Insulating your loft is often quoted as the top thing which you can do to improve your home’s energy efficiency. Many homes may already have some level of insulation, but guidelines have changed over the years, and it is certainly worth taking a look to see whether you could top up what is already there, or ensure that it has been correctly installed.
Current building regulations for new builds require a minimum depth of 270mm of mineral wool or similar insulation (the depth required for the same effect will be less if you are using rigid board insulation). For pitched roofs without any insulation already installed, you will need to decide whether you want:
- a warm loft in which insulation is installed directly under the roof in the plane of the pitch. This means that you will be heating a larger volume, but will allow you to use the loft for living space or storage without worrying about cold/damp
- a cold loft, in which the insulation is installed between and over the wooden joists immediately above the ceiling of your home’s top floor.
A variety of materials is available:
- Mineral wool – is the best value and most commonly used material. Normally a layer is rolled out between the joists and a second layer is rolled out at right angles on top of this.
- Thermafleece – natural insulation made from wool or hemp which is more sustainable. Note that wool must be correctly treated as it can harbour moths.
- Space Blanket – a premium product where the mineral wool is encapsulated in a part metallised polythene film. The encapsulation avoids irritation from mineral fibres, while the metallised surface helps reflect the heat.
- Rigid Insulation board – the most common brand is Celotex, which is a plastic foam. This provides the same level of insulation for half the thickness.
For many lofts, insulation may be a DIY job- if using wool, you will need to fill between the joists before laying a complete layer over the entire surface. It is important to leave some space around the eaves for ventilation, and also to remember to insulate any pipework and water tanks, as the cold space created in the loft could lead to pipes freezing. However if you have a cold water tank, don’t put insulation under it. Instead fold the insulation up around the sides of the tank at the bottom and then wrap the tank jacket round the tank and over the top of the ends of the insulation to form a draught proof seal.
In addition you need to be careful about leaks of hot air and moisture from the house into the cold loft, which can cause issues with condensation and rotting of timbers.
If your roof space is hard to access, you can get a professional company to blow in loft insulation. For loft conversions, you may decide to use rigid board insulation on the inside of the roof, rather than the loft floor.
- Don’t forget to insulate on the top of the loft hatch, and to draught-proof around the edges.
- Remember to look also for any smaller areas of uninsulated roof and sections of internal walls which are adjacent to unheated roof space or garages. In older houses with more complex layouts, this may involve using a number of different types of insulation.
Judith installed loft insulation herself, topping up a previous layer with standard DIY rock wool material from Wickes. She has a loft ladder so this was a fairly easy job, especially as the rolls came with clear instructions. The central area of the loft was boarded over the previous thinner layer of insulation and she had planned to do something about it but an LCON thermal image (part of the pilot using the camera) revealed that this wasn’t necessary.