A conservatory you can use all year

Many people built a conservatory to enjoy the garden, and then found the room hard to keep comfortable.

A common answer is to swap the glass or polycarbonate roof for a solid, insulated one. Local Authority Building Control (LABC) says many homeowners now do this to keep the floor space and use less energy. These notes follow the rules for houses in England. Wales may differ, and Scotland and Northern Ireland have their own.

The kinds of new roof

LABC describes three common choices. One is a lightweight composite solid roof. Another keeps the existing polycarbonate roof and lines it underneath or covers it over. The third is a traditional tiled roof.

Some lightweight roof systems have an LABC Registered Detail. That gives an approved design, quality control and accredited installation, which can make the building control check simpler.

Building regulations

A conservatory is usually exempt from building regulations while it stays at ground level, under 30 square metres, and separate from the house. The separation is walls, doors or windows of outdoor quality. The house heating must not run into it.

LABC says that when work greatly reduces the glass in the roof, the room can no longer be treated as an exempt conservatory. The new roof then has to meet the building regulations in full. The rest of the conservatory must be no worse than before. So a solid roof normally needs building control approval before work starts.

How warm the new roof should be

Approved Document L, the energy guidance for England, sets the most heat each part of a home may let through, as a maximum U-value. A lower figure means less heat lost. For a new roof on an existing home, the maximum is 0.15 W/m²K. For a new rooflight it is 2.2 W/m²K.

When a conservatory is no longer exempt, the guidance also asks for any fixed heating in it to have its own temperature and on and off controls. LABC's guidance assumes the conservatory stays thermally separate from the house.

The structure underneath

A solid roof is heavier than the roof it replaces. LABC says the window frames may have been designed to carry only the old roof. A builder may check for a steel core in the frames by drilling a pilot hole or using a magnet. If there is no reinforcement, new frames or extra posts may be needed.

Building control may also ask for a trial hole to check the foundations. LABC says a 150mm concrete strip or slab on original ground will be enough in most cases.

Planning permission

The Planning Portal says most changes to roofs are permitted development, as long as they meet the limits in law. If the change greatly alters the structure or appearance of the roof, planning permission may be needed. Some areas have extra planning restrictions, so it is worth asking your council early.

Before work starts

Citizens Advice suggests getting written quotes and a written contract before choosing a builder. It also says work done without the approval it needs can cause problems when you come to sell your home.

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