Concrete Floor - Raise by 150mm

[sotal]

I'm now getting further with my utility room project (which was put on hold due to lack of time!)

It started off that I wanted to just redecorate the utility and wc, but as I removed the tiles the plaster board came too, then I decided whilst I was at it I might as well improve it and try and bring it up to current standards.

Part of this was to raise the floor to seperate it from the garage.

I have now built a 2 brick high wall where the stud wall used to be, which I will then build the new stud wall on top of.

This gives me two small areas to fill up to raise the floor.

I'm just hesitating a little as I don't want to get the raising of the floor wrong and I've found it hard to get definite answers on how to do it correctly.

Both rooms are at the back of the garage. The WC was added about 20 years ago as part of an extension (bedroom above the garage and garage widened) - From looking at neighbours originally the WC was where the utility is - so was just moved into the new space to the side.

The WC has a brick outer wall and a concrete block inner wall to 2 sides, my new 2 brick high wall on one side, and a single brick wall between it and the utility.

The utility (which was the WC) has just a single brick wall to the rear, 2 brick wall to one side, my new 2 brick high wall, and the single brick wall to the toilet.

Both have a concrete floor.


From previous research/advice I was going to do the following:

Put DPM down
Put Polystyrene on top
Tape the joints of polystyrene
Concrete over the polystyrene

Firstly does that sound right?


Secondly I have a few little issues/questions:

1. In the utility area the floor isn't fully level. There is a step of about 5mm in the middle - this was covered by the floor covering. I'm guessing this could be enough to cause problems with the Polystyrene. What should I use to level the floor - would sand be OK?

2. Should I just overlap the dpm up the wall a few inches above the floor level?

3. The current single brick wall has a DPC 2 bricks up which just happens to be the same height up that I'm wanting to increase the floor to - will this cause any problems? - This single wall was tiled. All the tiles were stuck on well except the ones below the DPC which just pulled off and smelt a little damp. Obviously this will now be under the floor but will it cause any problems?

4. Someone said it would be better to put the DPM above the polystyrene - which is best?

5. I've seen somewhere a picture where it showed putting edging bits of polystyrene round the edge so the concrete was just in the middle - is this neccessary for my project?

6. Should I use concrete (ballast & cement) or screed on top of the insulation?

7. What thickness of concrete/polystyrene would you recommend to make up the 150mm?


Sorry for all the questions but I must have started this project about a year ago and really need to get it finished off now whilst I have some enthusiasm! It's all stripped out now and I have a few days off next week.

Many thanks

 

[sotal]

The above post was a bit long, to help I've put a picture together. This picture shows what I am proposing to do:

Untitled

• sotal
• 23 May 2011
• 1

I've guessed the answers to my own questions to generate this, and gone with 75mm insulation with 75mm screed. DPM under insulation and overlapping up the wall past the DPC.

If the above is all correct can anyone answer the two remaining points:

Will sand be OK to 'level' the concrete floor before putting the insulation on top?

Do I require the polystyrene edging so that the screed never touches the walls? Somehow I prefer the thought of the concrete going right to the edges!

Thanks in advance

 

[theoldun]

Have guessed the answers to my own questions to generate this, and gone with 75mm insulation with 75mm screed. DPM under insulation and overlapping up the wall past the DPC.

Answer. Okay

Will sand be OK to 'level' the concrete floor before putting the insulation on top

Answer. Yes, just a whisper to level her up.

I require the polystyrene edging so that the screed never touches the walls? Somehow I prefer the thought of the concrete going right to the edges!

Answer. Suggest you use 75mm Celotex instead of polystyrene, then 75mm grit sand and cement screed 4 to 1 with added fibres as reinforcement. 25mm x 150mm deep perimeter insulation to all eternal edges and unheated adjoining edges
oldun

 

[sotal]

Thanks for the reply.

Is the suggestion for Celotex just down to the fact that it is a better insulator, or is there any other reason?

It's just the cost that's putting me off!

It'll cost me about £120 for celotex or £45 for Polystyrene.

I know it can't be done again etc but I'm guessing the 75mm of polystyrene will be better than what's there now!


The edging is probably just unneccessary worrying from me - but does it make it weak around the edges? My floor covering should stop that but it just seems odd to me to have this floating lump of concrete in the middle of the room!

 

[sotal]

Also does it make any difference if I use 50mm insulation with 25mm inuslation on top - instead of 75mm?

It's just I can get 50+25 cheaper than 75.


Thanks

 

[theoldun]

If you are not doing it under Building regs, then use polystyrene. Why we said celotex, is that you need approx half the thickness again of styrene to equal the u value of celotex.
The old story. Yous gets whats yous pays fors.
50 and 25 will be okay and you can use the 25 round perimeter.
Put the 50 on top of 25.
Do not reduce screed under 75mm and do not forget fibres
oldun

 

[sotal]

Yeah I'd read up on Celotex vs Polystyrene. From what I read it starts off 60% more effecient than polystyrene but loses it's effeciency each year until after approx 7 years it has the same effeciency as polystyrene.

So to me it seemed a bit of a waste of money in the long term.

Got everything else now for the first bit to fill - ended up with 75mm thick, as they were out of 50mm. Will have to try and cut it for the perimeter.

Screed will be dead on 75mm - just need to find the fibres as I couldn't see any at Wickes - is it the sort of thing Build Center will sell? Or can I get it from a DIY place like B&Q?

Thanks