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Repair a low-pitched roof with a membrane

Dear Ms. Builder: I have an older house. The attic was converted into a Cape Cod type bedroom for children. The old asphalt rolled roof is leaking again. What do you suggest as the best method to fix it? - Michelle G.

Dear Michelle: Your problem is certainly not unusual, especially for the type of attic conversion that you have on your house. Asphalt rolled roofing was the preferred type of roofing used for flat and low-sloped roofs. It was less expensive to install as compared to the alternatives (tin or copper) when your house was built.

A quick mop over is always the least expensive option, but it may not seal the leak, and if it does, it will not stay sealed for very long. Working on the roof, for an inexperienced or experienced do-it-yourselfer, is not safe. A low-sloped asphalt roof is not difficult to walk on, but if you stumble, there is not much to hold on to. If you try, wear a mountain climber-type safety harness and secure it to some strong object like a chimney.

Definitely do not install a standard asphalt shingle roof. With the low-slope on your roof, it will surely leak. A shingle roof relies on gravity to keep the water from flowing up under the shingles and down into your room. During heavy rains or when there is a strong wind driving the rain up against the shingles, gravity will not be adequate to keep it out.

Your best bet is to install a newer type of membrane roofing. Although asphalt rolled material is still being used, the new synthetic membrane materials seal better and for a much longer time. When installed professionally (this is not typically a job for a do-it-yourselfer), it is often warranted for up to 20 years.

Although the initial price to install synthetic membrane roofing is more than asphalt rolled materials, it is a better long-term investment. Other than an annual visual inspection of the seams and where it mates with other surfaces (chimney, vents, flashing, etc.), it will not require much maintenance over its life.

You may have to search for an experienced residential installer if you are not in a major city. These membrane materials are most often used for commercial and industrial flat roofs. Many commercial roofers will not want to do a small residential job.

If you have a problem finding a local roofer to do the work, contact the following membrane material manufacturers: Carlisle SynTec (717-245-7000), Dupont (302-792-4200) and Firestone Building Products (317-575-7000). They may be able to supply you with names of some local installers.

Synthetic membrane materials offer many advantages over the lower-priced asphalt rolled material. The seams in the membrane material can be sealed better than with asphalt roofing. With your relatively small roofing area to cover and the large membrane roll widths available, you may not need many seams, if any at all.

Many of these synthetic membrane materials have long chemical names and are referred to by acronyms such as EPDM, CSPE, CPA, CPE, EIP, etc. Don't feel overwhelmed by the choices because there are really three major classes for membrane materials thermoset, thermoplastic and modified bitumen. Your roofing installer will know which acronyms refer to which class of material.

Any of these material types would satisfy your roofing needs. They all are also bonded or attached with fasteners to the roof sheathing. The thermoset membrane materials are probably the best overall because they are chemically cross linked, so they are unaffected by heat and most chemicals.

The seams in thermoplastic materials are easily bonded with chemical solvents or heat to create wide pieces. Modified bitumen still uses asphalt with reinforcement and is sometimes called a sandwiched material. The installer will usually use a torch to seal any seams together.

Send your questions to Ms. Builder, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit www.dulley.com/msbuilder.