Problems with Crawlspaces – Venting and other Underhouse Ills

by Erik North on August 19, 2013

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Crawlspaces are like the Loch Ness monster; talked about, rarely seen and potentially a bit scary. The crawlspace is that empty, barely accessible pit under the house filled with swampy water, cobwebs and spiders the size of dinner plates (that was the Google result for ‘spiders the size of dinner plates…enjoy). At least that’s what we imagine.

Out of Sight, Out of My Mind

The reality is hardly any prettier (but hopefully no Loch Ness or Shelobs). Persistent problems live in crawlspaces, ones that stick around because the homeowner never sees them. My all-time most ridiculous find was a running hair dryer, warming water pipes that had frozen. The homeowner’s daughter had done it without telling anyone and forgotten about it in the intervening two months. The electric bills were … impressive.

There are other widespread problems that remain similarly out of mind. Moisture is a major one. Whether it’s running or standing water or moisture evaporating from a sand crawlspace floor, any damage or problems won’t be seen. If a full basement leaks or floods, sumps and mops will be deployed immediately. The unseen moisture can damage wood, concrete, and make it’s way into the house.

The Connected Crawlspace

That shouldn’t be a problem, right? I mean your crawlspace is entirely separate from your house … right? Actually, no. When conducting a blower door test, we check the house in all states, one of which is with basement/crawlspace access open.

When a blower door test is performed, sometimes the pressure reading doesn’t change whether the crawlspace access is open or closed. Big deal, right? Actually, it means that the holes (and air flow) between the crawlspace and first floor are so large and so profound that it doesn’t matter if the door is open or not. All that grimy water, dust, pest waste, can float up into your house and breathed in. *Ugh* What could be worse? How about locating ducts in that crawlspace.

Mechanical Monsters

Yes, thank goodness there’s no giant mechanical system moving tons of air into the house. Oh wait, your ducted HVAC systems. Often your HVAC system ducting is run through crawlspace which is just an awesome way to move all that dust, moisture, rodent poop, and chemicals into the rest of your house.

A well-taped and mastic sealed duct shouldn’t be an issue. In theory. The reality is loads of poorly installed and unsealed ducts running through the nasty crawlspace. This can act as a ‘crap in the crawlspace’ ventilation system. If the ducts handle cold, conditioned air in a humid crawlspace then condensation is in your future. If the ducts have a foil sleeve, the condensation may accumulate within the sleeve. Scary potential for creating a breeding ground of awfulness.

Venting Problems…Not just for Attics

Another common issue is the vented crawlspace. Venting can be a crapshoot in attics but a vented crawlspace can be a problem in humid climates. The idea behind ventilation is improving the interior air and conditions.

What if the exterior air is worse? Then opening a hole into the crawlspace will let in problems. This can be adorably compounded when some right thinking owner puts a dehumidifier down there. It’s a noble thought to try dehumidify the whole planet.

Last would be any efforts to insulate the ceiling joists with fiberglass batts. I detailed the thermodynamics in this article. Practically they’re not great, either. Between gravity, moisture and cold, there can be problems. It’s a rare install where 3/4ths of the batts aren’t hanging down or fallen off entirely.

Crawlspaces can be a pain in the butt. Unlike basements where the homeowner may see and fix the problems, crawlspace problems can fester for ages. And problems that occur in the crawlspace affect the whole house. Take care of your crawlspace and you’ll take care of the whole house.

{ 1 comment… read it below or add one }

Prime Energy Group May 19, 2014 at 1:47 pm

I like the term ‘out of sight, out of mind’, because this is what many people think when it comes to their crawl spaces. Many people neglect their crawl space because they never use them. It is fine to not use your crawl space, however, it is important that it remains in good condition, or it can have a negative effect on your house.


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