Attic Ventilation

[Redneckwannabe]

Hello, I'm looking for some advice. I was told I should double the ventilation in my attic when I do my new roof. Its a low slop roof approx 1500 sqft and currently has 2 whirlybirds. I'm upgrading the insulation as well. Does anyone know the advantage/disadvantage of adding more vents? Is more always better?
Thanks!

[roughneckin]

From when I was doing roofing, which was a bit ago, that you are supposed to use the 1:300 rule, so every 300ft of square footage you need 1 foot of ventilation, but we added a few more to ensure that it was not going to sweat in the attic. This will lead to rotting of your insulation. I only did it on and off though, pretty sure there is more qualified roofers here that will help.

Remember to add the soffit venting in your equation as well.

[bagwan]

Do you have other venting at the eaves or ridge cap? Also change out the whirly gigs when the shingles are off unless they're fairly new. Not expensive in the scheme of things.

[Redneckwannabe]

Yes I should have mentioned - the soffits are the ventilated type

[fishtank]

a whirly bird is good for 500 sq ft of ventilation, have the vent closer to the top ridge of the roof . proper ventilation will help keep moisture and excess heat out of the attic, better life for the shingles .

[Selkirk]

Originally Posted by fishtank

. . . proper ventilation will help keep moisture and excess heat out of the attic, better life for the shingles .

That ^^^

Within reason, it never hurts to add more ventilation during a re-shingling. We re-shingled 25 years ago and increased the ventilation then. We'll be re-shingling again next spring, and will add even more ventilation during that process.

Also, there is one other benefit to adding more attic ventilation that hasn't been mentioned yet ... not only does it reduce the heat build-up in the attic, it also reduces the amount of attic heat that radiates down into the house during the summer, making the living quarters of the house much cooler, and more comfortable.

Mac

[Fox red lab]

I installed a power vent in my previous house as the upstairs was always hot in the summer. It was on a thermostat and kicked in at about 100 F. Made a difference for sure. Will extend the life of the shingles I expect.

I always seem to think there are never enough vents in houses. Especially garages.

[Redneckwannabe]

Thanks for the info everyone

[Whiskey Wish]

Sort of on the same topic but with a twist.

Is there supposed to be a certain amount of spacing between whirlybird type attic vents and the old static "open hole" type vents?

We had the whirlybird type vents installed a few years ago and they are quite close to the existing ordinary vents.

Is it possible for a whirlybird type vent to actually pull air in the static type vents and then vent it right back outside, thereby failing to vent the remainder of the attic properly?

Thanks for any help.
Regards,
Dave

[Selkirk]

Originally Posted by Whiskey Wish

Sort of on the same topic but with a twist.

Is there supposed to be a certain amount of spacing between whirlybird type attic vents and the old static "open hole" type vents?

We had the whirlybird type vents installed a few years ago and they are quite close to the existing ordinary vents.

Is it possible for a whirlybird type vent to actually pull air in the static type vents and then vent it right back outside, thereby failing to vent the remainder of the attic properly?

Thanks for any help.
Regards,
Dave

I would say 'yes'.

For the whirlybirds to work effectively (draw air into the attic from under the soffits), you may want to consider blocking off the old static vents on top of the roof.

Mac

[Kim473]

Originally Posted by Fox red lab

I installed a power vent in my previous house as the upstairs was always hot in the summer. It was on a thermostat and kicked in at about 100 F. Made a difference for sure. Will extend the life of the shingles I expect.

I always seem to think there are never enough vents in houses. Especially garages.

I put one in my house too. Noticably cooler in the summer months for sure. I also added a in take vent at each gable end at the time for more air to enter the attic. Took the power from one bedroom light/fan so if I don't want it to turn on, I just leave that light switch off. Will still vent in the winter but not powered.

[MK2750]

Originally Posted by Redneckwannabe

Yes I should have mentioned - the soffits are the ventilated type

I was at a buddy's house in a new area and I noticed an unusual amount of vents on the roofs.

He told me that updraft through the soffits created a domino effect when there is a fire. The flames apparently enter a neighboring home via the ventilated soffit and are impossible for the firefighters to get ahead of.

It makes sense to me as a fire took out 3 or 4 in a row here a couple years back and it happened in minutes.

Anyhow, they are putting vents both up and down on the roofs to combat this effect but I am unaware of all the details. I would do a quick study on the subject if I was redoing a roof and adding insulation. A person could add end vents and the new roof vents no problem. Rather than removing the ventilated soffit you could just cover with insulation so air/fire wouldn't enter there.

This is obviously not an issue if your neighbors are not close.

[bsmitty27]

I wouldn't cover my soffet vents for fear of fire. Yes fire can definatly get in your attic via soffet and is compounded by ventilation. But I would say your odds of having damage done are greater from poor ventilation.
Brad

[moosemad]

Originally Posted by Whiskey Wish

Sort of on the same topic but with a twist.

Is there supposed to be a certain amount of spacing between whirlybird type attic vents and the old static "open hole" type vents?

We had the whirlybird type vents installed a few years ago and they are quite close to the existing ordinary vents.

Is it possible for a whirlybird type vent to actually pull air in the static type vents and then vent it right back outside, thereby failing to vent the remainder of the attic properly?

Thanks for any help.
Regards,
Dave

Not sure of the distance between but when I had my roof done last year by a reputable company the estimator recommended I replace my whirly birds with regular roof vents, which I did (they were only about $12 each). His concern was on windy rainy days the whirly birds spin and throw the rain water into your attic and onto the insulation, made sense to me.

[Whiskey Wish]

Originally Posted by moosemad

Not sure of the distance between but when I had my roof done last year by a reputable company the estimator recommended I replace my whirly birds with regular roof vents, which I did (they were only about $12 each). His concern was on windy rainy days the whirly birds spin and throw the rain water into your attic and onto the insulation, made sense to me.

I honestly do not know if what you described is possible, and I do not intend this as a slam, but my understanding of physics is that centrifugal force would throw water out not in...?? That is a spinning whirlybird would throw water away from its center.

As I said, I am not a roofer nor a carpenter so I could be wrong. I was once.....lol
Regards,
Dave.

[MK2750]

Originally Posted by bsmitty27

I wouldn't cover my soffet vents for fear of fire. Yes fire can definatly get in your attic via soffet and is compounded by ventilation. But I would say your odds of having damage done are greater from poor ventilation.
Brad

It's code for close built homes to have non-vented soffits.

There are solutions for adequate venting if one takes a look.

The reason they made it code is because you can have a well ventilated attic without the added risk of fire.

[thefloormat]

i put vents in my garage I just build, 22x20 with 10' walls that I'm going to heat. I only put two vents in on the west side of the roof, should i have put more and on the east side as well? curious if two are enough.

[Six point]

My great big roof only has a couple of the static type vents and is very warm inside during the summer.Can anyone recommend a decent roofing contractor that could a few more?

[bahmt]

Another issue is heat loos through your insulation. If you have heat loss into the atic from your home it can actually melt snow and create ice damming which lets water back up under your shingles in the spring when things start to melt. Makes a large mess that I wish on no one. If you have whirly birds it will remove said heat keeping attic cool.

[Fish along]

Originally Posted by thefloormat

i put vents in my garage I just build, 22x20 with 10' walls that I'm going to heat. I only put two vents in on the west side of the roof, should i have put more and on the east side as well? curious if two are enough.

in my opinion you should have more vents, in the eaves for sure .im a firm believer in lots of ventilation.Look at the underside of your roof after one year,if theres discoloratioin, then you need more vents. The down side is rotting your whole roof, the shingles wont rot they`re made of oil product.ps Im a carpenter VENTILATE .

[Fish along]

Originally Posted by bahmt

Another issue is heat loos through your insulation. If you have heat loss into the atic from your home it can actually melt snow and create ice damming which lets water back up under your shingles in the spring when things start to melt. Makes a large mess that I wish on no one. If you have whirly birds it will remove said heat keeping attic cool.

yes of course if you don't have adequate insulation ,you will end up with condensation,but lots of ventilation can help this situation .

[Selkirk]

Originally Posted by Fish along

in my opinion you should have more vents, in the eaves for sure .im a firm believer in lots of ventilation.Look at the underside of your roof after one year,if theres discoloratioin, then you need more vents. The down side is rotting your whole roof, the shingles wont rot they`re made of oil product.ps Im a carpenter VENTILATE .

Originally Posted by Fish along

yes of course if you don't have adequate insulation ,you will end up with condensation,but lots of ventilation can help this situation .

That ^^^ X2

When it comes to attics ... insulate & ventilate ... insulate & ventilate ...

The benefits are tenfold.

Mac

[Vingiu]

More is generally better. I just started framing recently but we cut vents every 5 feet on the backside of the roof along the ridge. It looks like a lot but it isn't. I've also been told that alternating front/back helps tremendously... not sure why they aren't doing that on my build sites.