Laying new timber floor over Victorian solid floor

[Flipjango]

We're knocking two rooms together in our new kitchen. One side has floorboards and joists, but the other side has a victorian solid floor with quarry/teracotta tiles on top. Apparently the quarry tiles act as the damp membrane. We would like to insulate the floors before laying new parquet flooring across the two sides, but I've no idea what to do about the solid floor. We're going with lime plaster render to keep the house breathable so I'm worried that laying any kind of damp proof membrane will just push moisture into the walls. Does anyone have any idea what we should do with the solid floor in order to make it suitable to lay timber on top of, and to allow us to get a level floor across the two sides?

 

[Flipjango]

Anyone?

 

[MatthewC]

We're knocking two rooms together in our new kitchen. One side has floorboards and joists, but the other side has a victorian solid floor with quarry/teracotta tiles on top. Apparently the quarry tiles act as the damp membrane. We would like to insulate the floors before laying new parquet flooring across the two sides, but I've no idea what to do about the solid floor. We're going with lime plaster render to keep the house breathable so I'm worried that laying any kind of damp proof membrane will just push moisture into the walls. Does anyone have any idea what we should do with the solid floor in order to make it suitable to lay timber on top of, and to allow us to get a level floor across the two sides?

Anyone?

You asked pretty well the same question on 19th Feb. If you have an old solid floor the last things that you want to do are either cover it with a damp proof membrane (damp will be retained underneath and eventually reach the walls...) or to put a wooden floor on top of it (the dampness will be trapped in the void and the wooden floor will slowly rot.)

If you really want to have the same parquet floor the whole way through then you would really need to dig out the old solid floor and make it a suspended floor, with a void and PLENTY of ventilation under it. But that would possibly be a shame for your old (original?) solid floor. Having said that, mine was in very poor condition and I laid a limecrete floor - very happy with that, albeit quite a task.

 

[Flipjango]

Apologies, it looks like I was not subscribed to replies last time and didn't realise anyone had answered.

Thanks for the reply. I'm leaning towards a suspended timber floor as we will struggle with the drying times of Limecrete. The solid floor area is very tiny - only 6m2 out of a room that will be around 60m2 when finished so it would be hard to realistically retain it. The tiles are also quite damaged so would need a lot of remedial work anyway.

 

[Flyfisher]

If you have an old solid floor the last things that you want to do . . . . . or to put a wooden floor on top of it (the dampness will be trapped in the void and the wooden floor will slowly rot.)

I can confirm that scenario from personal experience. We have a room with pamments laid on earth, which I suspect are original to that part of the house and at least a couple of hundred years old. At some time a wooden floor was laid on top - simple battens laid directly on the pamments and floorboards fixed to the battens. No underfloor ventilation. I don't know when this was done but I'm sure everything was fine for (probably) many decades.

Predictably, the permeable pamment floor allowed sufficient moisture through to eventually cause the wooden floor to become rotten and the previous owners ripped it all up to expose the pamments - which are perfectly serviceable.

To the touch, the pamment floor is perfectly dry, but if we cover it with anything impermeable the moisture builds up underneath. We first noticed this when the soggy bottoms fell out of cardboard boxes we were storing on the floor!

To test your own solid floor, try laying a sheet of polythene over part of it for a few weeks. You might be surprised at how much moisture accumulates underneath it, whereas the uncovered areas are likely to remain perfectly dry to the touch because of evaporation.

In contrast, we have other rooms with suspended wooden floors where proper joists have been supported on bricks about four inches above bare earth and with airbricks providing underfloor ventilation. I don't know for sure but I suspect these floors were laid at the same time as the one laid directly on the solid floor. Anyway, the suspended floors all remain in good condition, so I think the lesson is fairly clear.

 

[MatthewC]

If you have an old solid floor the last things that you want to do . . . . . or to put a wooden floor on top of it (the dampness will be trapped in the void and the wooden floor will slowly rot.)

I can confirm that scenario from personal experience...

My experience was the discovery of a large gap between the panel at the back of some choir stalls and the floor beneath, which was sagging. The gap caused a huge draught.

Lifting a floorboard revealed that the platform for the choirstalls (done in Victorian times I think) had been laid directly on the previous wooden floor and - guess what? - that older floor, laid directly on the apparently dry earth, had mostly rotted away. I was able to use a couple of car jacks (repeatedly moved from joist to joist) to incrementally lift the current floor almost to where it was originally, placing some engineering bricks and slate underneath the joists.

I reckon my fix will last longer than the original. Those Victorians just did not understand dampness and ventilation, did they?

 

[Flipjango]

So, the plan is now to dig out the solid floor, and then lay a suspended timber floor in the old scullery, adding air bricks to ventilate. The extension will have a concrete floor and there will be a beam dividing the old house and the new extension.

Our architect is saying we need to install a damp proof membrane to the sub-floor of the old house when we've dug it out, or to paint a damp proof course onto the wall, but this seems to go against everything I'd understood - I thought the whole point of us having permeable walls and ventilated floor was to remove the need for damp proof membranes? Could anyone advise please?

 

[a twig]

Punch your architect on the nose

 

[Flipjango]

Yes, that was my first thought. But seriously, i'm pretty new to this, so I'd be super grateful if someone could just summarise what we ACTUALLY need to do. Without an architect to ask, I have nobody else to consult! Is it just a case of dig out, install floor and the jobs a good 'un?

 

[MatthewC]

Where does the architect think the moisture under the membrane will go? Eventually it will reach the walls...

You need to well ventilate the sub-floor volume, so that dampness that comes up from the earth is able to escape. So you need some decent size ventilation holes in the right places so that the whole area is ventilated sufficiently. In the large church I mention above (that work was done in 1862), the huge volume was very poorly ventilated with only one exit point that I have found. They should have had at least two if not four or even six exit vents, and possibly put some vents into the floor itself, farthest from the exit points. They did lay a thin layer of lime mortar on the ground - not quite sure why! The air smelled so damp when we lifted a floorboard, even though there is no ventilation through the gaps in the rotting floorboards!

If the floor is that well ventilated, you will have to think about insulating the floor as well.

 

[Flipjango]

Thanks, that's really helpful. The architect is talking about putting vents through the floor of the extension, and we have an outside wall we can also add air bricks to. Its a pretty small area - only about 3x3m so I hope that will be sufficient. Plan is to insulate between the joists when they are laid, as well as under all the other timber floors in the house. Then it will be boarded before we lay parquet. Hopefully this will work. Really appreciate the advice. Thanks

 

[urowho]

I've got a similar question. I'm replacing lime/rammed earth floor in the kitchen and gorgeous 1970s concrete floor in the lounge with limecrete with underfloor heating. The kitchen will sadly loose its pamments (they are really knackered hence having been covered by 4 later floors) and they will be replaced with handmade terra cotta.

The bigger question is the lounge as we'd like parquet (like you) on the limcrete floor. What is interesting is that in my search for a house one we saw was a 1770 farmhouse which clearly had a very early parquet floor laid on a lime ash/rammed earth base. Apart from being a bit loose around the edges it seemed perfectly serviceable. Parquet floors were introduced really very early in the 1600s and must have originally been on lime ash as suspended floors didn't exist on the ground floor.

Anyone else seen this? would it maybe be better to have the blocks directly on the floor to naturally transmit the moisture? The other alternative is a paraphernalia of battens/ply etc.

Anyone got any experience?

 

[Flipjango]

It certainly sounds appealing to do it that way! It’s not too hard for us to dig out as we’re having an extension abutting to the solid floor anyway, but even then, it’s more work, more cost!