concreting my downstairs wooden flooring.... advice pls

[pappasmurf]

i have a 1930's semi and wish to concrete my downstairs flooring. heres the plan...... take out the floorboards and joist leaving me with about 1 1/2 foot drop down to the base void floor. i intend to DPM the floor, concrete and jablite (100mm) the sub floor and then add underfloor heating (piped-copper 22mm) then screed and tile the final finish. i wud like to know if this is viable seeking advice for any future damp problems and also blocking up the external vent tiles as i wont need to vent the underfloor anymore . pls can someone advise. many thanx

 

[julesmountain]

First you need to consider the basic structural change. You currently have a suspended floor where the floor load is transferred to the wall foundations. You are looking to replace that with a ground bearing floor where the floor load is supported directly by the ground. Before you build the new floor someone should check the ground and ensure that is suitable for the new floor and you will probably have to dig some of it out and then put down a layer of hard core to spread the load properly, you wouldn't want a cracked floor due to settlement!

You also need to think about the insulation of the new slab, there's no point in heating the ground or the external wall.

Another thing to watch out for is buried services under your floor. If you find a drain under there then you will have to do some work before you put the floor slab down.

Providing you put down a dpm and ensure the finished floor level is level with the external wall dpc then damp shouldn't be a problem. Yes the wall vent is there to maintain air to the suspended timber floor and isn't necessary for a solid floor.

Another thing you should pay careful attention to is the underfloor heating and screed. I'd be surprised if you were really using copper piping as most underfloor heating is 15mm plastic coated aluminium. Take great care with the screed as most manufacturers recommend a minimum of 75mm cover over their pipes and also require a minimum drying time before you put heat on to prevent cracking of the screed. Make sure your plumber does a thorough pressure test before you screed, don't want any leaks after you screed! And don't screw anything to the floor afterwards unless you know exactly where the pipes are!

Sorry if this all sounds rather negative, what you're trying to do should be quite achievable and relatively straightforward but its better to know the pitfalls before you start!

Best of luck!!!

 

[pappasmurf]

thanks for the advice julesmountain..... i think i have covered the basics that u have described in your post. but my main concern now is the cabling below the existing floor. u see i have about 3 million cables down there as i have a very hi-tech home cinema setup and all the cabling is down below this existing floor; and am not sure wot to cover them with in order for the screed and concrete not to contaminate and destroy them! i dont know if ordinary plastic cable conduit will do.i also have to consider the covering up of the electrical socket cabling on possible conduiting, but maybe with a conduit with a spilt in the middle as i dont want to rip out the existing sockets from the walls!..... i also have my my electrical and gas supplies coming into the house which i also have to consider. wot do i cover these up with?......i know i will be covering all the new pipework for the under floor heating with 4" denzo tape before applying the 4" of screed and then tiling. but i dont think i wud wonna add denzo tape to cover the wiring..... pls advice in this protection of cables issue, with maybe a link so that i could see the product myself. many thanx will wait for your reply.

Untitled

• pappasmurf
• 18 Dec 2008
• 1

Untitled

• pappasmurf
• 18 Dec 2008
• 1

 

[julesmountain]

Need plastic pipe as conduit, metal will corrode. Choice of pipe diameter will depend on whether or not you want to try and pull cable through pipe once screed has been laid, say for future rewiring, but you talk about forking the pipe so i guess this is not on the cards.

I'm assuming when you talk about gas and electric you are not refering to a mains supply running under your house but are talking about your own internal supplies coming from the meters? If they are not coming from your meter then you'll need professional advice.

Make sure you've got enough cover on the pipes, best to lay the services completely under the screed if you can. The gas pipe will need to be completely covered in plastic pipe to protect from corrosion and you shouldn't bury compression fittings, you will need a corgi man to help with this.

In terms of product, that will depend on what diameter pipe/conduit you want/need. As a general rule you want a relativley thick plastic that won't deform when you put all the screed on top.

 

[pappasmurf]

no im talking about the "main" supply of electrics and gas from the "street"......im not gonna be using compression fittings under the screed anyways!........ need a corgi man my bum!..... why wud i pay a nasty smelling bear gut unshaven ass showing every time he bends over so called corgi chap to do the job anyway?..... i do "all" the work myself!.... i just needed abit of advice thats all. thanks anyways!

 

[chappers]

well as you seem to know best then just carry on regardless, just hope that nothing ever goes wrong and the gas board need to come and sort it out. only to find out you have illeagaly carried out controlled works. the least that will happen is you will have to foot the bill , the worst could be prosecution and a hefty fine.
But hey you know best.