[TowerTalk] Rohn House Bracket and Stucco Siding

jim Jarvis jimjarvis at optonline.net
Sat Jul 5 07:17:20 EDT 2008

Jeff, Ke7FRJ wrote:

> Stucco isn't particularly common in my area.  What is the proper  
> way to
> attach a house bracket to a building with stucco siding?  This is  
> cement
> stucco over metal lathing -- not EIFS.
> Of course, following the manufacturer's specifications is the way  
> to go.
> Radian *does* show the bracket attached directly to the exterior  
> siding
> -- however the diagram shows horizontal overlapping siding -- not
> stucco.  Do I bolt right through the stucco?  Do I put a backer  
> between
> the bracket and the stucco?  Do I remove the stucco and put in a
> properly flashed ledger board to bolt through?

To which Dave Robbins, K1TTT replied:

Only a proper architect could tell for sure... but I would be afraid  
of the
bracket cracking the stucco.  Remember, the bracket takes all the side
forces on the tower so its going to be pushing and pulling on that  
spot as
the wind changes.  So personally I would go with a separate ledger  
board and
be sure to bolt well into the inside structure.  Remember, lag bolts  
into a
2x4 wall probably won't hack it... the note in my older rohn catalog  
house bracket installation is "the interface of tower brackets to  
structure is to be designed 'by others' and must support a minimum
horizontal force of 815 pounds."  The way I look at that is to  
picture the
attachment point with the wall laying on its side and think about 5  
hanging from it, if you aren't comfortable with that its probably not  

To which I will add N2EA personal experience and bias:

The rohn house bracket is intended to clear a deep overhang.  It's a bit
flexible, as a result.    I have always backed my house mounted towers
with a 2x8 which extends over 3 studs or roof joists.   That is, it  
must be
over 48" long.

In VT, I had a situation where I couldn't use a backing board, and  
had to lag
screw into the face joist, and roof truss joist ENDS.   Not a  
preferred situation.
I used 1/2" x 12" lag screws, rated at 2500lbs extraction force if  
installed with
pilot holes providing 100% thread.   I performed a 1,000 lb  
extraction test
on one bolt using a come along and a tree as a deadfall.

You might want to calculate the worst case overturning moment on the
bracket, in the extraction axis, just to make sure you have a safe  
reserve.   That calculation, in itself, should be a thread here!

After excruciating investigative work, I managed to position 6 lag  
screws into
the center of the roof joists,  2 per joist, spread over 48", with  
the load distributed
across a 2x8.   Carriage bolts were seated in the back of this plate,  
allowing the
bracket to be bolted on.

This mechanism was repeated at the floor truss system.   The tower  
was thus
supported at 6' and 16', and was floored by sitting on bedrock.   No  
foundation.   It held 60' of 45G with a foldover section, with 10sf  
topside windload,
and through two hurricane backwashes, with no problem, for 6 years.

When we sold the house, it was a simple matter of filling 12 holes  
and touching up
the paint.

As for the stucco texture, you may see some compression of it, but I  
cut it away and flash.   Leave it intact, and touch it up, if needed,  
when you strike
the tower.

Jim Jarvis, President, N2EA
Corporate Coach
The Morse Group, LLC
coach at themorsegroup.biz

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