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[Towertalk] Tower Buidling 201 or How I Beefed Up a Wall To Whicha Tower

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Subject: [Towertalk] Tower Buidling 201 or How I Beefed Up a Wall To Whicha Tower Is Bracketed (very long)
From: (Jim Smith)
Date: Tue, 03 Sep 2002 22:15:59 -0700
The following is quite long and is the work of a demented, 
anal-retentive paranoid.

Ever since I joined TT 18 months ago I have been seeing cautions about 
house brackets.  I have a flat roof with access from inside the house 
via a normal staircase.  To accomodate the staircase, a structure I call 
"the penthouse" was built on the roof.  Here's a view of the side of the 
penthouse while standing on the roof.  

            /      | <--- penthouse  7-1/2 ft high
           / _____ |
          /  |   | |
         /   |   | |
        /    |door |
       /     |to | |
      /      |roof |
_____/_______|___|_|_______roof level______________
    /    _|
   /   _|
  /   |  <- stairs

The angle with respect to the horizontal of the sloping part is much 
shallower than what the keyboard allows me to portray.  It is the same 
angle as that of a typical set of stairs.  At the top of the stairs 
there is a small landing.  When you reach the landing you turn right, 
open the door and step onto the roof.  This was all done before I got 
back into ham radio after a many decade absence.

All was serene until VE7IN, a former mentee and now a mentor (would that 
be remle and now elmer?) invited me to his QTH a couple of years ago for 
a mult-single "for old times' sake."  Those who have read my subsequent 
stories on 3830 will know the details of how this led to my fall from 
grace into the hellish underground world of contesting.  To seal the 
devil's bargain he gave me 2 10 ft and 1 5 ft section of Rohn 25G. 
 Hmm... I still have a TH3 and Ham M plus some mystery mast from the old 
days.  All I need to do is prop up the 25G somehow on the roof with the 
TH3 etc on top, hook it all up to the 75A-4 and 100V and I'm in 
business.  "Not so fast," says 7IN.  First of all, the old rig doesn't 
cut it any more so, if you're serious, get something decent.  Sigh. 
 Several K$ later I got a MkV.  He was right.  

With respect to my idea of putting the TH3 on top of 25 ft of 25G 
sitting on the roof and attached to the penthouse with a couple of 
U-bolts he suggested I subscribe to TT before doing anything.  "What do 
they know?", I asked in my haste to taste the forbidden fruit of 
contesting under my own call.  "At least a hundred times more than you 
do," was the chastening reply.  Nowhere have I read of Adam having to 
learn to calculate wind loading and overturning moments before indulging 
in that temptation which led to his expulsion from Zone 21 but, I 
suppose, modern times lead to modern torments.

So, here is my house bracket story.

Below is a plan view of the penthouse showing the location of the 25G.

        landing ____     o
                    \       <--- 25G
|                  |  \   ^      |
|                  |      |      |
|                  |   beefed    |
|  stairwell       |<--   up  -->|  <--- top (plan) view
|                  |   portion   |
|                  |      |      |  North ----->

The 25G rests on the roof and is flush against the wall.  The diagram 
shows some space between the tower and the wall.  This is a limitation 
of what you can do with ASCII drawing.  AutoCAD it ain't.

 From reading TT and doing some calculations it became evident that 
there is a risk of the tower prying the penthouse right off the roof 
(think of a giant claw hammer with the tower being the handle) so I 
decided to "beef up" the penthouse structure.  Here's what I did.

1.  Removed the drywall (gyproc, sheetrock) from the W, N and E sides of 
the to be beefed up portion as well as the ceiling.  From here on 
"Beefed Up Portion" will be referred to as "BUP"  (Not to be confused 
with BIP or BOP)

2.  Bolted the sill plates of the BUP to the underlying roof joists with 
lag bolts every 16" wherever possible.  Where there was no joist under a 
16" run of plate I used a Hilti toggle bolt to anchor that portion of 
the plate to the 3/4" T&G ply which forms the roof.  (Maybe the phrase 
"sill plates" is regional.  I'm referring to the 2x4s which lie flat and 
which support the vertical 2x4 studs which comprise the frame of a 
typical wall.)

3.  Bought some 1-1/2" x 1/8" angle iron.  Cut it into 3" lengths and 
drilled 6 holes into each piece, 3 into one side of the "L" and 3 into 
the other.  They are now called brackets.

4.  Placed a bracket on each side of each stud where it meets the sill 
plate and secured the brackets to the studs and sill plate with #8 x 
1-1/2" wood screws.  Did the same where each stud meets the top plate. 
 Did the same with the ceiling framing.

          _______________________   <-----top plate
                 | |
                 | |
                 | | <--- stud
                 | |
   bracket ___   | |   ____ bracket
              \  | |  /
               \ | | /
          ___________________________   <---- sill plate

5.  Added a stud in the NW corner to fill in the gap left by normal 
corner framing practice.

6.  Screwed (and maybe glued) all NW corner studs together at a number 
of places along their length.

7.  Used metal framing connector plates at the NW and NE corners at the 
ceiling to rigidify the corners.

8.  Added 2 2x4 studs to the West wall.  These 2x4s are directly in line 
with the 25G legs.  Brackets applied top and bottom here as well.

9.  Added 2x4 X bracing to the W, N and E walls of the BUP as well as 
the ceiling.

10.  Clamped 25G to the wall at the 1 ft, 4 ft and 6 ft 8" levels as 
follows, repeat for each level:

10a. Cut a 1-3/4" x 1-3/4" length of "purple heart" wood.  (This is a 
very dense tropical hardwood.  Anything else would work as long as what 
follows won't crush it and it won't swell or shrink with weather.)  Let 
2 U-shaped holes into one edge.  The hole widths to be the same (no 
slop.... the same) as the diameter of the 25G legs and spaced the same 
as 2 25G legs.  i.e. the wood length, when installed, will be 
horizontal, will fit over the tower legs and will clamp the 25G to the 
wall.  (Do I see the Prime Director cringing?  Don't worry, Steve, 
there's more to come.)  The depth of the holes is such that the tower 
legs project past the edge of the wood about 1/8".  The idea being that 
the 25G legs, once clamped into place, can't move without moving a bunch 
of other stuff, i.e. the wall.  How long is the wood?  The entire width 
of the wall in the BUP.  In my case, about 4 ft.

10b. Cut a piece of 1-1/2" wide x 1/4" thick galvanized steel the length 
of the wood.

10c. Drilled 1/2" holes through the steel and the wood for carriage 
bolts.  These bolts to pass through the wall such that they graze either 
side of the 2x4s behind the tower legs.  i.e. when the bolts are 
installed there will be 4 of them on each level, one on each side of 
each 25G leg.  See illustration below.

10d. Drilled 1/2" holes in 4 ft length of 1" band iron to match the 
carriage bolts.  Filed holes square to accomodate square porion of 
carriage bolt heads.  Length same as the purple heart.  This will be 
placed against the studs on the inside of the wall.

10e. What about all that extra length of wood, steel, band iron etc? 
 Drilled holes for lag bolts wherever there's a stud.

10e. Screwed and glued 1/4" plywood to W, N and E walls of BUP as well 
as ceiling.

10f. The big moment.  Took two people.  Pushed the already assembled 25 
ft of tower up against the wall.  Placed the purple heart wood over the 
legs and the steel bar over that.  On the inside, positioned the band 
iron and poked the carriage bolts through the holes.  When done, the 
carriage bolts were locked in position in the square holes in the band 
iron and projected through the wall, the purple heart and the steel bar. 
 On the outside, put a washer and nut on each bolt and tightened, but 
not real tight.  See illustration below.

                               o <--- tower leg (did you find
                                                 the other 2?)

1/2" carriage bolts--->|-->|      | <--|<--- 1/2" carriage bolts 
                    ___|___|______|___|___  <-- steel bar
                    ___|_o_|______|_o_|___ <-- purple heart
                    ___|___|______|___|___ <-- wall cladding
                       ||2||      || ||
                       ||x||      ||<||---- 2x4 stud
                    ___|___|______|___|___ <-- 1/4" ply
                    ___|___|______|___|___ <-- band iron
1/2" carriage bolts--->|-->|      |<--|<--- 1/2" carriage bolts
       bolt heads ---> U   U      U   U

10g. Plumbed the tower and installed the lag bolts through the band iron 
on the inside and into the studs.

10h. Tightened the carriage bolt nuts on the outside.

10i. Installed the lag bolts through the steel bar and purple heart on 
the outside and into the studs.

10j. On the inside screwed and glued 1/4" drywall to all surfaces but 
left a gap at the band iron slightly greater than the width of the band 

10k. Covered the gap with 2" wood trim such that the trim may be easily 
removed so I can get at the carriage bolt heads in the future without 
damaging the drywall.

10l. Painted the inside of the penthouse.

So, I have a 25' tower clamped to the wall with about 17' of tower 
projecting above the penthouse roof.  No guy wires.  (This puts the beam 
at about 45'.)  The clamps, being lagged to several studs and the studs 
being tied together by the X-bracing and the plywood skin screwed and 
glued to them on the inside, distribute the tower forces over a good 
chunk of wall.  (Almost sounds like I know what I'm talking about.)

Does it work?  I've got the old TH3 tri-bander on the tower.  A few 
months ago we had the worst wind in 25 years.  Some (not all) 2 ft 
diameter trees on the boulevard lay right over leaving 5 ft deep holes 
where their roots used to be.  I went up on the roof (it's flat, 
remember) to check out the tower.  The top might have been moving 
laterally an inch or so, no more.  The next day I checked the drywall in 
the penthouse.  Not the slightest sign of a crack anywhere.

There is no vibration/noise issue.  I sleep really well at night and, 
more importantly, so does my wife.

Hope this was of some intrest.

73 de Jim Smith    VE7FO wrote:

>Here's another N4KG  'NEVER  DO'
>NEVER  use a House Bracket to support a non-self supporting tower,
>unless you have at least one set of guy wires 30 ft or less above the
>Besides the Vibration / Noise issue, if you get a really STRONG
>wind and lose your tower, you will also have a HUGE repair bill
>for your house.
>There is nothing STRONGER,  SAFER, and more COST EFFECTIVE
>Note that for tower heights under 70 ft, Rohn shows a 35 ft (50%)
>guying radius for their (discontinued) fold over tower intallations.
>Tom  N4KG

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