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In response to an e-mail, you were kind enough to explain how to best insulate our old house attic. We are now seriously considering finishing the attic. I’m guessing this would change how to insulate. Would we just put the insulation between the roof rafters, or am I missing something? If you have time, I would really appreciate some guidance.
Finishing an attic seems straight forward and simple, but there are some things to consider. Planning ahead, research, and correctly installing materials can help make an attic into comfortable extra living space.
Attic spaces are typically very hot in the summer and very cold through the winter. Without properly insulating, your finished attic room will also be cold in the winter. Without properly ventilating the roof, your finished space can be just as unpleasant as an unfinished attic. Since parts of a finished attic are usually very close to the roof, insulation often blocks proper ventilation that is needed under a roof structure.
Ventilation
The best method for ventilating any roof is to have some type of venting up high on the roof that allows for rising hot air or warm/damp air to escape. For this to be fully effective, low vents should be installed to replace the air that is escaping. Continuous ridge vents and soffit vents are often the most effective, but it’s best to have an experienced professional evaluate to determine the best method.
Insulation
I suggest designing the walls and ceilings to minimize the area where insulation behind these surfaces is near the roof as this can restrict air movement.
- The area near where the roof rafters meet the floor doesn’t have much clearance so “knee walls” are often constructed. The area behind these walls is often used for storage of seasonal items and luggage.
- Instead of the ceiling following the slope of the roof all the way to the peak, a flat ceiling can be easily installed by attaching joists horizontally across pairs of rafters.
Both of the above creates some spaces where a good amount of insulation can be installed and areas are created for ventilating under the roof. These spaces aren’t really useable in a room anyway.
Where insulation will have to be installed between the roof rafters, “baffles” should be installed first. Baffles hold the insulation away from the underside of the roof decking, creating a channel for air movement.
Finished Attic
25 Responses to “How to Insulate a Finished Attic”
Thanks for your article.
Would the same advise apply to the tin roof with no ridge vent?
Hi Kit,
Old metal roofs typically didn’t have any ventilation and have held up quite well. Ventilation could reduce moisture condensing under the roof though.
If you’re finishing an attic space under a metal roof, the living area can be quite uncomfortable on hot, sunny days. The ventilation and insulation I’ve described above would likely make it more comfortable.
please tell me if you have to insulate the walls in the attic,when you have insulation on floors, we have 4 vents in attic.
We have a big problem in our finished attic bedroom . The roof is facing north and we were having leaking problem. We took off the plywood and insulation and installed flo-thro(strofoam)vents, installed insulation again and plastic vapour barrier. We thought this would solve our problem until we had a mild spell following very cold weather and water started running down the ceiling inside the vapour barrier. Does anyone have any other suggestions? How much venting is required in the eaves and on the roof? We have vents at each end of the attic at the peak of the roof.
I’m finishing the second floor of a pre-fab home.There is a knee wall about 4′-9″ tall then the rafters (@4′-6″) upto the ceiling which is @ 8′ tall. Because the home is manufactured w/ 2×6 studs including roof rafters, there’s not a lot of space for batt insulation after installing the rafter baffle up above the ceiling height. Is this enough space for exterior wall rated insulation, or do I need to pad out this area to allow for more room for insulation/ refter baffle? Thanks
I have an attic in 150yr old home that is large enough to be used as third floor. How do I insulate and vent this? It has large beam work that I’d like to keep. Can I insulate from the exterior instead? And how would I ventilate? There is knee wall all the way around but ceiling goes to roof peak.
I want to insulate the roof rafters of an unfinished attic with intention of finishing the room eventually. The floor is not insulated. How do I vent using ventilation channels? What type of insulation foiled or not? Vapor barrier or not?
Thank you for that good post. I enjoy your website very much.
I have a cape cod style house (built in 1949) with no soffit vents, it does have gable and ridge vents. This home is NH. The finished attic area seems to be very hot and very cold during the year…The knee wall areas are insulated on the roof and possible the floor (we believe the floor area is insulated). What R rating insulation should we use if we decide to rip all of it out and start over? We also experience ice build up around the edges of our roof. No leaking yet. Any advice would be appreciated. Thanks.
We’re thinking about finishing our bonus room in the attic and need some help. We live in GA and my main question is after putting up the raffles, what type of insulation we put behind, or should we even put any. Our main concern is also that neighbors that had their bonus room done around here are having problems with temperature not staying very stable. Most of them are having very warm rooms and having to run the air almost all the time. Is there a way for me to better prevent that? Will the insulation behind the raffles help? Should I use insulation with vapor barrier or not behind the raffles?
Thanks in advance for any help!!
I’m looking at purchasing a home built in 1875 and added onto as well as upgraded in 1951. During the attic inspection, I noticed several things. Not enough insulation and no venting of any type that I could see. The space appears to be dry with no signs of moisture fro leaks or condensate. Is an unventilated attic a problem?
I have just finished my attic (July 2010) into a usable living space. Of course its rather hot in the summer. I am in the process of insalling soffit vents, but I am quite afraid that there will not be proper air flow because I do not have a ridge to incorporate a ridge vent– the roof of the my house is exactly the shape of the pink outline iullustration in the diagram you have shown. The top of the roof is flat (about 7′ x 12′) with no place to allow for incorporation of the air to exit at the top. The actual size of the house is 24′ by 25′. There are also two dormers on opposite ends of the south and north. What do I do? The contractor is literally on his ladder installing soffit vents, but do not seem to have an answer that makes me comfortable for how the air will be circulated. He says that the air will move through the baffles and down to the soffit. Please let me know if this strategy is best, because it makes me nervous since every article i read on venting an attic properly says that the air needs to escape at the top of the roof. I do not want to spend bad money, not to mention jeopradise the integrity of my home. Your quick response will be greatly appreciated.
Also, the soffit that is being installed is done by drilling three 3″ holes through the solid wooden soffit, and between each other joist– then installing aluminum soffit. I prefer individual soffits for the look. Is this sufficient…
In my cape house, I have a cathedral ceiling. I have a ridgeline vent and soffit vents, and side attics behind the two knee wall areas. Should the baffles go from the soffits to the ridge, or should the baffles only be used to separate the insulation from roof sheathing, meaning that they go from the kneewalls to the ridgevent?
Selecting a good roof that works well with the aesthetic appeal and efficiency requirements is a huge part of keeping your home insulated. Don’t invest all your time (and money) insulating a home that doesn’t have a reliable roof to support it.
In the south we see a lot of homes with asphalt shingles because of weather and climate restrictions. Asphalt is durable and economical for many of our clients.
Roofing Company Houston
The huge cost of roof repair may be expensive now, but it will save you more after a few years Roofers Austin
Im going to insulate the walls in the attic but my friend said its not necessary as we have insulation on floors, we have only 2 big vents in attic.
Hi Maxine,
The vents only need to seperate the insulation from the roof sheeting so it should not need to run clear down to the soffit. I just put vents in and ran them about a foot beyond the knee wall and up to maybe a foot from the ridge vent. The venting only has to be placed where insulation would meet the roof sheeting.
Thanks for the article. I am in the process of getting quotations from contractors to insulate my attic.
Two contractors have proposed blowing insulation into the sloped portion where you show baffles. They are not proposing baffles. In the lower triangular area they are proposing insulating the knee walls and the floor area.
My concern is there are no soffit vents and they will be blocking air flow to the upper attic by packing the sloped area. Will this lead to problems with humidity in winter and overheating in summer in this lower side attic?
thanks for any help you can provide.
Good point on itemizing the proper ways of insulation and giving a diagram so that the redeara could visualize the explanation.Keep up the good work and please post some more letters so that readers are encouraged to e-mail and share their roofing and home structure concerns.
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Good Day and Thank you for information, I have a question. What about an older home in NE U.S. with a slate roof that is at least 100 years old in good condition. Many older homes with Slate roofs here have no venting. Can I still insulate this way or better yet, spray foam to underside of roof. Thank you.
in this scenaro do I insulate the side walls all the way to the ridge or do I stop at the cieling?
is it best to change the ventilation when and if you ever repair or change your roof?
I have heard that you can cause damage and leaking if it isn’t done properly
Attic ventilation was one of the first things I did to my home in Palm Harbor, Florida. The attic get heated up so much in summer. 160°F is reached easyily.
With the attic fan I was able to decrease it below 120°F. And I can see it on my electricity bill.
I highly recommend installing a solar attic fan!
i’m updating my insulation and have the same design as the above diagram and was wondering about vapour barrier.the room is completely gutted to the studs and rafters,do i put vapour barrier around entire room between drywall and insulation?also how many baffles do i use and do they go all th way to the soffits?