Concrete floor design

ryanrod

I am building an extension and have a question on the concrete subfloor/floor.

The largest room on the ground floor will be 7M x 7M.

I am using 100mm Kingspan insulation.

What would be the min thickness slab necessary for a floor this size.

The builder suggests compacted fill/ 75mm concrete slab / 100mm insulation /50mm screed.

I am not an engineer but would think fill / 150mm slab / 100mm insulation / 75mm screed min.( I will be putting in UFH pipes).

What would be the typical design?

Martron

150mm slab is all i ever saw. you could probably get away with 100mm. depends on what type of traffic it will have. but 50mm screed should be grand

Slig

150mm slab for a min 7M span

Contact a pre-cast manufacturer, they usually have in house engineers to design these and give you a price so shop around. Alternatively if you have an engineer on board they could probably do up the calculations.

Mellor

I think you mis read the OP Slig, its a ground floor, not first floor. At least, thats what it appears to me.


Ryanrod, you right that you builders suggestion is too low. I would be going with your suggestion.
I also disagree with Martron that 50mm screed is enough. For a bonded screed it is, but a floating screed with UFH needs to be bigger. 65mm min. 75mm to be safe, or as per manufacturers guidance

Slig

Mellor wrote: »

I think you mis read the OP Slig, its a ground floor, not first floor. At least, thats what it appears to me.


Ryanrod, you right that you builders suggestion is too low. I would be going with your suggestion.
I also disagree with Martron that 50mm screed is enough. For a bonded screed it is, but a floating screed with UFH needs to be bigger. 65mm min. 75mm to be safe, or as per manufacturers guidance

Sorry your right, I misread it, 150 + 50 floating screed. any bigger than 100mm floating scred tends to crack especially if you have a large room.
I would push for 100mm screed (on 100mm insulation on 150 floor slab) in this instance as the room seems be quite large.

RKQ

150mm thick floor slab is minimum thickness in Building Regulations!
100mm insulation and 65mm screen is fine, assuming ufh is oil or gas.

I'd recommend a thicker reinforced screed if using geothermal ufl - cheap rate electricity at night, so heat slab at night to radiate during the day and minimise electricity use during day.( Thicker screen takes longer to heat up but also holds heat longer and can be "topped" up quickly)

Slig

RKQ wrote: »

150mm thick floor slab is minimum thickness in Building Regulations!
100mm insulation and 65mm screen is fine, assuming ufh is oil or gas.

I'd recommend a thicker reinforced screed if using geothermal ufl - cheap rate electricity at night, so heat slab at night to radiate during the day and minimise electricity use during day.( Thicker screen takes longer to heat up but also holds heat longer and can be "topped" up quickly)

I agree that the thicker slab will take longer to heat up but will also retain the heat longer. If using underfloor heating then response times will be slow anyway

ryanrod

I think I will go for 150mm slab with UFH pipes tied to steel mesh.
I will also be putting a couple of half inch pipes for possible solo rad if
I ever need it.

Thanks for your suggestions