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Why vacuum double glazing is best for a passive house window

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Green energy passive house graphic for vacuum windows

Why vacuum double glazing is best for a passive house window

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Published on: June 10th, 2021

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The best passive house window option for sustainable housing

When it comes to double glazing, there are a number of options for improving your home’s insulation and energy efficiency. But when it comes to the best window insulation option for passive houses, the answer is clear: vacuum double glazing.

Here’s why.

What is a passive house?

According to Wikipedia:

Passive house (German: Passivhaus) is a voluntary standard for energy efficiency in a building, which reduces the building’s ecological footprint.[1] It results in ultra-low energy buildings that require little energy for space heating or cooling.”

In simple terms, a passive house is a ‘sealed’ house. They are designed to heat and warm air escaping, and stop draughts entering the rooms to alter the temperature. Air flow is controlled, rather than restricted and means that rooms can be kept at more consistent temperatures. This in turn means that it takes far less energy to maintain comfortably heated (or cooled) rooms. 

Air is stopped from entering/leaving the building by making the structure air tight. Superinsulation is used to reduce heat transfer, with special attention being paid to thermal bridges []. Thermal Bridges include:

  • Wall to wall junctions
  • Window to wall junctions
  • Door to wall junctions
  • Recessed lighting
  • Areas with gaps

A passive house does not always need a conventional heating system – the exceptions being in particularly cold climates. Instead, consistent temperatures are maintained by using solar, ground heat exchangers and heat recovery ventilation systems. Space heating is also taken into account – the heat generated by appliances and occupants.

Why is a vacuum double glazing the best insulation choice for passive houses?

Windows are an Achilles’ heel for most houses when it comes to insulation. The requirements of a passive house window are that it is:

  1. A Super-efficient insulator; a double glazing unit that employs a vacuum is an excellent choice. Vacuum double glazing is highly efficient – much more so than conventional double glazing.
  1. Airtight; a window which is built and tested to achieve a higher standard for all aspects of weatherproofing.

Sustainability of the manufacture and installation of the project is something often overlooked in the official considerations, but it must form part of the decision if you are looking for a holistic approach.

Window Technology

Vacuum double glazing is made from two Low E panes of glass separated by a vacuum. Traditional double glazing can use more efficient panes of glass, but it has a cavity filled with air, so it is much less efficient. Many units use a noble gas such as Argon which has 30% less conductivity than air, which improves the efficiency. However, as neither heat nor sound can cross a vacuum, then a vacuum unit is the best choice.

The use of a vacuum in a passive house window also allows the gap between the two panes to be reduced from 16 – 26mm to a miniscule 0.3mm. This also makes for a more attractive window too, as the unit has less of the ugly internal spacer bars on show.

Passive house window materials and construction

Construction also plays a part in making a passive house window. Specially constructed uPVC window frames with insulated cavities do improve efficiency. However, these windows are manufactured at a great cost to the environment (see our study with Derby University here), which goes against the passive house concept. 

Windows made from sustainably sourced, enhanced timber such as Accoya® or Red Grandis offer excellent thermal insulation with the added benefit of better looks and a much longer service life.

The manufacturing process also plays a part. Windows with frames built to high standards using craftsmen with meticulous construction processes are perfect for a passive house window. A well-constructed frame will eliminate gaps, and with an enhanced timber that minimises expansion and contraction, the seals will stay intact for many years to come.

Installation is the final step. A well-constructed window will fit more snugly into the aperture. Again, the use of enhanced timber helps this due to the reduced expansion from heat. Therefore, a tighter seal can be made between the frame and the wall, and the seal will stay intact for longer periods of time.

What additional benefits does vacuum double glazing offer?

Well, in addition the increased thermal efficiency, there are other benefits that we have previously touched upon – 

  • They are better for the environment
  • They last for much longer than standard windows
  • The quality of construction makes them easier to operate
  • They look great
Vacuum insulated glass cutaway diagram
Cross section of LandVac vacuum glass

Saving Money

Another benefit of using a quality passive house window made with vacuum glass is that they can save money.

They make the house cheaper to maintain at an ambient temperature – heating and cooling bills can be reduced by up to 75% compared to other low energy houses.

Also, because they are made from enhanced materials and carefully constructed, they will last longer than other windows. This means that they will not need replacing as often, giving them reduced financial and environment impact.

Finally, the opportunity to install a relatively traditional looking product into a super-efficient home can give you the benefit of “character” when you are looking to sell a property – we know that this is a highly sought-after feature for homebuyers.

Gowercroft makes the perfect passive house window

Gowercroft have worked hard to create a range of thermally efficient, environmentally friendly windows that meet passive house standards in our Frontier Range. Our most advanced window yet, the range uses FSC Certified Accoya® timber frames with super-efficient LandVac vacuum cavity glazing and a specially formulated Italian paint system.

If you are involved in passive house projects, or you simply want to have the most efficient window system available, check out the Frontier Range here.