Secondary Double Glazing for Insulating Windows
If your windows are single glazed, then installing secondary glazing will upgrade them to modern window insulation standards.
The secondary windows will also provide you with additional benefits:
- Reduced heating bills
- Much cheaper than replacement double glazing
- Improved Energy Performance Certificate
- Window draught proofing
- Condensation on windows resolved
- Increased Security
- Decreased noise
- Retains the Character of Traditional & Period Windows
So, if an existing single glazed window is not in need of replacement, you can gain all of the insulation benefits of double glazing with a discreet secondary window.
Energy Insulation Values
The window insulation energy standard is expressed as the U Value.
The U Value measures the Heat Loss through a window.
The Lowest U Values provide the Best Levels of Window Insulation.
Exact figures depend upon the type and condition of each individual window, including things such as:
- Frame material
- Glass thickness
- How well the glass is sealed to its frame
- How well opening casements are draught proofed and sealed to the main frame
- If sealed units, glass type, cavity and air or gas filled
- If secondary glazed, glass type & cavity/reveal depth
The following chart shows the Typical Average U Values of the most common single glazed, sealed unit double glazed and secondary glazed windows:
Typical U Values
|Frame Type||Glazing||Glass||Cavity Fill||U Value|
|Metal||Single + Secondary||4mm Float||Air||3.20|
|Wood||Single + Secondary||4mm Float||Air||2.75|
|Wood or PVC||Double||4mm Float||Air||2.70|
|Metal||Double||4mm Low E*||Air||2.60|
|Wood or PVC||Double||4mm Float||Argon Gas||2.75|
|Wood or PVC||Double||4mm Low E*||Air||2.25|
|Metal||Double||4mm Low E*||Argon Gas||2.25|
|Wood||Single + Secondary||4mm Low E*||Air||1.80|
|Wood or PVC||Double||4mm Low E*||Argon Gas||1.60|
* Low E is low emissivity glass – an energy efficient glass that prevents heat escaping from within a building through the windows to the outdoors.
Installing Secondary Double Glazing Reduces Heat Loss & Saves You Money on Energy Bills.
On average, installing secondary double glazing for thermal insulation will reduce heat loss through the windows by between 60 and 70%.
This will result in both:
- a more comfortable ambience, warmer & no draughts
- in you being able to turn down the heating
You’ll see a corresponding saving on your energy bills.
Based upon the Government’s (2016 to 2017) annual Housing Survey, you can expect to save, in an average sized property type:
The above figures assume that you fit secondary glazing to all the windows throughout the property.
Over the years, the energy cost savings will help to offset your capital outlay.
Energy Performance Certificates (EPC)
Energy Performance Certificates (EPC’s) have been with us now since 2007.
Anyone selling a property has to provide an EPC, which will show an overall Energy Efficiency Rating for the property, on a scale from A (good) to G (bad)
Landlords & Tenants
Since 1st April 2018, landlords have been required to achieve a minimum rating of E on the EPC for new lets and tenancy renewals of their rental properties.
Existing tenancies must become compliant by 1st April 2020.
Secondary glazing provides an excellent and cost-effective improvement to a property’s EPC.
Additionally, the installation of secondary windows benefits tenants by:
- Reducing energy bills
- Reducing outside noise
- Increased comfort – draught proofing & warmth
- Increased security – additional glass barrier & internal catches
- Any condensation on the windows eliminated
And benefits landlords by:
- Increasing rental values
- Decreasing tenant complaints
- Extending tenancy renewals
We provide our services to a large number of private landlords, letting agents and property management companies, as well as direct with tenants – and can provide references upon request.