Replace floor in Georgian house

[aliCannon]

Hi all. I've moved onto a Georgian house in serious need of renovation and care. The flooring in the main downstairs room is rotten in the corner so i'm pulling up the floor to see how far the problem extends. It looks like the joists are plonked straight onto the ground so not surprising the joists have rotted near the external wall. Is this likely or should their be something like sleeper walls supporting the floor?

 

[Bonni]

Whatever space you're spanning, you need to choose the correct sized timbers for the distance relevant to the centres/spacing

https://www.timberbeamcalculator.co.uk/en-gb/span-table/floor-joists?load=1.5&class=C16

Dwarf walls reduces the span and thus reduces the size of timbers required.

 

[aliCannon]

Thanks Bonni. Is it worth digging out a cavity so there's room to put in dwarf walls and rest new joists on those? I'm thinking I should do this "properly" with dwarf walls, breathable membrane etc but that would require digging out a fair bit of earth which the joists are currently resting on.

 

[Mr Chibs]

Hello

Have you got air vents installed in the outside walls?
If so, and you are wanting to have a suspended floor, you would be better digging and removing some of the soil/rubble say 300mm to allow for ventilation, this helps control the damp from the 'earth'

Depending on room size this will dictate new timber sizing and where/if you need sleeper walls building etc.

If you choose to make the floors solid concrete, you will still need to dig out some of what's there
As you'll need hardcore (100mm), sand (50mm) DPM sheet, Concrete (100mm) insulation (100mm min) and finally screed (65mm) = 415mm approx.

Wood doesn't want to be in direct contact with soil.

Hope this helps.

 

[aliCannon]

Thanks Mr C; Yes, there are a few airbricks in the exterior wall, though no air will have got through to the rotten joists. I will excavate to 300mm. Do you think sleeper/dwarf walls are the right way to go? Would positioning new joists on single bricks also work? Willing to be shot down by those with experience but given how the house was originally built (e.g. joists straight onto earth) I wonder if this might be a big improvement for much less disturbance & effort?

 

[Tigercubrider]

You need to check with the council if it’s Georgian?
From my (limited) knowledge of Georgian architecture, what you have is normal but any conservation/listing officer should be able to advise on the correct procedure.
I would be extremely cautious about doing anything without checking the regs.

 

[Mr Chibs]

I take on board what Tiger has mentioned and if your property is listed then you will have to go through whatever step the officer will ask.

Personally I couldn't put up with your floor and would repair/replace/improve where needed. I would try to re-use any useable parts floorboards etc.

On a side note, if this is normal Georgian practise of sitting joists on the floor I wonder what the point of fitting air vents is?

In older properties I've lived in (with suspended floors) there is usually a dwarf wall around two opposing walls, and honeycombed sleeper wall if the span is large. Guess you could dig less out and rest new joists on brick/blocks but you'd need to get the air vent clear and establish some airflow in and out, otherwise you are increasing the chance of damp/rot again.

Will be interested to see how you get on. Good luck.

 

[Tigercubrider]

There is a high possibility of some kind of restriction on carrying out works.
The financial penalties for failing to do so could render you homeless and in debt.

A DIY forum is useful info but Georgian houses require very specialised supervision of works (a mate is an architect specialising in such buildings) and a DIY job based on internet advice could well result in worse damage than you have. Incorrect materials can cause walls to fail