spray foam also reinforces the roof system.

my in-laws house (icf- spray foam under roof deck) went though a tornado with just shingle loss... NO STRUCTURAL DAMAGE

I have a home in Coastal California that was built in 1940. There is no insulation. I am interested in applying closed cell insulation to the bottom of the roof rafters, but can find no source for it, other than shipping it from back east. I find many online outlets for it, but not in California. The shipping would kill me. Does anyone know of a retail source of closed cell insulation in California?

Has anyone applied the 2-part closed cell insulation yourself? Any advice?

Thank you.

I just posted on the SIP forum about this subject. I normaly only build with steel SIPs.But when I am forced to build with wood framing and sheathing .I always use spray foam to help bond roof decking to the trusses,makes it much stronger,and the r value well worth it.And as a bonus you will need less heating and cooling.And down here in florida it is a must!
Think Green-Save Green
Thanks,Ralph Locke ,Deland,Fla
www.Lockeconstruction.info
[email protected]

Guys i'd like to ressurect this topic for a newbie like me who isnt a techie...

Im building a super insulated ranch home in Maine where its extremely cold climate. Are you saying that instead of dumping a couple feet of cellulose in the vented roof, to NOT vent the roof and spray foam the underside of the roof and NOT use the cellulose at all ?

Newbiejohn,

Yes.

Newbiejohn,

By the way Maine isn't cold, we Minnesotans go to Maine in January to suntan.

Opinions vary on that. Building Sciences recommends both vented & unvented attics.

If we insulate the ceiling and vent the attic, why would went insulate the underside of the roof? To keep the attic at a more constant temperature? Is that cost effective?

You wouldn't. It's an either or proposition...

I misunderstood your statement "Building Sciences recommends both vented & unvented attics."

I think Grainger sells 600board-foot 2-part kits for 2lb foam, but unless it's a very small application that contractors won't touch, you're better off letting a real insulation contractor do it. 

Around here multiple contractors all install 2lb foam for ~$1.10-$1.25/board foot (last time I got it quoted, anyway, which was over a year ago now.) This is comparable to what the DIY kits cost, before you start adding up the cost of the extra gun tips, protective clothing & respirators etc.,  Then there's the learning curve and the lousier temperature control you have with the small kits vs the high-tech commercial sprayer controls it goes on...  Keeping the component temps in the right range is critical for getting consistent results- the commercial sprayers control that temp all the way to the spray gun with good precision, while with the kits you have to goof around getting and keeping the tanks at the right temp.  Spraying lowers the pressure, and they cool off as you spray, and the temps in the hoses themselves change on you depending on the air temp, etc.  It's not rocket science but you'll end up with a better job (or at least somebody else to blame :-) ) for the same money if you let a foam contractor do it for you.  The better equipment & experienced technicians actually count for something (at least most of the time.) Get references and actually LOOK at their work if you can, but most are pretty good, and will do the job for the same money (or less) than what it would cost you for materials & tools (let alone the value of your TIME.) 

Those kits are better used for less critical jobs like lining pickup-truck beds or air-sealing around plumbing, etc than they are for full-on insulation jobs.  I'd only go there if I were truly desperate and no contractors were available. YMMV

So what is the REAL advantage of spraying under the roof instead of insulating the ceiling? Is it only if you want to use the attic space? If in cold climate and I didnt want to use that space, I wonder if its worth the trouble..

In some cases the advantage is slim/none.  But in houses with many penetrations of the attic floor (for electrical, plumbing, or worse-ductwork) it's easier to get the perfect air-seal by going with an unvented attic with insulated rafters.  Sealing around attic-access doors also becomes less of an issue since the insulated rafters form both a pressure & thermal boundary.  In heating dominated climates insulating between the rafters it keeps the exposed wood of the rafters & attic joists on the warm side of the thermal boundary, limiting condensation & mold potential.  It also keeps ice-damming under control far more reliably than any roof ventilation scheme.

In air-conditioning dominated climates, insulating with foam (either on the rafters or the attic floor) outperforms fiberglass at equivalent R-value due to the translucency of fiberglass to radiant infra-red.  (Foam won't necessarily outperform cellulose on the attic floor if all penetrations are perfectly sealed however.)

Even an inch or two of 2lb foam adds significant structural rigidity & adhesive bonding, lending resistance against wind-loading/hurricanes- it's like an extra-extra thick coating of Gorilla Glue keeping it all together.  (Half-pound foam, not so much.)

Continuing this thread I would appreciate some help with an insulation decision.

I have purchased a fire damaged 1750 sq foot, hip roof ranch bungalow home in Florida zone 1. I am doing an owner build for the restoration. All the drywall has been removed so the home is now a bare shell. I have built in the north, but not in the south. The engineer working on my permit drawings is suggesting Icynene (which I have used before) on the underside of the roof. I’ve read the various debates here and elsewhere and believe it to be one of the better ways to insulate in the south. However the extra cost gives me pause, particularly because this house will be a vacation property and for the few weeks a year the house will be occupied the A/C is unlikely to be on. Thus I will never recoup the added expense.

My thoughts are to put the ductwork below the ceiling in the conditioned space spray 2 inches of Icynene on the top of the ceiling, sealing it up well, then blow in cellulose to meet the R30 code. This is often done up north but with a vapour barrier on the warm side of the house. For this home there is no vapour barrier, so the question is; is 2 inches of the open cell Icynene, (a little over R7), enough foam to prevent condensation within the product in a zone 1 area (WPB)?

Further, the walls are currently exposed block with 1X3 strapping 16 inches on center. My thoughts on insulating the walls is to use ¾ inch foil faced iso board (tapped seams) on top of the strapping and screw through it to attach the drywall to the existing strapping. Good idea or another suggestion?

Thanks,

John

jcwells, if you re-build and make it a really tight house, but only occupy it for a couple of weeks a year, wouldn't you run into mold problems if the house is closed and locked up with no AC for months at a time?

John

Read your post,Being a green builder in central fla,you have thought it threw very well,but I like to put the spray foam about 6 to 8ins on the back of the deck boards to tie in decking boards and trusses for strength and R value.Which means you need no ventilation in attic area and plenty of space to run ac ducts.For your concrete walls we like to install the blue board with is a closed cell foam which you can get at lowes between your fuffing strips. The more r value you add the lower the power bill and better for resale value later down the road..........

Think green-Save green
Ralph Locke, Deland,Fl
[email protected]

Uh... up north the warm side it the INSIDE of the house, but in Zone 1 it's flipped completely the other way- the warm side is ALWAYS considered to be the exterior, and that's where the vapor retarder belongs (hard to think that way if you've mostly lived/built north of the 45 parallel, but 'tis true!) 

Do NOT put foil faced iso on the interior (but it's OK on the exterior in Zone 1).  In the attic, spraying the icynene on the rafters then filling in the floor with cellulose is probably a better stackup than icynene on the attic floor with the cellulose on top.

Whether you go for a vented or unvented attic, the roof type dramatically affects the vapor drive.  Terra cotta tiles will hold a HUGE amount of water, and having some drying capability on either side is a good idea.

Dew points in hot humid Florida are quite high- no matter WHAT you'll likely need to provide some mechanical drying control for the down period, no matter how tight you make the house or how high you let the temps run when not occupied.  A dehumidifier on an accurate humidstat to keep the RH under 60% will be cheaper to run than using the AC.

Icynene is generally preferred to cellulose in the walls since it's hydrophobic and will dry without losing function even if allowed to saturate, say in a hurricane or flooding event.  Cellulose would take weeks/months/years to dry, and wettiing/drying induces shrinkage (even dense packed- about the only way you CAN get settling in dense-packed cellulose.)  But sprayed cellulose (which you can do with open studs) will form about as-good an air barrier as icynene, provide a measurable thermal-mass benefit, and a hygric buffer moderating the RH of the structural wood (the wood will stay drier, lowing the mold potential.) 

No  matter what, DO NOT use interior vapor barriers, highly vapor-retardent paints or wallpapers (like vinyl or foil types) or you'll create mold issues.  Let the walls breathe (vapor-pressure, not air convection) more toward the interior than the exterior. Again, it's the inverse of what happens in heating dominated climates.

Were it me, I'd probably bite the bullet and foam the walls-  potential problems will be fewer, and resale value likely higher, but a no-vapor-barrier sprayed cellulose (with at most, UNfaced polyiso on the interior for thermal break at the studs) would also be good.  A skim coat of 2lb foam under the roof deck with cellulose below will put the vapor barrier on the correct side, and provide a hygric buffer for stabilizing interior humidity.  Keeping the AC ducts & air handler completely inside the thermal boundary is also the right way to thing.

Google [building science hot humid] for best practices on insulation & vapor retarders in FL- trust me, it's WAY different than what you're used to.

Thanks for the responses. I’ve since had a quote on Icynene (or equivalent) for the full attic sheeting and it’s not too bad. Given the extra freedom it gives us for duct placement and flexibility with electrical changes down the road, I am strongly leaning toward this for the attic. I also like the idea that we can get the house insulated now, rather than wait until electrical and drywall is completed. As you can imagine the house warms very fast with the attic open to the house.

I am still uncertain on the walls however. Remember, I have no stud cavities, just 1X3 strapping on top of the block. I don’t think ¾ inch of ½ pound foam would do that much good in those cavities (difficult to spray too), whereas ¾ inch iso board over the complete wall with no thermal breaks, gives me R5 plus a ¾ inch air space over the full wall. I realize that the foil faced iso is a vapor barrier, but from what I have read the dew point is within the board so the foil does not create a condensation problem. I like the idea that it does, however, restrict vapor entry into the house even though technically it would be better on the outside (not an option). Still thinking on that one.

Further, I’m surprised that the consensus is I will have mold problems in the unoccupied house. With nothing to trigger condensation and a careful selection of finishes, I would not have thought this would be a problem. Can anyone share any first hand experiences of homes left unventilated for months in a zone 1 climate?

Thanks,

John

In the humid south any 'almost closed' container accumulates moisture inside. It's almost impossible to have a completely air tight container, especially a house. This is a particular problem with equipment such as motors and valves, wrapped with plastic, stored outside. What happens is the container acts as a vapor pump. In the night when the container cools down and the air inside contracts it pulls in outdoor air that has a higher humidity than daytime air. In the daytime as it heats the air expands and is expelled out. But the air is now warmer and can hold more moisture so it doesn't carry the same amount moisture back out that came in. The result is over time the humidity level continues to increase inside the container and the vapor condenses into liquid water in the cool of the night.

I wouldn't gamble against this happening with a house that's closed up tight in a humid climate.

I worked at the Strategic Petroleum Reserve in Louisiana and Texas. We had to completely strip the interior of an office building near Houston because it had vinyl wallpaper on the walls. Tremendous amount of mold built up behind the wall paper because of humid air passing through the wall and coming up against the drywall. Plan on humid air passing through the blocks.