Go Back  DoItYourself.com Community Forums > Interior Improvement Center > Basements, Attics and Crawl Spaces
Reload this Page >

High Home Humidity-Could My Crawlspace be the problem?

High Home Humidity-Could My Crawlspace be the problem?

Reply

  #1  
Old 07-16-15, 05:39 PM
B
Member
Thread Starter
Join Date: Jun 2015
Location: USA
Posts: 8
Received 0 Votes on 0 Posts
High Home Humidity-Could My Crawlspace be the problem?

Hi All,

My house was built in 1944, it has a 2 ft (in most places) crawl space with a dirt floor. The crawl space has 4 small passive vents. There are no AC or Heat ducts down there and only some plumbing. It gets humid in my house, it stays around 50-53% despite living in Utah where the outdoor RH is about 30% year-round. I have gone through the space and can't seem to see any leaking plumbing. Sometimes water will come in with heavy rain but it usually dries up within a reasonable amount of time. It's damp but I don't think its abnormal. I can't seem to see where the humidity is coming from however. I have had HVAC people look at my system to see if that is the issue and they seem to feel its not the cause of the humidity although they recommended moving the air intake from the upstairs bedroom(small attic room) to the main floor and that may help. I only have one bathroom and it is exhausted outdoors, as is my kitchen fan. Is there a possibility that the humidity is coming in as vapor through my floor from the crawlspace? Has anyone noticed a drop in humidity post-encapsulation? I have been told to move the air intake, and I have also been told to encapsulate the crawlspace. Does anyone have any insight? I just want to make sure I don't end up doing the wrong thing and having to pay to do both.
 
Sponsored Links
  #2  
Old 07-16-15, 07:21 PM
J
Member
Join Date: Jan 2011
Location: USA
Posts: 4,834
Received 79 Votes on 74 Posts
Just adding a 6 mil. black plastic vapor barrier on the ground in the crawl space will go a long way to dry things up.
Just 4 vents for a whole house sounds like there's not near enough vents.
Where required to have them every 10'.
With proper grading, gutters with down spout leading away from the foundation, no mulch or flower beds up against the house, a water proofed foundation there should be no water getting in the crawl space.
Has the crawl space bee air sealed. Need to go under there and seal up anyplace wiring or plumbing is run though the subfloor.
Got soffit vents and proper roof venting?
 
  #3  
Old 07-16-15, 07:27 PM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
Hi books,
@ "Is there a possibility that the humidity is coming in as vapor through my floor from the crawlspace?" I think that is certainly a major contributor. A dirt floor may look dry, but that is because the moisture from below has already turned to vapor. Some numbers I have read put the moisture from a dirt floor at several gallons per day.

Typically, you either seal the bottom of your floor to isolate the house from the crawl and increase the ventilation down there or you insulate the walls and encapsulate the crawl and connect it to the conditioned living space. I prefer the encapsulation.

The other major source of moisture is people and their activity. Cooking, showers, hanging laundry inside, dryers vented inside, and just breathing.

You mention ac ducts. If your ac unit is oversized one of the side effects will be high humidity. An ac unit that cools in short bursts never runs long enough to take out the moisture.

Bud
 
  #4  
Old 07-16-15, 10:15 PM
B
Member
Thread Starter
Join Date: Jun 2015
Location: USA
Posts: 8
Received 0 Votes on 0 Posts
Greetings and thank you for the quick reply!

So I was leaning towards encapsulation myself but I was just under the house and I noticed that the condensate from the central AC drains under there. It didn't look like a lot, just a damp spot in the dirt but should I be worried about this? Do I need to re-route that drain Or should I just consider the sealing the underside of the floor and increasing ventilation? Since Utah is a desert, encapsulation is pretty unheard of here but I would still like to do what is best for the house.

As far as attic ventilation goes, I don't see any soffit vents but I do have a ridge vent. The house is pretty small (1350 sq Ft) and the ridge runs more than half of the length of the roof. I believe the ventilation is adequate there. What I do wonder though is... would it be possible to over-insulate a house and cause the humidity? The previous owner put R22 insulation throughout the house, plus the attic looks like an exploded pillow fight of insulation and is lined with foam insulation in parts. I don't know about insulation but it almost looks excessive to me.

I probably should have paid closer attention to this stuff when I bought the house but I was a single girl buying my first house and thought that paint and decorating would fix anything. I know better now!
 
  #5  
Old 07-17-15, 06:36 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
@ books "I probably should have paid closer attention to this stuff when I bought the house but I was a single girl buying my first house and thought that paint and decorating would fix anything. I know better now! " That got me to smile as I remembered back to the first house I put a deposit on. Fortunately, I took a more experienced friend over to review our choice and after he pointed out the many HUGE problems I was able to get our deposit back. The excitement makes us blind to the things we don't want to look at.

I think the vents Joe mentioned were for the crawlspace. Attic ventilation is another issue, but should have little effect on the humidity. But having just a ridge vent is not sufficient. You need low venting to compliment the high. Best to discuss attic venting in another thread, when you are ready. Looks for gable vents or roof vents.

@ books "would it be possible to over-insulate a house and cause the humidity?" yes and no. It isn't actually the insulation, but the air sealing that can raise the humidity levels, but it would be rare for a retrofit effort to reach the "well sealed" levels where that would be a problem.

Yes, reroute that ac drain to the outside. Dumping that moisture in the crawlspace just sends a lot of it back into the house. Something like 50% of the air you breathe in a home comes from that crawl.
Info bit: approximately 1/3 of all of the air inside the average home escapes to the outside EVERY HOUR and is replaced by whatever is out there. Homes that are nice and tight still lose 1/4 of all inside air every hour. Less than that causes problems.

Encapsulating the floor (crawl ceiling) and protecting all pipes from freezing is difficult. When protecting water pipes you need to insulate them from the cold, yet keep them exposed to their source of heat. Looks like you are in climate zone 5 so you do get a bunch of cold weather.

Getting too long so I've added some reading for you.
Bud

BSI-009: New Light In Crawlspaces — Building Science Information
Building an Unvented Crawl Space | GreenBuildingAdvisor.com
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: