Rising damp and interior flooring

[Bethanyh]

Hi, we have bought a house (1906) and upon getting the keys, found that there were damp issues in one particular room.

The exterior floor height was about 1ft above the interior, cement render on the exterior stone wall, and about 6 inches of plaster on the interior stone wall (basically all exacerbating the damp issues).

We have removed all the internal plaster with a view to lime pointing and washing it and leaving it sort of exposed, allowing it to breathe. We have also removed the cement render outside again, to be lime pointed and bagged.

We have also dug a ditch down as far as we can, died this with graded gravel (no perforated pipe as getting it to a drain is a bit of a pain as they are back up the garden so would need to be lowered to work) outside to stop bridging of water.

However, we noticed the cement floor inside seemed blown around the edges, we dug an inspection hole and the cement has been laid straight on to the soil, so we've started digging that up (fun!).

My question is, what flooring option should we go for? We are leaning towards a suspended timber floor, but my friends dad who renovated their very old house, suggested we relay cement but do sand, polystyrene, membrane, cement and then sort of raised batons on top with wooden boards on top.

Do people thing the steps we've taken so far will alleviate the damp!?

Many thanks, Beth

 

[Pennyviz]

Hi

Do you have a dpc ? otherwise if you put concrete down again the damp will just wick up the walls instead, move to another downstairs room etc

Penny

 

[88v8]

Do people thing the steps we've taken so far will alleviate the damp!?

Hello and welcome.
Edit your Profile to show your location.

Nasty surprise you've had with your new house, bad luck.

What you've done is good, and it will certainly help. If the walls are damp, reckon on 12 months per foot thickness for them to dry out.

I think the ditch needs to go somewhere, even if only at the lower end. Otherwise when it rains hard, it risks becoming a sump.

Floor... as Penny said, if you put a dpm under the floor, the damp may go sideways into the walls. Someone did that with our sitting room years ago, when we came here in 2011 the perimeter was so damp the Gripperods had rotted. We had the floor dug out and replaced with Limecrete http://limecrete.co.uk/limecrete/ then laid stone on top, bedded and pointed in NHL. Now we have no problems.
There are many companies offering limecrete now, but it's quite a big job.

I said 'may' go sideways. Depends whether the floor is damp. You only mentioned the walls. Put a plastic sheet on the floor - a couple of square feet - leave it a few days and see if there is any condensation underneath. If so, the floor is damp and your friends' dad's idea won't work. It will appear to work, but only for a while, the damp will run sideways under the dpm until it gets to the edge and then the trouble will start.

The thing with limecrete is it's breathable, so the damp can escape.

Suspended wood floor... needs a space underneath for ventilation, 6" or more beneath the joists, and enough air bricks both sides. Air bricks can still be put in even if one side is underground, like this https://www.castironairbricks.co.uk/product/per3-periscopic-vent-duct-telescopic-sleeve-air-brick/
Depending on the size of the room, the joists may need sleeper walls to sit on.
The joists will be 6" deep, 6" for ventilation, perhaps another 8" for sleeper walls and then there's the oversite.
So overall, a well built suspended floor also requires some excavation.

Me, I like wood. Didn't have the choice here as we're listed. But I like wood.

Ivor

 

[Bethanyh]

Thanks for the replies,

I'm also not a fan of the more cement idea given the issues it has caused already. If we have a wooden floor, at least we can keep an eye on it without digging it all up again.
I did read something about limecrete so I will do some more research.

Thanks so much for the link to the periscope type air brick- really good idea. Not so sure on where we can get the water to go, its a really difficult set up with the drainage but I think we might just need to bite the bullet and look at replacing a bottle drain and running another pipe to that from the drainage ditch. We are also going to out in a few surface drains to help divert water.

I have no idea how to 'tag' people in this who have replied or how to add my location to my profile either!

 

[Bethanyh]

Hi Both,

Thanks for the advice.

Limecrete does seem like a good solution but I am guessing it's fairly pricey!? I've had a look online and can't see any price guides so I've emailed a local company for further info.

With a suspended timber floor, the thing I am unsure of is what we put 'underneath' that. It is just soil at present and hence I am wondering how we build the brick supports we would need for the timbers on to soil, or would we need to lay some areas of cement to build those on to? Although,going by your suggestion on depth Ivor, I also don't think we can dig down that far the foundations are only about 30cm below what was the floor height!

No DPC that I am aware of either.

Really starting to resent buying this house !

 

[plasticpigeon]

Sounds like a good idea to take the cement off and lower ground levels. i don't think retrofitting cement flooors with membranes works too well in old buildings. Limecrete if probably a better option for a solid floor.

 

[CliffordPope]

So overall, a well built suspended floor also requires some excavation.

Do you just leave the bare earth exposed? Surely the damp, if that is the problem, still has to go somewhere? Does it escape through the wooden flooring? Do you leave gaps between the planks or have ventlators? What about insulation and floor coverings?
Or do you rely entirely on underfloor airbricks or vents and then seal the floor? One surveyor I once spoke to said that unless you had a howling gale under the floor the timber would always be vulnerable to damp, and he suspects all suspended floors of having rot.

 

[Matt Green]

Do you just leave the bare earth exposed? Surely the damp, if that is the problem, still has to go somewhere? Does it escape through the wooden flooring? Do you leave gaps between the planks or have ventlators? What about insulation and floor coverings?
Or do you rely entirely on underfloor airbricks or vents and then seal the floor? One surveyor I once spoke to said that unless you had a howling gale under the floor the timber would always be vulnerable to damp, and he suspects all suspended floors of having rot.

The surveyor's suspicions make me rather sad.

The relationship between relative humidity and equilibrium moisture content (EMC) is worth looking at. the graph here:
https://www.wood-database.com/wood-articles/wood-and-moisture/

(scroll down a bit) shows it quite nicely.

Here are some things to bear in mind:

>28% EMC: required for spore germination of of decay fungi
~22% EMC required for growth of existing decay fungi
~28% EMC required for Furniture Beetle egg laying
~14% EMC required for Furniture Beetle activity to be sustained

There are more variables and those above are the rough average for Scots Pine, but it serves to demonstrate the point that in order to start a problem you would basically need standing water under the floor- at which point you have bigger issues.

A lack of ventilation is unlikely to ever cause a problem but it will sustain an existing one.


Matt.

 

[paulc]

Sounds like a good idea to take the cement off and lower ground levels. i don't think retrofitting cement flooors with membranes works too well in old buildings. Limecrete if probably a better option for a solid floor.

I'm pretty sure that replacing a concrete floor will require compliance with building regulations, in particular, the section pertaining to insulation. So a limecrete floor over a suitably thick layer of foamed glass would probably meet the requirements without the need for a membrane. But this would only be suitable if the foundations are deep enough.

A suspended timber floor would work as long as there are air bricks every eight foot or so along each wall. Ensure there is a god airflow through the sleeper walls, and appropriate insulation can be fitted between the joists.

 

[CliffordPope]

A lack of ventilation is unlikely to ever cause a problem but it will sustain an existing one.

That's interesting. I don't think I've ever heard anyone say that before - most people just assume that generally ventilation is absolutely vital wherever there is wood.

 

[88v8]

Do you just leave the bare earth exposed? Surely the damp, if that is the problem, still has to go somewhere?
Or do you rely entirely on underfloor airbricks or vents and then seal the floor?

The suspended floors of which I have experience had oversite, that is a thin layer of cement perhaps 2" or less, covering the earth beneath the floor. On the whole though, the essential ingredient is ventilation, and not having dead areas such as corners where there is no ventilation.

One does indeed have to seal the floor in terms of lino, carpet, etc, otherwise a rather unpleasant draught will ensue. Mind you, a little air percolation beneath the skirting can be part of the air ingress essential in making a fire burn well.

Could have mentioned to the OP that if there is a fireplace, opening it up will help to dissipate the moisture rising through a limecrete floor.

Yes, Matt's point is interesting. However, in that case I'm not sure how there came to be so much beetle upstairs in our cottage, and none downstairs.

Ivor

 

[Bethanyh]

Hi all,

I have tried posting a few replies but they don't seem to be showing (I'm new on here and don't have a clue how to use it!).

So, still not sure about what to do with the floor, I'm more inclined to think the Limecrete solution is best and should have a quote back from a local company tomorrow.

The main thing is cost- a new suspended timber floor would be cheaper and if there any any future issues, easier to inspect. I do however wonder how we would insulate this without it causing other damp issues, or how we would ventilate it, given that the wall to the rear is so thick I don't know how we would possibly install any more air bricks!

Also, I contacted another local company who deal in restoration/ renovations of older properties and now I'm worried as they suggested we get a structural engineer in before we do any further digging out- phoned a few and there is a 6 week wait for them to even come out and have a look! Now I'm really worried.

 

[Cubist]

Hi Bethany,

First off regarding the website; new accounts are held in a kind of limbo for a while and during this time any posts you make are reviewed by the moderators before they are added to whichever thread. Sooner or later they will realise you're not a terrorist, a sociopath or conman and will allow your posts to be immediately added to whichever thread you're interested in. Also, I have noticed that on occasion a post will vanish if you happen to be preparing a reply on a topic at the same time as someone else - I was recently surprised to see one of mine go missing in this way .

The advice to get a structural engineer to take a look before you do any more digging is wise as its possible that any excavation work could seriously damage the house by weakening the ground upon which the walls stand. Only qualified professionals who carry appropriate insurance should undertake such excavation work near to the foundations or footings of load bearing and or masonry/heavy walls - in the event of such damage your own insurer would wash their hands of any claim you might make as a result of your doing such work yourself.

Have you already dug below the level of the foundation/footings?

If yes, stop and get some professional advice on how best to proceed.

If no, then make sure you know where the foundation/footing level is in relation to the rest of the floor before digging out any more material - after talking to a professional.

Hopefully I am being a little alarmist but I would rather that than see someone take a needless fall.

It may also help if you could share some pictures - but that too can be a painful process with this site.

Cheers,

Cubist

 

[Spoilt Victorian Child]

Another benefit of limecrete is the possibility of having underfloor heating put in at the same time for that room (if it's not too far from the boiler and you plan on staying in this place long term). I've only got it in the kitchen, but I love it.

@88v8 - 'sealing' a new breathable floor with lino would just make any more damp travel towards and up the walls, wouldn't it? OP needs to make sure the top finish is breathable too?

 

[Kearn]

Hi Bethany, if you haven't already searched the site, it's worthwhile as this is a relatively common topic - concrete cowboys have done some damage during the last century!

The most recent thread is here, my experience with the two main lime suppliers is contained along with others' thoughts...

https://www.periodproperty.co.uk/forum/viewtopic.php?f=1&t=16334&p=222561#p222561

The hard and messy part is removal and excavation of the offending materials, which you're hopefully on top of by now!

Good luck!

 

[88v8]

You can dig down as far as the base of the foundations. Any further and you risk undermining the house.

For the suspended floor, you will need some brick sleeper walls. Put 3-4" of concrete under them for a footing. The walls should have a dpc in them, above the first course.

The joists (4 x 2") need to run from side to side so the air can flow through the air bricks. So the floor plates (6 x 3" on their sides) that sit on the walls will run from end to end. So the sleeper walls need to be oriented end to end. 18" of wall then a 24"" gap then 18" of wall then a 24" gap and so on. You can build the sleepers with cement mortar :shock:
The floor plates need to be bedded on mortar so they are bearing on all the walls. Spirit level..... Mind you, you don't have to make the floor exactly level or flat, it is an old house after all.
At the ends, the joists need to sit on a wall plate. But not in contact with the walls.

Don't use flimsy C16 or C24 timber.

If the room is small you could get away with 4 x 2" joists although it might make the floor a bit springy. Otherwise 6 x 2" or more sleeper walls.
How big is the room?

Underfloor insulation will make the space under the floor cooler, so more risk of damp. Good airflow important. Insulation, use solid bats on battens down the sides of the joists.
Air bricks can be put through with a diamond core drill. You can hire, or get someone to do. Insufficient air bricks will doom the floor before you even start.

If you use t&g boards, be blooming sure you won't want to take them up again for wiring or pipework.

This is all quite a faff if you've never done it before, whereas with a limecrete floor you just spend the money and watch someone else sweat. Out 12 x 15ft was about £4k iirc.

The external drain could go to a soakaway if you have the space; a 3ft cube full of hardcore with a membrane and soil capping. Alert - a cubic yard of earth weighs over a ton........

Can understand you being peeved about all this. But it will pass. And you'll still have the house but not the damp.

To insert your location.... just under the Search box, your user name with a down arrow... User Control Panel... Profile tab... edit.. Submit.

Ivor

 

[malcolm]

I guess the contact a structural engineer comment from the builder was in response to wanting new solid floors inside. I looked into that myself and realised I would need to dig down about 0.5m for all the stuff building regs would want (can't avoid them as they are already around). 0.5m is way deeper than the foundations for a badly built early Victorian extension so expensive clever people and expensive solutions would surely have been needed.

I left my floors as they were and they seem to be working. I have 1 or 2 inches of concrete on soil with no damp proof underneath. My external ground levels were very high, and to fix the damp I dug a trench around the house, no gravel fill, and covered it with a nice fibreglass grating. That was to replace a French drain that didn't work. When I dug out a couple of inches of gravel in the French drain the gravel was wet and the wall was wet too. Figured if the walls were dry below floor level I wouldn't have much need for a lime floor.

I can't think what advantage the gravel has other than helping to avoid building a tiny easy to build half brick retaining wall about 8 inches from the house wall and stopping small children falling into the trench. If water is going to puddle it will do that with or without gravel. I put a soakaway in mine but have the advantage of a sloping site.

 

[MatthewC]

I looked into that myself and realised I would need to dig down about 0.5m for all the stuff building regs would want (can't avoid them as they are already around). 0.5m is way deeper than the foundations for a badly built early Victorian extension so expensive clever people and expensive solutions would surely have been needed.

I found my Building Control inspector very reasonable - I explained what I wanted to do for my limecrete floor (as per Mike Wye's instructions); he agreed that of course I couldn't go too deep and was happy to agree with my proposals (as described on my blog). Was it really over 7 years ago?!