Waterproofing Roofing Membranes

Waterproofing Roofing Membranes

Roof membranes — for flat and low-slope roof systems — belong to one of three types: plastic membranes, rubberized membranes and modified bitumen membranes

These three types of roof membranes comprise several sub-types and differences that make their comparison and rating very difficult.

The best roof membrane should provide waterproofing, durability, energy efficiency (to reduce cooling bills), cost-effectiveness and ease of installation.

The main function of roof membranes — for flat and low-slope roofs — is to keep the rain out of our homes; but they should also be used to keep the heat out, and to reduce cooling bills. Thats very important, even in cold climates.

Durability and waterproofing depend largely on manufacturing details and how the roof and the membrane is installed (mechanically attached, fully adhered). Thats why choosing a reputable brand and installer is so important.

Flat roofs and low-slope roofs are challenging in terms of waterproofing, even using the best and easiest to apply membranes.

Choose a good membrane from a reputable manufacturer, and an experienced and knowledgeable installer. Manufacturers technicians can help you through the choices and their pros and cons.

Energy efficiency

But also do not underestimate the energy-efficiency issue; roofing materials should prevent overheating (and high cooling bills).

To this end, choose the right roof membrane, with the right color and reflectivity. Membranes vary a lot in their reflectivity, and color is always important (lighter colors provide increased reflectivity, namely white elastomeric membranes). New roof membranes vs. Built-Up-Roofs

New roof membranes are replacing traditional built-up roofing, based on several layers of different waterproofing materials and fabrics.

Built up roof (BUR) membrane systems — commonly known as tar and gravel — are more difficult to built and more expensive. It involves alternating layers of bitumen (asphalt, coal tar or, in some cases, cold-applied asphalt adhesive) and reinforcing fabrics (ply sheets or roofing felts) and an elastomeric or aluminum coating, gravel or hot asphalt.

Rubberized membranes (Thermoset Membranes)

EPDM (Ethylene Propylene Diene Monomer), a rubber compound, is by far the most common type of rubberized membrane. Like plastic membranes, this is a single ply membrane with a good reputation for durability. An EPDM roof can last 30 years or more, properly installed.

Seams are a common problem; they render EPDM vulnerable and are a source of water leaks over the long term.

EPDM can be mechanically fastened, fully-adhered and ballasted (gravel, pavers, stones); it’s an economical choice for large surfaces.

White EPDM rubber membranes provide high levels of reflectivity (above 70%; often 80%). They are among the best for energy efficiency and to reduce air conditioning costs.

Plastic membranes: Thermoplastic Membranes

Plastic membranes for flat and low-slope roofs includes acrylic, TPO (abbreviation for Thermo-Plastic Olephine) and PVC thermoplastic membranes They are increasingly common, cheap and easy to apply.

They are single-ply membranes, very similar in their appearance. Installation methods are also very alike: the membranes are installed fully adhered or mechanically fastened.

As expected, thicker membranes are more pricey — and typically more durable and with longer warranties. PVC membranes are usually slightly more expensive and durable, but installation or details like their thickness can be more relevant.

Light-colored TPO roofs are the more energy-efficient.

Modified bitumen membranes

Modified bitumen membranes are very popular in residential low slope roofs.

Its a tested and effective option, but their duration, warranty and price depend largely on the number of layers. Modified bitumen can be installed using a torch or by factory-applied adhesives.

Duration is often limited to 10-12 years, but a good installation and maintenance can extend it up to 20 years or more.

Roof Membrane Manufacturers and contractors

Its very important to choose a good brand and installer, and manufacturers may help you find a certified contractor.

Look for high-rated and energy-efficient products.

When buying, pay attention to the manufacturer’s warranty, but also to the roofing contractor’s warranty. The manufacturer’s warranty covers membrane defects, while the contractor’s warranty often 1-2 years — covers installation and related issues (be sure of exactly what it covers).

If you are looking membranes, contractors or stores, see:

Energy Star list of qualified roof products: Energy Star list (PDF)

Stores with Energy-Star roof membrane products: Stores with Energy-Star roof membranes

NRCA (National Roofing Contractors Association) members: NRCA

Online resources

For more information, see:


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