Planning the roof, the loft and electrics

The roof and the loft decide how warm the house is and how dry it stays. A new covering is a job for a roofer, but you can check the quantities in a quote. Loft insulation is the cheapest way to cut heating costs, and a DIY job. And a basic grasp of watts and amps helps you read an energy bill and choose appliances.

This planner covers the roof tiles, the loft and the electrics at a planning level. Wiring and gas work must be done by registered professionals.

Step 1: Measure the roof and choose the tiles

The sloping area of the roof is bigger than the footprint of the house, depending on the pitch. Plain tiles and interlocking tiles need very different numbers per square metre, and each has a minimum pitch. The batten gauge is set by the tile maker.

Step 2: Insulate the loft

A typical recommendation is about 270 mm of mineral wool for a cold loft, laid in two layers, one between the joists and one across them. Take care not to block the eaves ventilation, and keep insulation clear of recessed lights and flues.

Step 3: Size the radiators

A room needs a radiator whose output, at the standard rating of ΔT50, matches the heat the room loses. Rooms with single glazing, solid walls or several external walls need more, and a heat pump, which runs at a lower flow temperature, needs radiators with roughly twice the ΔT50 output. Adding insulation first can let you fit smaller radiators and a smaller boiler or heat pump.

Step 4: Understand watts and amps

On UK mains, amps are watts divided by 230. A 13 amp plug supplies up to about 3 kW, which is why kettles and heaters are limited to that. A ring main on a 32 amp breaker supplies all the sockets on it, and showers and cookers have circuits of their own.

Step 5: Work out what it costs to run

The cost of an appliance is its kilowatts times the hours it runs times your price per kilowatt-hour. Heaters and tumble dryers cost the most to run, and LED lights the least.

Before you start

• Roofer quotes that state the tiles, the battens, the membrane and the areas.
• Building Regulations approval where re-roofing or insulation needs it.
• Ventilation at the eaves and the ridge before and after insulating.
• A registered electrician for new circuits (Part P of the Building Regulations).
• Your tariff, to work out running costs.

Mistakes that cost people money

• Blocking the eaves ventilation with insulation.
• Choosing tiles that are not suitable for the pitch.
• Covering recessed lights with insulation.
• Running several 3 kW heaters on one ring main.
• Doing notifiable electrical work without a registered electrician.

Frequently asked questions