I want to maximizing venting, diagram included.

cbzdel · 07-27-2010, 12:59 PM

Here is a quick sketch of my house roof.

In red is my current venting, the new area has:
(1) gable end vent
(6) eve vents, I call these bird blocking (there are only (3) 1.5' holes in each bock)
(4) square roof vents providing I think 48" sq in of venting

The old roof has:
(4) square roof vents providing I think 48" sq in of venting
(3) gable end vents

Now my old roof has no overhangs so I have on venting in the eves.

After having to crawl around in my attic the past few days I have realized how hot it gets up there! I know without having the eve vents in the older area of the roof is probably really hurting me as well. Any input would be greatly appreciated! I am willing to try out pretty much anything, to maximize my venting.

Thanks!

RST · 07-27-2010, 02:13 PM

Here is one site (of many) you can use to calculate your venting needs:
http://www.askthebuilder.com/B335_Ca...of_Attic.shtml

You can use this site to estimate how much NFA your current vents have:
Exhaust: http://www.lomanco.com/RoofVentmain.html
Intake: http://www.lomanco.com/intakemain.html

You should add intake vents for the older part of the building. If you are getting a new roof soon there are a variety of products you can use. If not... well, the pros will be able to give you a better answer than me.

RST

**Gary in WA** · 07-27-2010, 10:21 PM

If the holes in the bird-blocks are 1-3/4" (standard from most of the truss companies here in Tacoma since the '90's) you get 8 NFVA for each block. There should be 9 NFVA per lineal foot! So you need 18 NFVA per 22-1/2" bay. If the side addition is 14' long, you would need a b.b. in every bay and still only have 1/2 enough supply vents.

The gable vents are not very effective, only moving the air close to them and undersized: pp. #604: http://books.google.com/books?id=Z8a...0vents&f=false

You really need way more pot or turtle exhaust vents, especially in the dead air spaces where one roof is over-framed on the other. Have you figured out your NFVA required yet?

Be safe, Gary

seeyou · 07-28-2010, 05:55 AM

Quote:

Originally Posted by GBR in WA

If the holes in the bird-blocks are 1-3/4" (standard from most of the truss companies here in Tacoma since the '90's) you get 8 NFVA for each block. There should be 9 NFVA per lineal foot! So you need 18 NFVA per 22-1/2" bay. If the side addition is 14' long, you would need a b.b. in every bay and still only have 1/2 enough supply vents.

The gable vents are not very effective, only moving the air close to them and undersized: pp. #604: http://books.google.com/books?id=Z8a...0vents&f=false

You really need way more pot or turtle exhaust vents, especially in the dead air spaces where one roof is over-framed on the other. Have you figured out your NFVA required yet?

Be safe, Gary

Hey Gary -

Thanks for your links. I seldom have the time or patience to search out some of these references. I've bookmarked many of your links and thought I should let you know that your work is much appreciated.

Grant