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  1. #1
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    Default Foam Insulation on roof rafters

    Inspecting a high end home today that was built in 2008. When i was inspecting the attic, here's what I found. Foam insulation in the roof truss area, not the ceiling joist in the attic. Is this practice acceptable and how???? It seems to me that you would be heating the whole attic area with no insulation in the ceiling.. I need your feedback Please....

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  2. #2
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    Default Re: Foam Insulation on roof rafters

    Start by reading up on what you may have seen:

    IcyneneŽ Foam Spray Insulation: Common Residential Applications

    Dom.

    Attached Files Attached Files

  3. #3
    Darrel Hood's Avatar
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    Default Re: Foam Insulation on roof rafters

    Sam,
    That was a correct way to install the foam insulation in 2008. If installed today, it may require an additional fire protection step. The attic is part of the "conditioned space" and should be within 3 or 4 degrees of the normal living area. Also, the type of insulation system should have been considered in the manual J so the AC should be smaller than with a standard insulation system. Also, in the AC system you should see an air inlet from the exterior. If the home has fuel burning appliances, there are several things that should be present to assure proper ventilation and make up air. Dom is right in saying you should do a little reading before reporting on an inspection that uses this insulation system.


  4. #4
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    Default Re: Foam Insulation on roof rafters

    Sam,
    The attic becomes part of the conditioned space and is then calculated in for the HVAC.
    The insulation on the rafters still has to meet state requirements for R factor.
    Installation to rafters would not be my choice due to long term effects on roof deck, but that is another story.


  5. #5
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    Default Re: Foam Insulation on roof rafters

    It is called a "conditioned attic" or "semi-conditioned attic" and is best for hot humid regions.


    Building Science

    Info-602: Ducts in Conditioned Space
    Info-602: Ducts in Conditioned Space — Building Science Information

    IRC FAQ: Conditioned Attics
    IRC FAQ: Conditioned Attics — Building Science Information

    BSD-102: Understanding Attic Ventilation
    BSD-102: Understanding Attic Ventilation — Building Science Information

    Last edited by Don Martin; 03-04-2012 at 08:28 PM.
    Don Martin, ACI
    Preferred Home Inspections

  6. #6
    Phil Brody's Avatar
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    Default Re: Foam Insulation on roof rafters

    So what would be the advantage to adding that space to the total volume of conditioned or semi conditioned space ? from an energy usage standpoint ?


  7. #7
    Phil Brody's Avatar
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Darrel Hood View Post
    Sam,
    That was a correct way to install the foam insulation in 2008. If installed today, it may require an additional fire protection step. The attic is part of the "conditioned space" and should be within 3 or 4 degrees of the normal living area. Also, the type of insulation system should have been considered in the manual J so the AC should be smaller than with a standard insulation system. Also, in the AC system you should see an air inlet from the exterior. If the home has fuel burning appliances, there are several things that should be present to assure proper ventilation and make up air. Dom is right in saying you should do a little reading before reporting on an inspection that uses this insulation system.
    I would love to see a differential test on a 90 degree day with a 3 or 4 degree temperature difference, quite possible but would love to see it. Even if spray foamed there are still baffles right ?


  8. #8
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    Default Re: Foam Insulation on roof rafters

    One advantage is that (if done correctly) this type of insulation can greatly reduce or eliminate various sorts of vexing condensation-related problems at some older residential properties.

    One down-side is that if the roof is leaking, there may be a *lot* of damage to sheathing and structural members before the leak becomes apparent.

    Michael Thomas
    Paragon Property Services Inc., Chicago IL
    http://paragoninspects.com

  9. #9
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Phil Brody View Post
    So what would be the advantage to adding that space to the total volume of conditioned or semi conditioned space ? from an energy usage standpoint ?
    1/2 the energy bill. Much smaller, quieter equipment. A much less leaky, more controlable environment from temperature, humidity, and iaq perspective.

    No risk of condensation or wind driven leakage. No critters coming in soffit, ridge, box or gable vents.

    Those a a few advantages.


  10. #10
    Phil Brody's Avatar
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by ted kidd View Post
    1/2 the energy bill. Much smaller, quieter equipment. A much less leaky, more controlable environment from temperature, humidity, and iaq perspective.

    No risk of condensation or wind driven leakage. No critters coming in soffit, ridge, box or gable vents.

    Those a a few advantages.
    I can understand the inherent advantages, but I don't understand how if an equivalent r value insulation is placed on roof rafters it will perform better than if placed on ceiling joists, especially if the attic is properly vented. Show me the data....especially the 1/2 reduction in energy usage.


  11. #11
    Phil Brody's Avatar
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Michael Thomas View Post
    One advantage is that (if done correctly) this type of insulation can greatly reduce or eliminate various sorts of vexing condensation-related problems at some older residential properties.

    One down-side is that if the roof is leaking, there may be a *lot* of damage to sheathing and structural members before the leak becomes apparent.
    So let's look down the road, roof leak occurs and is unattended because we don't even know it's leaking. It's now revealed structural members and sheathing must be replaced AND all the disturbed spray foam must be repaired properly ? This is starting to sound pretty expensive ... to bring in a spray foam setup for spot repair .....


  12. #12
    David Walker's Avatar
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    Default Re: Foam Insulation on roof rafters

    Sam,
    See IRC R806.4 Unvented Attic Assemblies with the table and specifics by climate zone.
    Also: Spray Foam Insulation products and tools for Building Professionals
    and GIC07B - Designing for the Future: Understanding Light Density and Medium Density Open Cell and Closed Cell Spray | GreenCE.com, your first choice for sustainable continuing education. Always Free All the Time. will have a CEU course on the topic

    I am not sure about northern regions, but in South Texas where for 85% of the year the A/C system is in the cooling mode, this foam insulation on the roof deck and a sealed attic makes sense.

    If the A/C ductwork is in the attic, there is a significant loss of cooling capacity through the (poorly) insulated ductwork. Blowing 60-degree air through 140-degree attics with 1 or 1.5 inch duct insulation is the ventilated attic of the past.

    I prefer open cell foam even though it has a lower R value. Being open it does not trap moisture which can cause future problems.


  13. #13

    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Phil Brody View Post
    So let's look down the road, roof leak occurs and is unattended because we don't even know it's leaking. It's now revealed structural members and sheathing must be replaced AND all the disturbed spray foam must be repaired properly ? This is starting to sound pretty expensive ... to bring in a spray foam setup for spot repair .....
    Not really, you can use 2-part foam for touch ups if want. Comes in many sizes and no need to bring in a whole rig to do the work.


  14. #14

    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Phil Brody View Post
    I can understand the inherent advantages, but I don't understand how if an equivalent r value insulation is placed on roof rafters it will perform better than if placed on ceiling joists, especially if the attic is properly vented. Show me the data....especially the 1/2 reduction in energy usage.
    Also keep in mind that this prevents attic heat gain which later radiates down on the living area (for hours after the sun has set). Even if the decking stays warm in thsi setup, it is many feet away from the living area ceilings unlike a traditional insulation settup where it is sitting on top of it. In a traditional insulated attic, no matter how good your venting is, you will have some heat gain trapped in the attic and your ducts exposed to that heat which reduce the A/C efficiency...


  15. #15
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by champainspectionnews View Post
    Not really, you can use 2-part foam for touch ups if want. Comes in many sizes and no need to bring in a whole rig to do the work.
    So if we replace (1) 16' roof rafter and maybe 2 or 3 sheets of sheathing,( I'm assuming that the foam will come out with the plywood and not make it impossible if the plywood would be glued to the rafters through the foam) we can use the 2 part foam for 150 sq.ft repairs ? Do you have a link for the different packaging ? Don't get me wrong I think it's a great product for the proper application and properly applied.


  16. #16
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    Default Re: Foam Insulation on roof rafters

    What you have is 4-5 inches of closed-cell foam insulation. The best place for the insulation is the underside of the roof. Now all the HVAC runs in the attic do not need to be insulated. Any can lights do not have to be the heat-rated. This is a very tight installation. Any future work in the attic, wiring etc. will not bother the insulation.


  17. #17
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by John Feick View Post
    What you have is 4-5 inches of closed-cell foam insulation. The best place for the insulation is the underside of the roof. Now all the HVAC runs in the attic do not need to be insulated. Any can lights do not have to be the heat-rated. This is a very tight installation. Any future work in the attic, wiring etc. will not bother the insulation.
    John, how do you know it is closed cell? How do you know it is 4-5 inches? Do you think that framed attic has 2x4 rafters? What do you think of the metal chimney going through the foam insulation? The spray jobs I have seen are much more evenly applied and professional in appearance. I like conditioned attics but this one does not impress me.

    The beatings will continue until morale has improved. mgt.

  18. #18
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Vern Heiler View Post
    John, how do you know it is closed cell? How do you know it is 4-5 inches? Do you think that framed attic has 2x4 rafters? What do you think of the metal chimney going through the foam insulation? The spray jobs I have seen are much more evenly applied and professional in appearance. I like conditioned attics but this one does not impress me.
    Vern, you bring up a very good point how do you know the depth of insulation ? and if it was 4-5 inches it would be r16-r20 and under insulated for 2008, also open or closed cell ? if it was closed cell it would be wrong.


  19. #19
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    Default Re: Foam Insulation on roof rafters

    I think we all do a lot of guessing how foam will perform. It's still a little new. I think the jury is still out... I do know what will tell the story, TIME.

    Randy Gordon, construction
    Michigan Building Inspector/Plan Reviewer

  20. #20
    Phil Brody's Avatar
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Door Guy View Post
    I think we all do a lot of guessing how foam will perform. It's still a little new. I think the jury is still out... I do know what will tell the story, TIME.
    Not all that new but it reminds me of the stucco learning curve all over again, anybody want to become a certified insulation inspector ?


  21. #21
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    Default Re: Foam Insulation on roof rafters

    With insulation under the roof deck, if the roof is covered with asphalt shingles, they will roast and wear out faster. Also the metal chimney through foam doesn't look good for fire ratings.


  22. #22
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Phil Brody View Post
    Not all that new but it reminds me of the stucco learning curve all over again, anybody want to become a certified insulation inspector ?
    I think it's a little new in comparison to our time frame of insulating homes. Really almost all techniques are in infancy. We don't even have a hundred years into insulating yet... your are very correct Phil, it will have a learning curve.

    Randy Gordon, construction
    Michigan Building Inspector/Plan Reviewer

  23. #23

    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Phil Brody View Post
    I can understand the inherent advantages, but I don't understand how if an equivalent r value insulation is placed on roof rafters it will perform better than if placed on ceiling joists, especially if the attic is properly vented. Show me the data....especially the 1/2 reduction in energy usage.
    Quote Originally Posted by Phil Brody View Post
    So if we replace (1) 16' roof rafter and maybe 2 or 3 sheets of sheathing,( I'm assuming that the foam will come out with the plywood and not make it impossible if the plywood would be glued to the rafters through the foam) we can use the 2 part foam for 150 sq.ft repairs ? Do you have a link for the different packaging ? Don't get me wrong I think it's a great product for the proper application and properly applied.
    you can just cut the foam; it is not that tough. This is an example of 2-part foam Tiger Foam Spray Foam Insulation Kits

    Also, as far as I've seen distiguishing between open and close cell is not a big deal (close cell is hard and open cell is fluffy like a sponge)


  24. #24
    Phil Brody's Avatar
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Lisa Simkins View Post
    With insulation under the roof deck, if the roof is covered with asphalt shingles, they will roast and wear out faster. Also the metal chimney through foam doesn't look good for fire ratings.
    OK after doing some investigating, what Lisa states is correct, asphalt roofing manufactures specify 1" air space above and below the shingles. You can certainly spray the foam directly on the underside of the sheathing and substantially reduce the life of the shingles that is your choice, and the shingle failure would not constitute a manufacturing defect in the shingle, so baffles might be a good choice.
    The spray foam is easy to cut, but the roofer may have to enter the attic to cut the foam prior to being able to remove the sheathing or rafter. I believe there would be substantially more work involved with a foamed rafter/sheathing.
    The foam insulates nearly equivalently to an equal r value of batt insulation whether on the rafters or on the ceiling joists. The a/c and lighting cans undoubtedly benefit from insulated roof raters/sheathing.
    The price to restore damaged spray insulation at an R-30 is roughly $13./sq.ft. not cheap.


  25. #25
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    Default Re: Foam Insulation on roof rafters

    This application can be very damaging to a roof system in certain cases. Because of differences in the transfer of energy between the framing members and the foam, you can end up with a condensation issue within the framing due to the delta T correlation of indoor and outdoor temperature. You can also, as was mentioned previously, have water infiltration that does not show up. Look for any tiny black or dark brown droplets at the framing/foam connection. This is usually an indication of water infiltration. We always use a probe and check the area where the roof deck and the rafter meet within the foamed area at a few different areas. Also, if carpenter ants live in your area, they LOVE this foam. Check for any indication of insect entrance.


  26. #26
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Todd Russell View Post
    Because of differences in the transfer of energy between the framing members and the foam, you can end up with a condensation issue within the framing due to the delta T correlation of indoor and outdoor temperature.
    I'd like to know more about this, do you have a link handy?

    Michael Thomas
    Paragon Property Services Inc., Chicago IL
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  27. #27
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    Post Re: Foam Insulation on roof rafters

    This type of "conditioned attic" is similar in mind-set to that of a "conditioned crawlspace", which are suddenly becoming very popular due to moisture control (re that "mold"). However, one still has to look at the big picture.
    1) All that space DOES become part of the air-conditioned space, and must be calculated in for any new HVAC systems.
    2) Ventilating an attic has a lot of advantages when things aren't perfect (and nothing is every perfect nor stays that way) -- THEY DRY OUT!
    3) I'll bet that foam-applied insulation system distinctly shortens the life of the plywood roof sheathing -- and I'll bet it completely voids the warranty of the roofing shingles!

    Houses benefit from a free-flowing vent system of air moving inward from a properly vented eave overhang, upward along the bottom of the roof sheathing, and out through a a good well-installed continuous ridge vent. Thermostatically and humidistatical- controlled mechanical attic ventilation fans installed behind air louvers set high in the attic gables (and blowing outward!) are helpful and worth their price and their electrical costs. All that works together to vent interior moisture in the winter that passes upward through the insulation in a cold (and therefore dry) attic... (It can actually freeze on the roof rafters if not vented out.) And that also works in the summer to lower the attic temperature significantly -- greatly easing the heat damage done to the roofing materials.


  28. #28
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Phil Brody View Post
    Even if spray foamed there are still baffles right ?
    Quote Originally Posted by Phil Brody View Post
    especially if the attic is properly vented.
    That's the key ... with spray foam insulation the attic is *not* vented, the attic is now a sealed attic.

    And, yes, it does make a big difference.

    The attic is not added to the conditioned area, think of it as a house where the exterior temperature above the ceiling (in the attic) is no longer 140 degrees on a hot day, it is now typically 1-3 degrees warmer than the conditioned space below the ceiling. Makes a BIG difference in the energy used to cool the conditioned space when it is not next to a 140 degree attic.

    Jerry Peck, Construction / Litigation Consultant
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  29. #29
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    Default Re: Foam Insulation on roof rafters

    This article at inspectapedia will give you a good idea of the correlation I am talking about.

    How to Calculate the condensation or dew point in buildings, when does moisture condense on surfaces and in cavities

    The other big item to keep in mind when dealing with condensation and the ability of a home to disperse that moisture is the degree heating/cooling days in your area. The other thing you must remember when dealing with urethane foam is that it is a vapor barrier and any framing member encapsulated in foam could be considered inside a double vapor barrier situation. Some foam installer overfill the wall and attic spaces and remove the top layer of the foam and then treat with a poly vapor barrier. Areas in a system like this will be tight, but you will have greater potential for accelerated air movement at those areas not covered with foam and not covered with a vapor barrier such as header connection, trimmers and girder trusses in walls or roofs.


  30. #30
    Todd Russell's Avatar
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    Default Re: Foam Insulation on roof rafters

    The attic may now be within the thermal envelope and treated/conditioned area if there is not a vapor barrier separation at the home. Now you must cover this foam with a fire retardent because it is inside the conditioned space. You may want to look in section R314.4 in the 2006IRC or section 316.4 in the 2009IRC depending on the age of the home and when your area adopted which version of the code.


  31. #31
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    Default Re: Foam Insulation on roof rafters

    Since it looks like you would have fallen under the 2006IRC then make sure you see R314.5.3.


  32. #32
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    Default Re: Foam Insulation on roof rafters

    Some of you make me laugh! There's this image of a guy with his head in the sand, what's the logo?

    Lol.

    Hey, I come here to learn about building inspection. Being a building science guy does not make me an inspector. I get that and I can still learn.

    But those who think they already know everything, if your glass is full then there is no room for new information. That's too bad.

    To "show me the data" Pay my rate and I'll consult all you like. Otherwise I don't care to offer studies of the benefits of foam. Believe it or don't, I care not.

    I'm dying to learn how condensation occurs within a solid. I thought it was moisture laden air coming in contact with a surface whose temperature was below dew point.


  33. #33
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    Default Re: Foam Insulation on roof rafters

    Interesting responses on this topic.

    Shingle life and condensation are issues but in a very cold climate, like 8 feet of snow, the real enemy becomes ice dams. Or is it damns?

    The project where I used it required calculations to show that the thickness would not accomodate the dew point so that condensation would not occur within the spray. The design temperature was ~-20°F as I recall meaning that the thickness had to be 10" plus. The homes were very well built and very well insulated.

    Also, the shingles were NOT asphalt but clay or masonry of some type. (I don't know shingles).

    If I could afford it, I'd love to have this type of roof insulation.


  34. #34
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    Default Re: Foam Insulation on roof rafters

    No Ted, it does not. And from the sounds of it, that's a good thing. In your area of the country this should interest you. I am from VT originally and know of these issues occurring there. I'm not a scientist, I'm a 25 year veteran builder, an ICBO inspector, an existing home inspector and an energy auditor. If you don't know building science in this day and age...get out now while you still can.


  35. #35
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Todd Russell View Post
    Now you must cover this foam with a fire retardent because it is inside the conditioned space.
    That's not the reason for the ignition barrier.

    If there was no attic access, no thermal barrier over the spray foam insulation is required as the 1/2" drywall ceiling already provides that thermal barrier.

    When there is attic access, no thermal barrier is required either when the attic is entered only for service of utilities (such as wiring, duct work, etc.). However, now the spray foam insulation requires an ignition barrier, and while the list of ignition barriers seems a bit impressive and why would anyone want to do that, there is a spray-on ignition barrier which helps the spray foam meet 314.6, which negates the requirement for items in that list.

    Those sections are in constant flux as more and more is found out about the characteristics of spray foam, its uses, and spray-on coatings.

    Jerry Peck, Construction / Litigation Consultant
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  36. #36
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    Default Re: Foam Insulation on roof rafters

    A good read: Geography plays a major role in insulation methods.
    BSD-102: Understanding Attic Ventilation — Building Science Information


  37. #37
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Jerry Peck View Post
    That's the key ... with spray foam insulation the attic is *not* vented, the attic is now a sealed attic.

    And, yes, it does make a big difference.

    The attic is not added to the conditioned area, think of it as a house where the exterior temperature above the ceiling (in the attic) is no longer 140 degrees on a hot day, it is now typically 1-3 degrees warmer than the conditioned space below the ceiling. Makes a BIG difference in the energy used to cool the conditioned space when it is not next to a 140 degree attic.
    Understood, for the record, its reported that the temperature on a 90 degree day above the ceiling (in the attic) would experience a 5-10 degree temperature differential warmer than the conditioned space below the ceiling, sure still better than 140 degree's. There is a rough formula, for every 1 degree you can lower the attic temp. over the roof deck temp you increase the life of the roof 1%. IE: Roof temp 170 F attic temp: 120 F 50% increase in longevity.


  38. #38
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Phil Brody View Post
    Understood, for the record, its reported that the temperature on a 90 degree day above the ceiling (in the attic) would experience a 5-10 degree temperature differential warmer than the conditioned space below the ceiling, sure still better than 140 degree's. There is a rough formula, for every 1 degree you can lower the attic temp. over the roof deck temp you increase the life of the roof 1%. IE: Roof temp 170 F attic temp: 120 F 50% increase in longevity.
    "its reported that the temperature on a 90 degree day above the ceiling (in the attic) would experience a 5-10 degree temperature differential warmer than the conditioned space below the ceiling"

    Down here, where it gets nice and warm and over 90 degrees, that difference between the attic and the conditioned space is typically only a couple of degrees.

    When I was in South Florida, the difference was still just a couple of degrees, there might have been 5 degrees difference.

    Jerry Peck, Construction / Litigation Consultant
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  39. #39
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    Default Re: Foam Insulation on roof rafters

    Here in the desert of central California the temperatures in the summer can exceed 105 degrees. And attics get hot. A well ventilated attic less so and if tech shield or polar ply radiant barrier decking is installed it may be another 20 degrees cooler, but nothing compares to a semi-conditioned attic space. The idea of insulating the attic rafters and sealing it up tight at first makes no sense. But after you experience one first hand in the summer you become a believer.

    Don Martin, ACI
    Preferred Home Inspections

  40. #40
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Lisa Simkins View Post
    With insulation under the roof deck, if the roof is covered with asphalt shingles, they will roast and wear out faster. Also the metal chimney through foam doesn't look good for fire ratings.
    A builder north of Denver is putting in this type of insulation in all their homes. I had a lengthy conversation with them concerning it and then did some separate research. The builder says that the foam reflects the heat back up and the deck never gets hot enough to damage composition shingles. Some other foam industry sources echo that.

    As some of you have opined, time will tell. None of the installations that I have seen are old enough to test that. Here in Denver, we see plenty of prematurely aged composition shingles from inadequate ventilation, so foam installation will definitely be tested here.

    As for the leakage question, I haven't seen that addressed by any industry source. My own take is that a simple nail hole or screw penetration may not lead to big problems, except possibly in wetter climes. The foam seals tightly to the deck and it seems that the small amount of water would be localized at the site. Around here, the sun will come out a few hours later and I think will quickly dry the spot out. Obviously, a penetration that goes completely through the foam would likely be found by the brown stain on the drywall ceiling in the living area.

    Some other kind of damage leading to wider water penetration could lead to the kind of problems mentioned here.

    Over the years, there have been many great new ideas that in a few years we learned were terrible ideas. This might prove to be another one. Foam has worked well in metal quonset huts, etc, but like many of you, I have some doubts about these applications.

    But I sure love the look and the sparkling clean attics. Now if these smart guys can do something to make crawlspaces look this good, I might actually enjoy a crawlspace.


  41. #41
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Lon Henderson View Post
    A builder north of Denver is putting in this type of insulation in all their homes. I had a lengthy conversation with them concerning it and then did some separate research. The builder says that the foam reflects the heat back up and the deck never gets hot enough to damage composition shingles. Some other foam industry sources echo that.

    As some of you have opined, time will tell. None of the installations that I have seen are old enough to test that. Here in Denver, we see plenty of prematurely aged composition shingles from inadequate ventilation, so foam installation will definitely be tested here.
    I don't understand the logic of that -> if the foam reflects the heat back, it will go through the shingles again - like being in a reflector oven! Anyway, like you said, time will tell if there are enough foam sprayed underside roof decks with asphalt shingles.


  42. #42
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Lisa Simkins View Post
    I don't understand the logic of that -> if the foam reflects the heat back, it will go through the shingles again - like being in a reflector oven! Anyway, like you said, time will tell if there are enough foam sprayed underside roof decks with asphalt shingles.
    One of the things which kills composition shingles is heat, and attic spaces have a lot of heat build up - the attic get much hotter than the exterior air is - agreed?

    Now take that heat from the attic and remove it so it can no longer re-radiate up against the roof ... the exterior temperature is the same, however, the shingles, underlayment, and sheathing are now only being heated from the exterior air temperature and the radiant heat from the sun (the same as affect a house with a ventilated attic), except that the sealed attic is no longer an oven set to pre-heat to 150 degree, the oven is turned off.

    No more 'oven' with the door open directing heat to the roof sheathing. Cool! (Actually ... 'cooler' ... )

    Jerry Peck, Construction / Litigation Consultant
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  43. #43
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    Default Re: Foam Insulation on roof rafters

    That would all seem fine...other than the shingles are the heating element for the oven and the ventilation is cooling the attic space somewhat. Now, attic is cooler, but the shingles and deck are hotter...no ventilation effects.


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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Todd Russell View Post
    That would all seem fine...other than the shingles are the heating element for the oven and the ventilation is cooling the attic space somewhat. Now, attic is cooler, but the shingles and deck are hotter...no ventilation effects.
    The shingles are the heating element for the oven, but the attic is what let's the heating element heat up and store the energy - no attic, no burned crispy food.

    It seems that you are thinking that the ventilated attic is like opening the oven door and letting the heat out - not even close, the vents in the attic are more like the vent for the oven which let's out heat, usually found either in the upright control panel or the right rear burner, allows all that heated and expanding air to escape. Ever touch the metal parts of the oven after it heats up? Hot, right? Even with the door open, more so with little vents open. All that heat reflects back up to the roof from the attic (oven).

    Now take the pan out of the oven (hot, isn't it?) and set it on a pot holder, not so bad now is it? The insulation is the pot holder. You now have one heat source (outside from the sun and hot air) and not two heat sources (outside from the sun and hot air and inside from the reflected heat from the oven.

    If you could take a ventilated attic and open the roof up like butterfly wings, you could let all that heat out, but that is not practical, is it?

    It is better to simply not let the oven heat up inside.

    Jerry Peck, Construction / Litigation Consultant
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  45. #45
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    Default Re: Foam Insulation on roof rafters

    I think it's great.........makes attic inspections a lot easier and hides all the water staining from a leaky roof.... right?

    Jerry McCarthy
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  46. #46
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    Default Re: Foam Insulation on roof rafters

    Jerry, I think you are completely missing how these hot roofs work, I think maybe if you had installed a roof using foam or repaired as many failed urethane hot roofs as I have, you would get it. Not a funny subject and a very serious problem which the insurance companies and foam manufacturers have created BS policies to leave the homeowner holding the bill for a product that is often poorly installed and misrepresented.


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    Default Re: Foam Insulation on roof rafters

    Todd, why did you assume I was kidding? The problem with foaming the roof rafters & sheathing is it may hide visual evidence of stress & damage.
    Keeping excesive heat out of attics is a great idea and reducing cooking roof coverings, but there are other ways do do it rather than shooting foam all over the underside of a roof.

    Jerry McCarthy
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  48. #48
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    Default Re: Foam Insulation on roof rafters

    Todd,

    I talked to one of the biggest roofers in our area and he hasn't been called out for any evaluations or repairs for the systems being described in this thread, i.e., insulating expanding foam applied to the underside of plywood or OSB roof decks with composition (asphalt) shingles applied. So, my questions for you are; what damage have you seen from this, how many times have you seen damage requiring repair and what kind of repairs have you been doing?


  49. #49
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    Talking Re: Foam Insulation on roof rafters

    There is no problem with that technique until the asphalt shingles fail
    once the water start to go between the plywood and the shingles, nobody will know (because spray foam is waterproof), but suddenly the roof will collapse everything will be just ROT

    believe me i have seen it!

    i been spraying foam since 1988 and stop in 2009


  50. #50
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Guy Bosse View Post
    There is no problem with that technique until the asphalt shingles fail
    once the water start to go between the plywood and the shingles, nobody will know (because spray foam is waterproof), but suddenly the roof will collapse everything will be just ROT

    believe me i have seen it!

    i been spraying foam since 1988 and stop in 2009
    That's why a good quality peel-and-stick underlayment should be used under the shingles. Those peel-and-stick underlayments self-seal around the nail and other penetrations (not large one like plumbing vent stacks) and provides a secondary water barrier should (when) the roof leaks.

    This is regardless whether the roof covering is shingles, concrete/clay tile, metal, etc.

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  51. #51
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    Talking Re: Foam Insulation on roof rafters

    I don't know at your place but here in canada asphalt shingle company void there warranty if you apply that type of peel and stick membrane

    but to be honest with you that's what i did on my house


  52. #52
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Guy Bosse View Post
    There is no problem with that technique until the asphalt shingles fail
    once the water start to go between the plywood and the shingles, nobody will know (because spray foam is waterproof), but suddenly the roof will collapse everything will be just ROT

    believe me i have seen it!

    i been spraying foam since 1988 and stop in 2009
    Now there you go, real life testing and experience, there is no better substitute. Although they do recommend open cell foam so a leak may weep. And if we return to the oven analogy and agree that the shingles are the element (darker colors= high wattage) and they are in fact heating up the attic then the application of foam prevents the radiation of heat. Less radiation of heat higher shingle temperature (conservation of energy physics law.) In real world testing roofs backed by foam are hotter and asphalt is probably not a good candidate, especially since asphalt shingle manufactures require a 1" airspace above and below the shingle.


  53. #53
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Jerry Peck View Post
    That's why a good quality peel-and-stick underlayment should be used under the shingles. Those peel-and-stick underlayments self-seal around the nail and other penetrations (not large one like plumbing vent stacks) and provides a secondary water barrier should (when) the roof leaks.

    This is regardless whether the roof covering is shingles, concrete/clay tile, metal, etc.
    Agreed,but is that currently a prerequisite to having foam sprayed, me think not.


  54. #54
    Phil Brody's Avatar
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Jerry Peck View Post
    That's why a good quality peel-and-stick underlayment should be used under the shingles. Those peel-and-stick underlayments self-seal around the nail and other penetrations (not large one like plumbing vent stacks) and provides a secondary water barrier should (when) the roof leaks.

    This is regardless whether the roof covering is shingles, concrete/clay tile, metal, etc.
    Quote Originally Posted by Guy Bosse View Post
    I don't know at your place but here in canada asphalt shingle company void there warranty if you apply that type of peel and stick membrane

    but to be honest with you that's what i did on my house
    Now why would that be, it is approved for valleys and eves?


  55. #55
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Phil Brody View Post
    . . . .And if we return to the oven analogy and agree that the shingles are the element (darker colors= high wattage) and they are in fact heating up the attic then the application of foam prevents the radiation of heat. Less radiation of heat higher shingle temperature (conservation of energy physics law.) In real world testing roofs backed by foam are hotter and asphalt is probably not a good candidate, especially since asphalt shingle manufactures require a 1" airspace above and below the shingle.
    I don't think this oven thing was the perfect analogy but I do like the logic that Jerry Peck pointed out in an earlier post. It's the heat from the attic itself which radiates the heat back thru the shingles that does the major damage. If the heat is stopped AT the shingle the heat is radiated back to an ambient temperature which is lower than the attic temperature would be. The shingle will get hot either way.

    Consider the cause (or one of the causes) of shingle curl, it's moisture in the attic from non ducted exhaust fans. The damage comes from the attic.


  56. #56
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Guy Bosse View Post
    I don't know at your place but here in canada asphalt shingle company void there warranty if you apply that type of peel and stick membrane

    but to be honest with you that's what i did on my house
    In Florida, it is an approved, even recommended, underlayment. Probably 90% or more of the newer shingle roofs have peel-and-stick for the underlayment.

    You even get an insurance discount for using peel-and-stick.

    Jerry Peck, Construction / Litigation Consultant
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  57. #57
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    Talking Re: Foam Insulation on roof rafters

    can you tell me names of the shingles company in your area?

    just curious if it could be some of them in my place, if it is, they are going to have some questions to answer

    also, i have one of my friend who's was using ceramic paint instead of spf under his roof and from what he told me it's working


  58. #58
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Guy Bosse View Post
    can you tell me names of the shingles company in your area?
    GAF, Owens Corning, Certainteed, all the big name manufacturers.

    Jerry Peck, Construction / Litigation Consultant
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  59. #59
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    Smile Re: Foam Insulation on roof rafters

    after i read all the thread, here is what i have to say to the post 17, just to let you know, the way that this spray foam job is looking, it is a open cell foam, anybody, even if he is just starting spraying foam, can spray smoother than that with close cell polyurethane spray foam


  60. #60
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Phil Brody View Post
    Agreed,but is that currently a prerequisite to having foam sprayed, me think not.
    Nope, not a requirement, just a good idea.

    Kind of like installing shower enclosure doors is not a requirement, you can use a shower curtain if you so desire.

    Jerry Peck, Construction / Litigation Consultant
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  61. #61
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    Default Re: Foam Insulation on roof rafters

    At first Jerry P's idea seemed logical to me. But the reason attics get hot is because some of the heat from the roof is allowed to pass into the attic. The argument only works if the attic is hotter than the shingles.

    The shingles aren't the heating element, the sun is!

    Do not think of knocking out another person's brains because he differs in opinion from you. It would be as rational to knock yourself on the head because you differ from yourself ten years ago.
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  62. #62
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    Default Re: Foam Insulation on roof rafters

    Quote Originally Posted by Lisa Simkins View Post
    With insulation under the roof deck, if the roof is covered with asphalt shingles, they will roast and wear out faster. Also the metal chimney through foam doesn't look good for fire ratings.
    Not true. The temp difference is about 5 degrees, not enough to affect the shingles.

    The chief advantage of moving the insulation to the roof line is that the HVAC is now inside the thermal envelope. That is any duct leakage stay in the house and the ducts are not subject to a vented attics temp. It also make the top of the house air tight.

    Closed cell foam is very stiff and hard. Open cell is soft and spongy. Due to the cost of foam many times it is applied at depths that do not meet code.

    Roof insulation alone will not save 50% and is not cost effective if applied to code R value.

    There are other air sealing and insulation strategies that would be as effective if not more effective at a lower cost. Cellulose is cheap and can be installed at greater than code R at a lower cost.


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