Some examples of vents are:. The rule of thumb used to determine the number of roof vents to install is one for every square feet of attic area if your attic has a vapour barrier, and one for every square feet of attic area if the attic does not have a vapour barrier.
Vents are rated by their net free area NFA , which is the amount of space the vent has for air to flow in or out.
That rule can change if the slope of your roof is more than the average slope a rise of six feet for a run of 12 feet because there will be more space, heat and moisture to ventilate in the attic. If you liked this post, check out our recent article about the best roofing materials for the Canadian climate.
Please note: Chouinard Bros. How many roof vents do I need? To answer this question, we must first define what roof vents are and what their purpose is. A roof vent is a type of fixture installed on the roof as a means of exhausting hot air.
They are a crucial element that maintains a healthy attic , roof, and home. The size of your roof and attic will dictate how many of these roof vents you will need. By allowing airflow within the attic, roof vents achieve many things at once. This increased ventilation will:. Roof vents have two basic functions. The construction of your roof also plays an important part in determining how many roof vents you need.
If your roof was installed with a vapor barrier you would need at least 1 square foot of roof ventilation for every square feet of attic space. If you do not have a vapor barrier you will need 1 per every square feet of attic. The roof vents should be evenly spread throughout the roof and there should be 1 for 1 ratio of inlet and outlet vents.
A steeper roof will have more attic area and thus affect the amount of ventilation required. If you live in the Delaware Valley, the professional roofers at PJ Fitzpatrick can help you achieve the proper amount of roof ventilation. Contact us today for an estimate. Hope this helps. Sandy, Baffles are usually installed before insulation is blown in to prevent it from clogging up the vents. When figuring out soffit vent requirements for an attic—and calculating total vent area needed—does height of the attic come into play?
Hi Ben, I have an older ranch style home which I recently had re-roofed and a ridgevent installed. I would like to install soffit venting to take full advantage of the ridge vent. My soffits are aluminum covered with the wood soffit under that. Must I be sure to get deep vents that push through both the aluminium and wood soffit and into the attic?
Or is it ok to just cut through both the aluminum and wood and only place a surface vent over the aluminum? Thank you for your help. Hi Derek, As long as you cut through both the aluminum and wood so that there is a clear path for air to flow through to the attic, a surface mounted vent attched to the aluminum should be fine. I have square feet of attic space and have 50 soffit vents. One of my attics has both a turbine and power fan, and seems to have the minimum needed soffit vents.
The other attic has adequate soffit vents but only a turbine. My idea was to run a couple lenths of clothes dryer duct to the top of the attic area, thru a fan, then out thru the soffit in an area where there are no intake vents. Does this sound workable?
I had soffit vents installed several years ago. As I walked around my house inspecting things, I noticed that the openings in the soffit vents were pointed toward the house and the air it vented left a dirty area on the brick moulding below the eaves. Why should soffit vent openings point toward the house? Is it because windblown rain could possibly get in the attic if vent openings are pointed away from the house.
It would seem that you would get better air flow if the vent openings were pointed away from the house. Your speculation about blowing rain being the cause is the only one I can think of, and, like you, I think the odds of that are pretty slim.
It was about 3 years ago. The roof is about 15 year old and will need to be replaced in the not too distant future. However, in the interim, we would like to address the ventilation issue. When the previous owner had the roof replaced, a ridge vent was installed and soffit vents installed. The problem is that the soffit vents do not have visible openings in the attic. The attic floor is covered with tongue and groove boards, part of the original construction. Cellulose insulation was added some time in the past as well.
What is your suggestion for connecting the soffit vents to the attic area? I was thinking it might be possible that the air current might move up the house to the soffit then outwards?
Then again I have never seen an air current analysis on a roof. I need to install soffit vents in our home; several years ago we had 12 inches of insulation blown into the attic. Will this complicate installation of the soffit vents? The attic is small and difficult to work in especially considering the blown in insulation, is it necessary to be in the attic in order to install the vents or could this all be done from outside?
Hi Andy, Installing soffit vents can and often has to be done from outside due to space limitations in the attic. I need air flow in my attic badly. I took off two soffit vents only to find batt insulation from the vent back up to the inside of the attic. I have about three feet of slopped ceilings in each room that mirror the roof slope and the insulation is between the roof and the room ceiling. Can I pull out the insulation, put in baffles and then blow in insulation arouind the baffel?
I am also putting Radiant barrier on the underside of the attic roof. I installed a new roof last year with a ridge vent; took out the old powered roof vents ugly! There is perforated vinyl soffit material running the full length of 90ft under the soffit on the north side of my house. There are no soffit vents on the south side of my house. Three questions; first, are the 2 inch holes enough ventilation or should I remove the perforated vinyl soffit material and cut larger holes?
Second, should I remove the perforated product completely because it it prevents the passage of air and is not efficient enough? Third, must there be a equal amount of soffit venting on both sides of the house?
Thank you for any help! I want to know if 1 gable vent on the back wall as high up as I can install it would be enough for this sq. When I did research on this I focused on net free area. I wonder why this article fails to mention net free. This can make a big if you put in 10 vents but really need 30 vents. I am not a professional but would it makes more sense to me….
Kevin Says: January 24th, at pm Is there an answer to B. I have a sqft ranch, when the roof was redone aprox. Is it possible that too much ventilation could be causing incresed energy use, and causing erradic temperture fluctations. Oh I might add that on windy days it is impossible to keep any heat.
The house always feels cold even when it is warm outside. Also in response to an earilier post about vents above windows and doors, I was told that this should not be done, because in the unlikely event that a fire should occur the air currents would draw the flames into the attic causing more damage.
Hi Randy, Good point about fire and attic vents, thanks. Plus, you do live in Michigan where it gets pretty darn cold in the winter! Thanks for your reply Ben. I should have stated that the attic has an origianal r13 layer then I added a r30 layer a few years ago. We do have a whole house attic fan that gets covered in the winter time. It seems the more I try to be efficient the higher the bills go.
The problem with blocking the vents in your attic during the winter is that it might cause moisture to build up in the attic which could lead to mold and rot. Randy, I want to install attic baffles before blowing in insulation. The area I need to install baffles the roof trusses and joists are at almost a 30 angle from each other below this area is cathedral ceiling. Is there any way to remove the soffit outside and somehow slide the baffles in from there?
Is there something else that could be done? Thanks, Craig. I am going to add blown-in insulation in my attic. I know I need to install soffit baffles in order to avoid the insulation from blocking the soffit vent.
The challenge is my attic is very low and installation of the baffles is almost impossible. Any suggestion? I currenlty have a powered attic fan near the peak and gabled louvers though not directly accross from each other.. I need to replace some rotten soffits. I currently have no soffit vents or roof vents. As I replace the soffits, should I hadd vents.. Hi Jamie, I would add soffit vents if possible.
The vent fan and natural air currents will draw cool air in from them to lower the temperature in your attic. Good luck with your project! My house has ridge vents at three different levels as the roof profile creates three different ridges.
I am assuming if it can be split between the three levels, you would do three separate calculations, one for each amount of square footage the ridge covers. Is this correct? I live in Colorado arid environment in a small house and have a small attic approx. I do not have any soffit vents or an eave for that matter and just two vents on the side of the house near the top of the attic.
I have blown in cellulouse insulation on the floor of the attic. Should I add small vents above the new windows that can effectively vent the area behind the knee walls that would be connected to the small area above the ridge? Or should I just create my room in the middle that includes all space up to the ridge , effectively separating the attic into three parts — area behind the kneewall on one side, conditioned area, area behind the other kneewall — then just add four vents two on either side of the house at each kneewall?
I could by way off base with what is even possible here. Any insight is appreciated I also realize this fairly in-depth, so if anyone had a suggestion on a good book on the subject that would be great too. Hi Tim, Your problem comes up a lot when converting an attic to a room with a vaulted ceiling, since filling the space between the rafters with insulation effectively eliminates much of the ventilation.
Rather than bringing your ceiling to a peak, I would suggest flattening the top to leave room for insulation, wiring, ducts, and venting.
In fact if you have all three, flow of air through the attic will not be adequate. Is there any truth to this? I have all three vent types and currently have a mold problem in my attic that I am remediating and am wondering if I should block off the gable vents and just go with the soffit and ridge vents. Any ideas?
Hi Matt, The idea is to create a balanced, natural flow of air through the attic due to cool air coming in through the soffit vents, rising as it heats up, and then exiting out the ridge or gable vents at the top. Where you can run into trouble is combining ridge vents with a power vent fan, which can reverse the flow of air through the attic, by drawing in air and rain at the top through the ridge vent.
Hi, I had aluminum placed over my soffit for appearance, but mostly for additional venting. Granted the aluminum is not pressed up tight to the soffit so air should be able to enter through the other holes, but not sure.
Hi Tim, Since most perforated aluminum soffit is set below the existing wood soffit with an air gap between the two, you should figure up the area free air space of all the aluminum soffit for each area of the house, then figure up the area of the holes drilled in that same eave and use the lesser of the two for your vent calculation.
Thanks for the response. Based on the calculation above, I need sq inches. Even if I cut the entire soffit and install the vented aluminum I would only be getting sq inches. Any suggestions? I guess that explains why that room is so hot. You could make all the eaves perforated and drill more holes. If it makes you feel better, I have a similar situation at my house. The previous owners put up vinyl soffit with a perforated piece every few feet, then blew insulation in the attic which appears to have filtered out over the eaves and probably blocked up any vents in the old wood soffit.
Our attic is about square feet. The only vents now are small 1 inch round louvres. Should I replace each of them? I counted 20 total. Is this even enough vents? Or both? How many would I need? I have been reading the horror stories about icles and mold in the attic. It just the blowm in insulation between the joists on top of the dry wall.
It there is a lot of moisture, try lowering the humidity level in your house using the tips found in our article on How to Cure Sweating Windows. If you still have a problem with condensation, consider priming your ceilings with a paint that acts as a vapor barrier, such as an oil-based primer, and topcoat over it with a standard latex ceiling paint.
I just had this argument with my roofing contractor who has the family busines for 60 years installing roofing. I am in the north east in Ontario, The house is dual brick contruction built about 60 years ago. There bricks go right to the top of the underside of the roof. At lease one quote I received and the most epensive the he said lower vents on the roof would help to try and get airflow from the soffit would be costly, though others say that rain and snow could get in, some suggest knocking out some the bricks to allow air in through the soffits.
Never seen any icicles in the attic or outside with my old room, surpisingly. I would put two or three on each side of your roof. The reason to point the vents toward the house on soffit vents is so that you can not see in and they are less noticable. Just like when you install wall return vents for your forced air Heating system.
It only slopes up the rafters for about 2 ft, to add about 1ft of height to the ceiling. If i removed this insulation, that would be 2ft all the way across the living room, master bed, and office that would remain uninsulated. I was on the roof the other day and decided to take a closer look at my ridge vent.
I noticed that on the shorter ends perpendicular to the vent run that some ends had a foam piece in them, some had some folded shingles in them and others had nothing. Should all of the ends have something in them, maybe to keep rain out? Or should they all be open to allow better airflow? I also have a powered exhaust vent that turns on when the temp in the attic becomes hot.
Some questions: a. If I add a ridge vent should I remove the power vent? I plan on adding some soffit vents so the Sq footage of the soffit venting matches the ridge venting. The soffit vents I plan on using are metal with finned intake set at an angle. Should the soffit vent have the slotted angles point towards the house, or away from the house. It appears there may be a correct or incorrect method. I have a ranch style house with a hip roof on one section and am going to have the whole roof replaced.
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