an 8" by 8" by 16" cinder block used for ballast is about 28 lbs on average from what I could tell, and with the weight of the metal structure its about 35 lbs on average focused on each base leg.
take a closer look at the photos and you'll notice that there is an extra bit of roofing material, but what ya can't see under that is a bit of thin metal roof flashing that in effect distributes the 35 lbs over an area about 6" by 6" which isn't a problem from so far (been using set ups like this since 2004) http://www.phaster.com/golden_hill_free_web/non_penetrating_roof_mount.html because my home brew NPRM is 8 ft x 8 ft, its very stable, just try and lift a 35 lb weight at the end of an 8 ft pole, bet ya can't do it! IMHO NPRM that use lots of cinder blocks for ballast and is placed flat on a roof is a pretty poor design because they don't taken into account the very real problem of trapping moisture. As far as wind loading, there have been a few storms in the area that I know have gusts up to 60 MPH, and I'm pretty sure a design like this it could take lots of wind gusts much higher because of min surface area. I guess I could find out how much wind a set up like this could take by setting up a rig behind my old cessna and fire walling it, but that seems kinda like over kill testing. did ya find my page because of a post I made on the SoCalFreeNet board a few days ago? If not take a look at the attached photo(s) and note the cinder blocks used to typically hold down a typical NPRM. If ya look carefully at the attached photos you'll notice the blocks are darker at the bottom. The darker color I'm pretty sure is strong evidence of moisture, and the darker color on the block indicates moisture wicking upward, point is, I'd bet 99.9% of "tech" guys don't realize that if a penetrating roof mount traps moisture, there exists a much higher probability for roof rot right under the non penetrating roof mount, because that design consideration was not accounted for! On Sun, Mar 21, 2010 at 8:32 AM, ralphlists <[email protected]> wrote: > Interesting piece on your home-built non penetrating roof mount. > > > > I am wondering how/if you determined that the load on the four small > circles of roof area was not going to damage the roof. > > Not only do you have the weight of the antenna installations and all that > fence pipe and flagpole, you have the cinder blocks as well. > > It doesn’t seem like you are accomplishing what the NPRM was designed to > do, which was spread the load. > -- ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ DISCLAIMER: This is your last chance. After this, there is no turning back. You take the blue pill - the story ends, you wake up in your bed and believe whatever you want to believe. You take the red pill - you stay in Wonderland and I show you how deep the rabbit-hole goes. http://phaster.com/_peak/_peak_expectations.html P.S. during an economic crisis, isn't it comforting to know that "For every economist, there exists an equal and opposite economist." ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
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