Concrete floor insulation

[saveasteading]

11 hours ago, Roger440 said:

 the odd chipped corner.

If you are staggering overlaps these don't make much difference as they become air pockets. And consider the proportion of area....negligible.

[ColdHouse]

@Kacha , have you had any quotes yet for how much it'll cost to dig up the existing floor?
I'd like to do the same with my house (1990's, ~65m2 ground floor area) as you're planning, but have no idea how much it'll cost.

[saveasteading]

3 minutes ago, ColdHouse said:

have no idea how much it'll cost.

How long would it take?

X £500/ day

How many skips? X £200  for clean concrete.

L X w X depth in m3. X 1.5 for bulking.

Add £500 sundries.

 

That's just a guide.

[Wil]

Hmm spec for my retro fit floor is hardcore and sand 160mm. 200mm PIR. 150 concrete. Pipes in the concrete. Tiles likely on top.

 

Sounds like there are options to cut 50mm off the concrete at least. So useful post. The 200mm was me insisting on exceeding BR, architect and contractor not keen.

 

I have a QS cost for rates of digging I can try and find if useful.

[saveasteading]

20 minutes ago, Wil said:

. 150 concrete

150 pir is the  pragmatic choice, even 100 if it helps a lot.

100mm concrete is plenty. You can drive forklifts on 150 if the hardcore is good.

[Wil]

I lied- here’s the spec- it’s 125mm concrete and much more hardcore/ blinding:

 

 

[saveasteading]

1 hour ago, Wil said:

it’s 125mm concrete and much more hardcore/ blinding:

OK. what thickness might help you practically?

 

This is a house so nobody is going to break the floor. The weakest layer is of course the insulation. After that the loads are very well spread over the stone below.

 

If the hardcore is good quality , ie not a heap of old bricks, then that can be reduced in thickness. Likewise the sand. The sand is  there for adjusting the level so there might be none above the highest point in the stone.  

so i am suggesting 100mm concrete, on 150  PIR, on 150 of stone and sand (total).  that is still 400mm which is a lot to dig out, but a lot less than 500.

IFFFFF you do it to a high standard of level control and compaction.

 

[Wil]

Realistically, every little helps. That’s a useful breakdown, thank you- I’ll discuss with the contractor who’s bidding. A couple of questions if I may?

 

In my spec above it looks like there’s a vapour layer over the insulation with a damp membrane/ radon barrier under. Is this second barrier necessary? I was imagining pinning the UFH pipe to the insulation direct with the concrete and reinforcement poured directly on top (or even follow the spec and tie to the rebar). 

 

Does 100mm concrete differ from 100mm screed poured?

 

 

[saveasteading]

You only need one layer of plastic. Choose a radon spec and it does the dampness thing too.

You need an extra  plastic layer on top of the pir as it stops concrete or grout from running into gaps and floating it. I've seen it and isn't fun.

Screed or concrete. Either will do.

BUT I would say put a thin concrete screed down for the pir to sit on, and then 60mm pumped screed goes on top with the ufh in it.

[Wil]

So that would be 100ish hardcore, sand, concrete(how much?), 150mm insulation, plastic membrane, 60mm screed with UFH pipes?

[saveasteading]

This is becoming non standard but then so is ( to me) having insulation straight on stone.

 

So I'm going to say, stone as thick as you like...but at least 100, laid really flat and with 0 to 10mm max sand blinding but zero if you can.

Dpm, to radon spec if necessary.

 

Then a concrete screed about 75mm, hand tamped and nicely level. A light mesh (A142) would be a nice touch. Shop around.

 

150mm insulation

Dpm, taped,  any spec as it is only to close the joints.

Ufh pipes pegged to the pir.

60mm pumped screed.

 

I like the level control in this, so the thicknesses are controlled. Plus having the lower screed keeps it all clean and the pir laid solid.

 

BUT it depends who is doing it.

 

[Wil]

Thank you for the advice, much appreciated. I’ll discuss with the contractor tomorrow if they can give assurance on the quality control.

[ColdHouse]

On 11/11/2024 at 16:23, Wil said:

I have a QS cost for rates of digging I can try and find if useful.

If you could, that'd be very helpful. Thank you 👍

[Clark Kent]

On 31/10/2024 at 08:51, IGP said:

Might be worth taking a look at 

 

 

to see how they did underfloor heating as well. About 5 mins in. 

 

This is really interesting, I’m doing a similar refurb but cannot dig out the ground floor. This guy isn’t either and adding no insulation at all and yet reckons his heating bills are £80 a month?

[IGP]

10 minutes ago, Clark Kent said:

This is really interesting, I’m doing a similar refurb but cannot dig out the ground floor. This guy isn’t either and adding no insulation at all and yet reckons his heating bills are £80 a month?

The system is visible on https://heatpumpmonitor.org/system/view?id=139 so make of it what you will but it looks impressive to me. 

[IGP]

It looks like he’s gone for what he’s losing in actual heat loss, making up (and possibly more) with efficiency of the system.