How To Measure Your Home For Attic Insulation

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You believe you need fresh attic insulation, but how big is your attic? In this article, I will show you the quick and easy methods we use to get a good idea of the size of your attic during your virtual phone estimate!

Of course, the absolute most reliable method for knowing the size of your attic space is to get up there and measure it yourself! However, here at Bird Family Insulation we know climbing around in your attic is not a reasonable option for many homeowners. If you need to know your attic size without personally measuring it, consider these methods.

Measure the Heated Rooms Directly Under The Attic Space

Grab your tape measure, and measure the length and width of each room, hall, stairwell, closet, etc. whose ceilings touch the attic floor. Multiply the length x width, and you will arrive at ft2, (square feet). Total all your answers, and you will arrive at a good estimate of your attic size. Keep in mind, when the attic is measured by your attic pro, it will be larger, simply because we include adding insulation over top plates of your interior walls, and over the perimeter top plates. When you measure the rooms, you probably aren’t accounting for the walls.

Use Online Sites to Estimate Your House Size

This method of estimating the size of your attic space can get a little tricky. The accuracy of your answer will depend on the reliability of the website you are using, to have updated and useful information.

For our (phone) virtual estimates, we like Zillow. While our homeowner is on the phone with our attic pro, we use your address to pull-up Zillow’s information for your home. We read the pertinent information to you over the phone, “Does this description of your house sound accurate to you?” If you’re comfortable with what Zillow shares about your home, you’re in good shape! Simply take the total area of living space that you see listed, and account for the number of heated floors. Keep reading, and I will show you how.

Multi-Level Homes

Calculating the attic space for a (more-or-less) rectangular Multi-level home can require a few math drills, due to two-story entries, two story family rooms, drive-under garages, bonus rooms over garages, etc. We find these types of homes throughout Dunwoody!

Step One: If there is no drive-under garage, simply take your total ft2 and multiply by 50% (.5) for a two story home built over a crawlspace or on a concrete slab. Multiply by .33 if you have a finished basement that is included in your total heated living space.

Step Two: If your home has a drive-under garage with a heated room above it, perform the same math as in the paragraph above, and ADD 400 ft2 to your attic space. A typical two-car garage is a bit larger than 400 ft2, but the accessible ceiling space over that bonus room is smaller… sometimes much smaller! You’d rather over-estimate than come up short.


For those of us living in a single-level ranch house, it couldn’t be easier to know how big our attic is. There are loads of beautiful, large ranch-style homes in Tucker! The attic space is usually identical to the size of our living space. Exceptions are rooms that have sloped (vaulted) ceilings. I’ve climbed through plenty of attics where I had plenty of access over vaulted and tray (raised) ceilings. However, there are those homes with vaulted ceilings that are attached to the roof and may not be accessible for adding insulation. If you have an addition, and you’re not sure if the area above the ceiling is accessible, go ahead and include that area into your actual attic space calculation. Your attic pro will back-it-out during his home visit, if he discovers otherwise.


For the Exceptional, One-of-a-kind House Design

So you live in a retired architect’s home where he showcased all of his skill. I’ve seen some like this – especially in Midtown – where the online research and their descriptions leave me completely clueless. For these virtual estimates with homeowners over the phone, I simply tell them my average invoice for the service they are asking about, and follow-up with this: “For a phone estimate, let’s add ___ % due to the difficulty factor with your attic.” If my caller is comfortable with my estimate – they invite me to the house for an accurate quote and consultation, and either pay my consultation fee (currently $50) or schedule the project with a 20% down payment.

Don’t See Your House Described Here?

Some of our Atlanta neighborhoods, such as Morningside, Kirkwood, Eastlake, Grantpark, and other intown neighborhoods have 100 year old houses with what I call an “attic buildout”. Because the house roofline is so steep, a previous owner “built out” the attic into more heated living space, and added a stair for access. These older upstairs area’s can be an inferno and almost impossible for a homeowner to cool in the summer. These type insulation upgrades usually require spray foam insulation, and drill & fill insulation – and I simply give our caller our current average invoice for this type of insulation upgrade, without trying to calculate all the specific areas that need to be addressed.

Addition Built on the Back of the House

Do you live in a house with an addition built onto the house, and the addition has a shed roof? A shed roof describes a flat, sloped roof that is not peaked like a traditional roof. Usually, these roof designs have no accessible space – although I have seen exceptions. If we can thread our hose into the joist bays, we will – and fill these voids with high-performance cellulose insulation. Don’t worry about ventilation. It’s a small overall percentage of the entire attic, and we treat it like a vaulted ceiling. If you believe that your addition has a hollow space above the ceilings, simply measure the room and add that ceiling area to your calculation for the main attic!

If the addition has a peaked roof, and the ceilings are not vaulted – measure the room and add that area to your main attic space. We generally find a way to get above these types of rooms while in the main attic and improve the attic insulation.


If you aren’t actually climbing in your attic and verifying the accessibility above a vaulted or raised ceiling – it’s best to assume that it can be accessed by your insulation pro. Your insulation pro will back-out any ceiling area(s) that are not accessible for his crew.

In my experience, most homeowners would rather have the online or virtual estimate for their attic insulation upgrade to be a little higher, and we explain that our attic pro will accurately lower it to the exact quote when we perform the home visit, rather than be surprised with a higher insulation quote at the home visit.

Have you got an idea of your attic size? Congratulations! You’re now ready for your instant, online attic insulation estimate! Use my calculators HERE!

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