Flues through timber frame building

[New_gas]

Hi I’ve got my ACS exams in 2 weeks and am working a few days a week with a registered gas engineer. Today I was given the task of doing the flue for a Glow Worm boiler. This is a new build and is timber frame, I’d heard before that through a timber frame wall the flue needs a sleeve, the engineer I was working with said he normally wrapped them in fireproof insulation. My question is this a correct way of doing it? I suggested a metal sleeve from the inside off the building to the outside with 25mm around the flue. Then filling the sleeve with fire foam to keep the insulation value of the wall. Would this sound alright? Also would need a metal plate on the external wall where the flue exits or would the normal flexible sealing collar be ok on its own?

 

[ShaunCorbs]

Normally a 5” or 6” metal duct I use