Mold From Dryer Vent On Joist
The mold forming on the wood floor joist in the damp and
moist crawlspace area with a warm dryer vent that is leaking moist air
from it, is the ideal breeding ground for molds and mildew's. The wood
provides a nice surface for mold and moisture to accumulate.
Even if the dryer vent isn't leaking air, warm temperature provided by them metal dryer vent pipe can produce condensation or moist air. This moist air can soak into the surrounding wood floor joist leading to mold, termites and even dry rot eventually.
Home Repair Tip: When installing dryer vents, metal or plastic, make sure that there aren't any holes or gaps where warm air can escape easily. Try to keep the dryer vents at least 6 inches away from the wood framing, if possible. Only in some instances will you be able to keep the dryer vent away from the wood.
This problem is more common in colder, the damp climates, where molds and mildew's are continually a problem inside and outside of the home and usually does not apply warm dry desert areas.
Home Building Tip: Most architects, contractors and homeowners seem to forget about dryer vents when planning their home building projects. I have ran into this problem more than once and sometimes it results in moving the washer and dryer to a different part of the home.
Here's the building code for dryer vents where I live. Show a minimum 4" diameter dryer vent to exterior. Vent limited to 14'-0” length with two 90° bends. This is good advice, long dryer vents and too many bends in the pipe can create a lent build up, sometimes blocking off the entire system as the lent builds up inside of the pipe.
This is the inside of a plastic dryer vent with mold forming from moisture.