Concrete floor in victorian kitchen?

[Mat1]

Hi, I'm currently in the midst of a full renovation on a victorian terrace house. The previous kitchen area has concrete floor as you can see on the right hand side of the picture. The side return area on the left is also concrete. The previous kitchen area is about 5cm lower than the suspended floor and the side return is about 10cm lower. We'll be laying Nu-Heat overlay UFH with Engineered Oak on top throughout the ground floor, 100mm insulation between the joists. 

 

I'm unsure as to how we should be treating the concrete area so we don't have problems with the UFH, damp or the wood flooring. I'm getting different views from builders. One builder just wants to build up the concrete area so it's level with the rest of the ground floor while another wanted to demolish the whole area and lay a new solid floor to building regs standard.

 

Nu-heat said I shouldn't worry about insulating the slab as the loss is very small. 

 

My gut tells me at a minimum there should be some sort of Damp proof membrane. What do you think?

 

 

[Russell griffiths]

Nu, heat are talking out of their backsides, the heat loss will be huge, get it all broke out, new dpm and new insulation 

the amount of effort you have gone to already don’t skimp on getting the rest done right. 

[ProDave]

Yes you need a very minimum of 100mm of GOOD insulation so it all has to come out.  Unless you want a step up as you enter the kitchen?

[Mat1]

3 hours ago, ProDave said:

Yes you need a very minimum of 100mm of GOOD insulation so it all has to come out.  Unless you want a step up as you enter the kitchen?

 

I think the plan was just to build up the existing concrete. Dismantling and relaying floor a big job? 

[Mat1]

4 hours ago, Russell griffiths said:

Nu, heat are talking out of their backsides, the heat loss will be huge, get it all broke out, new dpm and new insulation 

the amount of effort you have gone to already don’t skimp on getting the rest done right. 

 

Sounds about right. Bit worried about costs though so if there's any other solution I'm open to it!

[Mr Punter]

Break out the concrete.  Should not be a huge job.  If it is just the area at the back it should only take a day or 2 including disposal.  You have spent enough on this that it is not worth cutting corners.

[Mat1]

1 hour ago, Mr Punter said:

Break out the concrete.  Should not be a huge job.  If it is just the area at the back it should only take a day or 2 including disposal.  You have spent enough on this that it is not worth cutting corners.

 

4 hours ago, ProDave said:

Yes you need a very minimum of 100mm of GOOD insulation so it all has to come out.  Unless you want a step up as you enter the kitchen?

 

Definitely do not want a step up!

 

I'm assuming there isn't a good solution for lowering the section on the right by 60mm?

 

If there was there would be enough room for a vapor membrane, 100mm insulation and screed.

 

 

My builders are trying to make up for lost work due to coronavirus so I'm fully expecting a silly number if I go in unaware.

 

 

[Mr Punter]

If it was me I would consider taking out the suspended floor at the front as well so all is insulated ground bearing.  No more rot.

[Mat1]

1 hour ago, Mr Punter said:

If it was me I would consider taking out the suspended floor at the front as well so all is insulated ground bearing.  No more rot.

 

The builders want £6000 to level the ground floor with ply and screed over the existing joists. I can't imagine what they would want to do something like that!

[Mr Punter]

Is this what was originally specced and quoted?

 

My favourite would be to take out the concrete, boards and joists.  Level the sub base to, say, 320mm below finish level.  Blind with 25mm sand.  Fit plastic DPM.  Lay 100mm concrete. Fit 100mm insulation with additional 25mm wide x 75mm high perimeter strip .  Fit UFH manifold.  Clip UFH pipes to insulation.  Lay 75mm screed.  Fit floor finish (20mm allowed for).  You will also need to allow for any electrics and other services.

 

You could do a lot of the work yourself.  It is fairly unskilled.  Leave screed and electrics to others.

[Tom]

More chance the suspended timber floor will suffer from rot/other damp problems now that you've lost the air bricks ventilating the suspended floor in the side-return. Taking it all out and starting again with a well insulated slab sounds like a good idea.

[Mat1]

On 22/04/2020 at 18:30, Tom said:

More chance the suspended timber floor will suffer from rot/other damp problems now that you've lost the air bricks ventilating the suspended floor in the side-return. Taking it all out and starting again with a well insulated slab sounds like a good idea.

 

On 22/04/2020 at 17:00, Mr Punter said:

Is this what was originally specced and quoted?

 

My favourite would be to take out the concrete, boards and joists.  Level the sub base to, say, 320mm below finish level.  Blind with 25mm sand.  Fit plastic DPM.  Lay 100mm concrete. Fit 100mm insulation with additional 25mm wide x 75mm high perimeter strip .  Fit UFH manifold.  Clip UFH pipes to insulation.  Lay 75mm screed.  Fit floor finish (20mm allowed for).  You will also need to allow for any electrics and other services.

 

You could do a lot of the work yourself.  It is fairly unskilled.  Leave screed and electrics to others.

 

 

The void is 400mm deep (I think). They've suggested reducing the void to 50mm by filling the bottom of the void with 200mm of concrete+DPM and dropping the joists. The concrete section will be the same and the joists will be extended all the way along. Insulation will still be inbetween the joists.

 

Won't the ventilation be a bit rubbish with the void reduced from 300mm to 50mm??

 

For some reason I have an irrational fear about replacing the suspended floor with concrete slab! Feels very invasive somehow ?

 

[Mr Punter]

You don't need ventilation with a ground bearing concrete floor.  You do need at least 100mm of insulation if it is Celotex type, 150mm min if expanded polystyrene.  Lovely and warm and dry.

[Mat1]

On 03/05/2020 at 11:39, Mr Punter said:

You don't need ventilation with a ground bearing concrete floor.  You do need at least 100mm of insulation if it is Celotex type, 150mm min if expanded polystyrene.  Lovely and warm and dry.

 

Hi mate, so this design should work?? 

 

200mm - Filling+concrete

DPM - 

Void - 150mm

Joists with insulation in between - (or add insulation to the void?)

 

Thanks

 

[Mr Punter]

There is no point in having any void.  It will just make the floor cold and it cannot be properly vented as you are mid terrace and the rear section is concrete.

 

The floor make up depends on what finish you want and if you want underfloor heating, but it should always include min 100mm insulation.

[Mat1]

Just now, Mr Punter said:

There is no point in having any void.  It will just make the floor cold and it cannot be properly vented as you are mid terrace and the rear section is concrete.

 

The floor make up depends on what finish you want and if you want underfloor heating, but it should always include min 100mm insulation.

 

Thanks. The void was more for services and in case anything is screwed up along the way. There is room for 100mm insulation between the joists. 18mm Ply ablove the joists, 15mm UFH boards then 14mm engineered wood to finish.

[Mr Punter]

Get rid of the joists.

[Tom]

7 minutes ago, Mr Punter said:

Get rid of the joists.

... or get rid of the concrete. Struggling to see why you need both? You're essentially paying for two floors, but will only ever get to stand on one.

[Mat1]

25 minutes ago, Tom said:

... or get rid of the concrete. Struggling to see why you need both? You're essentially paying for two floors, but will only ever get to stand on one.

 

I believe NHBC (whatever that is) requires 100mm of concrete and a DPM for new suspended floors?

[Mike]

If your other ground floor rooms have timber floors, you need to either add ducts below any new solid extension floor and terminating in airbricks (to ventilate the timber floors), or replace them with solid floors too, as @Mr Punter suggests.

[Mat1]

 

Bit the bullet, now we're replacing the entire ground floor with concrete as was suggested by you guys way earlier. Sometimes you just have to come to things in your own time ??

 

Just trying to figure out the ufh screed situation so we're not waiting months for it to dry but that's another thread!

[wozza]

22 minutes ago, Mat1 said:

 

Bit the bullet, now we're replacing the entire ground floor with concrete as was suggested by you guys way earlier. Sometimes you just have to come to things in your own time ??

 

Just trying to figure out the ufh screed situation so we're not waiting months for it to dry but that's another thread!

 

There are a few fast drying screeds out there = we used Cemfloor and are very happy with it.

[Mat1]

30 minutes ago, wozza said:

 

There are a few fast drying screeds out there = we used Cemfloor and are very happy with it.

 

Great do you remember what depth you went for?