Diary Of An Eco-Builder

The Romans realised the benefits of underfloor heating, so why do we use clumsy radiators?

Despite this basic physiology, most houses in Britain employ wall-mounted radiators to supply their central heating, a system that works precisely contrary to this ideal temperature gradient. Radiators deliver most of their heat not through radiation but through convection, creating upward air-flows that drive warm air to the top of every room and suck in cold draughts at floor level. The result can be rooms that are stuffy, uncomfortable and prone to cold spots; rooms where "putting your feet up" may be the only way of getting thermally comfortable.

This clumsy approach to heating is far too inefficient for "zero carbon" tree house. Instead, we are using a system that will deliver room temperatures that almost exactly match our bodily preferences: the admirable Roman invention of underfloor heating. Although the seductive idea of the warm floor has survived unchanged, the technology has moved on, for where Roman hypocausts used warm air blown into a sub-floor from an adjacent furnace, modern systems rely on piped hot water or, for a lot more carbon emissions, electricity.

Unlike the misnamed radiators, a warm floor heats a room principally by radiation, so you get a very consistent, stable output with no swirling currents of air. Because the heat is greatest where you appreciate it most, you don't need as much heat to reach the same level of comfort, and because the water in the pipes does not have to be as hot as in radiators (50C rather than 80C), your boiler can operate at a more efficient temperature. This is especially important for condensing boilers that work best when the water returning to them is cool. It is ideal for our ground-source heat pump, which cannot supply the scalding temperatures demanded by radiators.

A big advantage of the system we are installing, supplied by Osma (www.osma.co.uk), is the integration of the pipework and flooring in one product. This made it possible for Mark and Nick to do two jobs at once: installing the underfloor heating as they laid the floorboards. On our solid ground floor, we will be threading the pipework on to special insulation panels before laying a concrete screed on top. When complete, the other great benefit of underfloor heating will become apparent: it does the job without getting tangled up in your furniture.

Because the system works by heating up a radiant floor, underfloor heating takes time to respond to changing needs. It, therefore, works best in frequently occupied, well-insulated houses that don't require a lot of heat quickly to bring them up to a comfortable temperature. It's not worth the money if you're never at home.

We will be finishing our floors with reclaimed teak upstairs and Kirkstone slate on the ground floor (www.kirkstone.com). The result should be stunning, even if it doesn't quite match the extravagance of the Romans' mosaic floors.

What did the Romans ever do for us? Interior design, the Mediterranean diet, moisturising cosmetics and the perfect personal temperature gradient. Two millennia later, it seems our faddish modern lifestyles are still just catching up.

www.treehouseclapham.org.uk