extension slab with ufh, advice for newbie

[redlee]

I've an extension underway and want to check that what i'm planning is correct as far as the base goes.
The specs that were approved for bc say:-
well consolidated 150mm hardcore,
sand blinded,
1200g visqueen,
100mm concrete,
125mm polystyrene or 80mm kingspan insulation (poly approx £100 cheaper)
polypipe ufh tray (egg carton type) & pipe
65mm screed (sand/cement or pumped liquid)
25mm polystyrene insulation stood on end around periphery to prevent cold bridging

does that sound right, do i use building sand for blinding the hardcore, the room is 3.2m x 7.6m how wide are visqueen rolls/sheets, will the visqueen need protecting when they come to barrow in the concrete, how long should the concrete be left to cure before covering with insulation/ufh?
Apologies for waffling on but i only want to do this once and am a complete newbie to extensions, any advice from professionals or those with greater experience much appreciated.
Cheers
Lee.

 

[redlee]

Anybody? i was hoping to start digging out this weekend.

 

[noseall]

does that sound right, do i use building sand for blinding the hardcore, the room is 3.2m x 7.6m how wide are visqueen rolls/sheets, will the visqueen need protecting when they come to barrow in the concrete, how long should the concrete be left to cure before covering with insulation/ufh?.

Sounds about right.

I would increase the screed depth to at least 75mm.

Building sand is fine as a blinding layer.

Visqueen is usually 4m wide when opened out.

Drop some scaffold boards down for the barrow run and tip.

The concrete will be ok after a couple of days. Try and keep it relatively smooth when laying as opposed to a heavily peaked tamped finish.

 

[redlee]

Cheers, the 65mm was based on polypipes optimum for the underfloor heating, i'll have a check but think they said upto 90mm - so i'll up it especially as the egg carton panels that the pipe lays in has castellations 35mm high.
Now to work out quantities.....

 

[mointainwalker]

If you choose self-levelling anhydride, then 50 - 55 mm is usual and you will pay quite a bit more per extra cm.

If normal mortar screed then I would say 70 mm max. Adding more increases the thermal storage effect, but not really necessary for most people unless you are using off-peak electricity which you are not.

 

[redlee]

Is it MOT limestone 40mm to dust that i need for the hardcore?
Any ideas how many grab bags to do 150mm deep 3.2m x 7.6m?
How much building sand do you think i'd need to order?

 

[hotrod]

Is it MOT limestone 40mm to dust that i need for the hardcore?
Any ideas how many grab bags to do 150mm deep 3.2m x 7.6m?
How much building sand do you think i'd need to order?

1. Yes. MOT 40mm to dust.
2. 8 grab bags.
3. 1 grab bag @ 50mm depth will see you just short so fettle it out a bit.

 

[redlee]

Thanks all for the advice so far, hardcore and sand now down. Once building control have been i'll be looking to order the concrete which will be from a barrow it in mixed on site firm. If i put battens around to the height of the top of the concrete and use a length of 3x2 will i be able to tamp and level on my own or is it a two man job?

 

[redlee]

Ok building control are happy for me to continue, i take it i put the battens in place then the visqueen up the wall and not the other way around?
is it a two man job to tamp and level across a 3.2m span?