Mounting bat house on cedar siding - too heavy?

Question

I have built a pair of bat houses using these plans at Bat Conservation International.

A finished house
weighs about 25 lbs (11 kg) and I would like to attach it to the
outside of my house, over horizontal 3/4" cedar plank siding.
Here's what I have in mind.
I made some wedge mounting plates that
fit into the natural slope of the siding and provide a flat surface.

I plan to attach the plates to the siding (liberally caulked) with 4"
construction screws and then attach two horizontal "french" cleats
(upper and lower) on which the bat house will rest. The top and bottom
halves of each cleat will be secured to each other at the exposed ends
with a metal bracket so the bat house
cannot be lifted off the cleats in strong winds.
My question: Will the siding tolerate this load if the plates are
screwed into the siding?
Based on recent work replacing gable siding, I expect there's a gap
between the siding and the OSB sheathing, so reaching a framing stud is
unlikely, and I'm not sure I would want to put a screw through the
Tyvek anyway.
Also, assuming this will work, is there anything else I need to be aware of?

batsplatsterson · Accepted Answer

Nice work with those mounting brackets you made.  I think your basic plan is totally sound.
Ideally you'll want to locate studs and mount those brackets on studs, and drill through the siding and sheathing and into the studs.  I think three 4" x 1/4" lag screws on each bracket would be good, there's enough meat to lag screws that size to hold the weight of the bathouse.
Rather than seal those brackets to the siding, I'd put a thick washer between the brackets and the siding.  I'd rather have that little gap for the siding to get wet and dry out.  That's just my opinion.
I see one possible problem with the design.  The french cleat will leave space between the bathouse and the siding.
The bats won't know which crevice you intended for them to take up residence, and roost between the siding and the bathouse.  You might want to add to or modify your design to close off that space.

isherwood · Answer

If you're using 4" screws the plates won't be hanging on the siding. They'll be hanging on framing. Right?
No, you shouldn't hang anything on siding that you wouldn't want hanging on your nose. Use screws that penetrate at least 1" into the framing. Even screwing to siding + sheathing would be sketchy over time.

Mounting bat house on cedar siding - too heavy?

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