Installing a French cleat on lap siding

[Brian Behrens]

I'm making some large planter boxes to attach to the house under the windows (82" wide).

I would like to attach them using a French cleat to make the boxes easily removable for cleanout / refinishing.

I'm thinking of ripping the cleats to match the angle of the siding, so the boxes sit plumb against the wall. I'm concerned about water penetrating the screw holes and rotting the sheathing, since I can't put a piece of flashing over the top of a French cleat . The lap siding is fiber cement.

Does anyone have any suggestions to mount these boxes? They will be pretty heavy, since they are made of PT 2x10, with decorative cedar panels attached to the 3 show sides, in addition to the weight of the dirt and plants. Thank you for any advice.

[Bill Carey]

Hey Brian - the first thing that comes to mind is that I would not trust the holding power of the cement siding (or the 1/2" sheathing) with a box that heavy, nor would I trust a thin french cleat. If you planter is 12" x 12" x approx 7' you have about 280 pounds of dirt alone. I would lag screw it to the studs, or you might get lucky if you push the box up tight to the sill you might hit the double sill framing. I would wrap a strip of ice and water shield around the top 1/3 of the lag screw so that when driven home it compresses around the threads of the screw. And a piece of flashing caulked to the top. When you want to refinish just back out the lag screws.

[Jim Becker]

I think you would be best served by mounting the piece on stand-offs that you can seal around. They can be beveled to provide a mounting surface that is parallel to the wall and if they are circular or at least rounded on top, any rain, etc., would run off cleanly. It would be best if you can locate them so that a stud is there to screw into. You could still use French Cleats, but they would mount to the standoffs rather than directly to the wall.

[Brian Behrens]

Thanks for these suggestions Bill and Jim. I will definitely be going into the studs with a long timber lock screw. I intended to make the French cleat out of 1.5" PT wood, but I hadn't thought about using several small standoff sections of French cleat, as opposed to one long strip .I think this is a good approach because then I can seal around each cleat with silicone, and fill the countersink for the mounting screw with silicone also . Now I just have to figure the geometry of the sides where they touch the house, I guess I should extend the faux panels on the sides to take up the gap left by the standoff french cleats. This will also let me use a thicker cleat for strength. Just thinking out loud with hopes somebody has experience in this situation .

[Jim Becker]

I was viewing the stand-offs and the cleat as separate items, but depending on the load, you could also use short cleats as you mention. One of the strengths of the French Cleat system is that it helps distribute weight. The stand-offs I mentioned were to help alleviate the moisture infiltration challenge you mentioned in the OP.

[Paul Girouard]

I was viewing the stand-offs and the cleat as separate items, but depending on the load, you could also use short cleats as you mention. One of the strengths of the French Cleat system is that it helps distribute weight. The stand-offs I mentioned were to help alleviate the moisture infiltration challenge you mentioned in the OP.


I’m going to agree with Jim, cut some PT stand offs that you can Ledger Loc or Head Loc into place , you’ll need to cut the sawtooth of the siding into the so the planter box can sit plumb.

Run the bolts in then back them out and shoot caulking into the hole , then run the bolts back in.
The stand off could be 4x4’s ripped down to 2” .
From there you can come up with some simple metal tabs that could interlock similar to a French cleat.


I’ve never used these but they look promising:

ETB hidden connector by Simpson Strong Tie.



396791



396792

[Brian Behrens]

Thanks Again everyone. I have some options now

[Charles Lent]

Having had planter boxes on a previous house, you need stand-offs to get air circulation behind the planter and between the planter and siding. Cedar siding holds up well to moisture, but not so well if it remains moist constantly. Make the stand-offs with the back edge beveled to match the siding angle. The French Cleat can then be attached to the stand offs, if you still want to go this way.

Charley