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TOPIC: General Discussion

Ventilation

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I live in South Alabama, and there are no local codes where I am building, so there is nothing to check with to help or hinder my plans. I am going with corrugated through fastner metal panels for the roof. I am engineering my own ventilation system in the attic. I have heard 1 sq. ft. of vent space per 150 sq. ft. of ceiling space is a nice estimate for adequate ventilation. I am installing a vented ridge cap. The house is a simple roof with 2 gable ends. Questions. Should I install gable vents with the vented ridge vents? I've heard too many vents up at the top will not let the air flow properly from the soffits. How much venting at the soffits should I install? Do you figure the sq. ft. of a vent as the total area of the vent, or just the holes that are in the vent? What choices are there as far as soffit vent materials? I don't like vinyl or aluminum, and wood will breakdown. Isn't there some metal galvalume soffits on the market in this area? Thanks for the help in advance!
Guest User

4/26/2006
Ideally, you want your venting to be pretty evenly balanced between intake vents and exhaust vents. The concept you want to achieve is a continuous and complete "bath" of the underside of the roof deck with airflow. The best way to achieve this completely is with soffit vents (intake) and ridge vent (exhaust). Gable vents will disrupt that flow. www.airvent.com has good info on general venting concepts. Venting area is based upon free airflow ares of the vents -- the holes. The vent manufacturer should be able to tell you what this is for their product. There should be a wide variety of vents available at lumberyards or home centers in your area. Todd Miller
Todd Miller
Isaiah Industries, Inc.

4/28/2006
Hi Todd, The vented closures at the ridge that I have, provide 1/12th of a sq ft of vents per 3 foot panel. So 24 panels would provide 2 sq ft of vent area on each side of the ridge. This gives me 4 sq ft at the top, and 4 sq ft at the eaves from the soffits, if they are evenly split, for a total of 8 sq ft of venting area. The floor of the attic is 2160 sq ft. However, when you add it all up, this gives me about a 1:270 ratio rather than a 1:150 ratio that is recommended as ideal. What is the best way to lower this ratio? Gable vents disrupt the system. Turbine vents in addition to ridge vents? "There should be a wide variety of vents available at lumberyards or home centers in your area." I agree. I'm still looking for those other varieties. :) Thanks for the help so far, and I sure will appreciate additional help as well!
Guest User

4/28/2006
If you have continuous ridge vent and lots of soffit vents, you should be fine. Some of the information you have received pertaining to free air flow on these vents may be incorrect. As long as you have complete soffit and ridge vent, I would not do anything to disrupt that. Todd Miller
Todd Miller
Isaiah Industries, Inc.

4/29/2006