Best way to join shutters to prevent splitting/gaps

rstermer

I am going to be making a set of 16"x40" decorative exterior shutters for my daughter's house out of pine. They will be painted. The design she wants is very simple, 3 boards wide, 40" long, tied together with 2 boards near the top and bottom, each 16" long on the side away from the wall so the cross boards will be visible from the road. They are on the south wall and thus will be exposed to significant sun and extremes of dryness and humidity. How should I join them to accomodate swelling and shrinking of the wood (tongue and groove, pocket screws, biscuits?). I may put either a chamfer or a decorative bead on the edges of the boards. I'd like a no gap situation at all times, but at the same time don't want to set myself up for splitting due to changes in temperature and humidity. Am I correct in thinking the wood will expand much more along the grain than across the grain? I was thinking of driving screws through from the back into the front boards to attach them together. If I do, should I slot the hole in the back board to allow the back (long) board to move along the grain?

Here is a top view to make it a little clearer what I am talking about, nts:
_____________________
|_____________________|
|______|______|_______|
wall

and side view, nts:
________ ________
_____|________|_____________________________|_____ ___|_____
|_________________________________________________ _________|

(Edit: can't keep side view looking the same as when I put it on the post, looks fine in the data entry mode, moves around when I post, should show 2 boards on top, you will have to use your imagination since I can't figure out how to fix it.)

The house is concrete block. I will probably need to use tapcons or anchors of some kind to attach to the house, which also raises a design issue as to how to do it, allow expansion of the boards and have it still look ok. Any thoughts you could offer as to the joinery or any other design aspect would be appreciated.
rstermer

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Mike

I think you are best off to glue up the 3 upright boards and simulate seperation with a v groove highlighted with a thin black paint stripe. Cut two slots across the two "Outer boards" and use them to mount your screws to the cross boards.

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Mike
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rstermer

After doing some research, it appears I had the expansion direction wrohg. Expansion across the grain is much gteater than with the grain. Here is a link:
What is Wood Movement?
and another:
http://chestofbooks.com/architecture...ntraction.html
rstermer

rstermer

This reference: http://www.fpl.fs.fed.us/documnts/fp...tr113/ch03.pdf
says that the coefficient of thermal expansion across the grain is 5 to 10 times as large as the coefficient along the grain.
rstermer

Mike

Think of wood as a bundle of straws. When you add to the bundle it does not get longer, it spreads out sideways. This is why you want to cut the slots sideways across the grain top and bottom to attach your cross pieces. Does that explanation help to clarify things?

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Mike
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