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Author Topic: Floor joists laid directly onto earth  (Read 474 times)

Womble

  • Joined Mar 2009
  • Stirlingshire, Central Scotland
Floor joists laid directly onto earth
« on: November 16, 2020, 10:48:40 am »
Hi Folks,

As a lot of us live in old houses, I'm hoping somebody will have solved this one before!

We live in a 200+ year old farmhouse, and most of the ground floor has a solid concrete floor (not original). However, the two ground floor bedrooms still have timber floors, which are just floorboards laid onto 6" wooden joists, laid onto earth.

The internal floor level is roughly the same as the outside ground level, the walls are 1m thick random stone and mortar, and there is no damp proof course. The earth the floor joists are laid on is damp to the touch, and of course the joists themselves are rotten. There is currently no ventilation under the sub-floor (e.g. air bricks or tubes).

The question is, what to do next? The options as I see them are:

a) Lift the floor, dig out some of the earth, lay a damp proof membrane (DPM) and then concrete on top, followed by a solid floor (basically the same as the rest of the ground floor)
b) As above, but followed by a suspended wooden floor with ventilation underneath
c) Dig out the earth a bit, put in some small sleeper-walls with DPC, then wood joists over the top, and ventilate underneath. (In other words just repair what's there, leave it as earth underneath the floor, but sort the ventilation.
d) something else!

My dilemma is, would a) cause the damp to start coming out of the side of the DPM and up the walls instead? This does seem to happen a little in the rest of the house. If this is the case, c) sounds like the better bet, but is better ventilation going to be enough, or are we going to have to do something more drastic?

So, if you've been in this situation before, what did you do to sort it, and how did it work out for you? :thumbsup:
« Last Edit: November 16, 2020, 10:50:31 am by Womble »
"All fungi are edible. Some fungi are only edible once." -Terry Pratchett

chrismahon

  • Joined Dec 2011
  • Gascony, France
Re: Floor joists laid directly onto earth
« Reply #1 on: November 16, 2020, 11:50:49 am »
Floors in old houses are a big problem here Womble. I know that a wooden floor must have cross ventilation (our joists in UK rotted for that failure), or the alternative is not to make the boarding continuous, so a gap of 20mm between the planks (our bread oven room here), just like decking outside. The joists must always be isolated from the earth floor as well.


Lots of people here have put in concrete floors with a membrane and as you say, the damp rises up the walls so they have had to remove them. You get the same problem with glazed floor tiles that can't breathe. Are you sure you have a DPM under the concrete floors?


So whatever you do won't be ideal. I'd go for the sleeper-walls myself and leave the floor boarding able to breathe. It will still be a damp floor but not as damp as concrete without a membrane and it will take years to deteriorate if the wood is treated. Don't know how you could ventilate it? Of course if you try to dry the building floors by exterior drainage you are likely to get subsidence (seen that).


We just accept the damp floors- we have concrete on some with porous tiles, earth with the same and a wooden floor which is raised with air holes either side of the building. That room was terribly damp when we got here because the last owner sealed up the holes! Fortunately the building is built on rock which naturally drains, so it's never going to be terribly damp but will always have some. :hug:

Fleecewife

  • Joined May 2010
  • South Lanarkshire
    • Wester Gladstone Hebridean Sheep
Re: Floor joists laid directly onto earth
« Reply #2 on: November 16, 2020, 12:44:15 pm »
There has been a house here for at least 500 years, and we moved here 25 years ago.  We knew nothing about stone houses, having both been brought up in brick houses and lived in modern ones since.  So the mortgage company specified the work to be done on the floors.  The kitchen and main bedroom were most alarming, with the kitchen having a cheap pine floor perched over a one foot gap above earth, with joists which were not deep enough, and no damp proofing.  The bedroom was not so bad, not having such a big gap under the floor, so was more like you describe with joists on earth.  The kitchen also had a recent internal wall balanced on plastic wedges and house bricks onto a wooden floor with no other support  :o
Basically, we had a chemical damproof course injected into the walls just above ground level, and concrete poured into the underfloor cavities.  The wooden floors were then placed on top, on small joists (about 3"x3") resting on the concrete.  There has never been a lack of ventilation anywhere in this house!  The only problem with damp since then was once we put in double glazing a few years ago.  It would seem sensible though to lay a damproof course of plastic sheeting on top of the concrete as well as underneath.
www.scothebs.co.uk

Do something today that your future self will thank you for - plant a tree

Draco dormiens nunquam titillandus - let sleeping dragons lie

Steph Hen

  • Joined Jul 2013
  • Angus Scotland.
Re: Floor joists laid directly onto earth
« Reply #3 on: November 16, 2020, 02:01:03 pm »
I’ve enjoyed reading this website, might have stuff on floors? https://www.heritage-house.org/stuff-about-old-buildings/maintaining-your-house.html

Heritage house.
Where as builders have given us varying and conflicting opinions, about everything I’ve seen with our old house’ stonework has been explained by this guys website. He seems to think the main thing is Lime mortar and all the plastic, fiber glass and insulation panels cause damp. Builders have told me our house should be rendered or painted to stop the corrosion. Not convinced.
Maybe see if he’s got anything on floors?

Perris

  • Joined Mar 2017
  • Gower
Re: Floor joists laid directly onto earth
« Reply #4 on: November 17, 2020, 11:33:44 am »
thanks Steph Hen; that's a really useful website  :thumbsup:

doganjo

  • Joined Aug 2012
  • Clackmannanshire
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Re: Floor joists laid directly onto earth
« Reply #5 on: November 17, 2020, 05:31:30 pm »
Our cottage in Aberdeenshire was completely built on half trees with floor bards at right angles across them.  Our mortgage provider told us to put in an injected DPC - I'm not au fait with how it's done but it worked and it was a lovely cosy house
Always have been, always will be, a WYSIWYG - black is black, white is white - no grey in my life! But I'm mellowing in my old age

Womble

  • Joined Mar 2009
  • Stirlingshire, Central Scotland
Re: Floor joists laid directly onto earth
« Reply #6 on: November 17, 2020, 06:54:50 pm »
Thank you everybody!

@Chris - you're right, I don't know if there is a DPM beneath the "new" solid floors - possibly not. I do know that we get damp around the skirting boards though, and I'm sure the solid floor isn't helping matters.


@doganjo, when we bought our house, our mortgage provider told us to put in an injected DPC. However, in our case the walls are 1m thick stone with lime render in between, so I just couldn't see it working and told them to get lost. They said "Oh, ok, sorry!", and gave us the money anyway.


I can see that an injected DPC may work with brickwork, but I can't see it with stone, and also I'm sure most of the damp is coming up through the earth floor, rather than through the walls. Fleecewife - what are your walls made of?


@Steph Hen - thank you for that link. I've had a good read of the website and am starting to get an idea of things. There's a load of good information on all sorts of things in there!  :thumbsup:
"All fungi are edible. Some fungi are only edible once." -Terry Pratchett

Fleecewife

  • Joined May 2010
  • South Lanarkshire
    • Wester Gladstone Hebridean Sheep
Re: Floor joists laid directly onto earth
« Reply #7 on: November 18, 2020, 12:32:13 am »
Our walls are stone, about 2'-3' foot thick, of 'Lanarkshire rubble' which is partly dressed stone pinched from the ex castle next door, some from field stone, and stone rubble plus rats between the inside and outside, with lime mortar now, but it was unknowable when we bought it - probably none!  Our walls were wet for the bottom metre when we bought the place so that had to be replastered, but now the house is mostly dry.
www.scothebs.co.uk

Do something today that your future self will thank you for - plant a tree

Draco dormiens nunquam titillandus - let sleeping dragons lie

Steph Hen

  • Joined Jul 2013
  • Angus Scotland.
Re: Floor joists laid directly onto earth
« Reply #8 on: November 18, 2020, 08:19:50 am »
Womble, I liked his explanations: that a stone house if dry is a good insulator. I see cement strapping everywhere causing erosion.
And people with new expensive houses with kingsman insulation complaining of damp and concrete thresholds crumbling.
Whoever the builders who put all the underfloor vents in here have caused a lot of damage; they seem to have just knocked holes through from the outside. Where we’ve had the plasterboard off on the inside there’s cut stones, rubble and mortar in a collapsed heap around the hole (about 2*1.5ft!) and corresponding cracks emanating up from this. Of course on the outside the vent panel is about 6“ and very inconspicuous. Whoever did this was not a skilled conservation builder.

The chimney had been lined 25years ago with sections of ceramic pipe. None were found when we put the new metal flue pipe in. Not convinced this guy and his team did anything.

Guessing it was about the same caliber of builder who advised replacing the lime mortar with cement once and for all. I guess it was an easy sell as degraded lime mortar does look rubbish -as in powdery and like the whole thing is about to fall apart.

Some people said to render or cement or just paint the whole outside to preserve the stone and stop the damp. I can see the masons marks from when the house was built. I can also see the erosion which has happened over the last 30 or so. If this rate of erosion had been going on for 250 years there wouldn’t be any masons marks left. Therefore something has to have changed in the more recent history. Some said acid rain is what causes stone work to disintegrate these days but I like the website guy’s explanation. Sadly removing the cement strapping and replacing with porous lime mortar costs a bloody fortune. I think we estimated something like £40K to do the whole house, it’s many weeks work. We will have to attempt to do it ourselves over the next twenty or so years. As with everything here, it’s just about trying to hang onto what we have, fix, simplify, improve resilience for the next generation.

Womble

  • Joined Mar 2009
  • Stirlingshire, Central Scotland
Re: Floor joists laid directly onto earth
« Reply #9 on: November 18, 2020, 09:08:00 am »
It’s many weeks work. We will have to attempt to do it ourselves over the next twenty or so years. As with everything here, it’s just about trying to hang onto what we have, fix, simplify, improve resilience for the next generation.


Yes, this, exactly!! We stripped the old plasterboard off yesterday and found that when somebody decided they didn't want the fireplace any more, they completely destroyed what would have been a beautiful inbuilt stone hearth  :( .


When we moved in here, we had a ten year plan. We've actually been here ten years to the day, and have completed about a third of it. However, I'm pleased that we're getting there bit by bit, and that actually we're restoring things to how they originally were, rather than 'modernising' them.
"All fungi are edible. Some fungi are only edible once." -Terry Pratchett

Dan

  • The Accidental Smallholder
  • Administrator
  • Joined Oct 2007
  • Carnoustie, Angus
    • The Accidental Smallholder
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Re: Floor joists laid directly onto earth
« Reply #10 on: November 18, 2020, 09:11:21 am »
When we moved in here, we had a ten year plan.
Can't offer any advice about your floor, but happy anniversary!  :cake:

doganjo

  • Joined Aug 2012
  • Clackmannanshire
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Re: Floor joists laid directly onto earth
« Reply #11 on: November 18, 2020, 10:11:19 am »
@doganjo, when we bought our house, our mortgage provider told us to put in an injected DPC. However, in our case the walls are 1m thick stone with lime render in between, so I just couldn't see it working and told them to get lost. They said "Oh, ok, sorry!", and gave us the money anyway.

I can see that an injected DPC may work with brickwork, but I can't see it with stone, and also I'm sure most of the damp is coming up through the earth floor, rather than through the walls. Fleecewife - what are your walls made of?
Photo attached(I had a programme that makes photos into art), apart from the front extension, all granite blocks.  Don't ask me how they did it, but there was a lot of noise, a lot of water spray, and a lot of swear words  :innocent:
Always have been, always will be, a WYSIWYG - black is black, white is white - no grey in my life! But I'm mellowing in my old age

 

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