Attic temperatures

[JackOfDiamonds]

I'm in Southern Idaho, Climate zone 5B. We have dry summers over 100F, cold winters down into the teens, low humidity, and less than 12 inches per year of precipitation. Lots of sun, pretty big temperature swings between day and night.

I built an addition, and I'm not sure the attic venting is correct. The eaves have plenty of venting...continuously vented soffit panels and full soffit baffles. For the ridge, there's a continuous ridge vent. I'm told this is supposed to be sufficient or even optimal, but the attic gets very hot, and when you are in the attic, you can't "feel" any airflow.

I put a temperature sensor in the attic, and it goes up to 150F during the day in the summer. Even on days it's only 80F outside, it will be 120F in the attic. There is plenty of cellulose insulation, so climate control in the addition is fine, but I might want to store some items in this attic, and there's not much you can store in a space that gets up to 150F. I'd like to moderate the temperature, if not for energy reasons, to make the attic more usable for storage, and so a person won't literally die if you need to go up there in the summer.

• Is there something wrong with my venting? Is continuous soffit vents and ridge vent not enough? Do you sometimes need even more venting?
• Are these normal attic temperatures, or higher than expected?
• If I install an attic fan, what type is best? I have electrical feed available in the attic to power it.

 

[pcmeiners]

is there something wrong with my venting? Is continuous soffit vents and ridge vent not enough? Do you sometimes need even more venting?

Sounds about normal for ventilation. My ranch attic stays about a couple degrees above ambient because I have a back wall open, air comes in by an over hang soffit which is equivalent of approx 144sqft opening plus the soffit and ridge vent. If possible get as much ventilation as possible, the advantage is my roof is 46 years old and good for years to come and AC cost are low.

 

[fitter30]

The solar heat gain from shingles outside temp 100°is 150-180° surface temp. Square foot attic X .7= cfm needed to drop temp 60°. Plus would need 1 sq ft for ever 300 cfm ventilation. With a powered ventilator.

 

[billconner]

What color is your roof? That has a much larger effect on attic temperature than venting. And the purpose of the race and ridge vents is to get moist air out in cold weather.

 

[aggie113]

I think my attic space started out properly vented with a grilled opening on the east side wall, but when additional insulation was blown in they likely covered up the soffit air flow. When the roof was replaced I asked for a ridge vent. They installed the metal part for the venting but never put any cuts in the decking! So still hot as balls in the attic.

 

[zendriver]

I think my attic space started out properly vented with a grilled opening on the east side wall, but when additional insulation was blown in they likely covered up the soffit air flow. When the roof was replaced I asked for a ridge vent. They installed the metal part for the venting but never put any cuts in the decking! So still hot as balls in the attic.

No doubt.

Sound's like workers didn't do both the insulation and the roof install right.

Need the soffit vents clear for "convection" air flow out the ridge vents (if they were actually installed properly).

 

[danski0224]

They installed the metal part for the venting but never put any cuts in the decking!

I have seen this many times. Also no chutes to keep insulation off of the vented panels.

I even caught the assholes trying to do it to me on my house- put in a vented soffit panel, but no hole in the original wood soffit. Then they tried to get away with literally busting a hole in the wood with a hammer.

Most people will not think to look, so the people doing this stuff get away with it.

 

[mm08822]

I would verify from inside the attic that any sheathing at the ridge vent is removed and you can see daylight through it.

Also at the soffits, if the insulation is up to the roof sheathing at the eaves, you will need to rake it back, again to see daylight. The foam spacers should be added to preserve the gap.

Vents in the gable ends will add more vent opening near the peak.

Check all of these methods before adding a fan as it will just be one more electrical consumer and one day need to be replaced.

 

[FTG-05]

I used to be a big fan of powered attic fans. No more. The problem is that they put a small vacuum on the top of our attic floor (your nside house ceiling) and **** air conditioned air out of the house. It, of course, being replaced with hot outside air, defeating the whole purpose of the exercise.

When I had my house built in north AL in 1994, the builder told me most homes and houses don't have enough inlet air at the soffits. So I added a bunch, then added a powered fan as well. This was before the internet.

I also added a lot of that double foil attic radiant insulation to the deck of the roof. That made a HUGE difference in attic temps.

Good luck.

 

[lolaetype]

I also added a lot of that double foil attic radiant insulation to the deck of the roof. That made a HUGE difference in attic temps.

I put a radiant barrier in the attic of our Houston house, it made a big difference, about 30-40 F degrees worth in the summer. I did it myself; I'd get up around 3:00 AM and work until 9:00 AM on Saturday and Sunday mornings. Later was too brutal.

I'm considering having one or two solar powered attic fans put in the storage space above the attached garage. That area already has soffit and ridge vents, but I think they need help.

 

[BurtEggley]

There is no reason someone has to have a hot attic if they plan good venting and roof tiles.

Go up there early in the morning while it is cool and look around. Make sure that the soffit vents have a path for air to flow. Sometimes insulation can cover those up. Personally I like more than a ridge vent, but attic venting is a two edged sword. If someone lives near where there are forest or grassland fires, the vents are where embers are going to get in. While there are solutions for that, the cost is quite high - meaning a regular soffit vent might be $8. A fireproof one might be $75. Instead of $150 worth of vents, it turns into $2000 just for the vents. And- someone who lives in an area where there are high winds and/or driving rains, one has to be sure that the wind and/or rain does not get in and cause damage.

Many years ago I added a whole house fan. It came with instructions of how many sq.ft of attic venting it needed to operate correctly. I added a lot of venting to get there, at least double what the house had when built. The side effect of that was the attic temperature in summer now isn't much more than sitting in a car with the windows down and a light breeze. In general with whole house fans, one needs about 1 sq.ft of free vent area per 750 CFM. The 1/2 hp 6 blade whole house fan we have flows about 8,000 to 10,000 cfm so that needs about 12 - 13 sq.ft of venting. Venting in many older homes is what, maybe 10 ea of 3.5" x 22" soffit vents and 2 ea 18" x 22" gable vents?That is 5.3 sq.ft plus 5.5 sq.ft for a total of 10.8 sq.ft TIMES THE LOSS FACTOR based on screens covering the vents. A vent loss factor of 50% is common. That gives the real venting at about 5 or 6 sq.ft. I had to double the attic venting. The side effect was a cool attic in summer. However we do not have hurricanes, or derechos here.

Also, next time the roof is done, chose one that has a thermal coefficient engineered to be cooler. Even some of the medium dark tiles now have special materials in them that reflect a lot of the light and infrared that hits them. That helps with a hot attic and also if there is a fire nearby.

 

[JackOfDiamonds]

I put a radiant barrier in the attic of our Houston house, it made a big difference, about 30-40 F degrees worth in the summer.

This is intriguing to somebody who wants to keep attic temperatures more reasonable. There's a lot of things that are safe to 120F, and lot of things that could cause trouble at 150F if they accidentally get put in attic storage.

Are you talking about the foil-faced bubble wrap stuff? Did you staple it directly onto the plywood, or to the underside of the truss boards?

 

[lolaetype]

Are you talking about the foil-faced bubble wrap stuff? Did you staple it directly onto the plywood, or to the underside of the truss boards?

It was a thin silver sheet (mylar?) that came in rolls, stapled to the underside of the trusses. That left space between the radiant barrier and the back side of the roof decking which allowed the trapped air to move upward to the ridge vents while cooler air flowed in below from the soffit vents.

 

[danski0224]

This is intriguing to somebody who wants to keep attic temperatures more reasonable.

The only realistic way you will be able to do this is to make the attic space conditioned space.

Spray foam the roof deck (underside) or rigid foam above, covered with plywood for a regular shingle roof.

 

[geneg]

I'm in Southern Idaho, Climate zone 5B. We have dry summers over 100F, cold winters down into the teens, low humidity, and less than 12 inches per year of precipitation. Lots of sun, pretty big temperature swings between day and night.

I built an addition, and I'm not sure the attic venting is correct. The eaves have plenty of venting...continuously vented soffit panels and full soffit baffles. For the ridge, there's a continuous ridge vent. I'm told this is supposed to be sufficient or even optimal, but the attic gets very hot, and when you are in the attic, you can't "feel" any airflow.

I put a temperature sensor in the attic, and it goes up to 150F during the day in the summer. Even on days it's only 80F outside, it will be 120F in the attic. There is plenty of cellulose insulation, so climate control in the addition is fine, but I might want to store some items in this attic, and there's not much you can store in a space that gets up to 150F. I'd like to moderate the temperature, if not for energy reasons, to make the attic more usable for storage, and so a person won't literally die if you need to go up there in the summer.

• Is there something wrong with my venting? Is continuous soffit vents and ridge vent not enough? Do you sometimes need even more venting?
• Are these normal attic temperatures, or higher than expected?
• If I install an attic fan, what type is best? I have electrical feed available in the attic to power it.

The first consideration is to make certain that the path for the soffit vents are clear.
Second is to confirm that the sheeting was cut prior to the roof vent installation. I've seen both situations in attics.

You should feel airflow on a hot day. Any flow up thru the access hole? If not, I'd say ridge vent issue. Baffles for soffits is easy to verify. Can you add a temporary gable vent? It will short circuit the ridge vent if its working at all, but I'd prefer not adding a roof penetration. If it helps, use the hole for your attic fan. Correcting the ridge vent is much more invasive & probably more expensive.

Finally, I'd rethink storage in an attic with blown in cellulose. It does drift & move. You'll be bring some of it down with you on every trip unless you have platforms built above it. Also inconvenient as hell.

 

[Fav Onefour]

Sounds like the soffit venting is great. It's a pretty easy check to see if the venting is blocked by insulation. Even with proper baffles, the insulation could have been blown into those cavities.
Next step would be checking the ridge vent. The mesh style is prone to plugging with dust and debris.

The idea of installing vent covers without cutting holes seems nuts but I guess it's possible. In that case I wouldn't be so surprised if the roofers didn't cut the decking as well.

Active air flow can create more of what @FTG-05 mentions about pulling conditioned air out of the house. If you still want to go with an attic fan, I'd verify gap sealing into the attic. Gap sealing is a good idea no matter what you do in the attic.
I've been through the powered attic fan scenario. They are another hole in the roof and something to maintain. You should be able to avoid going that route with good venting and a properly insulated attic.

@JackOfDiamonds , you mention this is an addition. Is it configured in a way that airflow is blocked by the main house? Do you have any photos of your layout and sun orientation? I've seen additions tucked into the side of a home creating hot pockets on the roof. One neighboring home has two sections of roof that must dang near melt shingles. Those sections have been an ongoing battle with ice dams as well.

 

[1320stang]

Many years ago, my A-coil would freeze up. There were three speed taps on the fan motor from factory it was set to low, my hvac guy moved to medium. Updraft system, duct in attic, he said 85*F-90*F switch the fan from Auto to On to gain some cooling off the stiil cool coil while keeping air moving thru the ductwork.

Later I started cracking the attic stair door in the garage and laying a box fan over the end of the opening. I installed a security scrren door on the side door to the garage and crack it open a couple inches, block of wood on one side to keep it open and a weight to keep it from blowing open more.

Does all this waste energy? Probably, is my wife happy? Yes. I will say when I've gone to the attic in the summer, its only a few degrees higher than ambiant outside, very noticable difference. I need to blow in some more figerglass. I may install some foil bubble wrap. I have the 6x12 wood framed soffit vents maybe every 4 feet, no baffling and ridge box vents.

If I could afford it, I'd have the insulation removed and the roof deck foamed. My boss did his and it made a world of difference.