Digging out floor and installing new foundation? Damp problem...

[Jaide2012]

Hi everybody,

I am newbie here and looking for some advice. We recently bought a 1930s house. On the ground floor we noticed the parquet floor was uneven and sounded hollow, and there was a crack in the screed in the hallway and several cracks under the parquet in the living and dining room. None of the cracks were particularly wide but the slab underneath crumbled away with some light prodding. On further investigation, we found out that the house has no DPM or DPC (apart from a small line of bitumen on the bricks, which are below floor level). The floor is not very deep, with bitumen under the parquet flooring, a screed (possibly lime), a 2" slab and then hardcore/soil. The soil is very wet (like wet clay).

After having a damp specialist round, we have figured out that the problem is that water can't drain away. The outside floor level and inside floor level are identical, water from gutters just drains onto the paved drive and seeps into the ground and then horizontally into the foundations.

To solve the problem we think we should lower the outside ground level and also dig out the floor in the house and replace it with a new one (incl a DPM). However, I have no idea where to start with this. Who would do this kind of work? A builder? A specialist? Has anyone had a similar problem and/or removed and replaced the floor? Any tips, thoughts and advice would be hugely appreciated - thanks!

 

[malcolm]

Water draining away is not the problem normally. It is water getting in that tends to be the issue. Don't hang on every word of a modern damp specialist (or any modern specialist) as they don't tend to understand old buildings or basic science or anything else much.

I think you might have a problem if water has been finding it's way under your floor and washing the soil away. Is it happening near any obvious water source? Burst pipe, natural spring, gutters?

Roof drainage is worth sorting anyway - In an old house you are often allowed to pipe gutters to the foul drain. I have done that with some of mine, and have dug a soakaway for the others. You need a man with a digger to create a hole for a soakaway. http://www.pavingexpert.com/drain08.html offers useful advice.

High external ground levels will tend to only cause damp at the base of the external walls. That isn't a good thing but can be fixed by making the external ground level lower than internal. You can assess levels by buying a plastic see through pipe, filling it with water, getting someone to hold one end outside while you hold the other inside, and measure the level of the water at both ends from the ground. If it is only a little difference then a shallow trench outside against the wall filled with gravel might be enough to fix it.

Your floor system was reasonably common in the 1930s and works fine. I have an early version from 1910 with thinner concrete. I am in no mind to dig it up as it would be hugely expensive and it isn't a problem in itself. The hollow cavity under the floor is a symptom not the problem. Digging it all up and replacing it might hide the problem but won't fix it.

Never wishing to be left out of structural problems I also have a hollow bit of floor which I have been avoiding but which I should look at over the holidays. It could be a well or badly filled cellar, a water leak, or erosion from the downpipe that used to be there. Maybe I should have a look.

 

[88v8]

Hello and welcome.

What is the black & white? Quarry tiles? Looks rather nice.

As Malcolm says, I'd forget digging out the floors at this stage. Limecrete, LECA, all very nice, but not yet or perhaps not at all if it can be avoided.
And especially forget a dpm. That will just send the damp into the walls, and as there is no dpc you will then have rising damp, so you have expensively exchanged one problem for another.

Start with the external drainage. Weird that you have no drains. Make soakaways &/or quietly pipe the rainwater into the foul sewer.

Then as a second step look at external ground levels. What options do you have, depends on your surroundings.

And perhaps a French drain around the house but that might or might not do much.

One thing at once.

Meanwhile fill up that little hole with some loose rubble and a weak cement mix.

Uneven floors are just part of the old house experience.

Happy Christmas.

Ivor

 

[malcolm]

I had a look under my hollow floor today. The floor turned out to have been made up of tiles laid onto earth with half an inch of concrete on top. It was surprisingly dry underneath, so fortunately no burst pipes or water tipping into the building. I will re-lay the floor with thicker concrete.

I think water may have tipped in to the building in the past from a downpipe, and the ground levels used to be very high outside which wouldn't have helped. My hollowness could be to do with drying out (said hopefully ignoring the 3 inch settlement on that corner of the building which I have decided is not moving quickly enough for it to be my problem).

 

[plasticpigeon]

I have a feeling this is an all or nothing kind of job. Obviously the first thing to fix is to make sure the rainwater goes somewhere suitable, preferably a drain. The bitumen between bricks is a dpc. I'm sure the bitumen on the parquet is also acting as a dpc of sorts. My course of action would be to stop the water draining onto the paved area by the house, perhaps lower ground levels. If you can live with the damp for a bit it might abate after a while. I'm not surprised the soil is damp under though, it always will be, the important thing is to make sure little moisture gets into the house, and that what does can escape. The problem with a retrofit floor is that it isn't very easy to lap the plastic dpm into the wall. I doubt many builders would do that properly either. You would also loose your very nice floor finishes. perhaps that hole in the tiled floor could be filled in and the tiles put back down. Another option of course is limecrete. I have such a floor in my kitchen and it seems to work well with tiles. Probably not right if you are putting wood over though as it does allow a small amount of evaporation from the surface.

 

[MatthewC]

I agree with Ivor - do one thing at a time. Personally I would go for the high ground (which is never a good thing for a house) and in doing so that could also sort the water at the base of your walls. Check for all possible sources of water - are there signs that the rain water goods had been (or still are!) pouring water down the walls? Do any of the drains work properly? Does water flow from your neighbour's house or the road? etc

High external ground levels will tend to only cause damp at the base of the external walls.

I don't think I agree with Malcolm - I am sure that the high ground combined with porous limestone in the wall was the cause of the dampness across my old kitchen floor here (now replaced with a lovely dry and warm limecrete floor, with NO DPM).

Can you tell us your approximate location, and give us some more details of the surrounds of the house? Is it terraced?

Matthew

 

[malcolm]

I don't think I agree with Malcolm

But I do agree with you so there!

Old fashioned practice for walls is to try to keep the water out but when it gets in give it a route out again. Modern practice for walls is only to try to keep water out, then shrug shoulders when water gets in past the damp proofing and accept that you will need a new building because the damp course won't let the water out again. Every damp treatment I have removed has been very wet on one side.

For floors external ground levels need to be lower than internal (a little trench round the outside will do), and you don't want to let water from drains to get under the floors as that will cause this sort of trouble - that water needs to go elsewhere. A dry underfloor is the first step towards a happy life. My floors are mostly concrete but my walls are very breathable inside and out. I don't see issues with any floor system so long as the happy life criteria are met. Colleague of mine had the ground floors replaced in his house - he followed his own path and not the happy life path.

 

[88v8]

The bitumen between bricks is a dpc.

Mmm, but the OP says it's below ground level. So it can't be an effective dpc now.
Which is in itself interesting. Surely it would not have been built that way... ? would have been 6" above ground ideally.... this may say something about the evolution of ground levels since the house was built.

Ivor