Subfloor advice

[Paul78]

Hi everyone,

I'm hoping someone might offer some advice/experience on my current situation?

My cottage was built 17h century and after lifting up the old carpet in our Dining room (4.5mx4.5m) we discovered an old pine floorboard floor about a third of which is still in good condition. The remaining 2 thirds has rotted away in places, it seems mainly at the point of the boards being nailed into the battens underneath.

I've lifted a couple of boards and it seems that a previous owner (in their wisdom) has actually poured concrete/screed in between the battens ???? The battens are now soft and crumbly. The boards don't feel damp but now I'm unsure on how to proceed.

I'd like to replace the pine flooring with Oak (Probably engineered) but I'm not sure what to do with the sub base. I know in an ideal world I'd probably take up the pine, smash up the concrete and then get a limecrete type floor down but I'm wondering if there is a simpler (and cheaper!) option ? I've had a couple of builders around for other jobs and they've all just said to dig out the battens and then pour a self leveling compound and then lay straight on top of that. I'm worried this will force any moisture out up the walls ?

Any advice welcome.

 

[88v8]

Hello and welcome.
For some reason I can't see your picture, but.... I'm afraid a wooden floor is a non-starter. I wish. My house is also C17 and I too would have liked a wooden floor.

Your battens... I would assume that the concrete was used to hold the battens in place. Underneath is, what? Earth, most likely. Nothing to anchor anything to.
It was a bodge. It will seem OK for a while, but the earth will be damp in varying degrees, and inevitably the battens will rot and the boards.

And as to your builders' ideas, you're right, it's a non-starter. No wonder the building trade has such a bad name. Why does it attract such a high proportion of botchers? The fact that you recognised it as a bodge gives you a head-start over most householders.

Limecrete is not our saviour here. We had a limecrete floor installed in one room. The point of limecrete is that it breathes. This means that any damp is slowly released into the house where it can be dispersed by ventilation - what some people mistakenly call 'draughts' - instead of the damp being pushed sideways into the walls as it would be by a concrete slab with a dpm.

Anyway, in terms of putting a timber floor over the limecrete, the limecrete will still be slightly damp and in time the floor will still rot. You might get away with it for a few years, depending on the degree of damp. If you're in your 90s and don't care what you leave to the next owner, and your sense of smell isn't great so you won't notice the eventual mouldy odour, you may feel it's what you want to do. But as you say, limecrete is a lot of work or a lot of expense.

In reality, a wooden floor can only be fitted over a ventilated space. In other words, it has to be a suspended floor, with air bricks in the walls.
Alternatively there has a to be a complete damp exclusion, as in a modern house with its envelope of dpm and dpc.

Our houses have neither dpm nor dpc, nor can such an envelope be created. So, unless we are going to excavate down 18" or so and create a suspended floor and put a lot of airbricks through the walls - ours are 24" thick - we cannot have a wooden floor. And the excavation would have its own problems as we have little in the way of foundations and it wouldn't take much digging to undermine the walls.

Sorry to rain on your parade, but an old house is not like a new house and cannot be made so.

A solid floor is required.... must be breathable, laid and pointed in lime. No cement! No self-levelling! Otherwise in time the walls will become damp. Flagstones, pamments, brick, quarries, etc. Turkey rugs.
Find another builder.

If you edit your Profile to show your location, someone may be able to suggest.

Ivor

 

[Kearn]

As Ivor says, welcome and yes, don't speak to that 'builder' again!

Where I would add a slightly contrasting opinion, though is on the possibility of a wooded suspended floor - obviously very dependent upon your building, and a choice on what you wish to do and achieve.
We do have a suspended floor in the downstairs of the two bay original 16C cottage. As best we can tell, the pine boards were added in the 1950/60s when lots of other 'modernisation' took place along with a reasonably serious chimney fire in the principle room in the oak frame above the inglenook. So, assuming these boards have been down for the best part of 80 years, they are not mobile nor are they damp. We have approx 10inches of breathable space under the boards, wooden joists supported on brick to break contact with the ground below. I must add, our house was built very sensibly 400 years ago, at the top of a hill, so our ground is dry as a bone and also contains a lot of natural chalk so there isn't a high level of moisture to come up into our setup. We have only two airbricks on opposing walls, which would have been beneath the level of the sill beam, but that has been missing for well over a century. Additionally, our boards are square edged and not too closely packed together and we have recently restored the inglenook and adjacent room, leaving a small gap along the entire edge of the room where board meets re-laid brick floor, so there is airflow which can be felt around the edges noticeably (which also has become our new puppy's favourite sleeping place to cool down unsurprisingly!).

If it were my choice now, I would be one for more originality, so I would almost certainly be going with limecrete and reclaimed tiles which is what I have done in the adjoining room (if only I could find a stash of 12x12 Tudor tiles...I do know the whereabouts of more than half of what I believe to be our original floor, but that is another story) but as it stands, the pine boards are serving a good purpose and causing no issue in our particular scenario. What I personally wouldn't want to introduce or live with is modern engineered wood.

When considering a gap for airflow, it is obviously not just the depth under the board but points of access for air to get in and out, which may not be feasible for you to easily achieve, particularly without damage to the walls. However, to lay limecrete on top of the RFG insulation layer, then you will still have to consider some digging down to achieve the required depths of material, which means care around the perimeter to not disturb the footings. A thought may be that if you need this depth for the new floor, then it could I suppose be used as an air gap for a suspended floor.

However, as Ivor said, wood will not work on a solid floor.

Good luck, hopefully you will be able to add images soon, I would be interested to see - I think there is an initial delay after you join the forum if I remember correctly.

 

[Feltwell]

Unfortunately we can't see your picture. Your "battens" are definitely that are they, thin strips of wood laid in the concrete, and not the tops of old floor joists?

My neighbour's early Victorian house at some point in the past had the original floor void filled with concrete, no dpm - and they just pulled up the presumably rotten boards and poured concrete in between the joists, leaving them in situ. Of course they then rotted. The proper fix now would be to dig the concrete out, replace the joists and re-introduce a suspended floor, ensuring adequate sub-floor ventilation.

However, my neighbour is a builder of shall we say the "modern mindset", so his fix was to take out the rotten joists and then fill the "tramlines" with more concrete, prior to placing floor tiles on top. I really do feel sorry for whoever buys this much abused house in the future, what it's receiving at the moment is just the latest chapter in this abuse.

Is introducing a proper suspended floor possible for you? A lot of work and disruption but sounds like the only way you'll get a timber floor, if that's what you really want. I presume the house isn't listed.

 

[steveb]

for the image, try this. I had a floor that looked like that once. To fix it, someone built another timber floor on the top of it. That rotted too

 

[Salty]

Hi

I have no words of.wisdom to offer so am reading the suggestions with interest.

We lifted the horrible disintegrating concrete floor in our kitchen and found soft bricks underneath bedded on sand. We are now at a loss as to what to do, the bricks are too soft to have as a floor, we don't have the depth of foundation (and in an area which has high groundwater in winter) so reluctant to dig down for full limecrete system.

I want to lay flooring with lime grouting, but there is such an uneven level i would be nervous to and then we cycle back to timber floor with airbricks.

I have learnt so much.from here already, but will have to make decisions soon (i want a kitchen! )

 

[MikeG]

When you say "battens", I presume you mean joists? In other words, the original floor was a timber suspended floor, with joists spanning from wall to wall?

Well, if that was the case originally, then I am sure it could be done again, by taking up the flooring, removing what's left of the joists, and breaking out the concrete. This should leave you with the original ground level below the floor. You may have to rebuild intermediate dwarf walls if there is a large span (any originals will have been wrecked in getting the concrete out). The critical part of the whole procedure, though, is ensuring airflow below the new floor. There should be lots of airbricks, above ground and clear of all obstructions, and ideally on 2 opposite walls. If you can achieve this, then it should be quite straightforward to put in some new timber joists, with insulation between, and a timber floor above.

 

[88v8]

(i want a kitchen! )

They are useful. Although of course a modern invention. The original inhabitants of our cottage would just have cooked on the fire.

Best if you start a new topic. Running two enquiries in the same thread is a bit muddling.

The only point I would make here is that in a small room you need less depth for limecrete than for a suspended floor.

Ivor

 

[Paul78]

Hi everyone, thank you for all the replies.

Apologies for the image not displaying I think I've fixed it now.

I'll try and answer all the questions below.

Subfloor : Underneath the concrete I'm fairly sure it will be earth. A cottage next door has lifted quarry tiles in the living room to excavate a little deeper and it was indeed earth, interestingly bone dry to the touch. I know that's not very scientific but it certainly felt dry and powdery.

Joists not battens : Yes I think they probably are old floor joists I've just taken a video which will hopefully show more detail.

https://youtu.be/Dg5hPG8IuR4

Suspended floor possible : I would say probably not. The house is built on a slope and while ground levels to the front have approx 18 inches internal to external in level, the rear is only a few inches lower outside (I'm trying to fix this by digging out the earth to the rear.) Also the front has an ugly concrete plinth the entire length of the cottage covered in bitumen. That's another story but I'm not sure how I would get airbricks in without destroying the plinth and most likely the original brickwork underneath. The house is Grade 2 so I'd need permission.

As much as I would love a wooden floor I'm starting to think flagstones or quarry tiles might now be the better option. At least it would be fairly straightforward to pull out the concrete and old joists and have the tiles laid with lime.

Thanks for all the advice.

 

[88v8]

At least it would be fairly straightforward to pull out the concrete and old joists and have the tiles laid with lime.

Good that the earth appears dry. If you lay some plastic sheeting on part of the floor overnight you'll soon see how much damp is currently under there. Seasonally may vary.

You know about limecrete?
If tiles are laid without a solid base they'll soon start wobbling.

As regards airbricks - shame about the ground levels - one can get new ornamental cast iron bricks that are brick-size, not too difficult to drill and chisel your way through the wall quite neatly. Start from the outside, chisel the plinth with a scutch until you find the perimeter of a brick, then away you go.
Set the airbrick level with the face of the brick and return the plinth onto it.
https://www.castironairbricks.co.uk/
As regards LBC the whole process of changing the floor strictly speaking requires LBC, just saying.
Air bricks I'm sure would be regarded as de minimis.

Ivor