Attic Vents

[Pantlegz]

The house I'm living is was built between the 50's and 60's and we're having issues keeping it cool - it's always been a problem but it seems to be getting worse. I was looking options for reducing the cooling bill, between the 2 upper level units the electricity bill increases by roughly 350 a month and the house is warm 80-85 recently, hopefully it doesn't get much higher. We have adequate AC(window units) they may be slightly small(online calculators suggest 16,000-20,000) 18,000BTU cooling a main space of ~600 sq ft with smaller units in each bedroom - when we're not in them we have to use fans to direct cool air out into the main living area to help cool it. I'm slowly replacing windows, which I'm sure is helping but it's still HOT and humid. So as I was researching possible causes, attic temps and lack of proper circulation could be some of the cause for it getting so hot.

Currently the attic has soffit vents, gable vents and 2 box vents and they don't seem to be doing a very good job(I'm assuming the boxes/gable are preventing much pressure build up so it's not flowing naturally). I was thinking of blocking off the gables and boxes then adding 2 powered attic fans. However, my research has been VERY conflicting and I don't know which 'camp' to listen to. One side suggests that a radiant barrier is all that's needed, plug all the vents and install closed cell insulation. And the other side saying insulation isn't what is needed, and will ruin the roof, just properly vent the roof and you're good. Since I'm not looking to live here for more than a couple more years I'd rather not dump a ton of money into a solution, or attempted solution only to find that there was a better way of fixing the problem.

So what do you guys do to keep you attic from turning your house into an oven? Any suggestions outside of the 2 I've found - or evidence that one side is more correct than the other?

 

[edro]

Chances are it is insufficiently vented.
2 box vents is your problem.

Check out any modern house.
They will have soffit, gable and MANY MULTIPLE box vents (and/or in addition to ridge vents).

 

[Blain]

My 2' overhangs have all vented soffit down the whole length of the house.
I have two 14" turbine vents and two standard size gable vents.
I'd like to swap out our turbines for solar powered vents, when we reroof the house.

 

[Pantlegz]

Chances are it is insufficiently vented.
2 box vents is your problem.

Check out any modern house.
They will have soffit, gable and MANY MULTIPLE box vents (and/or in addition to ridge vents).

So would it makes sense to go with a passive cooling system like a ridge vent, which would be more expensive to install or powered fan vents?

 

[WilliamM2]

So would it makes sense to go with a passive cooling system like a ridge vent, which would be more expensive to install or powered fan vents?

Ridge vent wold work best of you have enough soffit vents. It will vent more evenly than an attic fan, which will just pull air from the nearest inlet, probably the box vents, which are usually already high up on the roof. My attic is much cooler after adding ridge vent. Although I needed a new roof at the time anyways.

 

[Humpy]

You're going to live there for 2 more years?

I don't see how anything you do would make financial sense over such a short time. Save the money you would spend on improvements to pay the utility bill. If you're hot add another AC unit.

Assuming an unconditioned attic, it's doubtful roof venting will have any effect on your comfort anyway. If you do anything it should be air sealing and insulating the ceiling.

 

[Pantlegz]

You're going to live there for 2 more years?

I don't see how anything you do would make financial sense over such a short time. Save the money you would spend on improvements to pay the utility bill. If you're hot add another AC unit.

Assuming an unconditioned attic, it's doubtful roof venting will have any effect on your comfort anyway. If you do anything it should be air sealing and insulating the ceiling.

It might not be a great ROI but to be comfortable inside without spending another 100/mo on top of the already high cost to cool the house doesn't seem like a good idea either. I haven't measured the exact sq ft but I'd guesstimate somewhere around 1200 is currently costing ~150 a month if I remember correctly (I don't have the bills in front of my but in the winter it seems like electricity is around 100/mo and last month was 250 and it hadn't gotten that warm yet) So adding more AC units doesn't seem like a cost effective solution to me.

Got home and checked electric bills Jan was $80 and June was $245 - the only difference between the 2 is we watched more TV in the winter and obviously the outside temp. $165 to cool in a month with a mean temp of 80 and an average high of 92 and having the house warm more often than not is sort of upsetting. If it were comfortable inside I'd probably be ok with paying $165 to cool the house but paying 250+ just for cooling a house this small, no freaking way. I came to my $100/mo increase by estimating another 18,000 BTU AC running 24/7, just like the current one is, taking ~1700 watts to run times the average rate of electricity after delivery last month was roughly 7.5 cents per kwh which comes out to about $3/day and with all the other fees, I rounded up from $90.

 

[slashbinslashbash]

Set a thermometer up in your attic and see how hot it gets up there. If it's above 120F then you probably need more ventilation.

Powered ventilation is not always the answer. It can just as easily suck cold air up through the house, which is generally not well sealed (think the holes in the drywall for light fixtures, etc. which are pretty much never sealed). The attic door can also be a giant cool air loss site. If you don't already have an insulated cover over your attic door, get one.

Adding insulation in your attic could give a bigger return. Adding radiant barrier can work very well as well.

Ridge vent is the best kind of passive ventilation at the top of a house's roof, but if it's not matched with sufficient quantity of bottom ventilation (soffit vents etc.) then it won't do much. Also if there is not much of a ridge then it will definitely not be sufficient. Ridge vent works best on gable style houses where there is a continuous ridge running all the way across the roof. On hipped roof houses, if the ridge is at least 20' in length or so, then it may be sufficient. If the ridge is small, as on a peaked roof house then ridge vent will be worthless. You say that you have gables so hopefully you have a bunch of ridge.

Ridge vent is actually super easy to install. Most houses you could probably get a roofer to do it for you for $1000 or less. For a reasonably handy person, it is fairly simple to do it yourself.

A practiced roofing installer with a nailgun can install a 30-40 foot ridge vent in an hour or two... under an hour with an assistant. The initial ear-off would add a bit of time, since they have to be careful not to damage the other shingles while removing the cap shingles. (Not normally an issue when doing whole roof replacement.)

 

[Pantlegz]

Set a thermometer up in your attic and see how hot it gets up there. If it's above 120F then you probably need more ventilation.

Powered ventilation is not always the answer. It can just as easily suck cold air up through the house, which is generally not well sealed (think the holes in the drywall for light fixtures, etc. which are pretty much never sealed). The attic door can also be a giant cool air loss site. If you don't already have an insulated cover over your attic door, get one.

Adding insulation in your attic could give a bigger return. Adding radiant barrier can work very well as well.

Ridge vent is the best kind of passive ventilation at the top of a house's roof, but if it's not matched with sufficient quantity of bottom ventilation (soffit vents etc.) then it won't do much. Also if there is not much of a ridge then it will definitely not be sufficient. Ridge vent works best on gable style houses where there is a continuous ridge running all the way across the roof. On hipped roof houses, if the ridge is at least 20' in length or so, then it may be sufficient. If the ridge is small, as on a peaked roof house then ridge vent will be worthless. You say that you have gables so hopefully you have a bunch of ridge.

Ridge vent is actually super easy to install. Most houses you could probably get a roofer to do it for you for $1000 or less. For a reasonably handy person, it is fairly simple to do it yourself.

A practiced roofing installer with a nailgun can install a 30-40 foot ridge vent in an hour or two... under an hour with an assistant. The initial ear-off would add a bit of time, since they have to be careful not to damage the other shingles while removing the cap shingles. (Not normally an issue when doing whole roof replacement.)

So a couple questions and a couple concerns, I'll start with the concerns:

The roof is LONG - if I had to venture a guess I'd say a good 100' so given your estimates for 30-40 foot, it would cost $2,000-$3,000 to get a ridge installed. I'm fairly handy but honestly don't have the time or patience for a project. Installing fans shouldn't cost more than 400 but I have a feeling I'm looking at close to 600 all said and done. We do have insulation in the attic which I'm hoping will help prevent some of the suction of air out through the not so sealed ceiling. Is there an easy way to tell how much/where air would be leaking prior to installing the fans?

With the radiant barrier, I'm assuming you're talking about either open or closed cell insulation? Doesn't the attic have to be sealed for that to be effective? I agree this would probably be the best solution but also the most costly. I'd much rather spend the 600 and if we're getting too much air flow from the living area that shouldn't be too difficult to track down and seal.

 

[Humpy]

It seems like you are a bit off track in your thinking. I question the logic of installing electric fans in the hope of reducing electricity bills.

The focus is temperature/comfort in the living space, not the temperature in the attic. You don't live in the attic.

The first step is to air seal the ceiling as best as possible. The second step is to ensure sufficient insulation (I'm still assuming this is an unconditioned attic? i.e. the insulation is adjacent the ceiling, not the roof). The walls (and maybe a crawlspace) follow those same steps in order.

Then the attic can be addressed. The first step is to block radiant heat gain, possibly with a reflective roofing material or I guess a radiant barrier. The second step is to vent the space. Temperature is a related but secondary goal to moisture control in venting the attic though, so it has to be done accordingly.

 

[edro]

You might want to do a quick cheap test first, to see if you can tell a difference.

Buy 2 large box fans ($40?) and put one on each gable vent (one sucking in, one blowing out).
See if the temperature in the attic drops and see if it is noticeable in the house.

You should test things out before spending money and cutting holes in your roof, especially if you are only going to live there 2 years.

 

[Pantlegz]

It seems like you are a bit off track in your thinking. I question the logic of installing electric fans in the hope of reducing electricity bills.

The focus is temperature/comfort in the living space, not the temperature in the attic. You don't live in the attic.

The first step is to air seal the ceiling as best as possible. The second step is to ensure sufficient insulation (I'm still assuming this is an unconditioned attic? i.e. the insulation is adjacent the ceiling, not the roof). The walls (and maybe a crawlspace) follow those same steps in order.

Then the attic can be addressed. The first step is to block radiant heat gain, possibly with a reflective roofing material or I guess a radiant barrier. The second step is to vent the space. Temperature is a related but secondary goal to moisture control in venting the attic though, so it has to be done accordingly.

How does one go about air sealing the ceiling? As far as I can tell there aren't (m)any gaps for air to get up aside from possibly light fixtures. The heater cold air return does run along the attic and there might be gaps there - but just testing that seems expensive. Some background might be helpful here, the air return is just a drywall duct that was added to the bottom of the ceiling, not my doing, but checking for leaks seems like it would require that to be torn out. Unless there is a way to check from the top, through insulation(it may not actually be over the air return I haven't been up there in a while to remember 100%).

I'm not against adding a radiant barrier. Is this something that could be done after installing the vents or is it ideal to to it first? But would that effect the ridge vents?

I don't necessarily want to reduce the electricity bill, I'm ok with it being where it is assuming the house is comfortable. The attic fans would cost ~10/mo to run considerably less than adding additional AC units. The ceiling it insulated - the walls could probably use better insulation it was last installed in the 80's but the cost associated with that vs the benefit don't seem worth it to me.

You might want to do a quick cheap test first, to see if you can tell a difference.

Buy 2 large box fans ($40?) and put one on each gable vent (one sucking in, one blowing out).
See if the temperature in the attic drops and see if it is noticeable in the house.

You should test things out before spending money and cutting holes in your roof, especially if you are only going to live there 2 years.

That's not a bad idea. If I end up installing the radiant barrier this weekend I might throw a couple fans up there to see how it does.

 

[slashbinslashbash]

So a couple questions and a couple concerns, I'll start with the concerns:

The roof is LONG - if I had to venture a guess I'd say a good 100' so given your estimates for 30-40 foot, it would cost $2,000-$3,000 to get a ridge installed. I'm fairly handy but honestly don't have the time or patience for a project. Installing fans shouldn't cost more than 400 but I have a feeling I'm looking at close to 600 all said and done. We do have insulation in the attic which I'm hoping will help prevent some of the suction of air out through the not so sealed ceiling. Is there an easy way to tell how much/where air would be leaking prior to installing the fans?

With the radiant barrier, I'm assuming you're talking about either open or closed cell insulation? Doesn't the attic have to be sealed for that to be effective? I agree this would probably be the best solution but also the most costly. I'd much rather spend the 600 and if we're getting too much air flow from the living area that shouldn't be too difficult to track down and seal.

Wow, 100' long? On a 1200 square foot home? So is this a trailer home? 12' by 100'? I think you must be mistaken. Even most trailers top out around 80 feet, and they are by far the longest roofs around aside from 4000+ SF mansions. In any case the materials would double in cost (probably from $200-$300 to $500-$600) and the labor would double (figure $15/hour for most roofing installers) but they would not add on as much of a "trip charge" (i.e., minimum profit for a job). At the roofing company I worked for, our repair minimum was $400 (to replace a few shingles or a leaky pipe jack) but the company still ended up making at least $200 in profit on each of those jobs.

The best way to tell where air is leaking is to go up in the attic with the AC turned to full blast, and walk around and find drafts. You can do this with your hands for free, feeling for the drafts. On a hot day you will feel the cool air even if you don't necessarily feel it moving. You can also get a thermal camera and look for cool spots. You can also get an IR thermometer and sling it around looking for cooler spots.

Holes in the ceiling where the light fixtures and vents come out, are the primary culprits. Second is around the top plates of the walls. Every single light switch and electrical outlet in your wall, is a hole in the drywall that is rarely sealed. Cold air can escape through there, and into the wall cavity, and escape out the top plates. These are just the 2x4 pieces of wood that form the top of your walls and they are laid next to each other but rarely caulked or otherwise sealed. So cool air can actually follow that path out through your walls and into your attic.

Properly sealing around your windows can be critical too. See if you can find or borrow an IR camera and walk around the outside of your house. Your electricity company might provide a free or low-cost "Energy Audit" which is basically a guy walking around your house and checking all of these things and seeing what would give you the biggest bang for your buck. Just a $10 tube of caulk to replace cracked or missing caulking around the windows can fix a substantial conditioned air leak.

Radiant barrier is not insulation (although it can be coupled with insulation). It can be a sprayed-on shiny coating underneath your roof decking, or a thin metallic film that is nailed to the bottoms of the roof rafters. I have no actual data but a lot of anecdotal reports that they work pretty well. The sun's radiant heat energy can penetrate things like wood and shingles, but it can't penetrate the radiant barrier, which reflects this energy back upwards. It sounds hokey and I have heard some scientific criticisms, but pretty much everyone that I have talked to with one has reported good results.

If you only have a few inches of insulation on the attic floor then sealing the ceiling and adding some more insulation would probably be your best bang for your buck.

I wouldn't necessarily try to draw air in through your gable vents. I would exhaust out both of them, and let them pull air in through the soffit vents. The idea is to draw cool air up from the lower areas and let it flow out through the higher areas. But if you experiment with box fans then it might be worth it to see if having some cross-ventilation (in one vent, and out the other) might help. But most gable vents are at the peak of the gable, so having air flowing across the top of your attic might not help with airflow in the lower parts of your attic. But then again, natural convection might help. I don't know, and there are engineers who can model your house and figure this all out but it would require a lot more detail than we have here.

 

[boomerang]

OP, why don't you see if your utility company has a program where they will come out and make recommendations. You're not getting any consistency within the answers you're getting here.

 

[Pantlegz]

Wow, 100' long? On a 1200 square foot home? So is this a trailer home? 12' by 100'? I think you must be mistaken. Even most trailers top out around 80 feet, and they are by far the longest roofs around aside from 4000+ SF mansions. In any case the materials would double in cost (probably from $200-$300 to $500-$600) and the labor would double (figure $15/hour for most roofing installers) but they would not add on as much of a "trip charge" (i.e., minimum profit for a job). At the roofing company I worked for, our repair minimum was $400 (to replace a few shingles or a leaky pipe jack) but the company still ended up making at least $200 in profit on each of those jobs.

The best way to tell where air is leaking is to go up in the attic with the AC turned to full blast, and walk around and find drafts. You can do this with your hands for free, feeling for the drafts. On a hot day you will feel the cool air even if you don't necessarily feel it moving. You can also get a thermal camera and look for cool spots. You can also get an IR thermometer and sling it around looking for cooler spots.

Holes in the ceiling where the light fixtures and vents come out, are the primary culprits. Second is around the top plates of the walls. Every single light switch and electrical outlet in your wall, is a hole in the drywall that is rarely sealed. Cold air can escape through there, and into the wall cavity, and escape out the top plates. These are just the 2x4 pieces of wood that form the top of your walls and they are laid next to each other but rarely caulked or otherwise sealed. So cool air can actually follow that path out through your walls and into your attic.

Properly sealing around your windows can be critical too. See if you can find or borrow an IR camera and walk around the outside of your house. Your electricity company might provide a free or low-cost "Energy Audit" which is basically a guy walking around your house and checking all of these things and seeing what would give you the biggest bang for your buck. Just a $10 tube of caulk to replace cracked or missing caulking around the windows can fix a substantial conditioned air leak.

Radiant barrier is not insulation (although it can be coupled with insulation). It can be a sprayed-on shiny coating underneath your roof decking, or a thin metallic film that is nailed to the bottoms of the roof rafters. I have no actual data but a lot of anecdotal reports that they work pretty well. The sun's radiant heat energy can penetrate things like wood and shingles, but it can't penetrate the radiant barrier, which reflects this energy back upwards. It sounds hokey and I have heard some scientific criticisms, but pretty much everyone that I have talked to with one has reported good results.

If you only have a few inches of insulation on the attic floor then sealing the ceiling and adding some more insulation would probably be your best bang for your buck.

I wouldn't necessarily try to draw air in through your gable vents. I would exhaust out both of them, and let them pull air in through the soffit vents. The idea is to draw cool air up from the lower areas and let it flow out through the higher areas. But if you experiment with box fans then it might be worth it to see if having some cross-ventilation (in one vent, and out the other) might help. But most gable vents are at the peak of the gable, so having air flowing across the top of your attic might not help with airflow in the lower parts of your attic. But then again, natural convection might help. I don't know, and there are engineers who can model your house and figure this all out but it would require a lot more detail than we have here.

It's a very long duplex, total sq ft is roughly 3,000 give or take. I'll see what I can do with an IR thermometer and/or feeling for a draft with insulation already installed above the ceiling I feel that's going to be a huge pain but probably worth it. And I'll see if I can get some help to try to tackle the radiant barrier too, it seems easy enough to staple stuff to the trusses.

Thanks for the info!