We are renovating a pre 1830's building. The walls are Norfolk clay lump (Clay, chalk, straw) laid on flint followed by 2 or 3 courses of brick. Except for one small area of damp proof injection, there is no other damp proofing other than that provided by the flint. Almost all of the door surrounds and skirting boards were rotten. Much of the timber flooring (laid on concrete over floor tiles or bricks was rotten). Exterior ground levels were about level with concrete floor levels inside; though there is a French drain all around the building. All of the concrete floors have been removed, lowering the floor level by between 6 and 8 inches (so now below the top of the shingle in the French drain). I expect the foundations to be almost non-existent. Plaster on the inside walls is modern, we will remove it and replace with lime plaster and lime wash. The outside walls have 'modern' render and plastic paint; in the near future, we will not do anything about this.

OK that's the background...

We will re-lay the floor tiles and bricks, we will not have fitted carpets.
We think that underfloor heating in this property is a good idea (especially as we have dug up all the ground floor anyway).
We may heat with ground source heat exchange, wood burners, or wood pellet boiler -- not decided yet.

Questions...
1 Is a damp proof membrane under the floor necessary? The old building did not have one, but then it did smell damp, and is damp. I am inclined to think that a dpm will direct the damp outwards towards the walls, causing problems in the clay lump walls.

2 several options for the rest of the floor construction have been suggested: compacted agricultural chalk only (with a lime screed to lay the tiles and bricks onto); limecrete only (with a lime screed to lay the tiles and bricks onto); and both limecrete ad chalk together.

I am sure that there are many other options.

Any ideas?

Steve

Thank you Tony.