Ask The Guru: Attic Ventilation
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Ed - I live in the Dallas area and am getting ready to install a new roof. I plan to have the decking replaced with radiant barrier decking. The house faces north with the main section running east/west. There is a south facing 2 car garage and a south facing extension of the master bedroom. Both of these have roof extensions coming from the main east/west roof. There is currently about a 1600cfm electric fan on the main roof and another of approximately 1200 cfm on the garage roof. There are large gable vents on the east and west ends of the main roof and a large gable at the south end of the garage roof. The master bedroom is just an extension with no gable vent. My question is what kind of ventilation do I need? If I leave all the roof vents off and add additional soffit vents, will the large gable vents exhaust the heat adequately? The gable vents are probably 10 - 20 ft. long by about 3 ft. high and extend to the peak of the roof.
Ideally, you would have plenty of soffit vents for air to enter and then exit though the fans. Most likely, you have air entering through the gable vents and exiting through the fans. This creates good airflow through the top of the attic but you don't get the "in the bottom out the top" which is preferred. I'm not big on electric fans and they probably will be overkill after installing the radiant barrier decking which will greatly reduce the heat in the attic anyway.
The best ventilation method would be to have plenty of soffit vents and then block the gable vents and either go with several 14" wind turbines or a high-profile baffled ridge vent. This will FORCE the air to come in the bottom and out the top. You've got pretty big gable vents, but I'd probably lean towards the ridge vents while a new roof is being installed.
I have corner areas in the attic which are so remote that ventilation is nearly impossible. What to you suggest in the installation method for those areas: lay over insulation or staple to rafters? Will the lack of ventilation effect the foil's performance?
You have a couple of choices. Lack of ventilation does not effect the foil's performance, it effects the attic as a whole in the ability to help move heat outside. So if you don't have great ventilation in a limited area, I would not worry about it. You can either lay it out or you could staple it up but let it "droop." This would allow a little more airflow over/under the radiant barrier.
FINISH GARAGE BEDROOM ABOVE GARAGE THE HALF THAT IS OVER THE GARAGE IS COLD YOU CAN FEEL THE DIFFERENCE JUST WALKING ACROSS THE ROOM COULD I JUST STAPLE THE FOIL RIGHT ON THE CEILING AND WALLS
If you have access to the inside of the walls (from the attic space), then yes, you can staple the foil directly over the insulation, across the rafters.
If you haven't put the sheetrock/drywall on yet, then I recommend you watch the 3rd video down on this page, called "How to Install Radiant Barrier in a Cathedral Ceiling" and install it that way. Go with foam strips like in the video and afterward you can put in R-19 insulation. Then, if you REALLY want to insulate, put 3/4" foam board on the bottom of the rafters BETWEEN the sheetrock and the rafters. This will significantly reduce "thermal bridging."
I installed a gable fan and am also wanting to install a radiant barrier. The insructions for the fan say to cover the vents closest to the fan so the fan can pull the air fron the other side of the attic. When installing the radiant barrier do I still need to plug the vent holes closest to the fan?
Yes, you want to allow the airflow to circulate as if the foil isn't even there. For more information, check out one of my newest videos about installing AtticFoil radiant barrier and the recommended air gaps around the foil.
Ed: I have a large attic with soffits all along the 36' length of the house, front and back, and a ridge vent all along the roof. With that type of ventilation, would reflective paint or foil help much?
Your attic is just like your car and ventilation (which you have) is like rolling down the windows of your car. It helps, but if the car is in the sun it STILL gets hot due to radiant heat gain. Installing AtticFoil® Radiant Barrier Foil is the most effective method to stop heat gain; just like parking your car in the shade would help with the heat gain, radiant barrier it is like putting the roof of the house in the SHADE from the HEAT.
How much will it help? If the roof gets hot, it will help a lot. If the roof is in the shade and does not get hot, then it will have limited benefit. You can call us at 800-595-8772 with any more questions.
Do I need an attic fan if I have proper attic holes: Low and high? I am installing a new roof with comp, I will spec an radiant barrier, we already have attic insulation.
Most customers opt for a passive ventilation system which is just a combination of working (ie. clean, unobstructed) soffit vents and either a ridge vent or a pair of gable vents; oftentimes nothing more is necessary. Once a radiant barrier is installed, your attic air temperature should be within 10 degrees of outside air temperature. If it's not, then more ventilation is probably the next step.
I am going to do a vinyl siding job soon. I have read a number of articles about radiant barrier products. Questions: Our typical exterior remodel consists of old siding tear off--apply 1 inch Dow brand foam board with taped seams--apply a house wrap--after the wrap is that when I should apply the radiant barrier or should I put that on first before the foam board goes on? In the attic should I do a layover on top of the attic insulation or should I staple to the underside of the rafters instead?
You should apply the radiant barrier OVER (after) the housewrap - you want it to be the LAST layer before the battens and the siding. Take a look at the second to last row of photos on this page: DIY Radiant Barrier Customer Installation Photos
In the attic it's hard to say without some more details from you; installation is not based solely on where you are located, there are several other factors that determine the best installation method for your home. Every home is different, so while there are general recommendations for certain climates, sometimes one method is best for a particular home. To determine which installation method would be best for your home, I'd recommend you read this article on our website: Best Radiant Barrier Installation Method
Read the article and consider your situation and then decide. Either way you go, the first layer of foil is going to offer you the benefit of blocking 97% of the radiant heat gain that you are currently allowing all 100% of it to enter the home. The difference between 100% heat gain and 3% heat gain is tremendous, not only for comfort but for energy savings as well.
I am preparing to reroof with metal. My house has no overhang for soffit vents. I have one gable vent at the front of the house. I have no ridge vents, but currently have a power attic fan. I want to eliminate the attic fan and use ridge vents. My question: Is one front gable sufficient of air intake? If not, is there an edge vent system that works with metal? Thank you, Sandy Bourdon
Most customers opt for a passive ventilation system which is just a combination of soffit vents and either a ridge vent or gable vents; oftentimes nothing more is necessary. Once a radiant barrier is installed, your attic air temperature should be within 10 degrees of outside air temperature. If it's not, then more ventilation is typically the first place to start.
This question is in regards to new construction. Part of the project is for a detached 30' x 54'garage that will have manufactured attic trusses for a habitable room over the garage. The roof design is a simple 8/12 pitch gable. The insulation sub recommended using closed cell foam and blown cellulose at the top portion of the trusses to get the mandated R-38. This is great for R value, but now I can no longer use a soffit vent/ridge vent combination because the airflow to the ridge is now blocked by the closed cell foam. Making the entire roof a "hot" one would be the easiest but would add about $7000 to the bid. Yikes. We know proper ventilation for the cold section of the garage roof is essential. What are some realistic options? Thanks for your time. Don
Foam is a great insulator, but it only works to slow conductive heat flow, not radiant heat flow. Is this garage going to be conditioned? Where are you located? Send me an email at support(at)atticfoil.com so we can get some more details from you and help give you the best advice for this situation.
Ed: I live in Southern CA and want to place a Solar Powered Attic fan in my single story, S tiled roof. My home is positioned with a front roof vent facing North West, and the back facing Vent facing South East. What is the best position of the fan to get best air current for mounting an attic fan? Thank You. Marv
I'm not a big fan of solar fans since they are expensive and quit working as soon as the sun goes down. I'd rather have two wind turbines that will pull MORE air and work 24/7.
I'd install a radiant barrier and THEN decide if you need more ventilation. Measure the air temp in the attic. If it's MORE than 10-20 degrees above outside air temp, then add more ventilation. Essentially the air is getting "stuck" in the attic like a clogged drain.
I live in Atlanta, Ga. and have a 10:12 shingle Hip roof that faces South with full exposure to the sun. The other areas of the roof are shaded and do not get as hot in the summer. Can I install the Radiant Barrier to the rafters on the Southern exposed roof and not the Northern side? Or do I need to cover 100% of the exposed attic. Thank you, Tim Richardson Atlanta, Ga.
Partial coverage works with radiant barrier. If one side is not getting sunlight at all, then you can simply cover the sides that do have sun exposure.
We recently had our roof redone in a house that is about 100 years old. There was no ventilation in the attic areas. The roof is heavy clay tile. The roofer used a underlayment material that creates a vapor barrier in the attic. The roofer said that this is not a problem. We were told that a form of insulation or radiant barrier would be a good idea. We are thinking of having a radiant barrier put in (tacked on the bottom of the rafters) and we asked about the lack of ventilation problem (moisture problems causing mold, etc) and the company representative said the lack of any ventilation is no problem. Another insulation person said that the only thing to do is put up a bifold material covering all of the rafters and shooting cellulose into the area between the bifold material and ceiling and this will prevent any moisture problems. Which is correct?
Thanks for the question.
I really need more information. If you are in Arizona, then I would say it's not a problem. If you are in New York, then it could be a problem.
Where are you?
Do you have any soffit/intake vents?
Do you have ANY method of installing ventilation?
Ed-I have talked to so may people-all say something different. I live in Maryland, house is 33 yrs old, a 40 foot by 26 foot 2 story with a very narrow ridge vent and 2 14x24inch gable vents.I want to do both 6 inch circular soffit vents and radiant barrier then add more insulation later when we can afford it. What type of product(if any) do we need to funnel air from our new soffits to behind the barrier to the ridge vent OR leave a 6 inch gap at the bottom so air flows throughout the attic space & not just behind the radiant barrier? I have seen Accuvent (and other stapled shields that don't allow any air into attic space) but if these are not needed-what type of smallish product do I buy just to keep insulation away from soffit vent? Or do I need a 48 inch shield that runs from the soffit to be stapled 30-40 inches up between the radiant barrier and the roof deck? I talked to at least 5 different people-all from different jobs(sells soffit vents, sells insulation, etc). I watched all your viseos and read all these questions and haven't seen any thing to address the "insulation dam" factor....also called rafter vents I think. What do I really need?? Thanks for your videos-you have really been a great help to so many people.
A simple gap at the top and bottom of the staple-up run will address the air flow from the soffits into the attic space. I made a video talking about air gaps here: http://www.atticfoil.com/faq/videos/92-how-much-of-a-gap-should-i-leave-at-the-top-and-bottom-for-ventilation.html
As far as the vents go - I don't think they are necessary. If you think you will blow in insulation in the future and your concern is clogging the soffits with the new insulation, then try the SKIRT method with the foil - it can be found on this page, about halfway down: http://www.atticfoil.com/applications-a-uses/attic-applications/staple-up.html
I have a 1700 sq ft home located in Austin TX. The house came with a centrally located attic fan but the motor burned out some time ago. When I had a new AC unit installed some 14 years ago, the guy gave me a foam barrier for the fan louvers, and told me to keep it covered when the attic fan wasn't actually being used. Now I am thinking I might want to keep it open, using the logic that "heat rises, so having the louvers open will allow the heat a chance to escape the house." On the other hand, when the louvers ARE open, I can feel the heat radiating down out of them, leading me to think that the first guy was right and I should prevent the heat from radiating out to the rest of the house. So -- should I keep the louvers open, or keep them closed? thanks!
Just to clarify, hot air will rise but HEAT itself does not necessarily rise. Heat has a unique property in that it moves from areas of HOT to areas of cold (or the absence of heat).
Now, it sounds like you are talking about a whole house fan... if this is the case, then when you open the vents that heat is attracted to the cool interior of your home and would therefore migrate to the inside of the home. The reverse would be true in the winter - if you open those vents in the winter, the heat inside your home is going to be attracted to the COLD areas above the vents and will migrate out the vents, making it harder to keep heat inside. I recommend keeping them CLOSED as the installer suggested.
If you are trying to cool off the attic (and the house) then you need to consider installing a radiant barrier if you do not have one. Doing so will prevent 97% of heat from even entering the attic space and thus the home via the roofline and this is going to have the biggest impact on comfort for you during the summer and wintertime.
Our house was built in 1949. There is no overhang/soffits. There is a gable vent on each end. We are in North Dakota and get terrible ice dams. We found there was no insulation in the floor of the attic spaces and we added that which helped but still pretty bad dams. There was very old insulation between the rafters in this area so we have now removed that which seemed to help the temperature come down in there in the winter but we know it's still not quite right. I'm hearing a lot about intake vents so I'm wondering.....we don't have those. It gets very hot in there in the summer and we do have some humidity so I worry about the moisture even in the summer. Any ideas for us?
Using radiant barrier in your attic will reduce radiant heat coming from the home, preventing the warm air from getting into the attic and forming the ice dams. The key to preventing ice damming is to SEAL, SEAL, SEAL - any heat escaping from the home is a potential contributor to ice dams forming. I'd lean toward the "over insulation" method for your area: http://www.atticfoil.com/applications-a-uses/attic-applications/lay-out.html
You also want to make sure your attic is well ventilated - so adding intake vents is a good idea. This will keep the attic cold and thereby keep the roof cold; by doing this you can prevent ice damming. So keep the warm air in the house and keep the cold air in the attic! Take a look at this case study as well, it's from a guy who had the same issues with ice daming and how he addressed it: Ice Damming in NY Fixed with Radiant Barrier
I live in Massachusetts in an older house with a hip roof and about 1000 sq. ft. of attic space. Ventilation consists of a powered roof fan at the top with soffit vents. The thermostat/humidistat is set at 100 deg. in the summer, 70% in the winter and works well maintaining those settings.The problem is that in the summer the rooms below are hot and I was hopeing that a radiant barrier would help. The attic floor consists of 6" of lose rock wool insulation over horsehair plaster ceilings with no vapor barrier. Can I lay the radiant barrier over the rock wool, (under the floor boards because I use the attic for storage), without worrying about trapping moisture underneath in the insulation below.
No, unfortunately you cannot do this because eliminating the necessary air gap means the heat is not radiant, it's conductive. A radiant barrier does not stop conductive heat flow, only radiant heat flow. In this situation you would be better off stapling up the foil to your rafters since the floor space is occupied. Otherwise, the foil would only work in the areas where it was applied to the plywood floor and OPEN to the attic air (ie. nothing stored on top of it).
Hello, I have a Cap Cod from the 1950's. I want to add a radiant barrier. Can I put foil ontop of foam boards that will go up in the slopes between the sheathing and the cieling of the 2nd story bedroom as long as I leave a gap for ventilation. also can I put a vapor barrier on the other side so it will go from inside out(between rafters in slopes); drywall, vapor barrier, foam board, radiant barrier, 1-2 inch gap for ventilation, and sheathing.
Yes you can create foil-faced foam board to block heat from the roofline from coming in through the cathedral ceiling so long as the FOIL side is facing a clear, unobstructed air gap. As far as adding a vapor barrier into the assembly, if you are in a cold climate, then you will be ok adding a vapor barriers where you suggested in the layering.
We are building a new 3600 sq ft home in the Phoenix area. The builders are adding a radiant barrier roof in addition to r-30 insulation. They offer r-38 as an upgrade for $480. Would it be worth it to upgrade to the high rated insulation?
That is hard to say because a lot of times once people add a radiant barrier they find that it makes the insulation they have much more effective so there is no need to add more. I would look at the Department of Energy's website for the recommended level of insulation they suggest for your geographical area and as long as you are within those parameters you should be fine.
I have a good sized attic that I would like to finish and use as living space. I had somebody tell me that I could put 1x1 or 2x2 boards in between the rafters and stretch the reflective barrier across those between each rafter and put insulation then wall board. I don't have soffit vents all I have is gable vents on the east and west but he told me I could close those off eliminating the need for vents. Is this correct?
The best way to approach this is to gain access to the ceiling/walls of the room and add radiant barrier, along with insulation, via the Cathedral Ceiling install method.
In the Cathedral Ceiling installation method the air inside the assembly is not vented/ dead air; but there is no risk or damage from "holding" the hot air in the wall. Just keep in mind that the total assembly will probably be a little warmer since it does not have the ability to vent some of the heat.
I am a widow, living in Texas Panhandle. My home is 1600sq.ft. and is older. My house is too warm, i installed radiant barrier insulation a few months ago.My ventilation consists of 4 passive roof vents and 10 soffit vents. What type of more ventilation do I need, I'm confused. Please help! AC bill is very high!
Well the attic should be properly ventilated, but if you have a radiant barrier installed the attic air isn't what will contribute to your home getting too hot, it's the SURFACE temps that make it uncomfortable. Do you have a lot of exterior walls that catch sunlight? How about your windows - do you have a lot that the sun shines though? Since you have addressed the roof line with the radiant barrier - the next practical thing to consider are other areas of radiant heat gain that are making the home hot. The attic ventilation is important to keep the attic dry, but again, this isn't likely the source of your problem.
I've been searching the internet and have not found a video of anyone installing a radiant barrier above a vaulted ceiling. Most of my house is vaulted and I am not sure how I'm going to move around on top of the vaulted ceiling and keep from smashing all the blow in insulation while I'm installing the radiant barrier to the roof structure.
Typically when you have access to the back side of the vaulted ceiling from inside the attic, the best way to apply the foil is to lay it directly on top of the vaulted areas. This prevents the heat from entering and escaping (summer and winter benefit) and it eliminates the need to get above the area and risk falling.
I am having a roof extension done on my home to cover a large portion of our deck. There is no attic, but we do have soffits, with can lights. Do I need soffit vents?
Typically porch areas don't have ventilation systems since they are pretty flat roofs and open to air on all sides.
I live in the Northwest part of Alaska...my friend & I plugged 6 out of 8 eave vents with 14" x 7" pieces of cardboards in our new house because we were burning 20 gallons of heating fuel in 8 to 9 days...is that a mistake? I am inquiring on this confusing topic...please let me know. Thank you!
I'd need more information to say for sure but if you were having trouble keeping heat in the home, plugging up your attic ventilation is not the way to stop that heat loss. First you need to make sure the home is sealed air tight. If it is a new home, it is generally safe to say this should already be done. Then, you need to add a radiant barrier over your insulation on the attic floor so you can stop convective looping in the insulation and help the home retain its heat. The ventilation in the attic should not be altered - you need this to prevent ice damming and to keep the attic dry (prevent moisture accrual). For more information on using a radiant barrier in the attic to retain heat, please see the installation information on this page: Installing Radiant Barrier Over Existing Insulation
Should turbine vents be covered with burlap during the winter in Arizona southwest to retain the heat? Everything I read says not to because of moisture and snow... both of which we have a severe lack of in AZ... so is it worth covering the vents in dry climates?
No, your attic vents should not be covered. If you're trying to reduce heat loss from the home into the attic, you need to consider adding a radiant barrier over your insulation to help the home from radiating heat into the attic space. More information can be found here: Installing Radiant Barrier Over Existing Insulation
I have an old house with a new roof shingles. I want to insulate my living in attic space with a radinate barrier. My houses dose not have any vented soffits, just vented gables on both ends of the houses. Would a radinate barrier work with no vented soffits
Regardless of your ventilation, the foil will still work to block 97% of radiant heat attempting to enter the home as long as when you install it there is an air gap on at least one side of the foil.
I am building a new detached garage with upstairs living space. I am going to install to velux skylights. Do I need to have soffits or gables. I don't want to waste energy by letting cold air enter in the winter through knee walls. The garage will be 22x 26. What suggestions do you have t,o insulate or vent most efficiently? Yank you very much!
If the entirety of the space above the garage is going to be living space, then you don't have to vent it. It can be sealed air tight - which is how it is done if you will be conditioning this space. As for the garage however, you might want to add either a window or some way to vent it out since it can gain radiant heat from any walls (including the garage door) that catches sunlight.