You don’t say what timber frame system you are using, so I’ll cover both softwood and oak. For a typical softwood open or closed panel timber frame this is the right thing to do so your brickie is giving you good advice. I spoke to Simon Orrells at Frame Technologies and he confirmed that you can expect 5-6mm of settlement per storey on a timber frame structure over the first few years, so 10-20mm of of expanding foam strip would be required rather than bedding the soffits in with mortar. A specialist tape such as Compriband should be used, but it is not cheap at around £5 per metre. The good news is that it is self adhesive and very easy to lay so there shouldn’t be a huge labour cost attached. I don’t know the size of your project, so I can’t say if £500 is a fair price or not, but it doesn’t sound too far off the mark. Work out a sensible price based on the perimeter of your walls and allow for a couple of hours of labour.

For a green oak frame. I spoke to oak frame specialists Oakwights and they confirmed that if it was a traditional English oak frame with infill panels, they would use expanding foam seals which are installed as the frame is erected and are included as part of their package. For post and beam frames which are enclosed by their encapsulation system, they have a built-in mechanism to deal with any settling of the green oak Frame.

Mike Hardwick (Build It expert)