Kingspan v Knauf (or phenolic boards v glass mineral wool)

[AChristie]

Evening All,

 

Currently having some work done on my 1970s house, my builder has suggested we could save a significant amount if we were to use a different cavity wall insulation method to that quoted by my architect, for my external walls. 

 

Architect has spec'd Kingspan K106 90mm, leaving a 10mm gap (in the 100mm cavity), my builder had initially suggested we could look at Knauf Dritherm 37 100mm instead, though this would end up needing some additional insulation internally (insulated plasterboard) to achieve required U values for building regs. So our builder has suggested we could look at a different type of Knauf, suggesting there are other thicknesses available. 

 

I've taken a look at both the Kingspan K106 and Knauf Drithem 37, there is a difference in the thermal conductivity between them, 0.018 (Kingspan) and 0.037(Knauf). 

 

As a complete newcomer to insulation types, I'm a bit confused, is there mineral wool out there that can compete with the U value of Kingspan?

 

Also, with the Kingspan, we'd leave a 10mm gap, but with mineral wool it would take the entire 100mm cavity, are there drawbacks to this?

 

What is it that makes Kingspan a superior product? Is it the U value alone, or is there more to it?

 

I'm not sure whether to fork out the additional to keep with the spec, or look for alternative ways to insulate if the saving is in the 000's?

 

Any ideas, guidance or pointing me in the direction of info would be appreciated. I'm sure there are ways to meet regulations using mineral wool, else why would it be available, but I guess i'm trying to understand the points to consider to help guide why one chooses one over the other.

 

Cheers

 

Ant

 

 

[nod]

Probably better sticking with ridged insulation The brands are pretty generic 10 mi cavities arnt workable That needs to be increased 

[AChristie]

Thanks Nod, so from that I take your recommendation is some brand of rigid insulation (like the Kingspan K106) rather than glass mineral wool. 

 

Re the cavity gap, I thought 100mm was pretty standard. Why is it unworkable?

[Canski]

Nod was talking about the 10 mm gap left in the 100 mm cavity after your Kingspan has been installed. 

[Sparrowhawk]

Hi Ant, there is a way to meet regulations with mineral wool: build wider cavities.

 

@nod is an expert here and if he says you need more than a 10 mm gap then he'll be right. Though @nod why not just go for full-fill cavity instead of leaving a gap in new construction?

 

8 hours ago, AChristie said:

As a complete newcomer to insulation types, I'm a bit confused, is there mineral wool out there that can compete with the U value of Kingspan?

 

No, it's the difference in the materials. Mineral wool can't compete with the U value of PIR boards. So you have to use much thicker mineral wool to get the same effect.

 

8 hours ago, AChristie said:

What is it that makes Kingspan a superior product? Is it the U value alone, or is there more to it?

Got it in one.

 

If you use Kingspan or other PIR boards, be aware that the quality of installation makes a difference (from the data: seemingly quite a big difference) to the thermal performance. Gaps between the boards let air circulate, negating the benefit. This paper on thermal bypass is well worth a skim through to get the idea of the effect.

 

If you care about how well the insulation works, figure out a way to ensure your builder spends time installing it properly. Then patent and sell your approach, as controlling builders is like herding cats

Edited February 15, 2023 by Sparrowhawk

[Kelvin]

Have you actually costed the difference? The general mantra is take a fabric first approach when building as you can’t improve it very easily later. Therefore stick to the original recommendation. The better the U value the better the thermal response of the area you’ve insulated. But as above that only works if it’s installed well and not just bunged in. 

[Kelvin]

To add. We’re using a full fill mineral wool for our timber kit 302mm space stud walls to give you some idea of the difference. U value of better than 0.15W/m²K

[AChristie]

9 hours ago, Canski said:

Nod was talking about the 10 mm gap left in the 100 mm cavity after your Kingspan has been installed. 

Thanks, I just wasn't sure why a 10mm remaining gap wasn't workable. 

[AChristie]

8 hours ago, Kelvin said:

To add. We’re using a full fill mineral wool for our timber kit 302mm space stud walls to give you some idea of the difference. U value of better than 0.15W/m²K

This is a good comparison, thanks. Essentially you're getting a better U value than I would with a PIR of 90mm (leaving 10mm gap) but your trade off is additional cavity size required.

[AChristie]

8 hours ago, Kelvin said:

Have you actually costed the difference? The general mantra is take a fabric first approach when building as you can’t improve it very easily later. Therefore stick to the original recommendation. The better the U value the better the thermal response of the area you’ve insulated. But as above that only works if it’s installed well and not just bunged in. 

Thanks, I had to Google the fabric first principle.... but makes sense, achieve insulation during initial construction, not by 'topping up' or having to take remedial action later. 

[saveasteading]

19 hours ago, AChristie said:

is there mineral wool out there that can compete with the U value of Kingspan?

Not on straight U value comparison.

 

19 hours ago, AChristie said:

What is it that makes Kingspan a superior product? Is it the U value alone, or is there more to it?

Superior is an overstatement. 

Firstly let's call it PIR, then there are fewer thoughts about fire on blocks of flats.

You will likely choose another brand name on cost anyway.

 

It is the U value alone. twice as good as mineral wool or polystyrene.

The downside of it is installation, as it is more rigid and so there are more likely to be gaps unless rigorously supervised.

It is generally thought that it shrinks over time, so gaps will appear between boards. Gaps can allow air movement so cause more heat loss than might be expected.

It is also tricky to cut accurately so it is better used in full areas than cut between obstructions.

 

For our conversion, we had limited spaces between rafters. Installing 100mm PIR was fiddly and wasteful and it really didn't fit well. But we needed those U's.

So we used 50mm PIR, which was much easier to install, then 50mm mineral batt which squeezed in and closed the gaps.

 

In your case, the insulated plasterboard would have the similar benefit of providing a separate layer. You might combine it with a service gap which also increases insulation.

[Canski]

1 hour ago, AChristie said:

Thanks, I just wasn't sure why a 10mm remaining gap wasn't workable. 

Mainly due to the retaining clips that are 10 - 12 mm wide and also there is no room to get a trowel in at an angle to remove any snots from the back of the masonry.

[AChristie]

 

Just found the below document online,  thought it summed up some different options nicely. Basically, my original spec was Option 5.

 

 

 

Part L1B of the Building Regulations – Extensions

Under the new Part L1B 2021 for Extensions, Alterations & Conversions, there are some key changes you should really be made aware of.

Below is a summary table for the changes for new extensions for extensions with an initial notice lodged after 15th June 2022:

Element	Part L1B 2013   (Current)	Part L1B 2021 (From 15th June)	% Improvement
External Walls	0.28 W/m2.K	0.18 W/m2.K	36%
Roof (Ceiling Level)	0.16 W/m2.K	0.15 W/m2.K	6%
Roof (Slope)	0.18 W/m2.K	0.15 W/m2.K	17%
Roof (Flat)	0.18 W/m2.K	0.15 W/m2.K	17%
Heat Loss Floor	0.22 W/m2.K	0.18 W/m2.K	18%
Windows	1.60 W/m2.K	1.40 W/m2.K	13%
Rooflights	1.60 W/m2.K	2.20 W/m2.K	-38%
Doors	1.60 W/m2.K	1.40 W/m2.K	13%

The general improvements are standard,. But the external wall stands out as a challenge because the planning drawings may be drawn with a 300mm cavity wall.

The original U value for Part L1A 2013 was 0.28 W/m2.K. Typically, a 100mm cavity within a cavity wall would achieve this.

Under the new Part L1B 2021 regulations, this will need a 35% improvement to achieve 0.18 W/m2.K.

Typically, you should allow a 150mm cavity to achieve this.

Some options are presented below with cavity width ranging from 100-150mm:

OPTION 1 – FULL FILL MINERAL WOOL WITH AIRCRETE BLOCKWORK – 150MM CAVITY

• 102.5mm brickwork
• 150mm cavity with;
• 150mm Knauf Dritter 32 insulation (0.032 W/mK)
• 100mm aircrete blockwork (0.15-0.18 W/mK);
• 12.5mm plasterboard on dabs

OPTION 2 – PARTIAL FILL PIR INSULATION WITH LIGHT MEDIUM DENSE BLOCKWORK – 150MM CAVITY

• 102.5mm brickwork
• 150mm cavity with;
• 100mm Celotex CW4000 insulation (0.022 W/mK)
• 100mm light medium dense blockwork (0.49 W/mK);
• 12.5mm plasterboard on dabs

OPTION 3 – PARTIAL FILL PIR INSULATION WITH AIRCRETE BLOCKWORK – 135MM CAVITY

• 102.5mm brickwork
• 135mm cavity with;
• 85mm Celotex CW4000 insulation (0.022 W/mK)
• 100mm aircrete blockwork (0.15-0.19 W/mK);
• 12.5mm plasterboard on dabs

OPTION 4 – PARTIAL FILL PIR INSULATION WITH BLOCKWORK – 125MM CAVITY

• 102.5mm brickwork
• 125mm cavity with;
• 75mm Kingspan Kooltherm K108 Cavity Board insulation (0.018 W/mK)
• 100mm aircrete blockwork (0.15-0.51 W/mK);
• 12.5mm plasterboard on dabs

OPTION 5 – FULL FILL PIR INSULATION WITH AIRCRETE BLOCKWORK – 100MM CAVITY

• 102.5mm brickwork
• 100mm cavity with;
• 100mm Xtartherm CavithTherm (0.021 W/mK) OR 90mm Kingspan Kooltherm K106 Cavity Board insulation (0.018 W/mK)
• 100mm aircrete blockwork (0.15 W/mK);
• 12.5mm plasterboard on dabs

Edited February 15, 2023 by AChristie

[Marv968]

2 hours ago, saveasteading said:

Not on straight U value comparison.

 

Superior is an overstatement. 

Firstly let's call it PIR, then there are fewer thoughts about fire on blocks of flats.

You will likely choose another brand name on cost anyway.

 

It is the U value alone. twice as good as mineral wool or polystyrene.

The downside of it is installation, as it is more rigid and so there are more likely to be gaps unless rigorously supervised.

It is generally thought that it shrinks over time, so gaps will appear between boards. Gaps can allow air movement so cause more heat loss than might be expected.

It is also tricky to cut accurately so it is better used in full areas than cut between obstructions.

 

 

From the Passivehaus truss document on Thermal Bypass (Thermal bypass risks A technical review September 2022)

 

Quote

At the 2008 AECB National Conference, Berthold
Kaufmann from the Passivhaus Institute observed
that foam insulation materials have a tendency to
shrink by a substantial margin during the first six
weeks post-manufacture. Shrinkage can be up to 0.2-
0.5%, thus a 1 m board could shrink by 2-5 mm.
If new boards are installed before they have
matured, then there is a risk that a 4-10 mm
joint could open up after installation. To ensure
performance, this joint would need to be filled with a
low expansion foam, which could add considerable
time and cost penalties. Kaufmann recommends that
a maturation period of six weeks be given to foam
insulation boards prior to installation.

So perhaps once past the first 6 weeks, any additional shrinkage will be minimal?

I know with Celotex the date and time it was manufactured is printed on the side of the sheets.
 

[Iceverge]

EVERYONE, STOP PUTTING RIGID BOARDS IN CAVITY WALLs!!!!!!!!

 

It's a terrible idea. 

 

Use mineral wool or EPS beads.

 

If you need a thin wall use timberframe or SIPs.

 

Architects please can you get your heads around simply drawing thicker walls rather than updating your 1980's 300mm thinking with a very expensive and not very workable solution no doubt provided by the insulation manufacture. 

 

 

 

 

 

[Kelvin]

10 hours ago, AChristie said:

This is a good comparison, thanks. Essentially you're getting a better U value than I would with a PIR of 90mm (leaving 10mm gap) but your trade off is additional cavity size required.

It’s not a trade off it was a design decision as we wanted thicker walls as it gives us deeper reveals. There were a few other reasons too. Ironically what was the  least expensive framing method is now the dearest. It went up by £9000 from when we started talking to kit manufacturer to the final price over an 18 month period. Their SIP build is now their least expensive frame. 

[AChristie]

15 hours ago, Kelvin said:

It’s not a trade off it was a design decision as we wanted thicker walls as it gives us deeper reveals. There were a few other reasons too. Ironically what was the  least expensive framing method is now the dearest. It went up by £9000 from when we started talking to kit manufacturer to the final price over an 18 month period. Their SIP build is now their least expensive frame. 

 

Thanks Kelvin, yes I hadn't meant you had traded off, sounds like your plan was clear! I meant your approach for me would mean that's where I'd trade off.