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?
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.
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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.
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.
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.
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.
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.
I'll disagree to the extent of scrapping the turbines. You are correct that they don't work as efficiently when there's no wind - although some heat escapes through those 18" holes - but when there IS a wind, they will move an enormous amount of hot air. Plus, they do it at no electrical cost!
As for cosmetics, they can sometimes be installed below the ridge line so they're not easily visible from the street.
And speaking of ridges, be sure to install a ridge vent. These are dirt cheap and will probably give you the biggest bang for the buck.
Note: None of these suggestions are meant to be exclusionary. Do 'em ALL.
Again, I'll slightly disagree. You're correct that one can't have too much soffit venting.
The usual standard is one sq ft of soffit venting for every 150 sq ft of living space. If you've got a venting area 4' long and 6" wide on the soffit, that's 2 sq ft. BUT, you've got to subtract the screening area. If hardware cloth type screening, subtract maybe 10% of effective venting. If it's that HardiPlank stuff with itty-bitty holes, subtract 98%.
exhaust fans with ridge vent is the tops for inefficency. the fans just suck the air from the nearby ridge vent, and that doesnt really ventilate the attic.........
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.
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:
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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?
Anyone that likes to get a tan in the summer will know this:
When the sun comes out from behind the clouds, the wind mysteriously dies down. Then when the clouds come back - so does the breeze.
That fact doesn't help you when your chosen method of active ventilation is wind powered.
Attic fans (typically 1/8 or 1/10 hp) consume pennies of electricity a day. Worth the cost when they give you a reliable, dependable CFM of air movement when you want it.
Depends on the style of roof.
Once upon a time, soffits were faced with 1/4 plywood, and you had to buy and install screened vents that were visible and you had to do a nice job of cutting the hole and positioning and installing the vents so you wanted to install the minimum necessary if you were the builder.
But it was a pain in the ass as a home owner to paint the soffits every
5 or 10 years so you got them covered in aluminum, and with slotted sheeting it wasn't a hassle anymore to create venting anywhere you wanted it - including the entire length of the soffit. The only problem is that unless you cut more holes in the original plywood facing, the extra aluminum venting will do you no good.
For new construction, you don't even need to put the 1/4" plywood facing on the underside of the soffit any more. Just mount your J-channel and slide the perforated aluminum soffit sheeting into place.
The problem with having one vent every 4 or 6 rafters is that you won't get much airflow along those rafters that don't have a vent down at their soffet end. Air will preferentially flow along those rafters that do have a matching vent where they meet the soffet.
But the same could be said regardless if the fan is wind-powered or electric-motor powered.
A fan that pulls outside air through the ridge vents and then exhausts that air right back outside will nonetheless create air currents inside the attic and it will lower the temperature of the warmest part of the attic - the area in the peak or top part.
If you have a ridge vent then you probably have an inverted V style roof, which means you could mount a fan on the side wall of the attic (or both side walls) and have it blow outside air into the attic, thereby helping to force the hotter attic air up and out through the ridge vent.
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
My front shingles facing north still looked good after 25 years, when my rear shingles facing south looked terrible. I could only see the roof from the front, or from the rear if I was up on a ladder.
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