When thinking of the insulation of your house, it is important to consider all the areas where heat can be lost, and not just to look at the attic. In this section, I have tried to cover all the main problems associated with loss of heat.

It is also important to note that lack of insulation may affect your receipt of FITs for generated electricity.

The government considers that it is essential to have 10inches (ca 250mm) of insulation on the floor of the attic, before one gets a grant to help with the installation of any form of Renewable Energy - some door to door salespersons are stating this at 11inches (270mm)! I am currently trying to get a definitive answer as to the rating that DECC actually require. All insulation materials differ in their insulation properties, and 1inch of one, may be equivalent to 2inchs of another; it all depends on the thermal conductivity i.e. how much heat the material lets through. For the units and how to work out your level of insulation see Insulating Materials below.

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Air Circulation

Although it is essential for health to have movement of air through a house, it is essential not to lose the heat that costs so much to provide; and this is where insulation comes in. Equally important therefore, is a ventilation system that does not lose heat from the building in the winter, yet can cool the domestic or commercial property in the summer. Specialized companies are very experienced in dealing with these problems. Ideally the warm out-going air will heat the cold air as it enters the roof space. Being cool it will fall and could conceivably be piped through the attic to the ground floor, thus being considerably warmed before starting its circulation through the house. Air circulation is essential to avoid problems with condensation and it is said that 25% of the air in a house should be exchanged per hour. NB. a draughty house is likely to have an air exchange rate of 4+ the volume of air per hour. Monodraught is one of the companies specializing in providing natural ventilation and lighting solutions for your property. The U-value of such systems is 2.18W/m² according to Nottingham University.

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Hot Water Systems:

The first consideration needs to be how best to retain heat in hot water cylinders, tanks and piping. Invariably the modern Water Cylinder is encased in foam insulation. If not lag it with the same type of insulation matting that you are using in the attic/loft and while doing this wrap strips of the roll around any exposed pipe work and its joints. Many houses now have pipes forming a network about 1foot (30cm) above the floor beams of the attic; these have been partially covered with preformed, push on, fixed lengths of polystyrene that leave a narrow gap along the underside of the pipe and leave gaps between the lengths and around all the bends. To do a good job remove these gappy lengths and lag the pipes properly by winding strips of insulation material around them and the bends. Better still, if you have the luxury of designing a new/refurbished house, revert to the older, more sensible practice of using gravity to feed kitchen and bathroom from a single lagged hot water tank in the attic. Radiators can be linked in series - with by-passes to allow them to be turned off when not required - and the lagged pipework can be placed behind the skirting boards, or under the floor boards. In old houses, pipework is always so placed and organised so that the lifting of one floor board reveals the length of the pipe.

The walls of the house and plaster, may be nearly as warm as the rooms, but will be a lot colder than the water that has just been heated and then travelled through the house to the bathroom or kitchen; this is where most of the electricity for water heating is lost. The other prime site of heat loss is the hot water tank in the attic where the lagging is frequently inferior, if only because the shape of the tank is highly variable and it is difficult to get a good fit all around. Even if the sides and top sport a padded covering, it is common to find that the underneath of the tank is completely uncovered.

Windows and Doors:

Having checked the hot water system, these are next. Double-glazed windows may seem impermeable to draughts on a warm summer's day, but in mid-winter the reality can prove to be very different. I have personally found that icy blasts emanate from the odd corner or a bit of cracked infill where the installer has done a quick job; plaster brakes off very easily when the installers are trying to fit new windows into an older house. These can usually be blocked by the use of a commercial plastic sealant, but flexing due to vibrations and temperature changes have reduced the lifespan to <4 years in my current home. Putty and wood formed a much more solid and inflexible solution, that with occasional maintenance lasts over 30 years. More difficult are the occasional holes at the corners of the glass panes. These are caused by poor manufacture of the windows, so that the bedding strips into which the glass is fitted do not stretch flush into the corner of the frame; hence the wind whistles in. Here either a sealant or even blue tack can be used to cure the problem, if it is not known which Double Glazing firm is at fault. Double-glazed doors are a worse problem as the plastic frames are frequently very flexible, and the plastic fractures easily, but sometimes a sealant can be squeezed into gaps in the frame. Original wooden doors in wooden frames are easier, since the frames are always properly fitted and cemented in place, while there are many proprietary draught excluders available to tack or stick into place around the opening.

Traditional housing on the continent invariably uses wood or metal for window frames, and sports a double window i.e. both inside and outside windows can be opened independently of each other. In central Europe, the inner and outer windows are separated by the width of the window sill; and the space is frequently used to house plants - like a mini greenhouse. Here too, the glass used is of the same thickness as that in a normal single pane window, and not the extremely thin variety used in the plastic double-glazed windows used so much in this country.

Roof space/loft/attic

Materials used for this are usually of the fibrous mat variety that one buys in rolls. However, in many cold countries the insulation is fixed to the rafters, directly under the tiles/slates etc. In this position it is more usual to use a semi-rigid material or batt. This means that it is easily removed to gain access to any storm damage to the roof. In the section below on Insulating Materials I have given: information on some of the characteristics of the materials; the thermal conductivity of a variety of materials that are available; and how to convert thermal conductivity values with thickness into R-values,

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Insulating Materials

Of these the only truly renewable/sustainable type is sheep's wool - a natural product made by felting the wool and treating it to prevent attack by moths. It can be easily cut into all shapes and sizes of block to insulate the underside of your roof; or the floor of your attic.

The rest of the insulation materials are all either man-made, or involve considerable processing before use e.g. cellulose; polystyrene; polyurethane; glass wool; rock mineral wool; recycled plastics; or a range of spray foams.

Those that are made from recycled products are yet another excellent way of re-using a waste material that has in the past gone to Landfill. Being a bit sceptical that a hot flame might cause the recycled plastic insulation to convert to a hot sticky liquid plastic, I tested a piece over the hottest flame of a gas cooker. To my relief its form did not change, it became rather black looking, but did not even smell, results that assure me that it is as safe to use as the manufacturers state.

Ratings for Insulation All these materials are sold by the roll/block/sheet/batt and most will have a figure indicating their Thermal Conductivity which is stated as a U-Value (sometimes stated as a lamda value or even k-value!). This is expressed in watts/metre.Kelvin (temperature scale introduced by a British physicist whose degrees are the same 'size' as Centigrade degrees, but whose 0° or Absolute Zero is equivalent to -273.16°C). This is usually accompanied by an R-Value, which is a statement of the resistance of the material to the passage of heat. So. . . .

thermal resistance (Km²/W); = thickness of the material (metres) divided by the thermal conductivity (W/mK).

In the UK the thermal resistance should be stated as an RSI-Value, but we seem to have shortened this to R-Value which makes it look the same as the American unit. So for the purposes of the following calculation, I will state the R-values as RUK and RUSA e.g.

for 1 inch thick Fibreglass insulating board: the thickness in metres is 0.0254m (equivalent to 25.4mm); and the U-value = 0.048W/mK.

Therefore, RUK-Value = 0.0254/0.048 = 0.529Km²/W

The RUSA-Value = 0.529 x 5.678 = 3.0046

One of the sites that explains all these matters

Hopefully this explains what the units should be and how to convert from one to another. In the shops, there does seem to be some confusion as to what the rolls are labelled. The variety of ratings used suggest that whether the label states U-values, k-values or lamda-values; these seem to be used synonymously with the U-Value - I have even seen a W-value whatever that meant; however, they all seem to give the same value for the same material. So look for one of the recognised units mentioned under Ratings, above. Basically, whatever the unit, it is a representation of the amount of heat that can travel from one side of the insulation material, of given thickness, to the other. Thermal Conductivity can be defined as the energy loss in Watts through a piece of the isolated and sealed insulating material, and is equal to the temperature difference (°K) x area (m2) / thickness (m). A discussion of Thermal Conductivity and its units can be found at

List of some insulating materials with their thermal conductivities (W/mK) - some good conductors have been included for comparison!

Air = 0.024; Argon = 0.016; Brick work = 0.69; Copper = 401.0; Cork board = 0.043;

Fibreglass insulating board = 0.048; Glass window = 0.96; Glass Wool insulation = 0.04;

Hair Felt = 0.05; Kapok insulation = 0.034; Mineral Wool insulation = 0.04;

Paper = 0.05; Plaster & Wood lath = 0.28; Polystyrene expanded = 0.03;

Recycled Plastic Bottles = 0.044; Rock Wool insulation = 0.045; Sawdust = 0.08;

Snow = 0.05 - 0.25; Straw insulation = 0.09; Water liquid & vapour = 0.58 & 0.016;

Oak = 0.17; Softwoods = 0.12; Wool Felt = 0.07.

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Top Tips new and used

  • Light in the darkness! How lovely to have bright summer light illuminating our homes once again. However, by fitting a Sunpipe through your roof, you could have a lot more daylight and sun reaching the darkest corners even in the winter. These are flexible, water tight and can be fitted to any roof. Being an air filled tube sealed at both ends they are pretty well insulated anyway. However, they are also fitted with an insulated screen that can be moved across for further insulation on dark winter nights. For further information click to Energy Saving/Building related & Other.
  • Salesmen selling insulation for cavity walls are everywhere at the moment. However, it is worth noting that in the 1980s Building Regulations have required all new houses to have cavity wall insulation incorporated in the build. This takes the form of either: rigid foam boards; or semi-rigid mineral wool or fibreglass batts (the fibres are aligned vertically to shed water to the bottom and protect the inner wall). These are fixed to the cavity side of the inner wall and all must still leave a gap between the insulation layer and the outer wall. It is important that this gap remains clear, since its purpose is to prevent driven rain, soaking through the outer wall and reaching the inner wall, thus causing dampness in the house.
  • If a cavity wall is filled with dry blown fibres, these will settle by 20% - no matter what the salesmen tell you - forming a denser layer that may very well bridge the gap. If this becomes wet, due to driving rain soaking the bricks, then the water will be conducted to the inner wall and so through to the interior of the house. The wet insulation can be mostly removed by vacuum, but this is yet another expensive operation. If approached, think carefully; and if necessary check whether it is right for your house, by consulting a trusted builder, before you agree to anything.
  • Need to get more insulation? First experiment with 1 or 2 Max. and Min. thermometer(s). Note the maximum temperature reached in a sunroom that is double glazed except for the roof, or any room without double glazing, and then note the minimum temperature reached when it cools down over-night. Repeat the exercise on a similar day (weatherwise) in a room whose double glazed window(s) are shut and face the same direction. From these basic 4 readings you will note that the max. temp. reached in the sunroom is much higher than that in the other room, and usually the min. temp. will be lower. Some heat will be lost from the other room by people entering and leaving the house, but in general the other room will have an overnight heat loss of 1.5 - 2.5C° whereas the sunroom with undouble-glazed roof will reach 10+C° higher and will cool to the outside night temp. For comparison my readings for the sun room and the other on the same day were 34°C and 24°C with a min.temp of 21.5°C in each.

Please mention TigerGreen whenever you contact any of our linked Top Providers, Suppliers and Contractors.