how to deal with old floor construction

[Coll659]

Evening all

 

Just started a completer renovation of an old building and need some advise on how to deal with the floor. Its a simple square building with a stone and concrete foundation base and after lifting a few floorboards it looks like it was infilled with a light, loose gravel or something and it has large wooden beams placed in the gravel. It looks like these are just sat into the gravel to support and provide a fixing for the floor boards. As far as i can see so far they are not connected to the walls or sat on anything other than the gravel. However after digging my hand down to the bottom of them at a few places it seems they are rotten. 

 

My plan is for a wet underfloor heating system and a laminate/viynl floor covering in most of the rooms and tiles or micro cement in another. 

 

Looking for advise on how to proceed. I was thinking of pulling out all the old beams, raking the fravel level, doing a blinding layer of sand (approx 50mm) compressed with a compacter machine, then a DPC layer. And then laying the underfloor heating and a anhydrite screed on top to cover pipes (50mm). But im new to this part of construction so not sure if this is right or totally wrong. 

 

I don't plan to lay extra insulation as the loose and light gravel sort of mixture I believe provides good insulation and we have at least a meter of it. however Im not sure how to fix the underfloor heating pipes as the normal clips would obviousley pierce the DPM layer so would I need the rails stck to the dpm or perhaps the castellated panels

 

Any advice here would be very appreciated.

[Conor]

Dig it all out, level the ground with blinding, install whatever insulation thickness you need to get to floor level with 50mm liquid screed. Not putting insulation would be madness. if you are doing a complete renovation, building control will require you do do it anyway.

Edited August 4 by Conor

[Coll659]

Thanks for the info. 

As was lying in bed last night I was thinking that I would need a concrete slab under the insulation. So that would be digging out some of the old rubble, then:

-sand blinding later

-dpm

-concrete slab (100mm??)

-insulation

-underfloor heating pipes and topped with anhydrite screed

 

Or can I do without the concrete slab? This would be ideal, time and money are seriously tight so every penny and minute is valuable. 

 

Thanks again

[Onoff]

I dug my bathroom floor down and from the bottom up put back:

 

-Compacted 40mm max dia graded hardcore ("Type 2" near enough). Whacked direct into the clay.

-Sharp sand blind

-25mm EPS

-DPM

-150mm PIR (100+50)

-Polypipe tray with UFH

-A142 mesh

-100mm wet concrete laid to screed rails

-Tiles

[Coll659]

Thanks, sounds like an ideal base (and more expensive than I wanted 🤣). 

[Coll659]

After some research it looks like it's foam glass under my floors. Now considering doing a limecrete floor. If I'm correct and the glass foam is ok I can remove the wooden beams, level out the glass foam, add a geotextile fabric and a grid for securing underfloor heating pipes, then lay the pipes and put something like 100-150mm limecrete on top. But just started the research on this so maybe totally wrong about that? 

[Mr Punter]

If it is lightweight it could alternatively be expanded clay, such as Leca, but either way at a metre thick you may not need to add more insulation.  Find out exactly what you have and do the calcs.  Yes, you can lay your limecrete on this once all the timber has been removed.

[Coll659]

yeah you may be correct there Mr punter. Il be confirming this tomorrow hopefully

[Coll659]

After much deliberation I decided to go with the option of pulling everything out and properly insulating.

 

The house is of two parts, new and old, the old has the wooden beams simply sat in the expanded clay to support the floor boards. Below the expanded clay (approx 300mm) is just a rubble. Here I intend to:

-dig out all the expanded clay,

-compact the layer of rubble with a whacker plate

-50mm sand leveled and compacted with whacker plate

-dpm

-300mm EPS insulation (there will also be house wiring and plumbing laid into this)

-ufh foil and underfloor heating pipes stapled to insulation

-100mm cement screed (probably done by hand with a mixer, looking for advice on this cement type and make up) 

- finished floor, mixture of vinyl and tiles

 

 

In the new part we are in the process of ripping out the old slab and will be the same idea but since we won't have so much depth here we will do 100mm PIR insulation to keep floor levels equal. 

 

Looking for advice if this is ok. 

 

Do I need another layer of concrete at the bottom? Or a thicker concrete layer or reinforcement or something? I'm worried over time the concrete layer will settle and crack and possible damage and break the underfloor heating pipes so not sure if I need a stronger layer on the bottom or a top screed over the concrete or something. Any advice would be greatly appreciated

 

Thanks in advance

 

[Redbeard]

You may know this already but PVC cable sheathing reacts with PS, so don't let them hug each other!

[Coll659]

Thanks I actually didn't know that but it's my plan to have everything in ducting but I'll make double sure to make sure they don't touch now

[Coll659]

On 05/08/2025 at 07:51, Onoff said:

I dug my bathroom floor down and from the bottom up put back:

 

-Compacted 40mm max dia graded hardcore ("Type 2" near enough). Whacked direct into the clay.

-Sharp sand blind

-25mm EPS

-DPM

-150mm PIR (100+50)

-Polypipe tray with UFH

-A142 mesh

-100mm wet concrete laid to screed rails

-Tiles

@Onoff I'm looking to do very similar to you, couple of quick questions. 

 

Why the EPS? Just to protect the DPM more? 

 

I'll be clipping my underfloor heating pipes to the insulation without the polypipe tray and then thinking just to lay the A142 mesh on top.

 

Did you mix the concrete yourself or have it delivered? I need to do approx 110m2 (across 8 rooms so it can be split into smaller sections) and due to access and cost (truck would have to block the road) I'm looking to getting in a bunch of friends and doing it all with a mixer but still looking for advice on the correct mixture. Just a simple 1:2:4? 

 

 

 

[Onoff]

9 hours ago, Coll659 said:

@Onoff I'm looking to do very similar to you, couple of quick questions. 

 

Why the EPS? Just to protect the DPM more? 

 

I'll be clipping my underfloor heating pipes to the insulation without the polypipe tray and then thinking just to lay the A142 mesh on top.

 

Did you mix the concrete yourself or have it delivered? I need to do approx 110m2 (across 8 rooms so it can be split into smaller sections) and due to access and cost (truck would have to block the road) I'm looking to getting in a bunch of friends and doing it all with a mixer but still looking for advice on the correct mixture. Just a simple 1:2:4? 

 

 

 

 

The 25mm EPS goes atop the Type 2 and under the DPM to yes protect the DPM from puncturing. Also EPS is damp proof.

 

I mixed it myself. 4:1 ballast/cement mixed with Everbuild 202 Integral Waterproofer to the tub ratio. The A142 mesh hold it all together. Meant to add fibres but kept losing them! 

[Onoff]

The Everbuild 202 has a de-aerator in it so less air to tamp out. Also makes the mix just "better".

[Coll659]

Great info thanks for the reply, helps a lot. I think this is the direction I will go as well

[Onoff]

@oranjeboom dug down every floor in his bungalow and built back up.

 

Check out this and his other threads: