Belly Condensation

[Bob]

I have a 26 X 44 home. I have used a total of 6, 14x6 automatic vents. I placed them 2 each on the sides and 2 to the rear. Previously, before the venting, I would get puddling under extreme humidity. Although the puddling is gone, I still get some condensation build up on the frame rails and the underbelly barrier. It seems to dissipate quickly, but I was wondering if more vents would help, I think I'm at my maximum for my square footage, or will this be a natural occurrence no matter how many vents I install, much like the water tank on my toilet?

[rmurray]

Make sure your vapor barrier on the ground is intact..Ground moisture leaching out of the ground can be gallons per day for a home this size...

[Bob]

Murray, I'm on a concrete pad. I'm not sure if that makes a difference.

Thanks in advance as usual for your help. Bob

[Roy T. Bonney]

Bob:
The ventilation formula for your home is one square foot of free area, for each 150 square feet of floor space. 26 x 44 = 1144 sq ft/150 = 7.63 sq ft of FREE AREA.
The fact that the vents are 14 x 6 is irrelavent. They will be marked with the free area, probably 56 or 64 sq inches. The automatic vents, also work on heat, as opposed to humidity, and would be well replaced with a standard open vent. Check the markings on the vents and remember 144 square inches to a square foot. To further stress the importance of a ground vapor barrier, this ventilation formula drops ten fold in the ANSI code, if the proper ground vapor barrier is in place.

[Roy T. Bonney]

Bob:
The ventilation formula for your home is one square foot of free area, for each 150 square feet of floor space. 26 x 44 = 1144 sq ft/150 = 7.63 sq ft of FREE AREA.
The fact that the vents are 14 x 6 is irrelavent. They will be marked with the free area, probably 56 or 64 sq inches. The automatic vents, also work on heat, as opposed to humidity, and would be well replaced with a standard open vent. Check the markings on the vents and remember 144 square inches to a square foot. To further stress the importance of a ground vapor barrier, this ventilation formula drops ten fold in the ANSI code, if the proper ground vapor barrier is in place, and the corner vents are within three feet of the end of the home.

[Bob]

If I did convert to regular vents, would I need to close them up during the winter months? I will need to move them closer to the center as they are only about a foot from the corners. I thought I would also add two more to the front section to see if that will help any.

[Roy T. Bonney]

The fact that the vents are close to the corners, is a good thing. Just add the others to the longitudinal sides of the home, to provide cross ventilation. Leave them open all year, the belly board is doing its job effectively, and will continue to do so in the winter months.