Care for the Ageing - for example

In my post Care for the Ageing (11 October 2021) I wrote in broad terms about the importance, in tackling the climate crisis, of making our existing - and ageing - housing stock more energy efficient. Here I will get much more specific and discuss the practicalities and nitty-gritty.

I spent my childhoood in a neighbourhood on the south side of Sheffield. We had a primary school, a park, shops, a public library, two cinemas, the family doctor, several churches and chapels, a chippy and a couple of pubs all within walking distance. Our housing estate comprised several streets of identical semi-detached houses, most built of ugly faux-stone concrete blocks, with a few of red brick, with bay windows on one or both floors. Built, I think, just after World War II they were a first step into home ownership and lower-middle-class status for working-class families like mine. These quiet streets where kids could play safely, with everything people need nearby, off-street parking and a half-hour bus ride (quicker still on the 'supertram') into the city are still good places to live. The houses are soundly built - not spacious but not cramped either - and have good size gardens. They have many more years of life but need updating to suit modern needs - particularly in terms of energy saving.

The construction is brick/blockwork cavity walls, tiled roofs, suspended timber floors and wood windows. The house in the middle of the picture was rendered not because of damp problems but because our neighbour's son was a plasterer! By now, most houses have new windows - typically double-glazed uPVC and will have some glass-fibre quilt in the roof and cavity-fill insulation along with new kitchens and bathrooms. Originally heated just by open fires with a back boiler in the kitchen range for hot water, most will now have gas boilers and radiators and most of the chimneys will be disused. Few, if any, will be anywhere near current standards of energy efficiency, but I will suggest how this problem might be addressed.

Insulation

Starting from the top, the roofs of these houses are easy to insulate, and most will have had glass wool laid between and over the ceiling joists. Sufficient insulation here will minimise heat loss via the roof. The roof access hatch should also have insulation and draught stripping.

The external walls are a major route for heat loss. The cavity-wall construction provides a small improvement over solid brickwork but its main function was to reduce damp penetration. Many houses will have cavity-fill insulation but this will still leave insulation levels well short of current standards. Internal insulation - lining the walls with insulation board faced by plasterboard - is the best option where external appearances are valued but 100mm thickness of insulation would be needed and this would reduce internal space and require work to skirtings, power sockets and (sometimes) cornices. These houses, though, lend themselves to external insulation. Most are not particularly attractive as built and the projecting eaves means the roofs and gutters can remain as is. Slabs of insulation fixed to the outer face of the walls would be weatherproofed by a breather membrane and cladding. 100mm or more (depending on the choice of cladding) insulation could be added and there are many options for cladding, each with its own visual style. Cement render is a popular choice, while larch or cedar boarding are being used more and more. Other options are tile hanging, cement-based planks or slates, heat-treated timber rain-screen cladding,...

External insulation and cladding is ideally combined with replacement windows and doors. Unless these have already been upgraded to a good standard of thermal insulation and air-tightness they are best replaced with triple-glazed windows with good draught-proofing and thermal breaks.

Once insulation has been increased in the walls, roof and windows, the ground floor becomes a serious conduit for heat loss. The original construction had just 20mm or so of wood boards between the inside and a cold, well-ventilated undercroft. The best approach here is to lift and re-lay the boards after filling the spaces between the timber joists with insulation supported by a breather membrane draped over the joists. Another, air-tight membrane below the floor boards will reduce air leakage, and it is even possible to incorporate underfloor heating, as discussed below.

With good levels of insulation in the roof, walls and ground floor, plus triple-glazed windows one of these houses could match the low fabric heat loss of a new house built to today's standards.

Heating and ventilation

Once insulation has minimised fabric losses (heat flow through the roof, walls, floor and openings) ventilation losses become a much more significant cause of heat loss. The house heating warms up the air indoors but this warm air escapes through open windows, extract fans in kitchens and bathrooms, up chimneys, and through gaps around windows ad doors and anywhere building components meet. A well-insulated but leaky house will lose most of its heat this way.

Step one is to deal with leakage so that ventilation can be controlled (by opening windows and switching on fans) and draughts are eliminated. Many new homes, especially timber-framed ones, incorporate an airtight membrane lining the inside of walls and ceilings and sealed at joins and edges to minimise leakage, but this may not be necessary for existing homes. Plastered walls and ceilings are a good barrier to air leakage, but air can escape around edges - around windows, doors and roof hatches, behind skirting boards and architraves, and where floor joists are built into walls. If new doors and windows are installed they should have good draught-strips and be sealed around the edges, otherwise any doors, windows or ceiling hatches that are retained may need new draught-stripping and sealing. Suspended timber floors are a major route for air leakage - between floor boards and around edges below skirting boards. The best solution is to lift the floor boards, lay a breather membrane across the joists to act as a support for insulation filling the space between the joists, and finish with an air-tight membrane sealed at joins and edges.

Building Regulations set limits on air leakage through the building envelope but also require mechanical ventilation of kitchens and bathrooms as well as natural ventilation by opening windows and trickle vents. Unintended air leakage is controlled but extract fans throw out large volumes of air together with the energy used in heating it. A much better solution is mechanical ventilation with heat recovery - MVHR. A simple device incorporating quiet-running fans, filters and a heat exchanger (usually located in a roofspace) runs 24/7 pulling moist and sometimes smelly air from kitchens and bathrooms, passing it through the heat exchanger and to the outside. At the same time fresh air is drawn from outside, passed through the heat exchanger and fed into living rooms and bedrooms. Instead of simply extracting warm air and all the energy it contains, to be replaced by cold air from outside, the heat exchanger recovers around 80% of the heat energy in the extracted air and transfers it to the fresh, filtered air being introduced. This enters rooms typically only one or two degrees cooler than the extracted air. Far more heat energy is recovered than is used by the fans, no extract fans or trickle ventilators are needed and windows can be kept closed in cold weather.

The MVHR unit and its ducts are easy to incorporate in a new build, and most existing properties have a roof space where the heat exchanger can be sited and ducts routed to the upper rooms. Most will also have redundant chimney flues which can serve to route ducts from the unit in the roof to ground-floor kitchens and living spaces.

Open fires of course draw enormous amounts of energy from homes straight up the chimney. Wood-burning stoves are more efficient but should have the combustion air fed by an under-floor duct from the exterior. Burning wood does not use fossil fuels but does still produce CO2 which would be better left captive in the wood - trees being harvested for construction or making furniture rather than for firewood or bio-fuel heating and power generation.

The best current choice for domestic heating is indisputably the heat pump, and air-source heat pumps (ASHP) are relatively easy to install in most existing homes, replacing boilers. They are closely related to refrigerators and air conditioners, and similar in size and appearance to air-conditioning units. Standing outside a house, the ASHP has a fan, a compressor and a heat exchanger which shift heat from the outside air to the house's heating system. In the UK this usually means warming the water circulating through radiators or underfloor heating pipes. The magic of heat pumps is that they can use a modest amount of electrical energy to convert a small amount of heat from cool outside air to useful heating temperatures indoors. They do this very effectively: one kilowatt of electrical power will typically produce two, three or more kilowatts of usable heating. This ratio (known as CoP or coefficent of performance) is highest where the temperature of the heating medium - the water in the pipes - is warm rather than hot. This is why heat pumps are best paired with underfloor heating where a large surface area (the floor) is heated to a moderate temperature - unlike many radiator systems where radiators can be too hot to touch.

It is widely held that where boilers are replaced by heat pumps a house will need more or larger radiators fitted or, more radically, the whole heating system replaced by underfloor heating, but this does not necessarily follow. Suppose all the advice above has been followed - the house insulated and made airtight so that fabric and ventilation heat losses are drastically reduced - then existing radiators will be able to provide the reduced heating needs while running lower temperatures.

The home owner will have been used, with their powerful gas boiler, to the heating coming on for two or three hours in the morning, shutting off when everyone leaves for work or school, then running again in the evening until bedtime. But underfloor heating usually takes hours to get the floor up to temperature and start heating the house, so cannot heat the house quickly from cold. On the other hand, the floor holds the heat and the house stays warm longer when the heating shuts off. Underfloor heating is best controlled by programmable thermostats which can boost the temperature for the evening and let it drop a little overnight. Now this approach is needed for a system with a high thermal capacity but can be applied to a radiator system too. Running the radiators at moderate temperatures, under thermostatic control, without necessarily shutting the heating off completely - the same heat from lower temperatures for longer.

If the floor boards are lifted to insulate and leak-proof a suspended timber ground floor (see above) there is the opportunity to install underfloor heating which will work well with a heat pump and allow the downstairs radiators to be dispensed with, freeing up wall space. Heat rises and many of us prefer a cooler bedroom, so the original radiators should be fine upstairs.

Making an example

So you bought one of these old houses in Sheffield. Previous owners had installed roof and cavity-fill insulation along with small-bore central heating with a gas boiler but the house is draughty and there are one or two small damp patches where the cavity-fill had allowed water penetration. The original round-pin electrical sockets had been replaced with square pin but the original wiring remains. The boiler is getting old and gas bills are high and set to get much higher with fast-rising energy costs. You are rightly concerned about the climate crisis and very keen to do whatever you can. The house was reasonably priced, being in need of improvement, and your mortgage is not excessive, while the government has recognised that it can only stay in office if it reacts to the increasing public climate and cost-of-living worries and has introduced real, substantial and easily accessible grants and subsidies for energy-saving improvements*.

You double the thickness of roof insulation and fit a new insulated ceiling hatch with a loft ladder. Outside, you give the house a completely new look, adding 100mm of insulation protected by a waterproof breather membrane and larch cladding, fitting new triple-glazed doors and windows, wood on the inside and maintenance-free powder-coated aluminium on the outside with weatherstripping and sealed around perimeters. You have the house rewired and the plastering repaired. The kitchen needs refitting so after stripping out the old fittings you take up the ground floor, seal the walls between the joists with plaster and mastic around the joists, insulate and draught-proof it and lay underfloor heating pipes before replacing the floor boards, consigning the rusting old radiators to the skip, and assembling your new kitchen units.

The old boiler went out with the radiators and was replaced with an air-source heat pump against the back wall feeding the underfloor heating, the first-floor radiators, new heated towel rails and a big, insulated hot-water tank. An MVHR unit goes in the loft with ducts to vents in the bedrooms and bathroom, exhaust and fresh-air grilles at the eaves, and dropping in the disused chimney flues to vents in the kitchen-diner and living room. After a bit of experimentation over the first few weeks, you settle on the right settings for the room thermostats and the heating and ventilation just run themselves with barely any attention needed.

Your roof does not have a large south-facing slope but you have a flat-roofed garage at the back which you re-roof with a south-facing monopitch roof covered in photovoltaic solar panels wired to an inverter and a Li-ion 'solar' battery in the garage. With the battery, electricity generated by the PV on sunny days when you're not using much energy yourself will be saved in the battery for use in the evening or to charge your new electric car.

You are now the proud and slightly smug owner of a 70/80-year-old house which you have brought right up to date and which can compare with a brand-new home built to Passivhaus standards. The house is the most comfortable one on your street, the most energy-efficient, least polluting, and the cheapest to run, while the estate agent's valuation suggests the improvements have already added more value than they cost. You're not the sort to brag about it but your neighbours are curious and have questions: what did you have done? how much did it cost? In a few years every house on the street, and many more on surrounding streets and throughout the country have done similar things, thousands of sound older buildings have been brought into the 21st century and given many more years of life, a generation of young men have learned new skills and technology, and Britain is a shining example of what can be done to tackle climate change.

* Remember, this is about what is possible, not necessarily what is probable.