Home humidity - increasing after remediation?

[Scott Stewart]

This summer, I have been attempting to rectify moisture problems in a

40 year-old brick veneer ranch home (one storey) with a crawlspace. This home is located in North Carolina where high humidity is the rule. Below are the steps currently taken:

1) Installed heat pump (14 seer). Home was originally cooled via window units. The indoor portion of the system is installed in the crawlspace.

2) Replaced insulation between floor joists in crawlspace. Original insulation had fallen down in spots and was moldy in many areas.

3) Installed plastic vapor barrier (4-mil cross-laminate poly) over entire ground surface in crawlspace. Overlapped and taped seams. Ran plastic 4-6 inches up crawlspace walls.

4) Sealed interior crawlspace walls with UGL waterproof paint. Also painted UGL on outside walls in one corner where improper grading led to excessive moisture.

5) Replaced all windows. (This was done more for energy efficiency, rather than humidity control).

6) Dug trench down to footing around house in above mentioned corner. Placed Akwadrain sheet drain against foundation. Installed solid pipe to carry downspout output away from structure. Backfilled in trench with gravel up to 6 inches from surface, then remainder with dirt.

7) Temporarily sealed crawlspace vents and installed crawlspace exhaust fan in remaining open vent to create negative pressure in crawlspace.

Before accomplishing tasks 6 & 7, the humidity had been running around

48 - 51% with the A/C running (thermostat set for 70 degrees) and a Sears 50-pint dehumidifier running full-time in the center of the home. The dehumidifier would normally need to be emptied every 1.5 days. After steps 6 & 7, the humidity has been running 53% - 56% and up to 61%, if the dehumidifier is off (it fills up in a little less than a day now.) Outdoor humidity was in the 73% - 100% range both before and after that crawlspace sealing, so I don't think that is a factor in the humidity increase.

My suspicion is that sealing the crawlspace vents is the culprit. There seems to be two schools of thought with regards to keeping them open in the summer in the southeast. Some state that the vents must be kept open for proper air flow, others state that the vents are only pulling in humid air from the outside. The latter group suggests sealing the crawlspace and creating negative pressure with a vent fan, thereby allowing the cooler, drier air from inside the house dry the crawlspace. Oddly enough, I've notice a few "hot spots" throughout the house and think that attic air is now being pulled down into the living area. I've re-opened one of the vents to see what, if any, difference it makes.

It may be that humidity levels in the low 60% range are ok for a home in North Carolina, but I would like to have a few second opinions.

Thanks! Scott

[Jums]

Move to AZ crybaby.

[Speedy Jim]

I think you're on target about the fan pulling hot/moist attic air down. If you add up all the sq inches of penetration holes to the attic, it will be a sizeable gap even if there is no unusual construction opening. Unless you get the humidity down to 50-55%, you will encourage mildew growth.

Jim

[Eric Tonks]

I think your negative air pressure in the crawlspace is the problem, the air the fan takes out has to be replaced somehow, and it seems to be from your air conditioned space which in turn is pulling air in any crack and opening possible.

Why don't you do what we in the great north, Canada do. It isn't cold all the time up here, especially in the great lakes region. In summer we have temperatures ranging from mid 70's up to 100, with humidity levels from 60% up to 90%, and this year we seem to be getting a lot of rain which keeps the humidity levels high. Because of deep frost in the winter, we have to have foundations 4 feet deep minimum, virtually every house has a basement. Basements can be damp and humid if nothing is done. Normally air conditioning uses the heating ducts to distribute the cool air, resulting in the basement being air conditioned. This dries up all moisture, I have never had any bare iron tools gather any rust dispite the high humidity outside.

Possibly you should seal up your crawlspace fan, and add airconditioning supply and return ducts into the space to remove all the moisture. I am sure it will work just as it does with a basement.

[Joseph Meehan]

Make sure all the ducts are well sealed.

Good.

!!! Improper grading !!!

Did I miss something? How are you draining the water from the base of the foundation?

Bad idea. Never create a negative pressure. You can't get rid of air (moisture) without replacing it with something.

I would open up the vents in the craw space and make sure they are large enough. That will keep the craw space humidity close to that outside. Blocking it will just increase it.

As an alturnative, you can start heating and cooling it, but I would not bother.

Unless you are using professional equipment to measure it your readings are likely to be +- 10-15% I suggest not worring about a specific number, but rather decide if you are comfortable inside your home. If not, then it is very possible that the HVAC is not properly sized. Too big is not good.

I don't like two things. First the grading problem needs to be fixed, not patched. You need to regrade. You also need to open up those vents.