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## Re: [TowerTalk] Will my roof stay on?

 To: towertalk@contesting.com, dieven@msn.com Re: [TowerTalk] Will my roof stay on? K7LXC@aol.com Wed, 24 Aug 2005 08:53:04 EDT
 ```In a message dated 8/22/2005 9:08:21 AM Pacific Daylight Time, towertalk-request@contesting.com writes: > I'm about to install a roof tower with a 2.5 square feet winload antenna. I'm contemplating mast length and have come to realize that I don't really know what computations I should be making to avoid damage to my roof. > I was thinking of a 10 foot mast, 6 feet would stick out of the tower. But why not a 20 foot mast? How about 13? How would I know? > I'm looking for references for the computations involved and the forces that a roof can be expected to endure. I need to decide what the mast is going to be made of and how long it can be. At 80 mph is the roof going to lift off? Okay, I'm not an engineer but I've installed 5-6 roof-mounted towers with varying loads (one of them has a C4 and a pair of 2M CC plus a pair of 440M antennas). Yes, with a mast sticking out the top you've got more lever arm and bending moment but consider your typical roof construction. You've got roof joists with a layer of good-sized plywood over it. The footprint of the GME 9-footer is 32" by 32" or almost 9 sq.ft. Using thru-bolts instead of lag bolts and 2x4 backing plates in the attic across 3-4 joists, your load will be spread over a larger portion of the roof structure. Using an aluminum mast will help to dissipate wind forces by bending before it sends the forces down the tower to the base. Your combined tower and antenna windload is probably less than 5-6 square feet. If you're really concerned about it, you can guy the tower and spread the load over a MUCH LARGER area - then you can probably go up as high as you want. If this were my installation, having 6 or 8 feet of mast sticking out of the top wouldn't bother me. If the antenna was an HF tribander I'd be more conservative. Cheers, Steve K7LXC TOWER TECH - Professional tower services for commercial and amateur Cell: 206-890-4188 _______________________________________________ See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA. _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
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