Wet UFH System issue. WWYD (Piglet John?)

[AesopsMables]

Currently undergoing house extension and have just discovered that the existing part of the galley kitchen area does not have enough screed topping to take off and fit wet UFH it is just hard core underneath approx 150mm of screed, this represents approx a quarter of the size of the new room.

Builder is suggesting either fit Wet UFH heating in new bit and electric to old bit (DH is adamant he does not want this to happen) OR fit all of it on top of existing kitchen floor level.

I want them to dig up concrete in old bit so that all the system is under current level and all is fed from same wet system. Been told it may add up extra ££££ to budget.

Anyone else with similar experience? Ideas/suggestions most welcome.

[lalalonglegs]

If they have to pour concrete for the new bit, it shouldn't cost too much to do the old kitchen area as well and, as the existing concrete is 150mm deep, it shouldn't take too long to dig it up and excavate down to the required level. I don't see the problem - your builder obviously doesn't want to, ask why. Unless there is a step down into your kitchen which could be effectively filled by lifting the floor level up a few inches, then I wouldn't want to lay the UFH on top of the old floor and raise everything (wouldn't the cost of extra concrete also make that quite a pricey alternative?) I agree the simplest thing would be to use electric but the running costs could be high.

[didireallysaythat]

We are in the exactly same position. To dig down (the suggestion was 300mm to allow insulation etc below) for the unextended bit (4m x 6m) will take days, skip space, materials etc so add 2+ days, hence cost. Not sure it adds up though so I sense reluctance is a major thing.....

[AesopsMables]

didireallysaythat we are going to get a price from the builder and if this is reasonable then we are going to push back and insist this route.

lala yes to extra costs either way, I think they want the easiest option.

Another real bug bear at the moment is until this is decided we cannot confirm final floor level to allow bi folds to start being produced so had to put hold on order for a couple of days.

[PigletJohn]

digging up the whole floor with a Kango or similar will be boring, dusty and noisy but I expect they'll put a labourer on it. There will be a lot of heavy waste to barrow out and skip away.

Your new floor will need a dpm lapped up to the DPC in the wall, and rigid insulation foam slabs under it and round the edges to absorb insulation or movement. Done properly it will be a lot better than your old floor and will not crack, even where the old and new floor join. It will be dry and lose less heat. Get a drawing done of the specification of the new floor, and see that it is done correctly in every detail. It is a vast amount of work if it needs to be put right afterwards. You should be able to read FFL off the floor drawing. If you know what you want it to be, tell the specifier.

[AesopsMables]

piglet Thank you for the answer!

We have full working drawings but cannot see FFL shown on it so will call the architect tomorrow.

[Marmitelover55]

I think if you are planning to put a wooden floor down on top you need to let the concrete dry which I understand takes I day for each mm of concrete thickness. This may not (hopefully) affect you but I was really surprised by this.

[AesopsMables]

We are laying porcelain tiles marmite but guessing we need to look into this a lot more!