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  1. #1
    Geoff Stewart's Avatar
    Geoff Stewart Guest

    Default Attic rafter bay insulation

    Ok, see this rarely on the OR coast; 60-80" rain per year, wind gusts common at 60-100 mph. It's really a good idea to be able to observe the roof sheathing around here. The paper side was facing the inside of the attic. Bad.
    But what's the deal with insulation installed in the bays. Potential condensation issues maybe (on the sheathing)?

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  2. #2
    Leigh Goodman's Avatar
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    Default Re: Attic rafter bay insulation

    Paper backing is meant to face in to the living space so that is right.
    Often the attic is included in the conditioned space, especially when it contains hvac components. Should have provision between insulation and deck for ventilation.
    There are light weight foam channels made for this situation that are installed to underside of deck before insulation is installed.


  3. #3
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    Default Re: Attic rafter bay insulation

    If that were a story and half that would be the way to insulate, including air space or chutes.

    Randy Gordon, construction
    Michigan Building Inspector/Plan Reviewer

  4. #4
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    Default Re: Attic rafter bay insulation

    Paper faced insulation burns like gasoline and should never be left exposed. That is the biggest problem with this installation.

    With a proper vapor barrier you can have the insulation at this point and it need not be vented between the insulation and the roof sheeting. The purpose for the attic ventilation is to remove the moisture that would migrate from the living space, reach a dew point and condense.

    An effective vapor barrier would not let the moisture get up into the insulation or past it were it would reach it's dew point and condense. This is the same in walls as in an attic. But in this case there is no "unconditioned attic".

    Yes there is a secondary reason for attic ventilation, removal of heat buildup.


  5. #5
    Leigh Goodman's Avatar
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    Default Re: Attic rafter bay insulation

    In my area it is foolish to omit a vent space between insulation and underside of deck.


  6. #6
    Geoff Stewart's Avatar
    Geoff Stewart Guest

    Default Re: Attic rafter bay insulation

    No provision for ventilation between insulation and sheeting, however the insulation was cut at the passive roof vents. Fire hazard is my main concern. That flue in the picture is for a pellet stove 2 floors down. Obviously the flue installation was not completed. The pellet stove was ready to rock and roll. I did not operate it, damn good thing, the place would probably gone up in flames. Quickly.

    I just wonder why inslulation was not installed between the ceiling and the ply attic floor, but whatever. There were wall mounted doors in the floor below, 3 of them. Someone goes in to have a "smoke" or whatever, insulation paper is everywhere. That someone may be, ah, "compromised". Get my drift?

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  7. #7
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    Default Re: Attic rafter bay insulation

    All I can say is check with the AHJ, without knowing more details this would not pass code in WI based on the following:

    1. You would have to have a 1-1/2 inch air gap between the roof sheeting and the insulation.
    2. Odds are there is a warning somewhere on that paper faced insulation saying not to leave it exposed.
    3. I would also question the amount of insulation, as WI requires R-38.
    4. If this is to be conditioned space, a whole new set of potential problems.


  8. #8
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    Default Re: Attic rafter bay insulation

    There is so ventilation. The open strapping separates the insulation from the tar paper and shingles, which are probably cedar. It's OK.

    The paper on the inside needs to be drywalled for fire safety.

    The paper will never be able to prevent some moisture from migrating thru, so yes, ventilation is needed. Cedar shingles allow moisture to pass thru to the outdoors. If they nail plywood or OSB sheathing over the strapping for a new roof, they will then need to improve ventilation somehow, such as by adding furring strips.

    I see an attic living space that needs finishing. Along with a chimney installation that isn't finished yet.

    John Kogel, RHI, BC HI Lic #47455
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  9. #9
    Geoff Stewart's Avatar
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    Default Re: Attic rafter bay insulation

    Mike,
    The warnings are there alright. You can see them in the first pic.


  10. #10
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    Default Re: Attic rafter bay insulation

    Iím guessing the strapping is 3/4 inch (not 1-1/2 inch) and runs perpendicular to the rafters so you are not getting air flow across the insulation from the eaves to the ridge (vent to vent), the strapping is basically a dam for air flow every 6-8 inches. Not to mention, the insulation probably pushes back up against the felt between straps. The roofing felt is not going to allow any moisture to pass through, you are trapping moisture in the insulation.

    I could not the read label in the picture, but was guessing the warning was there.


  11. #11
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    Default Re: Attic rafter bay insulation

    Hopefully ... the fireplace was also abandoned?

    Quote Originally Posted by Geoff Stewart View Post
    It's really a good idea to be able to observe the roof sheathing around here. The paper side was facing the inside of the attic. Bad.
    Not bad, or at least not necessarily bad. As stated in posts above, probably cedar shakes/shingles on the roof, with the paper underneath the cedar shakes/shingles instead of inter-layered with them, or maybe both?

    Or was the roof originally cedar shakes/shingles and then the roof re-decked with solid sheathing and asphalt composition shingles installed?

    But what's the deal with insulation installed in the bays. Potential condensation issues maybe (on the sheathing)?
    That was an attempt at taking the thermal envelope up and around the attic, to the underside of the roof sheathing. When that is done, no ventilation is needed, and in fact, no ventilation is desired as the attic is not a "sealed attic" instead of a "vented attic".

    The problem is that fiberglass batt insulation is not "air-impermeable" and is not allowed for that use in those climate zones (4 or 5B for Oregon).

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  12. #12
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    Default Re: Attic rafter bay insulation

    That chimney is incorrect for a pellet stove. The pellet stoves I am familiar with have vent pipes cool enough to just go out through a wall, and are only about 3" in diam. The pipe goes straight out the back of the stove usually.

    That chimney was used for a standard woodstove in the past, judging by the soot.

    I would classify that attic arrangement as old school "vaulted ceilings". Ventilation is needed between the undersurface of the roof and the insulation, because there is leakage of air through the insulation.
    But as I said above, cedar shingle roofs perform well as a rule with just a 3/4" gap provided by the strapping. The correct tar paper is perforated to let small amounts of air through. Air moves across the roof to the gable ends as well. Sometimes a bit of moisture gets trapped on the upper surface of the strapping if it is wide planks. That is where you find the odd rotted plank when you tear off a 25 yr old roof.

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  13. #13
    Geoff Stewart's Avatar
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    Default Re: Attic rafter bay insulation

    Proper sized pellet stove flue was present from the stove to the ceiling. Then to an adapter which connected the two flues together; yeah, the upper length was an old 8/10" wood stove flue. Wood stove had been since removed.

    What's incorrect about the pellet stove installation is that only a 3 or 4" (depending if it's a wall or ceiling install) flue made for pellet stoves may be used for the entire run. The exception is that some manufacturers allow the duct to enter an existing masonry chimney for exhausting. Roof venting is OK in general.

    There was an in-line booster fan present for the larger flue (see pic), but that's irrelevant really.

    As far as the insulation goes, buyer has the choice to sheet rock it if they want to make an attic studio, or remove it due to obvious fire hazard. But then there is the ventilation requirement re the insulation to the sheeting. This insulation was in full contact with the vapor barrier. And no, the skip sheathing was not cedar. I used to buy, sell and grade instrument quality western red cedar in a previous life by the 40' container load.


  14. #14
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    Default Re: Attic rafter bay insulation

    The strapping or skip sheathing would be SPF or Hemlock, which it appears to be, but with Cedar shingle roofing, it's can be OK with a minimal ventilation gap.

    However, as is, without the drywall to improve the seal, it is not right, because a lot of moist warm air is leaking past the fiberglass and there could be too much moisture trapped against the tar paper. Also, with that pellet stove installation, the place sounds like a deathtrap.

    John Kogel, RHI, BC HI Lic #47455
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  15. #15
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    Default Re: Attic rafter bay insulation

    Quote Originally Posted by Geoff Stewart View Post
    .....That flue in the picture is for a pellet stove 2 floors down. Obviously the flue installation was not completed. The pellet stove was ready to rock and roll. I did not operate it, damn good thing, the place would probably gone up in flames. Quickly............
    That incomplete pipe looks used with what appears to be soot or discoloration at the lip. Somebody may be using that stove system as it is. Make sure you warn them not to operate it and document this as well. Was there any warning sign on the stove to warn against using it?

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  16. #16
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    Default Re: Attic rafter bay insulation

    Geoff,

    I'm sure you also got the lack of fireblocking around that abandoned chimney section, and any additional fireblocking needed down below (photo does not show what is down below).

    Jerry Peck, Construction / Litigation Consultant
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  17. #17
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    Default Re: Attic rafter bay insulation

    Question?

    What if this a an A frame House and what you see in the picture a roof but also also an uncompleted outside wall. Would this be acceptable if it was an exterior wall, just missing the drywall ?


  18. #18
    Leigh Goodman's Avatar
    Leigh Goodman Guest

    Default Re: Attic rafter bay insulation

    In my area the standard installation for a-frame type construction
    would include the light weight foam channel applied to the underside of the sheathing covered with fiberglas batts and drywall with soffit and ridge vents.


  19. #19
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    Default Re: Attic rafter bay insulation

    Quote Originally Posted by John Kogel View Post
    That chimney is incorrect for a pellet stove. The pellet stoves I am familiar with have vent pipes cool enough to just go out through a wall, and are only about 3" in diam. The pipe goes straight out the back of the stove usually.

    That chimney was used for a standard woodstove in the past, judging by the soot.

    I would classify that attic arrangement as old school "vaulted ceilings". Ventilation is needed between the undersurface of the roof and the insulation, because there is leakage of air through the insulation.
    But as I said above, cedar shingle roofs perform well as a rule with just a 3/4" gap provided by the strapping. The correct tar paper is perforated to let small amounts of air through. Air moves across the roof to the gable ends as well. Sometimes a bit of moisture gets trapped on the upper surface of the strapping if it is wide planks. That is where you find the odd rotted plank when you tear off a 25 yr old roof.
    All I can say is in WI this would not be allowed. Perforated felt would not be allowed as it would let water in, and with the insulation touching the underside of the decking it would soak moisture up like a sponge. The reason moisture is getting trapped on the upper surface is because there is no air movement going on and the peak would be the first place of condensation as warm moist air rises.

    I don't see the side to side venting, and still see the insulation filling up the cavity anyway. If you have soffit vents and ridge vents how does air move side to side, these vents are blocked off from each other.

    Cedar roofs are not common in my area, but when installed they do the typical 3-ply system or put down an all weather cover on the decking then come back with a mesh material (~1/8 inch thick) on top of that, sorry I donít remember the product names. But, there is always separate attic venting going on, regardless of the type of roof being installed.


  20. #20
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    Default Re: Attic rafter bay insulation

    Quote Originally Posted by Mike Kleisch View Post
    All I can say is in WI this would not be allowed. Perforated felt would not be allowed as it would let water in.
    The paper is punched from the back side with tiny holes that allow the sheathing to breath. The holes are too small for rain to pour in. No doubt it would not work in every climate. It works fine on the West coast from California to Alaska.
    I helped build and roof a lot of houses in the Pacific NW when everybody had to have Cedar shake or shingle roofs. Back in the 70's, eh? I tore a few roofs off as well. Cedar roofs don't suffer from condensation problems as long as the strapping is spaced and that is why they are nailed to open strapping. Google Lindal Cedar Homes.

    With most of the old growth cedar cut up and sold for roofing and a few guitar tops, we are converting most of those old roofs to solid sheathing and fiberglass reinforced shingles. Now that sheathing needs better ventilation.

    John Kogel, RHI, BC HI Lic #47455
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  21. #21
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    Default Re: Attic rafter bay insulation

    Hang some game, fire up the woodstove...WAALAA a Smoke House !!!


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