Retrofit Insulation in Concrete floor depth?

[mattwaddy]

I'm hoping to dig out my solid kitchen floor at the weekend to retrofit insulation and wet ufh. In terms of depths the current guidance seems to be

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1081194/solid-floor-insulation-best-practice.pdf

"Today, new solid floors are more substantial, typically comprising 150mm of compacted hardcore, 50mm of sand, a polythene sheet DPM, 100mm of concrete, then around 100mm of insulation and a 60mm screed."

But I'm not sure what the building regulations are, I'll see what I can agree on with my build control officer

Do I really need 150mm of hardcore and 50mm of sand? I'm thinking 100mm of PIR is good, but would it be worth putting in 150mm or is 100mm more than sufficient? I need to work out the right depth to get to for the material layers whilst I have some helping hands around

 

[SpecialK]

The more PIR the better, think mine was 130mm. In my opinion 50mm sand is if you are using crushed hardcore. If you use MOT1 you don't need much sand.

I guess it depends on what you dig out for the hardcore depth. I should think its probably pretty settled and dry under the house by now so 150mm hardcore should be fine?

You may need a temp sensor for the UFH buried in the screed for the controller.

I used a decoupling layer between the liquid screed and insulation to stop any going places it shouldnt.

 

[jks7492]

The building regs part L cover U-values for floors - you should be able to google them and various websites have calculators to tell you the thickness of their insulation you'd need to achieve the required value. I'd go for the 150mm insulation.

150mm type 1 beneath a slab is pretty standard, and then usually a sand blinding to prevent the DPM being punctured by any sharp stones, but not essential.

 

[mattwaddy]

I was questioning if the mot1 layer could be reduced to 100mm potentially, but ill aim for 150mm insulation. Good call on the probe before screed

 

[mattwaddy]

would 10mm of sand be ok or does it need to be 50mm?

 

[jks7492]

would 10mm of sand be ok or does it need to be 50mm?

There is no minimum requirement for sand blinding underneath a slab - its just good practice to cover the hardcore with sand or fines so that if someone is walking around all over the DPM then you don't end up with a load of holes in it before you pour the concrete.

If you've got a lot of fines in your sub-base or you're not too clumsy once you've put your DPM down, than arguably you could do away with a sand blinding altogether

 

[mattwaddy]

There is no minimum requirement for sand blinding underneath a slab - its just good practice to cover the hardcore with sand or fines so that if someone is walking around all over the DPM then you don't end up with a load of holes in it before you pour the concrete.

If you've got a lot of fines in your sub-base or you're not too clumsy once you've put your DPM down, than arguably you could do away with a sand blinding altogether

Yeah ok, so I'll just go with 10-20mm and likely 130mm of MOT1 which would compact down to 100mm hopefully. Then 150mm for the PIR insulation and 100mm for concrete. I'm thinking 70mm for screed, but I need to check for UFH as that would be dry, but probably less for liquid depending on cost

 

[mattwaddy]

One other question is that when the DPM is lapped up the walls, how is the room generally finished i.e plastered? The kitchen walls are all currently plastered and were due some bonding fills and reskim, how would the DPM lap work, would all plaster need to come off or is there another way for the plasterer to deal with the DPM layer?

 

[SpecialK]

One other question is that when the DPM is lapped up the walls, how is the room generally finished i.e plastered? The kitchen walls are all currently plastered and were due some bonding fills and reskim, how would the DPM lap work, would all plaster need to come off or is there another way for the plasterer to deal with the DPM layer?

Only needs to be above wall DPM? Skirting should cover it? Current plaster shouldn't be below DPM?

I went for a 55mm liquid screed. Cost a grand for a 9x3m room. Was a few years ago though!

 

[mattwaddy]

Only needs to be above wall DPM? Skirting should cover it? Current plaster shouldn't be below DPM?

I went for a 55mm liquid screed. Cost a grand for a 9x3m room. Was a few years ago though!

very true, only small areas will have skirting as its going to be mainly kitchen cabinets, but i could run skirting all around i guess

 

[SpecialK]

very true, only small areas will have skirting as its going to be mainly kitchen cabinets, but i could run skirting all around i guess

If its blocked by kitchen cabinets then just leave it?

 

[Mr Chibs]

Yeah ok, so I'll just go with 10-20mm and likely 130mm of MOT1 which would compact down to 100mm hopefully. Then 150mm for the PIR insulation and 100mm for concrete. I'm thinking 70mm for screed, but I need to check for UFH as that would be dry, but probably less for liquid depending on cost

I have done a floor to this kind of spec, all should be well, put the MOT in and compact, preferably in 2 goes, rather than just dumping the whole amount in, in one go.

I did insulation over the concrete slab (under screed). UFH warm up times will be reduced, but will hold less thermally than concrete on top of insulation. Don't forget perimeter insulation upstand, and foam compression roll for UFH.

Good luck

 

[noseall]

Do I really need 150mm of hardcore and 50mm of sand? I'm thinking 100mm of PIR is good, but would it be worth putting in 150mm or is 100mm more than sufficient? I need to work out the right depth to get to for the material layers whilst I have some helping hands around

100mm well compacted hard core plus whatever thickness sand (25mm +) is needed to overcome the hard core layer. 100mm Celotex will be fine.

 

[Loofah]

Don't forget the pics when you're doing it!