I need to build some exterior fixed louver shutters. Are there any standard specs for the size, angle, spacing, and overlap of the slats? I don't have an example to copy. Any formula or rule of thumb for layout? Assume 1 inch thickness.
(Architectural Woodworking Forum)
From contributor D:
There are no standards that I have ever seen. All that I examined and measured fall into a few groups, but there is variance within the groups.
The slats are almost always 1/4" thick by 1-3/8" or 1-3/4" wide. They are angled into the stiles so they center front to back, with about a 1/8" clearance to the face of the stile either face. The slat width and clearance from the face of the stile will determine the angle of the slat, as driven by the stile thickness. Much of the work I did for many years was with 1-1/8" thick stiles and rails and 1-3/4" slats. The 1-1/8" was from the old plump sawn pine 5/4.
The full width and thickness of the slat fits into the mortises, jigged up with a router and an index stick for vertical spacing. Some people use a hollow chisel set at an angle, and put tenons on the slats. Either way, ensure your angles are identical from left to right stiles, or you will make twisted panels.
I suggest you draft out full size what you want to do so you can see the overlap of the slats. You should not be able to see through when looking straight at the louver. A lap of 3/16" to 1/4" is good for being blind. Size your slats after making the mortises, and let the width of the slat make the fit in the mortise, not the thickness. It is much easier to fit in 40 to 60 slats by width than thickness, especially when you have glue on, and you are trying to pull each slat into the other stile, without knocking out others.
It is good practice to rabbet the rails so they are light tight, also. Working out the vertical spacing is a head scratcher, but if you can have variable width rails, it is more forgiving.
And congratulations on asking how to do it instead of who to outsource to. Nothing beats know-how, and your shop will be better for it. Have fun.