Options for raising the floor level in my garage conversion...
Mike Armstrong
Quick history. I'm creating a kitchen extension out of my 28ft x10ft
garage. I have divided the garage roughly in half with a blockwork
partition (with a door hole) and have built a blockwork inner leaf
around the kitchen 'portion' of the garage and laid a row of bricks at
the bottom of the new door hole.
The floor now needs to be brought up to level with the rest of the
house as per Building Regs. Total to be raised is about 80mm.
Existing garage floor is concrete.
As I see it, there are a few options and I would appreciate some
feedback as to which of these you DIY experts would go for.
1. Wooden suspended floor.
--------------------------
I guess this would be fairly expensive but is ready for use as soon as
it is finished. It gives me a convenient gap for routing services
through but also means installing air bricks etc.
2. Concrete.
------------
I could lay a DPM and infill with concrete. This would involve a lot
of mixing although I could get blue circle to dump the required amount
through the garage door. I guess 80mm of concrete would take an
eternity to dry. The floor would also be very cold.
3. Concrete + Polystyrene insulation board.
-------------------------------------------
Laying the boards should be easy and there is less concrete to mix
than method 2. This also means that drying time will be reduced.
With a 50mm polystyrene board, there will only be about 3cm of
concrete. Will this thickness of floor be strong enough to withstand
sustained bouncing around of heavy washing machines etc, bearing in
mind that the polystyrene will presumably be slightly flexible? The
floor should be a little warmer under-foot with this method.
4. Concrete + Wood/Polystyrene Insulation Board.
------------------------------------------------
As above I guess, but the floor should be a little stronger because of
the wood layer. It did occur to me that I could lay the concrete
first and then put the boards on top. This would give me nice warm
feeling floor. The wood/poly boards are Ł20.20 for a 8x4 board as
compared to Ł6.20 for the polystyrene.
General questions :-
Are there any regulations regarding under-floor insulation?
I see a lot written about screeds and self-leveling compounds. If I
can get my concrete floor to be level and float it flat, is a further
layer of screed even neccessary? The eventual floor covering will be
either tile or water-resistant laminate flooring.
Thanks for any input.
Mike Armstrong
Peter Taylor
> Quick history. I'm creating a kitchen extension out of my 28ft x10ft
> garage. I have divided the garage roughly in half with a blockwork
> partition (with a door hole) and have built a blockwork inner leaf
> around the kitchen 'portion' of the garage and laid a row of bricks at
> the bottom of the new door hole.
>
> The floor now needs to be brought up to level with the rest of the
> house as per Building Regs. Total to be raised is about 80mm.
> Existing garage floor is concrete.
Hello Mike:
80mm is awkward! There are only really 3 options.
1 Sold 80mm screed. (Cement/sharp sand 1:3 mixed up fairly dry so it is
still "loose" but forms a ball when you squeeze it.)
2 Any screed as above needs to be MINIMUM 50mm thick to prevent cracking
etc. so you could lay max 25mm polystyrene insulation, but then you need to
reinforce the screed with 12mm gauge galvanised chicken wire.
2 Lay 50 x 50 sawn preserved timbers at 400mm centres (unfixed) on dpc on
a thin mortar bed to level them up. Flooring of T&G softwood or
moisture-resistant chipboard. Fix a batten on them temporarily at each end
and across the middle to stop them moving about. But you MUST have through
ventilation to every gap between the timbers..
I specified an Option 2 floor once on a job converting an old outbuilding to
a new laundry room for a nursing home. It was fine when finished, but
shortly afterwards one of the big washing machines developed a leak due to a
split plastic pipe. No one knew about it at first as the water was going
under the vinyl flooring and the screed. 3 months after finishing the new
floor we had to take it up and completely renew it. (Ł18,000 plus major
disruption).
So, once bitten, I would now always go for option 1, solid screed, even
though it's cold. Drying out fully takes 1 month per 25mm thickness if you
are laying totally non pervious flooring or wood blocks, but you could lay
ceramic tiles or quarry tiles in cement slurry (not tile adhesive) after 2
weeks or so.
Your BEST option, though, is to break out the old floor and have new a new
floor consisting of:
50mm screed on
125mm concrete on
1200 gauge polythene dpm (taken up walls to FFL) on
75mm polystyrene board on
50mm dry soft sand blinding
HTH
Peter
Mike Armstrong
<snippage>
>80mm is awkward! There are only really 3 options.
>1 Sold 80mm screed. (Cement/sharp sand 1:3 mixed up fairly dry so it is
>still "loose" but forms a ball when you squeeze it.)
>2 Any screed as above needs to be MINIMUM 50mm thick to prevent cracking
>etc. so you could lay max 25mm polystyrene insulation, but then you need to
>reinforce the screed with 12mm gauge galvanised chicken wire.
Thanks for the reply Peter.
You are confirming what I had feared wrt 30mm a concrete/screed slab.
I think option 1 appeals the most in that case with the one proviso
that 4m x 3m x 80mm sounds like rather a lot of concrete/screed for
one man to mix. How much work would you say I'm looking at here? 1
day/weekend/week? I guess the hire of a cement mixer will be
mandatory?
Could you explain to me the difference between concrete and screed? I
ask this as I had thought of calling blue circle to get a price for
them to come and tip the required amount of concrete straight into the
garage. I'm guessing that concrete has a rougher consistency and
would therefore be harder to get flat. For ease, could I use concrete
followed by a thin self-leveling compound perhaps?
One thing wich concerns me is the 'cold floor' aspect. I'm not too
bothered about the temperature of the concrete/screed as I will be
most likely laying a laminate floor over it. What worries me is
whether the cold floor will act to cool down the ambient temperature
in the room. It would be a shame to have included all that insulation
in the walls and ceiling just for the floor to act as one big
refregerator element!
>2 Lay 50 x 50 sawn preserved timbers at 400mm centres (unfixed) on dpc on
>a thin mortar bed to level them up. Flooring of T&G softwood or
>moisture-resistant chipboard. Fix a batten on them temporarily at each end
>and across the middle to stop them moving about. But you MUST have through
>ventilation to every gap between the timbers..
Although the appeal of having a floor which is ready to use as soon as
it is finished is quite high, I feel that this option will be rather
expensive and fiddly wrt the ventilation.
>
>I specified an Option 2 floor once on a job converting an old outbuilding to
>a new laundry room for a nursing home. It was fine when finished, but
>shortly afterwards one of the big washing machines developed a leak due to a
>split plastic pipe. No one knew about it at first as the water was going
>under the vinyl flooring and the screed. 3 months after finishing the new
>floor we had to take it up and completely renew it. (Ł18,000 plus major
>disruption).
Ouch!
>
>So, once bitten, I would now always go for option 1, solid screed, even
>though it's cold. Drying out fully takes 1 month per 25mm thickness if you
>are laying totally non pervious flooring or wood blocks, but you could lay
>ceramic tiles or quarry tiles in cement slurry (not tile adhesive) after 2
>weeks or so.
>
>Your BEST option, though, is to break out the old floor and have new a new
>floor consisting of:
>50mm screed on
>125mm concrete on
>1200 gauge polythene dpm (taken up walls to FFL) on
>75mm polystyrene board on
>50mm dry soft sand blinding
This is not an option as the inner leaf was constructed of celcon
light-weight blocks layed directly onto the concrete pad.
>
>HTH
>Peter
>
Thanks
Mike
Peter Taylor
> I think option 1 appeals the most in that case with the one proviso
> that 4m x 3m x 80mm sounds like rather a lot of concrete/screed for
> one man to mix. How much work would you say I'm looking at here? 1
> day/weekend/week? I guess the hire of a cement mixer will be
> mandatory?
>
> Could you explain to me the difference between concrete and screed? I
> ask this as I had thought of calling blue circle to get a price for
> them to come and tip the required amount of concrete straight into the
> garage. I'm guessing that concrete has a rougher consistency and
> would therefore be harder to get flat. For ease, could I use concrete
> followed by a thin self-leveling compound perhaps?
4m x 3m x 0.08m = 0.96m³ Quite a hard day's work for one man to mix and
lay. Better off taking two days or, even better, getting some help. Better
still, find a ready-mix firm which can supply 1m³ of screed ready to lay.
Most of them do it these days.
To answer your questions as best I can (and I could never claim to be a
plasterer):
Concrete is made with cement, sand and gravel (or cement and all-in ballast)
of normally 19mm size, sometimes 38mm size stones. Usually ready-mix
concrete is ordered by the strength required (eg 21N/mm²) or by British
Standard grading (eg C35). It has a high water/cement ratio so is much more
fluid than screed, and it is a lot stronger normally.
Screed is just cement and gritty sharp sand (not soft bricklaying sand)
usually in proportion 1:4. Because it is much finer than concrete it can be
trowelled with a steel trowel to a very smooth surface. The gravel in
concrete would prevent this. And it's much drier - as I said, you should be
able to squeeze it into a ball.
You will probably need some advice on laying if it is your first time. I
could tell you my experience here, but you can probably get much better
advice from a book or a website. Just a couple of things:
You will need a clean shovel and rake, a large steel trowel (sometimes
called a "float"), and a rigid straight edge (preferably metal) min 2m long
(you can hire these). Also very useful is very strong knees. Get some knee
pads or make some from an old tyre if you can.
Don't forget you need to lay a damp-proof membrane on the old garage floor.
Under a 80mm thick screed you could use either a bitumen liquid like RIW or
1200 gauge polythene sheeting. Turn it up all round the edges and trim it
off afterwards. And if you need to have a joint, overlap the polythene min
300mm and tape it. (I hope you put a dpc in the blockwork!)
And don't forget to work backwards towards the door!
> One thing wich concerns me is the 'cold floor' aspect. I'm not too
> bothered about the temperature of the concrete/screed as I will be
> most likely laying a laminate floor over it. What worries me is
> whether the cold floor will act to cool down the ambient temperature
> in the room. It would be a shame to have included all that insulation
> in the walls and ceiling just for the floor to act as one big
> refregerator element!
Millions of houses have solid ground floors with no insulation. It would be
better with insulation but it's not a major problem IMHO, especially if you
lay laminated flooring on that felt underlay. Don't forget warm air rises
and cold air sinks. Allow the screed to dry out for as long as you can - at
least 3 months would be ideal. It may look and feel dry but it will be damp
below the surface.
And lastly, the alkaline environment and residual dampness will corrode all
metals, including copper and lead. So cover any copper pipes with lagging
or, better still, lay them in a purpose-made steel or plastic duct set into
the screed. This is a legal requirement if you have any pipe joints under
the floor. (The Water Byelaws I think).
Best of luck
Peter