The issue is of particular interest to farm families living in older houses. By older, I mean anything from 30 to 300 years.

I’ve been in many lovely old stone farmhouses which have no effective insulation in the attic, no wall cavity or wall insulation and — just in case the bills weren’t high enough — a fine old, bare copper cylinder in a hot press which was the only warm space in the house. These houses were prevented from freezing in winter by a big spend on oil or electricity or by burning lots of anthracite or logs, etc, in kitchen ranges and open fireplaces.

Many of the farmhouses built 40 to 60 years ago are little better. They have minimal attic insulation which is now at the end of its working life. Typically, this would be fibreglass wool material which was laid to an original thickness of three to five inches, between roof joists. Material like this had a life of about 30 years at which point it flattens and shrinks, with areas of attic floor then becoming exposed.

These older and colder houses will get the best value from a spend on insulation. A good way to measure this is payback, which is how long it will take for the savings you make to cover the cost of carrying out insulation. Some rules of thumb are:

Insulating a bare copper cylinder in a hot press will cost about €15 to €20 but pay for itself in as little as three months. From then on, you’re saving money.

Insulating an attic which had poor or even no insulation will cost about €4 per square metre and typically pay for itself in three to four years. Savings will be even better a bungalow than in a two-storey house of the same internal square footage — the bungalow typically has twice as much roof area through which to lose heat.

Insulating the wall cavity of a 1,500ft2 house will typically cost about €1,200 and will pay for itself in about six years. Some of these jobs are simple, some require a professional.

Insulating an existing hot water tank falls within the DIY category. Insulating jackets can be bought in most local hardware stores. These are fitted around the tank and held in place by tape or laces, etc.

Jackets cost from €15 to €20 for a 30-gallon tank. If buying a new tank, go for one with insulation fitted in the factory — it’s a far better job.

Attic

The most important route for heat loss from your home is the attic. In a well constructed house, there are ventilation gaps at the edge of the roof to allow a small airflow of wind blow through your attic space. This is to prevent moisture building up and keep the roof timbers dry. But it means that the floor of the attic is the only barrier keeping in the heat in your rooms. It is not at all effective at doing so.

As the attic space must remain ventilated, in the majority of houses, insulation is placed on the attic floor to prevent the heat from getting up into the attic. When the job is done properly, the rooms will be warmer but the attic space will now be colder as it is no longer receiving heat from below.

Burst pipes

Unfortunately, every winter, many homeowners in Ireland insulate the floor of their attics only to then suffer water damage after pipes in cold attics freeze and burst. If the floor of an attic is insulated, water pipes in the attic space must be insulated by lagging, or in some other way to protect them from freezing.

In houses where the attic is used as a working or living space, a different approach is taken. The insulation can be placed against the sloping rafters of the roof. Now, heat is allowed to rise into the attic space but prevented from escaping through the roof. In these cases, ventilation must be maintained in the small space between the insulation and the roof rafters to prevent fungal attack. But airflow can usually be reduced in the attic living space so as to keep in heat.

Contractor

Many homeowners choose to insulate their own attic — look at the pallets of insulating material for sale in local hardware shops. A good contractor should do a better job and may not charge a lot more for their time and expertise. The cheapest and most popular insulation method is to unroll quilts of rock wool, glass wool or mineral wool insulation on the floor of the attic. Meeting the requirements of the 2002 building regulations requires 250mm to 300mm of such insulation.

The Sustainable Energy Authority of Ireland (SEAI) recommends that 400mm of mineral wool is probably optimal.

The insulation should be placed in two layers to minimise heat loss through the joists themselves. The normal procedure is to unroll the first layer between the joists and the second across the joists.

You must leave access to water tanks, pipework, electrical cables, etc. This can be done by making a walkway using timber planks, with insulation underneath. In these cases, or where storage area is required in the attic space, and a second roll across the joists is not possible, have the storage over a part of the house with less of a heating requirement, e.g. the bedrooms rather than the living room.

Make sure to leave the openings at the eaves unblocked since it is important to allow for ventilation to prevent mould or dampness occurring.

Another option is to have glass fibre, mineral fibre or cellulose fibre (i.e. recycled paper) blown into your attic by a professional between and above the ceiling joists.

Where you want to floor all or part of an attic for storage, etc, an option is to use high-density rigid foam insulation sheeting between the joists. A four-inch thick layer of these insulation materials is roughly equivalent to eight or nine inches of wool insulation. Flooring can then be nailed on to the joists without compressing this insulation.

Another option is to place insulation between the joists and attach a second network of timber across the joists, to lay insulation between them, and then floor across these new timbers.

Competition drives down insulation prices

Competition among hardware stores and online has driven down the price of attic insulation. So, 100mm mineral wool insulation can cost anything from €2 up to €4 per square metre; 150mm material €2.75 to €3.50 and 200mm material €4.50 to €5.50. The attic of a typical four-bedroom house covers about 70m2; a four bed bungalow double that area. Labour costs are extra.

Cavity fill, labour included, costs in the range of €5 to €7 per square metre. The more architecturally complicated the house design is, the higher the cost. A detached, four-bedroom farmhouse will typically cost €800 to €1,500 before any grant.

The cost of external wall insulation varies widely. A guide is €17,000 to €20,000 for a detached, four-bedroom house of straightforward design. Internal stud insulation again varies very widely; a guide is €6,000 to €8,000 for a detached, four-bed house.

Purpose-made 50mm lagging jackets for a small 10-gallon central heating tank in the attic sell for €8 to €12. A 30-gallon cold water storage tank would require three or four sets.