Concrete floor insulation

[Kacha]

Hello, 

 

We will shortly begin a refurb on a 1950s house. 
 

We would like to install wet UFH system. In order to do that, upon researching to topic, the advice is to insulate appropriately. To do so this is what we are thinking of having done:

 

Dig up 650mm

Hardcore backfill -150mm

Sand blinding - 50mm

EPS100 - 150mm

DPM

PIR Insulation - 130mm

Concrete - 150mm

UFH - 20mm

Self leveling compound - thin layer

 

Does this seem reasonable? And who would I need to engage for the works? I have spoken to a couple of builders who have tried to talk me out of more that 150mm insulation - we have not budged. 
 

Any advice would be much appreciated. 
 

Thanks. 

[Andehh]

Your insulation there is more then sufficient, and you could loose/cut back the 150mm EPS. 150mm PIR is plenty sufficient in reality (0.14 ish?), law of diminishing returns really kicks in at these levels of insulation. The extra digging and cost of insulation will have a payback of many decades, so you should save that money and invest it in another area of the house to bring that up to better spec.

 

A 1950s refurb will come with additional costs and limitations, so save your 'tippy top' expectations for other areas for investment.

 

We ended up with block and beam 150mm PIR in floor, 150mm PIR roof and 150mm full fill rockwool in the walls (which isn't great, and wish we'd gone for more) but our running costs are around £160 a month for all energy, incl the fact we're a big family so hammer the hot water, dishwasher, washing machine hard.... So can't really complain esp as it's a 6 bed sprawling bungalow.

Edited October 30 by Andehh

[crispy_wafer]

Whilst you are doing all that good work don’t forget your perimeter insulation.

[Conor]

What sort of I underfloor heating and how will it be heated?

 

Don't listen to the builders re insulation, they are used to doing things to the minimum standard.

 

Saying that... 300mm EPS is probably the best option here.

 

You won't need SLC if the floor is done right.

[Kacha]

@Andehh, thanks for this. Those bills are encouraging! Can you share are a bit more about the challenges and limitations of refurbishing a 1950s house? 
 

@crispy_wafer, thank you. I hadn’t considered that. Will do now. 
 

@Conor, thank you. We are planning using the wet UFH system from Wunda. Digging in to the ground will also allow for us not to have to increase floor height. 

Edited October 30 by Kacha

[Andehh]

Just the nature of a refurbishment vs a new build.

 

Digging out per your suggestion will be challenging working around the existing building, and that's a lot of spoils that need carting off site, around existing building and site. Foundations and make up of that ground will also need considerations.

 

Fabric of the house will inevitable need contingencies as well, bringing it up to a good structural standard before you start on the luxurys like uber amounts of floor insulation.

 

Massive insulation is also quickly undermined by a drafty build, and maintaining good air tightness is more challenging on a refurb then a new build... By the nature of more penetrations and settlement on a 70 year old building. So again insulation becomes a diminishing returns on top or drafts undermining it.

 

Routing of services, pipework and wiring as well is more challenging then a new build, and will drive costs and impact air tightness again what you're adding vs what's already there.

 

None of this is insurmountable or new to a builder, but you will need a broader appreciation of the build vs significantly above average insulation as the first hill to die on! Ie the cost of digging out the 150mm for EPS is probably more expensive then an extra 300mm loft insulation , on top of 300mm possibly planned for.... Or an extra 25mm insulated plasterboard. The extra 20mm screed buys you a lot of expanding foam and air tightness tape for sealing gaps everywhere vs embedding UFH in your concrete slab.

 

Building and refurbishment is ultimately a measure of compromises and taking a holistic view of what you can 'win' on vs what you can accept a 'loss' on cis compromise.

 

My view is accept a loss in your floor ambitions and stick to 'only' 150mm PIR (which is still highly highly insulating!) and go for a 100mm concrete slab with UFH embedded, and cut down in your excavations there, then use the money saved to 'win' more of the future compromises you will need to consider.

Edited October 30 by Andehh

[jfb]

You might want to do a test dig to see what your walls sit on.

650mm is a lot to dig out.

[Iceverge]

I like EPS but for this instance I would be tempted to use say 200mm of PIR to avoid too much digging. 650mm is a lot of wheelbarrowing muck. 

 

Buying PIR in 100mm thicknesses is often cheaper than odd sizes too. 

 

Have you considered a pumped screed to avoid too much labour? 

 

How about this. 

 

Excavate 350mm. 

 

100mm type 804 hardcore leveled and compacted. 

100mm PIR from secondsandco

DPM. 

100mm PIR

Slip membrane. 

UFH pipes spaced closely, say 100mm for quick response time. 

50mm pumped screed. 

Floor finish. 

 

Should be a good bit cheaper than the one you proposed and with a higher heat loss house a quicker heating response time would be advantageous. 

 

 

 

 

[Kacha]

@Andehh thanks for the detail. I appreciate your point and will take a more holistic view re air tightness etc. 

 

@jfb, thanks for the suggestion. I will ask for this to be done. Although, I am now leaning more towards @Iceverge suggestion of a 350mm dig out. 
 

@Iceverge, thank you so much for this. Anywhere we can save is very welcome, in addition to “less” work. 
 

I’ll be back with an update.

[saveasteading]

As above. Digging deep is to be avoided so minimise it.

Eps is half as effective as pir, for half the price. V approximately.

So I suggest :

reduce the sand to the minimum to get a smooth surface.* Use quality stone rather than hardcore then add 10mm sand. 140 + 10. 150

dpm

150mm pir

Membrane

60mm screed.

Total 360mm. 

 

that is saving money all round and reducing risk. Way more than the energy cost saving you are losing long term.

OR even 100mm Pir and add more insulation elsewhere.

 

*50mm is only necessary to overcome rough work in texture or levelling. Plus you get footprints.

[Kacha]

@saveasteading thank you! Any concrete? 

Edited Wednesday at 18:19 by Kacha

[Kacha]

@Iceverge, sorry - any concrete in your suggestion? 

[Andehh]

Screed replaces concrete! We went with cemfloor pumped screed over our 150mm PIR, 60mm deep. We went over flat block and beam, so I can't comment on potentially more uneven dug out.

Edited Wednesday at 18:30 by Andehh

[Kacha]

@Andehh oh, I see. Thank you. 

[Temp]

I agree with others..

 

150-200 mm PIR and UFH in screed of 70-80mm

 

Avoid Anhydride (spelling?) screed because it's hard to tile onto.

 

Form expansion gaps at doorways don't screed right through as it will crack. The expansion gaps is just a deliberate gap so you ensure it's straight not curving into one room or the other.

 

If carpeting go for special low TOG underlay and keep total TOG to 2.0 or less. 

 

Stone and tile is great with UFH.

 

[saveasteading]

2 hours ago, Kacha said:

Any concrete

Oops. Sorry.

100mm will do it.

Total 460 so still safer and cheaper than your 650.

 

You don't add the 20 for ufh. It is in the screed , so 630.

 

It may be possible to skimp more, but I'd need to know the circumstances.

[Roger440]

Or hardcore/stone (thickness dependant on  ground) with sand blinding.

 

150mm PIR, 100mm concrete.

 

Even less digging.

 

Only negative if you can call it that is slower response time on heating. Worked fine for me in an old house with uninsulated walls. It just sat at a constant temp all winter.

 

Without knowing the foundations situation less digging = better in my world.

 

 

[Iceverge]

Whatever the final thickness you pick I'd prefer to see the boards in two layers with the joints staggered. 

 

It would also allow you to insert the DPM into the middle reducing the risk of puncturing.

 

[Susie]

11 hours ago, Iceverge said:

 

100mm type 804 hardcore leveled and compacted. 

100mm PIR from secondsandco

DPM. 

100mm PIR

Slip membrane. 

UFH pipes spaced closely, say 100mm for quick response time. 

50mm pumped screed. 

Floor finish. 

 

I noticed you suggested secondsandco for the first layer of PIR which keeps the cost down, but I believe you can have variance in thickness, rumpled tape or crushed corners etc would you not do two layers from secondsandco because of this or was it just omitted?

 

[Roger440]

19 minutes ago, Susie said:

I noticed you suggested secondsandco for the first layer of PIR which keeps the cost down, but I believe you can have variance in thickness, rumpled tape or crushed corners etc would you not do two layers from secondsandco because of this or was it just omitted?

 

 

Having used seconds and co a couple of times, the stock i bought showed no discernable issues aside from the odd chipped corner. Id have no hestitation doing so for something like this. For both layers.

 

[Kacha]

@Temp, thanks - we are planning on laying ceramic/porcelain tiles. 
 

@saveasteading thanks. Does the fact we are using Wunda which come with trays/panels with grooves for the pipes change any of this? Wunda have told us we can tile right on top of the pipes/trays for an even better response time. However, a thin layer of say slc is recommended to protect the pipes in the event you need remove the tiles. Does any of this change your recommendation?

 

[Andehh]

I'd delete the wunder, just have the UFH pipes clipped to the top of the insulation, then screed over it. Wunder is generally for retrofit type UFH solutions.

 

https://www.google.com/search?client=firefox-b-m&sca_esv=ac906d086053e2fc&sxsrf=ADLYWILx105RMbvDOxf-zlkWoOuniAaNAQ:1730356982083&q=Ufh+clipped+to+insulation&udm=2&fbs=AEQNm0AAii1lAhsPaaai4wByEaaipRAHWexzqXOes0FJK1_cCNcUFPPaxlyqBmr552nx3oIdFmFVO-OYSmQ6Gk3927r7w-t_mEMV1VSh-D5CmUgrota0Y23Tc96ea72Hhr6ZrhTNSaUCtq6qMlLLaMfYA9ZnAE2wrP63LGwcadZMK3PIxxf-vkjdLvClApQAENmVQoy6Npx7KR9TQIsTi-SwMqWmvvx7SQ&sa=X&ved=2ahUKEwiypIGKgriJAxUOUUEAHWu1BIMQtKgLegQIFBAB&biw=248&bih=487&dpr=2.07

[Kacha]

@Andehh, got it. Thank you. 

[IGP]

Might be worth taking a look at 

 

 

to see how they did underfloor heating as well. About 5 mins in. 

 

[saveasteading]

2 hours ago, Andehh said:

I'd delete the wunder

You don't need to complicate it.