How we build these pages

Every page on PropertyRoofs is written from published sources, checked against them, and reviewed by a person before it goes live. This page explains where the facts come from and what we leave out.

Where the facts come from

• Manufacturer data sheets and warranty guides, for thicknesses, attachment methods, seams and warranty terms. These are the manufacturers' own statements, and the pages say so.
• FM Approvals test standards, for how roof assemblies are rated for hail: FM 4470 for membrane, modified bitumen and built-up roofs, and FM 4471 for metal panel roofs.
• Federal guide specifications for roofing, published on the Whole Building Design Guide.
• Professional Roofing, the magazine of the National Roofing Contractors Association.

A general statement about a roof system needs two manufacturers' documents or a neutral source. When only one manufacturer says something, the page names that manufacturer.

How claims are checked

Each claim is stored with the words in its source that support it, and checked against the source document itself, never a search result or a summary. Each page lists its sources at the bottom with the month it was last updated, and a person reviews every page before it's published.

Warranties, not lifespans

Manufacturers publish their warranty terms, so the system pages show the warranty available, stated as the manufacturer's. A warranty's length isn't a prediction of how long a roof will last, and we don't publish lifespan figures unless a study supports them.

Costs

We don't publish cost figures yet. There's no free, authoritative dataset of commercial roof prices, so we're building ranges from public bid records: school districts and cities that publish the winning bid and the roof area for roof replacements. A range will appear only once about 30 projects support it, shown as the middle half of the cost per square foot, with the number of projects and the date beside it.

Brands

We name manufacturers only where we cite their documents. We don't rank them, endorse them or take payment from them.

Sources

Each page lists its own sources at the bottom. The publishers we draw on most are FM Approvals, the Whole Building Design Guide, Professional Roofing, and the technical libraries of roofing manufacturers including Carlisle SynTec, Elevate, Johns Manville, Sika, Duro-Last, Versico, Tremco, Garland, MBCI, McElroy, Butler and Gaco.