Omitting screed layer

ds1980

Currently building a new extension and access is tight as well as budget. Am thinking of omitting the screed layer and using the concrete base as my finished level. There's no building regs prob with this but any issues i should think about apart from getting it as smooth as possible for finished flooring which will probably be karndean or alike.

Johnandabby

You won't get the concrete smooth enough to lay flooring directly on. You could use a latex levelling screed rather than a concrete screed to reduce depth, but you will need something. The concrete screed is normally part of the overall structure stability so you need to check this out fully before making a decision.

You would also normally install the insulation above the concrete base, and then screed over the top? Are you going to wrap insulation below the concrete slab?

warmhands.coldheart

What will makeup of floor be.?
I've renewed entire ground floor of my house a few years ago.....Made up of:
Hard Fill (Compacted)
100mm Concrete,
100mm Kingspan Insulation,
75mm Screed.. (Under floor Heating laid on top of insulation hence the thicker Screed)

What are you proposing. I wouldn't advise leaving out the insulation...

System

it can be done technically (obviously as long as the slab is over the insulation) However, with no screed the finish of the edge can be untidy - you would normally have 25mm plus of insulation around the perimeter of the slab to prevent cold bridging, and the dpc edges may be visible…
As it's an extension are you not going to have issues with the finished floor levels?
You could maybe look at a floating floor to give you a better finish.

teneighty

It is possible but very time consuming so you probably would not find any financial or time saving. Extra care needs to be taken to make sure the slab is laid very flat and then as it cures work the surface to form a smooth surface. It is a skilled job requiring an expert.

Other floor finishes can be used other than screed, chipboard laid on insulation or timber battens etc. but you have to make sure the slab is laid flat.

By the way, a usual 50 to 75 mm screed has no structural integrity, it is just a finish like wall plaster, the 100mm concrete floor slab is the structural element. Most of my projects have the insulation underneath the concrete floor slab, I assume yours is the same.

ds1980

Thanks. All issues raised I've looked into. As said screed is only decorative which is why you can omit it. There's lots of info on web about people doing it and thought it might save me some hassle but the additional work to get smooth and prevent cold bridging etc doesn't seem worth it. Am thinking I will go down traditional route. Am hoping to get 100mm plus of insulation.

Ta

jc808

i omitted a screed in my basement a few years ago and insulation

signed off my building regs as we put in a wooden 3"x2 subfloor insulated between joists

it can be done but how will u insulate floor

ds1980

http://www.diyhomeextension.co.uk/the-slab.html

This is a good example of someone omitting the screed.

One other point. I will speak to building control but what are the minimum depths depths for each section why and whats most important? I know insulation is for u values but what about the other layers? I have room to do them all but just curious?

Ta
Ds1980