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Why don't wood construction sites get damaged in the rain?

  1. Jul 10, 2017 #1
    They're building new condos across from my parents house right now (adjacent neighborhood). I see this site everyday and it's growing. Right now, they've got a lot of the framework up for the condos and it's all wood (as far as I can tell).

    It's also raining a lot here.

    Question - why don't these things get soaked in the rain water and get damaged ...and fall over?

    Is the wood really that sturdy? We've had three straight days of super humid weather and pretty big rain showers with one of those days giving us minor flooding.
  2. jcsd
  3. Jul 10, 2017 #2
    A forester or someone else who really studies wood could probably give you a technical answer; but here are my simple thoughts:

    1) Some amount of water is natural to wood & trees. Trees are built to siphon water from roots up to the very top of the tree via the outermost, living layer of wood. Milled wood usually retains some amount of moisture depending on local climate; for example, if a piece of furniture is built in a shop with a fairly normal temperate humidity of, say, 40 percent, and is then moved to a house in a very arid climate, gaps in joints etc. will likely start showing up. Anyway, the point is water is not a foreign substance to wood, whether living or harvested.

    2) Excess water can of course damage milled wood . . . but in my experience (handyman level), this shows up mostly as deterioration if unprotected wood has been allowed to stay soaked and/or in contact with the ground for too long a time and is starting to rot. That's why they make treated lumber for outdoor use. Whereas when considering an exposed frame erected for a house, and getting rained on, there's no reason to think you'd see drooping, bellying, or "falling over" in the 2x4s and 2x6s used for framing. Fibers in wood are pretty tough; and of course a skeleton frame has very little load on it.

    Plus consider that boats have traditionally been built of wood; as well as floating docks and piers etc.; and there too the concern isn't the deformation of the structure when exposed to water, so much as the long-term potential for rot or weathering if not protected to some extent by paint, oil, chemical treatments, belonging to naturally resistant species, etc.

    Here's a decent mid-level article on wood's structure and its usefulness as a construction material: http://www.explainthatstuff.com/wood.html

    And this PDF, if you read a ways, explains that wood isn't damaged so much by getting wet as by rotting and weathering; rot can come from fungus and weathering from repeated cycles of wetness and dryness. So again, just a few days or even weeks of rain by itself isn't a big concern for framing: http://www.lsuagcenter.com/NR/rdonl...248E54EB4E83/51180/pub2703WoodDecayLowRes.pdf
    Last edited: Jul 10, 2017
  4. Jul 10, 2017 #3
    Appreciate the very detailed post and time you put into it, UT.

    The point about wood boats is quite good. I had forgotten about that and it makes sense that if they can withstand constant water contact that housing frames should too.

    I shall take a look at those reads later in the day. Good stuff!
  5. Jul 10, 2017 #4
    You will have noted that log cabins can stand for decades or more, right?
  6. Jul 10, 2017 #5


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    But haven't the logs used in those cabins been treated with insulants, etc?
  7. Jul 10, 2017 #6
    There's one here here, the "Bacon Log Cabin" (no kidding) that has been in place since at least 1835.
  8. Jul 10, 2017 #7
    I am certainly not an expert but I think many of the log cabins pre 1940 used "old wood". Meaning the trees weren't from some logging farm. These old wood trees are far better at resisting rot.
  9. Jul 10, 2017 #8


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    Presumably they will let the wood dry out before encasing the framing in drywall, to prevent future rotting. There may be building codes about how wet the wood can be before sealing it off, but I'm not sure about that.

    BTW, water and even humidity can make a difference in the dimensions of the wood. I've build several sets of cabinets for my homes and as volunteer work for my kids' schools, and I once made the mistake of preparing some wood for shelving and letting it sit for a few weeks before I could install the system. The humidity was higher when I wanted to install my shelving system, and the wood had swelled a bit with the higher humidity, so the shelves no longer fit into the dados I'd cut in the support structures. Ack!

    So I re-did the dadoes and it all worked out, but from that I learned to respect how humidity affects raw wood. Maybe @phinds can offer more thoughts.
  10. Jul 10, 2017 #9


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    I'd never thought about this before but I do know anecdotally that the logs in old log cabins are not treated in any way. I'm not even sure they were always properly seasoned before use although it would be odd if they were not since unseasoned logs would suffer from the movement problem that @berkeman mentioned. Possibly the logs were chosen for a high pitch content. Some varieties of pine have that.

    Oh, and log cabins in the early days in particular tended to be made using "old growth" logs with a high ring count. These are somewhat less prone to decay because there are no wide areas of soft latewood in the growth rings.
  11. Jul 10, 2017 #10

    jack action

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    How about underwater logging:
    And if you don't like your wood wet, you're probably not a fan of log driving:

  12. Jul 10, 2017 #11


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    "sinker" wood can last FAR longer than above-ground wood because of a lack of oxygen in the water. There are 50,000 year old "ancient kauri" trees in New Zealand that were discovered some years back in bogs. The lumber from them looks brand new.
  13. Jul 10, 2017 #12

    jim mcnamara

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    Green wood (logs, too) are about 30+% moisture (call it MC)

    S-Dry (construction grade framing timbers in the US) lumber is kiln dried to ~18%MC, which reduces the movement discussed about building with logs. It can also take getting wet and drying out. Uneven drying causes warp because wood MC on two sides changes relative to each other. Wood has a coefficient of expansion as a function of MC.

    If you take furniture grade wood (7-9%MC), build a nice chair, put it outside unfinished, and then let it expand and contract with relative humidity changes over several years: the chair can literally fall apart.

    It is the repeated expansion and contraction of wood that does the most damage to wood joints. Not just one or two dousings from a rain storm. In places like Portland Oregon, builders entomb partial house frames in clear plastic because of daily rains over weeks and months will trigger rot in timbers, as well as prolonged expansion/contraction issues if the project drags on.

    See R. B. Hoadley 'Understanding Wood', or go to the USDA Forest Products website for more information. https://www.fpl.fs.fed.us/
    Last edited: Jul 10, 2017
  14. Jul 10, 2017 #13

    jim mcnamara

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  15. Jul 10, 2017 #14


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    Yeah, that too, although both bog oak and swamp oak turn an ugly gray black. The "ancient kauri" wood is pristine, as is sinker pine, sinker cypress, sinker ... etc
  16. Jul 11, 2017 #15
    There's a industry devoted to recovering sunken logs from the bottom of the Great Lakes. Almost no oxygen, fresh water, very little marine life.

    @ Greg Bernhardt

    The tree farming industry is fairly new and aimed at making pulp wood, IIRC. The original growth trees used for log cabins back in the day were whatever was closest.

    And history buffs love to note that Abraham Lincoln was born in a log cabin he built with his own hands.
  17. Jul 11, 2017 #16


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    Not necessarily. Out my way (Washington state) most of the tree farms grow wood for lumber or plywood. Pulp wood is used for making paper.
    The trees grown out this way are predominantly Douglas fir.
    I don't know about the old-time log cabins, but people who have log cabins nowadays treat the wood with some kind of oil to protect it against weathering.

    Also, some kinds of wood are naturally bug-resistant; e.g., redwood (Sequoia species) and Western Red Cedar.
  18. Jul 11, 2017 #17
    Lumped it all together, not a tree person.
  19. Jul 12, 2017 #18
    This happens to be an actual case where I'm familiar with the subject (a rarity on this forum). The stud walls you see being framed in the rain will absorb and loose water with no issues, (providing there is adequate venting to release trapped moisture) after the wall is framed, there is some expansion when exposed to the rain but your looking at "rough framing" where + - three eighths of an inch is a normal margin, it's the Finish work that hangs on the rough where details are more important. Any building code will call for "treat lumber" in the case of concrete or steel connections (these require special fasteners to avoid failure from a chemical reaction). The one thing above all else that would be a problem with the wet wood is uneven or fast drying, (one side exposed to the sun so that it dried faster). Concerning Log Homes, besides good old fungal rot, they are a smorgasbord for ants I usually have to deal with "black carpenter ants". With the exception of a desert situation untreated logs don't last long, all they old ones will be sealed in one way or another. (yes, Red Cedar does make one of the best house logs you could get, providing its clear of heart rot. also outstanding from a Seismic Engineering standpoint) :smile:

    Good one :wink:
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