insulation and airtightness

Insulation and airtightness makes an enormous difference to how much heat is lost in a house.  People generate heat simply through living – through cooking, taking a shower, having the television on, even just breathing. In an ordinary house, this heat seeps out through the roof, walls and windows.   A key component in reducing the need to heat houses, is to retain the heat that is already there.  Through ingenious insulation and airtightness measures, zero carbon house stays warm without any central heating.  Even when there are ice crystals on the windows outside, we stay snug indoors.

Here’s how we stop the heat escaping from our home:


When we enter the house, we come in through a sealed draught lobby. Closing the front door behind us before we slide open the inner door helps keep the heat in.

Airtight membrane

The whole house is lined with a membrane like a giant balloon.  Called an Intello Plus airtight membrane, it stops air, and therefore heat, escaping through the insulation, mortar or construction joins.

Outside wall insulation

The old and new walls at the side and back of the house are insulated on the outside. The insulation is a material called Neopor, a bit like polystyrene but using graphite which reflects radiant heat back into the house.  Normally the insulation is fixed to the masonry wall behind with stainless steel fixings, but they conduct heat and compromise the insulation, so here (a UK first for the Sto system) we just used epoxy adhesive – stronger than the material itself.  It’s finished with a waterproof external render, mostly white, but with some zaps of colour.

Inside wall insulation

The front of the old house has lovely historic brick and stone features, so here we chose to insulate the walls internally, lined with Warmcel 500, an insulation material made from recycled cellulose fibre – old newspapers. It’s now 16 times better at keeping the heat in than before. You can experience how thick the walls are when you sit in one of our window seats.

Insulating wall ties

Houses with a cavity wall construction have ties to stop the inner and outer brick skins from parting company. These are usually made from stainless steel. Ours are called Magmatec TeploTies and made from basalt fibre.  The fibre conducts much less heat than the stainless steel and so contributes to the insulating effect.  You can’t see it, but it makes a difference.

Roof insulation

We kept the original roof slates, battens, roofing felt, timber rafters and purlins but removed the old flat plaster ceiling and added a new sloping ceiling following the line of the roof but set a bit lower to create space for insulation. We filled it with Warmcel 500, as the internal wall insulation.  Combined with the airtight membrane, it is now 28 times better at keeping the heat in than it was before.

Earth floors

Our floors are made from rammed earth dug from the foundations of the house and mixed with some extra red clay.  This material is so dense that is holds the heat of the house, keeping us warm in winter and cool in summer. Under the ground floor slab, and in the cellar of the old house, is 300mm of insulation.

Triple-glazed windows

The windows are triple-glazed with double air seals around all the edges. They are 14 times better at insulating than the original single glazing.

Sealed letter box

Our letter box is sealed at three different points to prevent draughts. It’s called an Ecoflap.

Covered power sockets

Heat can escape even though power sockets and the gaps in construction around them. We have made a floor duct around the edge of most rooms for our electrical power and TV cables and covered the duct with a strip of maple wood so we have easy access.  That keeps all our electrics off the external (airtight) walls, so we avoid all those complicated air leaky junctions altogether.  Every little helps.

Recessed picture rails

We have recessed picture rails so we don’t have to bang nails into the walls. This means no mess but also no compromise on our airtightness layer.

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