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Part 2: Visual Roof Exam, Moisture Survey Can Help Spot Zombie Roofs
By Karen Warseck, Contributing Editor
January 2013 -
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The problem with zombies is that they are already dead — they just don't know it. So you can't actually "kill" one. Then how do you deal with a zombie roof when you have one?
The first thing is to know exactly what you do have. There may still be a shred of life in the roof or at least a possibility of a resurrection of sorts. So the first step is to have a roof consulting architect or engineer thoroughly survey the condition of the roof. This survey, which should include a visual examination, core samples and a moisture survey, will identify roof problems.
The visual exam will provide an overall view of the roof and a starting point for more detailed analysis. The moisture survey will tell you where the worst spots are. Core samples will correlate the results of the moisture survey and provide snap shots of the subsurface conditions. It may be that only one side of the roof is causing the problems over the whole area. Breaking things down like this can help you bring the zombie under control and make it less of a threat.
Once you have analyzed the zombie and found its weakest parts, you can then embark on a plan to correct them. For instance, the situation may be that the flashings have deteriorated to the point where they are hanging in shreds from the parapet walls. That's an easy one: Replace the flashings and the zombie is subdued for a while.
But what if the roof itself is where the problems are? This is where that moisture survey has such benefits. Using the results of the moisture survey, you can look at which areas of the roof are in the most dire straits and replace them section by section. The next year, you can move on to the next worst area and so forth until you can replace the whole thing.
Two important points to remember here. One is that the new patches should be completely isolated from the existing roof by a water dam. Otherwise you will be getting water into the new patch from the old roof. The second item to remember is that whatever material you use to patch the existing roof should be a compatible with what is there now. Do not attempt to patch an asphalt base system with a single-ply membrane and vice versa.
There's another benefit to the moisture survey: It may reveal that it is possible to eliminate the zombie by recovering the existing roof. If the moisture survey shows that less than 25 percent of the roof is damp, it makes a re-cover roof economical because you can leave the dry parts of the roof in place. Code requires that the wet areas be removed, so the economic benefit of a re-cover gets smaller the more wet area you have. After the wet area reaches 25 to 30 percent of the total roof, the difference in the cost between a re-cover and a complete replacement reaches the point where complete replacement makes more economic sense.
Part 1: Zombie Roofs: Reasons Roof Failure Is Ignored
Part 3: Coating Can Be Short-Term Solution For Deteriorated Roof