Our wooden home on an island on the Thames had burned down. We had the insurance money, and we needed to replace it. It had to be an appropriate design to harmonise with the older timber homes on the island, but safer, as fireproof as possible and well insulated against the weather. In the centre of the Thames, this can be quite extreme, even with a south-facing plot: hot in summer and very cold in winter.
The challenge
Between us, we came up with a design based on ideas drawn from some Edwardian boathouses on the riverbank opposite. Ours would be built with concrete blocks with a proper slate roof, unlike the neighbouring homes. These had mainly felt, and even corrugated asbestos, roofs, but with lots of glass to maximise the river views.
And that’s when, quite by chance, we met a young Polish builder called Marcin, who was looking for work in England, had a skilled crew of Polish contractors at his disposal and lived nearby. He was fascinated by the challenge of overcoming the logistics of building an entire house using small boats to bring in the materials. As it turned out, he was a qualified civil engineer who had built new properly and fully insulated homes in his native Krakow before coming to the UK.
A different approach to insulation
Marcin invited us to visit him in Poland and meet his warm and welcoming family near Krakow. He showed us how new houses were built there. They were designed to be not only attractive but also very energy efficient, clad externally with insulation and self-coloured rendered finishes. Fascinating. We asked what the advantage was of building this way; the simple answer was to think about basic physics.
“The shell of a house is constantly exposed to wild variations of temperature, whether ambient or through the effect of hot, direct sunlight or cold, stormy weather. If the ‘shell’ of the house is heavily insulated, the inside is stabilised and needs little space-consuming insulation” (and in any event it’s not that effective). We had wooden walls, lined with plasterboard but filled with fibre glass wool with the aim of insulating them well.
So, armed with this, that’s what we out set to achieve, but still with timber facings, using treated, fire-resistant, natural materials. We designed the house ourselves. (I had qualified as a graphic designer in a previous career, so I could draw a bit.)
After many months, it was something of a triumph, celebrated in the national press and then featured in House & Garden. For us, as TV and film producers, this was a bit like getting a BAFTA nomination recognising creativity and craft skills!
The finer details of insulation
Given the enthusiasm of both national and local government to promote home insulation, sometimes with grant support (although how long that will last with dwindling tax-derived funding, who knows?), as well as spiralling energy costs, insulation is a ‘hot’ (sorry) subject today. It needs to be taken seriously, as it has been for decades for nearby European continental housing.
Many houses have been built, especially since the 1960s, with cavity walls but with little in the way of insulation. Our builder despairs of the ‘poor quality’ of British construction. He says he can’t believe how little attention is paid to such a basic idea in most of the homes he sees.
A partial remedy (see Editor’s Note) is to engage a suitably qualified contractor to inject the cavity with foam insulation. This can also be used to good effect in lofts, either directly under the roof covering or across the top floor ceiling beams within the roof space. It can be beefed up by double-lining the internal walls with plasterboard.
This also provides better fire resistance and protection from internal damp, and is definitely a good idea for the internal cladding of timber framed structures. But, although it will improve the outcome of an energy performance certificate (EPC) survey, this approach is only partially effective. It doesn’t fully address the temperature stability of the external ‘shell’.
External aesthetics – to clad or not to clad, that is the question
Many homes, particularly those built in the post-war years from the 1950s onwards, especially in the 1960s, are built using often rather ugly red, engineered bricks. Those looking for visual improvement render their homes and paint them, often using wonderful colours. The evolution of these has been led by paint suppliers such as Farrow & Ball and many others. But these coloured finishes need maintenance. Depending on the local environment, they need repainting, sometimes every five years or so, which is costly and time consuming. And these finishes don’t contribute effectively to the insulation of the ‘shell’.
The options
We have discovered, having experimented on our own home and others we have completed as projects, that external insulation can easily be added to an existing building. This is done using fire-rated polystyrene sheets. The specifications of these can easily be checked on the internet for fire ratings as specified by EU directives (after all, no-one wants to see another Grenfell disaster caused by poor quality or inadequate firebreaks and materials). They vary in thickness, perhaps 2–3 cm thick, and are fixed directly to the original brick or blockwork.
These can then be rendered using proprietary products (we use a German-based supplier with UK outlets such as Bolix, although there are many manufacturers available through a careful internet search). This leads to not only significantly improved EPC ratings through proper insulation but also an instant visual uplift.
The final external finish can vary widely: it doesn’t have to be render. ‘Slips’, which closely resemble traditional bricks but are applied like ceramic tiles to the external walls, can also be used, and the choice is quite wide. If, for example, traditional ‘stocks’ are favoured (traditional warm, yellowish bricks), this is quite possible, and useful if the house is in a Conservation Area.
The suppliers of external insulation also offer other finishes such as shiplap ‘wooden slats’ manufactured from recycled wood pulp but also with in-built fire resistance. So, the ‘New Hampshire’ timber look is achievable.
Editor’s note
Readers considering imitating any of this type of construction should research the risks carefully to ensure they choose the safest products. See this leaflet about expanded polystyrene (EPS).
There was a thread from 2012–2020 discussing the risks. A loss adjuster stated that it was a risk and he would increase the insurance if it was used. He says it is better to use polyisocyanurate, which is more fire-retardant.
The fire-retardant used for the ‘fire-resistant’ EPS is hexabromocyclododecane (HBCD), which health experts warn against. The insecticide used is an endocrine disruptor.
‘There are online warnings about injecting foam into old-style cavity walls: a) the ties between the two walls may be left unrepaired and rotten, b) ants get into the foam and it breaks up, letting in the water.’
