Introduction to warmer

‘Measuring carbon footprint’ and ‘becoming more sustainable’ are phrases that we hear with greater regularity. There is also growing importance of good to high EPC (Energy Performance Certificate) ratings, to ensure buildings meet acceptable standards for letting and also enhance their market value. High energy prices have put budgets of all sizes under strain and  longer term indicators suggest that energy prices will remain high. Our buildings also account for more than 40% of all carbon emissions so any method of reducing this through controlled measures or improved insulation is very desirable. 

One way to cut down on draughts and keep heat within is to create a second barrier to the elements from the inside and install secondary double glazing.

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Warmer

Benefits of secondary glazing for thermal insulation

  • Reduces heat loss
  • Minimises draughts
  • Increases the rating on an EPC (Energy Performance Certificate)
  • Improves comfort

  • Reduces energy bills
  • Reduces air infiltration
  • Assist with BREEAM ratings
  • Meets heritage guidelines

Guidance and regulations

Approved Document L:

Part of the building regulations, it sets strict standards of energy efficiency for new buildings, renovations and upgrades. Secondary glazing is not covered by Part L except for use in heritage buildings where projects come under building control regulations.

Window Energy Ratings:
The British Fenestration Rating Council (BRFC) scheme assesses the performance of the whole window. Rating is based on thermal loss from the glass and frame, air leakage and solar heat gains. Secondary glazing is not assessed through this scheme as the outer windows construction will always be different.

EPC:
An Energy Performance Certificate identifies the performance of a building and provides recommendations for improving the energy rating. These are required when a building is constructed, sold or rented under the European Union’s Energy Directive.

U-value:

U-vlaue is a measure of heat loss in W/m2K and shows the rate of heat loss per square meter of material, the lower the figure the better the insulation. As secondary glazing is used in combination with a wide variety of primary windows, U-values are calculated using modelling software.

g-value:
g-value is the solar factor of a window expressed as a number between 1 and 0, where 1 indicates the maximum solar gain and 0 equals no solar gain.

The warming effect of high g-value windows can be a benefit in winter but a problem in summer months. Generally high g-value is beneficial in cooler climates and lower g-value in warmer climates.

U-value performance

  Timber Primary & Secondary Unit with 100mm cavity Metal Primary & Secondary Unit with 100mm cavity
Product 6mm 6mm low-E 4-12-4 Sealed unit low-E 4-12-4 Sealed unit low-E & Gas 6mm 6 Low-e 4-12-4 Sealed unit low-E 4-12-4 Sealed unit low-E & Gas
S10 2.629 1.807 - - 2.911 1.936 - -
S20 2.617 1.802 - - 2.897 1.930 - -
S30 LO 2.585 1.787 - - 2.858 1.913 - -
S40 FL 2.574 1.781 1.517 1.435 2.843 1.906 1.606 1.515
S40 SHC 2.581 1.785 1.676 1.627 2.852 1.910 1.786 1.731
S40 DSHC 2.588 1.788 1.865 1.832 2.861 1.914 2.003 1.964
S45 FL 2.575 1.782 - - 2.845 1.907 - -
S45 SHC 2.576 1.782 - - 2.846 1.908 - -
S45 DSHC 2.585 1.786 - - 2.857 1.912 - -
S46 FL 2.579 1.784 - - 2.850 1.910 - -
S50 FL 2.602 1.795 1.549 1.469 2.879 1.922 1.643 1.553
S50 SHC 2.589 1.788 1.758 1.700 2.862 1.915 1.879 1.813
S50 DSHC 2.598 1.793 1.966 1.927 2.874 1.920 2.120 2.074
S55 SGL 2.612 1.800 - - 2.891 1.927 - -
S55 2H 2.633 1.809 - - 2.916 1.939 - -
S60 2.639 1.812 - - 2.924 1.942 - -
S80 2HS 2.64 1.81 - - 2.92 1.94 - -
S85 2HS 2.70 1.84 - - 3.00 1.97 - -
S90 2.615 1.801 - - 2.894 1.929 - -
S95 2.698 1.840 - - 2.996 1.974 - -