Measuring a Roof Safely

Measuring a roof from the ground can be a much safer way to get the information you need to do a roof.

This week I was asked to teach a new solar estimator how to measure a roof from the ground.

The basic idea of measuring a roof from the ground may sound ridiculous but it can be done and done very accurately. I think everyone should measure at least the perimeters of the roof from the ground because the risk of a fall walking along the eaves of the roof can be avoided. If you are a professional and you are up and down ladders, crawling around steep, wet, damp and slippery roofs year in and year out, the odds are against you. These tips can reduce the risk of a fall. This web page is to show how the whole roof can be measured from the ground and a order for materials to be placed.

So, What tools do I need to measure a roof?

1. Tape Measure. a 25 foot or longer works well. I use a laser for speed and it is very accurate. There measuring wheels that work well also.

2. Graph Paper, some basic graph paper will help keep straight lines and scale your roof drawing. I use a two-foot scale drawing and most size homes will fit on an 8.5 x 11 sheet of paper.

3. A calculator is an important tool since it will help you with complex math with less or no errors.

4. Pitch Gage, will be needed to find the pitch of a roof. There are pitch gage Apps for smartphone free to download.

Familiarize your self with the names of the parts of a roof, like the Gable, Hip, Valley, Eave, and Ridge. Take a minute before you measure and Google your roof then highlight these parts of the roof like seen here to the left. It will help with your drawing later. Start from the left corner and start taking the measurement from the eave to eaves all around the home. Using the graph sheet you should end up right where you started. If you don’t, then you made an error somewhere.

Once the site drawing is done look at the drawing and in a red marker draw out squares like seen in this drawing.

A, Is { 48′ x 24′ } B, { 16′ x 24′ } C, { 12′ x 24′ } and D, { 6′ x6′ } Do you see the squares? Add these four totals and you have the foot-print of the roof which is 1860 sq. ft. Now we need to add the pitch factor which is the rise of the roof. Most homes have about a 4:12 pitch or 18.5 degrees. This is as low a pitch as you want when installing asphalt shingles. This roof we are measuring today is a 6:12 pitch or 26.5 degrees. The pitch factor I use for this is 1.12. This factor should be times the house footprint, 1860 sq. feet and your roof size equal 2084 or 20.84 squares. Let's call it 21 squares. Determine the waste factor and you have the total roofing sqs. you need to complete this roof.

Now to determine the length of the valleys and hips needs to be calculated using the hip factor of 1.50 for a 6:12 pitch. So here in the front right side is a hip roof and the width is 24 feet. x 1.50= 36 feet, divided by 2 for each side which equals 18 feet for the hip length. The valleys are the same formula as the hips. For this short valley on the right being 6 foot equals 6 x 1.50 = 9 ft.

The eave should be looked at by a ladder to see how many layers of shingles there are on the roof. With a good roof flashing count, you can place a materials order to the supply house. Here are the pitch factors rounded up for calculating the squares of a roof.

Degrees converted to roof pitch 9.5° = 2:12, 14° = 3:12, 18.5° = 4:12, 22.5° = 5:12,

26.5° = 6:12, 30° = 7:12, 33.5° = 8:12, 37° = 9:12,

40° = 10:12, 42.5° = 11:12, 45° = 12:12

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Disclaimer: The information provided on AskARoofer.com or information sent by emails is the opinion of the writers. It is the responsibility of the reader to check for accuracy in one's own jurisdiction, as there are different codes and restrictions for different parts of the country. AskARoofer.com does not accept any liability for the use of information on this website or email. AskARoofer.com has no controls over product failures, installation, or climate conditions that may change the roofing process in your area. Our information is in general to our area and cannot be the same as your local town or state. It is advised to seek the local Building Department, Licensed Contractor and local Product Representative for proper installation requirements and code enforcement when installing a new roof.