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# Calculating Roof Pitch

## Calculating Roof Pitch

#1
07-27-06, 03:47 PM
Member
Join Date: Nov 2001
Location: Washington State
Posts: 86
Calculating Roof Pitch

Getting geared up to start designing a gable roof 'on end' addition. The addition's roof line needs to match the existing roof line. What's the most accurate means of calculating the pitch? I don't have the design prints of the original house.

#2
07-28-06, 07:49 AM
Member
Join Date: Jul 2006
Location: St. Louis Missouri
Posts: 225
Roof pitch is usually stated as 4-12, 6-12, etc. which is some number of inches of rise for every 12 inches of run. A framing square and a level will usually give you an accurate (enough) reading. Go to the gable end. Hold the framing square along side the roof edge, long side horizontal, with the short side pointing down. Use the level on the horizontal side and hold the framing square with the 12 inch mark intersecting the roof line. The point where the roof line intersects the vertical side of the framing square will tell you the pitch. Be sure to use the same edge of the framing square for both numbers.

Be sure to compensate for any thickness differences in the shingles at the point you measure. (not a big factor with asphalt shingles, bigger for cedar shakes or tile). If your fascia board is parallel with the roof (most are), you could take the same measurements (upside down) underneath the fascia.

This is all easier to do than it is to explain.