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Old 02-28-2012, 07:27 AM   #16
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Milled lumber suitable for home construction?


The Douglas fir should be outstanding building lumber. And I believe you indicated you have a kiln available, so moisture content is not an issue. As for shrink and swell, that is almost entirely humidity driven. There are numerous on line tables available that will tell you the approximate dimensional changes you can expect for different species of lumber in all three axes (along the grain is lowest, then there are the two transverse grain directions).

Check out this website http://www.csgnetwork.com/emctablecalc.html
which gives you an online calculator that allows you to compute the equilibrium moisture content of wood based on the relative humidity and temperature. This will allow you to get a feel for how the moisture content of your wood is going to vary over the course of a year. Once you know that, you can go the the Forest Products Laboratory website and determine the percentage movement your boards are going to experience over the course of a year (see page 13-15 of http://www.fpl.fs.fed.us/documnts/fp...chapter_13.pdf).

You want to provide enough space so there is no chance the boards will swell and buckle. So far as I can tell, the normal technique for installing dimensional lumber sheathing is nailing, however I do not know the pattern, maybe one of the old time carpenters on this forum knows the secret. I would certainly consider using stainless steel nails to reduce corrosion.

As for shear strength, your Douglas fir is going to be just as strong as plywood or OSB of equivalent thickness, however not as dimensionally stable, and certainly will not provide equivalent lateral support to the frame due to the narrow width of the sheathing boards and the required gaps between boards. I am not familiar with historical framing practices that were used to compensate for the lack of lateral rigidity, perhaps the trick was the use of diagonal let in bracing. Again, maybe one of the carpenters on this forum can speak to this question, which is very important in seismically active California. One thing plywood sheathing is very good at is providing rock solid lateral resistance strength in framing when it is properly installed. By the way, just a note, OSB is claimed to be just as strong as plywood, and of course the tests suggest that it is, but I never use it, I am concerned about its sensitivity to moisture, and my experience with quality plywood has been excellent.

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Old 02-28-2012, 07:31 AM   #17
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Milled lumber suitable for home construction?


i wasn't suggesting osb would be better
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Old 02-28-2012, 08:04 PM   #18
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Milled lumber suitable for home construction?


One thing I didn't see mentioned is that a house sheathed lumber vs sheet goods is going to have a lot more routes for air infiltration.
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Old 02-28-2012, 08:07 PM   #19
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Milled lumber suitable for home construction?


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Originally Posted by Daniel Holzman View Post
I am not familiar with historical framing practices that were used to compensate for the lack of lateral rigidity, perhaps the trick was the use of diagonal let in bracing.
In some places, the lumber sheathing was applied on the diagonal. Probably not as rigid as sheathing with sheet goods, but a lot more rigid than sheathing with lumber run horizontally.

Last edited by A Squared; 02-28-2012 at 09:02 PM.
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Old 02-28-2012, 10:17 PM   #20
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One thing I didn't see mentioned is that a house sheathed lumber vs sheet goods is going to have a lot more routes for air infiltration.
Don't forget the bugs.
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Old 02-28-2012, 10:45 PM   #21
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Milled lumber suitable for home construction?


most of the board sheathing i see around here is t&g diagonally run,shiplap or notched type joint may be easier to fabricate and would help with infiltration issues while still maintaining a superior drying potential then sheeting
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Old 02-28-2012, 11:39 PM   #22
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Don't forget the bugs.
Yeah, that too.
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Old 02-28-2012, 11:42 PM   #23
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Milled lumber suitable for home construction?


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most of the board sheathing i see around here is t&g diagonally run,shiplap or notched type joint may be easier to fabricate and would help with infiltration issues while still maintaining a superior drying potential then sheeting
That's gonna add a whole 'nuther level of complexity to his lumber manufacturing though
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Old 02-29-2012, 12:44 AM   #24
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Milled lumber suitable for home construction?


I've been scouring the web looking for data on this topic. I found some interesting reports and thought I'd share what I had found.

I'm not arguing one way or the other because I don't know enough to have any position on this yet but I'll put this out there for you guys who do know what you're talking about to analyze, demystify and explain. Maybe some benefit can arise from all my search time.
Tests showed that horizontal lumber sheathing, even when combined with bracing, did not contribute as much to the strength and stiffness as the interior finishing materials. At a displacement of 13 mm, which is perhaps the limit of acceptable distortion, such bracing and sheathing contributed only 20 to 30% of the total strength. The remainder was due to the interior finish. On complete houses the exterior walls carry only part of racking forces. The partitions which are normally fastened to the ceiling diaphragm also carry part of the total racking force (Figure 2). The contribution of sheathing and bracing to the total racking strength would be somewhat less, therefore, than that indicated by tests on the exterior walls only.

These tests led to the conclusion that bracing and sheathing were not necessary to resist racking forces where the interior was finished (although sheathing may be necessary as a nailing base or support for some siding materials). This decision is reflected in current Canadian building code requirements 171. As a result, very few Canadian racking tests have been carried out since the 1950ís. Although most wood frame buildings continue to be sheathed, this is primarily to permit rapid protection from the weather and, in the case of insulating sheathings, to reduce heat loss. Tradition, however, is also considered to be a significant factor in retaining sheathing.
Trying to find clearly spelled out data in table form is like looking for the Lost Ark of the Covenant. I don't know if I'm just not hitting with the correct search terms or what, but I wasn't having much luck finding engineering tables on-line. This is the best I could find. Table #1 in this report: What exactly is "diagonal sheathing-special"?


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Old 02-29-2012, 01:27 AM   #25
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Milled lumber suitable for home construction?


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What exactly is "diagonal sheathing-special"?
Well, it's diagonal sheathing, but not the conventional kind
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Old 02-29-2012, 01:37 AM   #26
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Well, it's diagonal sheathing, but not the conventional kind
Thanks!!! Everything is now clear as mud.

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