remove old 1x2....place iso on wall....nail new furring 1x3 over iso...screw/nail drywall

if old 1 x2 are attached well...(not loose when new ones attached ) they can be left in place .....air gap...iso...air...drywall
mac

Hi All, This is my first post and hopefully I'm explaining everything right. I have read through the 4 pages of posts and replys to this original question and I think mine falls into place with this discussion. Our architecture firm is trying to come up with good, solid details for our roof insulation so that our contractors know exactly what to do so we can achieve our necessary HERS ratings. The problem is that all of our homes are shingle roof with 18" R&R shingles on top of 1x4 lath. Traditionally, our attics are vented and uninsulated. But now we are trying to design a tight building envelope so we are in debates about whether it's better to unvent the attic space and make the roof a hot roof by applying 4"-6" of closed cell foam insulation directly to the rafters and backside of the lath, or whether we should run Solarguard sheets up the rafters to act as both an air baffle and a ventilation space. The Solarguard sheets have an R value of @ 9 and act as a nice radiant barrier and might reduce the need for so much spray in, therefor reducing the cost (??). We live on eastern Long Island, which means we have fairly cold winters and very humid, occasionally hot summers (5234 hdd), so there is a great danger of mold and condensation. The question I am posing is which of these methods would be better, and which type of insulation would be better to use, closed or open cell? One of my contractors claims that the closed cell won't allow you to detect leaks and that the water could puddle if it finds a niche. Another claims that the open cell will act like a sponge and soak up and disperse the water nicely to the rafters where it will then wick into the wood and mold there instead because it will have no ventilation to dry it out. Either solution sounds feasible in my opinion, but there seems to be a lot of schools of thought for both, and maybe it is just a matter of 6 of one and a half dozen of the other in terms of the problems we'd face down the road, but I would appreciate any opinions either way. Thanks.

Mike

First off, this statement is incorrect. The term unvented in relation to attic or crawl space simply means they are not vented to the outside. In the case of an attic with under roof insulation you must provide some ventilation, but it will be to the inside of the home, not the outside. Probably the most common method would be small supply and return ducts connected to the heating & cooling system. The same goes for sealed and conditioned crawl spaces.

First off, leaks are bad, no matter what you've got up there, or whether the insulation is in the roof deck or attic floor, but leaks are guaranteed to happen eventually.

Open cell foam is still hydrophobic- it doesn't wick rapidly & easily sideways and hardly at all vertically. Though open celled, it's not exactly "like a sponge"- it won't draw water upward, and gravity is the primary determinant of which way leak water moves within the insulation. As long as you don't have a waterPROOF interior vapor barrier, the leak will be detected pretty much straight down from the actual location of the leak. If/when the timber gets wet it can still dry out through the insulation as water vapor.

Closed cell is highly vapor-retardent as well as waterproof , and will trap the liquid in the roof decking, and when detected on the interior, it can be fairly distant from the actual leak point. In order for wetted roof decking to dry, the other materials in the stackup have to be fairly vapor permeable.

The value of reflective insulation in roof with high R-values of foam insulation is very limited no matter what climate, and low/moderated insulated roofs in heating-dominated 5000HDD climates it's a net loss: You lose some of the heat that would have been transfered into the structure from the solar-warmed roofing during the shoulder seasons, and the savings in AC load, while significant, are less than the "free" heat that would have been gained. I'm assuming you're designing for higher-than code for Long Island, in which case you can forget about using the Solarguard. If the insulation material were fiberglass (which is somewhat translucent to infra-red), there might be some benefit, but even there the benefit is much reduced as the conducted R-value goes higher.

The fact that SolarGuard is a vapor-retarder can also become an issue- in heating dominated climates defining the material layup to dry toward exterior is more reliable for keeping the humidity within the materials low, since 8 months of the year the average dew points of the outside air is below the temperatures inside the wall structure. Keeping the warmer-humid air & water vapor from the interior out of the wall/roof structure helps, so the vapor retarders rightly belongs on the interior. But radiant barriers in roofs work best on the outside of the insulating layer, and placing a vapor-retardent radiant barrier there forces the designer into a less-optimal dries-toward-interior configuration. (Vapor & air permeable reflective insulations exist though, and can be useful in mixed & hot climates when designing for dries-both-ways or outward drying walls/roofs.)

There are volumes & volumes of well documented well-written information on the Building Sciences Corp. website. And (unlike the assertions material vendors, builders, & installers), it's usually backed up with peer-reviewed data, not WAGs, opinions, or grandmotherly building-lore. If you adhere to their roof & wall layups for buildings in your DOE hygro-thermal climate zone (the cooler edge of zone 4, moist) it'll tend to work. DO study and understand the attic venting document:

http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation?full_view=1

If you scroll down to figure 10 in the document you'll note that in Zone 4 no interior vapor retarder is needed, which may be the best thing in a roof structure, since it give it better inward-drying capacity in the event of a leak. (In colder climates during the winter some amount of water vapor finds it's way UP through open cell to condense on the interior of the roof deck unless a vapor retarder is applied. Vapor retardent paint on the warm side of the foam is recommended for Boston, just the other side in zone 5, but won't be necessary on Long Island.)

Keep any eye on this page (they haven't filled it in yet), but it is going to be an example profile for Martha's Vinyard type climate:

http://www.buildingscience.com/documents/profiles/designs-that-work-cold-climate-vineyard-profile/

...which is somewhat closer to L.I. than than Boston (but Boston's still "close enough" to count, only ~250 HHD more than Islip, with a similar humidity profile.)

http://www.buildingscience.com/documents/profiles/c_boston_profile_070908.jpg/image_view_fullscreen

The architects/designers/builder may also find the Oak Ridge Nat'l Labs' clever framing concepts for getting maximum insulative value for no or minimal additional framing expense useful:

http://eber.ed.ornl.gov/DOE_advanced%20framing-770.pdf

The corner clips etc. works, as does the bit about using structural sheathing selectively where-needed, and foam sheathing elsewhere.

On some of their super-insulating retrofit projects BSC has used closed cell foam between the rafters, but IIRC that was due to the narrowness of the rafters (5-6") and the needed high R-value goal (R60), and even more rigid insulation was added above the roof deck to get there. On a new design, with the luxury of being able to specify the rafter depth, type & spacing you can get the necessary R values more cost-effectively with open cell foam and doing it all from below.

Dana1 thanks so much for the detailed reply. We will definitely have to do our homework on this one. And thanks for the links to the Building Science site, I wish we'd had them a month ago. We'd have a lot more hair on our heads...

dmaceld, thanks for the reply and the advice. This is such a learning process for us right now and it's going to be good for us to do the research on our own instead of always relying on our contractors to give us the best advice, since many of them aren't quite up to speed yet either.

I'm still so confused. While this has been a great discussion I still have no idea whether this would be a good idea for me or not. I can probably insulate my ceiling for about $2000-$2500 (fiberglas or cellulose or a combo of both). The quotes for spray foam are about $7k to $9k. My electric bill is about $250 a month and I guess about half of that is for cooling/heating - so about $125 a month. Is it really worth the extra expense.

And then there is still the debate about open or closed. yikes!

It's not uncommon 'monst cheap Yankees to combine it.  In MA you can do a "hot roof" with foam+ cellulose as long as something like 40% (??- I'd have to look it up) of the total R-value is foam, with the cellulose on the interior.  (The reasoning is that the dew point in the thermal gradient through the insulation always occurs in the foam, not the fiber, where it can't get enough air infiltration to get enough condensation to cause a problem, whereas if it were all cellulose you can theoretically end up with a damp-layer in winter, which over time degrades the material.)

The other way to cheap out is to foam-seal the attic floor and blow cellulose over it, and vent the roof.  But in mechanically complicated structures with lots of vents/stacks/can-lights etc penetrating the floor it's hard to get a perfect air-seal.

Particularly in attics, blown cellulose usually performs somewhat better than blown fiberglass both winter & summer. (Fiberglass lets some radiant-heat though in summer, and has higher convection currents within the insulation when it's very cold out in cold-side-up applications, losing R-value somewhat when you need it the most.)  High-density fiberglass  ("cathedral ceiling") batting isn't bad, but it's guaranteed to have gaps at the edges- there's no such thing as a "perfect" installation of batting- "typical installation" performance of batting is ~15% below R-rating, according to research by the folks at Oak Ridge Nat'l Labs.  Spray foams and blown insulations tend to do much better at filling every gap seamlessly.

If you get a roof leak using fiber insulations, cellulose DOES act like a sponge, and you can potentially end up with a large heavy drippy section before it's discovered from below, whereas fiberglass will pass it straight through.  In those instances it would take forever for the section of saturated cellulose to dry, so you need to rip it out and apply some new stuff, whereas often fiberglass can dry in place. (Me, I'll take my chances on the leaks and use cellulose in attic floors- it provides some thermal-mass benefits- more so than fiberglass or all- foam. YMMD.)

Ahh, if it was all cut and dried with straight forward answers, just think how boring life would be!!!!!!! The grinding wheel of differing opinions and experiences is what keeps one's mind sharp!

Great discussion all -

I see spray foam is well lauded by many -

but I've been told that the blowing agents are global warming agents in some cases. Is this true? If so it seems like it might negate the low carbon benefit of spray foam.

http://www.appliancemagazine.com/ae/editorial.php?article=45&zone=214&first=1

While there is plenty of info out there suggesting that foam does a great job there seems to be very little info, in my opinion, as to whether the "substantial" additional cost makes it worth it. I hadn't even factored in the blowing agents.

(OK, this has gone WELL beyond the original thread subject but...)

Blowing agents should be the least of your issues- they've gotten a lot better over the past decade or two- there have been HUGE changes in the blowing agents, and most are getting away from CFCs.  Air-sealing & R-value will more than make up for any blowing agent issues in short years by the increased building efficiency.

But if you're into counting embodied energy, blowing agents, & other environmental footprint issues, cellulose buys you more brownie-points than any other insulation I'm aware of. It uses recycled material from renewable resources, etc. etc.  Recycled cotton batting can be good, but the heavy enviro-impact of cotton agriculture makes it not-so-great if high percentages virgin-stock is used.  But there are plenty of foam systems out there that use low-impact blowing agents these days- if that's an issue you care about, shop around.  Several half-pound foams use water as the blowing agent, and some use agriculturally sourced oils as the chemical feedstock for the foam itself.

Where foams excel is in perfect air-sealing, especially in difficult-geometry framing configurations, and around plumbing/wiring/venting.  This is a consequential factor- it's not all about R-value. R-value is primarily a measure of conducted heat transfer, and infiltration factors can be large, even in new construction.  But in simple stuff like straight walls, dense-packed spray cellulose does "good 'nuff", usually for far less money, with about the same R-value as half-pound foam (open cell), and has other benefits (like substantial hygric buffering to lower the mold potential as well as higher thermal mass.)  But under roof decks there are several other issues, and foam is usually less problematic/more effective than fiber insulations.

When using fiber insulation, you'll almost always get better performance out of blown installation than batts.  Batts are designed to work within standard framing geometries, and real world framing has myriad variations from the standard.  Cutting trimming & stuffing batts to conform well to framing-reality is labor intensive, and errors like compression behind wiring & plumbing are common, not just the gaps impossible to stuff.  ORNL data suggest that "typical" batt installation is 15% less effective than "rated" R-values.  Sprayed insulation conforms to any space, surface & cavity, and dense-packing fiber insulations can air-seal cavities sufficienty to reduce infiltration by over 95% (compared to over 99% for spray foam).

In a new designs you can ususally get better value by oversizing the wall thickesses and dense-packing celullose @3lbs/ft^3 or higher (or dense packing blown fiberglass), and using air-tight drywall techniques & housewraps.  In conventional timber-framed walls with 2x6" or less, substantial performance gains can be had by applying rigid foam sheathing to reduce the effect of the thermal bridging of the studs (1" of XPS or fiber-reinforced iso cuts the thermal bridging in half or more, and adds R5 to the center-cavity R-value.  In a 2x4 16" o.c. studwall insulated with cellulose, fiberglass or half-pound foam, an inch of XPS or fiber-reinforced iso adds ~50% to the whole-wall R-value. See: http://www.ornl.gov/sci/roofs+walls/AWT/InteractiveCalculators/NS/SimCalc.htm. The sheathing in the model is EPS- add another R-1 for 1" XPS/fiber-reinforced iso. )

In an unconditioned attic, splitting the total R-value with half-pound foam on the rafters and cellulose/fiberglass (either on the rafters or attic floor) is usually "worth it",  not purely for the R-value, but for ensuring the perfect air-seal.  Air infiltration in "typical" construction accounts for 25-40% of the total heating-season heat loss.  Winter air-infiltration is driven heavily by the stack effect, and reliably stopping air flow out the top, as well as air flow into the bottom of the structure is critical, far more important in most houses than sealing the windows & doors.  Even if you don't use it anywhere else, foam-sealing/insulating the foundation sill & band joists, and foam sealing the attic will be usually be "worth it".  Basement/crawlspace walls can also be worth it in many/most instances.

An approach to infiltration on new designs is to pick an infiltration factor number, put it on the final punch-list and get the blower-door test to prove it before signing off on it.  At 0.25 air-exhanges per hour (ACH) @ 50 pascals pressure you'll need active ventilation- preferably heat-recovery ventilation.  "Lower than 0.25 ACH" would be the design/construction goal- pick a number like 0.1 or 0.15 ACH@50pasc. as your maximum, and stick to it with verification testing, count on biting the bullet on the active ventilation system costs.  With air-tight drywall technique and judicious foam-sealing this is achievable without resorting to all-foam-everywhere insulation.  It does call for some design work and consistent construction methods up front however.  (It doesn't do any good to use air-tight techniques then let the plumbers & electricans punch 1001 holes in it without sealing every hole.)

Personally, I'm a big fan of going the super-insulation route on any new construction.  On Long Island, witho over 5000HDD of heating load, getting R-40/R-50+ clear-wall value walls & R70+ roofs can be cost effective in new-construction ( if not-so-cheap as retrofit).  Factor in the up front cost savings of the much smaller mechanical systems that would be needed to support the heating/cooling loads, not just the operational cost savings- it's significant.  Generally speaking, it won't be cost-effective to do supeinsulation with foam (maybe, if you can get a good deal on R-40 SIPs, but that's a whole other discussion.)  Double-studwall "Larsen Truss" designs superinsulated with dense-packed cellulose or fiberglass are tried & true, as is the PassivHaus approach using engineered trusses as super-wide studs.  On Long Island you won't need much of a heating system or AC if you go that approach, so mechanical systems costs will be quite ow, and the  relative efficiency of those systems inconsequential. (The Urbana IL PassiveHouse uses a 1kw resistance element in the active ventilation as it's "heating system", yet despite not-so-efficient heating, the house incurrs less than half the national average for total electricity use.)  Saving $20K or more on heating & AC systems can buy a heluva lot of framing & insulation.

Saving $1500-3K/year buys a lot of mortgage too.  Even if superinsulating ends up being a net cost-adder up front, the net savings in operating costs over a decade usually look pretty good in a present-value financial analysis.  (And even better from an environmental impact POV.)   If folded into financing on a 30 year mortgage it can even be a net-win due to the much lower operating costs.  (What's the 10 year NPV of saving $1500-3K /year in after tax costs, when financed by a tax-deductible mortgage? Do the math-  it'll probably beat your 401K even in a best-case market forecast. )

The majority of posts relative to roofs seem to prefer the non-vented attic. My reading of the referenced Building Science articles in favor of non-vented seems to be related to a situation where A/C or ductowrk is in the attic or where creating additional living space is possible.

I am considering an addition on my home where the attic area will be dead space...no air ducts and not even used for storage. In this situation, I am thinking that SIPs for the CEILING, not roof, would be a reasonable choice: I can get all the air sealing between walls and overhead but reduce the area available for thermal transfer as well as reducing the material requirements.

Comments?

A SIP ceiling would have very good air-sealing characteristics provided you didn't punch a bunch of holes in it for electrical, plumbing & vents. There may be loading issues if it has to clear large span (but that can be pre-engineered into the SIP.) Could work.

There's the question of tightly sealed access- do you plan to ever be able to get up there for inspection/repair?

And of course, recessed lighting would be almost out of the question. (Which is no big loss IMHO- downlighting is WAY overdone.)

Renegar,

By all means provide access to the attic area for the new addition.  My project in Florence used metal sips for the walls and flat ceiling.  Energy bills are very reasonable.  If need be, we plan to spray a couple of inches of polyurethane foam on the attic floor.

Dana,

Terminology clarification on air tightness:

0.25 ACH50 is extremely tight, <0.6 ACH50 is the Passivehouse standard. Very tight ACHnatural numbers are in the range of 0.04 ACHnat or so.

ASHRAE recommends mechanical ventilation at tightness below 0.35 ACHnatural, which could be the equivalent of over 5.0 ACH50. The conversion between ACHnat and ACH50 is based on an LBL table: http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/93/930309.html

We often provide CFM50 targets for the contractors, it's the number visible on the blower door while the test is running, and is easy to calc when you know the volume and the desired ACH50. Below 500 CFM50 is good territory to be for any house.

Thanks Jesse (My memory isn't quite up to the task of quoting the real numbers every time, eh? ;-) Nobody should ever just take my word for it- look it up!)

Well, I finally found an acceptable quote as follows;

Open cell foam (Demilec Agribalance Spray Foam) 4.5 inches thick, sprayed to the underiside of roof deck for my 1600 sq ft house $2650. Sounds like a good deal to me. Anyone care to weigh in?

Is it worth asking him to spray to 5.5 inches for add'l R value, or is it not worth it.

Have you checked into the cost of DIY spray foam insulation?  Might be worth your while.

Half-pound foam in my area (central MA) tends to run ~$0.45/board-foot give or take, usually depending on volume and difficulty of installation (it's usually dead-easy, for rafters in attics.)  Total board feet=square feet of coverage x inches of depth- it sounds like the right order of magnitude.

Will that be your only ceiling/attic insulation? (If yes, it's not NEARLY enough for your climate zone.  4.5" only gives you about R16 at center cavity (not reduced for thermal bridging of rafters/joists.)  On Long Island I'd thing something like 2x that would be more like code.  Adding an inch will bring it up to about R20, and lower the loss from thermal bridging a bit.  Personally I'd do it-  the price usually goes down a bit with more volume, so you'd probably be looking at a bit over $3k, but not by much.  But 4.5" may be the maximum allowed single spray for that product (IIRC the max single-shot runs ~5" for most half-pound foams), which means going deeper may require a second pass/more labor expense.  Find out.

If you're splitting the R value with R16 of foam on the roof deck, plus 6"+ of cellulose on the attic floor that should get you there.  With the perfect-seal of the foam at the roof deck, air leaks from penetrations in the attic floor are much less of an issue, since the top of the "stack" in the "stack effect"  is capped so theres not much driving flow between the "dead-air" attic and the fully-conditioned space except much lower convective pressure.  Cellulose is cheap stuff- going with more shouldn't break the bank.  R38 attic insulation is the minimum allowed for new construction in my area, but R50+ is still cost effective, especially if the additional R-value is from open-blow cellulose.  Cellulose will inhibit convection between the conditioned top floor and the semi-conditioned attic better than fiberglass, but foam-sealing all penetrations is still a good idea.

If it's already plumbed & rough wired when the foam guys show up, if you mark where it needs sealing and let them do it with a thin-shot of foam it won't cost much (1" over the gaps is more than enough for a decent air-seal against convection). Then you can blow whatever on top to your heart's content (as long as the ceiling/floor can take the weight load. :-) )  If you're reasonably handy, open blow cellulose can be a DIY project, but if there are any subsidies from the state/federal taxes/local-utilites it may be cheaper to let a pro do it.  (Often true for medium-scale retrofits in MA, where the subsidy is substantial.)

If you can get them to seal & insulate the foundation sill & rim joist with 3" (~R11) of foam on the same trip that'll also be worthwhile, and less money than having them do it as a separate job.  It's not a lot of material, so it it shouldn't be more than a grand or so in most houses, but if they have to come back it'll be more, since it ties up the equipment & crew for the road-time each way on a 30 minute- 1hr. job.  Foundation sills & rim joists are often the single-largest and most-often overlooked contributor to air infiltration- more than all the windows & doors combined.  Sealing it with a tiny DIY spray setup will take more time, and ends up costing as much money in the end (or even more, if having the pros do it is subsidized.)

The biggest DIY kits for 2lb foam (600 board-feet) usually cost ~$1.30/board-foot by the time extra nozzles, respirators & tyvek suits are factored in , which is more than the experienced pros with the temperature controlled heavy duty equipment charge.  I'd only use kits for tiny jobs where the pros can't be bothered.  In my neighborhood 2lb foam runs around $1.15-1.25/board foot, installed, for projects of any substance.  It's almost 2x the R-value per inch of depth, but pushin' 3x the price of half-pound foam.  It's great stuff- adds structure to the building as well as insulation, but it's not cheap.