If you have a crawlspace, don't neglect it just because you don't go "down there".  Granted, there are more enjoyable places to spend time, however, your crawlspace deserves periodic attention. 

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Images from the chexfiles

Noteworthy issues from the real world!

Building Envelope Moisture Penetration

Photos 1-5: An elevated flower planter on the front of this residence caused extensive damage to structural members. Moisture penetration had progressed almost half-way through the crawlspace from the front wall.  Note moisture running down the perimeter beam (photo 1) as well as dripping off the floor joists in photos 3 & 4.  Parquet floor tiles in the room started delaminating shortly after the new irrigation system was installed...  

Photos 6-8: Another property with similar problems although this one is just from rainwater.  Note the sill plate has disintegrated, efflorescence on the perimeter beam, fungal growth, and decay of band joist, floor joists, and subfloor.

Photos 9-10: Raised planter outside, Stachybotrys inside.

Ground-Water Problems

Photos 1-5: This residence reflects an attempt to deal with excessive groundwater.  (Swimming pools can add value to a home, but not when they are in the crawlspace!).  Photo 1 shows bulkhead material visible underneath perimeter beam which implies the builder knew there was a ground water issue.  Note how the soil has dropped leaving voids under the perimeter beam...structural failure of the beam is probable.  Photos 2 shows one of many drainage troughs to sumps (photo 3) which were designed to dewater the area.  Unfortunately, standing water means excessive humidity; the effects of which were apparent throughout this property on the subfloor and floor joists (photos 4 & 5).  Photo 5 also shows the telltale 'vein' pattern left by the plasmodium stage of a slime mold.

Photo 6: Fungal growth on concrete perimeter beam...it looked like this for approximately 40 feet.  Grading and drainage at this property was all sloped toward the foundation.  Occupants reported heavy 'mold smell' coming from the crawlspace.  Want to guess why?  Also note the exposed wiring!

Crawlspace HVAC Duct Problems

Photo 1 & 2: Strap broke and duct fell to ground, disconnecting it from the supply boot.  Homeowner was not aware he was cooling and heating the crawlspace, but noted the kitchen never seemed the right temperature.  Photo 2 at the same property shows damaged insulation and another duct on the ground.

Photo 3 & 4: Un-insulated supply boot results in condensation and excess humidity which causes fungal growth on adjacent insulation at this property.  Photo 4 at the same property shows condensation drops on un-insulated supply plenum.

Photo 5: Crushed duct.  Workers climbing over the duct not only crushed it, but opened the joint on the backside and broke the straps so it is now laying on the ground.  Tell your contractors to dig and go UNDER the ducts!

Plumbing Related Problems

Photo 1 & 2: Toilet overflows and small leaks over time can cause severe structural problems.  Subfloor and joist decay under toilet (photo 1) and at head end of tub/shower (photo 2).  From above, the tile floor showed no evidence of such problems, and frankly, I don't know why I didn't break through the floor when I inspected this one.

Photo 3: Leaking shower pan.  Note drops of moisture adjacent to drain fitting on plywood.  The plumber was more creative in his strapping and he didn't think anyone would mind if he notched the floor joist a bit (pipe behind the drain line).

Photo 4 & 5:  Leaking shower pan and tile enclosure caused extensive damage to subfloor (photo 4).  A considerable area of impact can be seen from above after the flooring was removed (photo 5).

Photo 6 & 7:  Leaking shower pan.  Note 'stalactites' of calcium, soap scum, etc. growing near the drain fitting.  Damage extends over 4 feet from drain point (photo 7).

Photo 8: Leaking toilet (note standing water).  This condition causes a very hazardous health situation due to the presence of heavily contaminated black water.  (The key reason I wear a full-face respirator and protective clothing before entering any crawlspace!)

Photo 9: Look out below!  This shows what is left of the subfloor underneath a 500 pound gas-fired water heater that had been replaced after the first one leaked!  After seeing this, the homeowner was encouraged to shut-off the gas line and get it repaired as quickly as possible...which he thankfully did!

Misc

Photo 1:  Debris in crawlspaces cause problems.  Such materials invite mold growth (Stachybotrys recovered from this piece of drywall), wood destroying insects, etc.

Photo 2: Vegetation growing through vent screens.  

Photo 3: Electrical cables on ground shouldn't be!  Also, carpet is food for microbes!

Photo 4: Transite Pipe - Cementous pipe that generally contains asbestos.

Photo 5: Unsealed gas valve.  Old-fashioned manual stop-valve on gas line.  Unused gas valves should be removed and permanently stopped.