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For years, housebuilders have been shoehorning more bathrooms into smaller floorplans. From October when the revised Part M will demand downstairs facilities, this trend will intensify. One solution has been to specify only showers for ensuites - a shower takes up less than half the space of a bath and can be set in an awkward alcove. The downside is shower cubicles and trays are expensive, the installed price being two to three times more than a bath.

What price then open showers running to a floor drain? It is common abroad, and in this country in special needs bathrooms. You dispense with the tray and only need a shower curtain for enclosure. The key is the floor drain which has to sit inside a floor void, and cope with the 30 litres per minute which a power shower will throw.

It also has to include a trap and yet be readily cleanable, which means that the grate and the assembly must be removable - good shower drains cost more than £100. Manufacturers include Harmer (part of the Alumasc group) and Caroflow and designs allow incorporation with either regular floor tile sizes or sheet materials such as Altro Safety Flooring. Altro's main shower product is Marine 20 which is a 2 mm covering laid over floors, which can be continued up walls as well. At just under £15/m² (material only), it is no more expensive than ceramic tiling.

The key to getting a floor shower drain to work well is to build in a fall of 1:40 for a metre around the floor drain. In masonry floors this can be achieved relatively easily with a 25 mm depression in the screed - the Harmer floor drain requires only a 25 mm-deep screed. However, you can rarely shave 25 mm off the top of a timber joist without weakening the floor so the usual solution is to build a fall up with firrings laid across the tops of the joists; this leaves you with a 25 mm threshold at the bathroom door to be addressed.

Building in a fall should prove simple. Chris Goodman, development programme manager of housing association Habinteg recommends keeping it so. "We did have problems with water ingress to hallways. It was always a result of inadequate falls in the bathrooms. Now we locate the floor drains in a corner to minimise the problem."