Ventilation

2134 Views 6 Replies 3 Participants Last post by Gary in WA, Jul 9, 2011

Gungho_15

Discussion Starter · Jul 6, 2011 (Edited)

I am sure this topic has been beat to death. I live in a 2 story 2300 square foot house. Last summer I put on a new roof with Shinglevent II ridge vents.(approx 39 feet)

Our upstairs of our house is always hot in the summer. This spring I had a heat pump installed. Best purchase yet. This fall I plan on adding insulation. I currently only have R12, Code is R40. I installed rafter vents and made sure all soffits are open. The attic is approx 1200 square feet.

The soffits currently have 9 - 16"x2.5" vents cut out. 4 on the front of the house, 5 on the rear.The soffits are cedar tongue and groove.

Should I be adding intake vents or just leave it be? I have tried to figure out the math, but it seriously had me dreaming of numbers all night...lol I live in Vancouver British Columbia if that helps.

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Gungho_15

Discussion Starter · #3 · Jul 6, 2011

josall said:
To have a balanced system you will need 14-8x16 soffit vents. Your ridge vent has 18 sq. in. of net free area of ventilation per lineal ft. which is 702 sq.in. of ventilation. Divide that by 56 sq.in. which is the nfa of ventilation off an 8x16 aluminum soffit vent and you get about 12.5 I rounded up to make it even on both sides. Hope that helps.

Thanks for the info. Unfortunately with the look of the cedar tongue and groove, I will not be putting 8x16 vents. If i were to cut the vents continuous along the entire soffit, would that be sufficient? The soffit length is 43 feet. So it would be 43 feet by 2.5 inches.

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Gungho_15

Discussion Starter · #6 · Jul 6, 2011

GBR in WA said:
Continuous would be way better than 8x16's as you will vent each rafter bay rather than one vent every 7' (depends on brand 8x16=65NFVA and 2-3/4 cont. is 8-9 NFVA) http://www.lomanco.com/intakemain.html

http://www.airvent.com/homeowner/products/intakeSoffit-specs.shtml

Install it closest to the fascia board for best air pressure, pp. 616: http://books.google.com/books?id=Z8...page&q=attic airflow with gable vents&f=false

Cont. soffit = 1/2 cont. ridge vent plus add the other side soffit = balanced. Be sure to air seal the attic, much more important: http://www.jlconline.com/cgi-local/...e.storefront/4d17fa04053d6e9327170a32100a05c7

Gary

Thanks for the great info. Some of it I don't understand. Currently the cedar is cut 1 inch away from the edge of the fascia board and is 2.5 inches wide by 16 inches long. The hole is protected with some sort of screening material.

So it sounds like what you are saying is that I should cut the entire length of the soffit to improve it. I was going to re-do the screen material after all the cuts were made.

Does that sound appropriate and will it make a noticeable difference in my house?

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