I was inspecting a house that had a new roof put on in May. It originally had 2 can vents and 2 gable vents with minimal soffit venting.
They added a ridge vent all the way across, vented the soffits and closed off the can and gable vents.
My question is should the gable vents be closed now that it has a ridge vent? Some say to close them so the ridge vent can work properly and some say to leave the gable vents open for more ventilation.
Your thoughts?
Thanks,
Kevin
From my understanding the gable to ridge venting is better than using the gable since the air is allowed to run up the bottom side of the roof and it can remove more moisture that could be on the bottom of the plywood. If fact the recommended venting is 1 sq ft-150 sq ft attic, but if it comes from low to high it’s 1-300. I think the gables were blocked to allow the air to come from the soffit since it will take the path of least resistance.
Most if not all the houses I see have woefully inadequate soffit vents. Usually not enough and often places in the least effective areas of the soffits (at the corner and only a few vents down the entire length). Secondly, I find them blocked off with blown in insulation much of the time or painted so many times there is no longer any way for air to be drawn in at the soffits. Those attics usually run around 150 degrees in the summer and you can’t stay in there for more than a few minutes. Equally puzzling is I find homes with ridge vents installed and no cut out underneath it for air to escape. Along with those I have personally listened to their contractor blow pure blue smoke up their behinds while explaining how none of that matters.
There is a post on this very issue and to answer your question no, do not close the gable vents.
The gable vents should be re-opened for they will not nullify or cause a ''Short-Circuit ‘‘the workings of the ridge venting.
There is a video on this very topic.
here is your link.
Now your wright up may read as this’‘reopening of gable vents would be justified’’ Can ask qualified roofer for opinion…
Doug:
Attic/roof venting is not a black and white issue that codes address correctly; the venting requirements in codes have a poor scientific basis. This summer I was called in to the 4th house in my career where increasing attic venting made the house cooler in winter and increased attic moisture problems. There has been research in Florida about attic venting and roofing material temps. Here’s a bit from the Florida Solar Energy Center (FSEC):
ATTIC VENTILATION
This investigation did not examine the moisture side of the vented attic question. There is a sentiment in the building science community for sealing attics totally. The object of blocking the ventilation is to exclude ambient moisture from the attic. Several problems are attributed to attic ventilation. Condensation problems in attics have been reported to the authors in humid southern climates. High interior moisture levels have been reported, which abate when attic ventilation is curtailed.
If attic air temperature is elevated, it holds more moisture. The dew point in attics can be elevated 10 degrees Fahrenheit or more above ambient on a summer afternoon (Fairey et al. 1988). Any surfaces that are below this temperature will condense. This elevation of dew point can drive moisture into the conditioned space by vapor pressure differences.
In light of common building practices these issues can be a problem. Many houses are built without vapor retarders in the ceiling. Even when retarders have been installed there are many pathways on which moisture can travel. Most houses have several penetrations into the ceiling for wiring and plumbing. Standard construction leaves the joint between the ceiling and wall leaky. Poorly constructed, leaky duct systems in the attic will cause surfaces adjacent to them to be at temperatures low enough to condense. Leaky duct systems will cause increased infiltration of humid attic air into the conditioned space.
Buildings near large bodies of water, especially salt water, have reported attic ventilation-related problems. The salt content of the ventilation air can foster corrosion on such things as truss plates and hurricane clips. These problems may be reduced by large ventilation rates, which tend to reduce the temperature in the attic, curtailing the amount of moisture that the air can hold.
However, attics containing poorly installed and maintained air distribution systems and many leakage paths between the attics and the conditioned space might not benefit from increased attic ventilation.
Building Science Corporation did some study in Jacksonville in the mid 90’s measuring the temps of asphalt roofing materials over vented and unvented roofs. Suprisingly, the unvented roofs had roofing material temps only 3-5*F higher than the vented roofs, hardly hot enough to prematurely destroy a roof! This study was reported in “Energy Design Update”, a leading energy newsletter ($385US/year; used to cost me about $550CDN/year when our dollar was worth $.70US)
Another study by FSEC about energy retrofits is found here:
See table 7…Notice that the cooling energy savings from adding attic venting are so low that the payback is 114 years!! Even a retrofitted radiant barrier would take 29 years to pay for itself.
Every home inspector should start educating themselves on roof venting. Most of the statements i this on this board are outdated.
The short answer…
Keep the conventional attic vents in place. Your roofer is right, in the sense that he’s repeating the ridge vent manufacturer’s instructions. But the ridge vent manufacturer is wrong.
The very long answer…
There’s a huge amount of marketing in favor of ridge vents. Some of that marketing includes the claim that ridge vents pull more air out of the attic because of the way those ridge vents are designed. In order to gain the benefit of the ridge vent design, the manufacturers say you need to seal all other attic vents, except the soffit vents. They have laboratory testing that says so. But it’s one thing to get a certain result in a laboratory under controlled conditions. It’s another thing to get the same results in real life circumstances.
The lab results don’t apply, if…
If your ridge line isn’t perpendicular to the direction of the wind, the lab results don’t apply.
If the wind isn’t blowing a certain speed, the lab results don’t apply.
If you have some trees around or near your house, the lab results don’t apply.
If your attic is cluttered with things being stored, the lab results don’t apply.
If it’s a hot day with hardly any breeze, the lab results definitely don’t apply.
On top of all of that, even if all of those circumstances were in favor of laboratory conditions, the difference in how much air would move through your attic due to the ridge vent design is minimal. It’s simply not that much of an improvement, under the best laboratory conditions. The marketing only tells you, under controlled conditions, that air is drawn out of the ridge vents, more than conventional vents. What about the difference in attic air transfer when you compare “only ridge vents” to “ridge vents plus other vents.” They don’t publish the difference in total air transfer between only ridge vents or ridge vents plus other vents.
On a warm day, when the air is fairly still, the heat in your attic is going to be much higher because you closed off the additional conventional vents.
I’m not against ridge vents. I like them. I just don’t like the huge amount of marketing that says you’ll have better results by sealing all your other vents. That’s foolishness. If you’re locked in your attic, and you have a choice of only ridge vents or ridge vents plus several conventional vents, you know what you’ll choose.
The bottom line is that warm air rises. As warm air goes up it finds openings and it leaves the attic. As it leaves, outside air is drawn into the attic through the soffit vents. The more attic vents you have for the air to flow out, the better your ventilation will be.
On a whole other aspect of the ridge vents issue…
If your rafters are the pre-manufactured trusses, then you don’t have a ridge beam in the attic. But if your rafter system was built as the carpenters were framing the house, then you have a ridge beam. That ridge beam closes off at least half of the ridge vent opening. That doesn’t make the ridge vents useless, but it dramatically cuts down how much air can escape through the ridge vents.
On yet another aspect of the ridge vent issue…
Your roofer needs to do a good job, otherwise the function of the ridge vents is diminished. For maximum benefit, the opening that the roofer cuts in the sheathing, along the ridge, needs to be as wide as possible. Some roofers don’t measure the gap, chalk a line and cut the sheathing. Some just eyeball it as they move their power saw across the roof. If they make that total cut out 1/4" narrower than it could have been, on each side of the ridge line, that adds up to 1/2". When you multiply that across the entire length of ridge, you’ve lost quite a bit of vent space. On a simple house design with 120 linear feet of ridge, that means you would lose 5 square feet of vent space. Visualize a 2 foot by 2.5 foot rectangle being cut out of your roof and the difference that would make in how much air flow you have, out of the attic.
You don’t want roofers building your kitchen cabinets. They generally aren’t known for their finesse and attention to detail. It’s very common to have the roofer short change you on the amount of vent space, just because they busted it out in a hurry. You would never know that when you look at the ridge from the ground.
To sum it up, ridge vents are good, but I recommend against closing your other vents. The value in ridge vents is the total amount of open vent space you have near the top of the attic for the rising air to flow out.
I hope this helps. Feel free to follow up in the future.
Your roofer with a keyboard,
Stan Skarbek
I thought this was pretty good summary. 
Marcel
What do you think pull’s out more air.
I installed turbines for years and the only complaint is cheep turbines have no ball bearings they use a bushing style hinge for rotation that wears and squeaks after a short limited time. I am tired and not explaining myself well.
I installed pots that octopus vent lines though out the home for what ever reason and out performed ridge, low profile, and did a small amount of studies on them talking to a manufacturing agent and read up on the literature he gave me.
[FONT=Times New Roman]As an example, take a 1500 sf house 25’ x 60’ with a 6:12 gable roof 60’ long. The attic volume is about 4700 cubic feet.
Assume the house to be fitted with three turbine vents on the roof and 30 soffit vents (4’ centers both eaves). The soffit vents let in the cooler air and the turbine vents let out the heated air. A 12" base dia. turbine vent is 0.78 sf x 3 each = 2.34 sf. The soffit vents are usually 4"x10" (or smaller) stamped vents with about 25% free area which, for 30 vents, translates to 2.00 sf. The smaller of the two areas is the controlling opening size. Thus there are 2 sf of area to ventilate 4,700 cubic feet of attic. If the heated air is moving at the velocity of 2 feet per second (generous) the system will remove 240 cfm of air. With the attic volume of 4,700 cf divided by 240 cfm, it will take 19.58 minutes for one air change (3 air changes per hour). That is not going to cool the attic very well.
Ridge vents advertise openings of 12 to 20 square inches per linear foot. Converting, 20 si = 0.139 sf x 60’ =8.33 sf for the entire ridge. That is nearly four times the area of the 3 turbine vents! Remember, equally large (or larger) soffit vents areas must be provided to supply the air for the ridge vents.
Traditional gable vents are 10’ to 12’ long with about 60% free area which calculates out to 21.65 sf per vent. With one vent at each end of the roof you have 43.3 sf of vent area. That is FIVE times greater than the ridge vent. NOW we are moving some air and heat!
To cut costs, builders have been installing ever smaller vents until, in the past decade, many houses have been built with no vents at all. In the 80’s and 90’s many builders used 2" dia. aluminum disk soffit vents with stamped slots totalling 0.5 square INCH of area. At every 4 feet that would be 0.10 sf for the whole house! That is so insignificant as to be criminal.
If you want to ventilate your attic, install anything you like as long as it has large FREE area to pass large volumes of air. Don’t be taken in by slick advertising. Remember that FREE area is much less than the NOMINAL size of the vent. [/FONT]
http://roofingcontractorreview.com/Roofing/Attic-Ventilation/Roof-Ventilation-%7C-The-Short-Circuit-Myth.html
Robert:
Venmar invented the turbine…and haven’t made them for about 12-15+ years now…I wonder why that is???
In CMHC sponsored research in the mid-late 1980’s, an engineering company stated that the turbine drew slightly more air out of an attic than did what is called “the chicken coop ventilator”- a piece of 6"-9" vertical galvanized pipe with a conical rain cap on it…think of the “Tin Man”. I have seen installed turbines closed off with plastic and even a pink insulation bag in one case!!.
The turbine is a great case of “Smoke and Mirrors”…what it appears to be is not what it is!! I have a list of 85 or so items (including the turbine) on my “Popular Energy Misconceptions” list.
Very good work Claude.
You really measure out everything in play to equate a proper conclusion.
The turbines I installed on new homes with pots and octopus venting (4 at the most per pot) allowed you to vent out problem area’s of concern.
Basements , bathroom, etc
.Builder would make a bulkhead vertically and run horizontally on floors were needed from there.
Theses vent could be mechanical with motor. or hand manipulated for the amount of air you wanted to move.
For venting an attic it was 1 per 600 sq feet.’’ I could be wrong?’'it was fixed and would have to be manipulated inside the attic to adjust flow.
It was a unique IDEA and then came the MAXI-MA VENTS early to mid 1990’s.In Canada if my memory serves me correctly.
Turbines were just coming into there own so to speck with engineering behind them to allow for specific usage.
Its because other manufactures where coming out with differences in styles being turbines where not a pleasing to look at firstly and foremost.
secondly other manufacturer’s had more money to through at advertising champagnes.
I did some reading and studies ( thats when I had a brain in my head) for most of the time I would be out womanizing and drinking with all the other roofers.(no joke I was not to swift…I see them even today housed in a maxi vent ( turbine inside the box) and lovers hiding the turbines appearance.
They were forced out by computation and should have been fighting harder for shelf space.
To me anyway.
As any good ad champagne agents them ( AMERICAN STYLED FOR DEPICT AND WELL LOBBIED) IT WAS TAKEN WHEN THERE WAS NO AIR MOVEMENT…
I can not remember the studies and do remember that one being similar to a low profile vent the same size and dimension for moving air ( windless condition) Brian.
Its when air was moving (wind ) the difference’s where then applied and turbines were in there own category. Superior to all. They did have growing pains , squeaks vibrations if installed wrong.,Not according to the manufactures specs…
I installed on engineers roofs and they where more than pleased having installed everything they could afford before and having ,noise, vibrations from mechanical fans , they were happy and looked further into there history but it was short and in its infancy.
Since I installed a ridge vent last year on my own home as well as foil in the attic, both manufacturers recommended closing off the gable vents.
Since I did, I was in the attic with the vents open and after I closed them.
There is definitely more air flow with the gable ends closed, at least from the soffits to the peak of the roof.
The problem is that most older homes do not have enough soffit vents.
Just cutting out the plywood dropped the interior temperature, immediately by 10 degrees. I of course, picked June to do this task!
I can tell you from first hand experience, here in South Florida, block off the gable vents.
Our house is now much more comfortable and, our electric bills dropped by $800.00 over last year.
[FONT=Symbol][FONT=Symbol]· **Improve: **When a Maximum type roof ventilator is installed, other roof vents be sealed. More info at: http://www.ventilation-maximum.com/[/FONT][/FONT]
Seems like more savings than would be normally expected. Hard to quote accurate savings without longer term study and comparing other electrical use/savings and weather data from year to year.
Many studies say if you have low insulation levels, improving attic insulation and airsealing will save more cooling energy than attic venting and radiant barriers.
Thanks Mr.Gratton
I have used them for years.
I agree with Brian, that air sealing and addittional insulation will circumvent the problems with inadequate venting as we sometimes see it.
They were not cut out by competition… they didn’t work that well and wer "Smoke and Mirrors. BTW, Venmar, the inventor, is now probably the largest HRV manufacturer in the world and has been owned by one of the world’s largest ventilation companies, Broan, since 1998. Please get your facts straight!!
Why would the engineers not have studied them in wind conditions!! Where do you get your information??
Here is from the Maximum Ventilation website:
*The Maximum Ventilator is a static ventilator which is used to replace stale, moist air within the attic space with fresh outside air which is being drawn in by the ventilator through the soffit air intake located on the underside of the eaves of the building. *
The ventilator functions with the combined effects of wind and pressure differentials, creating a chimney effect, thus drawing out the stale air from the attic space. Both the Turbine and the Maximum Ventilators function the same, except now the Maximum Ventilator does not have to turn to prevent rain or snow infiltrations due to it’s unique, storm proof deflector built within.
That’s right, the only reason the turbine is turning is to prevent rain and snow infiltrations into the attic. (Note this is their bold)
Refer to a chimney with a fireplace or wood stove. Do you see anything on top of the chimney that is turning to draw out the smoke? Of course not, this is being done the same way as the ventilator, wind and pressure. If you notice, as the velocity of the wind becomes stronger, the draw also becomes greater, thus forcing you to close the damper of the chimney flue so that you do not lose all your heat.
*The velocity of the wind is what activates these ventilators, but when comparing the Maximum Ventilator with the turbine, there is another flaw with the turbine, the turning of the head of the turbine is also preventing the full effect of the wind, thus reducing the drawing power and capacity of ventilation area. *
The Maximum Ventilator has no moving parts, and because of the design, it captures the full effect of the wind, producing a greater drawing power thus a larger capacity of area to ventilate. The Maximum Ventilator model #301 is capable of ventilating 1200 sq. ft. of attic area, compared to the 12 inch turbine ventilator, which is capable of only 400 sq. ft.
BTW, I think Venmar bought out Maximum a few years ago…If the turbine is so superior, why wouldn’t they re-introduce it through this subsidiary?
