Neighbor needing help

Phil S

Board of Directors, Events Director
Phil Soper
Staff member
Corporate Member
My DIY neighbor asked me to help so I came here for answers.
His crawl space is too humid - he installed a new plastic membrane on the floor and added one to all the walls.
What he noticed was the block was wet directly under his front door and the sill plate is reading 30% - not good
Wood framed two story house with brick veneer and masonry front stoop - see pics.
He drilled some weep holes in the bottom of the stoop, but did not help
He has sealed the intersection of the house and stoop - looks like he did a good job
Looking for a method to locate the source of water infiltration Thanks
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junquecol

Bruce
User
Just a thought. Because of high humidity, and thermal mass of stoop, could this be causing condensation in that area? Plus, inside of stoop box most likely didn't receive any water proofing during construction.
 

kserdar

Ken
Senior User
Gutters / down spouts / gutter drain pipe
Clogged foundation drain / does he even have one?
 

Oka

Board of Directors, Vice President
Casey
Staff member
Corporate Member
Typical for an under floor space per code is 1/150 ft for venting. I would expand to 1/50 (increase screens and add a couple fans one intake and one exhaust.
If you want to get tricky you can add a controller that turns them off via heat/cold or humidity
 

Phil S

Board of Directors, Events Director
Phil Soper
Staff member
Corporate Member
Typical for an under floor space per code is 1/150 ft for venting. I would expand to 1/50 (increase screens and add a couple fans one intake and one exhaust.
If you want to get tricky you can add a controller that turns them off via heat/cold or humidity
Interesting - When I built my shop my inspector insisted on no open vents and one fan blowing out 25/7. It is a small server style fan that consumes very little power. My shop "crawl" space is comfortable, not moist. The fan basically pulls some air from my conditioned shop above. Seems to work
 

Oka

Board of Directors, Vice President
Casey
Staff member
Corporate Member
The International building code (IRC) The IRC is a relaxed version of the now abandoned Uniform Building Code (UBC). The original UBC did not provide the exception for Class one vapor retarder material. Either way, Always over vent the underfloor and attic, the life of the building will benefit from it.
As a rule of good building never think it meet the minimum code requirement (unless it is a spec/bid job- :p) always exceed.

IRC Section R408:
The minimum net area of ventilation openings shall be not less than 1 square foot for each 150 square feet of under-floor space area, unless the ground surface is covered by Class 1 vapor retarder material. ... The code also requires that there be one ventilated opening near each corner of the building.
 

golfdad

Co-director of Outreach
Dirk
Corporate Member
Im guessing its a combination of things. All of what Bruce said is probably true. Could also be a crack or hole in mortar or grout in the tile. I would start with checking top for a leaking point. Then put a sealer on it. Make sure there is a gutter above the porch !
 

tvrgeek

Scott
User
Simple passive or even active venting does not work. One really needs a fully sealed system. Not cheap ( And I can't say I recommend Regional) but the results are worth it.

I go for the condensation. Before I enclosed my garage, the slab would have a full film of condensation on it. Of course, I also believe in front porches to keep the direct rain and sun off the door. Not in the Federal Colonial style though.

One may get more responses on the building forums. I go on GBA.

I suspect the muffin fan as in the shop description might work pretty well. Drawing drier conditioned air through and out. Of course, it must be on GFI by code.

I looked into a lot of venting solutions. One was to put in a ERU in the crawlspace using the entire crawl space as the exit flow plenum and intake from outside into ductwork. "Experts" on the building forums freaked out. I asked two ERV contractors and one said " it is not guaranteed for that way" and the other, who I think was an engineer, said, "I'll have to think, but don't see an issue" Looking into code, if you put one soda can in the CS, then it is "occupied space" so the issues of gas lines, electrical cables and plumbing do not apply so it is legal by code. I still think this may be th ebest solution and if my de-humidifier ( or when) fails, I think I would use the cost to do this myself. Just need a couple strategically located floor or badeboard vents with screen oin them from house to CS. If a 2 story, might run a duct down from the top.

It would depend on how efficient your HVAC Is. Modern units coils run just at dew point, do don't de-humidify worth a crap.

I asked two ERV manufacturers, got nothing from one, and the other said to refer to the installer. Game on the install. They want loke $3000 for a couple hours work to put one in. GFI outlet already available, hole through foundation ready. Just hang it and duct a couple feet into the return plenum. $3000 was the CHEAP estimate. No plumber, no electrician, no permits. Nope.
 

SJWiehe

Steve
User
Why not install a dehumidifier in the crawl space? I have a sealed crawl space that had high humidity. The humidifier is set to run until the humidity is 55%. Works great.
 

Mrfixit71

Board of Directors, Treasurer
Rich
Staff member
Corporate Member
Is the space under the stoop open to the crawl space or is it outside the foundation wall?
 

Joe Scharle

Joe
Corporate Member
I've seen this where the outside horizontal plane is very close to the bottom of the door opening and the flashing was poorly formed or even missing.
In both cases, I had to remove the sill back to the RO and apply membrane. If the flashing is improperly installed or no flashing, then it's only a matter of time until the rim joist and subfloor start rotting. If there are ants present, then it's usually too late. Both of my stoop floors sat on ledgers and the stoop box was open to the crawl, but I think if the stoop box was closed, I'd put a pair of screened vents in it.
 

SteveHall

Steve
Corporate Member
Hi Phil, a lot of good responses above. Moisture arrives from many sources and they all should be tested / confirmed:
  • foundation/masonry wicking underground moisture
  • overflowing gutters and/or downspouts
  • clogged/ineffective/non-existent foundation drains
  • condensation off AC equipment (many gallons a day)
  • poor / missing flashing conditions at windows, doors, and sills that actual direct water inward rather than outward
  • extra loads shedding off adjacent drives, patios, stairs, decks, hardscape, etc. (see recent Surfside condo collapse)
  • leaking water or sewer/septic piping
  • poor or ineffective foundation waterproofing
  • ineffective vapor barriers
Usually a well-sealed crawlspace doesn't need a de-humidifier any more than the home above it would. But it's definitely easier to buy one and pay the power bill than do a proper job of sealing.

For a decades now, unvented / closed crawlspaces have been promoted by building scientists since high humidity locations won't ever dry by ventilation or evaporation. One early well-written resource of wisdom was NC's own Advanced Energy non-profit. They still share a terrific crawlspace page with two different PDF guides on the topic from 2005 that are basically all you need to know.

Another good source of info and discussion is Taunton's Green Building Advisor (same publisher of Fine Woodworking, Fine Homebuilding, etc.).

The NC Residential Code has suggested/permitted closed crawlspaces definitively since 2009, in Section R409. But even the 1997 NC Residential Code permitted it with a vapor barrier plus 1 CFM mechanical vents/conditioned per 50 SF since the science was already pretty solid by that point.
 

LocoWoodWork

Steve
Corporate Member
Used to have a bad humidity/moisture problem. Had the crawl space totally encapsulated (vents closed, 2" insulation and plastic membrane) and industrial dehumidifier installed. Now crawl space is dry as a bone. AC runs less and cooler. It wasn't cheap but it worked.
 

tvrgeek

Scott
User
" Usually a well-sealed crawlspace doesn't need a de-humidifier any more than the home above it would. But it's definitely easier to buy one and pay the power bill than do a proper job of sealing. "

My experience totally disagrees. I use a remote sensor. When the dehumidifier fails, it jumps from 55 to over 65%. 65% for two weeks will develop mold. I monitor the house, and it remains no higher than 55% even when the CS climbs.

Santa Fe is probably the most reliable brand.

As I mentioned, conflicting viewpoints on GBA, but lots of good stuff.
 

Michael Mathews

Michael
Corporate Member
when I bought my house, there was some light mold on the floor joists in the crawlspace. I consulted several and ended up going with a company that sealed my crawlspace! NO vents, plus they added a large dehumidifier that keeps the humidity level down around 50% under there. The other thing that was done was all the insulation was removed, the mold treated, and zero insulation put back.
 

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