Subfloor - Needed??

[Moggaman]

Hi

I have seen how many house are built with a sub floor, then the walls go up and house. Then the insulation is fitted on the sub floor with  UFH sitting on the insulation and a screed poured over that..

Why don't people put in radon, insulation, ufh pipes and pour floor in one hit. This way you save on the screed... the obvious benefit is that you can work in better conditions if you do it in 2 hits but is that the only one?

Thanks

 

[Ian]

Many members of this forum inc me have successfully done the one hit process you describe however there are 2 main reasons that it’s not more commonly used as a method compared to the more traditional method of having a sub-floor and a separate screed:

 

- it’s not an easy job getting the flatness needed in order to be able to lay a floor finish such as a ceramic tile directly onto a mass concrete floor. (That’s why floor screeding tends to be a specialist job)

 

- the ground conditions need to be suitable to allow a ground bearing slab. For technical reasons many builds need to have a suspended floor construction and a mass concrete one-hit floor is not used in those situations.

[Onoff]

I used screed rails in a small room to get 100mm of wet concrete dead flat as a finished floor, ready to tile straight on to and it was too. Doorway was trickier and I had to do that by hand.

 

On a big open floor I guess power float?

 

The liquid epoxy screeds I've seen used on here have to be the flatest I've seen.

[PeterW]

The reason a lot of the mass build housing companies do not use ground bearing slabs and prefer block & beam or subfloors is the labour used to do the stages of the build.

 

A beam and block floor can be put in by one skilled with two or three labourers - its cheap and doesn't require a level of accuracy. Also, the pipework for UFH is also easily damaged on a large site, and that requires heating engineers or specialists to install. To reduce cost, and reduce time on site, it is easier  to use unskilled/semi-skilled labour in those first stages and then bring the skille first fix trades in toward the end of the build where the properties are secure and wind and watertight.