Need a moisture graphic

[James E. Braun, CMI]

I need a graphic that explains what rising moisture in the crawlspace can do when the roof is not vented properly. You can email it to jbraun@mo.nachi.org. Any help will be great appreciated!

[Brian A. MacNeish]

Originally Posted by jbraun

I need a graphic that explains what rising moisture in the crawlspace can do when the roof is not vented properly. You can email it to jbraun@mo.nachi.org. Any help will be great appreciated!

The roof venting should not be depended upon to take care of crawl space moisture.

[James E. Braun, CMI]

Yes, but the moisture will build up in the attic if the roof is not vented adequately.

[Brian A. MacNeish]

Originally Posted by jbraun

Yes, but the moisture will build up in the attic if the roof is not vented adequately.

Take care of the crawl space moisture by moisture barrier, better drainage, sump pump, etc.

The moisture is getting to the attic with air leakage mainly(98-99%) and 1-2% by vapour diffusion. The upward air leakage is an energy loss in both A/C summer use and winter heating. Airseal the ceiling extensively, make sure all exhaust fans are to the exterior and ducts are intact, and the need for attic ventilation diminishes greatly.

To simply increase attic ventilation to take care of condensation will increase energy use........and, in some special cases, can increase moisture in the attic. Earlier this summer, worked on the 4th house in my career in which increasing attic ventilation made the house colder [even in a milder winter] and moisture problems in the attic were worse. The increased attic venting to solve the original condensation problem was recommended by both a roofer and the local municipal inspector!!

[James E. Braun, CMI]

You do not understand what I need. I need a graphic explaining why the drywall is damp on the walls and wet on the ceiling. This building has a wet crawlspace and a hardly no vents in the attic. I need a graphic that explains how moisture rises.

[ldapkus]

How about Moisture Control in Homes?

[Roy D. Cooke, Sr]

Understanding Attic Ventilation


http://www.buildingscience.com/docum...lation_rev.pdf

[Roy D. Cooke, Sr]

Originally Posted by jbraun

Yes, but the moisture will build up in the attic if the roof is not vented adequately.

I disagree if the roof has too much ventilation then the moisture is pulled from the Basement .
Less is frequently better.... Roy

No attic ventilation is in our future soon .

[Bruce M. Graham, III]

http://en.wikipedia.org/wiki/Psychrometrics

[James E. Braun, CMI]

Thanks for all the help, guys!

[Nick Gromicko]

http://www.nachi.org/gallery/indoor_...ovement-3d.jpg

[Nick Gromicko]

http://www.nachi.org/gallery/indoor_...sation-3d1.jpg

[Nick Gromicko]

http://www.nachi.org/gallery/indoor_...sation-3d2.jpg

[Gary Farnsworth]

I come across often bare, metal HVAC ducting in attics. We have very adverse weather here, so in winter, heat from these ducts can cause condenstation on rafters and sheeting, and in summer, ducts can cause condensation on the metal itself, and drip onto walls/ceilings below. I always suggest to insulate this exposed metal duct work. Flex tubing seams to be better. Last year, we had several homes in the area that got snow blown into attics from upper roof vents just below roof ridges in high snow winds, pile up in the attics, and melt downward onto walls and ceilings when it warmed up. I am re-thinking attic ventilation. The time may be turning, along with higher humid weather, of less attic ventilation, or even attic sealing; the same as some newer crawl space studies.

[Brian A. MacNeish]

Originally Posted by gfarnsworth

I come across often bare, metal HVAC ducting in attics. We have very adverse weather here, so in winter, heat from these ducts can cause condenstation on rafters and sheeting, and in summer, ducts can cause condensation on the metal itself, and drip onto walls/ceilings below. I always suggest to insulate this exposed metal duct work. Flex tubing seams to be better. Last year, we had several homes in the area that got snow blown into attics from upper roof vents just below roof ridges in high snow winds, pile up in the attics, and melt downward onto walls and ceilings when it warmed up. I am re-thinking attic ventilation. The time may be turning, along with higher humid weather, of less attic ventilation, or even attic sealing; the same as some newer crawl space studies.

Heat is a form of energy and contains no moisture. I hear this incorreect phrase all the time in conversations and on TV programs, expecially Little Mikey Holmes:
"When the heat meets the cold, you get condensation" WRONG!!


Have seen snow blow into attics many times, including my own........how about one house in which 7-8 garbage bags of snow were pulled out of the attic after a 3 day record snowfall/ blizzard of 63 inches!! I worked on that house with a group of friends and recommended no soffit venting on the northeast facing interior corner soffits (an L-shaped house) but the code guy said vent the soffits. He did allow small soffit venting- the older style 2" wide strip vents......but the snow still blew up through these narrow openings to rest on the R50 cellulose insulation my company had blown in.

On another house (saltbox) about 1 km from the above, snow blew up through the regular perforated metal soffit, up about 12-13 feet of cathedral ceiling rafter cavity vents and into the main attic.

Since about 1983, I have been recommending as little venting as possible. In our truly efficient and airtight R2000 homes, there is really no need for venting as barely measureable to no moisture is getting into the attics from the house below.