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I am removing the lath and plaster (to add insulation) in my 1929 bungalow that I just bought in Portland, Oregon.

Along an exterior wall, the last piece of lath and a little bit of the plate were mostly wood powder.

I scraped away about 1/4 - 1/2 inch of the soft stuff around the corner of the the plate, after that it's solid. The studs also appear to be solid.

My question is, what is this, dry rot? Insect damage?

And what do I do with it? Should I replace this section of the plate? Spray some kind of anti-fungal agent on it? Leave it alone?

If it matters, the house was empty for at least a year (maybe two) before I bought it.

Distance Close up Before I cleaned up the wood powder


Update: I've found this in another room too, in a corner. My best guess is that it simply was dry rot, caused by moisture trapped in the corners. The moisture, I think, was left over from the original plastering of the walls. What I didn't show were large blobs of plaster that had fell behind the lath, and dried on top of the rotted area, getting trapped in the wall. I could be wrong, but everything left is solid and dry, so I assume the rot died a very long time ago.

  • that looks like dry rot ... get rid of it ... it can spread to the rest of the house – jsotola Dec 2 '19 at 5:55
  • That might be the answer @jstola. Seth, what room was this in? It doesn't seem like it saw much water, but could it have seen any? or was there an air passage nearby into this wall space that would allow heat - cool condensate to occur? – noybman Dec 2 '19 at 7:34
  • It is in a bedroom with a south east exterior corner. While I've been demoing, I have found maybe 4-5 lath boards that are similarly rotted. However, this is the only case I've found where the rot extended beyond the lath board. My early assumption was that when the wall was originally closed up, there were a few carpenter ants who were caught inside, except they don't leave dust behind. There are windows nearby, so it's possible that a window was left open or failed at some point, allowing water to enter for a little while. – Seth Dec 3 '19 at 21:48
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Pacific Northwest here Corvallis/ Springfield resident for 35 years , I don't see any evidence of ants, termites or beetles our areas chewing pests, it looks more like a fungus or dry rot but is very limited , I would take a screwdriver and press to see if the damage is only on the surface if the screwdriver doesn’t go far it’s only surface damage and a fungicide then a wood treatment to harden and seal the surface should be used. I have found homes that have used the wood Treatment on spongy dry rot , the area sealed and it passed inspection but was noted as a concern, I would probably shim the stud but nothing other than that is really needed from the photo, I might leave it open for a few weeks to see if you do have a small leak and any leaks would need to be fixed but after treating the wood with a fungicide and adding a shim or 2 , I would probably button it up once I was sure there are no leaks into that area if the wood is solid.

I do not believe it is pest based because in all 3 of our normal pests they chew channels and holes not just surface damage that I see. Do this is why I would treat the wood possibly saturate with a hardner based on the screwdriver test.

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In my opinion, there is not enough damage there to warrant a concern.

I would investigate a little more to see if there is deeper damage by taking the tip of knife or ice pick to probe and see how solid the wood is with that. To me with the pictures only, it looks very local. Nothing suggests damage could be anywhere else near there. The saw dust in the last picture suggests insects, but the very light wood after you cleaned it up looks like somebody dumped acid there somehow and it bleached and ate up the wood. But that does not seem possible, given it was inside a wall cavity. Insects will typically eat the softwood and leave the more dense rings alone. But it looks like everything was damaged equally. There is no evidence of water damage either that I can see.

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I am removing the lath and plaster (to add insulation) in my 1929 bungalow that I just bought in Portland, Oregon.

Howdy neighbor! I live just up the street (Seattle) in the same Climate Zone 4 that you inhabit.

My question is, what is this, dry rot? Insect damage?

It's Wood-decay Fungus, which is often colloquially referred to as dry rot.

The most important thing to know about wood is that when it's kept dry (humidity levels < 20%) and out of the path of beavers and fires, it'll last nearly forever. All the bad stuff that happens to wood (fungi, termites, carpenter ants, mold, and other undesirable biologicals) occurs when its humidity rises above 20% (especially above the 40-60% range).

The reason that wood rotted is because it experienced humidity levels above 60% for an extended (months) period[s] of time.

what do I do with it?

You have a few choices:

  1. Leave it. It's a small patch of wood and it won't significantly affect the structure of your home. So long as you keep the walls dry (humidity < 20%) in the future, the rot will go no further.
  2. Cut out about 12" on either side of the rotted section of the boards and replace. Check the cut ends for evidence of rot. If found, cut out more of the boards until you get back to clean wood. The rot travels best lengthwise in a 2x4 as that is the same orientation as the wood's capillaries that carry water and food up from the roots to the top of the tree.

Related Issues

Moisture in the concrete walls

Concrete is porous and wicks soil moisture up from the earth and into your sill plate. That's bad for many reasons: the house is literally resting on the sill plate, the sill plate is what holds the house on the foundation, and bad stuff happens to moist wood. If the sill plate rots away, what keeps your house on the foundation during the next earthquake or wind storm?

Newer homes have damp-proofing applied to the foundation walls and sill gasket material (usually an 1/8" pink compressible membrane) that is laid on the foundation wall before the sill plate is installed. The sill gasket air seals that interface and prevents moisture from the concrete from wetting the sill plate.

Some builders of older houses were clueful ahead of building code mandates (never forget, "up to code" literally means, "the worst quality that can be legally built") were dropping scraps of asphalt shingles or other such materials between the foundation walls and sill plate. Since you have a decidedly old house, odds are you have nothing between your sill plate and foundation wall.

Most of us with older houses are in the same boat. So what can be done?

  1. Make sure gutter downspouts direct water at least 6' away from the house.
  2. Regrade the earth around the house so that it slopes down and away.
  3. While doing #3, install a vapor barrier 6-12" below the soil. The vapor barrier prevents water from percolating down near the foundations by pushing it "down and out" 6' away from the home.
  4. Dig along your foundation walls down to the footings. Clean the concrete with a broom & wire brush, fill any cracks, and then paint the concrete walls with a concrete sealer.
  5. While filling the trench along your walls, drop a curtain of landscaping fabric in the trench. Fill the 6" nearest the house with pea gravel and fill the other (yard) side of the trench with soil. The pea gravel is a drainage layer that prevents bulk water from remaining in contact with your foundation walls. The landscape fabric keeps the dirt from infiltrating and plugging the spaces in the gravel.
  6. Since I have a basement, when I did all of the above to my home, I also added 4" of XPS insulation against the foundation walls. Why? Because I had a Flir infrared camera. Do yourself a favor, just don't.

sill plate bolts

Since you have your wall bays open, this is the time to have a look at those 100 year old foundation bolts. Odds are, you don't have them at most every 6' through the sill plates into the foundation as is now required. They're probably not at least 1/2" bolts either, which means that all of their strength corroded away about 25 years ago. Also since 1929, we've learned about the importance of plate washers in seismic zones. Now is when you have the access to do this upgrade.

drying potential

Make sure you understand how your walls gain moisture and how they dry out. The details of your insulation project will determine the future moisture content of the lumber in your walls. Do it right and your house will be there for another 90 years.

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    It's all good advice, but I disagree with your diagnosis. It looks like wood-boring beetle to me. There appear to be cylindrical channels eaten out of the wood. – Martin Bonner supports Monica Dec 2 '19 at 9:10
  • The discoloration of the wood evidenced in the first photo is not beetles, that's fungal and/or mold. My diagnosis is that the wood was exposed to humidity, which permitted the "undesirable biologicals" to gain a footing. The wood dust in the third photo certainly could be wood-boring beetles, but it could also be carpenter ants. When those are present, there's no "appears to be," it's obvious. What do all of the above need in order to eat the wood? Humidity. Fix the humidity problem and the rotting wood problem goes away. – Matt Simerson Dec 2 '19 at 17:48
  • In our area foam insulation below grade ends up calling to carpenter ants and all of a sudden you start seeing the foam close to the foundation as the ants chew it up, I made this mistake ~20 years ago in Corvallis. This worked great in Ohio but not in the Pacific Northwest. I had no ant problems on the main house with ants but when I built my shop I had a wall that was 11’ below grade, I don’t know how much of the insulation is left down there but it took 3 years of professional spraying to stop the insulation from showing up and it was carpenter ants. I guess they really like the stuff. – Ed Beal Dec 30 '19 at 14:18
  • @Ed, I don't doubt you. I've had a couple contractor buddies tell similar stories. Just working with EPS/XPS should be enough for folks to realize it will not remain in tact when exposed to mandibles, incisors, beaks, balls, or weed eaters. Therefore, I cover it with a fiberglass mesh and then trowel on a couple layers of Tuff II foundation coating. I've had good luck with that coating withstanding all of the above. – Matt Simerson Jan 2 at 1:14

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