New floor construction - without concrete!

[BlueC]

Hi

We're going to be sorting out our basement (converting it into living space) and have some questions about floor construction. The current floor is quarry tiles and very solid and flat. It has been down for 120+ years and is in really good condition but is not suitable for our conversion as there is no DPC. We dug some of the tiles up and they are just lying directly on the ground which is a sand/sandstone type of earth. It looks like about 6 inches of compacted sand lying on the natural sandstone rock that is everywhere in this part of the world.

We don't want to lose too much height so we considered digging the floor up by about 200mm and laying a new concrete base (100mm) then DPC then insulation (50mm) and putting a floating chipboard floor over this to bring us back to the original floor height. I believe this would be a fairly standard approach.

However when we have dug down to explore it is clear the house has no footings - it is just built directly on the sand/sandstone earth. Our architect reckons if we want to dig down we'd need to underpin it first, so recommended we don't bother. His suggestion is to either

1) Lay a DPC over existing floor, then about 25mm of insulation, then a floating chipboard floor on top of that. We'd lose about 50mm of height.

2) Dig up just the tiles, level the sand base, put 25mm of insulation on it, then a DPC, then a floating chipboard floor on top. We'd lose about 25mm of height.

What's your thoughts on these suggestions? We prefer option 2 because of the height issue but I am struggling to get to grips with the idea of a floor that is just a load of polystyrene laid directly on the earth with nothing "solid" and no anchoring... but maybe I'm just too used to seeing concrete everywhere?

Cheers
Chris

 

[MdB]

Do you have a damp problem in the room currently?

 

[BlueC]

Do you have a damp problem in the room currently?

Yes it is damp, but only mildly and there is never any "water". The damp is mainly penetrating from the external walls where they are beneath ground level, very little comes from the floor itself and any that does come up through the tiles (as they are permeable) evaporates immediately into the air so the floor is never wet. However, we would need to introduce some kind of DPC into the floor to satisfy building control.

I'm more concerned about the feasibility of laying a floor which has no "solid" base as it seems counter-intuitive.

 

[LadyArowana]

Unfortunately basements weren't designed to be dry and lived in. The same with under pavement vaults and other such spaces in period properties. As I understand it, if you put a dpm in the floor moisture which previously escaped that way will probably go into the walls and you will move the problem not solve it. The lower level of our house, which would originally have been the kitchen and a servants area has a *lovely* concrete floor which is totally dry, however there are patches on the walls. Sorry, I know this is not really what you were hoping to hear.

 

[BlueC]

Unfortunately basements weren't designed to be dry and lived in. The same with under pavement vaults and other such spaces in period properties. As I understand it, if you put a dpm in the floor moisture which previously escaped that way will probably go into the walls and you will move the problem not solve it. The lower level of our house, which would originally have been the kitchen and a servants area has a *lovely* concrete floor which is totally dry, however there are patches on the walls.

Thanks, I know all that. We will be treating the damp in the walls in a different manner and we are very familiar with the different approaches available to us in order to meet BS8102 and ensure the space becomes dry and habitable. My question was not about damp, but about the construction of the floor and whether the options provided to us are viable in terms of having no concrete poured.

Sorry, I know this is not really what you were hoping to hear.

It's not news to me, it just doesn't answer my question whatsoever. But thank you.

Can anyone offer an opinion on the actual floor construction?

 

[Lime]

Option one is my favourite if I had to make the choice.
The reasons being that the original floor is left in place and that the subfloor, whatever it is, is left undisturbed to maximise support to the house and minimise the risk of any structural movement.
IME of cellars each year is different. Some years are dry, some are less so and sometimes they flood.

 

[BlueC]

Option one is my favourite if I had to make the choice.
The reasons being that the original floor is left in place and that the subfloor, whatever it is, is left undisturbed to maximise support to the house and minimise the risk of any structural movement.

Thanks Lime, this was more what I was looking for. I think my instinct is the same - to leave well alone and just accept the small height decrease. We could be opening a world of pain if we remove the tiles.

IME of cellars each year is different. Some years are dry, some are less so and sometimes they flood.

Yes I agree but also the local land and environment are important. Even with all the rain we had last year we never had a drop of water in the basement. We live on a hillside that is made of sandstone and the drainage is exceptional. Fortunately there are much easier places for the water to go than in our basement!