Is less more?

Is triple glazing the answer to the stricter requirements for energy efficient windows and doors in the proposed changes to Part L? Mark Norcliffe, joint MD of Cornwall Glass, argues that double-glazed units with high performance glass can often present a more cost effective and greener solution.

This year may have been dominated by news of high demand, material shortages and Covid, but there is another issue looming on the horizon that has serious long-term implications for the industry.

Changes to Part L have been in the pipeline for some time, and while they have not yet been officially announced, the expectation is that there will be a requirement for more stringent U-values for windows and doors when the new regulations come into force in the spring or early summer of 2022.

For manufacturers of older systems, and especially aluminium, this will present a problem – and it’s not one that’s going to be easily solved with the specification of triple glazed units.

As part of the new Future Homes Standard, which is being introduced to ensure all new homes built from 2025 will produce 75%-80% less carbon emissions than homes delivered under current regulations, the government is first updating the Building Regulations. The aim is that all new homes built from 2022 will produce 31% less carbon emissions, with new rules also being introduced for the replacement market.

Consultation documents reveal that minimum U-values for retro fit window and doors will be changed from 1.6W/m2K to 1.4W/m2K and 1.8W/m2K to 1.4W/m2K respectively. For newbuild, U-values for windows and glazed doors will drop from 1.4W/m2K to 1.2W/m2K.

Is triple glazing the answer to the new Part L regulations? The pros and cons of triple glazing have been debated before. Seven years ago, we had the ‘Triple Glazing Question’, which was a well-attended, prominent event, and it attracted some high-profile speakers.

The focus back then was more on the commercial appeal of triple glazing, but the issues that were highlighted are still relevant today, and adding an extra pane to a unit creates a lot of problems.

You have a lot more materials, it’s more time consuming to manufacture, and that brings extra cost and more weight. It’s more expensive to produce and more difficult to transport, let alone handle on site.

For manufacturers, triple glazing may be technically feasible but the question remains: do they want the hassle, complexity and cost that comes with it?

Glass innovation itself presents a much more compelling and greener solution to the new Part L requirements.

The whole premise of the Future Homes Standard is to lower carbon emissions, whereas manufacturing and transporting triple glazing is only going to increase your carbon footprint.

But with the right specification glass, you don’t necessarily need triple glazing; you can achieve low U-values without the compromise of additional weight or cost.

Manufacturing and processing glass across three sites across the south west, Cornwall Glass supplies a comprehensive range of products designed specifically to produce lower U-values and reduce solar gain.

These include Saint Gobain’s SKN 176 and 183, which were first developed for commercial applications and to provide cooler conditions for office workers. Capable of producing a g value of 0.37 and a Uvalue of 1W/m2K on a 16mm cavity, it achieves light transmittance of 70%.

Available in a 4mm outer leaf, SKN176 can also be used to manufacture a very lightweight unit and can be combined with Saint Gobain’s SGG Stadip product range for improved solar or acoustic control.

Cornwall Glass also offers Saint Gobain’s high tech Planitherm One T. Manufactured using a unique combination of metal oxide layers, Planitherm One T can deliver exceptionally low U-values, regardless of frame material.

Planitherm One T represents a real step forward in glass technology. Depending on specification, you can get U-values as low as 1.0W/m2K, and the performance is exceptional even if you’re fitting aluminium bifolds or large patio doors. For newbuild, where energy efficiency specification is going to really come under the spotlight in the coming months, it’s a very capable product.

Meeting the new Part L requirements is certainly going to be a challenge for some manufacturers, especially for those offering older systems. It’s going to be even more of a headache for those operating in the newbuild sector.

We know, however, that with the right specification of glass, it’s possible to overcome those challenges without having to resort to a prohibitively costly third pane.