2010 Revision Of Document L of Building Regulations calls for complete window to be Window Energy Rated (WER) or have a U value of 1.6W/m2K.

Sealfast manufacture a wide range of Low E glass units to help with compliance to above.

Insulated Glass Units are manufactured the same as Double Glazed Units but have Low E Glass types are on inner pane to assist in the conservation of fuel and energy, with outer pane clear, obscure, tinted or self cleaning.