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My house is a 1960 Cape Cod, with hollow dutch lap vinyl siding over the original wood siding. I wanted to mount a 45-degree flagpole bracket to the side of the house to hold a 2.5x4 foot flag. To support this, I purchased a mounting block (specifically Builders Edge 130110008123 Surface Block) which conforms to the profile of the siding. I mounted the flagpole bracket against this block using 4 2.5" wood screws which penetrate the bracket, the block, the vinyl siding, the original wood siding, and I assume the plywood behind.

This works relatively well, however the screws loosen and work out over time. I have a few times over the past couple years needed to remove it, fill the screw holes with toothpicks+glue, and redrill. I think the problem is that I can't tighten the bracket completely, as is begins to crush the hollow vinyl siding (the profile of the mounting block helps this a bit but not completely.) This means there is some movement in the breeze (I try to take the flag down in heavy wind, but I'm not always home for it and moderate wind still moves it quite a bit.) One thing I tried was spraying some expanding foam behind the siding to add some support, but that didn't actually help much.

Has anyone had/solved this problem? One idea I had was opening the affected siding panel and putting some pieces of wood (furring strips?) inside the problematic bays. In my mind this would let me tighten the screws much better, as there would really be something to tighten against. It would also give the threads some more wood to hold onto, whereas before the threads in the void under the siding weren't doing anything. Is there a problem with this solution?

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I would recommend what you suggest about puling the siding piece, I have done that with great success, filling behind vinyl siding for deck ledger install.

In your case, I would use plywood that is the right thickness, that fill the backside of the siding. Since the dutch lap will require the strips to be narrow, using plywood will keep the backing intact, since it will not split when the screws go through it. Fill it up as much as possible,using pieces that are 8"- 1' long, keeping above the lower piece enough to allow for movement, just a paper thickness will do.. I do not know how the mounting block covers any holes in the siding, but with the siding properly backed up, in my opinion, you will not need the mounting block. Let the screws grab the well attached plywood behind the siding, as well as the wood siding and subsiding. That should give you approx. 1 3/4"+ of wood to mount to.

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  • I would agree if the block matched the siding but thought it was made for the vinyl. I found in windy areas the larger surface was needed but a non windy area just the mount may work. – Ed Beal Jul 7 '20 at 22:19
  • Its all in the screws and what they go into.... The vinyl may be denser than the block that was originally intended for the mount. But if there are too many holes in the vinyl from prior mountings, the block may need to be kept just to cover the extra holes. – Jack Jul 8 '20 at 3:51
  • This is what I ended up going with - 2 strips of plywood behind the siding. I did end up keeping the mounting block for aesthetics; without it, the bracket would have to span siding pieces, leaving a big triangular gap behind it I didn't like the looks of. The block covers this up nicely. The bracket is now screwed tightly into the wood and feels infinitely sturdier than before. – Kevin Jul 15 '20 at 18:36
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I suggest cutting the mount profile through the siding. this is how I start out and seal around the bracket. In some cases I use a square Hardwood piece to mount to that is thicker than the vinyl / aluminum siding. Squares are easier to cut and seal. Using hardwood creates a better base than soft wood and as it is usually larger than the holder process better protection for wind loads that batter a loose fitting bracket and cause problems that you have from the flexing.

You can make a round or square hole depends on how good you are , I suggest a larger size than the bracket for more square inches attached to the structure. I have lived on the west coast and never had My brackets come down but I did have a pole break in a storm (I forgot to bring my flag in).

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