I am building some external doors, and was advised that in US they have a product that is Plywood with vertical grooves .... so looks as aesthetically pleasing as T&G ... but has dimensional stability of ply.
In US this is known as T-111 sheet. Or T-111 siding
Initially it had a rough-sawn, textured surface with vertical grooves milled every 4 or 8 inches. Thickness ranged from 3/8 inch to 3/4 inch. Usually fabricated from Douglas fir, but also in redwood.
Anybody know of an equivalent product in UK ?