Concrete floor - dig up and replace or insulate on top????

Joined
2 Feb 2010
Messages
2
Reaction score
0
Location
Surrey
Country
United Kingdom
Hi,

I have just bought a 1917 3 bed house and have gutted it. We want to put in wet underfloor heating throughout the house.

The floor is currently screeded concrete.

I have had a couple of builders round who have said to remove the existing screed is not that big a job. The area is about 70m2.

They have both said that to remove all the concrete and replace is a big and costly job - any idea of how big and how costly? Neither seemed too keen to take it on.

Our problem is that we want to put insulation and underfloor heating in without raising the floor by much.

Really don't know what way to go.

Many thanks in advance!
Nathan
 
Sponsored Links
The concrete is a much harder than a screed and depending on the mix that actually got used, it could be anything from a hard job to very very difficult to remove. Since the floors abut a very old structure, possibly with less than ideal foundations the impact of breaking out the floor could even cause further problems.

In one extreme case on a project I was on, a foundation base in a courtyard needed to be broken out. We craned in a purpose made breaker which just chipped away at it. We brought in diamond cutters to core drill it and weaken it and still it took a lot of work to remove. Weeks!

On another project a similar base took just the weekend to remove, (done weekend so as not to disturb the office nearby).

So there is the difficulty, poor concrete is not to bad to remove, good concrete difficult at least.

It will probably be cheaper to raise the lintels on a few openings and raise the floor with the new thicker screed!

PS be careful not to bridge any DPC's in the walls.
 
Then you'll loose the bottom step on your staircase - half a step is a no no (obviously).

Not going to look good!
 
SNM

Agreed if the floor got raised that much! What level did you think this change was going to make? Never seen a replacement screed that thick yet!

He already has a screed and when replaced will be a higher but until a section is lifted we don't know by how much.
I mentioned the lintels half in jest and half because if the house has been gutted and you can fit standard doorsets, now would be a good time to do it.

The downside is the proposal for floor heating may need to tweaked or abandoned if the increase in screed height cannot be accomodated.

A slightly shorter step at the bottom of a stair flight can be tolerated. A short step at the Top is a no-no. Even replacing the stairs could work out cheaper than trying to breakout a concrete floor that was I am sure, done as part of an earlier improvement scheme.
 
Sponsored Links
Even replacing the stairs could work out cheaper than trying to breakout a concrete floor that was I am sure.

Good point.

The thing is, there is not likely to be any insulation under the screed, and possibly none under the base. So by the time you put in a minimum of, say 50mm (which in itself would not be ideal), and then allow for the extra thickness of the UFH, you've really come up quite a bit.

I want to do this myself and allowing for the fact that you can't get away normally with reducing the thickness of the screed if going over wet UFH and (at the very least) 50mm PIR, means the slab will have to come up.
 
Hi

You need to be aware that underfloor heating is not as effective as you may wish and you would be advised to install a conventional heating system to provide a backup when things get really cold - as recently experienced.

Depending on your ceiling height it may be an easier job to raise the height of the doorways rather than take up the structural floor slab, which will be a costly exercise as you will need to reduce the oversite levels before you can relay a structural screed/insulation etc. and you would be best advised to get a quote for both options before you proceed any further.

Regards
 
@ alittlerespect

My experience of UFH seems to differ from yours.

I live in an old stone barn in the French Alps at 1450m : insulation is only average (because of aesthetics) and I find that with an input temp of 40-45 C and 10 cm pipe centres,I am comfortable with outside temps of -8 C regularly and (rare) lows of - 18 C.

I know from talking to my local dealer that people complain of problems, but they have tried to skimp and go for 15 cm or even 20 cm pipe-centres.

Apologies for thread-drift, but it mightt be important to the OP.
 
Most people find the radiant heat produced by underfloor heating more comfortable than the convected heat from radiators.
 
Why use screed?

http://www.celotex.co.uk/downloads.asp?i=23
Edit: sorry this link seems to have stopped working... This is what it said:

Chipboard floor finish

A VCL should be laid over the velotex insulation boards and turned up 100mm at room perimeters behind the skirting. It is recommended good practice that all joints should be lapped 150mm and sealed.

The chipboard must be minimum 18mm tongued and grooved flooring grade type C4 to BS 5669. lay the chipboard with staggered joints glued with a woodworking adhesive.

Provide a 10-12mm gap at all perimeters and abutments to allow for expansion. This can be achieved by the use of temporary wedges.

Where chipboard is butted together without a tongued and grooved joint and all external doorways (for the width of the threshold), a treated timber batten must be used in lieu of the insulation boards.

Or:
http://www.jupiter-system.com/system_ideal.php

Depends on the floor covering of course.
Just a thought.
 
Interesting post by brig001

I will enjoy looking at these new systems for my own benefit. What you have to careful of is that the system is compatible with what you already have. e.g. An existing flat floor upgraded with a overlaid under floor heating system, or and oversite concrete slab. It would be interesting to consider if after lifting an existing screed, the concrete floor could be made flat enough to recieve one of these systems.

Trying something new unfortunately has the pitfall of finding out afterwards what you overlooked and has since become a problem!

Here is an example from 35 years ago.
Major office build in Nottingham using insitu concrete and forming a concrete unstand at the perimeter 100's m long. Later comes the wonderful window system with tolerances of +/- 2mm (Not known about by the main contractor until they arrive and try to fit). Nothing wrong with either system except that they don't work together! So who ends up paying for the extra work needed to marry the two together.

You need to make sure the marriage of the base and the heating system on top is going to work.
 
I don't understand brig001's post. Is the 18 mm chipboard being suggested as something to lay over the UFH ?

You don't have to worry too much about flatness with wet UFH - don't know about electric - you only need to have a min 30 mm screed covering pipes and so if you have a 60-70 mm screed , +/- 1 cm on pipe-height isn't going to be a problem.

Above scenario is where pipes are wired to a welded mesh for positioning. If you wanted anything like the Jupiter system shown on the above link, it might be more of a problem.
 
Hmm, not sure about the first link - seemed to make sense at the time.

The second link says: Solid or engineered timber floors can be laid directly either as a floating floor or nailed to floating battens.

Might be worth a look if you wanted this type of floor. I personally would try this type of system as I find that our pipes in screed system take a bit too long to heat up for my liking. Not too bad if you can predict when you will be in and set the heating to come on early.
 
When I checked out various scenarios some years ago, the prices of "engineered" polystyrene panels with either channels or "mushrooms" (another type of guide ) were very expensive.

Since this system incorporates aluminium spreader plates as well across the whole surface, I would expect t he cost to be eye-watering !

For me the floor acting as a giant radiator is a benefit as the heat is very gentle but that's with a mass of 150 kg/m2. If you just have parquet, then that might be 10 kg/m2 (?) and also an insulating material, so you are right , the heat would be much more on/off. A disadvantage for me , but for others, maybe not.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top