Thread: Pressurize Crawlspace???

Inspected a 3400 sq. ft. home with faulty grade on three sides and the fourth side had a solid concrete raised portch that prevented ventilation of that side. Altogether it came up about 8 sq.ft. short of the 1/150 rule.
Would a fan on a timer be a reasonable alternative to cutting in additional vents?

The grade problem will be fixed via drains.

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steve
not alot of info here. any pictures???

charlie

Originally Posted by Steve Lowery

Altogether it came up about 8 sq.ft. short of the 1/150 rule.

Are you sure it is not even worse than that?

Did you measure the vent opening size and use it, or did you calculate the NET free vent area of each opening and use that? There is a BIG difference between the two.

Originally Posted by Steve Lowery

Inspected a 3400 sq. ft. home with faulty grade on three sides and the fourth side had a solid concrete raised portch that prevented ventilation of that side. Altogether it came up about 8 sq.ft. short of the 1/150 rule.
Would a fan on a timer be a reasonable alternative to cutting in additional vents?

The grade problem will be fixed via drains.

SL: A fan on a humidistat would be appropriate.

Thanks fellas.
Actual available vent space was calculated.
Standing water, against brick/ foundation anywhere from a foot or two to several feet with very few spots not inundated. The front of the house is where the raised concrete portch w/out venting was. This area stood 3'' -5'' deep and tapered to 0'' at about 4' ft. from the house. The place is beautifully landscaped with a hill in the back of the house ( the entire house is on a hill that was placed there in a prune orchard in '92) and nice berms everywhere that keep water well within 5' of the house. Some drainage exists, and if the skys ever stop dumping on us here the extent and quality of drainage will be be checked and, if necessary, upgraded.

If a fan and humidistat is used what criteria are used to calculate volume/pressure. I want to be certain that overpressurization doesn't occur and create other problems.

http://www.smartvent.net/docs/crawlspacestudy.pdf

Originally Posted by A.D. Miller

SL: A fan on a humidistat would be appropriate.

There's a problem, as we know, with the humidistat. The fan will DE-pressurize the space, allowing fresh air to be drawn in.
If outdoor humidity is high, the fan will never turn off.
I copied this excerpt from that excellent article:

"The problem becomes when to ventilate? Ventilation should occur only when
outdoor vapor pressure (moisture) is lower than crawl space vapor pressure.
• Favorable ventilation periods, are shorter and fewer than unfavorable periods.
Therefore, air must be exchanged air at a high rate during favorable periods, and a
low rate when it is not favorable to ventilate.
• Only mechanical ventilation can fulfill this requirement.
• Ventilation schemes must be sufficiently intelligent to discern favorable periods f rom
unfavorable periods.
An intelligent vapor pressure controlled device can exploit weather variations that are
imperceptible to a human, detecting subtle, short duration weather changes that raise or lower
outdoor vapor pressure, and use these variations to advantage. When a favorable period is
detected, the fan is energized to exhaust air from the crawl space, and continues to exhaust
until it is no longer favorable to ventilate".

This one way to look at your problem.

Im with AM. The more air the better...

Best

Ron

Up here on the Wet Coast, I would prefer a Timer to a Humidistat. You guys in the Golden State or the desert should like humidistats, but there are cases here where people are pulling damp air into the home and making things worse.

Maybe that particular space needs heat as well as venting? Maybe I'd recommend a humidity Meter, so they can monitor the space.

If it was a newer home, I'd say this:

"There is limited crawl space ventilation at the right/left/rear due to a porch. We can elaborate, but you should consult with a crawl space specialist or licensed general contractor about this issue. Inadequate ventilation can lead to high moisture content in the wood floor structure, which can contribute to the fungi growth and decay in the long term. At a minimum you should have the crawl space ventilation and wood moisture levels evaluated during humid summer months by a pest control company, home inspector, or other specialist because an increase in crawl space ventilation may be required."

If it was an older home, any problems that may exist should have revealed themselves. If you didn't see any problems (fungi, high moisture count, deteriorated insulation, etc.), then there is nothing to report except for the poor grade.

Well said, Joe. There is some moisture in the insulation, said the plumber who installed new lines to the 'fridge.

Before you guys jump my butt, hear this. This was a no charge consultation for a friend of a friend three or four days into an 'El Nino" event in the Sacramento Valley. There is so much water around this house that I have NOOOOOOOOOOOOOOOOOOOOOOOOOOOO intentions of crawling this thing until the sea ceaseth. No report from the owner regarding the condition of the existing drainage.

Originally Posted by Steve Lowery

...This was a no charge consultation for a friend of a friend three or four days into an 'El Nino" event in the Sacramento Valley. There is so much water around this house that I have NO intentions of crawling this thing until the sea ceaseth...

Obama is going to fix your weather issues before his 1st term is over.

Thus suficeth us......