Mixed exhaust vents: Wind turbines and ridge vent
People who know me hear this often: “Don’t Over-Think It”. Things are usually never as complicated as they seem. Of all the questions I get from customers, Attic Ventilation is probably the most misunderstood, and overcomplicated topic in the home efficiency/improvement area. So hear me now: “DON’T OVER-THINK IT”
Attic ventilation is VERY simple. You have HOLES in the bottom of your attic (usually soffit vents) and HOLES in the top of your attic (ridge vent, wind turbines, static vents or power fans). Ideally, air comes IN the bottom and OUT the top. It’s just like a chimney in your home. Pretty simple. Holes in bottom, holes in top…got it?
Think about this. If I came to your home today and started ripping out your soffits and cutting lots of holes in the top of your roof eventually the air temperature in the attic would get close to whatever the outside (ambient) air temperature is. Air temperatures would drop but surface temperatures would not drop much due to the radiant heat gain. A radiant barrier works together with decent attic ventilation to drop both air temperature and surface temps.
Here is where many people screw up attic ventilation. More is not always better. The thought process goes something like this: “If I add an electric or solar attic fan, or some ridge vents, or a few wind turbines or static vents or maybe ALL OF THEM, I’ll move more air and my attic will be cooler” WRONG!!!!
Dirty or clogged soffit vent
Let me ask you. Have you EVER seen a chimney with a fan sticking out the side in the MIDDLE? Of course not, why? Common sense would say that the fan would pull air from BOTH the top and bottom of the chimney. Your attic is EXACTLY the same. Why on earth put an electric fan 15” away from a ridge vent or wind turbine? Yes, there will be great airflow in the top 2 feet of the attic and the rest of the air will be almost stagnant.
Air always travels the path of least resistance. Mixing exhaust vents is a bad thing. The strongest vent will dominate and the other exhaust vents will probably become INTAKE vents. This short-circuits the whole concept of air coming in the bottom and out the top. This can happen many different ways from actually mixing different types of exhaust vents to having ridge vents on EVERY ridge. Usually the ridge vents about halfway up the roof will become the intake vents and totally short circuit any air coming from the soffit vents. All the exhaust vents should be within a few feet of each other from the top.
How to fix it? Start at the bottom with your soffit vents. Have you EVER cleaned your soffit vents? 95% of homes have clogged, blocked or painted over soffit vents. Or, the holes behind the vents are so small virtually no air is coming into the attic. I’ve even seen million dollar homes where they just screwed in the vents and did not bother to even cut holes. I’ve seen many homes where just cleaning the soffit vents (use a dry nylon car wheel brush) will drop the attic temperature 20º in 20 minutes. And those wind turbines that were “broken” start spinning like crazy. Get it? Air comes in and now air will go out.
Hole cut too small behind soffit vent
Next, pick one type of exhaust vent and go with it. By combining a basic strategy of holes in top and bottom your attic will be cooler in the Summer and drier in the Winter. Remember, keep it simple, and don’t over-think it…Holes in the bottom, holes in the top.
Tags: attic fan, Attic Ventilation, attic wind turbine, ridge vent, soffit vents, solar attic fan
I agree completely!!! Ventilate, ventilate, ventilate! when I crawl up into the attic of an older home, I notice that there is never enough air flow. usually there is one or two roof vents and a very few soffit vents. One of the more successful experiments I have done, is to take an AC booster fan (~25watt) and secure it into the existing roof vents while adding more soffit vents. In the middle of summer, there is a difference between passive and active air flow. I prefer passive, but some homes just need a little extra help. If you figure out the basic air-in, air-out flow, then adding a little fan (with a thermostat) can help get rid of the heat faster than waiting for the heat to rise. I don’t like the huge 175 watt roof fans due to the amount of electricity they use and the fact that you can never get enough air into the attic through the soffits to keep the fans from pulling your good AC from the house into the attic.
I usually stick with my passive vents and occasionally use a booster fan when really needed.
Toff
Okay, after reading this, I’m canceling my ridge vent project. I have four exhaust vents a few feet from the top of my roof and my soffits are not clogged, so I’m fine. I cut holes in the radiant barrier by the exhaust vents just as your website instructed. Thanks for the help.
Kevin in Sugar Land
Attic vents? I haven’t vented an attic in over 10 years. Unvented attic… foam insulation against the roof line. Radient barrier with air space under a metal roof.
I totally agree. My first choice is a full foam enclosed non-vented attic with a radiant barrier to the outside as you mention. Unfortunately, this is usually only a cost effective option for new construction. This is for the millions of existing homes that have vented attics. Thanks for the feedback!!
I am now very confused. My understanding is that you must have a ventilated attic for the radiant barrier to be effective. The house I’m working on is essencially a new build. So do I plug the holes or vent the rood?
No, you want a ventilated attic. Zark and I were referring to using spray foam an fully enclosing an attic. This is done to move the “thermal enclosure” to the outside and bring all ductwork inside a semi-conditioned space and you would have no insulation on your attic floor. Talk to your builder about this technique or check out: http://www.buildingscience.com.....aled+attic for more info.
I am now very confused. My understanding is that you must have a ventilated attic for the radiant barrier to be effective. The house I’m working on is essencially a new build. So do I plug the holes or vent the roof?
What if you bought a house where the owners had a new roof put on using ridge vents. There are holes still cut out in the attic from the wood that used to have the roof vents. How do we close these off so that it is secure for someone to walk on the roof?
The best way to close these opening off so you can walk on the roof without danger of falling in would be to use some plywood with wood framing for support.
Hi,
I am confused on this topic. It sounds like the roof gets hot, radiates heat into the attic, and this does most of the heating up there. I do not have ridge vents, just two wind turbine vents in the roof and an old vent fan that really some idiot installed a long time ago that does little. So I wanted to install a radiant barrier. My trouble is that since I have to ridge vent, the air in the gap between the barrier and the roof is trapped there and stagnant, so it seems to me will just get hot and then conduction will occur through the foil. Am I wrong, or if not, how to avoid this?
I have looked over and read most of the information on your site. The “hybrid” method seems to be the fit for what I have in mind. I am thinking of using two separate inlet/outlet systems for the attic. I would install the radiant barrier, as per the hybrid method, at the eave, and incorporate the flat top method with static ridge vents. This would cause the heat to rise with a vertical vortex. Secondly, after covering the gable ends with radiant barrier to completely close in the attic, I would use the gable vents for the other system. I would probably add unfaced batt insulation on top of the blown-in fiberglass. One end open and the other has a thermostatically controlled fan for the exhaust. Please comment on this arrangement. I am planning to install the radiant barrier next week. Thank you.
Bobby,
Wow, I think you are WAY over-thinking this. Often, there is too much emphasis on attic ventilation when installing a radiant barrier. Let me give you an example: If you park you car in the shade, does it really matter if you crack a window? Here is why. The radiant barrier rejects so much heat that usually whatever attic ventilation you’ve got is usually pretty adequate. I always recommend installing the radiant barrier FIRST. Then, put a thermometer inside the attic below the foil. If the air below the foil gets more than 15-20 degrees hotter then the outside temperature THEN increase the attic ventilation. You do not want to “seal” the AtticFoil, this is not the intention. You want air to flow freely from the bottom of the attic to the top and you want to install the radiant barrier in a way that will not impede, restrict or bottleneck the airflow. Remember, the BEST CASE lowest air temperature inside the attic is going to be the outside air temperature.
I have a house built in the late 70′s I am looking to add a radiant barrier to. The ventilation in the attic consists of 2 whirly birds and 2 end gable vents roughly 2×3′s? Is this enough ventilation to support a radiant barrier or do I need more? (House is rought 1700 sq ft)
Thanks.
Josh,
Do you have soffit vents? Your home may have originally had a wood roof with no soffit vents. If you don’t have soffit vents, the the ideal system would be to install soffit vents to act as intake vents.
Radiant barrier will still be beneficial even with limited ventilation. I would be sure to leave a gap at the bottom near the attic insulation. Air will naturally be drawn in the bottom and head towards the top as it heats up. Here are some install instructions: http://www.atticfoil.com/radia.....uction.htm
Ed,
Thanks for the response. It confirms what I was thinking. I need to add soffit vents. How many would you recommend based on the size of my home of 1700 sq ft? I was thinking maybe 8 total. 4 on the front and 4 on the back with a large enough whole in each one to have plenty of ventilation. Of course I’d make sure to not cover the holes with insulation.
Thanks!
The general rule is about 1 square foot of NFA (net free area) or “hole” for every 150-300 sq. ft of attic space. If you have 1700 ft, then you would need about 5 and 11 total square feet of NFA. This is generally split between topside exhaust vents and lower intake vents either 50/50 or 40/60 with more on the lower side. If you go in the middle with 8 square ft. NFA then you would need about 4 sq. ft of of NFA for the soffit vents. At 144 sq. inches per sq. ft. this is 576 sq. inches.
An 8″ x 16″ vent provides 56 sq. inches of NFA per vent. http://www.airvent.com/homeown.....eave.shtml Note: NFA is different from the vent size. You would think that an 8×16 vent would provide 128 sq inches, but it’s only 56 of OPEN space.
Given all this, you are pretty close with 8 or 10 vents. 8″x16″ soffit vents will do the trick. If you arer using smaller vents 4″x16″ or 6″x16″ you will need more.
I am in a similar situation. House built in 1935 with cypress roof, 1 gable vent and 12 little domed vents under the two other gables. Previous owner reroofed with composite shingles and resided, getting rid of the 12 little vents (I am guessing that each one was 10 sq in. – I’ve only seen photos of them.) They added 2 turtlebacks with the roof job. The square footage of the house is 1070. What if soffit vents aren’t an option?
There is a covered porch and the attic space of that opens into the main attic. Could soffit vents be put in the ceiling of the porch? It would be the lower part of the attic space?
We are also looking at replacing the 2 8inch turtlebacks with 2 turbines.
Laura,
Yes, you can put intake vents under a covered porch area. You can use soffit vents or a better option is to use off-the-shelf air conditioning grills in just about any size.
I have about 2,600 square feet in my home. I currently have 2 power vents near the top of my roof line. I have 30 (8 X 16) soffit vents around the house. Yes, after two repaintings I am sure that those vents are somewhat restricted with paint, dirt, etc. I have bought 30 new vent covers to replace those old covers. We do need to repaint and/or install vinyl siding on those soffits. I will install the new vent covers if we repaint. However, if we go with the vinyl on those soffits I have noticed that the vinyl covering for the vents are only 12 inches wide with fairly small vent holes. Those would be placed over the current holes cut for the soffit vents. QUESTION: Would I still get adequate venting with the vinyl coverings over those soffit holes with those two power vent fans? I am probably over-powered with the power vents and I do not want to have too little venting from those soffit vents so as to cause the air conditioning to be pulled from inside my home into the hot attic. Your advise PLEASE!
John,
With vinyl siding, you can just take a circular saw and cut out a bunch of rectangles in the soffit before you install the vinyl siding. You are correct, the vinyl siding that has holes is a little lacking in open area, so you want to install a lot of it. Another option is to replace the existing soffit with a hardy board type soffit that has continuous vent holes. Finally, you can cut a hole in a porch and install an air conditioning vent grill and paint to match. It will act as several soffit vents. It’s easy and rain won’t be able to get up and inside.
Thanks again Ed for such valuable information. I see another project to add to my growing list!
I prefer large passive domes to whirlybirds or slantbacks. Whirlybirds have no screening against critters and wasps, and slantbacks are too small for effective ventilation even though they are very weather resistant.
My next project is radiant barrier up there.
Ed,
My attic is about 2500 sq ft. It has adequate soffit vents (2004 construction south of Houston). My plan is to install radiant barrier along the rafters and to install two solar fans (each 25-watt, 1600 CFM advertised) in the attic near the top of the roof a few feet from each other. Currently there is one non-functional electric fan in the attic near the top of the roof. Any objections, is this overkill? Any recommendations on a solar fan manufacturer?
Robin,
I’m OK with solar fans as long as the soffit vents are clear and open. The fact that you have a non-functional electric attic fan is probably due to the soffit vents getting too dirty. This limits air into the attic and cause a drag on the motor which eventually burns it out.
Clean the soffit vents with a wire brush and I would even pull out some of the wire mesh to allow air to flow freely.
Personally, I would go with 2 or 3 14″ wind turbines. They work 24/7, in the dark, and are cheap compared to solar fans. Plus, with a typical 8 mph wind, they will pull a similar amount of air as the solar fan. Plus, once you install a radiant barrier, so much heat is kept OUT of the attic, ventilation is not as critical. Just like if you park your car in the shade it does not really matter if you crack your windows. 3200 CFM with radiant barrier IS overkill.
Hi Ed,
I have about 2000+sqft attic space which my home inspector said doesn’t have enough soffit vents. I also have about 6 passive air vent near the roof ridge. I was planning to put more soffit vents and a 1250CFM solar fan. But reading your article, if I simply install one solar fan and leave the other 5 passive vents unchanged, that may simply pull air from outside and cylce it back again through the solar fan? So should I close off some of the passive vents? Do they have some mechanism to keep the air from flowing back in from the outside but still allow air flow from inside to outside?
The other option am considering is to relplace the passive vents with two or three wind tubines.
What would you recommend?
Keep it simple.
I’d go with two or three 14″ wind turbines. What many people don’t realize is that two 14″ wind turbines pull as much air as an electric or solar fan with an average 8 mph wind – which is pretty typical. This is pretty impressive. If you don’t think it’s windy, stand on your roof and you’ll be surprised. Plus, they work 24/7 pulling heat and moisture out. They don’t quit when the sun goes down.
For the remaining static vents, just staple something (cardboard, roofing felt, etc.) inside the attic to choke down the airflow. You don’t need to SEAL it airtight, just cause air to be drawn in from the soffit vents.
Hi Ed,
When I built my house, I asked the roofers to install three electric attic fans in my roof. I forgot to tell them to NOT install the several (what I call) static, or passive vents in the roof, that is, those small, square vents that you see near the top of so many roofs in North Texas. It sounds like having both types of vents is a bad idea. What should I do? Should I simply turn off the electic attic fans? Should I plug the passive vents? Something else?
Thanks.
Jerry,
It depends. Three attic fans for most homes is probably TOO much ventilation. Having THREE fans pulling air OUT of the attic is OK only if you have plenty of places for air to come INTO the attic. So, if you have plenty of soffit vents to “feed” the fans (just clean them every year or two or the motors will burn out) then you would probably be OK blocking the static vents. I’d measure the air temperature. With this much potential air movement, the AIR temperature should only be a few degrees above ambient temperature. I’d turn the one fan off and see if it change much and then decide if the 2nd or 3rd fan is really doing much. Remember your attic temperature will never be cooler than the outside air.
Do you have a radiant barrier? Are you planning on installing one? If you install a radiant barrier, it will drop the SURFACE temperatures inside the attic compared to the air temperature in the attic. This is really what drives heat flow – the top SURFACE temperature of the insulation. It can easily be 120º or more even if the AIR temperature is only 100º. This is like leather seats heating up in a car with the windows rolled down – great ventilation, but you still have HOT seats.
Most customers find that after installing a radiant barrier whatever attic ventilation they have is usually adequate. If you can keep the heat OUT, then you don’t really have to manage it. Using the car analogy, if you park you car in the shade, then it really does not matter whether or not you crack the windows.
Hopes this helps! Visit or call us for more info http://www.AtticFoil.com
Hi,
Have recently had all new plywood, a metal roof put on my house and radiant barrior also. Have attic vent fans at each end of the long roof. What temp should the attic fans be set at?—Central Florida location
Thanks,
Hank Fisher
The temperature at which an attic fan ought to be set differs, depending on climate. However, the average accepted optimal setting is about 110 degrees Fahrenheit.
Thanks much.
Before your note, I had set them to 120 because they seem to be starting up at 110. The temp here is 70-82 The problem may be the long attic 85ft long an about 50 wide. Lots of space under this metal roof. Attic fans at each end. Soffit feeds new an run both sides along the length.
Great questions and answers!
My house was built in 1952. There are no vents except for four triangular shaped gable vents right below the ridge line. The house is T-shaped, 2000 square feet. Each gable vent is allows approximately 100 sq in of venting. There is also a ridge vent along the long axis of the “T”. The attic insulation is blown in rock wool, and not very much of it. My plan was to add an attic fan at one end and increase the venting at the opposite end by 200 sq in. The fan mfr advised to block the ridge vent since this would defeat purpose of the exhaust fan. I’m impressed with the possibilities of radiant barriers and would like to use both systems….but my mind is wide open. Would really like to avoid drilling/cutting a whole bunch of soffit vents.
I would not do ANYTHING until the radiant barrier is installed. What most customers find is that after they install AtticFoil® Radiant Barrier Foil the attic is so much cooler they don’t need to adjust the ventilation. Radiant Barrier REJECTS heat from ever entering the attic. Therefore, since less heat is coming in, ventilation becomes less critical. This is like parking your car in the shade. If you park in the shade, you really don’t need to crack the windows right?
Just leave a few inch gap along the ridge when installing the AtticFoil®. Then AFTER it’s complete measure the AIR temperature inside the attic below the foil. Ideally, it will be less then 15 degrees hotter than the outside air temperature. IF it’s hotter, then you need to increase air flow. Based on experiences of thousands of customers, I think what ventilation you have will probably be adequate.
Hi,
I have 2 wind turbine vents ~2/3 up the roof and plenty of soffit vents, but no ridge vents.
I understand that with radiant barrier I need to leave open space round the turbines, but won’t the heat just pool at the top of the attic (hot air up, cool air down) since there is no way for it to get out?
Sean,
Think of your attic like a drain in the bathtub. Yes, Ideally the the top hole in the attic would be at the absolute highest point – ridge vents. However, the wind turbines will “skim” the air out of the top of the attic. It’s no big deal if the air above the wind turbines is a little hotter. It not enough to even notice. The most important thing is we want the air down low in the attic to be as cool as possible. This will keep your insulation, ductwork and framing the coolest.
Just leave a gap along the ridge and give the air a path to always find its way to the top. The wind turbines will work great. You should install the AtticFoil® Radiant Barrier in a way that does not change/modify the airflow in the attic one bit. The air should continue to flow through the attic as though the foil is not even there.
Hello Ed,
I have a 1981 NJ ranch house with a 45′x35′, 1,540 sq ft attic, with R-30 paper faced (down) fiberglass insulation. The intake soffit vents are the non-continuous double, pre-stamped aluminum type, alternating with solid soffits, and are fortunately in line with the WEST to EAST air flow that exits out a mesh ridge vent added with the new roof shingles. There is also one gable vent each on the NORTH and SOUTH side of the house.
I intend to install your radiant barrier on top of the attic floor insulation, and also on the hot, SOUTH side gable wall. My question: Are these GABLE VENTS REDUCING the draw/draft efficiency of the intake soffit/ridge exit vents’ airflow, and if so, should I seal them closed?
Thanks, John
John,
This can be a little tricky since all ridge vents are not created equal. In theory, yes you would block the gable vents and use a soffit/ridge system alone. However, this is assuming you have ridge vents that are clear/open and have a fairly high NFA (net free area). These ridge vents are usually the taller “baffled” type and not any low profile or “invisible” ridge vent – which often provide almost NO ventilation.
I would something like roofing felt and staple up to block the gable vents. It does not have to be airtight. You are just trying to choke down airflow from the gables. Then, see what happens. If the air temperature is good, then do nothing. IF the air temperature goes up, then I’d tear down the felt and use combination of the ridge and gable vents. In this case the gables are actually the main vent assuming the ridge vents are limiting airflow.
Finally, if you are installing OVER the attic floor insulation and ONLY have batts, then I would top off the insulation with blown-in insulation before installing AtticFoil® Radiant Barrier Foil. The most critical part of attic insulation is the few inches ABOVE the ceiling joists. By covering them, this will greatly reduce “Thermal Bypass” where heat will actually go around the batts by conducting through the wood.
One of the really stupid HVAC designs used here in Florida is
to run flexible ductwork thru the attic furnace. Mine reaches 135 degrees and results in duct air temp increases approaching 8 degrees from my heat pump exchange unit to my bedroom vents.
When the attic temps are 85 degrees or less, there is no heat gain of the air travelling thru the ducts. Therefore, while I
can understand the value of reflecting radiant heat to reduce the heat transfer thru the blown in insulation in the attic, I think perhaps just as important is to reduce the attic temps so that the ductwork can convey the cool air to the outlets without excess heat gain in the process. Where can I find that information on the atticfoil.com website?
Take a look on this page: http://www.atticfoil.com/best-install-method.htm Here I explain the benefits to different install methods and what to consider (including cooler ductwork).
The room above my garage is surrounded by attic crawl space and gets hot, i mean hot! There are soffit vents around the perimeter, no ridge vents, and a passive gable vent. I have started to install the radiant barrier and added an electric fan to the gable vent.
1. I have completely sealed off the attic with foil. I assume now i need to go back and open it up a bit to correct the airflow from the soffits in to the crawl space.
2. Is there anything to gain by adding a second radiant barrier over the insulation in the room walls?
I guess i felt i needed to trap the heat from entering, but after reading your blog it appears i don’t need to trap the heat, but rather let it flow and reflect what heat i can with the radiant barrier.
EJ,
Yes, you want to “open up” the foil to allow air to flow freely through the attic. Basically, air should flow through the attic as though the AtticFoil® is not even installed. I would check the soffit vents to make sure they are clean and free.
You are correct, we want to reflect the radiant heat and use air to help pull heat out of the attic and to provide a cooling effect for the roof.
I would not double up a radiant barrier. One layer should do for most applications.
I have about a 3,000 square ft. attic and just installed 8 additional soffit vents on each side of the house. This brings my total up to about 26 vents. I haven’t installed radiant barrier yet. This is the first I’ve read about ventilation not being important. Everyone I talk to says you need good ventilation. Before this weekend I only had 10 vents and my attic was already reaching 150 dregrees. Now that I have this much ventilation should I skip the radiant barrier and just blow in insulation? Since I did it myself I spent nearly as much on equipment/tools for soffit vents as I would for all the radiant barrier I need.
Thanks for all of the information.
Ventilation is nice, but it can only do so much. Think of your attic like your car parked in the sun. You want to keep the leather seats cool. You can open the window and have great ventilation and the actual air inside the car will be about ambient. However, if the sun (radiant heat) hits the leather they will STILL be very hot. Same thing with an attic. The top SURFACE TEMPERATURE (measured with an infrared thermometer) can typically be over 120º even if the actual air temperature is much lower. A Radiant Barrier will keep the top SURFACE TEMPERATURE DOWN. Think of “regular” insulation as an ice chest and radiant barrier is like putting the ice chest in the shade. You actually need both for best results.
150º degrees seems REALLY hot (for the air). Is this the AIR temperature or are you using an IR thermometer and measuring something with mass inside the attic (bottom of deck/supports etc.) ? Feel free to call me at 800-595-8772. Ed
Ed – Thanks for the info. It was done with an IR thermometer on various surfaces. I’m going to get a basic remote thermometer to put in the attic pretty soon.
In that case, 150º is no big deal. Typically, on a hot-sunny day the tops of the shingles will be over 170º and the roof deck below the shingles can easily be over 150º. Here is a thought to ponder? How does stuff 10-20 ft AWAY from the roof reach temperatures of near 150º…..yet the AIR inside the attic is much cooler? Yes, radiant heat transfer. Heat transfer by NON-CONTACT! Radiant heat transfer is an incredibly efficient method of heat transfer. However, we can also use this to our advantage. Since the heat MUST transfer to a wave-form to cross the air space we can literally direct it (radiant barrier) anywhere we want to. Heat flowing through a solid (by conduction) can ONLY be SLOWED down. Think of an oven mitt. You can pick up a hot pan for a while, but eventually the heat will make it through and it will feel hot.
[...] finishes up his interview by explaining surface temperatures, roof temperatures and the importance of attic ventilation to get the best results and the most comfortable living space. He also explains why predicting [...]
Ed,
You are doing a bang up job with the blog and I hope it is paying off. I know it has paid off for me as a consumer. Your approach is exemplary.
I had an attic installed 4 years ago and the roofer took two brand new vent fans and changed the system to a ridge vent system. Well, to make a long story short, the roofer never opened the ridge vents to the attic space. I just had this repaired and the metal (not low profile) vents replaced the plastic ones that also did not fit well. I took a drywall knife and opened every soffit vent opening that had been covered with paint. I then purchased a mini rake and made sure the bat and blown insulation was not covering the soffits from inside the attic. This has all helped but not enough to help with the upstairs heat issue in the hot Georgia sun.
So thank you for your informative information you provide on this site. I’m now going to make sure my knee walls are flashed. I’m also going to install a radiant barrier system.
It is amazing how I have never heard of this from any of the roofers or AC guys over the years. This internet rocks cause now I know. I also love your hot car in sun example.
Now off to http://www.atticfoil.com.
Thanks ED!!!!!!
I have soffit vents but do not have ridge vents. Instead I have 2 gable vents and also 2 vents in the roof about 1/3 from the top.
I want to install radiant barrier. If I install it on the rafters all the way to the top then the air in the top 1/3 of the roof under the radiant barrier will have no way to escape. It seems to me that radiant barrier on the roof rafters will not work unless one has ridge vents.
What is my solution. Can I guess I can install radiant barrier on the two thirds part below the roof vents but not sure if it will be good enough. The other possibility is to install it on top on insulation on the floor and perhaps add another batting on insulation on the top of the radiant barrier. This would stop the heat from getting into the house.
Don’t over-think this. Hot air will flow like water up to the highest point. Just follow the Radiant Barrier Staple Up Instructions and leave a gap at the top along the ridge. Air will flow towards the top and find it’s way out. It may not be EXACTLY at the highest point like with ridge vent, but don’t worry about it. Radiant barrier will work WITHOUT ANY airflow. It just works better WITH airflow. The air gets hot by extracting some of the heat off the roof. It’s basically a cooling mechanism and good airflow will keep the roof a LITTLE cooler – not much though. The main reason you want the hot air to get out is so it does not “backup” or get “plugged” and cause ductwork to be immersed in hot air.
Ed, I am in a similar situation as Sanjay. I have a 1500sqft house in North Florida. It has a hip roof and vinyl soffit all away around the house. It only has 3 4 foot passive vents about a yard away from the roof ridge. This seems way under vented to me. How much of a benefit would it be to convert to ridge vents and close the 3 foot vents if I installed attic foil to the underside of the rafters leaving the proper top and bottom gap?
James,
You can vent all day long and it won’t really drop surface temperatures in an attic. This is like blowing a fan on my sunny driveway – it does not do much. I always recommend installing radiant barrier FIRST and then if the actual air temperature inside the attic is still hot, then start cutting holes for air to flow in the bottom and out the top. Remember, the LOWEST the air temperature can usually get is the ambient (outside) temperature. No matter what most attics (even with radiant barrier) will be a little warmer than outside.
Ed,
Your website instructions are excellent as well as your product.I wanted to know what your opinion of the Aura vents are ( no moving parts just a vortex by air moving from bottom soffits up to vents)?
Are they as good as whirlybirds or does it matter?
Also I am installing radiant barrier in a 6000 sq. ft. attic with a cathederal ceiling 15 ft high on center about 100 feet in length. I have enough soffit ventilation, how many roof vents at the top would I need for adequate ventilation, if needed (it has a ridge vent partially blocked)?
Thank you, Ed
David,
What you will find is that after installing a radiant barrier, you don’t need as much ventilation. I would install the AtticFoil® Radiant Barrier and then measure the ACTUAL air temperature below the foil. If the air temperature STILL tops out over 15º-20º above ambient, then start cutting holes in the top of the attic assuming you have plenty of soffit vents as stated. Personally, I like ridge vents or wind turbines. I don’t have any experience with the Aura Vents. I’d like to see some actual 3rd party lab testing measuring actual airflow in CFM.
We have a 1 1/2 story home, 2100 sqft down, 1300 sqft up in south Mississippi. Has spray-in cellulois walls and 14″ blown in cellulois attic. Ductwork is in the attic. Has approx 90 7″x1.5″ styrofoam channels from contineous perforated vinyl soffit and 2 large porches with perforated vinyl soffit ceilings. Has radiant barrier sheeting on roof and ends of attic.
The builder installed ridge vents over sheeting without cutouts.
I am considering 3 14″ Whirlybird vents. Is this a good brand to use?
I installed a remote themometer and have the follow readings:
Outside Attic
07:00:00 AM 78.6 75.2 -3.4 Overcast
08:12:00 AM 80.2 76.1 -4.1 Overcast
09:12:00 AM 82.2 75.9 -6.3 Overcast
10:18:00 AM 84.0 82.6 -1.4 Overcast
11:21:00 AM 85.1 87.3 2.2 Overcast
01:30:00 PM 88.2 96.1 7.9 Sunny
02:36:00 PM 90.1 102.9 12.8 Sunny
03:37:00 PM 90.5 105.6 15.1 Sunny
04:32:00 PM 91.2 106.3 15.1 Sunny
05:35:00 PM 90.5 106.2 15.7 Sunny
06:30:00 PM 89.2 101.8 12.6 Sunny
07:30:00 PM 87.8 94.1 6.3 Sundown
08:20:00 PM 86.0 86.9 .9
Should 3 14″ wind turbines be sufficient?
Let me be clear. You have a path from the soffit to the ridge vent, but the ridge vent is not cut open? If this is true, then YES, I would say that 3 x 14″ wind turbines (Whirlybird Brand is good) would do fine assuming that after you cut in the wind turbines you STILL have a path for air to flow from the soffits up and out of the wind turbines. Can you send me some pictures? Go to the contact page at http://www.AtticFoil.com and attach some pictures.
Hi Ed,
Amazing website. Actually will be picking up some radiant barrier thanks to the info from this website.
Question about my ventilation: I live in San Diego. Most of the year we have very temperate climate and arid. So many of the posts here dont really apply (4 seasons).
I have a 1947 stucco bungalow with composite tile roof. 1k sq feet with 2 gable vents across from each other, a turbine and a small roof vent above the living room side (house is L shaped with bedrooms and bath on longer side of L shape and living room and kitchen on the smaller part of the L).
I dont see any soffit vents. The air seems somewhat stale and I have been opening the hallway attic door entrance to let in fresh air (ceiling).
The previous owner decided to install a solar powered ventilator from Costco and had installed it on one side of the house. While its blowing hot air out I am wondering if I am short circuiting the air flow since there already is a turbine already installed. I would say the the turbine is placed directly in the middle of the house with the ventilator approx 15 ft away. This morning I actually duct taped the passive vent above the living room because I was afraid the ventilator was pulling in hot air from that vent (they are about 13 feet from each other).
The attic is insulated and it seems the other gable vent is pulling in cool outside air, but not really bringing in fresh air throughout.
I am just trying to figure out what to expect temperature wise in the house. The mornings here can be ~65 degrees outside with the interior being about the same. But gradually as it warms up throughout the day, the interior of the house will reach 80 degrees and the outside going above that to 85-90.. I have dual pane low e glass, so I am pretty sure its not the solar heat coming through as I close the blinds etc.
So far the two HVAC companies I have talked have only tried to sell me more powerful ventilators or upgrade my HVAC system haha. Besides buying the radiant barrier (which I think will make a tremendous differnece) is there anything else I should expect or tips to do based on the info above?
Thanks!
James,
You have a mixed bag of attic ventilation. Ideally, you would have soffit vents to allow air in the bottom. The air would naturally heat up and flow towards the top of the attic. Your system is moving some air, but it is difficult to really determine what to expect as far as air temperature. The problem is that attic ventilation can only do so much. Think of a car. You can roll the windows down and get GREAT airflow, but if it is sitting in the sun, the car will still FEEL hot.
I would install the AtticFoil® Radiant Barrier before you do anything else with the ventilation. Most customers find that once the radiant barrier is installed, whatever ventilation they have is usually adequate.
Ed,
Thanks to your great website, I ordered radiant barrier and installed on the attic floor over the past few days.
The change in temperature is dramatically lower up there now. When I used to touch the beams, they would be quite warm to the touch.
The solar fan has a thermostat that is supposed to kick on when it hits 85 up there and it hasnt moved and current temps outside are 96 degrees.
Amazing stuff and info. Thanks!
hello, i have a north texas, dallas suburb home built in 1953, 2200 sq ft, was originally cedar shingles, has 2 gable vents and i have installed 2 whirly birds, am thinking i need additional blown in insulation and to install approximately 16 soffit vents (do they need some thing in the attic to keep them clear?) and is that enough for the exhaust or even block the gable vents off?
Keith,
You biggest impact item will be to install soffit vents. Old wood shingles were naturally vented. Once you deck and close up an attic, you need holes in the BOTTOM and the TOP to allow for airflow. I would install the soffit vents and then decide whether or not to block the gable vents. Have you considered installing a radiant barrier? http://www.AtticFoil.com
Combining, good ventilation, radiant barrier, and insulation are 3 of the 4 silver bullets I talk about in this article. http://www.radiantbarrierguru......-climates/
hello, i live on indiana ,michigan border. i’m getting ready to reroof, and add more insulation, and a radiant barrier. i have 22″ sollid alluminum soffits[non vented] and only 3 box vents on roof. am thinking of perforated soffits. should i replace all soofits with perforated and install a ridge vent and close off box vents. house and garage are 1500 sq. ft. Also, living up here, is it better to install the radiant barrier on top of the blown in insulation. i have no moisture barrier now, just shredded fiberglass insulation, about 8-10 inches deep. thankyou for your knowledge and help.
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 necessary.
I have two story Dallas home built in the 90′s with fairly large simple gabled roof. Blown insulation on the attic floor. Limited soffit vents. Two passive (looks like opaque plastic) vent domes near top roof line. Questins:
1. Radiant barrier: Foil or spray paint?
2. Do I add insulation to attic walls under gables?
3. Is foam an option or is just for use in what I would call an unconditioned attic room that has HVAC equipment?
Thanks!
Craig,
1) I would go with foil over paint. Not just because I sell foil http://www.AtticFoil.com , but it really is better and more effective. Did you read my post on Radiant Barrier Foil vs. Paint?
2) No need to insulate walls below gable vents. They are usually not part of the “Thermal envelope” – Just part of the roof in a vertical format. Walls in the attic that have living space on one side and attic on the other NEED good insulation. We call these “hot walls” for a reason.
3) Foam is an option, but unless you convert to a “sealed” or “conditioned” attic, foil is probably your best bet. I love foam for new construction, but it can get tricky on existing homes. One problem is that you can reduce the heat load SO much, that your air conditioner becomes too oversized and you run into moisture / dehumidification problems.
Hi, Ed. Can’t even describe how much respect I have for your data and the way you present it on your site. You’re a natural-born teacher. Here in cold Connecticut, a properly functioning attic system is vital, but so few people give it proper consideration. Recently did a new roof, added ridge vent across the peak, with high-NFA (Certainteed) soffit venting all around the perimeter. This is a dutch, and the gambrel poses some air-flow issues, although I have air flowing in and above the gambrel break in the attic framing. That said, I’m concerned that I’m getting resistance from the local building inspector when I suggested that I’m going to place your radiant barrier to my attic rafters. I think your barrier would help reduce the heat generated from, and transmitted by, my roof deck, which faces west and is a rather large gambrel surface. [One other complication…long before I knew to add soffits and ridge, we added a power attic fan through the roof, which cools down the attic, but I now have a mixture of exhaust vents. What do you, as the expert, recommend? I’m still committed to your radiant barrier as a proper next step. Don
Don, Thanks for the kind words. What kind of resistance are you getting from the inspector? I don’t see any issue with your plan. As for the mixture of ridge vent AND Electric fan, just set the fan for about 120º. Normally, the soffits and the ridge vents should do the trick. IF it gets over 120º then the fan will kick on and should help pull down the temperature. What you will find is that after the AtticFoil is installed the attic is so much cooler, usually whatever ventilation you have is adequate. My guess is that the fan will rarely turn on.
I am trying to insulate my cape style home built int he 50′s. The second story is finished with knee walls inside. On the back side of the knee walls within the attic space are the heating lines. I live in Vermont with very cold winters. I am getting a lot of icicles. In the upper attic flat space there is insulation batts rolled out. I currently have proper vent on the slanted roof line with fiberglass over the proper vents behind the knee wall but it does not reach as high as it should past the flat attic space. We are looking to fix the problem and I was wondering if I could foam the slanted roof line up to the height of the knee wall and then use blown in cellulose for the flat attic space. If this is some thing we do do I need proper vent behind the foam to allow for air ventilation up into the flat upper attic space? Or any other suggestions to solve the problem of icicles??
A radiant barrier will usually REDUCE the possibility of ice damming. Ice damming/icicle formation is caused when the top of the roof warms above the freezing point and the lower part of the roof is below freezing. To prevent ice damming, you want a COLD roof; right now the roof gets warm due to warm air leakage into the attic from the house AND from the home emitting radiant heat.
A radiant barrier installed on the floor over the insulation will help keep the radiant heat emitting from the home from hitting the roof; additionally you should wrap the attic side of the knee walls as well since they share space with a heated room and can emit heat. The result is a COLDER roof deck, which will reduce ice damming. Many customers have seen a significant reduction in ice damming after installing radiant barrier. I would also suggest inspecting your ventilation to make sure you have good intake vents, since cold air entering the attic will also help keep the roof COLD.
Living in Texas with our extreme weather causes me to ask what should I request when getting my roof replaced due to a hail storm.
Our summer of 100 plus temperature for 70 days this summer and ice storms in February cause my confusion. My roofer wants to put in ridge vents and 2 turbines for my 2 story 2,000 square foot home.
I already have the soffit air vents and I painted the interior side of the roof in 2000 with radiant barrier paint (since I painted it with a roller I couldn’t get to all areas). The house was built in the mid 90s. Do I need the turbines, will they help? My 2 air-conditioning units are in the attic as well as my tankless water heater.
The roofer plans to put the ridge vents on different levels since I have a multi-gabled roof and the vents would be at different levels which I believe you said would be overkill. Thank you for your comments.
As far as ventilation, I’ve done hundreds of homes. If you install the foil inside the attic decent ventilation is sufficient most of the time. I think passive is all most people need (with a few exceptions). Installing a radiant barrier is like parking your car in the shade, it really does not matter if you crack your windows (ventilation) or not.
GOOD INFORMATION! I have a 2600 sq. ft. home with ridge vents. I was actually going to install those solar powered fan type vents up towards the peak above the ridge vents. But now, reading this article, I know that is a NO NO! Will stick with the soffit/ridge vent system. Has worked for a long time. Thanks for the information ED!!!!!
Our house has a main attic above the second floor, but two lower inaccessible attics over the outside rooms on the first floor. The side attics don’t really attach to the main attic except for one duct chase on one side. The side attics don’t have any upper exhaust vents. Would you suggest adding some passive air hawk type vents near the top of these? They have soffit vents on them, but no idea how clogged they may be. Thanks for all of the great information.
Kyle, Yes attic ventilation must have holes in the bottom and holes in the top for air to flow in and out. If you have separate “cavities” then I would consider adding some passive vents (air hawks) for this area – especially if the area around the duct is small or far away from the main parts of the lower attics. Before I do this, I would focus on the soffit vents. You should be able to feel the difference in how much air is flowing through the duct chase by cleaning/opening/adding more soffit vents. If you can get good airflow through the duct chase (even if it’s a little small) then you be able to “flush” air through the lower attics without adding more passive vents.