To raise concrete subfloor 150mm

[SiGuy]

Hi All,
I'm newbie here...to the forum and to the UK! Currently renovating a house and have been coping well on how things are done differently compared to the States, but I am at a loss when it comes to raising the kitchen subfloor.

The current floor is a concrete slab with no DPM (based on the age of house), aprox 150mm below the finished dinning room floor. I would like to raise the floor to eliminate the step down and prep for plywood (perhaps hardiboard) then tile finish. As this is the kitchen I would ideally run the utilities (CH, H&C water, gas and electric to the boiler and other appliances) underneath.

Considering the construction of a suspended joist floor requires a minimum of 150mm void below joists and and air vent bricks this is not viable. I am considering Polystyrene (jablite or similar) floor slabs however am not too familiar with it. A number of questions regarding its use.

1) This product is structural on its own and doesn't require any additional support, correct ?
2) Is it able to be secure to the existing slab to prevent lateral movement? Any fixings would comprise the DPM necessary underneath. Will the poly and DPM react to adhesives? If the poly can't be secured, it stands to reason the plywood on top and tiles wouldn't be restricted as well? This would result in less than ideal surface for tile.
3) Can utilities be placed underneath? Specifically hot water and central heating pipes?

Do folks have any thoughts on using poly or the best way to raise the floor, insulate to building regs and sufficiently 'bury' the utilities? I'm interested to learn what I may be missing.

Thanks in advance for your insight!

 

[ree]

If, standing in the kitchen, you look down at the step up from the kitchen to the dining room you will possibly see some sub area air vents, and a couple just outside below the dining room window. If you raise the floor you will have to consider the sub area ventilation.

All your vertical dimensions will alter by shrinking 150mm, such as the height of the kitchen door, and FFL to window cill.

I'd suggest that you get in a paid professional, such as a builder, to give you a heads up on site

 

[SiGuy]

Hi ree,

Thanks for the response. Currently the step into the dinning room doesn't have a air vent. As standard the other exterior walls excluding the kitchen, have them to ensure addequate air flow to the crawl space. Already have a brickie lined up for raising the kitchen door lintel as well as making necessary adjustments to the window openings caused by raising the floors.

I plan to have a professional in shortly, however looking to be as educated as possible regarding the polystyrene flooring and other options prior to having them in.

Any other thoughts out there? Advice and suggestions always appreciated!