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Stop wasting money: Forget sheathing…

| Posted in General Discussion on March 4, 1999 04:05am

*
I can’t understand why I see post after post assuming sheathing is even needed. If its racking and shear strength you want, use cross bracing that is attached to each stud; or, use some occasional posts and girts in the wall (hidden or visible).

Roof and wall sheathing is overkill, overbuilding and redundant.

If its an exterior bulk water barrier you need; your siding, roofing and water wrapping can do that.

Sheathing frosts up, condenses and reduces the R value of your insulation unless you use mechanical ventilation (and who mechanically vents and dehumidifies a wall cavity — see below — you should vent the cavity in a way you can control its humidity level).

If you don’t like housewrap stapled to the ouside of the cross-strapped studs and rafters (surfactants may breakdown the wrap) use polyethelyne and strip-caulk the studs/rafters to bulk-water seal your wall and roof cavities.

Since the cavities are sealed on the interior, sealing the exterior will resolve those endless debates about convection-across-insulation. Insulation debates are incomplete without putting moisture factors and mechanical venting/dehumidifying into the formula. No insulation will work to spec under live conditions.

Vent the walls and roof cavities at the tops and bottoms, into the interior environment and let your HVAC system look after condensation. HVAV will manage humidity/frost-condensation levels more efficiently than any passive ventilation of the cavity to the outside could.

Raise your siding and roofing off the poly/housewrap covered studs/rafters with firring strips or purlins enough to prevent a capillary sandwich of siding against wrap/poly and keep the drain plane unrestricted. On the roof, purlins will serve as cross bracing and separate roofing material from the water-wrap.

If you use Type 2 EPS or XPS foam board on the outside, combining it with sheathing will turn your wall/roof into a sponge and rot the framing structure eventually. Whether its exterior or interior ply or OSB, it doesn’t matter.

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Replies

  1. Guest_ | Mar 02, 1999 11:32pm | #1

    *
    Tedd,

    My idea is to use foil faced foam w/ taped seams instead of poly or tyvak...and then fir strips between sidng and or roofing....Also in framed bays use dp and no poly...then drywall...and no venting of closed areas..just control moisture and penetration air leaks and allow dp to control inner assembly moisture...what do you think?

    Fred...How about you too?

    Jack : )

    1. Guest_ | Mar 02, 1999 11:46pm | #2

      *Being that the vapor barrier is on the outside of the wall (isn't that the wrong side in heating climates) then you propose to control interior humidity? Like with an ERV or dehumidifier?-Rob

      1. Guest_ | Mar 02, 1999 11:56pm | #3

        *Rob,Upstate New York...my area...needs no de-humidifiers if the cellar has been built properly...Also has to do with occupants and their lifesyle choices....there are people who take 24 hour unvented showers...always cook three meals a day boiling everything with the lids off etc...I've had these problems with homes that I worked on and was called back to ask where the water came from...Humidifiers set on 80% !@!As to exterior foam...I think it's much better than under the drywall and better than sheathing as far as Ted's talk about condensing surfaces adjoining insulation....Warm insulation is happy insulation.Working w/ my favorite law..."the law of opposites,"Jack : )

        1. Guest_ | Mar 03, 1999 07:13am | #4

          *Jacki "As to exterior foam...I think it's much better than under the drywall. . . "While I tend to do it that way myself, it has occurred to me lately (as part of an interior RFBI install.) that when installed carefully on the interior, RFBI could eliminate both moisture by convection and diffusion. If the best that the new VDR theory can do is slow down (retard) the inevitable diffusion of i some amountof moisture through the d/wall and framing, why not stop it all together? Does any one know if XPS or foil faced Plyiso can stop diffusion?i "Warm insulation is happy insulation."on the exterior???? Just wonderin'??-Patrick

          1. Guest_ | Mar 03, 1999 08:26am | #5

            *Patrick,Foam on the inside may work...but the problem I see is this....You seal the **** out of it...it leaks somewhere because it's not done perfect...the leaking spots leak into cold cavities in a big way...those few spots have to leak all that's going to leak...moist air is going to condense...water...rot...no way to dry to "the easy to dry inside warm side," cause the "super sealed" foam is in the way. You're creating a one-way "capillary still"...great if stranded at sea and no water to drink...not so good for homes...Also foam on the outside can be built possibly for less than standard construction and foam on the inside detailed with special handling for all electric boxes, and sealing and overlaying drywall and fir strips and lost interior square footage...and rockers who hate to work over foam and foam in fires outgassing and killing all or in twenty years all getting chemical sensitivity...I'll stop but I could go on...What do you think,Jack : )

          2. Guest_ | Mar 03, 1999 09:08am | #6

            *Jacki ... love that staccato writing style. . . very Jack Kerouac (have we been there already?).Can't disagree with the extra detailing. . . I do all my own electrical & d/wall anyway,(and who cares what rockers think anyway) but for others a major concern. . . still curious about diffusion and RFBI. . .Are off gassing and chemical sensitivity any worse than spray Pur.??Shouldn't need to say that a lousy install. does not reflect upon material used. I've torn out wallboard on two occasions that had poorly blown in cells in the cavities ( wish I had pictures. . . never occured to me . . . didn't prove anything except poor workmanship!!)Patrick :(

          3. Guest_ | Mar 03, 1999 09:17am | #7

            *Patrick,Not sold on pur yet either...for the same reason you stated...chemical outgassing and also its too d*** expensive!...Homes need to be inexpensive..simple...easy for anyone to build, first time...tolerances have to be wide enough to allow for b average installation results,and so forth....Simple Systems built dirt cheap with artistic flair,Aim at the target and shoot,Jack : )

          4. Guest_ | Mar 03, 1999 09:23am | #8

            *JackYour on a roll. . .i "Simple Systems built dirt cheap with artistic flair" shall we put this on your business card or your gravestone. . . LOLPatrick :()

          5. Guest_ | Mar 03, 1999 09:27am | #9

            *Both

          6. Guest_ | Mar 03, 1999 09:31am | #10

            *JackI'll have my people call your people. . .How's your health. . .any signs of decay???Patrick :)(

          7. Guest_ | Mar 03, 1999 09:34am | #11

            *The health of my stash in de Cayman Islands?Have you been following me aroungd the globe???De Stash makes fur de good health, ya...Jack : )

          8. Guest_ | Mar 03, 1999 09:43am | #12

            *Ja Man :) :) :)

          9. Guest_ | Mar 03, 1999 09:47am | #13

            *So JackSeeing as how we're the only ones awake here tonight, whadda ya think of this ugly new white posting page, with the designer grey boreder???Do ya think Sean is a yuppie???

          10. Guest_ | Mar 03, 1999 09:59am | #14

            *Well Patrick,Funny you should ask...I sent Sean email today already and mentioned the white and blue bright "look alike" being not nearly so "Fine."I also let him know a few other things about the lesser side of cyberland...he's all right...emails back always.The changes probably have made the site much faster and I think the edge is their for future use...like so many other sites..a place for a second and third window with lists and whatever that stay choosable even while the middle "read" area changes...Making me blow brain cells this late at night,Jack : )

  2. Brian_Lumley | Mar 03, 1999 11:57am | #15

    *
    Perhaps omitting exterior sheathing is fine in some areas. In my construction experience, which spans 35 years, the value of sheathing is self evident. Structures with only siding over tyvek and insulation have a tendancy to pop the interior drywall and plaster. The wind action on the unsupported tyvek weakens it and eventually it tears. Sheathing also helps keep the studs and rafters straight. There is a lot of torque on a building with the weather and movement of people inside.
    As far as insulation is concerned in a northern climate the condensation point of water is about 1/3 of the way through the insulation from the warm side. That is the ideal spot for the vapour barrier. A wooden house that allows the exterior to breathe is your best value home. If the exterior walls are masonary then foam insulation under the veneer is the best.

    1. Brian_Lumley | Mar 03, 1999 11:59am | #16

      *Perhaps omitting exterior sheathing is fine in some areas. In my construction experience, which spans 35 years, the value of sheathing is self evident. Structures with only siding over tyvek and insulation have a tendancy to pop the interior drywall and plaster. The wind action on the unsupported tyvek weakens it and eventually it tears. Sheathing also helps keep the studs and rafters straight. There is a lot of torque on a building with the weather and movement of people inside. As far as insulation is concerned in a northern climate the condensation point of water is about 1/3 of the way through the insulation from the warm side. That is the ideal spot for the vapour barrier. A wooden house that allows the exterior to breathe is your best value home. If the exterior walls are masonary then foam insulation under the veneer is the best.

      1. Brian_Lumley | Mar 03, 1999 12:00pm | #17

        *Perhaps omitting exterior sheathing is fine in some areas. In my construction experience, which spans 35 years, the value of sheathing is self evident. Structures with only siding over tyvek and insulation have a tendancy to pop the interior drywall and plaster. The wind action on the unsupported tyvek weakens it and eventually it tears. Sheathing also helps keep the studs and rafters straight. There is a lot of torque on a building with the weather and movement of people inside. > As far as insulation is concerned in a northern climate the condensation point of water is about 1/3 of the way through the insulation from the warm side. That is the ideal spot for the vapour barrier. A wooden house that allows the exterior to breathe is your best value home. If the exterior walls are masonary then foam insulation under the veneer is the best.

  3. Guest_ | Mar 03, 1999 08:13pm | #18

    *
    Brian, Brian, Brian,

    If you would like to remove two of your edited posts above, then just mouse on over to where it says "delete post."

    Condensation...Others here and there will argue that it(water vapor) doesn't just condense on a plane at a graphed delta T point in say fiberglass....There's much more science involved than that...Fred L mentioned a good one that is radiational cooling at night causing frosted roof decks on nights when the temperature of the air didn't drop below frezzing. And much more...

    As for tyvek and longevity and wind blowing all....yes yes and yes...I think it's definitely not the way to go...

    As for foam mounted tight to wood sheathing...that's a rot problem waiting for capillary "sponge" infused water and a rot disaster "time bomb a ticking" method of
    b not building a home that will last centuries.

    Here's to more insulation yak,

    Jack : ) )(

    1. Guest_ | Mar 03, 1999 09:55pm | #19

      *Ted:Nice post, which will surely attract a lot of different opinions. I unfortunately disagree with you and most of the other posts (except Brian). Here in California, the building inspector would probably throw a cease and desist at you, and you might have your contractor's license taken away for building without sheathing. You certainly would be sued.Fact: 1/2" ply or OSB is stronger than firring strips. Is there any doubt? You may feel that it is overkill, but it is stronger, yes? Here in earthquake country, and I suspect in the Gulf States as well, homes must be built to withstand earthquakes and hurricanes. It is the Code. All cripple walls have to be covered with 3/4" ply and the studs physically bolted to the sill, and the sill physically bolted to the foundation.All bearing walls must be covered with 1/2" osb or ply. Again, this is not an option, it is code, and rough framing will not be passed if sheathing is not securly nailed per standard detail. Studies and experts with more degrees that a thermometer have proved that this technique makes buildings last longer and withstand shear forces. For you to say something contrary is certainly your right, but it is simply wrong. Your technique might be fine for rural Missouri, but is improper building technique here in California. Others would have to comment on sheathing in their home states, and I would be interested in hearing posts from them. As for insulation, I'll leave that up to the experts as well, but most designers and architects that I work with still specify walls with fiberglass bats and a vapor barrier on the inside. I for one have never seen a failure, nor have I seen any literature or articles suggesting that this is improper in any way. If you have a FHB or JLC article that suggests otherwise, please let all of us know.Indeed, if any of you disagree, why not write your own article for FHB or JLC?

      1. Guest_ | Mar 04, 1999 01:47am | #20

        *Patrick. According to you "If the best that the new VDR theory can do is slow down (retard) the inevitable diffusion of some amount of moisture through the d/wall and framing, why not stop it all together?" Patrick I think the long Canadian winter bluse are geting to you. the VDR theory is not the doer, it's the VDR. The very definition of retarder acknowleges that the best way to stay out of court is to accept that we cannot stop moisture migration. Most materials will retard, but very, very few will stop. N'est ce pas? I posted a response to Tedd's calling for wood, metal or both let-in bracing, but it wound up under Energy. Wood or metal let-in corner bracing does not work. Simpson Strong Tie warns against the use of their metal strapping and let-in corner bracing for anything other than temporary bracing until the structural sheathing is applied.Scooter is right on. The Uniform Building Code, 1997 edition, does not allow wood corner let-in bracing in Seismic Zones 2B,3 and 4.In Canada for Part 9 buildings, national and provincial building codes do not require bracing where exterior walls will have one of the following interior finishes: gypsum board with taped joints, plywood, hardboard, insulating fiberboard, particleboard, waferboard or strandboard.GeneL.

        1. Guest_ | Mar 04, 1999 03:40am | #21

          *Greetings GeneCa va?Notwithstanding the effects of ouri 'drag on'winter ( another big snow dump today- more tonight) the point I was trying to make (awkwardly worded I guess) is that maybe we shouldn't stop at just accepting thei "retarding" of moisture diffusion, but should try to stop it . . . and I wondered whether RFBI can do that? I remain sceptical about my local Provincil code deleting any form of corner bracing from our code with the proviso that interior d/wall is installed.I still sheath with plywood.A bien tot-Patrick

          1. Guest_ | Mar 04, 1999 04:05am | #23

            *Scooter,I totally agree with the idea that seismic and earthquake engineering has to be used where called for.I however live and build in an area where the cost of heat is the only real annoyance along with problems with ice dams and moisture control...So a thread stating the region of discussion would definitely clarify all...Chill-in in Upstate NY,Jack : ) )(

  4. tedd | Mar 04, 1999 04:05am | #22

    *
    I can't understand why I see post after post assuming sheathing is even needed. If its racking and shear strength you want, use cross bracing that is attached to each stud; or, use some occasional posts and girts in the wall (hidden or visible).

    Roof and wall sheathing is overkill, overbuilding and redundant.

    If its an exterior bulk water barrier you need; your siding, roofing and water wrapping can do that.

    Sheathing frosts up, condenses and reduces the R value of your insulation unless you use mechanical ventilation (and who mechanically vents and dehumidifies a wall cavity -- see below -- you should vent the cavity in a way you can control its humidity level).

    If you don't like housewrap stapled to the ouside of the cross-strapped studs and rafters (surfactants may breakdown the wrap) use polyethelyne and strip-caulk the studs/rafters to bulk-water seal your wall and roof cavities.

    Since the cavities are sealed on the interior, sealing the exterior will resolve those endless debates about convection-across-insulation. Insulation debates are incomplete without putting moisture factors and mechanical venting/dehumidifying into the formula. No insulation will work to spec under live conditions.

    Vent the walls and roof cavities at the tops and bottoms, into the interior environment and let your HVAC system look after condensation. HVAV will manage humidity/frost-condensation levels more efficiently than any passive ventilation of the cavity to the outside could.

    Raise your siding and roofing off the poly/housewrap covered studs/rafters with firring strips or purlins enough to prevent a capillary sandwich of siding against wrap/poly and keep the drain plane unrestricted. On the roof, purlins will serve as cross bracing and separate roofing material from the water-wrap.

    If you use Type 2 EPS or XPS foam board on the outside, combining it with sheathing will turn your wall/roof into a sponge and rot the framing structure eventually. Whether its exterior or interior ply or OSB, it doesn't matter.

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