How to Measure Roofs with Parapet Walls

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The Origin of The Parapet

The modern concept of a parapet wall dates back centuries. The term parapet comes from a word in the Italian language – parapetto, meaning “for defense.” Indeed, long ago parapets were only used on structures that called for an extra degree of defense from enemy invasion, such as forts and castles.

But not until The Great Fire of London in 1666 did parapets begin popping up as a feature on residential and commercial buildings. Due to that disastrous event, England instituted fire safety legislation that would spell an end to the wooden eaves which were now blamed for contributing to the rapid spread of flames and destruction. Architects would have to design something new to protect building facades from streaky water stains. But instead, they revived an old design – Parapet walls. Builders began extending the exterior walls just beyond the roof surface. And, like today’s parapets, these needed to include a system of scuppers, gutters and downspouts to direct rainwater off the top of a flat roof building and neatly down through spouts made, back then, of lead or cast iron.

Today, the primary function of a parapet wall is to protect the edge of a roof assembly from destructive wind forces called vortices (plural for vortex). And, with the trend in rooftop gardening and entertaining, parapets serve to save people from accidental falls. In commercial construction, parapets are ubiquitous and they are often required.

parapet wall

Measuring a Roof with Parapet Walls

Measuring a flat roof on a typical commercial building with a parapet can be arduous and complicated.  First of all, commercial and multi-unit residential buildings are a lot bigger than single-family homes, in most cases. Also, there may be several roof penetrations and other obstacles that should be factored into the measurement. Roofing material must extend up a portion of the parapet wall, as well. 

Illustrated above is a real-time roof measurement of a commercial structure with a parapet wall. Clearoof™ high resolution imagery, available only on the iRoofing app, takes the satellite image and sharpens it for easier, faster measurement.

Automatic Parapet Diagrams

When a commercial or residential roofing contractor provides a property owner or property manager with a roof report, it’s not really complete without a clear depiction of the parapet walls. Incorporating those walls in a professional sketch doesn’t require a draftsman or AutoCAD anymore, it simply requires an app like iRoofing. With it, parapet walls are indicated automatically on the roof sketch as flattened panels, similar to an unfolded pizza box. 

Accounting for Roof Penetrations

When dealing with parapet walls, the extra material needed to cover the vertical surface of the inside face of the parapet isn’t the only added factor to take into consideration. The sprawling flat roofs of commercial buildings frequently support a variety of objects, large and small, including AC units, roof vents, plumbing stack vents, boiler flues, exhaust fan vents, skylights, solar panels, and electrical conduit. (Incidentally, another benefit parapet walls is that they help conceal such eyesores.) Some objects require that roof material run underneath them, while other penetrations omit the need for underlying roof material. For the latter, measurements should ideally subtract the space taken up by those penetrations, such as roof-mounted AC units and skylights. With roofing software, you can simply trace the footprint of such objects and subtract them from the total measurement. This will make the basis of your material order significantly more accurate. You’ll reduce waste and ultimately calculate the fairest overall project price for you and your customer. 

The Quintessential Mobile Roofing App

To complement the new parapet wall feature in the iRoofing app, the company is adding more and more commercial products to its extensive digital catalog of roofing material manufacturers. Already, the platform carries the products of Johns Manville, Carlisle, Duro Last, Polyglass, GAF, Certainteed, Englert, and others. 

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