How To ...

Here we'll tell you all how to match an exsiting roof, measure roof pitch slope, and measure heel height to help you place your order.

How to Match An Existing Roof


To match trusses to an existing trussed roof, follow the steps below for an accurate fit.

1. Measure the length of the bottom chord (1.)

2. Measure the length of the overhangs not including the fascia (2.) making sure to check both sides.

3. Measure the heel height (3.) or "thickness" of the truss at the ends from the bottom of the bottom chord to the underside of the sheathing. Click on How to Measure Heel Height for more details.

4. Measure the overall height (4.) from the bottom of the bottom chord to the peak. If you cannot accurately measure this, use the How To Measure Pitch / Slope details.

5. If the peak is not centred in the middle of the truss, fill in both mesurements (5.)

6. If the walls are not located at the end of the truss measure (6.) from outside of wall to outside of wall. Note any siding or brick face.

7. Note cantilever distance (7.) from outside of wall to end of truss - not end of overhang.

Truss Matching

How To Measure Roof Pitch / Slope


If you cannot measure the height of a roof accurately, the next best way to measure the roof pitch on an existing building is with a 48" level and a tapemeasure.

Roof pitch or slope is usually expressed in as "X/12" or "RISE over RUN"

Carefully climb onto roof (ensure to use proper tie-off methods or scaffolding) and hold a 48" level so the bubble is in the middle. This will be your RUN.

Next, measure from the end of the level down perpendicular to the top of the roof. This number will be your RISE. 

Take this number and divide mathmatically by 4 to get your pitch. This only works with a 48" level. If you are using a 36" level, divide by 3.

For example, if you measured 40" perpendicular from a 48" level then your pitch would be (40" / 4 = 10) and (48" / 4 = 12) or 10/12.

If you measured 24" perpendicular from a 36" level then your pitch would be (24" / 3 = 8) and (36" / 3 = 12) or 8/12.

For accuracy, we do not suggest using a level less than 36" long.

How To Measure Roof Pitch

How to Measure Heel Height


Other than Roof Pitch and Span, the most importand measurement need to match an existing roof is called the heel height.

Simply, it is the "thickness" of the truss or rafter measured from the outside of the wall from the top of the top plate to the underside of the sheathing.

Below are two diagrams to help illustrate the point.

Truss Heel Height

Birdsmouth Detail Standard Stick Frame Overhang