The Flexural Strength of Asphalt Shingles

Flexural Strength

• Flexural strength indicates the ability of a building material to resist failure through bending. This measurement provides information on how much weight you can place directly on top of something before it bends far enough to break. Flexural strength measurements prove common in heavy building materials like concrete, metal beams and surfaces like floors and roofs. Builders measure flexural strength by loading small concrete beams or other weights on a suspended material until it breaks, then measuring the full weight of the beams the material held before reaching breaking point.

Asphalt Shingles

• Asphalt shingles generally contain three layers of material, a mat, the primary compositional elements and a top layer. The mat, made of fiberglass or organic felt, supports the shingle and helps it adhere to the roof. The primary material, usually a mixture of asphalt and fillers like small stones or tar, makes up the bulk of the shingle. The top layer contains mineral granules for UV protection and impact and fire resistance. Builders use asphalt shingles because they resist extreme temperatures; don’t degrade with constant moisture, snow and rain buildup; require little maintenance and keep costs down; and resist fire and strong winds.

Asphalt Shingle Flexural Strength

• Measuring the flexural strength of asphalt shingles is a difficult task and a potentially pointless one. Roof shingles provide no weight support – they protect the roof from weather and UV damage. The actual roof – its beams, frame, trusses and more – supports weight. Because of this, manufacturers do not design asphalt shingles with flexural strength in mind and provide no flexural strength information on shingles. Furthermore, measuring flexural strength requires placing concrete beams on something until it breaks. Asphalt shingles are usually small enough that placing concrete beams or weights on top of them may not work at all.

Asphalt Shingles vs. Asphalt

• You should never use asphalt shingles in weight support applications unless a manufacturer specifically designs them for this purpose. Though new shingles may exhibit a high degree of flexibility, they can support very little weight. Asphalt, as found on roads, on the other hand, exhibits a high degree of flexural strength. It requires flexural strength in order to support the constant flow of extreme weight from cars, trucks and other vehicles. The flexural strength of asphalt depends upon the quality of the mixture used to create a batch of asphalt.