Expansion.....outside timber panaeling

[Stuart]

Using a softwood V Groved timebr paneling to clad an outside wall, The cladding will be on horizontal lats fixed onto vertical lats, should any spacing be allowed for expansion due to swelling in wetter weather? (the timber will be painted and is in a sheltered place, so should never get directly wet, I am thinking more on the lines of winter time when most timber swells slightly!

[The Natural Philosopher]

Outside, yes.

Indoors it shrinks in winter...

I'd leave a fair gap unless you nail it down so firmly it just goes into compression.