Floor in new extension - Do i lay on inner course of bricks

[Mick Leek]

Hi all,

Further to my earlier post ref: TRENCH BLOCKS. I am now upto DPC. Or am I ?

I have been told that the new floor level must corispond with the one in the house ( Ok thats no problem) But i have also been told that the external course of bricks should be built to the original DPC and the internal one should be left to the bottom of the thickness of the new floor slab ( now its got me)
Basically i think that this means that the internal wall will be lets say 2 bricks lower than the outer one , i then pack the cavity with polystyrene so the concrete doesnt go into the cavity, install the visquene ( is that how you spell it ) onto compacted subase along with a sand finish, lay the 65mm of underfloor insulation and then pour the floor slab so it infact sits on the internal cavity wall ????

Then i assume you simply continue building on the floor slab to create the inner cavity wall..

Is that correct? or has some one been telling me porkies

Thanks guys (& Gals)

Mick.

[Mick Leek]

Addition to above post...

Is this the correct way ? this is what i thought you were meant to do before i was told the way above ???



Thanks.

Mick

[Mick Leek]

Cant believe non of you guys cant help me with this one ???

Farmerboy, Are you there ? please help

Was hoping to pour the concrete this week

Thanks

[danensis]

Surely these are the sort of details that should have been on your building regulations approval. You do have Building Regs approval I take it?

[Mick Leek]

Danensis,

All i got from the planning and building reg people was a letter saying your proposal has been approved.. This was for Planning and then for Building regs

There were NO specs to work to. The only things i am working from are the notes made by the archetect on the plans.

The guy from the local planning office has been on several occassions to inspect the stages and said "Yes all is fine carry on" but at no stage as anyone given me a set of guidelines i should be following..

Where can i obtain these ?

Any help would be rewarded with several pints of your favourite alcholic tipple if you are close to me Blackburn Lancs..

Thanks

Mick

[Tony McC]

I have a drawing I've been trying to upload for a couple of days, but for some unknown reason, my FTP-client is playing silly buggers and won't upload owt over 2Kb. I'll try a different pooter some time tomorrow.

[Mick Leek]

Hi Tony,

Does this drawing refer to the correct method of laying the slab ?

I have been assured that the way above is NOT the correct way and the earlier description is the correct way ?

Could you try e mailing the drawing or send via a PM

Thanks Tony

[Tony McC]

I think this is how it should be done but you really need to check with your local BCO

[Mick Leek]

Hi Tony,

Thats how i thought except for the part where the concrete goes against the outside wall.

I have spoken to the guy at planning today and he tells me i am doing very well for a DIY project :p "Mick the master BUILDER" LOL i think not.

your diagram is close except the inner cavity is filled with polystyrene temporary to stop the concrete falling into the cavity. once hardened sufficently, it is removed leaving the slab resting on the inner wall and still leaving the 3" or 4" air space (depending on what you have built to)

One thing to remember is that if you are forming a floor this way then you must use type A reinforcing mesh and form it 1.5" above the top of the inner brick and 3" over the width of the brick. the steel must not come into direct contact with the brick the slab will be layed on. (dont know why)

Hope anyone who needs this info in the future will understand what i mean.. Im sure Tony will now ammend the diagram he drew to show you how i have explained.

Nice people at the building control office in Sunny Blackburn. Only to willing to explain how to do it when asked. I now have to demolish the brick built out house that is currently in side the new extension so i can prepare the floor... I will try and post a few piccies this week end so you can all laugh at my workmanship

Thanks to all so far for all your help....

Mick

[ABILITY]

Sorry to disagree Tony, but think Micks first drawing was correct, am sure it can be done other way, but as Mick then says floor slab will need to be reinforced to ensure it can take load.

Problem with Tony's version is that the 'wet' cavity would drop the water / damp onto the slab allowing it to penetrate into the internal of building via screed and inner wall.

Details like this are not always shown on regs drawing, although there are versions in the regs documants, if you can really be bothered reading them!!

Mick - depending on your propsed interal floor surface it is not always necessary to screed on top of the slab, do a decent job of slab finish and you can use this direct.

[Mick Leek]

Thanks for that Ability.

Tonys version is close. (Thanks Tony for trying to help) If you lose the concrete butting against the outer wall and add a reinforcing mesh, then you have a very usable drawing for future enquiries..

After looking at your drawing i was tempted to do it that way UNTILL Ability pointed out the fact that any moisture penetration from the outside wall will run down the cavity, collect on the slab and make its way through.. ( Thanks Ability for pointing that one out)

|Cant wait to start on the roof :laugh: Does anyone know of a good roofing forum ???

Regards,

Mick

[Sean Buxton]

Mick - Have a look at DIYnot.com. Part of the forum deals with roofing matters.

Good Luck

[Tony McC]

I don't have the Building Reg for floor slabs and it's over a decade since I last installed one, but I'll see if I can get the actual approved detail and post it later this week.

I'm much happier sticking to paving and drainage.

[Mick Leek]

Cheers all..

Sean, I will try DIYnot.com and see what else i come across.. For those interested here are a few piccies of the stage we are at after 1 week.

That includes digging out and removing 116 tonnes of earth..








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Im getting into the swing of this DIY lark now.. Can highly recommend doing the work yourself, i predict saving over 15k once completed in a few more weeks ( weather permiting