thinner solid floor construction

Thats OK

Mm. I would reinforce.

Thats good, but put them ABOVE the concrete not below.

I afree,

If he says OK, go fer it.

If you use Maxit LWA instead of the MOT, it contributes to the required insulation, so you can reduce the thickness of celotex.

Really. What price is it ? Can it be delivered in 1 tonne bulk bags ?

Celotex 75mm to cover my 20m^2 would be around 170 quid. Also, I guess it would support the slab better than celotex if the slab is going over the insulation. Simon.

What is the trick here ? prop up some of that steel grid on bricks and pour the concrete around it ? Simon.

My floor 20m^2. Quick calc based on bulk bag prices: for 100mm MOT, 2m^3 =3D 4 tonnes MOT =3D 5 bulk bags (850kg) =3D 5 x 30 =3D=

maxit 150mm for 20m^2 =3D 20 x 3 =3D 60 bags.

Factor in the hire of whacker plate for trad method, and there is not a lot in it, save time.

Does my quid calc seem about right ? I may well have a good think about this.

Simon.

Only snag now is, the level under my slab is too low for just 150mm max, 150mm concrete + screed. I guess I could just shovel back 2 inches of soil soak it and walk all over it for a few days. If I had to build up with MOT, thats taking me back where I started ! Simon.

Mmm. Not sure you would even need to prop it much..the loose stuff under ins more likley to compact, so you want the steel underneath really.

I must say I would be tempted to whack the MOT down, lay a grid, forget the sand and pour concrete..

Sorry guys - what's MOT ? Can cope with most TLA's but his one I don't know.

Rob

The LWA can be laid up to 3m thick without compacting, so you could just use more. Would put the price up, but improves the insulation performance.

It was Ministry of Transport type 1 sub-base I think. Basically crushed stone, you know the grey stuff used as a base for everything (roads, drives, floor slabs). Its one bit of jargon I learnt. Umm, jargon is GOOD ... Simon.

Starts to get rather pricey then. Interestingly, since it self- compacts (basically round stuff), I gues it could in theory be used to bed drains, thus insulating the drains. They are still a heat leakage route in floor slabs (especially an internal inspection chamber).

Does the LWA settle a bit when the concrete is poured though ? You'd want to account for that in ordering your concrete. Simon.

MOT type A. Ministry of transport TYPE A road base.

Crushed limestone to the rest of us. Its lime 'gravel' that you whack down to provide a permeable and stable and load spreading base for other work above.

Simon I agree with the posters that say a) you must reinforce the 100 mm concrete b) put the concrete below the insulation c) additionally, I would increase insulation to celotex 100mm d) use MOT no 1 e) additionally use Fibrogel or similar in the screed preferably premixed and supplied in a lorry There is the option of a pumped screed which is much thinner but I don't like gypsum

No mention of UFH but I would not be without mine in the screed.... Chris

e:

Hmm. The 2 bag deep setup is required for U value of 0.25, which is 5 bags per m^2, =3D 700 quid. Not so good after all. Celotex and MOT is a lot cheaper. Simon.

I hate UFH (especially wet, the amount of leakage stories you hear), and hate the idea of reinforced screed over insulation. My insulation is going under the slab. I agree though, if UFH, you would certainly want the insulation above the main slab. But, all seem to say 100mm concrete should be reinforced, especially over insulation. I wonder about 5" concrete (!) Simon.

On Tue, 13 May 2008 08:53:45 -0700 (PDT), a particular chimpanzee, sm_jamieson randomly hit the keyboard and produced:

The screed is there to provide a level, smooth surface. If it's laid directly on top of the concrete it can be reduced (usually about

If your plans were deposited prior to April 2006, then the 'old' Part L applies, so you may be able to use 50mm-65mm Celotex.

Again, a 100mm well compacted hard-core base should be OK, provided that what's below it is firm, uniform and contains no organic matter.

That always seemed like a skilled job to me - I could be wrong. Also, I am doing an ajoining slab as another job and screeding the whole lot (job i 2 parts so I can live there at the same time !), and also meeting another floor level, so the screen may need to be slightly sloped to align the various floors. I think screeding to 65mm / 75mm is common due to alignment with the brick courses and DPC etc.

I've actually got a big bag of glass-fibre (alkali-resist) that I used on a previous reinforced concrete project. Also, did you mean the fibres in the concrete, or in the thinner screed ?

Yep, thats my situation, the plans had 100mm polystyrene, although insulation is a good thing ! I did wonder if changing from the plans that were passed on the old regs meant I had to comply with the new ones. If I had taken out a building notice rather than full plans, is it the regs when the notice is taken out, or when the job is done ?

Yep, I wonder it its worth dosing the ground under with strong weed- killer before the job. Couldn't hurt I suppose.

Also, I've realised I've got an extra inch to play with (oo-er), would this be better in the hard-core or in the slab ?

Thanks for the info, my knowledge bank is on the up ! Simon.

On Wed, 14 May 2008 06:38:01 -0700 (PDT), a particular chimpanzee, sm_jamieson randomly hit the keyboard and produced:

Provided that the application is for substantially the same work (ie, not doubling the size of the extension or moving it from one side of the house to the other), then any changes to the design or materials are treated as minor alterations. IME it's rare for an extension to be built as per the plans anyway.

In most cases, work must comply with the Regulations in force on the day the full plans application or Building Notice were 'deposited' (ie, physically received by the Council with the correct fee, etc.). In the last decade there have sometimes been 'transitional arrangements' for some changes; these have usually taken the form of:

-for full plans, if the plans were fully approved (without conditions or all conditions discharged) before the change to the Regulations; or

-for either BN or FP, the work had commenced before the change;

then the 'old' Regs applied.