Ground floor structure

bbam

HI,
This may seem like an odd question but hear goes...
My block layer is recommending tha I pour a sub-floor and then the finished floor later in the build. Others are recommending I pour the finished floor all in one go before building the walls up..
Apart from the marginal extra cost of pouring twice are there any other reasons for one Vs the other?? At the moment I'm leaning towards pouring twice as was done in my current house.. Foundations will go in this week so I'll need to get of the fence soon
Advice/opinions welcome
Thanks
bam

If you pour the finished floor before you erect the main walls you can get a flatter floor easier as the screeders can work from outside the floor area, but there is an increased risk of damage to the finished floor from building work. Also you may have to do some damage to install a "forgotton" service.
Doing a sub-floor first means that the insulation has a level surface to lie on. and the radon barrier is protected.

I did a single pour without a sub floor, after the roof had been fitted.

Viking House

Insulation between two layers of concrete traps moisture in the floor and concrete above and below the insulation prevents it drying out. If your insulation is Polyeurethene then this moisture can seriously affect the U-value. If your Radon Barrier is below the insulation then you will get condensation between the insulation and the Radon Barrier adding to the problem.

De_man

i went for a finished floor leaving channels where i intended to put the services.

damage to the floor is minimal provided you powerfloat the floor correctly and get a smooth finish, mortar will be easily removed by using a scrapper on a regular basis .

if doing a precast floor (for upstairs) finished floor again,
to make life easier when building upstairs - i got a tracks machine and loaded buckets of sand up on the floor and mixed away up there - grand job no damage whatsoever

personally i'd go for the finished floor and get it over and done with, it's nearly impossible to get the levels correct later in the game

muffler

Viking House wrote:

Insulation between two layers of concrete traps moisture in the floor and concrete above and below the insulation prevents it drying out. If your insulation is Polyeurethene then this moisture can seriously affect the U-value. If your Radon Barrier is below the insulation then you will get condensation between the insulation and the Radon Barrier adding to the problem.

In all of my 30 years spent designing and supervising houses I have never seen anything like what you have described.

In fact your comment about the radon membrane and condensation is illogical to put it mildly. Unless of course you are referring to TF which I personally wouldnt involve myself with.

Viking House

muffler wrote:

In all of my 30 years spent designing and supervising houses I have never seen anything like what you have described.

Hi Muffler

Polyeurethene (Kingspan,Xtratherm) is not recommended in wet areas, because water destroys the U-value. Concrete takes over a year to fully dry so it is giving off moisture all this time, this moisture makes its way into the Polyeurethene (Kingspan,Xtratherm) that is between the 2 screeds and the U-value is seriously affected.

muffler wrote:

In fact your comment about the radon membrane and condensation is illogical to put it mildly.

The Radon barrier should as you know be always at the warm side of the insulation because water vapour from the inside of the house will condense on the cold plastic if it is at the cold side of the insulation causing moisture to form between the insulation and the Radon Barrier. This moisture will destroy the U-value of Polyeurethene (Kingspan,Xtratherm) insulation.

As you can't use Polyeurethene (Kingspan,Xtratherm) under the Radon barrier because of the risk of Rising Damp wetting the insulation and you can't use it on top of the Radon Barrier because of the risk of Condensation it seems to me to be a product that is not usable under the floor, so it is back to good old waterproof Polysterene.

This is just my opinion!!

bbam

Hi all..
Thanks for the inputs..
We've decided to go with a finished floor, we'll protect with sand which can be removed later in the build..
I'm interested in the comments about the insulation type in the floor.. I'd been planning to use Kingspan, should I be looking at polystyrene and what depth ??.
We got our foundations in with a bit of a struggle... needed an extra input from the engineer as the ground was soft when dug.. ended with
100mm lean mix as a "mud mat"
300mm 35N concrete (1500 along one wall)
2 layers 1/2 inch mesh steel (100mm & 50mm spaced)
Interestingly I "had" to use chairs as the enigineer wouldnt allow bricks to space the steel..

Advice on ground floor insulation would be welcome..
Cheers
bam.

Winnie001

Hi,

Also need to consider if you will be putting solid wood floor anywhere - if so then better to have subfloor.
Our floor was fully poured before we thought about this & regret it now. A number of people say it is ok to lay solid floor by glueing to ply so don't need subfloor but I understand that it is best to lay battons of wook & nail solid floor to this - less likely to warp, in which case you need subfloor otherwise wooden floor too high...................just something to consider