Not all double glazing

is created equal.

With up to 45 percent of a home’s heat lost through single glazed windows, double glazing plays a critical part in improving thermal performance within the building envelope, keeping your home warm, dry and healthy. 

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New building regulation insists on all new built homes feature double glazing given the significant energy loss and health consequences of poorly insulated housing. 

That said, there is a significant stock of houses around New Zealand that are well below healthy insulation standards, where they are cold and damp with excessive condensation.



European PVCu double glazing designed for New Zealand homes

For many years the extreme cold European climates demanded a more resolute window system with advanced thermal performance properties.

Aluminium is seldom used given it is a highly conductive material which naturally draws heat out of the home and promotes condensation. 

Timber for all its charm retains moisture meaning it can warp and twist, resulting in draughty air gaps,  or sticking windows that don’t open or shut properly, not to mention the inherent on-going maintenance.

As a result, PVCu windows have been well established as the leading window joinery system for more than 40 years in the Northern Hemisphere. Rigorous testing and development over these years has resulted in PVCu windows taking in excess of 85% of the United Kingdom market and becoming the market leader throughout greater Europe and North America.

Thermalframe PVCu profiles are sourced direct from our European manufacturer. We exclusively use the Sheerframe profile system which is extruded in Derbyshire United Kingdom and is owned by parent company Synseal Extrusions, one of the largest and most respected PVCu extruders. 

A strong and durable product, PVCu stands for unplasticized polyvinyl chloride and can be found in everything from construction, medical equipment through to space engineering. Thermalframe PVCu is a calcium-based profile that is completely lead-free, fully recyclable and has added titanium dioxide to withstand New Zealand’s severe UV elements.

Incomparable thermal properties that deliver home comfort and warmth combined with the tested resilience to withstand the harshest of weather elements, has seen Thermalframe installed in New Zealand homes for over 24 years.

Understanding double glazing options


Double glazing is literally defined as two panes of glass. The glass panes are separated and sealed by a spacer bar which is effective at keeping the inner pane comparatively warmer to the outer pane.   

Whist this is technically correct, there are significant implications associated with the window frame any double glazing is set into and how the window system functions as a whole. For homeowners looking to double glaze their existing home, there are three options that are commonly referred to including:

  1. Retro-fitting – where the windows remain intact, yet the single glass is replaced with a double glazed unit and set within the existing window. New beads are established in aluminium joinery to allow for the extra width glazing chamber, and timber windows are routered out to support the wider gap needed
  2. Insert windows – where the ‘non-performing’ parts of the window is replaced as a whole unit that can be successfully installed in the existing framework
  3. Replacement windows - where the entire window unit requires replacing
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Retrofit double glazing only partly resolves the issue

Although double glazing alone looks to improve the thermal performance of the glass component, this only resolves a small part of the issue. The conductivity of the existing window frames and the air gap between the double-glazing chamber greatly impacts on heat transfer.

Aluminium frames are a poor insulator, drawing an extraordinary amount of heat out of your home on a cold day or night. Coupled with this issue is that most older aluminium windows were not designed to house double-glazing and can only accommodate a very minimal double glazing chamber. The optimal glazing chamber gap is between 14-16mm – anything less than this and the double glazing becomes less effective and any benefit significantly compromised. 

Older timber frames given the period in which they were built are also not designed to carry the weight of double glazed units that are far heavier than single pane glass. This extreme weight load onto the sashes and large glass surfaces can create significant problems with future functionality. 

Typically many of the older timber windows were slim-line to reduce weight and struggle to support the adequate width in the sashes to accommodate effective double glazing. Because retrofitting timber sashes requires a larger cavity channel to be created in order to accommodate the double glazed unit, often the air gap between the double glazing is greatly compromised, resulting in less than optimal heat retention.

Replacement windows must complement character

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Replacing windows, particularly in character homes, requires confidence in a system that will compliment the period features. 

Aluminium does not suit period properties and whilst the charm of timber is appreciated, the issues of warping, twisting due to moisture retention is there, not to mention the high maintenance and painting requirement.

Thermalframe PVCu profile has very similar proportions to timber. With our unique ‘insert’ installation technique, often we can retain much of the hardwood surrounds of your window so that only the non-performing section of the window is replaced, preserving as much character as possible and providing a more cost effective solution than a full window replacement.

Fully Replacing Windows and Doors

For those aluminium or timber windows which need fully replacing, Thermalframe windows can be installed into all cladding types and can achieve the customer’s desired look.  A simple, clean design is often desired when replacing aluminium windows and replacing all of the original timber surrounds can also be done with our window system.

Our consultants will be happy to discuss all of these options for replacing your windows for your home.  

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5 Facts to consider when double glazing

If you are considering double glazing your home, here are some important facts:


1. Non-conductive window frames greatly impact double glazing performance

Aluminium is highly conductive and a poor insulator of heat. So conductive in fact, that even if  double glazed, condensation often forms on the aluminium frames, as moist air looks to deposit itself on the coldest surface. 

Double glazing using aluminium compared to non-conductive Thermalframe PVCu frames will experience up to twice as much heat loss, even with the same glazing composition. 

2. Double glazing is not just about two pieces of glass, but rather the gap between the insulated glazing units that counts

The optimal gap to derive benefit from double glazing is between 14-16mm between the two panes of glass. Anything less than this increases the incidence of heat transfer, and anything greater can create convection within the units. Retrofitting solutions are unlikely to provide the necessary 24mm glazing cavity required to support the optimal spacer gap between the 2 sealed panes of glass. Thermalframe is specifically designed to support optimum spaced double glazed units.

3. Seal technology greatly impacts air and water leakage

The seals within the window system greatly impacts air leakage which compromises thermal performance and water penetration. Thermalframe has a co-extruded seal system that is welded to the frame and each other in the corners to eliminate any potential leakage.

4. A multi-point locking system delivers more than security

Thermalframe multiple locking points shoot bolts across the entire length of the windows. This allows sashes to be almost vacuumed tight against the outer frame, vastly improving thermal performance and sound insulation.

5. Fusion welded mitre corners prevent water leakage

All Thermalframe units feature fusion welded mitre corners that to ensure no mechanical separation and completely eliminate the possibility of water leakage at these joins.