robert.thompson
Basic Member
Posts:243
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| 28 Nov 2012 02:58 PM |
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Hello:
Using a modified Larsen Truss (R-50), is it better to use 1/2" plywood or 1/2" OSB, or is sheathing required at all? Is the air-tight drywall system sufficient? Thanks, Rob. |
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Rob.
http://googlevoiceforcanadians.com/ |
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Bob I
Veteran Member
Posts:1435
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| 28 Nov 2012 03:28 PM |
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some builders are building without sheathing; I think that is false economy, so it is a matter of opinion. Any type of paper can be easily damaged by small animals or insects; OSB as well, but takes a little more effort. Either OSB or plywood or Huber OSB ZIP will work; (check the permeance of the material - you can do that online) ZIP is easiest to air seal using their tape. Plywood or OSB can be taped either by priming 1st, or by using imported acrylic Vana or Siga tape. In general the better the air seal the better the performance of the insulation and therefore the house. |
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| Bob Irving<br>RH Irving Homebuilders<br>Certified Passive House Consultant |
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Bob I
Veteran Member
Posts:1435
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| 28 Nov 2012 03:39 PM |
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Just read a much more detailed response here:
http://www.greenbuildingadvisor.com/blogs/dept/musings/how-risky-cold-osb-wall-sheathing?utm_source=email&utm_medium=eletter&utm_content=20121128-rotted-walls&utm_campaign=green-building-advisor-eletter |
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| Bob Irving<br>RH Irving Homebuilders<br>Certified Passive House Consultant |
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robert.thompson
Basic Member
Posts:243
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| 28 Nov 2012 04:14 PM |
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Posted By Bob I on 28 Nov 2012 03:39 PM
Just read a much more detailed response here:
http://www.greenbuildingadvisor.com/blogs/dept/musings/how-risky-cold-osb-wall-sheathing?utm_source=email&utm_medium=eletter&utm_content=20121128-rotted-walls&utm_campaign=green-building-advisor-eletter
Thanks Bob.
I guess that you are not too enthusiastic about Riversong's idea of a 'breathing wall'. For the $8.00 additional per sheet, I'll go with plywood - ZIP products are not available in Canada, to my knowledge. Rob. |
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Rob.
http://googlevoiceforcanadians.com/ |
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arkie6
Veteran Member
Posts:1453
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| 28 Nov 2012 07:02 PM |
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Where can you get plywood for $8 per sheet? 15/32" D-D grade plywood sheathing is running $17 per sheet here. Even the less expensive 7/16" OSB is $12 per sheet here. A couple years ago, the 7/16" OSB was running ~$5.50 per sheet here, but it has shot up in price during the last year. |
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MikeSolar
Basic Member
Posts:376
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| 28 Nov 2012 08:53 PM |
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I'm no fan of OSB for any reason. Maybe just old fashioned but I have seen too many floors and sheathing soaked and expanded and usually moldy to trust it. Plywood all the way. |
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| www.BossSolar.com |
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robert.thompson
Basic Member
Posts:243
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| 29 Nov 2012 10:40 AM |
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Posted By arkie6 on 28 Nov 2012 07:02 PM
Where can you get plywood for $8 per sheet? 15/32" D-D grade plywood sheathing is running $17 per sheet here. Even the less expensive 7/16" OSB is $12 per sheet here. A couple years ago, the 7/16" OSB was running ~$5.50 per sheet here, but it has shot up in price during the last year.
I meant 'for an additional $8.00 per sheet', i.e., $23.47 for 4' x8' x 1/2" here in Montreal. |
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Rob.
http://googlevoiceforcanadians.com/ |
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arkie6
Veteran Member
Posts:1453
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| 29 Nov 2012 02:32 PM |
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When I read the "For the $8.00 additional per sheet", I assumed that was in comparison to no sheathing as that was one of the options offered. |
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Rich Writes
New Member
Posts:2
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| 08 Dec 2012 07:01 PM |
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I prefer plywood to CDX in most cases and would use it on my home in this instance. The $8.00 per sheet additional does add up but is well worth the expense. |
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Alton
Veteran Member
Posts:2164
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| 09 Dec 2012 03:25 AM |
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Although the code tries to treat OSB the same as plywood, I prefer plywood. Joe Lstiburek says that plywood handles leaks better than OSB. In my part of the country, CDX is a low grade of plywood for limited exposure to weather. See http://www.ezwoodshop.com/plywood/cdx-plywood.html |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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Lbear
Veteran Member
Posts:2740
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| 09 Dec 2012 04:24 PM |
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Posted By Alton on 09 Dec 2012 03:25 AM
Although the code tries to treat OSB the same as plywood, I prefer plywood. Joe Lstiburek says that plywood handles leaks better than OSB.
In my part of the country, CDX is a low grade of plywood for limited exposure to weather. See http://www.ezwoodshop.com/plywood/cdx-plywood.html
OSB has a tendency to swell especially around the cut edges when exposed to water. They do put a water resistant coating on OSB but this is only meant to get you past the building stage when it is exposed to an occasional rain event. It is not long term protection. Plywood is more expensive than OSB, so most builders stick with OSB. Here in Phx Arizona they use neither on the homes. They simply stick frame it and cover it with 1/2" EPS and stucco it. As long as it doesn't rain and we don't see high winds, the homes do OK but in high winds they rack like crazy without the OSB shear panels in place. Code is very lax; 70MPH winds (3 seconds) and no seismic. I kid you not when I say I can go into an attic and move the gable wall end with one hand by pushing lightly on the wall. Zero OSB up there and no drywall, so you have basically no shear. Scary building practices out here. |
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jonr
Senior Member
Posts:5341
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| 09 Dec 2012 04:28 PM |
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they rack like crazy without the OSB shear panels in place They should be using diagonal steel strapping. When it comes to air barriers - use two. |
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Bob I
Veteran Member
Posts:1435
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| 09 Dec 2012 05:16 PM |
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What do you folks think of Advantech? |
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| Bob Irving<br>RH Irving Homebuilders<br>Certified Passive House Consultant |
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engineer
Veteran Member
Posts:2749
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| 09 Dec 2012 07:40 PM |
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Great stuff but pricey |
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Curt Kinder <br><br>
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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FBBP
Veteran Member
Posts:1215
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| 09 Dec 2012 10:20 PM |
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One thing to think about when comparing plywood and osb. OSB never delaminates. It might swell (only if prolonged exposure to moisture) but usually just the top flakes will swell and or loosen. Plywood has a bad habit of delaminating and more so if exposed to moisture. You can glue and screw a plywood floor and still have squeeks because of internal delamination. |
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Lbear
Veteran Member
Posts:2740
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| 09 Dec 2012 11:30 PM |
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Posted By jonr on 09 Dec 2012 04:28 PM
they rack like crazy without the OSB shear panels in place
They should be using diagonal steel strapping.
When it comes to air barriers - use two.
Bracing is only done in corners but when talking with engineers, they ALL recommended shearing the entire home with OSB. The reason WHY they don't shear the entire homes out here is because builders want to save $$$ with labor and materials. The code allows them to skimp on the OSB, so the builders do it. After a good 2-3 day rainstorm, although rare, we do get winter storms from California that can cause extensive rain/flooding. Many homes will experience leaking walls and roofs. A builder can build a new home and not get called back for numerous years (4+ years) until we get a good soaking rain. Once that soaking rain happens, the stucco gets saturated with water and water goes BEHIND the stucco and any rips or tears in the tar paper will allow water to flow inside of the wall cavity and soak the drywall. In addition, as the home racks in winds over the years, the tar paper begins to rip and tear and this adds to water leaks. |
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Alton
Veteran Member
Posts:2164
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| 10 Dec 2012 08:57 AM |
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Lbear,
Are custom-built (contract) homes in your area also built this way? I can understand the builders taking shortcuts if there is not a homeowner on site during the build but custom homes should be built according to the homeowner's plans and codes. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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Lbear
Veteran Member
Posts:2740
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| 10 Dec 2012 12:39 PM |
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Posted By Alton on 10 Dec 2012 08:57 AM
Lbear,
Are custom-built (contract) homes in your area also built this way? I can understand the builders taking shortcuts if there is not a homeowner on site during the build but custom homes should be built according to the homeowner's plans and codes.
The few custom homes I have seen are completely covered with OSB. Like you mentioned, with custom homes the homeowner demands better techniques and the contractor will completely shear the home with OSB. Another issue that comes up with these homes is that due to the lack of OSB, if you go to hang something from the outside and you don't hit a stud, the screw has nothing to grip to. The 1/2" of stucco just crumbles into dust, the styrofoam is useless, and that's all you got. At least with OSB the screw could grip that. |
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Dana1
Senior Member
Posts:6991
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| 10 Dec 2012 02:03 PM |
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Posted By Alton on 09 Dec 2012 03:25 AM
Although the code tries to treat OSB the same as plywood, I prefer plywood. Joe Lstiburek says that plywood handles leaks better than OSB.
In my part of the country, CDX is a low grade of plywood for limited exposure to weather. See http://www.ezwoodshop.com/plywood/cdx-plywood.html
It's true that plywood handles moisture loads far better than plywood due to the greater exposure of end-grain (to wick surface moisture into the wood) and the higher levels wood-sugars created out of the lignin & cellulose by the heat of processing it. But it's still pretty good stuff and will last as long as plywood or planking if you treat it right. With backventilated siding, high-perm housewrap (or even 5-perm roofing felt) the drying capacity toward the exterior is huge! (Which is the whole point of building that way- ventilated rainscreen gaps ROCK!) With a fat R50 layer cellulose on the other side of it, even if it took repeated soakings from wind-driven rain much of the moisture that did wick into the OSB would be redstributed by the absorbency of the cellulose. OSB & plywood only have a problems when it can't dry quickly. It takes quite a bit of moisture to create a problem in the sheathing of a rainscreened cellulose wall, but I'm sure there are people capable of screwing up the window & door flashing bad enough to make almost anything fail, eh? ;-) |
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Alton
Veteran Member
Posts:2164
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| 10 Dec 2012 07:23 PM |
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Posted By Dana1 on 10 Dec 2012 02:03 PM
It's true that plywood handles moisture loads far better than plywood due to the greater exposure of end-grain (to wick surface moisture into the wood) and the higher levels wood-sugars created out of the lignin & cellulose by the heat of processing it. But it's still pretty good stuff and will last as long as plywood or planking if you treat it right.
Dana1, I do not believe that the paragraph above says what you meant. |
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Residential Designer &
Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
334 826-3979 |
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