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Why Installation Matters as Much as the Window

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Avoiding expensive mistakes in high-performance builds

You've spent weeks researching U-values and selecting the perfect triple glazed windows for your project. The specification looks excellent on paper. But the uncomfortable truth is that even certified, high-performance windows can underperform dramatically if installed incorrectly.

UK building performance research shows that actual energy use in new homes can deviate from design predictions by over 150% – and heat loss around windows and doors is consistently identified as a primary culprit. The leading cause is rarely the product itself – it's the installation.

 

Four key factors that determine window performance

  • Certification doesn't guarantee performance: a certified window installed poorly can perform worse than a standard window installed well

  • The window/wall junction is critical: thermal bridging here can account for up to 30% of heat loss in well-insulated buildings

  • Responsibility gaps cause failures. The worst projects fail because "everyone assumed someone else was sealing it"

  • In-house installation with guarantees protects your investment. Separating supply from installation creates risk

What Makes an Installation 'High Quality'?

Window Position

Where your window sits in the wall matters enormously. The optimal position is within the insulation layer, overlapping with the inner wall face by 30–50mm.

Push the window to the wrong position, and even exceptional glazing becomes a thermal bridge.

The Airtightness Layer

Every window installation involves an interface with the building's airtightness layer. Someone needs to own this detail – we advocate for locking down the installation methodology and responsibility frameworks before a single unit arrives on site.

Professional installation means using appropriate materials: pre-compressed foam tapes, EPDM membranes, and specialist sealing systems designed specifically for window junctions. General-purpose expanding foam can shrink over time, lose adhesion, and compromise the seal. The materials engineered to perform for decades aren't typically found in a standard tool kit.

Pre-Installation Coordination

Before any unit arrives on site, someone must confirm: Are the apertures built correctly? Is the airtightness strategy documented? Who owns each junction detail?

Without these checks, problems get baked into the build – creating responsibility gaps and the kind of costly, stressful headaches that can overshadow what should be an exciting milestone in your project.

We run a 140-point check before installation and arrive with materials already prepared – the right tapes, sealants, and fixings for details that need to last decades.

Does certification guarantee performance?

Passivhaus-certified windows are an excellent point of reference, providing verified U-values, accurate Psi values for the window-to-wall junction, and full PHPP-compatible data.

But certification confirms performance under laboratory conditions – not on your building site, with your wall build-up and your installation team.

The difference between predicted and measured performance is the 'performance gap'. Passivhaus projects demonstrate smaller gaps than standard builds, not because the windows are inherently better, but because rigorous quality protocols address what happens at installation.

Does it matter who installs?

Absolutely. The biggest risk factors:

  • General builders unfamiliar with high-performance detailing – good tradespeople without training in passive house principles
  • Window suppliers who install without specific airtightness coordination – focusing on the window alone, without specific reference to the unique wall build-up of each project. 
  • No clear responsibility for the interface – the gap where problems fall
The best installations happen when the installer understands high-performance construction, knows the product well, and airtightness layer responsibility is clearly assigned.

Is specialist installation worth it?

Choosing the right windows represents significant investment – potentially 10% of your build budget. That investment delivers returns only if installation matches product quality.

When you separate supply from installation, you create a gap where responsibility disappears. If condensation appears, whose fault is it – product or fitting?

At Norrsken, when you purchase supply and installation together, both your double and triple glazed doors and windows and their installation are guaranteed.

Window specification is controlled in the factory. Performance is decided on site.

Which products are right for your project?

Take our short survey to discover the window and doors that differentiate developments.

Frequently Asked Questions

Can poor installation cause condensation or mould?

Yes. Thermal bridges create cold spots where warm indoor air condenses. Persistent condensation leads to mould growth. Proper installation eliminates these cold spots by maintaining consistent surface temperatures.

What is the 'performance gap'?

The difference between predicted energy performance at design stage and actual measured performance once occupied. UK research shows new homes can use 2.5 times more energy than predictions, with window junctions frequently identified as problem areas.

Can I use expanding foam for window installation?

High-performance frames require low-expansion, "elastic" foam that stays flexible as the building settles; standard foam can bow frames and crack over time, creating thermal leaks.

Crucially, foam is an insulator, not an airtight seal. For Passive House or similar standards, you should use a three-tier approach: internal airtight tapes, flexible foam for the middle insulation layer, and external weather-tight seals (like Compriband).

Relying on foam alone risks failing your pressure test. Coupling flexible foam with specialist tapes ensures the installation matches the high performance of the window itself.

How much does window positioning matter?

Significantly. Windows positioned within the insulation zone (30–50mm overlap with the wall's inner face) minimise thermal bridging.

Incorrect positioning increases heat loss regardless of product quality.

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SELECT YOUR WINDOWS

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The highest compliment is a recommendation. These are the voices of those who placed their trust in us.

"Excellent Company from start to finish… If only every window supplier operated like this! I have used many others over the years on various projects but Norrsken far exceeded all of them… I hope this helps you make a decision for what is probably a large chunk of your budget… They are totally worth it"

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Angela Smith

Self Builder

“Having used Norrsken in the past we were happy to recommend them to one of our clients who was looking for the best sound proofing and weatherproofing they could get being set on a hill top overlooking the sea and facing strong westerly winds. They were not disappointed. A quality product, delivered well and on time. Thankyou.”

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Ken Pearson

Homeowner

"Fantastic professional service, from the original design to the final installation. The triple-glazed windows and doors that have been fitted to our new house are of a very high quality and look amazing. We definitely made the right choice when we decided to use Norrsken, nothing is too much trouble for them."

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Nigel

Homeowner

"I did my research before contacting Norrsken but they had come highly recommended by our Architect for our Passive House self build.

From the first meeting with Nick we felt confident that they were the Company for us."

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Ali and Brian Manning

Passive House Self Builders

“The quality of the triple glazed, alu-clad windows and doors is superb. They feel so reassuringly solid ... I opted for a wood stain for the internal finish on the frames, and am so glad I did, as it shows off the beauty of the wood perfectly. The whole process from order to installation went smoothly. I thoroughly recommend Norrsken.”

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Gareth

Homeowner

"Norrsken provided attentive service from drawings to on-site installation for our project at National Trust Stourhead and we would definitely recommend and repeat commission them on future projects."

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Charlotte Hill-Baldwin

Architect, H-B Designs

“From our very first interaction to the aftercare support, Norrsken has been exceptional. The quality of their windows is outstanding - beautifully designed, expertly crafted, and a real standout feature in our home. They've truly elevated the overall look and feel of the house.”

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Neil Southwell

Self Builder Homeowner

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