How to Account for Oak Expansion in Outdoor Project

[Ron Kanter]

I am building two Little Free Libraries for a park. They will be similar to the attached picture except with a flat roof sloped front to back.
They want me to use white oak.The sides will be approximately 18" wide and 24" tall. My concern is that being outside summer and winter will create significant expansion and contraction issues.
My first thought was to create the sides using three ship lap boards and use only one screw in each board or maybe two screws with the heads in a short channel instead of a drilled hole.
Will this approach account for the expansion or is there a better way to keep the libraries from cracking? And how would you suggest joining the sides to the front, back and roof?
One more question: what finish would be most protective and relatively low maintenance?
Thanks for you thoughts and experience.

LFL Debbie Cropped.jpg

[ernest dubois]

I have always had the trouble with oak construction like that and will avoid it in these circumstances from now on. Not only is the dimensional expansion and contractions of the wood excessive but the related splitting at the connections, so where you would screw it, though slotting would provide a remedy. Even using kiln dried and quartered wood gives no relief, though with the former I wouldn't expect any. My mailbox, as a somewhat mundane exemplar, is from poplar wood but then decked off with an oak lid. This is the direction I will go from now on regarding such oak construction for outside. Otherwise you've got to go to a post and rail with panel build I think.

[Ron Kanter]

Only one reply so far.
Is there more information I need to include so that folks can offer suggestions?
I have most of the pieces prepped to rough size and don't want to do more until I have decided on a method of construction.
My plan is to make all the sides and backs out of at least three boards. Anything else that is relevant?
thanks

[Jerry Miner]

If you keep the grain running in the same direction for the sides and roof, you could make those parts solid, with T&G slats for the front and back.

But IIWM, I would probably mill the wood into relatively narrow (+/- 4") pieces with T&G edges and allow each piece to expand/contract individually and keep the frame parts narrow in section.

[Mel Fulks]

Your clients idea is not good. Jerry's idea is within the specs.

[John C Cox]

Any chance they will let you do cedar shakes (or something similar) on the roof and walls to keep water off the oak? This will reduce issues with oak swelling, moving, and shifting when it gets wet.. As others have mentioned - keep the grain on panels running the same direction... Include provision in the design for wood expansion/contraction and movement..

Another thing design wise.... Oak has a LOT of natural tannin and tends to stain black anywhere there is contact with iron/steel stuff like hinges and fasteners... And it can be ugly if stuff rusts and the rusty residue washes down oak - it leaves nasty black streaks...

Heartwood white oak is pretty good stuff outdoors in terms of resistance to the elements...

Finish wise... That can be tricky if they don't want to refinish it/stain it annually... Shiny/clear finish - I would look to sailboat varnishes or exterior urethanes... Even the best of these have to be redone every year or 3 to keep them looking decent... Overall for exterior finishes - I have had best luck with either quality exterior house paint or sailboat products...

[Yonak Hawkins]

While I tend to agree that keeping the grain all going the same direction will mostly mitigate your movement issues, my concern, for an outdoor oak construction, is the finish. If you want them to last any length of time and continue to look good, your best bet is to paint them with a good outdoor paint.

[John C Cox]

Any chance you could talk them into cypress?

[Jay Michaels]

I second John's recommendation for another wood choice - something like cypress is an excellent choice for outdoor construction. It has similar light tones and is MUCH more resistant to rot / decay and other problems posed by putting oak outdoors. Oak is an indoor-only wood choice for my projects.