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Attic ventilation
Posted on 8/6/19 at 10:02 pm
Posted on 8/6/19 at 10:02 pm
How can I tell if my attic has enough ventilation? Can an A/C person tell me? Measure it?
6
Posted on 8/6/19 at 11:26 pm to BengalBlood81
I’ve been flirting with installing an automatic vent fan in my attic... just haven’t because I’m not sure it’ll do any good. 
I do know it gets hot as balls up there at times.
I do know it gets hot as balls up there at times.
Posted on 8/6/19 at 11:50 pm to BengalBlood81
Do you have ridge vents? There are attic ventilation calculators on line, based on 1 sq ft of ventilation area per either 150 square feet of attic area (preferred) to 300 square feet of attic area (minimum I think).
Your soffit vent area (intake) should ideally equal ridge vent area (exhaust). I’ve calculated it on own my own house which is easy to do, but I have ridge vents, and I met the 1:150 ventilation area criteria. If you have whirlybird vents (wind driven exhaust vents) or power vents to exhaust the air then you’ll need different calculations at least on the exhaust side.
Your soffit vent area (intake) should ideally equal ridge vent area (exhaust). I’ve calculated it on own my own house which is easy to do, but I have ridge vents, and I met the 1:150 ventilation area criteria. If you have whirlybird vents (wind driven exhaust vents) or power vents to exhaust the air then you’ll need different calculations at least on the exhaust side.
Posted on 8/7/19 at 12:02 am to BengalBlood81
Current residential code (2015 IRC) states the minimum attic ventilation requirements are 150/1. This means that if you have a 1500 sq. ft. attic then you would need at least 10 sq. ft. of ventilation. This is area, not volume. You should try to have this split evenly between the soffit and ridge. A perforated soffit has about 5 in.² of free area per linear foot. A ridge vent is about 18 in.² per linear foot and a dome “mushroom” vent has about 144 in.² of free area. There are a bunch of different types of vents. You can look online and probably find the free area of whatever particular vents you have. Calculate your free area in square inches then convert to square feet.
From what I’ve seen, most homes don’t have enough attic ventilation. And I’m wary of ventilators. If your ceiling has cracks (attic stair, can lights), the fan will draw conditioned air into the attic. If this happens, your house could have negative pressure and draw in outside air. That’s what I’ve been told and it makes sense.
That’s all I got. Which is more than I ever wanted to know about it.
From what I’ve seen, most homes don’t have enough attic ventilation. And I’m wary of ventilators. If your ceiling has cracks (attic stair, can lights), the fan will draw conditioned air into the attic. If this happens, your house could have negative pressure and draw in outside air. That’s what I’ve been told and it makes sense.
That’s all I got. Which is more than I ever wanted to know about it.
Posted on 8/7/19 at 12:10 am to MarcusQuinn
I installed an attic gable fan a few years ago. There was a noticeable difference in attic temperature and reduction in my summer time electric bill. I used a BBQ meat smoking thermometer to monitor my attic temps before and after my gable fan installation.
This post was edited on 8/7/19 at 12:14 am
Posted on 8/7/19 at 7:01 am to BengalBlood81
The proper amount of quality turbine do the best at removing heat from the attic. People just done like the look. Ridge vents suck
Posted on 8/7/19 at 7:03 am to MarcusQuinn
What’s interesting in your post is that my ceiling developed two long cracks in the living room on the tape lines. Not sure if it’s just a coincidence or related to hot/cold air but it sure seems like it could be a cause of the cracks. Or it could just be that quick set mud they used when building the house.
Posted on 8/7/19 at 8:02 am to BengalBlood81
quote:
What’s interesting in your post is that my ceiling developed two long cracks in the living room on the tape lines.
Odds are this is improper framing in the attic that is flexing and/or sagging due to long spans
Posted on 8/7/19 at 8:09 am to wickowick
Wouldn’t doubt it. They repaired the Sheetrock tape lines. Hoping it doesn’t come back
Posted on 8/7/19 at 8:15 am to MarcusQuinn
quote:
Current residential code (2015 IRC) states the minimum attic ventilation requirements are 150/1.
There's an exception in there, 1/300 if using ridge vents, as they are more efficient than vents NOT places at the highest point of the attic space (hot air rises...)
Posted on 8/7/19 at 9:15 am to BengalBlood81
I have ridge vents on my house. I do not like them.
Wind turbines are used in the new construction and are preferrable.
Wind turbines are used in the new construction and are preferrable.
Posted on 8/7/19 at 6:52 pm to ItzMe1972
quote:
I have ridge vents on my house. I do not like them.
Wind turbines are used in the new construction and are preferrable.
Ridge vents are highly effective for the right type of roof design. Not all houses have enough ridge length to allow for proper ventilation with ridge vents. I do not like the wind turbine type of vents very much. These were very popular when I was growing up but by the time I was an adult, they were falling out of favor due to issues with bearing failing. I personally prefer power turbines, though they coast money to run and have a different set of issues with motors and thermostats going out.
Posted on 8/7/19 at 7:44 pm to shell01
I know. But I figured there was plenty of info to sort out without getting into exceptions and percentages. If it’s split high and low (40-50% high?) it can be 1/300. But if you have a continuous perforated soffit you end up with nearly 1/150 anyway to get the ratios to work.
Posted on 8/7/19 at 7:52 pm to MarcusQuinn
I’m pondering the same issue. My question: can you have too much attic ventilation. My soffit vent seem sparse with some exterior walls having none in 20’ or so. I’ve got a ridge vent up top. Thx. I’m thinking of adding some whirly gigs but don’t want to f it up.
This post was edited on 8/7/19 at 7:53 pm
Posted on 8/7/19 at 8:23 pm to White Bear
Posted on 8/8/19 at 6:42 am to BengalBlood81
Yes. I’m looking into an attic fan and encapsulating part of my walk in storage area as well. Probably wait until fall so it’s cooler to work in. I’ve got huge roof pitch (12/12 main, 14/12 gables) so it’s going to be pita but needs to be done.
Posted on 8/8/19 at 7:09 pm to CrawDude
quote:Thank you.
CrawDude
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