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Window flashing details/drawing when using external spray foam

TIM LANGE| Posted inGreen Building Techniqueson

Planning DER to start May 2016, starting with replacement of windows and addition of exterior insulation. Will be doing majority of work myself, I’m giving myself 6 months to get this phase completed. Found lots of drawings on use of external insulation (2 layers, seams taped and offset). Since I may be working alone much or most of the time, handling 4×8 foam boards, doing all the cutting then going back up to install etc and, handling rolls of housewrap is not appealing.

I’ve estimated the siding sq ft that needs to be sprayed at 2200 sq ft. Local contractor rule of thumb is $0.85 per inch per sq ft. Cost for this step of the project would be around $5600. I would install vertical 2×3 furring strips offset from the existing sheathing or remaining siding. There are 2 layers of siding, the inner has lead paint and may decide to leave this in place.

I found a lot of drawings for window installation and flashing for external foam board insulation. Not finding much for when spray foam is used. Can anyone point me to some examples. Planning on using ‘outie’ style windows.

Thanks.

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Replies

  1. GBA Editor
    Martin Holladay||#1
  2. Charlie Sullivan||#2

    A disadvantage of spray foam and XPS is that they are both made with blowing agents with very high global warming potential (> 1000X worse than CO2). So EPS, polyiso, and mineral wool are preferable from an environmental impact point of view.

  3. TIM LANGE||#3

    Thanks Charlie,
    I've been trying to make a comparison of using spray foam to the equivalent burning of gasoline in a car based on: one gallon of gas will emit 18 lbs of CO2.

    For my project:
    2200 sq ft 3" thick in cubic ft is: 2200*0.25 = 550 ft^3.
    Assuming 2lbs of foam per cubic ft: 1100 lbs of foam.

    How much CO2 equivalent is released per board ft of spray foam? Couldn't find a conversion in my limited searching. Certainly more complicated that the above but is useful for comparing the impact of spray foam to something tangible - filling the tank at the gas station.

    Thanks
    Tim

  4. Charlie Sullivan||#4

    That's a good question. Rather than calculating it myself I looked around and found this article,

    https://www.chemours.com/Formacel/en_US/assets/downloads/201109_Life_Cycle_Analysis_Spray_Foam.pdf

    Fig. 3 shows 22 lb CO2 equivalent per square foot per R-13, or in other words, 1.7 lbs per (sq foot R value). I'm not sure what R-value you had planned, but for R-16 and 2200 square feet, that's 60,000 lbs. of CO2, or 300 gallons of gas, or 120,000 miles of driving at 40 mpg.

    At that rate, you could buy EPS one sheet at a time, and drive 800 miles round trip to get each sheet, and still come out ahead! (On global warming emissions--not on your time or your sanity.)

    的一个rticle I used is from DuPont. They are unlikely to exaggerate the impact of the blowing agents they sell, so it's likely that result is conservative.

  5. TIM LANGE||#5

    Thanks Charlie,
    One math correction...
    60,000 lbs of CO2 / 18 lbs per gallon gas >3000 gallons of gas! Yikes.

    For propane, its 12.7 lbs CO2 per gallon. 60000/12.7= 4700 gallons propane.

    If current use is 1000 gallons per season and is cut in half by adding insulation (and new windows that are planned), then the CO2 emitted by insulating would be made up by less propane use in ~10 years.

    Useful discussion. I don't feel quite as guilty going with the spray foam - will be less CO2 overall in 10 to 15 years.

    Tim

  6. Charlie Sullivan||#6

    But why wait 10-15 years to get the benefit when you could have it in the first year with EPS...or with open cell spray foam.

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