The traditional specification for a conservatory base is a concrete foundation a concrete floor slab and brick walls. The preferred building regulation specification is, a six hundred millimetre deep by six hundred millimetre wide, footing excavation. Then a mass poured (that means all poured in one go) two hundred and twenty five millimetre (minimum) concrete strip foundation. The correct concrete strength, that is the proportion of sand, cement and stone mixture, will depend on the ground conditions. For very poor ground conditions, the concrete can be poured much thicker and steel reinforcing bars introduced. If you think your ground conditions are bad, the services of a structural engineer should be employed.
Once your concrete strip foundation has gone off, or cured, the plinth brick work needs to be built up to damp proof course (DPC). It is always recommended that an engineering brick be used below DPC, as they are a lot harder than normal bricks. Once the plinth brick work is complete, a hundred millimetres of hardcore , or class one MOT, needs to be evenly compacted throughout the base of the conservatory. Once you have achieved a flat, level stand of hard core, you need to lay the damp proof membrane, in one continuous sheet. The damp proof membrane is normally specified as, 1200 gauge visqueen, DPC.
On top of the damp proof membrane the insulation layer needs to be fitted. Note, whatever product you use, the sheets should be tightly fitted together. There are a number of different insulation products available, ranging from compacted polystyrene to foil backed polymers, that are much more thermally efficient. Once you insulation sheets fitted and level the concrete over site, or slab, needs to be poured to a minimum thickness of one hundred millimetres. The finish of the concrete slab can either be tamped or floated. Tamping usually requires a cement screed on top, as it is a rough finish, while a well floated or trowelled finish will allow you to lay your flooring directly onto it's smooth surface.
Next the brick walls need to be built, unless your conservatory design has full height glass walls or uPVC panels. The minimum specification, for the wall thickness, is a one hundred millimetre outer brick, a fifty millimetre cavity and a hundred millimetre internal brick or block. The cavity, in the instance where a conservatory is to be open plan to the house, could be up to one hundred millimetres in width, to increase the thermal efficiency of the wall. Again, there are different insulation products that will perform at various efficiency levels to keep the structure warm. It is also good practice to use tie wires to strengthen the brick walls.