Ground sub floor insulation advice

[KillyfadNewBuild]

Hi all and a very merry Christmas - I hope you are all enjoying some time off.

 

I was hoping to gain some advice/feedback on ground floor insulation over our ground sub floor.

 

We are hoping to go with a polished concrete floor which our architect noted the minimum depth would be 75mm, leaving 150mm of insulation to work with (total 225mm to work with)...

 

Our contractor advises 100mm for the concrete to be polished above the UFH (I am waiting until the concrete company and the floor polishing company opens to chat to them directly also in the new year). 

 

This would only leave us with 125mm of board insulation which from reading the forum and any reading I have done I am seeing a 150mm as the recommended depth of insulation - I am keen to get this right and to limit heat loss through the ground.

 

The aim was to achieve a u-value of 0.13 or better (figure from architect); our initial plan was to have liquid poured insulation but that has changed as we don't have the depths available to achieve the u-value with this method along with the polished concrete floors we would like.

 

I was hoping someone could advise on the insulation/concrete combination or steer me in the right direction as I would be very grateful.

 

Many thanks,

Joe

Edited December 27, 2021 by KillyfadNewBuild

[Andehh]

125mm should get you to 0.13, 150mm to get to 0.11. Reality is in this range of insulation your spending £1000s to save £10s.

[KillyfadNewBuild]

2 minutes ago, Andehh said:

125mm should get you to 0.13, 150mm to get to 0.11. Reality is in this range of insulation your spending £1000s to save £10s.

 

It's trying to get that happy balance; our current house suffers so much from heat loss and we just want the new house to be done right.

 

If 125mm should get us to the recommended figure from our architect it would help bring down our worry levels haha

 

Is there normally a two layer insulation application, i.e.  80mm then 45mm on top or below, or 125mm single boards throughout the ground floor?

 

Thank you for your reply, it's really appreciated.

[Onoff]

35 minutes ago, Andehh said:

Reality is in this range of insulation your spending £1000s to save £10s.

 

That's too much a black and white view. 

 

It may be wise to spend the £1000s now and be done with it. 

 

The £10s you're saving will only increase with time. 

 

You're insulating against more than heat loss, but energy price increases, shortages etc. 

[Andehh]

Yep, I'm 100% in the same situation! And fully agree in terms of the impact only increasing long term with energy prices. 

 

We have 150mm specified (0.11) but there is a £4500 saving if we brought it down to 100mm....(0.18 I think).... we'll prob settle in the middle on 125mm for a £2000 saving for use in the countless other areas I want to try and put more money into. Especially more tangible areas like wanting vaulted ceilings, bigger windows, larger sliding doors etc etc. 

 

100mm still achieves current building regs & in my research also looks like it will still exceed next year's building regs uplift as well. 

 

As ever more the merrier & I'd love to go uber insulated... But it becomes increasingly hard to convince myself & the wife when we look at the impacted value... Hence the "maybe another £10 cheaper per month!?" 

 

As we're a bungalow, we get hit even harder on sheer surface area to bleed heat through.... And cost to try and mitigate! 

Edited December 27, 2021 by Andehh

[Declan52]

At what stage of the build are you at??

[Declan52]

Ok going from your pic in the other thread can you not just lift head height by a brick, 75mm. This will give you more than enough room for more insulation.

You will have to go round and put a course of brick under any cills where the heights matter like if they are at a kitchen worktop area. Otherwise you can leave them as is and have slightly bigger Windows or build a course of brick to bring them up to the correct height.

Or just leave it as it is and accept the higher heat loss into the ground.

 

 

 

 

 

[KillyfadNewBuild]

3 minutes ago, Declan52 said:

Ok going from your pic in the other thread can you not just lift head height by a brick, 75mm. This will give you more than enough room for more insulation.

 

 

 

 

 

 

The photo I posted on the other thread is maybe a few weeks old (I don't have any recent photos at the minute) and the block work has progress a bit more since that photo. 

 

There are sills already in place which some are low and only giving 225mm in total to work with - plus forgive me, I have been reading this forum for a long time but I am still green and learning when it comes to new builds.  My main aim is to ensure we have a nice warm house to enjoy with the family. 

[Andehh]

This is a useful tool to have  a play around with. 100mm is actually 0.14, vs the build regs expectation of 0.25...which drops to 0.18 in next years uplift. So, in a nut shell...100mm is still very good & will give you a very warm house. 125mm is even better....150mm even better....etc etc....hardest point with all of this is when 'enough is enough'.

 

 

Calculator (uvalue-calculator.co.uk)

Edited December 27, 2021 by Andehh

[Declan52]

The ufh will still work. It will just mean you need to run it at a slightly higher flow temp to account for higher heat lose into the floor. You could maybe need a flow temp 3-5 degrees higher. The actual figure will depend on all the heat loss from your house.In the grand scheme of things 25mm less isn't a lot. You can easily overcome this by reducing the air leakage for example. 

Realistically the savings on 25mm less insulation should cover the extra heat demand for a good few years anyway.

[KillyfadNewBuild]

2 minutes ago, Andehh said:

This is a useful tool to have  a play around with. 100mm is actually 0.14, vs the build regs expectation of 0.25...which drops to 0.18 in next years uplift. So, in a nut shell...100mm is still pretty good & will give you a very warm house. 125mm is better....150mm even better....etc etc....hardest point with all of this is when 'enough is enough'

 

Calculator (uvalue-calculator.co.uk)

 

I know - I am literally having this conversation over a coffee at the kitchen table as I type this reply haha

 

I'll have a look at the calculator now - thanks for sending it across, it's appreciated.

 

 

[JohnMo]

I would question the pricing you are being quoted, our floor is insulated with 2x100mm and the material cost was £3500.  Floor area is 190m2

 

[KillyfadNewBuild]

8 minutes ago, Declan52 said:

The ufh will still work. It will just mean you need to run it at a slightly higher flow temp to account for higher heat lose into the floor. You could maybe need a flow temp 3-5 degrees higher. The actual figure will depend on all the heat loss from your house.In the grand scheme of things 25mm less isn't a lot. You can easily overcome this by reducing the air leakage for example. 

Realistically the savings on 25mm less insulation should cover the extra heat demand for a good few years anyway.

 

My only other option would be to push for reducing the depth of the concrete for the polished floors.

 

If I could drop it to 75mm, then I could achieve 150mm (or a reasonable combination) but then I might have issues with more cracking and my contractor having issues and probably lose benefits from the depth and thermal mass with the concrete floor.

 

Would grade of board come into play, as there might be a 125mm premium/platinum combination which could be the same as standard 150mm boards?

Edited December 27, 2021 by KillyfadNewBuild

[Andehh]

7 minutes ago, JohnMo said:

I would question the pricing you are being quoted, our floor is insulated with 2x100mm and the material cost was £3500.  Floor area is 190m2

 

We're locked into a builder now, so there will be a kick in the teeth changing spec he has quoted against (supply & fitment) not to mention peak pricing on materials across the board. 

 

[Declan52]

6 minutes ago, KillyfadNewBuild said:

 

My only other option would be to push for reducing the depth of the concrete for the polished floors.

 

If I could drop it to 75mm, then I could achieve 150mm (or a reasonable combination) but then I might have issues with more cracking and my contractor having issues and probably lose benefits from the depth and thermal mass with the concrete floor.

 

Would grade of board come into play, as there might be a 125mm premium/platinum combination which could be the same as standard 150mm boards?

I have a 75mm sand and cement screed and it is solid with no cracks. As long as you have expansion gaps at doors it shouldn't crack. 

I have no experience of polished concrete so not sure if it has to be 100mm thick. That will be for you and whatever company you go with to figure out.

[KillyfadNewBuild]

5 minutes ago, Declan52 said:

I have a 75mm sand and cement screed and it is solid with no cracks. As long as you have expansion gaps at doors it shouldn't crack. 

I have no experience of polished concrete so not sure if it has to be 100mm thick. That will be for you and whatever company you go with to figure out.

 

I'll speak to the contractor, concrete supplier and polishing people in the new year and see what they collectively say about dropping some mm from the concrete so I can use it towards insulation.

 

If not, the v-value calculator is displaying the below for 125mm - if I have selected the correct option "Solid concrete - Insulation below slab"?

[Declan52]

Is PA ratio correct??

[KillyfadNewBuild]

We both have achieved lower levels of stress from simply posting this question here - thanks everyone for your feedback, it's been very helpful and hopefully it's help others going forward in the same situation.

[KillyfadNewBuild]

5 minutes ago, Declan52 said:

Is PA ratio correct??

 

Ahh me being green again - I left it on the default figure when landing on the page.

 

Something I will look into here to get this output tightened up.

[A_L]

9 minutes ago, KillyfadNewBuild said:

I left it on the default figure when landing on the page.

 

Remember to use internal dimensions when calculating the exposed perimeter and floor area.

[saveasteading]

What do you mean by 'polished floor'. Some people mean a beautifully smooth concrete floor with exposed aggregate. Others simply mean smoothed and polished as in an industrial context, for another floor covering.

What is the construction of the floor? Raised or ground-bearing?

 

Your 0.4 PA would be right for a 10m x 10m building.

If bigger this will improve, but if less square it will be less good.

[Andehh]

Try being in a bungalow! ?  I defaulted to "1" for mine, but moved it back to a mid point before linking to OP! 

 

& yes, this forum is a huge wealth of information. Always be mindful though, whilst this place is full of hugely knowledgeable & helpful people, kind enough to help & advise others... Don't forget most of them are also enthusiasts! Where their "normal" is a loooong step away from normal normal. 

 

I live my life on here trying to achieve better then normal, but accepting I am likely below average for buildhub!! ?

Edited December 27, 2021 by Andehh

[Buzz]

On 27/12/2021 at 12:54, Andehh said:

 

We have 150mm specified (0.11) but there is a £4500 saving if we brought it down to 100mm....(0.18 I think).... we'll prob settle in the middle on 125mm for a £2000 saving .

Another alternative would be to stay at 150mm and swap pir for eps , you will save some money on the insulation and can keep the same depth screed.  

[Andehh]

12 hours ago, Buzz said:

Another alternative would be to stay at 150mm and swap pir for eps , you will save some money on the insulation and can keep the same depth screed.  

 

Thanks buzz, depth isn't an issue for us (but is for OP), so going after u value over depth. I presume EPS is less effective then PIR if it is cheaper? 

[saveasteading]

4 hours ago, Andehh said:

EPS is less effective then PIR

About half the price and half as effective.