Attic ventilation

[Inspector 102]

if a roof is provided with roof jacks and gable end vents, does this take away from the advantage of soffit venting by changing the air flow? I have been told that this would create a "short cycle" of the air flow and not let the lower portion of an attic space vent. Should there be a different ratio if this occurs? less then 1/300? Having a discussion with contractor on this install and find no code language to support or discount my thoughts. Any help?

 

[fatboy]

Without venting in the lower 1/3rd, the ratio is 1/150. R806.2, the exceptions allow the 1/300.

 

[Inspector 102]

There will be soffit venting provided providing ventilation for the lower portion. Will these work effectively if the upper portion of the attic space has roof jack vents and gable end venting? At 1/150 they are just short but with 1/300 they have plenty. Just seems like the 2 upper venting provisions would cancel out some of the soffit venting by not allowing convection to carry the hot air properly from the space.

 

[Paul Sweet]

Gable vents might theoretically reduce the overall venting effectiveness under some wind conditions, but they would help it under others. I think it's a toss-up. The venting ratios are arbitrary anyway.

 

[mark handler]

VENTILATION 101

http://cjmetals.com/paramountcasheetmetalfabrication/wp-content/themes/7b/pdf-library/Ventilating%20Products/attic%20ventilation.pdf

HOW TO FIND STATIC VENT FREE AREA

http://cjmetals.com/paramountcasheetmetalfabrication/wp-content/themes/7b/pdf-library/Ventilating%20Products/calc%20net%20free%20area.pdf

Ventilating Products

http://cjmetals.com/metal-fabricators-los-angeles/

BTW

Roof area SF x 0.96 = ventilation inches required for 1/150

Roof area SF x 0.48 = ventilation inches required for 1/300

 

[Min&Max]

Unfamiliar with the term "roof jack vents". what are they?

 

[Min&Max]

I believe you always want soffit vents and you can not have to many. There should be no mixing of roof vents, ridge vents or gable end vents.

 

[pwood]

I believe you always want soffit vents and you can not have to many. There should be no mixing of roof vents, ridge vents or gable end vents.

no comprende?

 

[mjesse]

Unfamiliar with the term "roof jack vents". what are they?

View attachment 1094

Mushroom vent = roof jackRegional vernacularView attachment 1094

/monthly_2014_09/Roof-Vent-1.jpg.f3834b6cee371dd36f89499e7b795b5e.jpg

 

[Min&Max]

If I understand your question you should not use gable end vents with roof vents(jack/mushroom/turtle) or ridge vents on the same roof. Soffit vents are necessary and you can not have to many because they will not allow any more air into the attic than the other vents can expel.