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Proper Roof Ventilation

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zendriver

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I finished the ceiling and insulated a 22x34’ 3 car garage, several years ago and frankly been too busy (lazy) to poke my head up there since.

There was some wasps on the garage window, try to figure where they came from so early in the season.

Poked my head up through access hatch and hokey smokes it was probably 135 degrees up there! Seemed very odd since it was only about 80 outside and it was the first warm day in a long time. The plastic on new insulation rolls was melted probably from 100 degree days.

It appears the PO was pretty stingy with vents (3) (8” holes). Which is the same problem with the house :dunno:




7FB2AB3D-30C6-4EBC-96B0-CB482AE9F76B.jpeg
Anyway what the best course to get air moving through there before some gets ruined from heat? Is there a formula to figure venting and possible to have too much?

Thanks
 
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kbs2244

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first add some soffit vents

then if that dosen't give you enough air movement
I like the wind powered turbin type roof vents
simple, quiet, and no need for a power feed

it looks like you already have the square "mushroom" style vents so replacement will be easy
 
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dfiler2

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It looks to me like it may already have vented soffits and 3 roof vents, which should be plenty for that building. Is it possible that the soffit vents got plugged when the building was insulated? How about a picture of the soffits from underneath and fairly close to the garage.
 
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zendriver

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I put in those foam soffit vent insulation protectors on the trusses both side of the garage roof. Unless the vents themselves are some plugged :dunno:

(3) 8” round holes in that large roof just don’t seem like enough vent but maybe it is.
 
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zendriver

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pcmeiners said:
"You should have used tech shield or one of the competitor's decking"

Especially if you like replacing your roof shingles often.

How about a side gable (or two) vent ?
Click to expand...
Thinking about that, but reading there can be “too much ventilation” that creates moisture problems presumably.

Just Want to get the right amount.
 
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bdbecker

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zendriver said:
Thinking about that, but reading there can be “too much ventilation” that creates moisture problems presumably.

Just Want to get the right amount.
Click to expand...

It's all about balance between your intake an exhaust. Too much net free area (NFA) on the exhaust side can be a problem because under certain conditions, the exhaust can turn into an intake and **** in rain or snow. Having too much soffit intake NFA is less of an issue as it doesn't really matter if air wants to exhaust out of it (but it does mean the air isn't moving through as efficiently as it could).

I've nerded out over this a few times, most recently in this thread:

Soffit vent options with limited area

I'm trying to figure out the best vent option for my soffit. I didn't plan out the overhang properly in the beginning, so now I have 6" between the brick backer board and the inside of the fascia board. I have a ridge vent that runs the entire length and it has a net free area of 18sq in per ft...
www.garagejournal.com www.garagejournal.com
 
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dcg9381

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I guess you could push/pull at the gables if you wanted to also on a thermostat?

OP, I wouldn't worry about "heat soak". Modern homes have "hot" roof decks where there if foam insulation under them. I'm not sure you can really burn up a roof that has basic ventilation. Your roof deck is probably cooler than foam insulated homes.

Soffit vents would be normal, but often homes are so leaky that it doesn't matter. You can also put solar fans where those existing vents are.

No, I didn't do any math or calculate anything.
 
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pcmeiners

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"Thinking about that, but reading there can be “too much ventilation” that creates moisture problems presumably."

My home has an opening area of 10x20 ', you can't get much more ventilation then that. I suppose if you have no insulation on the attic deck that might be an issue if a moisture laden air mass in the attic goes down to dew point level temperature in the early am hours. If you have insulation on the attic deck it will not be an issue.

"I'm not sure you can really burn up a roof that has basic ventilation."

You sure can destroy roof shingles with an over heated roof, as in using insulated roof sheathing. As a contractor I work on a few homes with insulated roof sheathing, keep the inside comfortable but the roof shingles only lasted about 8 years, even though the shingles were suppose to last 25 years; shingle life is mainly dependent on the roofs temperature. My roof is 28 years old, I know it will go at minimum another 20 years, due to ventilation and shade.
 
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zendriver

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A roofing contractor quoting our house stated it needed more ventilation as well which might have contributed shorter lifespan for the shingles.
 
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dfiler2

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I would listen to the contractor if I were you, those 3 vents would do a good job around here as long as the soffit vents were working properly but it may be that your area requires more. One way to increase your flow without cutting new holes would be to use some non powered roof vents like these.

Air Vent 17.8 in. H X 20 in. W X 20 in. L X 12 in. D Mill Aluminum Brace Turbine - Ace Hardware

A non-electric alternative to ventilation, these vents use the natural force of wind and air pressure to spin and vent out stale attic air. They do it with a series of specially shaped vanes that catch the wind and provide rotary motion. This pulls hot, humid air from the attic. Turbine vents...
www.acehardware.com www.acehardware.com
 
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bluedog225

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I’m curious about how many soffit vents. One way to address is to run a blower from the outside if it is blown in insulation. Will clear them out.
 
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zendriver

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bluedog225 said:
I’m curious about how many soffit vents. One way to address is to run a blower from the outside if it is blown in insulation. Will clear them out.
Click to expand...
Out of town I’ll check later. It all roll insulation and there are protectors

A lot of upgrades were done half assed, so maybe there is not enough soffit vents to (maybe none) :dunno:
 
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gmcgeo

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if you go by The shingle warranty standard. when you get shingles warrantied they see if you have Soffit intake, and the ridge vent for exhaust.

If you do not have that, then warranty is denied.
 
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Smokeem

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Attic venting really depends on your climate zone that your in. General rule of thumb is either 1 sq ft of venting to 150 sq ft of attic space or 1 sq ft of venting to 300 sq ft of attic space with not less than 40% and not more than 50% of venting at the ridge. The vents like you have come in T38, T50, or T70 size. The number of the vent is going to tell you the sq inch net free area of the vent. Most common that I see in our area is the T38 vents. It takes 4 of those vents to equal 1 sq ft of vent. Your soffit vents will tell you the same but give you a listing of aq inches of net free venting per linear foot of soffit. Personally I don't think that you can have to much attic venting. I think that for longevity of your roof that you need the attic temperature to be as close to outside temperature. If you look into code the reason that we have attic venting is to mitigate moisture build up in the attic. The other thing that needs addressed is if you have any trees in the area that produce cotton then a ridge vent will not work for you. In our area we have lots of trees that produce cotton and they plug up ridge vents.
 
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rharman

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pooterguy said:
Ridge vent lowered the temp in my attic by 50F.
Click to expand...

This is interesting as we will be getting a new roof in about 3 months - that much lead time due to all the local storms here.

We were considering doing ridge vents but decided against it (just tonight as a matter of fact) as we're concerned about wind blown rain working up under the edge between the ridge vent and shingles. Didn't used to have to worry so much about it but this year was horrendous for both wind and rain.

We do have gable fans on both stories so assume that cuts down the temp quite a bit. Just the design of the house causes the 2nd story to get quite warm. Center room where the stairs are acts like a chimney and all the hot air goes up there.
 
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zendriver

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dfiler2 said:
It looks to me like it may already have vented soffits and 3 roof vents, which should be plenty for that building. Is it possible that the soffit vents got plugged when the building was insulated? How about a picture of the soffits from underneath and fairly close to the garage.
Click to expand...
These are across both sides. Is there a chance too much air in not enough out? :dunno:

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dfiler2

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As long as those vents are open to the attic space it should be enough. However you are in a warmer climate than me so maybe it takes more on the roof. I have had really good luck with the whirley birds but I can understand not wanting them on your roof. Can you pull the top off of the roof vents to make sure everything is working the way they should? You mentioned the hole being small maybe just making the three holes larger would help.
 
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