The Problem with Conservation Double Glazing

The Problem with Conservation Double Glazing

Slim Double Glazing in Heritage Windows

Conservation area double glazing has always been a sensitive area in the restoration of Listed Buildings and those in Conservation Areas.

The owners of the building want to install windows with modern performance to make their rooms more comfortable, and their heating bills more manageable!

However local planning officers and organisations such as English Heritage put conservation first. They much prefer to restore original windows that to replace them.

In this post we discuss the dilemma facing home owners and conservation officers when upgrading listed building to slim double glazing.

The Background:

Slim double glazing came into use about 50 years ago and comprised of 2 panes of glass separated by air. Whilst this was a major step forward from single glazing it was soon found that the insulating value was poor. As technology advanced, the space between the glass panes was increased which improved it’s thermal performance. Also the edge spacer technology improved to ensure there was sufficient secondary sealant to maintain the integrity of the air space and enough dessicant to control any moisture within. So the now standard 28mm Double Glazed Unit was evolved and has been a reliable addition to almost every home.

Conservation Area Double Glazing

People who live in period homes, Victorian and Georgian properties, could not benefit from this technology . The original timber frames in Conservation and Listed buildings simply could not accept such a wide unit.

Slim Double Glazing was not the solution it was supposed to be

So the glass industry created the first slim double glazed units that could fit into such frames. The reduction of air space between the glass panes was compensated for by injecting noble gases such as Argon and Krypton. This slowed down heat transfer between the panes. The desire to fit them into the small glazing rebates led to very low sightline edge spacers, sometimes as low as 5mm.

Why Slim Double Glazing Units Fail

Whilst this achieved the desired aesthetics, and good performance, the fact is the reduction in secondary sealant and desiccant has led to these units failing at an alarming rate. Not helped by contractors attempting to squeeze a ‘quart into a pint pot’ by reducing the bedding compounds etc. 5 years of service life seems quite common before the units ‘mist-up’. I recently heard of an installation that failed after 1 year.

Role of Conservation Officers:

Conservation Officers are currently stuck between a rock and a hard place. On the one hand they are doing their job by protecting and preserving the built environment and the country’s heritage. On the other hand they are under pressure from all sides by Climate Change targets, energy saving and performance targets, as well as the demand from listed building occupants who claim the right to the comfort and energy savings than others enjoy.

It’s also an unfortunate by-product that a great deal of rot on existing single glazed timber windows is caused by the constant running and pooling of water caused by internal condensation.

Some Conservation Officers will allow retro-glazing with slim double glazed units so long as the existing profiles and glazing bars remain. In-advertently they may be driving the demand for such units that fail far too early.

The environmental story is poor. Retain single glazing and have poor energy performance and possible timber rot. Insist on slim units and the regular renewal will fill landfill sites.

The solution: Vacuum Insulated Glazing

One solution for conservation double glazing is to look to the new technology Vacuum Insulated Glazing. Ultra -thin by design and not reliant on dessicant or gas. Design based on the principle of the vacuum flask, two panes of glass separated by a vacuum space of 0.3mm. These units allow for retro-glazing of existing windows with single large panes of glass and with glazing bars bonded on to achieve the multi-pane effect if needed.

Vacuum Glass is a solution for Conservation Double Glazing

Whilst I can almost hear Conservation Officers and English Heritage screaming, think about the benefits. Glazing bars as fine as the originals, some as slim as 16mm wide and profiles as ornate as the original. More efficient windows, as the glass has a higher thermal efficient than timber glazing bar and putty. Conservation area double glazing that is 10 times more efficient than single glazing. No funny reflections as the panes are so close, and a service life in excess of 25 years, so less landfill and customer frustration.


Some close up shots of Heritage Windows with Vacuum Insulated Glazing

What Are Passive House Windows

What Are Passive House Windows
Passive House windows in a sustainable building mock up

You may have heard the term “PassivHaus” when searching for your new windows, but do you know what it really means? Trying to figure out the science behind it can be quite daunting, so we’ve broken it down here for you in our simple guide. 

“Passivhaus buildings provide a high level of occupant comfort while using very little energy for heating and cooling.” Passive House Trust

PassivHaus is a term applied to the design of buildings with specific occupant comfort and energy standards. Originating from the PassivHaus Institute in Germany, it aims to provide a high level of comfort whilst using very little energy for heating and cooling.

These buildings are ecological, comfortable, energy efficient and affordable, all wrapped into one. The purpose of this housing is to remain affordable whilst bringing the future of ecological efficiency into your home. This is achieved through use of proven technologies and build standards and quality. 

How does the Passive House System work? 

If you’ve ever lived in (or visited) an older house, you’ll have experienced the draughts that inevitably blow through the building. Due to older construction techniques, ageing materials and general wear and tear, older houses tend not to be the most energy efficient buildings. This isn’t news. 

Buildings designed to PassivHaus standards are required to be as air tight as possible with the necessary flow of air controlled and with appropriate heating and cooling to maintain the comfortable indoor air quality. 

Of course, a feature then had to be developed to allow proper ventilation. Passive ventilation occurs through assigned vents via a ground heat exchanger. This mechanism allows for fresh air to be heated and pumped into the building, as well as extracting out the waste heat from the exhaust system. Ventilating the building in this controlled manner equates in very little energy wastage. 

New advances also allow the system in passive houses to factor in heat created by the inhabitants and appliances within. More ambient heat is retained as a result of no draughts and better insulation, further reducing energy used to generate heat.

Diagram of how a passive house works

The Passive House System is environmentally friendly

As the world moves forward with new ways of being environmentally friendly, so does our housing. Science is progressing, and that means our homes are progressing too. Passive housing aims to have as little impact on the environment as possible, whilst also providing exceptional comfort levels within the homes. Environmentally friendly and sustainable energy sources are  used in passive houses to limit their impact on global warming to as little as feasible.

These sources include:

  • Ambient
  • Solar
  • Heat exchange

Passive Houses offer 90% energy saving

Passive houses are designed to maintain a constant temperature – unlike those older houses that regularly need the heat replacing. Due to this design, they are super easy to keep warm/cool depending on where you reside, which allows for outstanding energy saving. Passive houses actually use 90% less energy than the majority of typical buildings. Whilst passive houses have a comparable 75% energy saving on new builds, factoring in the costs still makes this an excellent saving. Being a passive house homeowner means less stress over rising energy costs as they only use 10% of the energy needed to run a typical house.

Passive house windows savings diagram

Is a Passive House expensive to build?

A passive house is an investment, as extensive energy savings means that money is redeemed within a few years. Although the initial cost is higher than that of a typical house, this is to be expected due to the high quality of materials used, as well as the extra components and elaborate construction methods. 

With the purchase of a passive house, there should really be no need for a heating system. The concept for the houses is structured around the belief that little heat should be needed in order to make the homes comfortable. That being said, in some climates this would not be possible, but even in central Europe houses would be able to thrive without a conventional heating system. Therefore, whilst the house would cost more to purchase with the required ventilation system, the energy savings from the more advanced system would be well worth the price. Not to mention the benefits of passive house construction on the environment and reduced effects on global warming.

Can Passive House be retro fitted?

Absolutely! A PassivHaus does not have to be built from the ground up – it can be applied to an established building. As PassivHaus is a concept and not a brand, the particular construction components can be adapted to any building in order for it to be classed as a “passive house”.

EnerPHit is a slightly relaxed standard for retrofit projects that shares the same principles, but where the existing structure and Conservation needs mean that full PassivHaus cannot be met.

Passive House Window Glazing

The U Value is a measurement of heat transfer [expressed in W/m2K], where the lower the U value the better, so windows used in the design and construction must have a Low U Value. Typical standard double glazed units achieve a value of around 2.5, reducing to 1.9 for Gas Filled units. This can be further reduced by the use of triple glazing to 0.7. However, the extra glass (+50%) and edge seals (+100%) needed for a triple glazed unit should be factored into to its’ environmental credentials.

The latest technology Vacuum Insulated Glass under the brand name of LandVac provides an exceptional U value of better than 0.5W/m2K., in a double glazed unit. Whilst Triple Glazing has a typical thickness of 38mm, Vacuum Insulated Glazing is only 8.3mm thick. Making it suitable for both new build and retro-fit applications

Vacuum Insulated Glass | The scope of VIG in the United Kingdom

Vacuum Insulated Glass | The scope of VIG in the United Kingdom

In 1913, the inception of Vacuum insulated glass raised on a very high level in front of people. The vacuum simply has a double glazed unit and not gas in the cavity. For refitting the heritage windows, from single glazing to double glazing and vacuum insulated glass is used for high performances and appearance to single glazing. With an ultra slim profile of just 10.3mm VIG can offer you a U value of 0.4W m2.K. Further, you find it helping in saving the lost energy in every window system of 8mm glass.

The scope of vacuum insulated glass

As it becomes more and more important every year to make every effort to protect our planets environment, VIG can help. People in the UK have been using Vacuum insulated glass (VIG) to help reduce energy usage (and bills!).

The basic purposes and uses of VIG

Here are some great applications for vacuum insulated glass:

High rise structures

VIG was developed in Japan’s earthquake zones to make buildings that are mostly class – i.e. skyscrapers, office buildings etc, stronger. The design enables engineers to make stronger, lighter buildings that are more resilient to earthquakes.

Passive House Systems

VIG is perfect for the Passive Houses where energy efficient windows that are tightly sealed integrate with the system. Passive Houses work by restricting air flow in and out of the building and being incredibly well insulated. This means that rooms can easily maintain regular temperatures, so it takes a lot less energy to keep them warm or cool.

Heritage Windows

The slim profile of vacuum insulated glass makes it popular with heritage renovation projects where the main objective for the local planning authority is to have an appearance of single glazed windows. Of course, using archaic and inefficient building materials is not what any home owner would want, so VIG fits the bill perfectly.

In Conclusion

So, it totally depends upon us to take care of the future and think outside of the box while using VIG for windows. To assist you completely in the selection of the right product, Grosvenor Restoration plays a very important role. For the renovation and new projects, we will provide you with VIG that will be of high quality and fulfil your needs perfectly. We are one of only a handful of LandVac distributors and installers in the UK. Our knowledge and expertise will ensure you get the right product for your needs.

Read More: Vacuum Double Glazing in Listed Buildings, What is Vacuum glazing? New effective technology for efficient buildings, Condensation problems with Glass | Vacuum insulated glass, Thin double glazing listed buildings | Grosvenor Restoration, Why choose Slimline double glazed units? Any Advantage?

What is Vacuum glazing? New effective technology for efficient buildings

What is Vacuum glazing? New effective technology for efficient buildings

Vacuum glazing as a highly efficient window technology that helps insulate and soundproof buildings. More efficient and with much slimmer profiles than standard or thin double glazing, vacuum glazing will help improve the efficiency of standard and special structures such as.

How Does Vacuum Glazing Work?

The concept behind vacuum glazing is simple. Standard double glazing has 2 panes of glass separated by a cavity filled with a noble gas, such as argon. The purpose of the denser gas is to make it harder for heat to pass through.

Rather than using air or other mixtures of gas between the panes of glass, vacuum glazing instead employs a layer of nothing. With there being nothing between the glasses, there is nothing to transfer the heat between the panes, and so it can’t go anywhere. 

In order to prevent further heat loss, the other elements of the window can also be improved to make them more efficient. All the different parts of the window, from the frames down to the minute pieces such as micro spacers and bars can be made more efficient.

There are improvements that can be made to the glass itself – such as a low emissivity coating, and specialist sealants to verify optimal efficiency for the long term.

The major advantage of vacuum glazing

The major advantage of vacuum glazing is the greatly improved efficiency. It also has superb soundproofing qualities.

Another advantage of this technology is how thin the units can be. The gap between standard or even slimline double glazing can be from 10 – 25mm. With vacuum glazing, the gap is reduced to a mere 0.6mm. This means that the windows can appear to be single glazed units with none of the unsightly inner cavity showing.

the major advantage of vacuum glazing

What are the applications of Vacuum Glazing?

Vacuum insulated glass is suitable for any property and will improve its efficiency. However, as it is somewhat more expensive than other units, it’s used in more specialised applications where either the slimmer profile or the improved heat insulating properties are more important than cost.

An example of a situation where energy efficiency is needed is the passive house system. 

For applications where the ultra thin profile is needed is for heritage windows in listed buildings. This is where an older property would have been originally fitted with single glazed windows. When replacing the windows, the planning authority requires the new units to be single glazed as per the original installation. This is not always acceptable to home owners who want lower heating bills and warmer rooms. In this case, the ultra thin profile of vacuum glazing is an excellent solution that keeps both parties happy.

Final verdict to take home on vacuum glazing

To conclude, for warmer, quieter and more relaxing rooms, choose vacuum glazing. They will improve the appearance of your home, make it more efficient and lower your contribution to global warming.

Read More: Condensation problems with Glass | Vacuum insulated glass , What is Vacuum Double Glazing? ,
Vacuum Double Glazing in Listed Buildings

Vacuum Double Glazing in Listed Buildings

Vacuum Double Glazing in Listed Buildings

Application of Vacuum Double Glazing in the Upgrade of Windows in Listed Buildings

Installing Vacuum Double Glazing in heritage windows is a delicate balance. 

 The Government has set out strong targets for reducing Carbon Emissions and the impact on our environment. The owners of the historic buildings themselves generally have a strong desire to make their homes more energy efficient – to protect the environment and save money on heating bills.

At the same time, there is also a strong desire to retain and maintain our historic built environment, for the purposes of this article the windows, which are notoriously energy in-efficient.

The problems with single and double glazing in a historic building

Installing Double Glazing historic windows in a listed property is often met with flat denial by local planning officers. The owner faces a difficult and expensive journey to try and achieve what other homeowners see as perfectly normal. 

To add to the dilemma, the internal condensation is among the greatest causes of timber window rot and decay. The windows by their very nature are speeding up the rate of decay.

Double Glazing does not look authentic in a listed building

It largely comes down to appearance. It is the duty of the local planning officers to make sure listed buildings and those in Conservation areas keep their original appearance as much as possible. Historic England have made it clear that repair is always preferable to replacement in this report.

Original glass has certain imperfections which give the characteristic look.  Modern glass is flat and reflects differently. This is exaggerated with multi-pane Georgian style windows having lots of small panes, all at very slightly different angles.

So how do the owners of historic buildings improve the performance of their windows while keeping their original appearance?

Slim Double Glazing was almost the answer…

Years ago the glazing industry saw the commercial opportunity and developed slim double glazing units that would ‘fit’ into the historic glazing rebates. These have been made ever slimmer with the heat insulation performance boosted by the use of glass coatings and gas filling such as Argon and Krypton. Sadly whilst these have been well adopted the failure rate is alarmingly high.

The width of these units mean that glazing bars are normally stubbier so less well defined. And the familiar ‘double reflection’ from the glass is pronounced. So not good news for the period windows.

Vacuum Double Glazing

So what of Vacuum Insulated Glazing (VIG)? This method of constructing a double glazed unit is technically very different. Two panes of glass, separated by a tiny space where the air has been evacuated to create a vacuum. The same principle as the vacuum flask we are all familiar with. The overall thickness of VIG is typically 8mm but with energy saving values approaching those of triple glazing.

The benefit of two panes so close together is they effectively act as a single pane, so no double reflection. The reduction of width means the glazing bar profiles can be near back to original dimensions.

Using the Toughened LandVac VIG has an additional benefit. The toughening process of glass takes away the ‘flatness’. It is a happy by-product that toughened glass looks more like the ‘imperfect’ original glass.


So is Vacuum Double Glazing the answer? 

For larger pane windows, typically sliding sash windows with 1-over-1 or 2-over-2 style then retro-fitting with VIG is definitely a great step forward. 

For the small pane Georgian windows then the only way would be to use a larger single pane and applied timber glazing bars to create the multi-pane effect. The advantage is the glazing bars can be as fine as you like (typically 16mm) and it will be thermally more efficient. 

We are sure that vacuum double glazing is the best option when upgrading heritage windows. You can read more about Thin Double Glazing in Listed Buildings in this post.

Condensation problems with Glass | Vacuum insulated glass

Condensation problems with Glass | Vacuum insulated glass

Here we look at the various ways condensation shows itself on Vacuum insulated glass:

Condensation can manifest itself on glass in a number of ways. Anyone that has lived in a home with single glazing knows only too well that, come the colder months, condensation forms on the inside of the glass. This needs wiping off each and every morning for fear of water puddles on the window ledge.

This internal condensation is also the cause of a great deal of rot on timber windows as the water runs down, sits on the timber ledges and gets behind the putty. Left to extreme it can also cause growth of mould.

It has to be remembered that condensation is a natural phenomenon. The air we enjoy is laden with water. Normally, at warm temperatures the air is able to hold that moisture without problems. Once the temperature drops the air can no longer hold the moisture (it’s dew point) and will deposit it on the coldest surface which is usually the window glass.

Particularly during the night as we sleep we breathe out copious amounts of moisture laden air, around 7 litres per person, which hits the cold surface. This happens whilst the heating is off and doors are closed, and creates the familiar misty condensation when we wake up.

Advantage of Double Glazing Vacuum insulated glass:

Double glazing your windows will prevent the deposit of condensation on the Vacuum insulated glass. Importantly double glazing does not cure condensation but it does enable the room temperature to remain higher so reducing the impact.

With modern high performance double glazing and particularly Vacuum Insulated Glazing, the heat transfer from the inner to outer pane is so good that the outer pane does not heat up a great deal. This leads to condensation, particularly in the Spring and Autumn, being deposited on the outside of the outer pane. This is a sign that the double glazing is working well. This normally clears away once the sun comes up.

You may also see condensation on the outside surrounded by a clear ‘border’. This is because heat transfer is greater through the window frame so the outer pane is heated by the transfer of heat from the frame edge.

Remember: Internal condensation is bad, external condensation is good. Hope so this article will help regarding various ways condensation shows itself on Vacuum insulated glass.

Read More: What is Vacuum Double Glazing?

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