How to Insulate a Finished Attic

By: Bill Kibbel , Contributing Writer
In: Obsolete Design Elements, Home Improvement Tips

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.

  1. 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.
  2. 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

Finished Attic

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  1. 26 Responses  to “How to Insulate a Finished Attic”

  2. Oct 17, 2013
    A strong durable roof with proper insulation, ventilation and other important aspects are critical while developing the roofs. Make sure it is the best of quality.
  3. Barb Fahrer
    Jun 30, 2013
    I have a old house that has a finished attic. Can we lay insulation on the floor to help keep the heat from coming down into the house in the later portion of the day?
  4. jeff
    Aug 29, 2011
    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?
  5. Aug 29, 2011
    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!
  6. Aug 29, 2011
    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
  7. David Batten
    Aug 29, 2011
    in this scenaro do I insulate the side walls all the way to the ridge or do I stop at the cieling?
  8. Tom Vergeyle
    Aug 29, 2011
    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.
  9. Aug 29, 2011
    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. Atlanta Roofing HQ is a premier directory of Atlanta roofing contractors, suppliers, articles, videos, and tips that answers all your roofing questions and needs
  10. Kevin
    Aug 29, 2011
    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.
  11. Aug 29, 2011
    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.