If you were stunned when your roofer quoted you for a 3200 square foot roof for your 1800 square foot house, here’s why: 

 1) Homes usually have two different square footages listed on a realtor’s listing sheet or the tax appraiser’s property records. One is the conditioned (heated and cooled) living area—which is what most homeowners think of as the square footage of their home—and the other is the total area under roof. A typical home that the owners know as being 1800 square feet may also have a 450 square foot two-car garage, plus front and back porches that total another 300 square feet, for a total of 2500 square feet under roof. 

2) But that’s just the beginning.  That 1800 square foot house typically has a two foot roof overhang that adds an average of 250 square feet of roof, for a total of 2750 square feet. 

3) Then the pitch of the roof adds more area. A 6/12 pitch roof (6 inches of rise for every 12 inches of run) has approximately 117 square feet of roof over every 100 square feet of floor below. In this case, the pitch would tack on an additional 450 square feet. That makes a total of 32 squares of roof for an “1800 square foot” house. 

4) Roofers calculate roof area in “squares,” with a square being 100 square feet of roof area. When you get a price for a new roof, the contractor may say something like “the roof works out to 32 squares and will be $9,500.”

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  To learn more about roofs and attics, see these other blog posts:

• Why is my roof sheathing sagging between the trusses?

• Why is granule loss a problem for an asphalt shingle roof? 

• What are the mistakes to avoid when doing attic improvements?

• What causes roof shingles to curl up at corners?  

• What causes shingles to buckle along a line on the roof?

• What causes leaks at a fake roof dormer? 

• What causes a sagging roof ridge line?

• What causes bubble-like blisters in a built-up and gravel roof?  

• Why does it cost so much more to replace a steep roof than a low slope roof? 

• What is "ponding" on a flat roof?

• Is an attic required to have a light by the building code? 

• How can I inspect my roof for hurricane damage?

• Why is premature curl of roof shingles a problem?

• How can I tell if a roof has more than one layer of shingles? 

• What are the common problems with attic insulation? 

• What is the life expectancy of an asbestos cement shingle roof? 

• What's the average lifespan of a roof?

• Why is it a mistake to replace a roof and not replace its flashings? 

• Why is there no attic access hatch in the house?

• What is the building code requirement for an attic access hatch, scuttle, or door? 

• Does a roof with multiple layers of shingles last longer?

• What can I do to prevent roof leaks?

• Are roof trusses better than roof rafters (stick framing)? 

• Why is a popped nail in a shingle roof a problem? How do I fix it?

• What are the most common problems with wood roof trusses?

• What causes a lump or dip in the roof? 

• If my roof is not leaking, why does it need to be replaced?

• How can I be sure my roofing contractor got a permit?

• How many layers of roofing are allowed on a home? 

• What are the dark lines running parallel to shingles on my roof?

• Can metal roofing be used on a low slope/pitch roof? 

• How can I make my roof last longer?  

• What are the warning signs of a dangerous attic pull-down ladder?

• How can I find out the age of a roof? 

• Should I buy a house that needs a new roof?

     Visit our ROOF AND ATTIC page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.