Mint Plumbing & Heating

Loft Insulation Insulating your House

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Loft insulation is one of the quickest and easiest ways of saving energy and money. Up to 25 per cent of all the heat lost from the average home is lost through the roof. Good roof insulation will make your home feel warmer, whilst reducing your energy bills. This is good for your pocket and the environment. The simplest way to reduce heat loss is to lay insulation between the joists.


When working in the roof space of your house, it is good practice to wear protective clothing. Some of the materials you will need to handle could be an irritant to both skin and eyes; it is therefore a good idea to wear overalls and gloves, goggles and a dust mask. It is also a good idea to wear protective headgear due to the low beams. You also need to remember that unless your attic has been boarded out properly, you can only stand on the joists. Standing between them will almost certainly result in a hole in the ceiling below, and also possibly a broken leg/arm/neck. Use strong boards or planks in the area you are working.

Insulation Materials

There are several different kinds of material you can use to insulate your roof. In almost all cases, the recommended depth is 200mm (8in). However, this might not be possible in some cases if, for example, the joists are not deep enough.

  • Loose-fill Insulation
    Loose-fill insulation such as Vermiculite comes in bags and is very simple to use. You simply pour the insulation granules between the joists and level it off by scraping a flat length of wood along the top of the joists. A dust mask and goggles are essential if using this material, as it is often pretty unpleasant to work with.
  • Blanket Insulation
    This is probably the insulation of choice in a large percentage of homes. Blanket Insulation is rolls of glass fibre, mineral fibre or rock fibre, which is laid between the joists. Check the spacing of your joists before buying the blanket insulation as it comes in a variety of widths. Rolls are usually 6 to 8 meters in length. If a length is not long enough to fill a complete gap, make sure you butt the two pieces together well. Also be sure to wear gloves and a mask before handling blanket insulation material, as it can be an irritant.
  • Slab Insulation
    This is basically the same as blanket insulation, but comes in large slabs rather than rolls and is often more dense. As with blanket, slab insulation comes in a variety of widths to fit different joists gaps. You can also buy extra high-density slabs, which can help with sound insulation. Simply lay the slabs into the gap between joists and cut to fit as necessary. As with other insulation types, wear gloves and mask to avoid irritation.
  • Extra Insulation
    As well as placing insulation in the gaps between the rafters, you can also attach insulation directly to the roof rafters. The easiest and cheapest way to insulate your roof is to insert sheets of polystyrene between the rafters. You can buy sheets of polystyrene in a variety of thicknesses and sizes, and it is quick and easy to work with and fix into place. Once you have bought your polystyrene sheets, hold them up against the rafters and cut them to size to fit in between them using a sharp knife. As you fit the polystyrene, remember to leave a gap at the eaves and ridge to allow air to circulate or you could create more problems than you solve.

    The polystyrene sheets can be held in place with simple nylon garden netting if you wish, or you can fix sheets of hardboard over the top. Whichever method you choose, be careful not to use long nails or you risk dislodging tiles and creating a real problem. Use a staple gun to attach netting or short screws to fix the hardboard in place. If you want to add an extra layer of insulation you can use foil-backed plasterboard to hold the insulation in place (with the foil facing outward). This should be attached using drywall screws driven carefully into the rafters.
  • Foam Insulation
    It is possible to have your roof insulated with expanding insulation foam. This foam is sprayed on to the underside of the felt which is laid under the roof tiles, or even onto the roof tiles themselves (this can also help if your house suffers from nail fatigue in the roof). You can buy DIY kits to do this work yourself, or there are numerous specialist companies which will do the job for you.
  • Thermal Insulation Foil
    You can buy rolls of insulation foil which can be fitted between the rafters or nailed on top of them. Thermal insulation foil is easy to install and quite effective at reducing heat loss. Products such as Thermawrap claim to offer the same amount of insulation in a 4mm layer, that a 55mm layer of polystyrene would offer.

Flat Roof Insulation

Flat roofs should be insulated at the time of construction, so if you are having a flat roof built, make sure that it is included in the plans (and the price). If your flat roof does not have insulation, you can still add some by removing the fascia board and accessing the space between the ceiling and external lining (the fascia should be screwed or nailed to the ends of the joists).

Once you have access to this space between the joists, you can cut lengths of polystyrene insulation board to size and slide them into the gaps between the joists. Use 50-75mm insulation sheets and remember that you will need to add ventilation above the layer of insulation by drilling through the fascia and then fitting insect screens over the holes. This ensures airflow into the roof void and will help keep the joists dry.

If you cannot access the ceiling void by removing the fascia, you can add insulation by lining the ceiling with a layer of thermal board. If you want to add insulation to the outside of a flat roof which does not have fascias, you will need to lay sheets of expanded foam insulation on top of the roof and seal them with a permeable geotextile membrane. A layer of gravel on top of this will help to protect the membrane and hold it in place. This is not a simple task however, and you should consider contacting a professional if this is your only option.

More Insulation Ideas

  • Lagging Pipes
    Taking the time to add Lagging to exposed pipes in the loft can save a lot heat-loss and reduce the risk of pipes freezing and bursting in cold weather. You can buy foam pipe lagging, in various thicknesses, reasonably cheaply. This almost always comes with a cut all the way along one side, allowing you to simply slip it over the pipe. Butt pieces together and join with strong adhesive tape.
  • Hot Water Tank
    This is not always found in the loft, but the same advice applies. Hot water tanks need an insulating “jacket” made of mineral fibre wrapped in a plastic coat. This is fitted around the hot water tank and held in place with straps.
  • Green Roof
    If you need a complete insulating solution, a green roof might be the best one. It consists of 6 to 8 different layers of roofing materials to provide perfect insulation and ultimate environmental behaviour. It will not only stop water and humidity entering the concrete, but it is an extraordinary UV rays barrier and also provides excellent heat and noise insulation. Environment Canada found that a green roof can save up to 25% of summer cooling energy needs.

Insulation Tips

  • Leave the space under the cold-water tank free from insulation material. Warm air rising through the ceiling can help avoid the water freezing in very cold weather.
  • Remember to insulate the back of the access hatch. This can be fixed with tape or glue around the edges.
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