Concrete Floor Makeup Detail

[Adrawk]

I'm back!

Having searched and read the forum the last couple of days, I have a couple of questions with regards the floor for my extension.

1 : The DPM at the corners, do I fold it neatly or can I cut it and tape it in some way to make it nice and neat? Will it matter if its folded up?

2 : The concrete slab is to be 100mm thick, do I need any reinforcement in this? I can add fibres to the mix from the company supplying the concrete. Any recommended strength for the slab, my drawings dont specify a mix?

3: Insulation is to be placed below the slab which will eventually have roughly 75mm screed installed near the end of the job. Are there any glaring advantages I'm missing from having the insulation above the slab? I will not be installing under floor heating

4: The plastic sheet atop the insulation, does this need to lap up or just be cut to fit the space? I will also have 25mm insulation up to FFL around the perimeter to prevent cold bridging, should the sheet also cover this?

 

[tomfe]

1. Fold them, your wall finish and skirting will hide anything.
2. No, not if it's not your floor finish.
3. I don't see why anyone would do a concrete floor and then put screed on top of it, it's just a waste of time, money and resources.
There will be more thermal mass if you put the insulation below the concrete, which means it'll take longer to warm up but also takes longer to cool down. It's easier to get a good fit ontop of concrete when using PIR/PUR as these don't flex as much as eps.
4. Lap this up the side same as the dpm, if you are using foil faced insulation (the aluminum in the foil affects the concrete) if you are using eps you may find it floating if the concrete gets underneath it, it'll take less time/effort to it this way anyway.

Why not add an extra 75mm of eps under your concrete floor and get the finish bull floated flat to put your floor finish onto?

 

[Adrawk]

I have services to go in the floor, mainly gas pipe and heating pipes, and work to do in the existing part of the house to expose the true level of the existing floor. I'll be removing the back of the house and installing steels so I'll want both floors to match perfectly.

 

[tomfe]

Can't you just wait and work of the hardcore?
But yes sounds good to me.