Current best practice for roof vents?

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We're re-roofing this spring and I'd like to replace the roof vents at the same time.
We currently have turbine-style vents which were installed decades ago when the attic was insulated and vented.
The turbines have moving parts and I'm certain that they'll start to fail soon, probably at the worst time. Last winter during a nasty cold spell following a heavy snow, one did start screaming as it turned, but quieted down as soon as the sun came out the next day. We probably won't be so lucky next time.
On the other hand, the turbines are tall and stick out above the snow on the roof. We often have a foot of snow on the roof for months at a time.
Other than trying to avoid turbines, does the style matter, so long as they're big enough and there's enough of them?
--
Bert Hyman St. Paul, MN snipped-for-privacy@iphouse.com

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Bert Hyman wrote:

What kills your shingles is heat.
Heat happens in the summer - not winter.
The worst heat happens when there is no wind. If there is no wind, your wind-powered vents will not turn, and the temperature in your attic will rise - probably to 140f or more.
Do yourself a favor and scrap the wind-powered turbines and replace them with electric fans controlled by a thermostat. You can have a powered vent as well as a few passive vents. All these vents are low profile and it's not uncommon for them to end up covered in snow by mid winter. There's no real harm in that.
You should also have styrofoam baffles or shields placed under the roof decking where the decking passes over your header plate and out over the soffit. Most people jam insulation in that area leaving no air gap where air can pass freely along the underside of the roof deck into the soffit. Your shingles will deteriorate the most in that area, and you will form an ice-dam in the winter because of heat conduction through the insulation into the roof deck.
http://products.construction.com/swts_content_files/20855/E715704.jpg
http://www.houserepairtalk.com/f106/proper-way-insulate-finished-cape-cod-attic-9704 /
You should also have a completely ventilated soffit along the entire length of the soffit. If you have soffit clad with aluminum trim, the soffit face should be the ventilated type (with small holes in it) and it should be this way for the entire length of the soffit - not just every 5 or 10 feet. If your soffit was originally wood then you will have 1/4" plywood as the soffit underside and you will need to cut holes in it between each rafter to allow for complete ventilation. A 6" hole is all you need.
Depending on the past history of water penetration through your existing shingles, age and weather conditions, it's not uncommon to have to replace some (or many, or most) of the roof decking around the perimeter of your roof during a re-roofing job.
And by the way, if you're planning to just lay a new set of shingles over top your existing shingles, then you're a bone-head.
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In wrote:

What "killed" our shingles was time.
Convection moves air from the soffit vents to the roof vents.
--
Bert Hyman St. Paul, MN snipped-for-privacy@iphouse.com

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high attic humidity from lack of ventilation can also shoten roof lives, and worse damage the decking
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" snipped-for-privacy@aol.com" wrote:

You solve high attic humidity by having a proper vapor barrier between your ceiling and the attic space above it, as well as having proper soffit ventillation.
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wrote:

Soffit vents are for "intake" of ventilation, where the cooler air infiltrates. You need additional vents to "exhaust". Power vents are much like your information you have, USELESS. They don't work in the winter.
A vapor barrier does nothing for the attic as far as heat loss to the attic in the winter. Heat WILL still escape into the attic, even with PROPER INSULATION. The vapor barrier is for the "interior" or "thermal envelope" of the structure.
At least read up on this stuff, since you have no real experience with it. Here's a hint, read about condensation. You probably think a cold glass of iced tea in the summer, is leaking tea through the glass.
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Chet wrote:

Power vents *can* work in the winter. Some attic fan control modules have humidity sensors in addition to temperature sensors. They can come on in the winter based on the need for humidity control.

We aren't talking about heat loss as much as we are talking about interior house water vapor rising up into the attic. If you humidify your house in the winter, you do not want that interior air to get into the attic where it will condense on cold surfaces like the underside of your decking and rafters and cause rot and mold.

That envelope includes the boundary between your ceiling and attic - not just the walls.
If you have a proper vapor barrier between your ceiling and attic, you will by definition have an air-tight barrier and no (or very little) interior humid air will find it's way into the attic.
Now if you are dumb and you exhaust your bathroom and kitchen fans directly into the attic space, then naturally any vapor barrier you have up there is wasted and you are causing the humidity problem that you claim is bad.
Heat loss is up to the attic is not the same as humidity or air leakage into the attic. If I had to choose between a good vapor barrier between my ceiling and attic, vs having any insulation in my attic above the ceiling, it's no contest - the vapor barrier wins hands down. But (naturally) it's not a choice between having one or the other - you can (or should) have both.
With a working vapor barrier, you don't need to have attic ventilation in the winter, but you really can't totally stop the ventilation either - even if your roof vents are covered in snow. Because if you have soffit venting, then winds blowing against one side of your house will flow up and into the soffit on that side, through the attic and out the soffit vents on the other side.

Speak for yourself.

Here's a hint: Any condensation or frost forming on any surface inside your attic is coming from water vapor that leaked into your attic from inside your house or was dumped inside your attic by an interior vent fan.
Air containing any humidity percentage you care to name will not condense on a surface that's at the same ambient temperature as the air in question. Air thats inside your house thats leaking into your attic will me MUCH warmer than the temperature of the surfaces it encounters, and hence the water vapor it's carrying will condense or form frost on those surfaces when it hits them.
Outside air thats at the same temperature as your roof decking will not condense it's water vapor on your roof decking when it enters your attic.
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Bert Hyman wrote:

Dream on.
Convection will not move enough air during the dog days of summer to keep your attic cool.
I have properly ventillated soffits, several passive vents AND a powered roof vent that I manually control. When I forget to turn the fan on until noon on some summer days, it's not uncommon for my $15 battery-powered temperature sensor to read a temperature of 140 F in the attic.
15 minutes after I turn the fan on, the sensor will be reading 120 f and still dropping.
This is for a roof section that is about 35 feet by 30 feet with a low pitch. I'm in the same climate zone you are - I'm about 120 miles more south than you, and a few hundred miles to the east.
Wind-powered roof turbines are a crock of shit. Maybe you have some sort of romantic or nostalgic attachment to them, but they will not do squat to keep your attic cooler as compared to just having a hole in the roof. And during the dog-days of summer when there is no wind, the turbine blades will actually HINDER convective air flow because of the resistance to air flow they cause vs just having an open hole.
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I upgraded some years ago from 2 tiny vents at each end of house to ridge vent plus those existing vents.
Put my fluke recording temp probe up there before and after.
Before top temp 146 degrees
after 116 degrees
Incidently home inspectors say the spec is the attic shouldnt ever be more than 15 degrees warmer than the outdoor temp
90 degrees outdoor 115 TOPS in attic my home for sale was 119 degrees
at the home I was attempting to sell the inspector said I had to add 2 large attic exhaust fans.,
The buyers wife didnt want the fan noise so that issue faded away:) the house had a ridge vent but no soffit vents and no place for soffit vents
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This will not make shingles last longer but will cool the space. I got some perforated aluminum/polyethylene sheeting and stapled it to the joists below roof. I used to walk into my separated garage in the summer and feel the extreme heat from the roof. Now, I don't feel any heat from the roof. A major improvement.
greg
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light colored shingles like white are best........ they reflect much of the heat
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" snipped-for-privacy@aol.com" wrote:

Assuming you can actually compare 2 similar situations:
- same time of year (or similar solar irradiance levels, angles, exposure times)
- same ambient external air temperature, winds, etc

Because - why?
Because it's bad for your roof/attic/house, or because it's hard to attain such a differential given unrestricted venting airflow?

I don't get what you're saying.
You're saying that you were able to keep your attic temp no higher than 115 (or 119?) with just a ridge vent and some hokey twirly vents, EVEN THOUGH you have no soffit vents ???
I assume you have a two-sided roof (inverted V) where you can have a continuous ridge vent from one side to another. The outside air you're pulling into the attic is coming from two vents mounted on the opposite sides of the attic - probably located 1/2 way or 1/3 of the way from the top of the roof line. The air currents inside the attic are such that most of your space and roof is baking in the heat, while the ends of the roof and attic that are in the path of the air currents will be cooler.
You might also have light-colored shingled, or have some trees shading your roof.
Either way, not having soffit venting is a major obstacle in keeping your attic cool and properly ventilated.
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all done within days mid summer outside temp in 90s during day.. its not scientific but the ridge vent definetely helped

its impossible to install soffit vents since none of these homes have soffits, they were built in 1950.the attic temp in the other home i sold was warmer than 15 degrees between outdoor and in attic, but the home inspectors were idiots. one dinged the house for no GFCI on the garage sump pump. the sale fell thru.
the next buyer got a different home inspector who dinged the home for having a GFCI on the sump pump. ( I had installed one to make the first buyer happy) neither inspector found the very loose light box mounting on garage light, i had left it loose so they would have something to find......
home inspectors the buyers best friend the sellers worst enemy./

your description appears about right. theres no way to install soffit vents when you have no soffits theres no roof overhang.
another neighbor installed roof vents down low for better airflow, which rewarded him with blowing snow in attic and water troubles.
yeah my roof is off white and i have a mature sycamore in back yard, it helps keep the home cooler
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"the next buyer got a different home inspector who dinged the home for having a GFCI on the sump pump. ( I had installed one to make the first buyer happy) neither inspector found the very loose light box mounting on garage light, i had left it loose so they would have something to find......
"home inspectors the buyers best friend the sellers worst enemy./"
The home inspection process just gives a timid buyer other ways of expressing "buyers remorse!"
The buyers who bulk at a GFCI on an outlet likely weren't serious in the first place. But you CAN simply say that as a part of the settlement you are willing to pay a reasonable estimate of the cost to change what they don't like. That will bring a serious buyer back to the table but the timid buyers will not come back.
Frankly, a good real estate agent should have worked that out. If yours didn't get a new agent.
Frankly, the same technique can work for most "problems" found by an inspector or on the walk-thru. Either say NO or offer to pay a portion or all of the estimated cost of making the repair/change. Don't get into the trap of attempting to "fix" your house beyond your original intentions. For all you know, a perfectly good buyer out there would like your house EXACTLY as it is.
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I had rather buy a house that needs "paint and carpet" that way I can get what I want and save the "reasonable estimate". I would probably have to repaint anyway.
Jimmie
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In wrote:

Maybe you should try reading my post.
--
Bert Hyman St. Paul, MN snipped-for-privacy@iphouse.com

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On 2/25/2011 9:50 AM, Home Guy wrote:

Just curious as to what type of vents you have. I have ridge vents running the entire length of all my roof sections. I have heel trusses with lots of room for insulation above the outside walls plus a good 5 inches of opening to allow air to enter the attic through the soffits. I have been up in the attic when the sun has been shinning all day and the outside temp are in the high 90's. It's warm up there but not hot. I would estimate the temp up there to be about 5 deg above outside.
My neighbor has the regular square vents on his roof. According to him he has the required amount of vents per code. He does have well ventilated soffits but his attic is hot.
You can work in my attic with little discomfort. I wouldn't even go up into his.
LdB
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LdB wrote:

Pretty much exactly like this:
http://www.single-family-home-remodeling.com/images/low-profile-roof-vents.jpg
It's about 12 inches on a side.
I have 2 roof sections on my house. One is almost square - 35 ft by 30 ft. It's got 4 sides (like a pyramid). If I had a ridge vent, it would only be about 4 or 5 feet long.
So I have 2 vents (like in the picture) on 2 sides of that roof, and a powered vent fan on the third side. The fourth side has no vents - you can see that side from the road (you can't see the other 3 sides).
The powered vent looks like this:
http://www.atticvents.org/wp-content/uploads/2010/06/Attic-Vents.jpg
The other roof section is about 25 feet by 50 feet. It's got 2 sides. I could put a 25-foot ridge vent on it, but because it's lower it doesn't get as much direct sun in the afternoon. I also have 2 passive vents and a powered vent on that roof.

I have tan or light-brown colored shingles (the lightest color I could find that matches the brick on my house).
In late july or early august, on a 90 degree day outside with full sun, with my fan running from dawn til dusk, I can barely keep the temperature at 125.
Unless you put a temperature sensor positioned just under the decking (but not touching it) you can't really do a good job estimating temperature by waving your arm in your attic.
And if you have an attic hatch in your ceiling, and you are estimating the temperture in the attic by standing on a ladder with your head poking through the hatch, then you will be fooled by the cooler interior air flowing past you up through the hatch and into the attic while the hatch is open. You will not get a true sense of attic temperature that way.

Code is crap. It doesn't mean additional insulation wasn't added since the house was built - insulation that is blocking airflow from the soffits to the attic space.
Codes are well known for skimping out on soffit venting.

What color are his shingles? What color are yours?
Does he have anything to shield his roof at mid-day? A tree, a building, some other structure? What about your roof?
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On 2/25/2011 7:31 PM, Home Guy wrote:

My shingles are a light brown, Ceder Tone as I recall. My neighbors roof is green and is bit darker than mine which would account for his attic being a few degrees warmer.
Our trees are too far from the house to shade the roof during the day. It would be nice to have the shade but it's also nice not having to worry about a tree falling on the place when the summer storms come through. I do get a lot of shade when the sun starts going down in the late afternoon.
I have a lot of room up in the attic and have a few radio antennas hidden up there. I'm a long way out in the country. Right on the fringe of radio reception. When I built the house I put in a catwalk the length of the attic along with a light and power plug.
I've been up in the attic many times on hot summer days. As a mater of fact I need to go up there now to put in another antenna but I'm putting it off until summer. I would rather go up into my attic in summer than in winter. Now how many times have you heard someone say that? :)
You can actuall feel the air moving up there. There is that much natural ventilation. I considered putting in a few additional gable end vents but found they were not necessary.
This is getting away from the subject but when built the house I put in a few large pipes between the attic and crawl space. I have the luxury of being able to fish into any part of the house with minimal effort. That's why the catwalk is up there.
Speaking of code I insulated way above code when built. I have R-60 in my ceilings. Even with all the glass I have this house is cheaper to heat than my old 50's bungalow that is half the size.
It really is a shame that it took so long for modern building techniques to evolve. Can you imagine how much energy would be saved today had these building practices been in place fifty years ago. Besides outright energy saving my house is very comfortable. I can walk around the place barefoot even when the outside temps are below -40 deg and I don't have carpets on the floors yet.
Perhaps I can be an inspiration to some of the readers here. I built this house myself with the help of family and friends over the space of about ten years.
http://www.mts.net/~lmlod/cabinfront7.jpg
Even the cupboards. These started out as pile of rough cut sawmill lumber. Most people around here that wood for firewood.
http://www.mts.net/~lmlod/cupboards3.jpg
Anything is possible. You just have to put your mind to it and have a good supply of elbow grease handy.
LdB
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Nice work on the home and the cabinets.
Colbyt
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