Old stone floor

[FM2015]

I have an 1800s farmhouse and in a couple of rooms, there are the original slate flagstones laid most likely directly on the earth. 

 

They do let a bit of damp through along the joints and obviously attract any condensation due to the underlying temperature.

 

I'd like to keep them and make some repairs/replace some.

 

I've bitten the bullet and decided to get a micro digger in so that I can lift them all up, dig down and lay an insulated floor before reinstating the slabs.

 

Question is, what would be an appropriate floor build up/structure?

 

My first thought was concrete, insulation and screed with dpm underneath, lapped up the walls, with slabs over bedded in kiln dried sand to level.  Not sure I'd get the slabs level if I mortared them down.

 

The slabs are smooth but uneven, it's an old house, but the joints are pretty perfect.

 

Any help or advice would be appreciated.

 

Tia

[Adrian Walker]

I would consider Foamed Glass, then concrete with UFH - https://www.mikewye.co.uk/product-category/brands/geocell-foam-glass/

[saveasteading]

Floors can be overspecified.

There is probably a practical limit as to depth without udercutting the walls.

Nobody has fallen fhrough this floor, in 200 years.

The issue is simply cold and damp.

So you could just spread sharp sand on the earth, then pir, then a dpm and screed.

After that you lay your slabs down again on sand or on mortar.

Instead of just sand as a base, it could be a sand and cement screed, the main purpose being level control.

Most heat loss is at the perimeter, the very place you don't want to excavate too far.

Perhaps we can look at detail later.

[FM2015]

Thanks,

Ufh isn't viable in my scenario

 

I guess my over engineered solution was only to provide a more stable base but I guess the screed does that job.

[saveasteading]

Bottom line is the low strength of pir. It's plenty but obviously anything below it doesn't have to be stronger. 

Sharp sand with 5% ement mixed in as a bed?

[FM2015]

Or whack some type 1/803 down as a base?

 

It should be fairly dry as the ground level outside is lower than the potential dig out level.  Damp is 90% condensation.

 

At this stage, I don't have any concerns with excavating right next to the wall.  Famous last words🤣

[SteamyTea]

1 hour ago, saveasteading said:

Most heat loss is at the perimeter

Not always. It depends on the areas of the floor, and to a smaller extent  the walls.

@FM2015

How much headroom do you have?

Can you create a thermal break between the slabs, floor and walls. Basically a small channel around the perimeter?

[saveasteading]

Just now, SteamyTea said:

Most

Define most.  Try this?

The heat loss from an uninsulated floor will be proportionally greater close to the external perimeter.

[SteamyTea]

2 minutes ago, saveasteading said:

Define most.  Try this?

The heat loss from an uninsulated floor will be proportionally greater close to the external perimeter.

I would need a spreadsheet to calculate there permutations.

 

Unless I am missing something stated earlier.

Edited December 26, 2023 by SteamyTea