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Spray foam against roof decking in NJ Victorian? Architect not sure its legit.

Kimball_house | Posted in Energy, Heating & Insulation on March 14, 2010 12:15pm

We are planning a renovation of our 1905 Victorian 3rd floor gable end attic space in central NJ and I would like some input on insulation.  The space is currently used as a play area by the kids.  It is not well heated or cooled.

We will be adding a few dormers and a single bedroom and bath of about 600 SF.  The architect favors familar solutions with a ventilated roof using foam channels and fiberglass batts.  From my reading this is suboptimal technology.  I favor sealing the roof with closed cell spray foam against the roof deck and down to the top plate and filling the remainder of the rafter cavity with batt insulation, or I suppose we could use spray foam to fill the cavity completely, but I gather than can be expensive.  The architect thinks this is not within code in NJ.  I think this is unlikely to be true as there are plenty of contractors offering spray foam of roof decks, and NJ follows the national building codes.

In addition to foam insulation is anyone familiar with adding insulated panels on top of existing roof decking?  That seems logical to break thermal bridging.  We have to tear the roof off down to the decking, and I am not sure if it will be plywood or might be lapped boards.

I do not know a contractor in central NJ familar with these methods.

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  1. GRCourter | Mar 14, 2010 12:13pm | #1

    Spray Foam

    I have been spraying Tiger Foam for over 2 years, and have done quite a few roof bottoms.  Closed cell is the most expensive, but there are some ways to reduce the cost.  If you have 2x6 roof rafters you may try spraying 1" of foam, to seal the deck, and add 3 1/2" of Dow Safetouch and then a layer of Astro-Foil.  This would give you between R28 and R-30.  The sq. ft material cost would be about $1.50 for the Tiger Foam, $.70 for the Satetouch, and $.40 for the Astro-Foil, for a total material cost /sqft of $2.60.  If you just used closed cell foam 4" thick you would be looking at $4.00/sqft.

  2. Aaron | Mar 15, 2010 09:55am | #2

    Roof venting?

    Is the architect concerned with the insulation or the venting?  What is the NJ code on roof venting?  You could still have a cold roof if you add an extra layer of ply over sleepers on the roof deck (or over the SIPS).

  3. Clewless1 | Mar 26, 2010 10:11pm | #3

    I've two comments ... why doesn't the architect know about the code requirements and he should know enough about the insulation options as to whether it is doable ... sounds like he is unsure of both ... but maybe it's the way you are writing it. Particularly for this kind of thing, he should know some ins and outs pretty well and give you the options.

    That being said ... w/ lots of gables, doesn't that make the traditional vented style construction somewhat awkward? Seems like LOTS of interruptions of continuous vents w/ dormer construction. How does the architect propose to deal w/ that?

    If you seal your roof, I hope you've also considered what your ventilation system (read 'exhaust fans') is doing. Is it up to date? Potentially, you may be eliminating the single biggest source of ventilation, so you should at least not be blind to how your house is vented and whether that venting is adequate or not.

    Just more food for thought.

  4. User avater
    Jeff_Clarke | Mar 27, 2010 10:59pm | #4

    and NJ follows the national building codes.

    Would be more accurate to say that the NJ Uniform Construction Code substantially adopts the IRC 2006 with changes and exceptions.

    That being said you can 'read all about it' right here -

    http://www2.iccsafe.org/states/newjersey/NJ_Residential/Residential_Frameset.htm

    View Image

  5. User avater
    mmoogie | Mar 29, 2010 05:46am | #5

    Why don't you call the codes office, ask for the person who will be reviewing the plans, and ask them specifically? Or better yet, sit in on the plan review process if possible. 

    Steve

  6. User avater
    NYCJames | Apr 02, 2010 11:16pm | #6

    Thermal bridging

    In attic spaces foam is applied over the rafters as well as on the underside of the roof deck but since you want finished ceilings the insulated panels are slightly better on the roof deck as opposed to between the wallboard and the rafters. (Search FHB #194, Betsy Pettit,Remodeling for Energy Efficiency, pg 53,55 and 57)

     I suspect that the architect is advising to go with tried and true because that's what flies through the DOB (not bad advice) and  that it is more work for the architect and more likely that he may have delays or inspections at the job site may lead to delays as Inspectors familarize themselves (like the rest of us) with how the new materials and installations mesh with existing code.

    I do see foam installations where the roof rafters or wall studs will act as thermal bridges because no break (a sealed insulation panel) is made part of the assembly and I am left pondering where the dew point is in these assemblies and will we be seeing mold and wood rot problems from these jobs in years to come?

    please keep us informed about how your project goes. 

  7. NJFoam | May 07, 2010 02:13pm | #7

    If you haven't arrived at answers to all of your questions, I'd be happy to help if you're in our area (Mountainside/Westfield).

    DIY foam is expensive and using rigid foam on top of the roof surface can be tricky - you have to devise a plan for sheathing, extra long fasteners and screw layout, etc. I'm not suggesting that's a bad idea, but you should use someone familiar with this process, and who can trim it out nicely. I do spray foam and reccommend it for this application. 3-4" Closed cell or about 6" open cell (and I don't want to hear any comments about OC from other posters). There are a number of factors that go into the decision on what type of foam can be used - CC is almost always ok, OC depends.

    [email protected]

    1. MAsprayfoam | May 31, 2010 09:57am | #8

      same here

      Ditto what Steve in NJ says. 

      If you have not already i'd be questioning the Architect who is unfamiliar with the best insulation available on the market, spray foam!  And it's only been around about 30 years.  If he doesn't have a clue on this what else does he not know about?  You're paying the architect for his knowledge & expertise, correct?

      Stu

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