I have a flat roof with rotting plywood under the rubber membrane. Should I remove existing or just go over the top with new plywood and membrane?
Always remove damaged or rotting wood before replacing or repairing your roof. Any roofer that tells you otherwise is simply offering bad and potentially costly advise.
Placing new roofing materials over a compromised structure will only lead to expensive and repeated repairs over time. Plus rot may be an indication of mold present which can lead to health concerns as well as other issues. If you are, however, often faced with roofing issues you may want to think about using a different roofing material, more info here: http://housetopexperts.com/Average-Cost-of-Roofing-Based-on-Material-Cost/.
There are many to choose from for a flat roof and, depending on your structure and current roofing materials, may be the best and least costly solution in the long run. A thorough inspection of your roof by a qualified roofing company is highly recommended to understand the scope of the repairs that are required and to offer solution options.
I think that in this matter you need to pay attention to the condition of the roof and the budget. I believe that repairing the roof is much cheaper than replacing the roof, but sometimes it turns out to be even more wasteful. Doing roof repairs every season isn't profitable. It seems to me that even when replacing the roof you can save money. My husband replaced the roof in our country house on his own. We spent only half the amount the builders told us, because we only paid for the materials, but not for the work. Now there are many articles on the Internet about how to build the roof correctly, what construction is necessary and what material is needed. For example, here myrooff.com it's written in the article. I agree that professional builders would do it faster, besides, it takes a lot of effort, but if you need to save money, it's real.
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