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xquercus 06-19-2007 02:01 AM

Wall Rot: Water, Mold and Ants
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Our house used to have a three car garage. One of the bays was converted by the previous owner to living space and a laundry room. The dryer duct actually runs embedded in the concrete floor. The duct comes up out of the concrete near an exterior wall where I use a short length of flexible duct to connect up to the outside vent.

Prepping the walls for a paint job I found a hole in the drywall behind the duct. Surprisingly, it was quite damp. I pulled off some drywall and found some nice moldy insulation, rotting wood, mold and *lots* of small red ants (not carpenter ants -- also non-aggressive).

Image 1 shows the duct work with some drywall removed. You can see the general rot inside the wall.

Image 2 is a head on shot of the general rot.

Image 3 show the duct and wet insulation removed. Mold is visible on the wood.

Image 4 shows the exterior wall in the adjacent room.

Mose likely, the drier vent is leaking moist air into the wall. I've removed a bunch more drywall and it's just the insulation and wood that is close to the vent that is affected. Just a few feet up the wall all is well. That seems to rule out a leaky roof. The soil on the exterior wall is damp. We have a stucco exterior. The soil is a bit closer to the stucco than it should be but doesn't actually contact anything except the foundation. We have large overhangs and gutters so splashing is not an issue. I went in to the crawlspace below and could not find any damp wood or ants. It looks OK.

That seems to leave the drier vent as the most likely possibility. I wouldn't even bother asking for another opinion except that I know the previous owners had a problem in the same location due to a leaking roof. The patch job doesn't look professional but I can't find any leaks in the attic crawl space nor is any insulation more than a few feet from the dryer duct wet.

Here's the catch... I'm not able to find a leak in the dryer duct that might be causing this. You can see in image 1 that that I put a reducer in the duct that comes up from the concrete floor and attach the flexible duct. When installing the reducer, I sealed the inside with metal duct tape and caulked the exterior where the duct meets the concrete. If this is a duct leak, this is the likely spot. Obviously I'm not properly sealing the duct. How do I go about doing this properly? Should I use a different sealer than metal duct tape on the inside of the reducer?

Thank you much!

mikemy6 06-19-2007 03:31 AM

do you have a downspout right outside that wall?

xquercus 06-19-2007 04:23 AM

The nearest downspout is about 20' away. It empties into a flexible pipe which runs underground to a large catch basing lined with rocks. The rain gutter appears to be working properly.

The house is in Western Washington so 10 months out of the year outside moisture is of significant concern.

AtlanticWBConst. 06-19-2007 05:56 AM

Looking at your pics, my first thought is that there is ALOT of moisture there. (FWIW-We usually see that amount of moisture coming in from actual water infiltration as opposed to a moist air vent leak issue).
I would suggest that you:

1.) Purchase a moisture meter.
2.) Use it to test the areas of the sheetrock to determine the area of saturation/moisture penetration.
3.) Draw it out on the wall with pencil.
4.) Open up the wall by removing the sheetrock that you marked out.
5.) Remove all wet and damp insulation from the cavities.
6.) Test the framing members for dampness using the moisture meter. (Framing lumber moisture content should not exceed 19%)*
7.) Allow the "opened" areas to dry out. You could also use active means to dry, such as a blower or fan.
8.) Purchase a fungicide solution (not just bleach and water)** to apply over the affected framing members in order to kill any mold spores that may be present.
9.) Important: As you are opening up the area: Look for the traces of water stains and water. Water/moisture leaves a trail. This is the best and easiest way to determine where the moisture is coming in from. If it is coming in from the dryer vent alone, then it would be evident by the moisture stains being isolated to the general area of the vent hole going into the wall. If it is coming through another area (like the outside/grade issue) - then you will be able to trace a moisture line into the home and towards the saturation point that you found in the wall on your initial inspection.
9.) ONLY AFTER YOU DETERMINE the positive location and cause of the water intrusion, and air out the wall cavities properly, should you then install new materials and close the area up.


** 15. Do not use chlorine bleach to kill mold or disinfect moldy areas. Bleach is not an effective or lasting killer of toxic mold growth and mold spores on and inside porous, cellulose building materials such as wood timbers, drywall, plasterboard, particleboard, plywood, plywood substitutes, ceiling tiles, and carpeting/padding.
19. Re-spray twice the cleaned out area with another wet spraying of an EPA-registered mold fungicide or an effective mold home remedy to kill any remaining, living toxic mold spores or mold growths. -

xquercus 06-19-2007 01:40 PM

The drywall and insulation is removed to the edges of the water damage that I can see. You are right. I should check the wall surrounding the area with a moisture meter to make sure it's not an infiltration issue. It probably isn't, but I can't be sure without either removing a whole lot of drywall or with a moisture meter.

johnny331 06-19-2007 09:27 PM

I would open the wall up all the way to the door and up some more to get a better view. Drywall is relatively cheap, and you want to make sure you fix this right, right?

xquercus 06-19-2007 09:55 PM

Yep, you are right. I should remove the drywall to the doors. The door pictured above, while it looks like an exterior door, is actually a door into the kitchen. There is an exterior door to the right that isn't visible above.

Anyway, I did some closer examination on the exterior of the dryer vent. There was a great deal of vegetation (a hydrangea bush) that was blocking the vent. The soil level is also quite high -- perhaps 2" from the stucco exterior. The soil is wet here in the Pacific Northwest 10 months out of the year, so I regraded so I can see about 8" of foundation.

I'm still not certain as to the source of the moisture. Leaning toward the dryer vent leaking but just don't see how moisture was leaking out.

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