Hi all,
Long time since I have been on here. Sorry to see that the forum is closing soon. I have received so much good advice on here, occasionally I have hopefully contributed occasionally in the other direction, but most importantly the end result has been a house that is a lot more energy efficient than it was before I started following the forum.

I am now tackling a small north-east facing room that has major dampness problems. I have already rectified some external issues like an open gutter at the external wall and dropped the ground level as much as is practical, but have finally had to bite the bullet and lift the floor as the air quality problem seems to be coming from below, rather than any visible dampness present in the walls of the room. I have lifted and numbered the solid wood floor as I intend to put it back down, sand the varnish off and cover with hard wax oil as I have done with the same flooring on the rest of the ground floor. I don't know what type of wood it is , but it has been remarkably resilient to dampness and is showing no signs of rot. There were parts of the house where the skirting boards had rotted and this wood right next to it showing no issues.

On lifting the first view boards of the subfloor I found what I had expected. The joists are more or less resting on the ground with at best a centimetre or so of clearance in places. Mould is growing on the ground and some of the bottom of the joists are rotted through. Once I have the rest of the subfloor lifted I will have to decide what to do next. Its seems that my options are:

a. Dig as much of the loose soil out and replace the joists, then rebuild a traditional raised wooden subfloor.
b. Dig out as much as I can and then fill with something like Leca insulation, then levelling screed and just float or bond the solid boards on top.

The problem with a is that it's unlikely that I will be able to dig very deeply due to the construction of the house. I can possibly create space by using joists of a lesser depth, reducing the spans with a few bricks, but the best I can hope for is about 80mm gap between floor and joists. This also leaves very little scope for floor insulation.

The problem with b is that it is a bit of an unknown. A Leca installation it looks fairly easy, but there are a lot of unknowns and possible complications due to the old and odd design of the house.

The room is north and east facing and I think the problem began with dodgy builders in the 1880's, possibly made worse by dodgy builders in the 1980's! I believe that the original house, built in around 1820, had solid floors and lower ceilings. The Victorians appear to have dug down to lower the floors in order to get higher ceilings in the two rooms at the front of the house and installed suspended timber floors at that time. On the west side due to a combination of factors this has worked and that side is reasonably dry. Where this room sits on the East side it backs on to a room with a solid floor, which currently has a solid wood floor, sitting on top of a thin concrete base and I suspect that it's just soil underneath that. The room with the solid floor is about 320mm higher than the room I am working on, which means I have an internal wall backing on to earth, probably without a damp proof course behind the wall. On another side of the room there is a hallway with a solid floor.

Sorry for the long post, but in summary, my preference is probably for the Leca fill, but that removes any chance of ventilating the base of the interior walls backing on to solids internal floors. If I go with Leca I was thinking of a DPM between the Leca and the screed and run the DPM up the wall to just above the final floor level, then have vents on the internal wall skirting boards so that any moisture that gets up past the DPM can vent into the room rather than build up. The unknown for me is how the Leca would interact with any build of dampness underneath. As the subfloor space is below ground level if it does start to fill up with water then there is no ventilation to dry it off.

Grateful as always for any input, or suggestions of something else I haven't considered.

Room plan - https://www.dropbox.com/scl/fi/8s0ped6n43cfpesl2qlz9/Room-plan.jpg?rlkey=9r44hga25pls6webfx73a6bnw&dl=0

Pics:

https://www.dropbox.com/scl/fi/bk4u0itzyr16mcvypj1mg/2024-08-24-17.06.25.jpg?rlkey=ium901mmuyzw6o3rke3hb8d1n&dl=0

https://www.dropbox.com/scl/fi/6mjkdirtcxc49n9579dfv/2024-08-24-17.06.52.jpg?rlkey=drbwp3mhdk9jb3mh6o6pb7dp2&dl=0

https://www.dropbox.com/scl/fi/xebiayoymyaoveeu5pek9/2024-08-24-17.08.04.jpg?rlkey=8h3ih13dan0yjfxunpoxfxhvl&dl=0

https://www.dropbox.com/scl/fi/3n5tw0pfrzqd39ey35950/2024-08-24-17.09.31.jpg?rlkey=3e5uolomk5wub8ljthx63yoou&dl=0

I have not looked at the pics, but based on the description perhaps foamglass (Ty Mawr sell it, among others, I am sure) instead of LECA. Agree with djh re the French drain, or perhaps sump-and-pump if it tends to 'fill up' (rather doubt any amount of ventilation will dry out standing water)! Shame, someone on here was giving away a bulk bag-and-a-bit of foamglass recently and couldn't get any takers. I worry about LECA and moisture - don't you potentially end up with a hardly-insulating -at-all 'slice' of clay? Obviously depends on the degree of moisture, but I have always understood that LECA must be kept dry.

Posted By: Nick ParsonsI have not looked at the pics, but based on the description perhaps foamglass (Ty Mawr sell it, among others, I am sure) instead of LECA. Agree with djh re the French drain, or perhaps sump-and-pump if it tends to 'fill up' (rather doubt any amount of ventilation will dry out standing water)! Shame, someone on here was giving away a bulk bag-and-a-bit of foam glass recently and couldn't get any takers. I worry about LECA and moisture - don't you potentially end up with a hardly-insulating -at-all 'slice' of clay? Obviously depends on the degree of moisture, but I have always understood that LECA must be kept dry.

You may be right about Leca. I don't know a lot about it. I was looking at the Leca insulation here - https://www.leca.co.uk/products/lecar-insufill-underfloor-insulation-50l-bags - which seems to be specified specifically for insulated foundations. It would seem strange that they would sell it for foundations if it would soak up water. I will take a look at the foamglass - a quick look at it on the Mike Wye site and it looks like a similar approach to the Leca idea, with the insulation compacted under a screed.

I may have given a wrong impression in my first post. There is no standing water in the void. There may have been at some point in the past, because there was an open gutter drain, but I dug a pipe in and redirected it away from the house a few years back and dropped the level a bit. That area and the outside wall was saturated when we moved in, but it has dried out a lot since.

I think the mould under the floor is due to the unventilated voids with enough dampness from the ground to encourage growth.

Posted By: GreenPaddyHi Kenny,

my advice to a client with this scenario (albeit not having inspected it) would be...

- remove the timber floor and make it solid
- get an assessment as to how much of the subfloor could be removed to give depth for insulation and a slab
- install a DPM, as it sounds like this room will be close to the external ground level (adjacent rooms being a foot higher). You done the external works already for removal of ground water (water level and precipitation).
- I'd use an env unfriendly rigid board insulation like PIR/PUR to get the best insulation for the limited thickness, laid over the sanded solum and DPM
- put a concrete slab on top of the insulation, as it needs to be structural, and the usual pumped screed is not. Thick perimeter insulation to the slab of course.

This ought to be done with Building Control, as you are altering inuslation, moisture ingress, and structural elements, and should have the appropriate professional input to design the above.

This is of course more expensive than complete DIY, but having had an 1880 bodge, a 1980 bodge, maybe time to get it done right so someone can admire it in 2080.

Thanks. I appreciate the feedback and suggestions. I have already been in touch with the council to confirm, as I expected, that a building warrant would be necessary.

I understand what you are saying about the average DIY attempts, but in general the DIY work I have done over the last 20 years or so has been of far better quality than the majority of professionals I have got in. Its fine if you get good people you can trust, but I haven't had much luck there in the past and I could write pages of examples of things I have paid people to do in the house where I have either caught them doing or not doing something that wasn't agreed, or had to put right something. I'm an Engineer, and while this is not in the building trade, I can get my head around the technical aspects, risks etc.

I'd be in two minds about the DPM, because the wall doesn't have one and if there was any water ingress from the walls it would just collect on the damp proof course with no where to go. I suppose there is always this dilemma between approaches that try to prevent the water getting in, and those that attempt to let it pass through.

So, just to update on this. I took up a few more boards, and as djh predicted the area in the bottom left of the plan is also very damp, in fact probably the worst affected as one smack and the joist in that corner fell apart.

I also got the boards up around the East facing vent and found it was almost completely blocked by rubble that had been left under the floor. I suspect that it has been this way for 10-30 years. What is most surprising is that the majority of the joists, with the exception of parts that are directly touching against soil or in the far corners, are completely sound and none of the T&G subfloor boards are damp or rotted. There is no wetness anywhere, just the mild dampness you would expect in an unventilated hole in the ground. Perhaps if the last people working under here had just cleaned up behind them, left the vents clear and enough space for air to circulate under the joists, there might never have been a problem.

I think my options are

A. Take a chance on sticking with the ventilated suspended floor. The quick version of this would be to scrape out the loose soil and rubble, replace the rotted joists and put it back to together. The better version would be to replace with joists of lesser depth and shorter span, to give a bit more room for airflow. I think this would probably be ok, but no real scope for insulation and I always like to add insulation whenever I am taking anything to bits!

B. Solid floor. Either the Foamglass suggested by Nick, or the approach GreenPaddy suggests, using DPM and Kingspan. Both of these are much better from an insulation point of view but probably carry some risks too. I am in contact with Mike Wye to discuss the foamglass system which is interesting. I think I am more inclined towards a system that would allow water to pass through to ground, just in case.

C. Do A with new joists, but seal up the vents and fill with EPA beads. This is based on a discussion I had on here a few years ago when I was thinking about another void in this house. I think it was Viking House who had done this on a number of houses including his own and I also found a research paper where this had been tested with some good results. I chickened out back then, because there were a lot of cables and other stuff to think about in that particular void, but with this void fully open it would be fairly easy to deal with all of that. The thing I like about this option is that it wouldn't be very difficult to reverse it if necessary.

There are pro's and con's with all of these options. As always I appreciate any feedback and suggestions.

Posted By: GreenPaddyA couple of things to clarify...

A building warrant... so you're also in Scotland. Let me know if you go for the EPS filled void, as I'd be very interested to see the approach to get that passed by building standards.

Interested to hear the final solution, as your dilema is not unusual with my clients.

I will do. It could be tricky I agree. I do have at least one academic paper to refer to if I can find it again, and I was thinking of leaving sensors in the void to monitor humidity near the joists.

I take it you have a business in Scotland?

Posted By: GreenPaddyA couple of things to clarify...

Likewise for the vented floor, achieving adequate ventilation to meet regs will be a challenge, as you will need a number on each wall, and those should really be on opposing walls, to encourage cross vent. You'll need 150mm min free void below joists, which I think you described as not being possible

For the vented floor alone I don't need to meet submit a warrant application or meet building regulations, which is why that is the easy option. I would just be repairing what's already there and clearing a blocked vent

Posted By: GreenPaddyA couple of things to clarify...

When I mentioned using professionals, I was referring to the design aspect and building regs compliance, rather than the installation works. I feel your pain with low quality contractors.

If you mean architects and others with professional qualifications, then I agree they are probably much less likely to provide shoddy work, but I haven't been particularly inspired by the ones I have had out. I got a few architects out before I started work on my extension. They were all coming up with the same idea, which was knock the whole thing down and build a long narrow extension with glass door on the end and looks like every other extension that's been built around here in the last 5 years, while the existing structure with some less invasive modifications would have given a far better outcome. In the end I did my own drawings and structural calculations, got through planning with only a couple of tick box requirements and got a far better result for a fraction of the cost. There are some fantastic architects and building professionals out there, and I have also dealt with some excellent trades, but it is such a minefield getting to the good ones. One of the things I love about this forum is the imagination and critical thinking from both the pro's and amateurs who are on here.

Posted By: GreenPaddyA couple of things to clarify...


A DPM, would be lapped up the walls to the slab level, so you wouldn't get water passing into it from outside. Indeed, it could continue above the fininshed floor level a bit, if that were necessary in certain areas. Plus there'd be little volume for water to occupy. If you think there's water likely to be running at sub-floor level, then I wouldn't want something with voids below the slab.

I always keep stone walls vapour open, and roofs as vapour emitters too where possible, but unless there's something very unusual with the ground, DPMs have not given me issues on any past projects. As you said, you've already dealt with damp ground around the building perimeter.

Thanks for the clarification, this makes sense. I don't like the idea of the DPM on the stone walls, but I suppose if it runs right up above the floor only an internal flood is likely to bring water in. I imagine the DPM would have to be continuous and run under the joists at the walls to be fully effective.

Posted By: djh

Posted By: Kenny_MFWIW, we have some foamglass at the bottom of our walls. It's there because not only does foamglass let water and vapour through, but it also forms a capillary break. That is, if there should ever be standing water at the bottom, it will still be dry at the top next to the bales. (there shouldn't ever be water at the bottom, but hey ho ...)

Thanks for the info, that's interesting, so kind of like a breathable damp proof course of sorts on the outside.

GreenPaddy,
I'd be interested on your take on this with respect to the need for a building warrant in Scotland for EPS under floor insulation.


0.5.2 Schedule 3

Table 0.3. Description of building and work, including the provision of services, fitting and equipment, not requiring a warrant

17. Any work associated with thermal insulating material to or within a wall, ceiling, roof or floor.

Exception: Any work associated with the application of an external wall cladding system that consists of thermal insulating material.


This seems to explicitly allow insulation to be added to or within a floor, without the need for a warrant. Of course I understand that there might be something else somewhere in the regulations that might counter this, but I am not seeing anything in the list of general exceptions at the start of the table.

previous posts overlapped.

Re. do you need a Warrant??

You're potentially doing more than just adding insulation, if you remove the timbers and install a solid slab. The floor is considered an element of structure, and as such would require a warrant.

From Handbook Definitions... "Element of structure means a part of a building which is part of the structural frame
(beams and columns), loadbearing (other than a part which is only self-loadbearing), a
floor, or supports a floor."

In any case, the exceptions require work to be carried out to regulation standards, just don't need to pay the local council to approve it. Of course, there can be relaxation granted, for historic or hard-to-treat homes.

In truth, people adding insulation without knowledge (not suggesting that's your case at all) carries quite a big risk to insterstitial condensation (most homes in the last 50 years are timber frame in Scotland, so higher risks than cementitious structures in England), but I suspect Building Standards just couldn't cope with all the warrant applications.

Interestingly, when I submit warrant apps, for works which include under floor insulation in a suspended floor, I still get asked to provide interstitial and surface condensation calcs as evidence with the warrant.

You still need to meet the regulations, even with the exception of not requiring a warrant. The regs, as I understand them, require a vented void sub floor, when there are structural timbers.

I'm not saying that filling the void with EPS is a bad idea, or won't work. On the contrary. I'm simply pointing out that if it doesn't meet regulations, and therefore it would not pass a warrant approval process, then you make a choice whether to comply or not.

I suspect there may well also be issues with EPS under the fire escape egress (which essentially floors are), in light of Genfell, regs are VERY focused on the fire aspect, and have been revised upwards on 4 or 5 occassions since Grenfell (Scottish Regs). I haven't reviewed that fire aspect myself.

Planning Applications are an almost entirely subjective process, interpreting guidance. Warrants are entirely objective, with 600 pages that you clearly either comply or do not. I prefer the latter

I should say that strictly I think what I have is Teknopor, which is more like the Geocell stuff. i.e lots of angular pebbles. I suspect GreenPaddy is thinking of the slightly different Foamglas products, which are more like bricks. I think he's been accurate and I've been a bit loose with terminology

Posted By: Kenny_Myou have probably hit the nail on the head with the regs requiring vents where structural timber is present.

Under the English Building Regs, the Approved Documents are 'deemed to satisfy' the requirement of the regulations. You can still use an alternative method, provided you can convince Building Control that will work. I guess that works the same way in Scotland too?

Some things to note regarding Geocell, (I've used it as a combined insulation MOT under the ground bearing slab in by side extension).

It's great stuff but hard to compact to the specifications required. Pouring and compacting it is hard physical work. You cannot move it with a shovel as the pieces 'lock' together even before compaction. a shallow saucepan works best. Buy lots, (I mean LOTS!) of heavy-duty work gloves too as the glass tears them to shreds and is an excellent industrial exfoliant on bare skin.

You will need the heaviest whacker plate you can hire to achieve anything like the compaction rates that Geocell / Mike Wye suggest - I think they greatly overestimate the amounts required.

Expect to have loads left over - not a problem for me as I will be using the excess for my garage floor using either the Geocell 'no slab' method or the system proposed by 'Back to Earth' that uses a Lithotherm UFH:

https://www.backtoearth.co.uk/guide/solid-floor-insulation-how-to-create-a-solid-insulated-floor/

Worst surprise when we ordered from Mike Wye was the arrival of 4 off nearly 3m tall FIBC bulk sacks, Like Hippobags only taller than a person. There was no way to shift them up our steep drive on the pallet truck we had so we had to empty, (off stepladders into wheelbarrows using saucepans and gloved hands as you cannot shovel this stuff) and refill into (smaller sacks) up the hill.

Mike Wye were made fully aware before delivery, that ours was a small domestic site with no forklift and manual unloading. I didn't even know they made bulk sacks that big... That was a hot, sweaty, sweary day :-)

I can laugh about it now, but it was an entire day of work lost using 4 labourers, my wife and me to shift off the road.

@sgt_woulds
How flat and level was the Foam Glass on top when you finished compacting?

My understanding is that it would be difficult to get it level and if not using a wet screed, either a dry levelling compound or shimmed subfloor would be needed to get it level enough to take the finished floor, but is it fairly flat or are there sharp edges/unevenness on the surface?

Just thinking ahead to the interface, whether the surface would be flat enough for timber battens like in the pic I attached previously, or it would need something in-between. Also whether it would be possible to put a vapour membrane directly on the top without it tearing up.

Since I was only creating a base for a floor slab, level translates as - level enough! It was sufficiently smooth to lay the fleece without fear of tearing before pouring the slab.

Thankfully for my back, my builders handled the levelling and are quite used to working with Geocell.
I've got photos somewhere, but unable to add to this forum.

You would need a dry levelling mix, (glass beads) for anything other than a poured screed. Back to Earth suggested 10mm of levelling, but my gut feeling would be to allow up to 20mm.

Chris at Back to Earth kindly sent me a case study from one of his customers, which gives a good feeling for how the system works for the Geocell / Lithotherm system but I cannot gauge what depth of levelling compound they used.

Kenney_M - do you have any info on the Fermacell system?