There is more than one way of putting underfloor heating in a solid floor, but this is one of the methods we have used at CAT. Floors should comply with building regulations, so do check your plans with your building control officer.
There are many commercial companies that install underfloor heating systems. The advantage of a professional installation is that the company will be able to pressure test it, checking for any leaks and ensuring it is stable before covering it over. It’s also feasible to do it yourself - but you'll need building and plumbing know-how.
First, lay a concrete or limecrete subfloor over your damp-proof membrane, and on this lay a layer of insulation - it needs to be something solid like expanded polystyrene or cork, and should also run up the edge of the floor to stop the heat from escaping into the walls. The underfloor heating pipes (cross linked polyethylene or barrier pipe) will lie top of the insulation, running back and forth along the length of the floor.
Underfloor heating pipe is fairly easily available from plumbing suppliers. 15mm bore pipe is better than 10mm, as it will be easier to pump the water round. You can buy fixing plates with the pipe to enable you to fix it down onto the insulation. Over this you then lay another layer of concrete / limecrete screed which needs to cover the pipes by at least 50mm.
A manifold connects the pipes to the heating system and heating controls just as in a normal heating system. You can then lay a floor finish such as tiles, slates or stone over the concrete.