a. A concrete slab (or suspended beam and block construction) is laid over a damp proof membrane.
b. A 20mm thick piece of insulation is fixed to the perimeter (external) walls, to a height to include the depth of floor insulation and screed. Whilst the edging insulation may be on show it is covered by wall plastering and skirting boards.
c. Floor insulation laid to the whole area, joints are taped to prevent the ingress of screed between the insulation boards.
d. A plastic sheet is laid over the insulation.

The floor is now ready for the underfloor heating pipework installation.

The pipe is laid at 200-300mm centres dependent upon design.

There are two types of ground floor screed, the choice of which depends on timescales, size of the project and available budget. Liquid screed drys quickly and after it has been down for seven days, the heating system can be switched on, and the floor can be forced dried. It is more expensive than standard screed, but has four times the tensile strength.

Liquid screeding is very economic for large areas and has the supreme advantage of being fast to dry. As a rule of thumb, for any large commercial project liquid screeding would be the most appropriate choice. Liquid screed is not an economic option for a small system, such as a conservatory.

Standard screed consists of four parts sharp sand and one part cement and a plasticizer additive. Provided it is properly applied, it offers the same insulation qualities as liquid screed, which gets in under the pipe and avoids holes and void spots. These affect the performance of the system. The same result can be applied with standard screed, but it has to be applied with more care.

The big disadvantage of standard screed is the drying time. The screed should be left to dry for 21 days, and then the system can be turned on, but at very low temperature. As the screed dries, the temperature of the heating system can be gradually increased, but if the heat is turned up too high too quickly, the screed could crack.

In order for screed to bind and last, it must be laid in an environment that allows the molecular reaction to take place. If screed is laid at a temperature of 3 degreed C or less, the water in the mix freezes, and the binding of the molecules does not happen. Without the binding, the screed fails, and eventually cracks and crumbles. Screed laid in temperatures below 3 degrees C never sets properly.

When screed is laid at temperatures above 35 degrees C, there are high levels of evaporation and water does not get properly absorbed into the mix. Once again the molecular reaction does not take place, the binding does not occur, and the screed will crack and crumble.

Finally the floor finish is laid. Underfloor heating works well with almost any floor finish; tiles, carpets (use carpets with a resistance of less than 0.15 m2K/W), timber floors, vinyl and stone..

The floor coverings and the adhesive must be suitable for the temperatures that underfloor heating will provide, the maximum temperature they need to resist is 40°C. Always check with the manufacturer of the floor covering if it can be used for underfloor heating. Timber floors need to have a moisture content below 10% to avoid shrinkage and warping. The maximum temperature when using timber floor should be 27 degrees C.