Why alu clad? Why not alu?

[SBMS]

Would be interested in why many favour timber alu clad over pure aluminium? Thermal efficiency for us is on a par (0.75 u value eg for aluminium windows). For me the internals of aluminium are preferable to more chunky timber. But would be really interested to know if I am missing something? 

[Russell griffiths]

Do your research 

would need to be a very special frame in aluminium to get those kind of u values. 
 

I believe there’s a fair bit of fibbing going around. 

[SBMS]

25 minutes ago, Russell griffiths said:

Do your research 

would need to be a very special frame in aluminium to get those kind of u values. 
 

I believe there’s a fair bit of fibbing going around. 

Have done. Largest privately owned fenestration company in UK turning over 53 million so would hope their claims and testing were robust. What do you think:

 

https://www.seniorarchitectural.co.uk/wp-content/uploads/2023/01/PURe®-Casement-Window-System-Technical-Datasheet-28.10.2024.pdf

Edited November 15, 2024 by SBMS

[JohnMo]

9 minutes ago, SBMS said:

What do you think:

 

https://www.seniorarchitectural.co.uk/wp-content/uploads/2023/01/PURe®-Casement-Window-System-Technical-Datasheet-28.10.2024.pdf

Interesting it doesn't state U_G or U_W.

SO pretty meaningless as far as performance.

[SBMS]

2 minutes ago, JohnMo said:

Interesting it doesn't state U_G or U_W.

SO pretty meaningless as far as performance.

It’s the Uw. Had the values back from local fabricator. 

[JohnMo]

2 hours ago, SBMS said:

Would be interested in why many favour timber alu clad over pure aluminium?

Mainly because all wooden framed windows are good thermally, the aluminium adds weather resistance.

 

Many aluminium windows historically (lots still are) had absolutely rubbish thermal properties. Newer one's can be good.  But they certainly are not pure aluminium. The aluminium forms weather resistant coating over plastic instead of wood. So pretty much the same just sold differently.

[SBMS]

Just now, JohnMo said:

Mainly because all wooden framed windows are good thermally, the aluminium adds weather resistance.

 

Many aluminium windows historically (lots still are) had absolutely rubbish thermal properties. Newer one's can be good.  But they certainly are not pure aluminium. The aluminium forms weather resistant coating over plastic instead of wood. So pretty much the same just sold differently.

Ah okay thanks @JohnMo  I was asking because my wife didn’t want timber internally (chunky) and we’ve had quotes from norrsken, rationel etc that are all more than the pure aluminium system. It seems like a bit of a no brainier for me but wasn’t sure if I was missing something 

[zelem]

@SBMS

Did you end up going for the Senior PURe window system in the end? I find it rather impressive if the Uw claims are true as stated. My understanding is that the performance gain over Aluclad wood profiles is coming from using a polyurethane thermal break instead of polyamide. If one can achieve passivhaus sub 0.8 uw values with the Senior system, high sound reduction values and not have to worry about chunky wood profiles internal and having to paint them periodically, what's not to like? 
 

Edited 15 hours ago by zelem

[Mike]

18 minutes ago, zelem said:

what's not to like?

Not necessarily not to be liked, but:

 

"When specified correctly the PURe® range can give Uw-Values as low as 0.71 W/m2K for commercial CEN Standard windows" - but are you specifying commercial CEN Standard windows?

"PURe® has been tested to relevant UK and European Standards for Shear strength, air permeability, water tightness and wind resistance" - but no mention of thermal testing (nor independent testing), though maybe they forgot to mention it.

From https://www.seniorarchitectural.co.uk/architectural-systems/pure-window/

 

26 minutes ago, zelem said:

not have to worry about chunky wood profiles

Alu-wood doesn't have to be chunky (and can have lower Uw values - for example https://database.passivehouse.com/en/components/list/window?filter_frame_type=Alu%2CWood%2FAlu&filter_location=GB&sort=u_value)

 

[Nick Laslett]

8 hours ago, Mike said:

Not necessarily not to be liked, but:

 

"When specified correctly the PURe® range can give Uw-Values as low as 0.71 W/m2K for commercial CEN Standard windows" - but are you specifying commercial CEN Standard windows?

"PURe® has been tested to relevant UK and European Standards for Shear strength, air permeability, water tightness and wind resistance" - but no mention of thermal testing (nor independent testing), though maybe they forgot to mention it.

From https://www.seniorarchitectural.co.uk/architectural-systems/pure-window/

 

Alu-wood doesn't have to be chunky (and can have lower Uw values - for example https://database.passivehouse.com/en/components/list/window?filter_frame_type=Alu%2CWood%2FAlu&filter_location=GB&sort=u_value)

 

I believe the “commercial CEN Standard windows” certification is more stringent than the domestic version. Due to commercial windows needed for high rise office blocks. 
 

If you look at their domestic Ali Vu window U-value spec, they state:

”Using a domestic CEN Standard window, U-Values as low as 1.1 W/ m2K”

 

PURe range is primarily intended for commercial use, so it makes no sense to get them certified for the less stringent domestic CEN standard. 
 

Good info here on some of the other lower U-value Aluminium windows with new types of thermal breaks. 
 

https://www.doorandwindowexperts.co.uk/13554/origin-twin-flush-window-with-aerogel/

Edited 6 hours ago by Nick Laslett

[zelem]

13 hours ago, Mike said:

Not necessarily not to be liked, but:

 

"When specified correctly the PURe® range can give Uw-Values as low as 0.71 W/m2K for commercial CEN Standard windows" - but are you specifying commercial CEN Standard windows?

"PURe® has been tested to relevant UK and European Standards for Shear strength, air permeability, water tightness and wind resistance" - but no mention of thermal testing (nor independent testing), though maybe they forgot to mention it.

From https://www.seniorarchitectural.co.uk/architectural-systems/pure-window/

 

Alu-wood doesn't have to be chunky (and can have lower Uw values - for example https://database.passivehouse.com/en/components/list/window?filter_frame_type=Alu%2CWood%2FAlu&filter_location=GB&sort=u_value)

 

Thanks Mike for your added insights. Very much appreciated. When manufacturers start caveating performance data with 'up to', it's generally a good idea to be finding the exit door. The lack of thermal / independent testing is another red flag. 
It's back alu/ wood options for me with more verified thermal performance tests. 

[zelem]

13 hours ago, Mike said:

Not necessarily not to be liked, but:

 

"When specified correctly the PURe® range can give Uw-Values as low as 0.71 W/m2K for commercial CEN Standard windows" - but are you specifying commercial CEN Standard windows?

"PURe® has been tested to relevant UK and European Standards for Shear strength, air permeability, water tightness and wind resistance" - but no mention of thermal testing (nor independent testing), though maybe they forgot to mention it.

From https://www.seniorarchitectural.co.uk/architectural-systems/pure-window/

 

Alu-wood doesn't have to be chunky (and can have lower Uw values - for example https://database.passivehouse.com/en/components/list/window?filter_frame_type=Alu%2CWood%2FAlu&filter_location=GB&sort=u_value)

 

Thanks for the attached link of producers; more higher quality options in Europe than the UK. 

[zelem]

4 hours ago, Nick Laslett said:

I believe the “commercial CEN Standard windows” certification is more stringent than the domestic version. Due to commercial windows needed for high rise office blocks. 
 

If you look at their domestic Ali Vu window U-value spec, they state:

”Using a domestic CEN Standard window, U-Values as low as 1.1 W/ m2K”

 

PURe range is primarily intended for commercial use, so it makes no sense to get them certified for the less stringent domestic CEN standard. 
 

Good info here on some of the other lower U-value Aluminium windows with new types of thermal breaks. 
 

https://www.doorandwindowexperts.co.uk/13554/origin-twin-flush-window-with-aerogel/

Thanks very much Nick. Heard about Origins's aerogel option / approach to improving thermal efficiency. When I last checked, they wanted a massive premium for the option, not quite sure how the pricing compares these days but worth looking at. Thanks again. 

[Kelvin]

We went and looked at alu windows and we didn’t like the narrow profiles for our build. I could see them looking great in more contemporary looking house though. We much preferred the chunky timber frames and also the timber (Scandi) look so ours are clear coated too. 

[SBMS]

14 hours ago, zelem said:

@SBMS

Did you end up going for the Senior PURe window system in the end? I find it rather impressive if the Uw claims are true as stated. My understanding is that the performance gain over Aluclad wood profiles is coming from using a polyurethane thermal break instead of polyamide. If one can achieve passivhaus sub 0.8 uw values with the Senior system, high sound reduction values and not have to worry about chunky wood profiles internal and having to paint them periodically, what's not to like? 
 

Hi Zelem

 

Yes we have gone this route.  I asked the very same question to both the fabricator and Senior themselves regarding the claimed Uw value.  They use a standard calculation method using EN ISO 10077, for the reference CEN window.  The window size they simulate with is 1.23 m wide × 1.48 m high.  This reflects a standard window size as the Uw value is related to the proportion of glazing to frame.  Remember - the larger the window, the closer the Uw value tends to the Ug value.  We have larger windows than the CEN standard so will tend to a better U value - although we have some spacer bars on some windows that will wash this out.  The problem with any claimed Uw value is it relates to a number of related components that won't reflect your window; and therefore all they can do is provide a reference size so you can compare between manufacturers.

 

The calculation of the Uw value (I looked it up because I wondered) is actually remarkably straightforward.  You need to know the u value of the frame, the glazing and the dimensions of the thermal transmittance strip.  One of the reasons Pure's Uw is low is they use PUR -polyurethane resin (~0.022 W/m K) whereas many other manufacturers use Polyamide (~0.30 W/m·K) thermal break. Thats an order of magnitude improvement in thermal conductivity.  PUR is already commercially proven in large systems.

 

So with this assumption, is their Uw claim reasonable? On average the frame area is around 15-25% of the U value heat loss, so the thermal break is going to improve the Uf value by around 30-40%, so I'd be looking at a reduction of around 0.2–0.5 W/m²K for a Uw value.  That pretty much checks out with the difference between their standard Polyamide broken windows, and the Pure windows.

 

Without independent verification then (which few glazing providers bother with because of the challenge of different window makeups - and the fact that the reference CEN window calc is pretty simple), you're left with looking at the reliability of the fenestration provider itself.  Senior are prevalent in higher specified commercial glazing - not massively prevalent in domestic glazing.  I see this as a benefit - they're a 34 year old company, which imparts a good degree of confidence.  Check out the NBS Source Case Studies (https://source.thenbs.com/manufacturer/senior-architectural-systems-ltd/dVSDoRHE7zaprhEbgnigyf/case-studies).  They've installed Pure in Grantley Hall Spa & Hotel, the main welcome building in RHS and the Castle Park View scheme in Bristol - tallest residential building in the city and it achieved level four standard in the Code for Sustainable Homes certification.  These are the typical installations Senior does -  high specification, high end commercial glazing.  I think they are one of, if not the, largest privately owned fenestration provider.  We're not talking safestyle UK here. 

 

Do I trust that they are putting PUR not Polyamide thermal breaks in? Yes.  So from this, do I trust the claimed U value of the window? Yes.  Did I look into Senior (£50m annual revenue last year, profitable, well reviewed?) Yes.  Are the windows fabricated to a high quality? Well that's down to the fabricator selected which I can't comment on, but I visited the factory where our fabricator is based, spoke to their MD, spoke to a seasoned installer who has had no issues.

 

So all in all, I'm pretty comfortable with the claims and my decision.