Why rocks on the roof?

Gravel on the roof - why?

Pardon my ignorance, but please educate me – is there a non-aesthetic purpose for this, or is it just cool? We don’t have this where I come from. Does it stop water from flowing quickly off the roof, or prevent something from running around up there, or discourage sunbathing, or what does it do, exactly? I want a white roof with little white rocks on it for myself.

La Quinta house

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9 Responses to “Why rocks on the roof?”

  1. LC Whittle Says:

    I don’t know why this was so common in desert areas in the 1950s and 1960s. Our house in Albuquerque, which is a high mountain desert, had red lava rock on the roof when we bought it. Ridiculous, considering how high the winds get here.

    You can still find houses here in the city with rock roofs. Personally, I dislike them.

  2. charlie vinz Says:

    This appears to be a form of roof ballast. Admittedly one that I have not seen, but I haven’t been in the desert since I was a kid. Roofing ballast is usually the little pebbles you see on a flat-ish roof. This is for a roofing membrane that is not fully adhered to substrate, and the pebbles are essentially acting as a paperweight.
    Why not fully adhere?
    With ballast, the individual roofing membrane layers and the building structure itself are able to move independently with changes in temperature, thus decreases the risk of cracking, splitting, and other forms of roof failure. Typically, the ballast is mostly built up around the edges of a building, since that’s where the greatest wind uplift occurs. It’s usually specified in something like PSI, so I guess that could be interpreted as larger stones placed more sparingly, as opposed to many more smaller pebbles placed evenly.

  3. dave Says:

    The depth or lightness of shade possessed by the roof indicates the times of day at a glance. Basically, if you stare at it from a fixed position at a small distance (maybe a pathway approaching the property) you are essentially viewing hundreds of small sundials again a white backdrop. You would eventually become adept at seeing roughly what time it was as you approach the house. Wooo!

  4. LB Says:

    Thanks, Charles! I thought it had to be equivalent to the roof gravel we see in Vancouver, but it seemed so strangely sparse. I guess high winds are less likely to take larger rocks away than smaller pebbles, and these houses were all in areas of high desert winds, so it makes sense.

  5. Darren Says:

    Charlie is correct. It’s a form of roof ballast, like the gravel you see in other areas. The larger rocks are more effective in high-wind areas.

  6. LB Says:

    I really like it for some reason. Especially in white.

  7. David Kerr Says:

    I saw them all over Europe and the Alpine ares. Does the heating/Sun on the rocks keep the snow off or building up on the roof? We live on the beach in NW Fl, we get sun E to W all day. Would rocks help?

  8. Tony Says:

    Actually, in the days before air conditioning, rocks on the roof helped to reflect the hot desert sun. Helpful when its 120 degrees outside.

  9. Not Charlie Says:

    Since iv’e seen rock on a regular asphalt shingled roof, I don’t see how it’s always used as a paperweight. One thing it would do is make the roof more resistant to sun damage as much of the roof is not directly exposed covered by rocks.

    I think some people do it because they like the look. Reminded me of Haiti where they use rocks of any type to hold the tin sheets on through a storm.

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