Whilst more efficient plant and better insulation can make a significant difference to the energy performance of a building it is less well known that unintended air leakage and uncontrolled ventilation usually accounts for the majority of energy losses.
In traditional and historic buildings the big wins can often be in the area of air leakage rather than thermal insulation.
When insulating the fabric of any building it is important to consider some potentially serious knock on effects. Installing insulation can encourage condensation on the cold side of the insulation. We once dealt with a building that had a good layer of insulation on the ceilings but above that was a very cold metal roof. When it rained water dripped through the ceiling and it was assumed that the roof was leaking. Actually the cooling effect of the rain and the moisture in the air meant that condensation was forming on the underside of the roof and dripping down in gallons.
The control of condensation becomes extremely serious in the case of lead covered flat roofs. Condensation is effectively distilled water and if it forms on the underside of lead it can result in destructive corrosion of the lead. Insulating masonry walls on the inside is also problematic as it leaves the walls cold and, again, there may be increased condensation that will render the insulation ineffective or lead to an increased risk of decay in built in timbers. The same applies to roofs. Good levels of insulation and limited ventilation can increase moisture levels in roof timbers.
Double glazing is often put forward as the ultimate solution to thermal heat loss and it is true that a lot of heat goes out through windows. However double glazing is usually difficult to install in existing windows and if it triggers the complete replacement of a window the payback on the investment is almost always derisory. Lesser and more cost effective solutions to heat losses at windows can include shutters, heavy curtains and draught stripping. Draught stripping of traditional windows can be particularly effective in preventing warm air from escaping or cold air from blowing in.