Installing Insulation to improve home heating systems

Whether you are more concerned to save money or running cost without loss of comfort, or to contribute to the urgent matter of conserving dwindling fuel supplies, the answer lies in insulation. It is not too much to say that it is more important than heating. If near-perfect insulation were possible, heating would not be required. Establishments such as the Centre for Alternative Technology at Machynlleth show how it is possible to save huge percentages of what might be considered normal household fuel bills, by a little planning in advance. This does of course include some planning in advance of building the house, a stage not available to everybody, but not to be neglected by anyone in that lucky position.

Insulation is a form of detective work, which to a large extent has been brought down to simple rules. Heat tries to escape, and the householder must find out where the leaks are, and stop them. We are by now fairly familiar with the tell tale, the house where snow does not settle on the roof in winter. The owner pays dearly to melt that amount of snow, and we all know that roof insulation would prevent it.

Roof insulation in the typical house or bungalow with pitched roof means insulation on the loft floor. It would take about twice as much, and a special rigid type, to insulate the pitched sides, though if the attic is brought into the occupied part of the house that is the way to do it. But if the attic is a place of dust and spiders then mineral wool or glass fibre, cut into widths to tuck cosily between the joists, is very suitable. It must not be laid under the cold water cistern, but may be carried up the sides and also tacked on to a wooden lid, as an extra precaution against the cistern freezing.

Vermiculite, a lightweight substance sold in granules, is another suitable material to be poured between the joists. After pouring it must be raked level.

The thickness of any such layer must be decided. When the subject was first popularised, those who advocated it were pleased if they could get people to accept a one inch thickness. Then it went on to become the ‘economic thickness’, the amount you could put in and still recover the cost within reasonable time. It should be understood that the thicker the insulation the greater the saving, except that the benefits tail off a bit as the thickness increases. After all, if the first 50 mm save say 60% it stands to reason that the second 50 mm cannot do the same. For a time economic thickness dictated the use of about 65 mm in the south, up to over 80 mm in Scotland. That was before fuel prices soared. Now we may take it that a 100 mm blanket is a good economic thickness, and it is of course a much better proposition than the original inch.

But insulation must be properly installed. This means being well tucked in, and in particular not allowing the wind, which always seems to blow in under eaves, to get under it or under any part of it and so carry away heat.

Suppose that you have to fit your insulating material on the pitch of the roof, it is possible to cut rigid or semi-rigid materials to fit between the joists as you would do for the floor. That is not however the best way to do it. Instead, take whole spreads of material and fasten them to and across the joists, so forming a complete surface of the material, as you would if fitting plaster board to a ceiling. By doing it this way you get the extra benefit of the air space between the material and the slates: or you may use that space to tuck in a non-rigid insulating material such as recommended for the loft floor. Or yet again you may use a cheaper front board, such as hardboard, and backfill the cavity formed with the insulating material.

After the roof come the walls, whose importance to heat loss lies mainly in their area. There are various ways of obtaining some benefit, even for instance planting a line of trees which shelter the wall from a strong prevailing wind, for wind encourages heat loss. A more uniform way of giving outside protection to a wall is by some form of cladding, it might be timber in the form of tiles or barge board, or slate or tile hanging. While these are not themselves outstanding insulators, they encourage the formation of a layer of still dry air, which is. In putting emphasis upon both ‘still’ and ‘dry’ we underline important principles. Referring to dryness, wall treatment will be less than satisfactory for any wall which suffers either from an inadequate damp course or from excessive porosity of the bricks. The damp course is rarely a problem with newer houses, and can be inserted, physically, or by chemical or electrostatic processes in older houses which do not have one. But brick porosity is relative, and is encouraged by driving rain and by north facing. It is only moderately expensive to apply a colourless preparation which will act to seal the front face of the brickwork.

Most houses nowadays are of cavity wall construction, having a cavity of approximately 50 mm between the inner and outer leaves of brick or other building material. A ventilated cavity does not do much as an insulator, since it does not fulfil the condition regarding still air. An unventi-lated cavity is better from that respect, but does not always succeed in keeping the air still. If the cavity is wide enough there is room for an up-and-down circulation. The air in contact with the inner or warm wall will rise, causing the air in contact with the outer and cold wall to fall. The warmed air has to travel down the cold wall, where it loses its warmth, and in this way transfers indoor warmth to outdoors. Thus, good though air is at insulating, it is not as docile a subject as some solid material. This is where we arrive at cavity wall insulation, which in existing houses is injected through holes drilled in the wall and later plugged. The filling can take the form of a plastic material which after injection sets like a rubber sponge, being riddled with holes. It is the holes, which are not in contact with each other, which are still and dry and do the insulating, the plastic compound acting as a carrier for the holes.

The other type of material, used by Rentokil, is a mineral wool fibre which is blown into the cavity and packs it, doubtless with air entrainment. The plastic injection method can go wrong, for such reasons as having the wrong mix, and in spite of the great value of cavity insulation it is not cheap. Intending users would be well advised therefore to deal only with contractors who belong to the trade association, the National Cavity Insulation Association.

We cannot overlook walls in older houses which have no cavity but instead are perhaps 230 mm or 330 mm brick, but if we are to treat them by interior insulation it is even more important that they are not excessively porous. In the case of an inhabited house in normal use, with a single skin wall, the wall acts as a battlefield in winter. On one side is water trying to get in, and creeping through the pores. From the inside comes warmth to drive it out again; and somewhere about halfway, with luck, the battle reaches stalemate. The warmth has given up and become cold, but its efforts have halted the forward progress of the damp. That is why such a house, left empty for a few weeks, often shows damp on the walls, because no heat is being passed through from the inside. If we put insulation on the inside it will have the same effect, and damp can come right up to the insulation, unless it is checked at source. We have already described thermal inner linings when discussing warm air systems in a preceding post and there is nothing more to add.

The treatment of windows reached a ridiculous peak when it was taken up by people whose real interest does not lie within the heating industry. Anything with two panes of glass in it was and still is sold as double glazing for heat retention.

The ideal is still a sandwich of still dry air, which calls for a means of drying the air; and a sandwich width which offers a substantial depth of air but not enough to allow an internal circulation to set up, as we described happening in a cavity wall. The best distance apart for the two glass panes is in the neighbourhood of 18 mm. At that, the heat loss can be considered halved. The saving falls off somewhat as the gap decreases or increases, and by the time it reaches 100 mm it is much more useful as a sound insulator than for heat. Since the price of proprietary double glazed units is so high many people are tempted to make their own, by adding an extra pane of glass. The handiest method of drying the trapped air is to introduce a little silica gel, a dehydrating agent, into the cavity. If this is properly sealed there will be only the original moisture to remove, not a continuing amount.

Questions are raised about triple glazing, which is not uncommon in parts of Scandinavia where the weather becomes really cold. But the diminishing usefulness of the extra pane or panes is very marked, and considering the current cost of even double glazing it could not achieve an ‘economic’justification in this country. It should not be forgotten, though, that during the winter a good half of every 24 hours is darkness, and windows have no functional use. There is nothing to prevent us, then, from bringing in the equivalent of quadruple glazing, or more, for half the winter, by means of shutters, internal and external, by heavy curtains well tucked in, by any means we can devise to put a heat barrier across the gap in the brickwork.

The real importance of windows as a source of heat loss can often be exaggerated. In some houses they constitute a quite small proportion of the total wall area, and their greatest nuisance value comes from the condensation which forms on them. Double glazing, and of course the other steps mentioned, greatly reduce this. The greatest problem from windows comes to those who plan their homes with perpetual summer in mind, with great areas of glass as picture windows, french doors and the like. Almost prohibitive to double glaze, they can certainly do with ample heavy curtains. It is wise, when planning to incorporate such expensive items as large picture windows, to consider at that time incurring some additional expense and having double glazed units from the outset.

In the average house a quite surprising amount of heat is lost through the ground floor. In the case of a suspended floor this can happen in two ways: by conduction downwards and by the infiltration of cold air from below through gaps in floor boards. It should be remembered that a suspended floor must be kept well ventilated and no restriction placed on the access of air to it through the air bricks.

It will be apparent therefore that a solid floor offers more chances of success. It will not suffer from cold air infiltration, and during construction can have an insulating material built into it.

But for most people, who have to put up with what is provided, the first thing to do with a suspended floor is to stop up all the gaps through which air can travel. This may entail carpentry, or moderate gaps may be filled with papier mache. Another sealer, possibly in addition, is to clad the whole floor in hard board, wall to wall, sealing the joints with adhesive paper tape. Then in the case of suspended and solid floors, use floor coverings with a view to retaining heat; heavy quality underlay, and either good carpet or, if lino, then plenty of thick mats.

That deals with the top, sides and bottom of the box which effectively comprises any house, leaving the openings into that box, the doors and windows. To find a really well fitting frame to either door or window is exceptional, and again if the discrepancies are too great it may call for carpentry to put things right. This does not of course apply to metal fitments, which should fit unless warped by fixing stresses during erection. But sometimes metal doors and windows do not marry for the very simple reason that a blob of paint has destroyed the smoothness of the mating edge. It is worth going round each fitting to look for this. For moderate aberrations of fit in doors and windows the cure, in the form of some type of draught excluding strip, is fortunately not very expensive.

It was mentioned in a preceding post, when discussing a fresh air intake to a warm air system, that the average house already lets in more than enough. It may well continue to do so even after treatment, but the probability has decreased. That is not a matter of vital importance, but the supply of air for combustion to any device in the house which burns a fossil fuel — coal, coke, oil, gas — whether it is the boiler or cooker, fire or warm air unit, is important. This gives us an opportunity to do things properly: instead of hoping that we live in a place so bad that in spite of ourselves it is self supporting in fresh air, we can now arrange to deliver fresh air to the exact place that it is needed, and in roughly the right amount.

There need never be serious misgiving about making a purpose built hole in a dwelling. Suppose that you put in an air brick or grille adjacent to the boiler. When the boiler is at work it will draw on it. When the boiler is not at work there will be no other force persuading air to enter through that aperture. If air is to enter, some must leave from somewhere, and you have already seen to it that there are no stray outlets. Indeed, the only stray air to enter a well treated house should be what comes in through the unavoidable opening of the front or back door.

It is quite easy to run a ducted air supply from a grille in the outside wall to a point adjacent to the appliance needing the air, but it is by no means certain that one should do so. A factor to be kept in mind is that in addition to heating there is ventilation to consider. In a sealed house we should gradually use up all the oxygen, and perish, and while there is little likelihood of this happening because of the near impossibility of achieving that degree of sealing, we must recognise it. In fact we do, numerically, since an allowance is made in heating calculations for a change of air in each room 1 ½ times an hour. Air movement within the house takes place of its own accord, by thermal currents and by the boosting caused by opening and shutting doors, and by the movement of people. Continuing our search for sources of unofficial air leakage we come to the chimney which is not connected to a modern appliance with a sealed in flue connection. It may be that the chimney is not in use. In that case the least that should happen is that the register plate should be closed, and if no register is fitted then a blanking plate in lieu should be placed in the throat. The permanent way to deal with such chimneys is described in a preceding post.

A fireplace which is still used occasionally should, if of the open fire type, first be reconsidered in case its importance warrants fitting a modern close-coupled appliance instead. If this is not done then quite clearly this chimney must be closed off in periods of non-use, either by a closeable register plate or by fitting a close screen across the opening. The amount of loss due to an uncontrolled chimney can be quite colossal. The effect of controlled leakage on the other hand is to give just that amount of room ventilation which is needed.

There is no doubt that a total programme of insulation, on the lines suggested here, will cost quite a lot. It is an unexciting subject, and unlike heating there is nothing to look at, nothing to burst into life at the turn of a switch, and a fairly common attitude is ‘We’ll have the heating this year, and do that next year — if we can afford it.’ That is to put things in quite the wrong order, for if one had to make a clear choice insulation should win. We mentioned earlier that with ideal insulation heating would be redundant, and if we go only half way, we can say that with good insulation heating is less important. The other fallacy in the ‘this year next year’argument is that heating plant needed before insulation is bigger and therefore more expensive than that which is needed after insulation. Further, if it becomes too large for the job its working efficiency goes down and creates another source of unnecessary running cost.

Briefly what happened was that in each experiment two identical houses were built, but one was turned out in ‘standard’ form and the other was given a full insulation treatment. Each was then equipped with central heating, and since they were in the same area they experienced the same local climate. The two results showed remarkable accord, both indicating a saving of about 41% for the insulated house.

We would be surprised if any of our readers could emulate this, for this experiment was, as they say, under controlled conditions. But is there anyone who may at this moment be looking with disgust at his fuel bill who would reject the chance to knock even 25% off it? The matter does not end there. If the insulation is done first, the system will need a boiler or heater 25% smaller than it would have done, and the same will apply to radiators or other heat emitters. And cost goes along with size, so right at the start there is a chance to recover some of the cost of insulating.

Then there is an uncostable factor, the physiological one. Indoor warmth arrives in two forms, radiant and convected. Convected warmth is what is due to the circulation of warm air. Radiant warmth is a form of emanation which is not dependent upon being air borne. It may be visible, as from a flame or gas or electric fire, or it may be invisible if at low temperature. Equally important, it may be positive or negative in relation to the human body. That is, we may feel cold radiation as well as warmth, and both are more noticeable and more effective than convected warmth. Only the air is as yet up to temperature, and it will take quite a long time before the walls begin to absorb and retain warmth. But in a well insulated room, not only is the warming time for the walls less, but there is a much greater chance that the walls still retain a good deal of warmth from the last period of room occupation. That slight shiver in spite of the thermometer might never occur with insulation.

Just in case we ever get another prolonged spell of very hot weather, it is worth recalling that insulation also keeps out heat.