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Community and Q&A

Re-roofing a tar and gravel home

Geobuilt | Posted in General Questions on

I have a small (approx. 900sq ft.) home with a flat tar and gravel roof. I know the roof is at least 10 yrs. old and I have not experienced any issues within the house from leaks or whatnot. I have however noticed that the overhangs of the roof that stretch the perimeter of the house at 2 feet, have become soft and fairly weak when stepping on them. They also show some signs of mold on the underneath side of the sheathing. I have not noticed these problems with the portion of the roof that covers the house. I have been looking into many different options to possibly replace the roof before it becomes an issue. Since it is my only residence and I live in west Texas where the weather is very uncomfortable for the majority of the year, I really do not want to be without a roof for longer than I have to. I saw in a previous post that spray foaming the roof and putting small gravel on top is a good option. I am also drawn to this option because I am not entirely sure that the roof is insulated well if at all. I plan on giving some spray foam contractors a call fairly soon but I want to know exactly what I am getting before I proceed. Are there any questions or concerns I need to be aware of before I meet with them? Is there a fairly standard cost for this job? Is there anything in particular that I should request?

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, you should know that roofers are able to complete re-roofing jobs without letting your house get wet. They do that all the time.

    Second, you need to find out why your overhangs feel spongy. You may have rotten sheathing, rotten rafters, or both. These issues need to be evaluated before deciding whether to go with spray foam roofing.

    Third, here is a link to an article that should answer many of your questions about spray polyurethane foam roofing: Roofing With Foam.

  2. Geobuilt | | #2


    I appreciate your response. The link you posted is the article that made me look into the spray foam option. If I do decide to go this route what thickness of foam should I be looking to get and do you have any clue what might be an industry standard on price? I want to make sure I get the correct amount without paying too little( which may be a red flag) /too much ( don't want to get ripped off). Thanks

  3. GBA Editor
    Martin Holladay | | #3

    The thickness is entirely up to you. As my article notes, 1 inch of roofing foam will work, but thicker layers insulate better. I doubt if there is any economic justification for more than 3 inches of spray foam, because it is expensive.

    However, 3 inches of spray foam isn't much R-value.

    If you want more R-value, you should think about insulating above your existing roof sheathing with rigid foam, and then installing membrane roofing like PVC roofing or EPDM roofing.

    My article also gives information on the cost of this type of roofing. Costs vary by region, however, and my article is several years old, so you'll have to get a few bids and evaluate them yourself.

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