my antique bungalow.)  IIRC you can get up to ~ R25 in panelized iso w/ nailer deck.  (Atlas & Hunter are the vendors I'm most familiar with, but there are others.)

Again, thank you for the generous and thoughtful reply. It will help me sift through the crap when evaluating contractors. I will definitely look into doing something to provide some separation between the XPS and the vinyl siding. That was also mentioned to me by one of the siding contractors (nice to see people are learning this stuff).

I'm in Milwaukee so I think I can get away with R38 until we figure out what we are doing with the attic.

I can sympathise with your situation, my last house was a 1925 bungalow. Let's just say we moved our master BR to the downstairs in the summer

Thanks for the sympathy- but it's a great house- very "arts & craftsy", it just needs work (as does most any house built in 1923.) Since moving in I've reduced it's energy consumption by about half, and by the time I'm through messing around with it it'll be under a third of what it was using in 1995, despite having added more than 500 square feet of additions in that time. (Houses are never actually DONE, really...) The retrofit game is a bit different from new- construction, but it's possible to eventually get there.

Not to hijack the thread but my wife and I are having our first home built in New Hampshire and im considering something very similar. I thought of doing a scratch coat of foam insulation on the exterior walls and roof and filling in the rest of the 2x6 studs and ceiling with cellulose.
Just not sure if we should use open or closed cell foam for the scratch coat and whether or not we should go wet or dry cellulose. The house will be approximately 1500sqft. and 2 story. Not sure on a basement yet.
To save money im thinking about getting some Tiger foam or a similar DIY kit and doing the scratch coat myself.

Feel free to chime in.

Not at all. My problem is that my house is basically a box. 22ft (roughly) high walls by 52 feet long by 30 feet wide. That is a lot of tiger foam. I figure it would take at least 6 of the 600 board foot kits to do a scratch coat of 1". I'm praying the bids come back less, but I doubt it. Would it be more prudent just to get a kit and go around and spray the cracks? Then finish with another product? Or would that be totally useless?

Again we are similar. Our lot is only 70ft wide and 179ft deep. The house plan we are set on, price permitting of course, is 30ft wide and 42ft deep. Our variance was approved for 32ft wide. I believe the house is 30ft high(probably at the highest point?). But yeh it is a lot of foam. Thing is if youre doing it yourself there is no labour costs. But filling in the cracks/corners is another option. Id probably still want to do the entire roof though.
Cost is definitely of concern too. I dont want to run thousands over if we were to go just batts.

Posted By Slug71 on 08 Jun 2010 08:25 PM
Not to hijack the thread but my wife and I are having our first home built in New Hampshire and im considering something very similar. I thought of doing a scratch coat of foam insulation on the exterior walls and roof and filling in the rest of the 2x6 studs and ceiling with cellulose.
Just not sure if we should use open or closed cell foam for the scratch coat and whether or not we should go wet or dry cellulose. The house will be approximately 1500sqft. and 2 story. Not sure on a basement yet.
To save money im thinking about getting some Tiger foam or a similar DIY kit and doing the scratch coat myself.

Feel free to chime in.

Closed cell foam, wet-spray cellulose.  The closed cell stuff is still more vapor-permeable than the sheathing at an inch or less of thickness (so you won't be creating vapor-trap issues) and it won't be compressed by cellulose the way the much lighter open-cell foam will.  With foam for an air-seal the advantages of dense-packing the cellulose are much reduced, and with wet-spray at standard densities it won't settle over time.  With dry-blown you'd have to dense pack it to avoid settling over a coupla decades. Wet sprayed would be less material and less labor == more cost effective.

But for 2x6 studwalls some amount of exterior rigid foam as a thermal break on the studs would be cost-effective in NH. (At least an inch of XPS sheathing.)

Tiger Foam is closed cell, but if you add up the cost of the tips/suits/foam for even the 600board-foot kits it's usually more expensive than the installed-price from a pro with the better temp-controlled spray equipment (not to mention, more experience==less likely to screw it up.)  If you have more than a few hundred board feet to do (and almost any house would) it's usually cheaper to contract it out.

It's important to use air-tight methods on the interior wallboard as well- caulk/foam every penetration, seam & edge, and use a vapor-retardent latex primer to limit the amount of wintertime moisture loading of the wall via vapor diffusion.  Cellulose will behave as a hygric buffer- it can take on a significant amount of moisture, wicking it away from structural wood, but it needs to be able to release it as well- making it only semi-impermeable on the interior enhances it's inward-drying capacity during non-winter months. Poly or foil vapor retarders should be avoided.

For the roof, if you're applying it directly the roof deck you need at least 2" of closed cell (4" is better) to avoid vapor-accumulation of moisture in the roof deck if used in combination with a cellulose rafter-bay fill in your climate zone.  If you provide soffit & ridge venting and something to maintain a gap between the deck & insulation, an all-open cell solution works.   If it's a ventilated attic and the insulation is at the attic floor level, either a full open-cell foam job, or inch of closed cell between the attic floor joists/truss-chords as a seal, and open-blow dry cellulose over that works. 

An alternative roof insulation would be to use a flash of closed-cell on the roof deck, and panelized rigid iso with factory applied nailer-deck (eg Hunter Panels or Atlas), can be cost-competitive if the roof lines are simple.  Then finish out the R with wet-spray cellulose blown-in-bag from below, or JM Spider super-fine blown fiberglass:  great outdoors/shingles/panelized iso (up to R25-ish)/roof deck/inch of cc foam (R6)/fiber (up to R30)    The advantage of above the roof deck iso is performance- it provides a significant thermal break over the rafters/trusses, so at equivalent total R values it outperforms an interior-only insulation job.  The interior foam is to ensure a good seal, but  if there are no overhangs (or you use post-applied framing for overhangs) you could use air-tight sheathing methodology to get the perfect air seal and do cellulose-only on the interior, provided at least half the R is on the exterior of the roof deck.

For the foundation, be sure to use a VERY good capillary break at the foundation sill (like copper flashing, or 10-mil poly under the sill gasket) to avoid ground water wicking up into the studwall, or the cellulose could accumlate significant moisture year round.  If you use insulated concrete forms, the bulk of the foundation insulation is already in place. Be sure to A: Put a capillary break like 10mil poly between the footing & wall B: waterproof the hell out of the exterior EPS before backfilling and C: use only vapor-permeable materials on the interior finish wall to avoid groundwater accumulation in the concrete to potentially wick into wooden structural materials.   In most of NH the subsoil is cold & wet enough that 1-2" of EPS or XPS rigid board under the slab (and above a 10mil vapor retarder) is cost-effective too.

beckkl, I think that going with an open-cell spray foam insulation as recommended by this company that does Milwaukee insulation, will be better to reduce air and water leakage into the attic. The only issue is that there's a chance it might be more expensive than what you're originally planning to go with, but I'm not sure on specific pricing. The specific product they carry is called Icynene

The design of the home you have shared in the post is really impressive one. Liquid EPDM, Liquid Rubber Coatings, can be one of the useful choices to get rid of any leaks for your home.

What is this, spam week on the forum?

Open cell under roof decks is a BAD idea in cold/very-cold climates in terms of the longevity of the roof deck- too much winter moisture finds it's way in. But as little as 2" of closed cell against the roof deck will limit that to tolerable levels. Open cell does NOTHING for water leakage into the attic (a roof leak will drip-drip-drip right on through, even saturating the open cell foam.) Closed cell stuff is waterproof, but makes it very difficult to find the leaks before the damage is done.

The 2lb density Icynene product is more permeable than generic closed cell SPF (and lower R), but at 3" or more it'll be sufficient to protect the roof deck in most of the lower 48 of the US. (In my own home I have open cell under the deck in places, but with a plan to add exterior rigid-board of equal R value within the next 5 years, which will raise the temperature of the roof deck in winter above the interior air's dew point- sufficient for long-term protection against rot conditions.)


EPDM on the exterior brings it's own set of design issues in cold climates, since it effectively blocks all drying toward the exterior year-round, making it difficult to control wintertime accumulation of moisture in the roof deck, as use of interior-side vapor retarders can thenl create year-round moisture traps (unless very carefully specified for the climate.) With EPDM roofs it's better/safer to put the insulation between the structural roof deck and the EPDM layer essentially putting all structural wood inside of the conditioned space where it's humidity is well controlled.