I was wondering about taking 6ft off the end of the internal garage and making it into a big storage cupboard accessible from inside the house. It’d need a partition at the end of the garage, a floor (the garage floor is a foot or so lower than the house) and a doorway into the hallway.

The garage floor is level with the outside floor, so I think that means it’s below the damp-proof course. Presumably then the new section would need DPC in it to keep the wooden suspended floor dry…?

As for the door – the wall is made of thermalite blocks so I could easily cut it, but I’d need to install a lintel first before cutting a doorway. No idea how to install the actual door and frame though.

Sound like a stupid idea? Terribly big job?

I think you need a firedoor between the garage and the main house.

There are a few videos on Youtube showing how to install a door frame. IME doors are a bastard to fit and I’d rather get someone with the ability to do it properly. 😕

No idea how to install the actual door and frame though.

Buy a huge bag of various size wedge shape packers as you need to get the verticals absolutely vertical….

Put a stud wall in one end of mine, just used some roofing felt to stop any damp. Bolstered both sides with chipboard, good for screwing shelves on to.

Already had a door, so easy job. Would get a pro in to review any ideas on a new one.

I think you need a firedoor between the garage and the main house.

I was going to go for a sturdy door for both insulation and security purposes.

Is it still the garage if I use blocks and properly brick up the end?

Regardless of wether you use block or something else to construct the wall you must also consider transfer of fire through the roof space/ceiling void above.

The bit left as the garage will still be classed as a garage.

Fire door for is to maintain fire protection from the garage.
As your going to put a wall up, the wall will be the fire protection. Double plaster boarded and skimmed if on wood.
I’d personally just block it up with a damp course at the bottom.
Is the garage ceiling plaster boarded already.

The bit left as the garage will still be classed as a garage.

Odd, but whatever, it’ll probably be an exterior grade door but in any case our house has three storeys so all the living space doors are fire doors.

Ceiling is already plasterboarded yes.