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Musings of an Energy Nerd

All About Attics

Answers to frequently asked questions about the space under your roof

Although this attic is clean and attractive, it wasn't designed by an energy-conscious builder. This unconditioned attic includes ducts that should have been located within the home's thermal envelope.
Image Credit: Todd Neville

Most six-year-olds can draw a house. The typical child’s depiction of a house shows a rectangular building with a door and a few windows, topped by a gable roof.

This type of house is fairly common in most areas of the U.S. If the house was built 100 or more years ago, it usually had a cellar or basement underneath the first floor and an attic above the top floor.

In the middle of the 20th century, modern architects attempted to do away with basements and attics. They designed flat-roofed homes on slab foundations. While many Americans are happy to live in this type of home, others feel that basements and attics are useful spaces, and have no desire to see them go away.

As originally conceived, attics were supposed to be outside a home’s conditioned envelope. Because of their location, however, attics (along with basements and unheated mudrooms) actually represent a type of in-between area that isn’t quite outdoors and isn’t quite indoors.

Types of attics

There are several kinds of attics:

  • The classic attic is located above a flat ceiling and has the same footprint as the house below.
  • Some attics are smaller than the footprint of the house, like the attic above the second floor ceiling of a Cape.
  • Some attics have a triangular cross section, like the attics behind the kneewalls on the second floor of a Cape.
  • Some attics are low spaces without enough room to stand up, like the attics under a flat or low-slope roof.

Traditional attics under steep-sloped roofs are easy for builders and insulation contractors to work in, while cramped attics with difficult access are not builder-friendly.

What are the advantages of a traditional attic?

A house with a traditional attic has several benefits compared to a…

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  1. prairieburner | | #1

    I used emergency blankets as
    I used emergency blankets as a staple-up radiant barrier and did the work myself. I got a 50 pack on ebay for $30. Works out to 1500 sq feet. Dirt cheap.

  2. GBA Editor
    Martin Holladay | | #2

    Response to David D.
    Installing blankets that have not been approved as building materials in your attic, as you describe, raises all kinds of issues, including fire safety issues.

    Moreover, if a building inspector ever noticed your work, or if you ever wanted to sell your house and a home inspector poked his head in your attic, the 50-pack of Ebay blankets might come back to haunt you.

    Leaving aside these issues of code compliance and fire safety for the moment, it's certainly possible for a homeowner to safely install an attic radiant barrier. It's best to purchase materials intended for the purpose you use them for, of course. While researchers looking into the payback period for this type of retrofit work have calculated that the payback period is very long indeed when the homeowner has to pay a contractor for the installation, it may make sense to install a radiant barrier if the labor costs are free.

  3. Expert Member
    ARMANDO COBO | | #3

    2012 IECC
    2012 IECC upgraded the insulation requirements: CZ1=R30, CZ2-3=R38, CZ4-8=R49

  4. GBA Editor
    Martin Holladay | | #4

    Response to Armando Cobo
    Thanks very much for your comment. I have edited the article to include information on the new 2012 requirements.

  5. jackofalltrades777 | | #5

    Attic Roof Trusses
    Talking with some firefighters who have fought a lot of house fires over the past couple of decades. A resounding statement was made known to me. Firefighters HATE modern attic roof trusses. The reason they gave was they are very weak in a fire situation and fail fairly quickly in a fire, causing the roof to collapse. When fighting house fires that have older timber, the roofs stay together much longer in a fire than modern roof trusses.

    I did some research online and from what I gathered it appears that modern day roof trusses use very low density, young growth trees to create the roof trusses. In a fire this dimensional lumber fails at a faster rate than old growth, high-density timber that was used years ago. Unfortunately, people want cheap and fast attic spaces and trusses are used in 95% of residential builds. Some custom homes that utilize heavy timber or glu-lam beams to create the attic space would do a lot better in a fire. While the homeowner probably doesn't think about this issue but the firefighters sure do.

    Also during my research it showed that roof trusses on modern homes are the first thing to fail in a high-wind event (microburst, tornado, hurricane, etc). Hurricane clips have helped to tie down the trusses to the wall top plates.

  6. Peter Hastings | | #6

    Plant in Attic Spaces
    I am currently planning a single-storey home for retirement - rectangular floor plan with a cathedral ceiling over the living/dining/kitchen space and flat ceilings above utiliy, bath and bedrooms. Obviously, I will need a sloped-roof-with-high-insulation-levels solution for the cathedral ceiling and I intend to continue this for the entire length of the house. This will give me a conditioned attic space which I plan to use principally for plant, ducting, pipework and cabling - all exposed, labelled, insulated (as needed) and accessible in a floored attic. Access to the attic is by a fixed ladder in what is, in effect, a stairwell directly opposite the front door of the house. The bottom of the stairwell will be hidden by a pair of doors.

    Are there any pieces of plant that really should go in the attic or, alternately, never go in the attic ? I expect to have a considerable amount of hot water storage, an HRV and its associated ductwork. The house is intended to be all-electric (grid-tied P-V) with a wood-burning stove for occasional winter use and some, electric, underfloor panels. Pros, cons and caveats welcome...

  7. STEPHEN SHEEHY | | #7

    response to Peter Hastings
    Your plan sounds much like my new house. We opted for a small mechanical room which will house the water heater, hrv, laundry, electrical panel, well pressure tank and also provide some storage. We'll also be using a utility chase that runs the length of the house, above the kitchen, bathrooms and mechanical room.

    Putting something like the hrv up in the utility space creates considerable inconvenience when doing any service or maintenance. And unless the space is tall enough, doing any work up there will be difficult.

    If you just run wires, pipes and ducts, but no mechanical equipment, you shouldn't ever need access and could skip the stairway.

    As for hot water storage, that will mean seriously beefing up the framing.

  8. Expert Member

    Peter L, As the president of our local fire department it's nice to hear builders thinking about firefighter safety, but in this instance i wouldn't use the difficulty in fighting fires as determinant as to whether to uses trusses or not. When new construction techniques are introduced they often pose a challenge to firefighters. This is true of light steel framing, foam, roof trusses and many others. Some are too dangerous and are legislated against. Most, like trusses, simply require a new protocol for fighting fires in buildings where they are used. In both Canada and the States firefighters train how they must approach these structures using guidelines developed by the occupational health and safety authorities.. Once you know what to do they pose no more risk than any other building. None of the firefighters in our department have any compunction dealing with trussed roofs.

  9. GBA Editor
    Martin Holladay | | #9

    Response to Peter Hastings (Comment #6)
    Since you are planning to build an unvented conditioned attic, your attic will be inside your home's thermal envelope -- so it's possible to locate your mechanical room in your attic.

    The main disadvantage to locating your mechanical room in your attic is access. If your hatch is narrow and your ladder is steep, regular maintenance tasks (like filter changes) may get ignored. If you can alter your design to change your ladder to stairs, access will be easier.

    All mechanical rooms deserve excellent lighting, so don't skimp on light fixtures. The more, the better. These light fixtures won't be operated for many hours per year, but when you need them, you need lots of light.

  10. rjparker | | #10

    Nice job of consolidating attic options and issues Martin. Peter, I wish I had the opportunity to build new as you are, congratulations. I am not sure if you are planning on a conventional water heater in the attic. Personally my use of the conditioned attic space would avoid large equipment that will need to be replaced at some point and I would not put water heaters or water storage up there. Leaks are very likely and conventional water heaters often get much heavier when mineral build up occurs. Finally if you are using spray foam to insulate an equipment space, be sure to protect it with drywall or other approved firebreak strategies.

  11. Peter Hastings | | #11

    Thanks to all
    Thanks to all of you who have replied. The next iteration has the MHRV down on the first floor in the utility room so that routine attention is straightforward. All the services are concentrated in the central third of the floor plan so I now intend to have some sort of room (den/office/overspill sleeping) in the gable end of the attic. I'll change the ladder for stairs (turn right at the top for services and left for the den) and make all the attic joists and flooring able to take significant live and dead loads. The hot water tank(s) will live up there - heated by grid-tied P-V and, occasionally, off-peak cheap-tariff grid electricity. Thanks again.

  12. user-998246 | | #12

    How to insulate an old walk up attic.
    I have a home built in 1850 with a walk up attic (via a full size door and staircase) with sloped ceilings and a few windows even. The home is constructed of brick exterior walls with plaster on the interior so little opportunity to insulate within walls. The attic, however, has a floor so I am wondering if it is possible to blow insulation into the attic, beneath the floor without having to tear up the floor. I'm sure that ideally you would want to seal all ceiling openings and possibly fixtures but tearing up a 2000 sf of 165 year old floor seems like it could be a bear.

    Also, with regard to fire safety, old heavy timber is one of the best building materials available. In a fire, the structural members char, which then acts as a form of insulation, protecting the dense core. Some of the worst can be light gauge steel and laminated or glued members such as joists and trusses, which yield relatively quickly when exposed to fire conditions. This is all before you account for fire fighter operations such as application of water hoses or sprinklers.

  13. GBA Editor
    Martin Holladay | | #13

    Response to Joe Schmo
    It would be helpful to have a little more information.

    1. Where are you located? (Or what is your climate zone?)

    2. Is there any existing insulation under your attic floorboards? Or is your attic totally uninsulated?

    It's almost always worth the hassle to perform air sealing work before you install insulation. Fortunately, old floorboards are fairly easy to remove and reinstall.

    You don't need to remove all of the floorboards -- just the ones near the areas that need to be air sealed. These areas include: around chimney chases; around plumbing chases or plumbing vent pipes; near bathroom exhaust fans; above soffits or suspended ceilings; and above partition top plates. For more information on the necessary work, see Air Sealing an Attic.

    Once the air sealing work is done, you can install as much cellulose insulation as you like. It should be fairly easy to blow cellulose insulation through holes in the floorboards. You can install additional insulation on top of the floorboards if you want.

    Don't forget the critical work of air sealing and insulating your attic stairway. For more information on this task, see Insulating Attic Stairs.

  14. user-998246 | | #14

    Do walnut shells count as insulation?
    I am located in Frederick, MD and there is no existing insulation. The house has a modern hvac system with insulated duct work in the attic but otherwise its uninsulated.

    I will see if I can discern where various ceiling penetrations might be and see what i can get at. The existing plaster work is actually quite extensive (with very few cracks or openings) and much of the electrical and piping is mounted on the interior of the walls since the house was built before most electrical and indoor plumbing existed.

    I've yet to find a good design for how to insulate the door to the attic since it is at the end of a narrow hallway as opposed to the type where the door is laid at the top of the stairs.

  15. GBA Editor
    Martin Holladay | | #15

    Response to Joe Schmo
    If there are ducts in the attic, it makes more sense to install insulation at the sloping roof line above the attic than it does to install insulation on the attic floor.

    For more information, see:

    Keeping Ducts Indoors

    Creating a Conditioned Attic

    Concerning your attic access door, the situation was discussed in my article, Insulating Attic Stairs. In that article, I wrote:

    "The usual location of the air barrier is at the base of the stairs. In this case, you’ll need to make sure that the door is insulated and weatherstripped. If you don’t want to buy an exterior door, you can attach a layer of rigid foam to the back of your existing door, and you can reduce air leaks by installing weatherstripping.

    "The two triangular walls on either side of the stairway need to be insulated. The underside of the attic stairs—the sloped ceiling created by the bottom of the stair stringers—also needs to be insulated and air sealed. This can be tricky; treads and risers usually leak air, and there isn’t much room above the sloped drywall to accommodate insulation. One approach is to remove the plaster or drywall under the stairs and to spray polyurethane foam against the treads and risers from below. Or, if the headroom is generous, it may be possible to install one or two layers of rigid foam in this location, followed by a new layer of drywall."

  16. TheEnergyGuy | | #16

    Do attic fans make occupants feel cooler when they're on?
    I fully understand the heat transfer logic behind powered attic ventilators and why they don't make sense. What I can't explain is why I have - repeatedly over the years - had customers swear they're so much cooler when the attic fan is running! How could this possibly be? A breeze from the makeup air flowing through exterior walls as conditioned air is drawn into the attic from ceiling leakage by the fan? =;-)
    I'm in the Sierra Nevada Foothills of California with customers from 1,000 ft to 4,000 foot elevation.

  17. GBA Editor
    Martin Holladay | | #17

    Response to Ray Darby
    Even though the customers you quote use a confusing term ("attic fan"), I'll take your word for it that they are talking about a powered attic ventilator, not a whole-house fan.

    There are a couple of possibilities. One possibility is the placebo effect, which has been proven to be a real effect in a variety of fields. (If they can hear the fan, the hum of the fan might evoke a Pavlovian placebo response.)

    The other possibility is that the fan sucks so much conditioned air through ceiling cracks that the indoor air warms up, causing the air conditioner, which was previously idle, to kick on -- giving the occupants a feeling of relief due to the cool air coming out of the HVAC registers.

  18. TheEnergyGuy | | #18

    Response to Ray Darby
    Yes, we're talking attic ventilators (bad fans), not whole house fans (good fans), not ceiling fans (somewhat good fans), but most of these folks have no AC! It's virtually impossible to convince them that the attic ventilator isn't making them feel cooler. I've tried. But I'm with you, all I can chalk it up to is the Placebo effect, but it's tough to tell customers they're imagining things when you're trying to build a relationship! Thank you for letting me share my frustration. PS - GBA and your posts are always spot on and much appreciated, I look forward to every one, thank you!

  19. dddjaafar | | #19

    attic furnace
    I recently bought a remodeled small colonial. It has two floors living space, a full basement and an attic with thick foam insulation ( do not know if open or closed cell) with a furnace in the completely foam insulated attic with only one tiny window. My house is located in Peabody Ma. which has long cold winters and hot summers. Since living here now 2 winters I have had many negative experiences. The first is a freezing cold basement that in turn makes the 1st floor very, very cold. I keep thermostat ( only one level temperature control) at 60F in winter and 71F in summer. My second floor with bedrooms, bathroom and the office is astonishing hot. My little grandson's playroom registers consistently between 80F -90F (I have placed a small digital temperature/humidity thermometer on the wall away from windows or sun. When the outside temperatures are 0F-38F and the only thermostat on the first floor is set to 60F, the playroom is, at least, 80F, and frequently in the 90's. I keep the window closed in this room. The colder outside the hotter inside. I have my bedroom thermometer recording 70F+ WITH 2 WINDOWS OPENED WIDE ALL WINTER! I feel waves of heat radiating down from the ceiling in all the upstairs room, and I am not referring to the vents in the ceiling. The ceiling is frequently hot to touch.
    I also have experienced numerous occasions of frozen pipes both downstairs and upstairs when the outside temperature drops low. I have lived through many days waterless and forced to melt snow for the toilets. I have installed an electric blower, on high it brings the basement above freezing. I also had pipe warming coils on the water pipes. Neither has prevented my pipes from freezing or improving temperature on the first floor. I have been told that it was a mistake to have placed the furnace in the attic. In the Northeast is is more appropriate for furnaces in the basement. Is the placement of the furnace in a fully foam insulated attic causing my pipes freezing and the horrible temperature discrepancy between the various levels of the house? What could I do to help address these problems. Thank you
    Domenica D. Djaafar

  20. STEPHEN SHEEHY | | #20

    Furnace inside or outside the conditioned space?
    Domenica: You want your furnace inside the insulated space. You say it is in the attic, but is it above the insulated attic floor (bad) or under the insulated roof (OK.)

    I doubt your problem with a cold first floor is caused by the location of the furnace. You probably need to airseal and insulate the bssement walls. My former 200 year-old house was much more comfortable and easy to heat once i had that done.

    Massachusetts has lots of energy efficiency programs. I'd look into having an energy audit done and see what is recommended.

  21. GBA Editor
    Martin Holladay | | #21

    Response to Domenica Djaafar
    The reasons for this situation are clear. The problem is that you are leaving your bedroom windows open all winter as you try to heat your house.

    You have an extremely leaky house (due to the open windows). Hot air is leaving your bedroom windows all winter long, at a tremendous rate. To balance this exiting air, cold outdoor air is being pulled into your basement through cracks near the sill and rim joists -- cold air is rushing into your basement, all winter long.

    The result is predictable: "My second floor with bedrooms, bathroom and the office is astonishing hot." Of course it is -- your furnace is running full blast, 24 hours a day, trying to make up for those open bedroom windows.

    "I also have experienced numerous occasions of frozen pipes both downstairs and upstairs when the outside temperature drops low. ... the basement [is] freezing." Well, duh! Huge amounts of outdoor air are being pulled into your basement to make up for you open bedroom windows.

    The solution is clear:

    1. Close the darn windows already.

    2. Seal up all those air leaks in your basement.

  22. dddjaafar | | #22

    Thanks for the responses
    I am getting an energy audit for heating, insulation and electrical status of my house. That was a great suggestion. I think I will have to get consults on how to best treat basement.
    By the way, last night I did close my windows, and it was 83F in my bedroom and the thermostat downstairs was set on 60F. My grandson's playroom recorded 87F, this room is directly under the furnace and the ceiling access to the attic is in that room. I wish I could figure out why it is so hot upstairs. I know warm air rises cold air sinks. The difference is 20+ degrees Is that normal? Thank for your time and advice. I have a few
    areas to work on. Sincerely, Domenica

  23. GBA Editor
    Martin Holladay | | #23

    Response to Domenica Djaafar
    I'm glad that you closed your windows. My guess is that:
    1. Your house is very leaky and would benefit from air-sealing work.

    2. Something is wrong with your heating system. It needs to be balanced so that it directs more heat to your lower floors, and less heat (or no heat) to your upper floor.

  24. dddjaafar | | #24

    understanding the why and hows of heat and insulation
    Thanks again for additional response. I have lived in many other houses old and new, never experienced this problem. I will have a thorough consult for the basement environment.Since you have all indicated that improving the basement will go far in improving the overall heating issue.
    I am at a loss to convey the extent this heating problem has made it so unpleasant to live here. Every single person visiting my house has been astonished at the range of temperatures.There is clear demarcation half up the stairs between the cold and hot zone. Everyone makes the same comment. "Oh my God, how can you stand it?" I was assured by the builder who did the rehab on the house that the system needed to be balanced. He "balanced" the system several times without significant improvement.
    I chose to inquire about my problem on your site because you all seemed to be so knowledgeable and have impressed me with so much great information available on this site. I am trying to understand how and why of the principles of heating and cooling with best results for our environment. I do not want to waste, but I think this excessive heat upstairs is affecting me physically, and of course, stressing me out. I was assured the house is "like new" all systems recently installed and to expect no problems. I do not know about you but trying to sleep with currents of heat rolling over your bed, makes it challenging.
    I wish the builder could spend the day (all day and night) and experience the situation for himself. I did not expect to spend so much time and money on a brand new system. I will have a HVAC specialist evaluation and make a plan. All this is very costly especially for a woman of my age and disability. I need to learn more about the principles and guidelines of this system. I depended on the builder's assurances. Now I realize I made a mistake and now I need education. I wonder can anyone suggest where I can go to learn more of the function of heat and insulation, heat and air exchange, that can be understood by the ignorant homeowner. I do not want to make another expensive mistake. I must rectify this system before next winter. I could use a bit of a road map as you folks are experienced and understand what should be prioritized. Any additional suggestions and/or direction would be most appreciated. With my sincere regards, Domenica

  25. GBA Editor
    Martin Holladay | | #25

    Response to Domenica Djaafar
    It is fairly common for older homes to be cold on the lower floors and hot on the upper floors. The main cause of this phenomenon is the stack effect. Here is more information on the issue: The Stack Effect: When Buildings Act Like Chimneys.

    When the temperature stratification problem is as severe as the one you describe, it's usually a sign of very large air leaks. It was easy to figure out where the huge air leak was on your top floor -- it was your open bedroom windows. The air leaks in the basement have yet to be located and sealed.

    Undoubtedly, a badly designed heat distribution system must be part of your problem.

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