Technical Information
Window Performance.
The performance of glazing elements is measured by measured by its U Value. The lower the U Value the better the performance.
To comply with current Building Regulations the average elemental U Value of external doors, windows, and roof lights should be 2.2 or less.
Norman Pratt windows offer window systems, which exceed the performance requirements of the currant Building Regulations.
Window U Value Code Dwelling Rating (indicative)
.9 or lower R1 Passive house
1.4 to .9 R2 A Rated
1.7 to 1.4 R3 B Rated
2.2 to 1.7 R4 C Rating
When shopping for windows look for high performance windows which have Low U Values. Units must offer good durability and materials, while meeting your design and budget requirements. Norman Pratt Windows offer a variety of new technologies and thermal improvements to reduce heat loss and condensation problems.
•Low-emissivity - Low-E coatings applied to interior (or exterior) glazing surfaces which reduce the radiant heat losses and can be used to control solar gains.
•Insulating, inert gases (like Argon or Krypton) between the window panes reduce convection heat losses.
•New insulating spacers and low-profile insulating frames combined with better air sealing on opening units, have improved solar gain while reducing air leakage and conduction heat losses.
•Low-E coated films made of thin polyester or plastic between two panes of glass provide lighter weight, high performance, multiple-glazing units.
Windows have a great impact on the energy efficiency and comfort levels of a home. Windows can account for 30 to 40% of the heat loss or heat gain. In an energy efficient home the overall energy performance of a window unit in a cold climate depends on the glazing (glass or sealed unit), window style or type, frame and sash materials, air leakage, installation and the use of interior coverings or exterior shading devices.
Low-E window units can reduce the UV portion of sunlight that causes the damage by 60 to 90% while still admitting visible light.