London · Certified components only
Passivhaus Windows London
What counts as a Passivhaus window
Passivhaus is a building energy standard, not a window brand, and "Passivhaus window" has a precise meaning: a window certified by the Passive House Institute as a component for a given climate zone. For the cool, temperate zone that covers the UK, the criteria are a component U-value of 0.80 W/m²K or better, 0.85 W/m²K or better once installed, and a hygiene criterion on surface temperature. A window either holds that certificate or it does not.
| Standard | Window U-value | Source |
|---|---|---|
| Passive House component, cool temperate | Uw ≤ 0.80 W/m²K | PHI transparent components criteria, Table 1 |
| Passive House component, installed state | Uw ≤ 0.85 W/m²K | PHI transparent components criteria, Table 1 |
| Building Regulations, replacement window | 1.4 W/m²K, or WER Band B | Approved Document L, Table 4.2 |
| Building Regulations, new dwelling | 1.6 W/m²K | Approved Document L, Table 4.1 |
| Notional dwelling, SAP calculation | 1.2 W/m²K | Approved Document L, notional dwelling specification |
Compliant frame systems
The Passive House Institute's component database is the only authoritative list of certified windows, and a system is either in it or it isn't. Below are the Schüco systems that appear in it, with the certified figures. Note that AWS 70.HI does not appear in the database and should not be specified as a certified Passivhaus window, whatever else it may be good at.
| System | Certified Uw | Efficiency class | Status |
|---|---|---|---|
| Schüco AWS 90.SI+ | 0.79 W/m²K | phC | Certified, cool temperate, since 2014 |
| Schüco AWS 90.SI+ optimized | 0.80 W/m²K | phB | Certified, cool temperate, from a face width of 117 mm |
| Schüco AWS 75.SI+ optimized | 0.80 W/m²K | phC | Certified, cool temperate, from a face width of 178 mm |
| Schüco AWS 70.HI | , | , | Not in the PHI component database |
Source: Passive House Institute component database and Schüco UK. If a window matters to your certification, check it in the PHI database yourself before ordering, and ask for the certificate ID. Plenty of windows described as "Passivhaus" in sales material are not certified components.
The glass spec that gets you there
The frame alone will not get you there, the glazing is the other half of the equation. The Passive House Institute publishes a reference glazing figure for each climate zone, and for the cool, temperate zone that applies to the UK the reference glazing is Ug 0.70 W/m²K. In practice that means a triple-glazed unit with two low-e coatings and a warm-edge spacer.
| Criterion, cool temperate climate | Limit |
|---|---|
| Component U-value (Uw) | 0.80 W/m²K |
| U-value in the installed state | 0.85 W/m²K |
| Reference glazing (Ug) | 0.70 W/m²K |
| Hygiene criterion, temperature factor fRsi at 0.25 m²K/W | 0.70 or better |
| Minimum efficiency class for certification | phC. Classes run phA+, phA, phB, phC by opaque heat loss. |
Source: Passive House Institute, Information, Criteria and Algorithms for Certified Passive House Components: Transparent Building Components, Table 1. Aluminium spacer bars cold-bridge at the glass edge, which is why warm-edge spacers are used on any window aiming at these figures.
Install detail, the thing nobody photographs
A certified Passivhaus window installed badly will not perform. The biggest avoidable losses come from the install detail, not the product spec. Here's what a competent install looks like:
| Frame seated on insulated sub-frame (Compacfoam, Purenit), no direct contact with cold-bridging steel lintel. |
| Thermal-break of frame aligned with thermal-break of wall insulation (centre of insulation, not face of structure). |
| External tape: weather-tight, vapour-permeable (Tescon Profect or Pro Clima Solido). |
| Internal tape: airtight, vapour-control (Pro Clima Contega Solido or Tescon Vana). |
| Reveal lining insulation continuous to plaster line, no thermal-bridge bypass at jamb or head. |
| Blower-door testing to baseline existing leakage before the work, where the project is targeting certification. |
| Post-install verification with the airtightness consultant, checking every frame perimeter. |
| Photographic install record retained for the certifier's sign-off. |
What a Passivhaus window costs
A certified Passivhaus window costs more than a standard aluminium one, and the install detail costs more than a standard install: an insulated sub-frame, taped perimeter and continuous reveal insulation all take time on site that a normal window fit does not. How much more depends on the system, the size and configuration, the glass make-up and the wall build-up it goes into, so we price it against your actual drawings rather than publishing a percentage. Every Apex quote includes the frame, glazing, fitting, removal, FENSA self-certification under Reg 40373 and our 10-year guarantee.
Frequently asked
What is a Passivhaus window?
A window certified by the Passive House Institute as a component for a given climate zone. For the cool, temperate zone that covers the UK, PHI's criteria are a component U-value of 0.80 W/m²K or better, 0.85 W/m²K or better in the installed state, a reference glazing figure of Ug 0.70 W/m²K, and a hygiene criterion on surface temperature. Certification also assigns an efficiency class, from phA+ down to phC, and phC is the minimum for a certificate.
Which windows are actually certified?
The only reliable answer is the PHI component database, which is public. Of the Schüco aluminium windows, AWS 90.SI+ is certified for the cool, temperate climate at Uw 0.79 W/m²K, class phC, since 2014; AWS 90.SI+ optimized at Uw 0.80 W/m²K, class phB; and AWS 75.SI+ optimized at Uw 0.80 W/m²K, class phC. If a window matters to your certification, look it up and ask for the certificate ID before you order.
Is Schüco AWS 70.HI a Passivhaus window?
No. AWS 70.HI does not appear in the Passive House Institute component database, and it should not be specified as a certified Passivhaus window. Schüco publishes a frame-only Uf from 1.5 W/m²K for the system. It is a strong aluminium window for a great many projects, with sound reduction up to 48 dB and burglar resistance up to RC3, but Passivhaus certification is not one of the things it has.
What's the difference between Passivhaus and EnerPHit?
Passivhaus is the standard for new buildings and EnerPHit is the standard for retrofits, where the existing walls, floors and roof limit what the building as a whole can achieve. For the windows themselves, the Passive House Institute applies the same transparent-component criteria and additionally checks EnerPHit suitability, including the hygiene criterion in the installed state, for step-by-step modernisation. The 0.85 W/m²K figure you sometimes see quoted as "the EnerPHit window standard" is in fact the installed-state limit in the same cool, temperate criteria.
How much do Passivhaus windows cost in London?
More than a standard aluminium window, both in the unit and in the install, because the detail takes longer: an insulated sub-frame, a taped perimeter and continuous reveal insulation are not a normal window fit. How much more depends on the system, the size and configuration, the glass make-up and the wall build-up. We price against your drawings rather than publishing a percentage that would be wrong for most projects.
What glass is used in Passivhaus windows?
The Passive House Institute publishes a reference glazing figure of Ug 0.70 W/m²K for the cool, temperate climate, which in practice means a triple-glazed unit with two low-e coatings and a warm-edge spacer. Aluminium spacer bars cold-bridge at the glass edge and will pull the whole-window figure the wrong way, so a warm-edge spacer is not optional on a window aiming at these numbers.
Why is the install detail so important?
Because PHI certifies two figures, not one: the component U-value and the U-value in the installed state, 0.80 and 0.85 W/m²K respectively for the cool, temperate climate. A certified window installed badly does not deliver the installed figure. The frame has to sit on an insulated sub-frame rather than bridging to a cold lintel, the frame's thermal break has to line up with the wall insulation, and the perimeter has to be taped weather-tight outside and airtight inside.
Does Apex Glazing do certified Passivhaus installation?
We are not certified Passivhaus tradespeople, and we would rather say that plainly than let you find out later. We have installed AWS 70.HI on a low-energy retrofit in north London where airtightness tape detail and thermal-bridge-free installation were part of the brief. On a project going for full certification we work alongside the project's Passivhaus designer and airtightness consultant rather than pretending to replace them.
