Kingspan Kooltherm K103 Floor K108 Cavity wall 0.019 W/mK

[Caroline]

Hi everyone

 

Our building control drawings are showing the above insulation for our newbuild.  The price of this Kooltherm is really high, however, all comparables seem to be coming out at 0.022 W/mK, so slightly less efficient.

Does anyone know of any alternatives which produce 0.019 W/mk or any advice if current building regs require this.  

All advice gratefully received.

[Russell griffiths]

Depends if you want to build a good forever home or an average home you will sell in 5 years. 
if a good one you will be in for a good while i would forget any form of pir boards in the cavity and go back to the drawing board. 
in laboratory conditions they pass building regs, out on site with a couple of knuckle dragging bricklayers installing them they come out as pretty poor, the figures just happen to add up so everyone advises using it. 

[crispy_wafer]

as above, do yourself a favour and the builders a favour, and get whoever is doing the drawings to widen the cavity and fill with woolbatts or pumped beads.  PIR is great on paper, it's just not worth the expense for cavity fill.  - We are not saying this cos we're mean, its just in reality so many stars need to align to get the installation spot on.

[Caroline]

3 hours ago, Russell griffiths said:

Depends if you want to build a good forever home or an average home you will sell in 5 years. 
if a good one you will be in for a good while i would forget any form of pir boards in the cavity and go back to the drawing board. 
in laboratory conditions they pass building regs, out on site with a couple of knuckle dragging bricklayers installing them they come out as pretty poor, the figures just happen to add up so everyone advises using it. 

What would you recommend in place of PIR boards?  Also, what to insulation floor with?

[Caroline]

3 hours ago, crispy_wafer said:

as above, do yourself a favour and the builders a favour, and get whoever is doing the drawings to widen the cavity and fill with woolbatts or pumped beads.  PIR is great on paper, it's just not worth the expense for cavity fill.  - We are not saying this cos we're mean, its just in reality so many stars need to align to get the installation spot on.

 

3 hours ago, crispy_wafer said:

as above, do yourself a favour and the builders a favour, and get whoever is doing the drawings to widen the cavity and fill with woolbatts or pumped beads.  PIR is great on paper, it's just not worth the expense for cavity fill.  - We are not saying this cos we're mean, its just in reality so many stars need to align to get the installation spot on.

Woolbatts/Pumped beads, not heard of these.  Can you recommend a manufacturer and who could install. Thank you

[Mr Punter]

The woolbatts could be dritherm 32 which are mineral wool and get installed by the bricklayer.  They are soft so easier to get right than rigid insulation so fairly idiot resistant.

 

Pumped beads are EPS beads that get injected after the shell is complete.  Makes the bricklaying more idiot proof.

 

Both the above are best with a 150mm plus cavity.

[Buzz]

4 hours ago, Caroline said:

Hi everyone

 

Our building control drawings are showing the above insulation for our newbuild.  The price of this Kooltherm is really high, however, all comparables seem to be coming out at 0.022 W/mK, so slightly less efficient.

Does anyone know of any alternatives which produce 0.019 W/mk or any advice if current building regs require this.  

All advice gratefully received.

Hi @Caroline how wide has the cavity been drawn at ? And what u value. I agree with the comments above, if you don't need to use pir then I would look for another solution 

[Caroline]

2 minutes ago, Buzz said:

Hi @Caroline how wide has the cavity been drawn at ? And what u value. I agree with the comments above, if you don't need to use pir then I would look for another solution 

75mm of insulation in the cavity with a 50mm clear cavity between brick and block.

[mistake_not]

43 minutes ago, Caroline said:

75mm of insulation in the cavity with a 50mm clear cavity between brick and block.

Yeah my builder specced the same. If you do a full fill cavity batt at 125mm you get basically the same u vale on paper:

 

https://www.insulationsuperstore.co.uk/product/knauf-dritherm-32-125mm-cavity-wall-slab---2184m2.html

 

* Note you might need to do something stupid like 130mm to pass building regs. Or just widen to 150mm. 

 

Side benefit, even at 150mm it's much cheaper than k108. At least half price. The same is true for EPS. Only issue I can see with EPS is the cosmetic element of holes. Not an issue if you are rendering though.

 

Also see my discussion and calcs on it here: 

 

https://forum.buildhub.org.uk/topic/43093-cavity-insulation-and-air-tightness/

Edited March 17 by mistake_not
Adding info

[Mr Punter]

11 minutes ago, mistake_not said:

Only issue I can see with EPS is the cosmetic element of holes. Not an issue if you are rendering though.

 

 

On a new build they drill the holes inside before plastering / boarding takes place.

[Buzz]

1 hour ago, Caroline said:

75mm of insulation in the cavity with a 50mm clear cavity between brick and block.

Get them to make it 150mm and then full fill with 32 wool batts , your brickies will be used to this method and is very difficult not to get it right. 

This will give you the same uvalue as pir.

Cost wise, pir is around £40 m2 woolbatts £17 m2 , but as always shop around for deals .

[ETC]

Look at what U-Value you are trying to achieve and then decide - I’m surprised that 75mm of PIR will comply - but I would be leaning towards pumping the cavity with insulation and if required dry-lining the inside with insulated plasterboard. As I said before (and got slagged-off for) you will be at the mercy of whoever is building your walls to get the PIR boards correctly installed.

[bmj1]

1 hour ago, ETC said:

Look at what U-Value you are trying to achieve and then decide - I’m surprised that 75mm of PIR will comply - but I would be leaning towards pumping the cavity with insulation and if required dry-lining the inside with insulated plasterboard. As I said before (and got slagged-off for) you will be at the mercy of whoever is building your walls to get the PIR boards correctly installed.

 

I ended up with rockwool in the cavity, and then dry lined with insulated plasterboard for belt and braces.

 

Is it okay to do insulated plasterboard with EPS beads in the cavity, or does that risk interstitial condensation ?

[Russell griffiths]

14 hours ago, Caroline said:

75mm of insulation in the cavity with a 50mm clear cavity between brick and block.

You must have some fairly thick insulated plasterboard on the inside as well, as that 75mm doesn’t come close to building regs. 

[FarmerN]

Our brick and block walls went up 4 years ago , 125 cavity  with 115mm Kooltherm. 

The builders did try hard but it’s impossible to keep it flat against the blocks, no matter how well laid they are. You therefore end up with a chimney effect and therefore thermal bridging, who knows what the actuall u value is, problably 20% - 40%  below the calculated value.   Equally impossible to maintain the 10mm residual cavity. 

The builders turned up with some cheap tape for the PIR boards, I insisted on Kingspan’s recommended tape , cost , in excess of £1000.00 ! for a 210msq bungalow.

 

The floor on the drawing was also Kooltherm,  we just changed to a much cheaper PIR and put 180mm in , deeper than the planned Kooltherm but still cheaper. As we are beam and block foundations it was easy to adjust the drawings to accommodate this.

[mistake_not]

9 hours ago, Russell griffiths said:

You must have some fairly thick insulated plasterboard on the inside as well, as that 75mm doesn’t come close to building regs. 

It does with super light blocks. You can technically hit 0.18 I value.... Sounds like a rubbish idea though hence I changed my spec.

[Caroline]

Thank you all.  I asked an insulation company today and they suggested:

 

"To achieve the same thermal performance you would need 90mm cavity and a 160mm floor, Celotex can provide you with 85mm or 100mm cavity 150mm or 165mm floor"

 

This would be far cheaper for us and they are saying would achieve the same thermal performance as the Kingspan.  I guess we might need to make cavity slightly bigger to keep the same void as currently on the plans.

 

[Russell griffiths]

34 minutes ago, mistake_not said:

It does with super light blocks. You can technically hit 0.18 I value.... Sounds like a rubbish idea though hence I changed my spec.

Really, I thought with 75 in a cavity you had to have about 50 internal. 

[crispy_wafer]

150mm or even 200 cavity is not uncommon these days, even on build sites. Don’t let it phase you, do more and have a comfortable new home that exceeds regs.

[bmj1]

51 minutes ago, mistake_not said:

It does with super light blocks. You can technically hit 0.18 I value.... Sounds like a rubbish idea though hence I changed my spec.

Had a nice moment when the builders laid light blocks as internal skin of cavity wall over the weekend.

 

I flagged it on the Monday and they had to take it all down.

 

Turns out they wouldn't bear the weight of the steels...

[Russell griffiths]

This isn’t a pick on @Caroline post, but you really need to decide what you want this house to be and the best way to achieve it. 
there have been a flurry of posts on here this year of people with badly insulated houses and extensions, that’s are really not living up to the owners expectations, and they are now having to re do bad workmanship, or live with the fact that they just spent two years building something that is not as good as they had hoped. 
have a think what you want to achieve and go from there. 

[mistake_not]

1 hour ago, Russell griffiths said:

Really, I thought with 75 in a cavity you had to have about 50 internal. 

Dodgy ubakus calc below. No idea what the aerated concrete blocks are I selected, and I changed the lambda value of the PIR to 0.019 to match k108. Note kingspans calculator suggests this as a way to hit u values, but no details on actual materials except the K108.

 

 

@Caroline I'm assuming the celotex you were quoted is still a PIR board, so even though it's a bit cheaper, you still have a load of issues. 

As you say slightly bigger cavity. I.e. If you have a cavity of at least 130mm and do EPS or mineral wool batts you will save loads and have decent insulation.

 

 

Edited March 18 by mistake_not
Adding lambda value

[SBMS]

If you have the benefit of a new build then why constrain yourself to such a small cavity width? I would absolutely widen the cavity to 200mm and pump EPS beads in. 0.15 u value and anything more was diminishing returns (brick tie expense, wider trench blocks etc). 

 

With the floor we settled at 180mm PIR (two layers of 90mm) which gives 0.1 U value. Again anything more is diminishing returns and that was the sweet spot when we did the calcs for UFH heat loss. 
 

 

[SBMS]

Also architects always specify expensive kingspan at 0.019. They specified 150mm 0.019 boards for our flat roof - super expensive. Two layers of 90mm were thermally equivalent and less than half the price!

Edited March 18 by SBMS

[IGP]

As other state earlier, don’t go PIR in cavity, all too easy to get wrong.

Example thread. 
 

 

Full fill all the way be that mineral wool batts or blown EPS beads.