Rooftop Tower mounting

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W8WJC, Jun 12, 2019.

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  1. W8WJC

    W8WJC Ham Member QRZ Page

    Hello guys,

    So I'm looking for thoughts about how to mount a rooftop tower. My plan is to put a either a W8IO or a Glen Martin tower on the roof of my garage. I'm going to put a Mosley TA-33 on it with a 40m add on kit. Now heres the issue, when reading the manuals for both of these companies, they both say the tower needs to be reinforced where the tresses are in the attic. My problem is, my master bath is above my garage. My bathroom ceiling to vaulted and goes right up against the peak of my roof. I can't access this space to reinforce anything.

    So, how important is the reinforcing of the tower? Could I drill extra holes in the feet and add a few extra lag bolts? I choose this roof peak because its the easiest to get too from the outside. The other peaks are much more steep. But the downside like I said is I can't get to the underside because the ceiling drywall goes to the peak.

    Looking for thoughts.

    Thanks in advance,
  2. K0UO

    K0UO Subscriber QRZ Page

    I guess when it rips off of your roof, you'll have an aditional shower head in your bathroom!!!!! Cuz you'll have a hole in your roof and it will surely leak, plus your antennas will be in disarray.
    Most people don't use guy wire on those types of mounts, if you're going to be putting a big tribander up on it, it certainly would be insurance to guy it.
    Last edited: Jun 12, 2019
  3. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Last edited: Jun 12, 2019
    NL7W, WB5YUZ, W2AAT and 1 other person like this.
  4. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Courtesy blow up...
    Glen Martin Install.png
    N9NY, KP4SX and WB5YUZ like this.
  5. KC8VWM

    KC8VWM Ham Member QRZ Page

    The real problem is you will have a giant corkscrew tool installed on your roof.

    Even guying it won't necessarily stop those kind of twisting forces from occurring to the footings, on the roof tower legs.

    Adding extra wooden braces to the existing rafters are nice to help prevent movement, but it's better to construct a sizeable framework consisting of steel unistrut under the roof, inside the attic, and then bolt the roof tower directly to that instead.
    Last edited: Jun 12, 2019
    K0UO likes this.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The 4-legged roof towers can be used without under-roof blocking and bracing for vertical antennas or beams with small booms and elements; but for an HF beam with a 40m element extension, that’s a lot of torsion and could be a problem.

    However, I’ve done this more than once: Add the additional blacing on top of the roof instead of under it. I use 2x6’s laying on the roof spread over six rafters and lag with 1/2” x long (6” or whatever is needed, depending on roofing thickness) lag screws into the far end (widest spaced) rafters, assuring the lags are all dead-center into rafters.

    Then use two rafters spaced 32” apart to lag through the external brace and dead center into those two rafters (12 lag screws required, 3 per leg bracket). Then lag the centermost point of the external brace to the single rafter midway between the tower legs. This requires sixteen 1/2” lag screws and two 2x6s x 8’ long braces in addition to the 12 screws required for the tower leg brackets, so doesn’t add much cost. If in doubt, double up on the 2x6s to make them twice as “thick” above the roofing, and use lag screws that are 2” longer.

    I use large fender washers under all the lag screw heads, then Henry roofing cement over all that, and of course paint the external wooden braces with good outdoor paint, and re-paint every few years as required.

    This isn’t quite as good as the internal blocking, but it’s certainly better than nothing and I’ve used this approach two or three times over the past 30 years with G-M model RT832 towers supporting pretty large HF beams frequently rotated and they’re all still up. All dimensions, including those for the RT832, assume 16” rafter spacing.

    For me, the trickiest part is finding the rafter locations from above the roof; it can take drilling some small pilot holes (small diameter, long drill bit) to test, and then patching those after finding the rafter centers. I’ve never had any sort of leak from any such installation.
    KA0HCP likes this.
  7. N7WR

    N7WR Subscriber QRZ Page

    Many years ago I faced the same issue. I used the largest of the Glen Martin towers and it had a Hygain Explorer 14 antenna with rotator. Mounted the tower to 2 X 8 lumber each 8 feet long and bolted those as I could through the roof. I carefully sealed each bolt point to prevent leaks. I then, using quality aircraft cable, 4 way guyed the tower with each guy terminating in a roof joist (not the fascia) It held up well for the 4 years we were at that QTH. The house was on top of a hill and winds were occasionally significant. This is NOT the recommended way to do it--see KA0HCP's post---but it did work and there was no damage to the roof
    K0UO likes this.
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Very similar to what I’ve done as described above.

    If you hit rafters properly and do it right, it works!
  9. W8WJC

    W8WJC Ham Member QRZ Page

    I originally thought you lag bolted the feet into the trusses. But now I’m starting to realize that’s not quite how it’s done. So now I either need to find a new spot on the roof or reinforce the original spot some how.
  10. AD5HR

    AD5HR Ham Member QRZ Page

    The factory specs. show silicone as a sealant.
    DO NOT use silicone for this.
    Silicone bonds very poorly to shingles. wood, and concrete tiles.
    Plastic cement (roofing tar) should never be exposed to weather,
    it is used more like gasket sealant, and will shrink, crack, and dry
    out in a relatively short time.
    A good sealant for using on mixed materials is NP-1, and available
    at most big box and hardware stores. Any exposed sealant should be painted. (UV)
    I have installed a large Glen Martin tower, and installed a TA33 Classic
    on it. The framing specs. in the factory sheet above is spot-on, but no one
    in the trade uses silicone on a roof.
    This is NOT inter-web info, I've been in the business over 40 years.
    AI3V and KA0HCP like this.

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