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Dry rot in siding: can I safely ignore it?

Camponotus | Posted in General Questions on

Hi folks,

I have some dry rot in the T-111 siding along the lower margin of the south side of my garage (Climate zone 4C, Pacific Northwest).  I’m not sure what the wall assembly entails, though I assume it’s adherent to code-minimum construction practices in Oregon at the time it was built (in 1984).

So here’s my 1st question: is there any risk to ignoring this?  My main concern is that the fungus would spread to structural elements, though I assume there’s some sort of moisture barrier beneath the siding… which I also assume would impede the growth of the fungus (?).

2nd question: should I ignore the rot… would it be helpful to repaint the affected area? (I.e., would it slow the spread of the fungus?) Or would this be pointless since the wood is already infected?

3rd and last question: are there any potential problems to ignoring the dry rot besides potential structural issues?

Any suggestions would be much appreciated!

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  1. Tim R | | #1

    It is possible that the t1-11 siding is the structural shear panel for the building.

    1. Camponotus | | #3

      Hi Tim,

      That's a good thought -- I didn't even realize that T1-11 could be used as a shear wall. Do you know of any clues I might look for that could indicate that's the case? (without tearing open the wall?)

  2. Deleted | | #2


  3. GBA Editor
    Brian Pontolilo | | #4

    Good morning Camponotus,

    It seems you have some understanding of rot. You know that part of the cause is a fungus. But you should also know that there is no such thing as dry rot in wood. For rot to occur, the wood must be getting wet, and staying wet for a bit. You could read this article from FHB to understand wood rot a bit better:

    Are your garage walls insulated and finished on the inside? If not, they should dry pretty well. So I suspect that the siding is getting splashed with roof runoff when it rains. Are there gutters on your garage? Are they working? How close is the T-111 to the ground?

    1. Camponotus | | #5

      Hi Brian,

      Thanks a lot for the excellent reference article! I found it very useful.

      Regarding your question of whether the garage walls are insulated and finished: they are finished on the inside, though I suspect no insulation. There’s one hole in the sheetrock already in a different wall in the garage, and – assuming it’s representative of the whole garage – there’s no insulation in the stud bay (and I assume that if the wall had insulation at all it would be fiberglass batts). Looking in the hole, there’s a grey-ish felt-like material that appears to be flush against the T1-11. I don’t know my building materials, but it looks exactly like landscape fabric. Tar paper maybe?

      As far as the roof goes, it’s a basic gable roof, and the wall in question is one of the two sides that lack gutters (perpendicular to the roof ridge) – so the roof is not offering a lot of protection to the siding here. It’s also a 2-story house, so the siding is even more removed from any shelter from the roof. The siding is about a foot off the ground. The rot is along the bottom margin of the siding (presumably because of splash-back from the ground or just lack of roof coverage). I’m thinking that this wall (being south facing with little shade) gets substantial photodamage, which weakened the wood and primed it for the fungus, which otherwise might have taken longer to get a foothold (there is negligible rot on any of the other walls of the house).

      Unfortunately, I don't know much about the building details of the house -- we just moved in a couple months ago, and other than a green light from the building inspector, I can only assume code minimum specs at the time it was built (1984) -- and I'm not even sure where to find a copy of local code from 35 years ago to get an idea of what that even means.

      1. GBA Editor
        Brian Pontolilo | | #6

        Thanks for all of the additional info. If the walls are empty, without insulation, vapor barriers, etc., and the garage is unconditioned, then you probably don't have a moisture drive/condensation problem. I'd consider installing gutters first and then replacing or repairing the damaged siding.

        1. Camponotus | | #7

          Hi Brian,

          Thanks a lot for your suggestions. I’m wondering, though, if the dry rot is mostly a cosmetic concern that I could safely ignore, though, or whether neglecting repairs now will likely lead to costly additional repairs in subsequent years. Do you think it’d be reasonable to just leave it?

          And if just leaving it is not recommended, is there something cheap and easy I could do to extend a reasonable period of “cautious neglect” (say, adding some sort of sealant)?

          As we just moved in, renovation funds are tight; plus, with small kids, DIY projects take a very, very long time to complete...


          1. GBA Editor
            Brian Pontolilo | | #8

            As long as the rotted panel is not structural and you stop the rot from continuing, then the repair is cosmetic. I don't think it is a problem if you don't want to fix it. I'm not sure how extensive the damage is, but if it is on the smaller side, you could use an epoxy repair kit, like System 3's End Rot:

  4. Camponotus | | #9

    Thanks a lot, Brian! The damage is not particularly extensive, and I think a repair kit like what you linked might actually do the trick. Thanks again for all your help!

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