Boxing in below stairs, conventional 3-bed semi

[js.b1]

In examining a relative's storage heater, attached to the ground floor stairs in the hall, I found it was just screwed to 6mm hardboard which had begun pulling over its nails.

The 110kg heater will be re-fitted to heavy studwork into 4x4 stair posts.

What should the boxing in be made of - 6mm plywood, 12.5mm red fire plasterboard, 6mm cementboard? Jewsons wanted =A350 for 6mm cement-board (might as well use two piece of =A315 from B&Q).

Conventional 3-bed semi, boxed-in understairs. I plan on 6mm butt-n- match MDF matchboard either side of the heater, simple rail above, retaining the wallpaper further up the wall.

[js.b1]

Boxing in the *stairs*.

Many understair areas in 3-bed-semi are boxed in. Simple studwork, hardboard or plasterboard or cementboard, door into the boxed-in area (the infamous under stairs cupboard).

The storage heater is fixed to the boxed-in stair studwork, as with any other studwork wall in modern houses.

I can use 12.5mm Fireline Plasterboard (red, Class-0) or much more expensive 6mm cement board.

I suspect Class-0 Fireline Plasterboard is quite ok for boxing-in the understairs area?