Loft conversion bathroom and ensuite planning

Drainage comes first

The position of the existing soil stack largely decides where the loft bathroom can go. Placing the WC close to the stack allows a gravity connection with enough fall. Where that is not possible, a macerator or pumped system can be used, though most building control bodies prefer a gravity WC where one can be achieved. Pipe runs have to cross the new floor joists, which needs planning with the structural design.

Head height and layout

Sloping ceilings dictate where fittings can sit. The WC and basin need standing height in front of them, and a shower needs full height over the tray. Baths fit well under the lower part of a slope. A dormer is often used to create the headroom a shower needs.

• Shower under the highest point or in a dormer
• Bath along a sloping wall
• WC near the soil stack
• Basin where you can stand upright

Water supply and pressure

Older houses with a cold water tank in the loft have a gravity-fed system, which gives low pressure at the highest point and means the tank has to move. A combination boiler or unvented cylinder may need checking to make sure it can supply a top-floor shower properly.

Extraction and condensation

Building regulations require mechanical extraction in bathrooms. In a roof space, the duct route and insulation around it matter, because warm moist air meeting cold roof timbers can cause condensation. Roof windows help with light and airing but do not replace an extractor fan.

Waterproofing and floors

Timber floors flex more than solid ones, so wet areas need suitable boards, tanking and careful detailing around the shower to prevent leaks into the ceiling below.

For fitting and finishes, see our bathroom renovations service.

Ensuite or shared bathroom?

An ensuite suits a single loft bedroom. Where the loft holds two rooms, a shared shower room off the landing may make better use of the space and drainage. The fire strategy and stair position also affect where a bathroom door can sit.

To plan the whole conversion, see our loft conversions service.

Planning the bathroom at design stage

Decide on the bathroom at the start of the design, not after the structure is fixed. The joist layout, steel positions and stair location all affect where pipes can run and where fittings can sit. Agreeing a shower or bath, the type of WC and any underfloor heating early means the structural engineer and the builder can allow for them. Sanitaryware sized for compact spaces, wall-hung fittings that save floor area and niches between rafters for storage all help in a sloping room. Lighting needs thought too, since ceiling lights must be rated for bathrooms and roof windows over a shower need suitable glazing and blinds.

Heating and hot water

A loft bathroom needs reliable heat and hot water at the top of the house. A heated towel rail on the central heating, an electric rail or underfloor heating can all work, depending on the existing system. Long pipe runs from a boiler or cylinder on the ground floor mean a wait for hot water, so the route and insulation of pipework are worth agreeing at design stage. Where the existing boiler is near the end of its life, it may make sense to review it alongside the conversion.

Common questions