Wherever walls and ceilings face regular humidity, condensation or splashes, moisture-resistant plasterboard is required.

It's the usual suspects that need a more specific plasterboard option: bathrooms, en-suites, cloakroom WCs, utility rooms and the area around a kitchen sink. However, it isn't waterproof so it can't be used on its own inside a shower.

It fits like standard plasterboard, but its core is treated to absorb less water (Type H1 under BS EN 520). It often has a green face, hence the nickname "green board", although colours vary by brand.

MGN Builders Merchants, which has branches in Romford, Woodford and Orpington, stocks 12.5mm moisture-resistant plasterboard in 2400mm x 1200mm sheets, with free same-day delivery on qualifying in-stock items.

Which rooms need it?

Use it in: bathrooms (walls and ceiling, outside the shower), en-suites, utility rooms and the wall behind the sink in the kitchen.

Worth considering in: cloakroom WCs, especially without a window, and the wall beside the hob.

Standard board is fine in: the rest of the kitchen, bedrooms, living rooms, and hallways.

None of this is a legal requirement, but a few extra sheets of moisture resistant board cost far less than redoing a wall. In small, windowless bathrooms, common in London terraces and flats, condensation collects on the ceiling, so board the ceiling as well as the walls.

Don't forget the hidden spots either: boxed-in pipes, the wall behind a washing machine and the inside of a laundry cupboard all benefit from moisture-resistant board. In an open-plan kitchen, a cooker hood that vents outside protects the walls far better than a recirculating one, which filters grease but doesn't remove moisture.

Can you use it in a shower?

Not on its own. It's designed for occasional moisture, and manufacturers require a tanking system before tiling anywhere that gets wet repeatedly.

• Tank it. A tanking kit (a liquid membrane plus tape for joints and corners) over the board makes shower walls ready for tiles. Pay most attention to corners and pipe openings, where leaks usually start.

• Or use a tile backer board. These are made for direct water and is the usual choice for wet rooms.

• A shower over the bath counts as a shower area, not just a splash zone.

• Damp walls need fixing first. The board won't cure rising or penetrating damp.

Tips for fitting it in a bathroom or kitchen

Do:

• Fix it like standard board: around 38mm drywall screws on timber, no more than 300mm apart on walls and 230mm on ceilings, and at least 13mm from cut edges.

• Pick the edge for your finish: tapered edge boards are made for taping and jointing before painting; on walls you're tiling, the edge type matters less.

• Check tile weight: around 32kg/m² is the usual limit tiled straight onto plasterboard, but only about 20kg/m² on plaster, so fix heavy tiles directly to the board.

• Use water-resistant adhesive and grout, and silicone where tiles meet the bath, tray or worktop.

• Prime before painting, then use a kitchen and bathroom paint.

• Fit a proper extractor fan: in England, Approved Document F sets minimum rates of 15 l/s for bathrooms and 60 l/s for kitchens (30 l/s for a cooker hood).

Don't:

• Fix boards tight to the floor: leave a 10mm gap so water can't wick up.

• Skim without a bonding coat: the water-repellent face needs a bonding primer first.

• Let boards get wet before fitting: store them flat and indoors.

In the right rooms, with tanking in the shower and good ventilation, moisture resistant plasterboard gives bathrooms and kitchens a lasting base for tiles and paint.