Measuring a roof area
For many people; the idea would never cross their mind, that they may ever have the need to measure their roof for roof shingles.
Invariably; for most homeowners, the time will come when somebody will have to measure their roof either when a replacement roof is needed, or when some structural change involving a permit, may become a requirement.
Due to the height and steepness of many roof configurations; it is typically not advised that people attempt to measure their own roofs. But it can be very important to those who are purchasing a replacement roof, to understand how a roof should be measured properly, and why.
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What are some common mistakes of measuring a roof size?
In my thirty plus years of experience as a roofing contractor, I can tell you that some people who are in the business of measuring and calculating roofs don’t do it properly. Many of course do. The problem for a homeowner comparing estimates is that they may not know which type of person they have had evaluated their roof.
As an example, I have witnessed people get out of their truck, and literally guess from the sidewalk. “ looks like about this size….”. I have also witnessed people read a measurement of 84’ on a tape measure, and record the number as 48’. A simple error, but a significant error nonetheless. I have further witnessed people who could not do the mathematical calculations required to determine the area of a triangle or an obtuse shape.
Why is it important to have an accurate roof measurement?
As a homeowner reading this; you may be saying ”so what”. If someone makes an error; perhaps this is in our favour.” The answer is, that often when an error is made on measuring, and a contractor has effectively under-sold the job; that corners can be cut, to make up for costs that were not originally factored into a job. Another result is that a job can drag on because of a material shortage is which is discovered when the project is underway.
Where a homeowner should be concerned is during the estimate process.
It is a good idea to ask the estimator to demonstrate how they arrived at the roof’s size. Here’s why:
- Because in addition to the actual raw square footage of the roof; extra materials will have to be factored for cutting, waste, and installation method. For example; on a large roof, if starter shingles are not being installed along rake edges, and lining both sides of valley areas; this can result in a difference of a few, to several hundred square feet of material and labour. The result will be one contractor demonstrates a lower price versus another, whom may be actually doing the job to a better standard.
- On roofs having a gable design; there is typically less waste, and so factoring 5% on the actual roof area is an accepted standard.
- On roofs which have a hip design (four-sided, or multi-sided ), having triangular, and or rectangular roof slopes; the waste factor is minimally an additional 10%.
- On roofs which have dormers, valleys, or unusual roof plains; the waste factor can increase to 15%-20% above the actual roof square footage.
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How does technology improve accuracy?
Technology in the form of areal measurements, taken from satellites, drones, and planes, is often used by professional roofing contractors, and those in the insurance, and construction industries; to obtain accurate imagery, and measurements for roofs, and exterior walls of homes and buildings.
This technology helps to insure accuracy for the purpose of calculating estimates, and saves valuable time to collect such information. Further; today’s health and safety requirements are making it difficult for estimators to do their jobs in compliance with the law, because of the need for safety harnesses, and support brackets to enter the roof. Particularly steep and tall roofs are difficult to mount, especially when just to supply a quotation.
The need for basic geometry skills, and the ability to look at complex roof designs and break them down into squares, rectangles, and triangles are must have skills, in spite of today’s technology advantage. This is needed when looking at blueprints as an example.
How to measure a roof for shingles (step-by-step)
The process of accurately measuring a roof involves first making a diagram of the roof to show the basic shapes of each roof plain and how they relate to one another. Then each measurement is recorded on the diagram, applicable to that roof surface. Required measurements include the following:
1) Length of all slopes ( measure from ridge to eave length)
2) Measurement of all hip rafters ( length from ridge to eaves)
3) Measurement of all roof eaves areas ( bottom roof perimeter areas)
4) Measurement of all valley areas ( where two opposing slopes intersect at an interior plain)
5) Measurement of all dormer surface areas ( whether they be sloped and / or wall areas)
6) Pitches should be noted for each roof plain (rise and run; which means how many inches a roof inclines over a 12’ horizontal plain)
7) Notes should be made on the diagram to reflect locations of items such as chimneys, vents, pipes, skylights, associated flat roofs, and their related details.
8) Based on roof plains that have a similar pitch; calculations should be completed for that specific pitch. The process is completed for each different pitch category.
9) Once the actual roof square footage is determined; the appropriate waste factor must be added for cutting and waste.
10) For purposes of shingles, extra material must be factored for starter shingles used at rake edges, roof eaves areas and for lining both sides of all valley areas. To convert linear footage of such items into square footage, one would divide the linear measurement in two, and the result would be a square footage calculation.
11) Also to be factored will be the additional shingle materials required to cover hips and ridges in “shingle caps” ( what covers and adjoins two opposing exterior roof plains). Depending on the product type used; which can vary between manufacturer and roof shingle type; the linear footage of hips and ridges, is then divided by the exposure of each individual shingle cap. This determines the number of caps required to complete the job. From there the area of caps supplied by the manufacturer, can be calculated against the required need for the specific project.
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To learn more about measuring and assessing roofs; contact www.avenueroadroofing.com .