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High performance buildings start with the right skin

Sustainability By Hannah Blossom, Director of Sustainability – 05 April 2023

Looking up at the brick exterior with multiple windows to a blue sky


Hannah wearing a dark top and jacket with arms crossed in front of a concrete wall looking to camera

Hannah Blossom

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Building performance is at the heart of climate adaptation – and the methodology and approach we adopt to deliver high performance facades is the first line of defence in protecting a building's occupants. Unfortunately, for most projects, we are not going far enough in terms of optimising the thermal performance of a building's envelope for energy efficiency.

Given the imperative to both reduce emissions and address climate change adaptation, we need to up our game and get the basics right.

If we consider the concept of high performance facades from a holistic perspective rather than ‘carbon tunnel vision’, it is therefore obvious that facades need to do more than simply enabling energy efficiency in buildings.

Facades absolutely must result in a building which is comfortable to occupy.

The building envelope should support health and wellbeing through positive daylight outcomes, and possibly openable windows.

We need to be assessing and seeking to reduce embodied carbon, and we shouldn’t be just relying on ‘big wins’, such as carbon neutral concrete, and ignoring façade materials. We need to consider the legacy at end of life and what we can do to enable deconstruction and re-use of materials.

From the glazing units to the aluminium fenestration assemblies and spandrel panels, we should design and construct for disassembly and re-use - and for maintainability throughout the asset lifetime. The fully glazed curtain wall that has enormous kerb appeal is notoriously difficult to repair should any glazing units suffer damage from a major storm or other misadventure.

Instead of the glass box, we should be seeking to use facades to support better biodiversity and greening outcomes in our urban environments – which also has co-benefits for human wellbeing and for the urban microclimate.

But before we go too far into how to balance all of these things and where our priorities should lie (which is important, and also becomes very complex very quickly), we need to start by getting the basics right.

Fabric first and passive house

I’m a firm believer in fabric first design. When we optimise the building fabric, we reduce our peak loads, flatten our demand curves and the services and technology in the building can be far simpler. And that means any facilities manager can run the building and we are much more likely to actually see high performance in operation. The performance gap between design goals and operational data is a continuing problem - and improving the building envelope is the quick win to closing that gap.

The fact is, we’ve been passing on the cost of comfort to occupants by delivering technology-heavy buildings with poor facades for far too long, and it’s time to change.

The problem as I see it is that the industry mostly uses the Deemed-to-Satisfy provisions of the NCC – whether its Section J for commercial buildings or NatHERS for residential - as a design tool. We use it to set the scope of our assessment, and even when we target improvements beyond NCC, the blind spots usually remain.

These blind spots include:

1. thermal bridging / continuity of insulation

2. air leakage paths through the façade

3. inadequate management of solar loads – for example, scrimping on shading or eaves, or failing to address orientation

The reality is that these blind spots severely compromise the good strategies we employ in optimising the performance of the parts we do assess. I’d much prefer to push for walls with R2 insulation that is properly detailed to be continuous, than ramp up to R4 but then stop and start leaving slab edges exposed.

I also want to emphasise that responsibility for these things is shared between the design and construction teams.

The solution is to draw on Passivhaus methodology. We don’t necessarily have to target passive house performance levels, but following the rigorous assessment approach that it dictates, and undertaking on-site testing, means we can be confident the façade is designed and acts as a whole system, and we’re not kidding ourselves that we’ve delivered a racehorse when actually the building will behave like a bad-tempered mule.