Highly insulated houses have their hazards

I’m writing this through streaming eyes and the occasional volcanic sneeze (do keep the page at a safe distance). Illness, as I’m being reminded, prompts us to hunker down and hope to recover rapidly in our favourite place of safety, which for most of us means home.

But, in reality, how safe is it? The easy answer is pretty damn safe. In fact, in historical terms, the health and safety levels of the modern home are within spitting distance of miraculous.

We have tiled roofs and double walls of brick and concrete to keep out the elements, waterproof membranes in the walls and floor to block rising damp, central heating, cavity insulation and double glazing to keep us warm, and disease-free water on tap.

So what’s to worry about? Well, our basic needs may not have changed through history, but our environment has, sometimes dramatically. Today the biggest change involves, of course, the climate. Rising carbon dioxide levels are causing milder, wetter winters and hotter, dryer summers.

One response to this has been to cut the CO₂ produced by home heating by beefing up insulation levels. This certainly makes houses cheaper to run, and more comfortable. But new builds are also required to be ever more airtight – since the smallest draught can halve the effectiveness of insulation. Again, entirely practical. Except in a heatwave when overheating can become a serious danger, especially to the very young or the elderly.

An airtight home can also trap moisture, encouraging the growth of mould, which can seriously affect health. It joins a host of common pollutants such as volatile organic compounds (VOCs) offgassed by new carpets, furniture and building materials, alongside carbon monoxide and nitrogen dioxide from burning fires, gas hobs and ovens. And that’s not to mention external pollutants, especially if you live close to a major road.

But this isn’t meant to be a scare story. Solutions to these problems are numerous, and, like so much else in self build, are best applied at the design stage. Here, then, are seven hopefully useful suggestions to make your new home as safe as currently possible.

1. Fit a whole house mechanical ventilation and heat recovery system (MVHR)

Here, a central double fan and heat exchanger are connected to separate systems of ducting. One system draws stale, moist air from kitchens, bathrooms and utility rooms and vents it outside, via the heat exchanger, which transfers its warmth to incoming fresh air. This is then distributed via the second system of ducts to living areas. Filters can be fitted to exclude outside pollutants.

Alternative: if your home isn’t sufficiently airtight, fit a positive input ventilation system (PIV). A single continuously running fan, usually sited in a loft, draws in fresh air from outside, filters it and channels it to a single central outlet. The higher internal pressure created squeezes stale air out through trickle vents in windows and other leakage points.

2. Treat ‘dot and dab’ plasterboard with caution

Traditionally, external masonry walls are covered internally with two coats of plaster. A quicker, cheaper alternative is to fit sheets of plasterboard, secured by dabs of mortar. But if even tiny gaps are left in the underlying blockwork, moisture can enter behind the plasterboard, creating mould. External air can also circulate, bypassing the insulation and cooling the house.

3. Install underfloor heating

Conventional central heating radiators actually work by convection, warming the nearby air, which rises, cools and falls to be re-heated. These air currents spread dust and pollutants. Underfloor heating (UFH) works by radiant heat, directly heating the objects and people above it, minimising convection currents.

Alternative: fit radiant heat panels which use the same principle. They work with infrared and can be installed on walls or ceilings, or can even be disguised as mirrors or artworks.

4. Consider natural insulation

These include sheep’s wool, hemp, flax, wood fibre and cork. All five are non-irritant in handling and hygroscopic, ie able to absorb and give up moisture and so regulate temperature. They’re also breathable, allowing moisture vapour to pass through without losing their insulation value. Sheep’s wool can also absorb and neutralise toxins.

Main drawbacks are: larger volumes are needed to match the insulation values of rigid, petroleum-based foams, and their higher cost.

5. Choose a room-sealed wood-burning stove

Wood-burning stoves, according to recent research, spray more particulates into the air than heavy duty lorries. New legislation will now ban the burning of coal or wet wood in domestic stoves. You can, however, still enjoy the benefits of a roaring fire by choosing a wood-burner with an external air supply. These are fed either from a duct in an adjacent external wall or a secondary duct in the existing exhaust flue. Look for a stove with a ‘total’ direct air connection – ie both combustion and exhaust are separate from the internal atmosphere. For an especially airtight home, opt for a ‘leak-sealed’ model.

6. Choose solid floors

Carpeting is enduringly popular for its warmth, comfort and colour range, but it also harbours dust, pollen, VOCs – either in its composition or backing – and a host of allergens. Solid floors are easier to keep clean, don’t attract dust mites or mould and are much more efficient at transmitting the radiant heat of underfloor heating. Choices range from ultra-durable ceramics, slate and stone to wood, either natural or engineered, to linoleum, which is naturally antibacterial.

7. Cook electric

Specifically using an induction hob, which only heats a pot or pan directly, leaving the hob itself cool. Gas hobs and ovens can produce carbon monoxide and nitrogen dioxide, both harmful.

April 2020