Re: Paston Effect

[Guest guest]

Air Infiltration in Coastal Regions - The " Paston Effect "

http://www.baileyeng.com/paston_effect.htm

This paper written in 1994-5 describes actual field conditions

encountered during investigations of high humidity (and mold growth) in

residential and commercial structures and their direct effect on indoor

relative humidities. Uncontrolled air leakage and moisture migration

into structures causes severe deterioration of building components as

well as resulting in poor indoor comfort.

Unfortunately, when moisture levels become excessive, a variety of

problems including destructive mold and mildew occur. This study is not

a theoretical approach, but a hands-on cause and effect cure that was

designed to aid readers in investigating and recognizing actual field

problems. The " Paston Effect " comes from an investigation of a large

residence, where numerous conditions existed that affected the indoor

relative humidity

Ron

www.themoldmanual.com

B. , PE

Engineering Corporation

880 Jupiter Park Drive, Suite 5

Jupiter, Florida 33458

Work-

Fax-

Cell

www.hurricanehideaway.com

Paston Effect

In another forum this term was brought up, I searched it and the hits

were a Mr. from Florida. Is this our esteemed member here?

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[Guest guest]

>> Air Infiltration in Coastal Regions - The "Paston Effect"> > http://www.baileyeng.com/paston_effect.htm

Ah one and the same. :-)

I read your article, it was very informative and reinforces my belief that framed construction with a vented attic is the worst way to build in any climate where the ambient dewpoint is higher than the temperature that occupants maintain their homes at.

I am south of you on Grand Cayman and from June through into early December the dewpoint is floating from 78 to 81F. For the rest of the year it is in the low to mid 70s however it may dip down into the 60s when an "American Cold Front" moves in. :-)

A good point on keeping the ductwork exposed to the hot air as it keeps surface temperatures up, but we will still get a problem at night with that approach or during typical overcast weather.

I like your point on the salt causing materials to be damp, I never really considered it before. We can't be more than 2 miles inland here so accelerated corrosion is common.

I have seen some disasters caused by power ventilating attics as well as constant negative pressure ventilation schemes, and by 'strange coincidence' the external walls were also framed construction with fibre glass insulation. This compounded the problem.

A favourite photo of mine which I like to refer to as "But it worked great in Arizona"

http://i32.photobucket.com/albums/d41/a_bee_normal/BedroomCondensate.jpg

To me, a framed exterior wall with fibre glass insulation is a 'filtered fresh air intake' and an accident waiting to happen. Perhaps icynene filling the wall cavity is better.

Mirrors on 'external framed walls', also an excellent point you make.

Soffit vents are problematic during bad storms as wind driven moisture is like blowing steam. It will defy gravity and go up into the attic through the soffit vents and saturate the insulation and sheet rock ceilings. The ceilings come down during hurricanes before the roof fails.

I am in the process of building four apartments as a investment for my future retirement. It is all concrete construction including a sloping concrete roof with a sealed attic. The only food source for mold will be the sheet rock ceilings.

The top of the roof will be insulated and a white metal standing seam will be installed on top of the insulation. I will also condition the attic space. I think I will be better off in the long run, keeping the heat out of the attic in the first place and then conditioning it slightly to keep the humidity down.

I routinely come across stuctures with generous attic vents and the mind set "to flush the heat out". This mind set goes back to hardy people who never had central AC and relied on cross breezes from trade winds to keep cool.

These old homes were wood or 'wattle and daub' construction and without AC never had a mold problem as they were never cooler than the ambient dewpoint. Goes back to my other theory that 'mold needs a wet spot to get started' and does not spontaneously generate from high indoor RH.

For those who are curious 'wattle and daub' was a post construction made from indigenous hard woods that were termite resistant. Sticks were 'woven around the posts, similar to lath of old North American homes. The post and sticks were then plastered on both sides. The homes had hardwood floors and were elevated above the ground by perhaps a foot to discourage vermin/insects and to allow water a path under rather than through a home during storms.