Controlling Humidity And Heat Loss In The Home

After much thought you may have installed the system of central heating ideal for your type of home. All that remains is for you to sit back and enjoy its benefits. But wait! Nothing is perfect in this imperfect world. Do you now suffer from sore throats, headaches or sinus trouble? Is your woodwork warping? Does your furniture show signs of cracking or becoming loose at the joints?

The cause of your distress is relative loss of moisture in the atmosphere. You have interfered with nature by upsetting the balance between temperature and humidity, and what you need is a humidifier.

Extremely dry air is as harmful as air that is saturated with water. The atmosphere of a room should maintain a healthy average of about 50 per cent humidity at 13° to 21°C (55° to 70°F). Do you remember when gas fires first came into being? Our mothers or grandmothers used to place a saucer of water in front of them, the reason being that warmth from the fire caused the water to vaporize, so avoiding undue dryness. There was no trouble about air being too dry with a coal fire because burning generates moisture, and in any case heat going up the chimney sucked cold moist air in from under the door, and through window chinks and gaping floorboards.

Insulation And Humidity

You can still use a bowl of water and hang it somewhere near a radiator. Flowers in it could hardly last because of the heat, but you might be able to use artificial ones providing they do not melt. More sophisticated humidifiers,some electrically operated, can be bought at ironmongers and department stores.

Insulation And Humidity

Let us suppose you have installed and are running central heating with some kind of humidifier — all at considerable expense. To keep your fuel bills reasonable you will have to cut down heat escape routes, which act like a thief in the night and by daytime as well.

In a house there are five principle avenues of escape: walls, windows, roofs, floors and air changes.

Starting with the last, which is the simplest: to maintain a healthy atmosphere, air change is of course necessary, but not to the extent that most houses permit. An average-sized room with three or four occupants needs only about half of the air changed each hour. Anything from two to six changes an hour are, however, very often found. Greater improvement is therefore necessary in sealing draughts than is generally realized.

If you want to reduce heat loss, you should understand something about the nature of heat. Once heat is produced by the burning of fuel it cannot simply die out. It must go somewhere. When a hot object cools, the heat it contained has not disappeared; it has simply dispersed into the surrounding air. Likewise, when the interior of a house is warm and the heating switched off, the noticeable cooling which takes place means that the heat has travelled by some means or other to the outside. The whole purpose of insulation is to keep all your expensively produced heat inside and not to let Jack Frost have the benefit of it.

Heat disperses by three methods: by conduction through a solid substance; by convection, whereby a layer of air is warmed, becomes lighter, rises and is replaced by cooler air; and by radiation, whereby heat is given off and warms distant objects in the same way as the sun warms you.

Therefore, to prevent heat loss from a house, the five avenues of escape for heat must be considered with reference to the three methods of heat dispersal. In other words, the walls, ceilings, windows and floors must be insulated in the best possible way, and air changes controlled, to prevent heat loss by conduction, convection and radiation.

Air changes

Warm air escapes under doors, through cracks in walls, window frames and ceilings, up chimneys, through ventilators, out of unclosed doors and through badly fitting letter boxes. Radiation and conduction do not figure here. Convection is the culprit. Warm air simply moves from within the house to the wide world outside, and is replaced by cold air.

To minimize this heat loss is easy.

Fill up gaps between floorboards and attach quadrant moulding round the edges of the floor so that it butts on to the bottom of the skirting board. Choose moulding of dimensions slightly larger than that of the widest gap under the skirting and pin to the floor with lost-head panel pins. Some people pin alternately to floor and skirting board; this is unwise because a pin driven by mistake into a gap will not hold. Even if this did not happen, structural movement of the house could result in tearing the wood. The cross-section of quadrant moulding is a quarter of a circle (obtainable at timber and do it yourself shops). If you do not like the appearance of wood moulding, plastic strip, doing precisely the same job, is sold in hardware shops.

Then correct ill-fitting doors with threshold strip and draught excluders.In brief, this means resetting stops and fitting a wooden strip to the floor between the stops of each door. At the same time reset stops in casement windows and fill chinks in the walls, particularly where doorcase and window frame adjoin masonry.

Proof that warm air is leaving your house is indicated by cold draughts coming in — which can be checked by holding a lighted cigarette or match to a suspected area to see if it ‘blows’. If it does, uninvited cold air is replacing warm air which is leaving somewhere else. If no air were leaving, no air would come in. The average home suffers 25 per cent of its heat loss through excessive air changes.


Approximately 20 per cent of loss is through ceilings and out through roofs. The warm air in the house rises by convection to the upper rooms. It is then conducted through the top ceiling into the loft area.

You can prevent this from happening by laying insulating material immediately above the ceiling of top storey rooms, working from the loft. Don’t lay insulation under a cold water tank, and see that pipes above ceiling level are wrapped, or they could suffer from frost damage through being deprived of warmth from the house.

The insulation material entraps air. Still air is a poor conductor of heat and, by definition, it cannot convect it.

Fibreglass and other mineral wools are finely spun and so about 90 per cent of their volume consists of air trapped between their fibres. These materials can be bought loose and packed between the ceiling joists to a depth of 50 mm (2 in), or in the form of a loosely packed quilt which is laid between the joists. Where joists are an even distance apart, quilts are easier to handle than loose packing. Make sure you protect your hands with rubber gloves. Such material can get under finger nails and roughen and even cut the skin.

This treatment is sufficient in itself, but it may be supplemented by also laying aluminium foil to reflect back any heat that does attempt to escape.


Between 5 and 10 per cent of heat loss is through floors. This is almost completely by conduction. Thick carpet is really the only answer, or thick underlay.

Cavity Walls

Walls are the chief offenders so far as heat loss is concerned. Cavity walls — two wall linings with an air space in between — are better than solid ones, but even these are responsible for between 23 and 33 per cent of heat loss. They are your worst enemy when you are aiming at whole house comfort, and the secret of a really snug home is to do something about those cavities.

Most houses built since the mid forties have an outer course of bricks, then 50 or 60 mm (2 to 2+ in) of air space, then an inner lining of bricks or clinker blocks and finally a layer of plaster. There are two reasons why modern houses are constructed in this way. First, a cavity is better than a solid wall from the point of view of insulation. Second, cavities prevent the penetration of damp from the outside to the inside — provided there is no accumulation of old mortar droppings in between to act as a ‘bridge’.

Heat transference through cavity walls should be explained.

Warm air circulates around your rooms, and the inner leaves of the walls are bound to absorb some of this heat, which is then conducted through to the cavity. Here it warms the adjacent air, which rises by convection and shoots straight out when the top of the cavity is unsealed. If the cavity is topped off, the warm air will about-turn and travel down the other side of the cavity adjacent to the outer leaf. Being cold, the outer leaf absorbs the heat, which continues by conduction into the air outside.

All very fine for the man who sells fuel, but not so good for you! Once the air has reached the bottom of the wall it is quite cold. But, as it is now adjacent to the inner leaf, and again absorbing heat from it, it starts rising once more. This vicious circle is continuous and surprisingly rapid.

The heat loss through the cavity can be stopped by preventing the circulation of air between the outer wall and inner leaf. At the same time, whatever is used must have a very low density in order to minimize conduction.

A technique has been developed whereby a plastic foam can be injected into the cavity from the outside of the house. Unfortunately, being a complicated process requiring special apparatus and skilled technicians, it is not a do it yourself job — at the time of writing at any rate.

Holes are drilled in the outside mortar courses, at something over a metre (about 4 ft) intervals, through to the cavity. Into each hole is placed a ‘sight stick’, which is rather like a pencil and is important to the technicians as it ensures that the complete cavity has been filled. Once the holes are drilled, the foam is injected through a special nozzle until the sight sticks of the next holes along and above indicate that the foam has spread to a little over a metre (about 4 ft). The foam enters the cavity in a swirl formation thus ensuring that no air spaces are left, particularly around wall ties. The material sets in approximately fifteen minutes, after which the drilled holes are filled with matching mortar and are undetectable.

One of these foams is urea formaldehyde resin bearing the ICI brand name Ufoam’.It looks rather like shaving cream from an aerosol can and, when hard, has the consistency of a cooked meringue made up of millions of minute resin-walled bubbles. The conditions required for mixing the various chemicals are critical, and the pressure used in injecting the foam must be strictly controlled. It is important, therefore, that the work be carried out by a reputable company. The foam lasts for the life of the house and a certificate supplied by ICI is of value when it comes to selling.

The complete operation can normally be carried out in one day and, because all work is done from the outside, there is no disruption to the household routine, no mess to clear up, and internal decorations are unaffected.

Ufoam works by completely trapping air in the cavity, thereby eliminating convection currents which carry off the warmth from the inner leaves of the walls. The material is so light that there is no conduction of heat and, being opaque, there is no radiation. In fact the heat loss through cavity walls is reduced by over 75 per cent. As has already been explained, 23 to 33 per cent of heat loss is through cavities, and reducing this by more than three quarters will show a reduction in overall loss of something in the order of 20 per cent — quite a proportion in terms of your heating bills.

Ufoam is an inert substance: it will not decay or rot, nor will it encourage vermin; also, it is water-repellent and will in no way impair the damp-proofing qualities of cavity walls. In addition to keeping your home warmer and considerably reducing fuel bills, a number of other important benefits are gained by having cavity walls insulated with such a material.

Warmer temperatures eliminate much of the discomfort normally associated with a cold surface. The inner leaves of walls will retain heat and act as thermal storage units; this means that the house will cool down more slowly whenever central heating is switched off. The effect of any sudden outside temperature drop will be evened out so as to be scarcely noticeable. Cold draughts, particularly under window sills, will be effectively sealed and wall condensation minimized — in many cases completely eliminated.

Cavity insulation makes more of the warmth created ‘by accident’ in the day-to-day running of the home. The heat from electric light bulbs, cooking and also winter sunshine are a few examples of these ‘accidental’ heat gains. A really well insulated home stays about —9.4°C (15 °F) warmer than the outside temperature without a penny being spent on heating.

Solid Walls

Plastic foam, with which we have just dealt, cannot unfortunately be injected into the solid walls of really old houses.

The only way you can insulate these is to hang aluminium foil over the plaster to reflect back heat attempting to escape, and secure the foil in position with vertical wooden battens of width and thickness about 50 x 25 mm (2 x 1 in). Space the battens at intervals of some 400 mm (16 in) and add cross noggings at a metre (4 ft) or so apart. On to the exposed surface of the battens pin insulating or medium fibreboard,which can then be decorated with paint or wallpaper.

This will naturally reduce the size of the rooms slightly. If your rooms are already small, all you can do is to line the walls with polystyrene sheetingwhich is quite good for the job but not nearly so efficient as the battening method.

Polystyrene can be emulsioned direct but not oil painted. If you require a smooth surface, hang lining paper on top and paint that.

You can also hang wallpaper over polystyrene.

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