The single best way to make your home consume less energy is to insulate it, before you even consider replacing the windows.
The first step to adding insulation to your house is to find out how much you already have. In ROI a Building Energy Rating assessor (list of accredited assessors https://ndber.seai.ie/PASS/Assessors/Search.aspx ) and in NI an Energy Performance Certificate assessor (list of accredited assessors https://www.epcregister.com/searchAssessor.html ) will visit the house to determine what’s there based on the year of construction and a site survey. This person will then supply a report explaining what level of insulation there is and what you can do to further insulate your home.
Unfortunately, it is not a simple matter of increasing insulation thickness and getting the same increase in performance, this is only true up to a point and this is where you will start weighing in the cost of adding more insulation.
There is an optimum thickness for each type of construction based upon not just the performance of the material, but also the space available in the wall, roof or floor. Once this has been determined go for the best possible U-value within reasonable cost.
The U-value is the metric that shows you how well insulated your house is. It takes into account the entire build up of the wall, from the plasterboard to the external finish.
In technical terms is calculates the combined thermal conductivity of all the components, and thickness of each, to give you a measure of how well the building element reduces the exchange of heat between two areas.
The lower the overall value the better the build-up is at keeping the heat in and insulation is what most reduces this number.
Airtightness and ventilation
Insulation only works if it is continuous, i.e. there are no gaps in the insulation layer. Insulation that is not correctly installed, with gaps in-between, will never perform to its best. Boards for instance should be held in place by stainless steel wall ties, usually covered by a plastic disc, against the inside of the inner leaf, when batts or boards are being used in a partial cavity wall.
The ties should be kept clean of mortar as this could cause moisture to travel from the outside in. If the insulation is blown in post construction, it should be evenly dispersed throughout the wall cavity with no gaps.
Once the insulation is in place and installed correctly new builds will add an airtightness membrane. Airtightness is an air leakage measure; weak points are usually found at openings, e.g. around windows. Where such a vapour barrier or vapour check is used, this should always be to the warm side of the insulation to prevent condensation.
A crucial aspect to bear in mind if you plan to upgrade the energy efficiency of your home is ventilation. The more you seal off your house the more you need fresh air to make sure the indoor air quality remains high. If you insulate to the hilt, you will need to tackle your ventilation requirements and oftentimes this will require that you add mechanical ventilation.
Note that if you’re building new you can build insulation into the structure itself.
One method is known as SIPs, which stands for Structural Insulated Panels. These are formed like a sandwich of two boards, usually OSB (Oriented Strand Board) or plywood with a ‘filling’ of insulation, normally EPS, XPS or PUR. All the openings for windows, doors and services can be cut in the factory and the panels delivered to site with the frame of the house erected in a matter of days.
Using a similar idea, only inside out in a sense, is Insulating Concrete Formwork whereby a shuttering of expanded polystyrene is erected and concrete poured into the ‘mould’. The double layer of polystyrene results in U-values ranging between 0.31W/sqmK (EPS) and 0.26W/sqmK (XPS) which can be increased with the addition of insulated plasterboard on the internal leaf.
The most common types of insulation can be categorised as being in rigid or roll form. The rigid forms tend to be boards used for walls, floors and as the backing on insulated plasterboard (the latter often PIR), and those in roll form are more commonly used in roof spaces because they can sag when left upright.
Mineral wool is generally considered the most cost effective and is made from molten glass, (glass wool) or stone (stone wool with superior acoustic qualities), spun into fibres and delivered in roll form.
For the same thickness you will however get less insulation from mineral wool than rigid boards made of plastic compounds which include the polystyrene and phenolic families.
Expanded polystyrene (EPS) also comes in bead form and is a common way to insulate cavity walls by pumping them between the inner and outer leaf. EPS is made with trapped air in beads and has a thermal conductivity in the same range as sheep and mineral wool with some modified types achieving better values. The incorporation of minute particles of graphite throughout the polystyrene gives a performance that is 15 to 20 per cent higher.
Extruded polystyrene (XPS) is formed by forcing the polystyrene through a die which closes the cells and is thus denser than EPS with better insulation values.
Polyurethane (PUR) and polyisocyanurate (PIR), meanwhile, are either sprayed on or come in boards, and are often made with a blowing agent.
Phenolic insulants are normally produced in rigid board form and are amongst the best insulators because of their fine cell structure.
Foil insulation is less commonly used, and most certified products require that it be used alongside other insulation types such as PIR.
Eco alternatives include sheep’s wool and recycled newspaper, cellulose and wood fibre. These are often treated with inorganic salts, (usually boron), to provide resistance to fire, rot and pests. Sheep’s wool comes in roll form, the others loose fill. Cellulose and wood fibre also come in rigid boards.
Calcium silicate boards are an alternative for period properties and can be installed on the walls directly.
Hemp can be mixed with lime to make walls and plaster, cork can be used with clay for plasters. Hemp is also available in semi rigid boards, pre-cast blocks and as part of proprietary eco building systems.