Replies

1. 
   Richard Beyer | Sep 08, 2014 02:50pm | #1

   George,

   Off-gassing is a risk regardless of CC or OC foam. Roof rot is also a risk regardless of the foam's density. A roofing contractor recently posted on Allison Bailes, PhD blog regarding foam and roof rot. This contractor claims he is removing roofs which have both densities due to rot.

   Everyone takes a risk of odor when they hire a SPF contractor. Industry claims some people are more sensitive than others. I see it as an excuse to a wide spread problem. To minimize your risk industry claims "YOU" need to do your homework on your contractor. The real risk you take is when "YOU" personally experience off-gassing. Is it to late to correct? Many experts say yes and few say no. I am aware of many people who are experiencing what you fear most. Whatever you decide, make sure your contractor is properly insured. ie; Error's and Omissions Insurance, Contractor's Pollution Liability Insurance and Workman's Comp coverage is in place. These policies seem to be the consensus of industry experts to help a consumer who faces odor trouble after SPFI installation. Without these policies you will find yourself eating the cost of remediation and/or years of court costs to recover your damages. Just my opinion.

2. Expert Member
   Dana Dorsett | Sep 08, 2014 05:28pm | #2

   Your local climate bears heavily how risky it is to use open cell foam at the roof deck. Where are you?

   It also matters whether the roof deck is plank, plywood or OSB (in ascending order of risk- OSB is the riskiest.)

   Vapor Barrier Latex runs about 5 perms when applied to un-trimmed open cell foam, which is fine in some locations, a disaster in others.

   Any polyurethane foam risks outgassing of polyols, as well as some of the fire retardents used. Only closed cell foam (ccSPF) risks outgassing of HFC blowing agents (which also add to global warming, BTW- use sparingly.)

   While leaving the pre-existing fiberglass on the attic floor would violate the letter of code when insulating at the roof deck, it's not particularly risky in most climates/conditions, depending somewhat on the R-valve of both the fiberglass and whatever you put at the roof deck. Leaving it in place will reduce the overall heating & cooling loads, even if it puts the ducts in an intermediate layer of the thermal envelope. (I suspect the primary reason for dis-allowing insulation at both the roof deck and attic floor is so that the builder doesn't try to make some R(roof )+ R(floor) = R(code-minimum) type of equation. The Rroof should meet code-min (if you can), but that doesn't mean the insulation on the attic floor still isn't doing significant good, even if it's not as effective as when there is no attic space separating the layers.

   In almost all climates 2" of ccSPF on the underside of the roof deck, and another 6-10" of dense packed cellulose in netting below that would work just fine, despite violating the letter of the IRC:

   http://www.buildingscience.com/documents/bareports/ba-1001-moisture-safe-unvented-wood-roof-systems

   http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_8_sec006.htm

   This works because the 2" of ccSPF is a class-II vapor retarder, whereas even 10" of ocSPF sprayed with vapor barrier latex is a class-III vapor retarder, with about 10x the vapor permeance. With dense packed fiber there will be condensing events at the foam/fiber boundary, but with dense packing the rate of air-transported moisture is pretty slow. Cellulose can even buffer quite a bit of moisture without damage or loss of function.

   Without a crystal ball to predict future energy costs accurately it's impossible to say what the payback period of any of it would be. It's also difficult to say with any certainty how big the efficiency hit from running your existing system is with the ducts not-so-perfectly sealed & insulated and located above the insulation.

3. GBA Editor
   Martin Holladay | Sep 09, 2014 07:31am | #3

   George,
   It sounds like you have done your homework, and you just need to make some decisions. Dana's advice is good.

   Many homeowners invest in weatherization work (air sealing and insulation improvements) even if the payback period is long. There are several advantages to doing this work that may not show up in payback calculations, including improved comfort and a reduced carbon footprint. Moreover, there is always some uncertainty about payback calculations; investments in weatherization work will reduce your exposure to sudden energy price spikes.

   If you have air handlers and ductwork in the attic, you should do your best to bring your attic inside your home's conditioned space. When this equipment is located outside of your home's thermal envelope, you are paying through the nose for energy that is released into the great outdoors.

   If your roofing is getting old, you might consider installing rigid foam insulation on the exterior side of your roof sheathing, followed by a second layer of roof sheathing and new roofing.

4. 
   spup345 | Sep 09, 2014 11:28am | #4

   Dana- Are you saying that if I seal my ductwork connections better (i.e. mastic, etc.) and make sure it's insulated properly (right now it'll all insulated-flex, but some are crushed a bit so I'd replace those to increase air flow), that having the air handlers/ductwork in the attic (and the ductwork would be covered in the cellulose, just not the air handlers which would be dammed off), that the payoff b/w foam & cellulose may not be an expensive difference in my case? I've seen a bunch of articles that say air handlers/ducts in attic tip favor in foam, but if that can be minimized...makes my decision a bit easier...

   (edit: Martin - you seem to imply that I may be wrong above...that it still could be very tangible difference in expense. Also, per your suggestion....my roof is in good condition, probably 5-10 years old at most)

   Since you asked, here are the home details:
   -Location: Zone 5 (4910 heating days per iccsafe.org website)
   -Blower Door: ~5800 CFM50
   -Sq. Footage: ~6750 sq. ft total floor area; ~6000 sq. ft heated floor area (2 upper floors, 1 basement partially above ground, 1 3-car attached garage level with basement so it has rooms above it)
   -Vinyl-sided, wood construction – 1982. Approx. 100 sq. ft of uninsulated cantilevers
   -Roof: Gable roof (2 – see attics below) - Plywood w/ brownish-colored shingles (oriented northeast/southwest)
   -Heating: 4 baseboard heat zones which includes 1 in basement – 80% efficiency
   -Cooling: 2 central air zones (one for each above-ground floor); 1 dehumidifier in basement
   -2 Attics (1 for main house w/ hatch, smaller 1 above rooms above garage w/ small door entry – rafters/collar ties, not a truss design) – each with gable vents, ridge vents, and soffits
   Main Attic 1: ~5.5” fiberglass insulation (R-7) on floor; Contains the 2 air handlers + insulated ductwork (leaky connections…). Contains 1 temp-controlled roof ventilator
   Smaller Attic 2: ~10.5” fiberglass insulation (R-13) on floor, also some ductwork here
   -Garage ceiling (660 sq. ft) & walls: A few inches of fiberglass insulation currently
   -Rim Joist: Looks like possibly a little fiberglass insulation shoved in there, but don’t think it’s doing much
   -Have 2 bay windows + most of my upper floor
   -Cooling Usage: Keep central air around 73-74 on both floors at all times
   -Heating Usage: Range between 68 (night) to 72 (day)

5. GBA Editor
   Martin Holladay | Sep 09, 2014 11:38am | #5

   George,
   The way you have worded your question is confusing, but I think you want to know how to choose between these two options:

   1. Leaving your air handler and ducts in an unconditioned attic; sealing existing duct seams and verifying that the ducts are in good condition; and adding cellulose to the attic floor.

   2. Creating a sealed, conditioned attic by installing spray foam insulation on the underside of the roof sheathing.

   In my opinion, Option 2 will cost more than Option 1, but will yield better performance (assuming, of course, that the specs are correct and the work is done well). It's hard to generalize, however, since construction costs vary a lot from one location to another.

   You have to look at your budget and get some bids before you can determine the best way to proceed.