We are building timber frame and had planned a render on board and circa 70% larch cladding.
Because of the type of people we are, and you never know, we did some research to ensure the result was mortgageable, by either as as a equity release in years to come or by others should we decide to sell.
We found several instances in mainstream lenders of more than 50% cladding being a no go, and other requiring more than 50% block. In the end we have a block skin to the ground floor and less than 50% wood cladding backed by cement board on our boundaries.