Design notes on the Zero Carbon House

Chris Duggan — Sun, 28 Mar 2010 21:50:18 +0000

These notes used as a guide to visitors on the Open Day on 28 March 2010 give an insight into many aspects of the design.

WELCOME to the zero carbon house!

Every self-respecting “green” house needs a draught lobby so it doesn’t lose all its inner warmth when you come through the door – so please close the door behind you before you slide open the inner door!
To open the back door, the handle must be horizontal.
Please close the door behind you!
Note triple glazing and double air seals around all edges of the door.
[Draught lobby] The door and screen are made from “Mykon”, a lightweight double skinned material that filters and reflects light into the house with a touch of magic. We like the honeycomb hexagonal core.
We have cut away part of the original brick wall of the house here, and replaced it 300mm of insulation and a laminated timber column. This means the cold and damp in the external brickwork stays outside and doesn’t come inside. Technically this eliminates “thermal bridging” which can cause problems even in very well insulated buildings.
Magmatec walls tie are thermally insulating, unlike normal stainless steel wall ties which conduct 3,000 times more heat than normal building insulation.
[Under the stairs] This is where our bicycles live, so they are easy to get at as we use them to cycle to school and to work.
Door into the garage has double air seals to prevent air leakage.
This is where we will garage our 24 year-old camper van – our carbon positive offset to the savings we are achieving in most other areas!
This was the outside wall of the old house. It is still sound, but by our standards offered very little thermal insulation. Now as an internal wall we like it’s raw colour and texture, so it’s not plastered or painted. It has stood here for more than 170 years, and the clay was probably dug quite locally.
Where Kurt the bricklayer sliced through the old brickwork to form a new opening, you can see little pebbles in the clay, buried like fossils.
[On lower stairs] There was once a window here, and you can see traces of it in the timber and steel lintel above. Gary the bricklayer has filled most of it in with reclaimed bricks from another part of the house. They have been stack-bonded like the new brickwork outside, to differentiate the old and the new. Natural lime mortar rather than cement has been used. Cement is responsible for 5% of global C02 emissions.
Composite honeycomb landing allows natural daylight down into the ground floor hall.
Ground floor cloaks/wc is large enough for wheelchair use and has the wc and basin at the right height. There is also a floor drain and plumbing already in place to allow a future shower so a disabled person with a bed on the ground floor could use this as their main bathroom.
The stairs are designed to take a chairlift if we can’t manage the stairs in our old age. There is a power supply already built in ready.
These shelves made lovingly by Eddie of Gallande Joinery on Tindal St are made from offcuts of the reclaimed timber used for the stairs. There is a recessed filter fan. The ventilation system extracts cooking odours.
Our door handles are modern design classics by the Danish architect Arne Jacobson. They were reclaimed from another building by Gary Williams of Williams Ironmongery, or they would have gone in a skip!
Hemp ropes for our stair handrails and sliding door handle: more renewable and less energy intensive than stainless steel. Hemp is one of the fastest growing plants known.
Kitchen work surfaces are recycled glass100% recovered from household and commercial waste. Glass makes up around 7% of the average household dustbin and 2.5 million tonnes go to UK landfill every year. Glass is unique as it can be recycled indefinitely without loss of quality. Recycling saves 315kg of CO2 per tonne of glass melted. Our work surfaces have been supplied by Bottle Alley Glass. The framework below is reclaimed honeydew maple like our staircase.
We cook with renewable electricity generated by our solar panels. This is an induction hob. It works by inducing a magnetic field in the iron-bottomed saucepans and is 2-3 times more efficient than most electric hobs. It also has the advantage of being as responsive as gas and very safe because there is no flame or hot ring.
This monitor displays temperature readings, including outside and inside temperatures, the temperature in the solar panels and at three points within the hot water cylinder. We use it to tell if there’s enough solar hot water for a bath or just a shower.
This monitor displays how much electricity our PV solar roof panels are generating, and how much electricity we are using.
Our bathroom floors are made with recycled glass from bottle banks.
We discovered some reclaimed 200 year-old Canadian Honeydew maple. It was the floor of a silk factory. Eddie at Gallande Joinery in Tindal St has used it to make our stairs, kitchen joinery and bedroom high door.
Look out of the window at the reclaimed bricks (from a demolished local garage). These form a framing element to our new front elevation, the same height as Noreen’s house next door. They have been stack bonded with fine 6mm joints to match next door by Gary the bricklayer.
Look carefully and you will see two nesting boxes for sparrows/black redstarts and two for swifts built in at the top. Sit here for long enough and you might even see the bluetits who have already moved in…
Full height storage for all our bits and pieces.
Sliding garage door made from local sweet chestnut laths. It is untreated and is weathering down to a natural silvery grey colour. The front door and projecting dormer window above are the same timber.
Even our letterbox is air sealed at three different points to prevent draughts!
The floor, wall lining and ceiling here are reclaimed 200 year-old Canadian Honeydew maple as the stairs. It had been the floor of a silk factory, and was all blackened so you couldn’t see the grain. John the carpenter lovingly put it together lining up all the joints. In places it has iridescent “bird’s eye” figuring. It has been finished with natural citrus oil and beeswax.
Throughout the house the floors are rammed earth dug from the foundations of the house mixed with some extra red clay. The more it is walked on, the harder it gets (like the earth floor of an old barn). It has been oiled and then finished with beeswax polish. The floor holds the heat of the house, helping to keep us warm in winter and cool in summer, which is why we have no fitted carpets, just a few rugs. The little cracks and undulations in the earth floor are like the grain of natural timber (someone said it looked like red elephant hide!)
We don’t wash the floors except for obvious spills so dirt simply becomes part of the floor! We sweep them, oil them and wax them – saves water and electricity.
This dormer window provides a stop end to the original roof overhang, and frames our amazing view back to city centre. We watched the New Year fireworks in Centenary square from here.
The dormer window articulates the step up in eaves height from the original roof of 103. With the first floor oriel window it relates to the rich local roofscape characterised by bay and dormer windows, and other projecting roof features.
Our brickwork, white render and 30 degree slate grey roof (in our case solar panels!) also relates to dominant local building materials.
The ground floor provides open-plan kitchen, living and dining areas. The tall top-lit living room allows natural light to flood down into the heart of the house, so we don’t need the lights to be on so often.
This is our top floor studio space. It sits beneath the solar roof above. It provides a quiet contemplative tranquil space (or a space for noise if our son decides to become a rock’n’roll drummer!) as it is acoustically separated from the main living area by two floors.
The maple strip round the edge of most rooms gives access to a floor duct with electrical power data & TV points. We hope it will accommodate future changes in wiring avoiding cabling clipped all over the place. It also avoided having to chop out the walls to put in power sockets – which would have made airtightness more difficult.
The roof has approximately 36 square metres of PV (photo-voltaic) panels which generate electricity just like a solar-powered calculator – in fact 5150kWh/year. This is 100% renewable “green” energy. We can generate over 5kW – enough to run 300 light bulbs continuously! We will export surplus electricity to the National Grid so we are like a mini power station. From 01 April 2010 under the new government “Feed-in tariff”, we are paid 41.3p for every kW of power we generate, including the power we use ourselves!
In this cupboard is a fan with a heat exchanger. It is called a mechanical ventilation heat recovery system (MVHR). Warm humid air is extracted from the bathrooms and kitchens and discharged to outside but 93% of the heat from the outgoing air is recovered and warms the incoming air. It also filters Birmingham grime from the air. In winter we don’t open our windows or we would loose a lot of the warmth we are trying to keep. In summer we’ll turn the fan off and just open our windows.
Unfired hydraulically compressed earth blocks are the main load-bearing structure for the three-storey new building. (Normal clay bricks and blocks are fired at high temperatures in a kiln (energy intensive) and concrete blocks are made from cement, which is responsible for 5% of global CO2 emissions). These unfired clay blocks use waste clay too earthy to make into bricks, and they have very low embodied energy. The blocks store heat very well, and being moisture-sensitive (hygroscopic) they also help control the internal humidity. They absorb moisture when it is too humid and give it out again when it is too dry, acting like a natural air-conditioning system.
Building with earth … balances the air humidity … stores heat … saves energy … reduces environmental pollution … is reusable … saves material and transportation costs … uses low technology … is ideal for self-help construction … preserves timber and other organic materials … absorbs pollutants … continues traditional building skills… and half the world’s population, 3 billion people on 6 continents, lives or works in buildings constructed of earth.
This wood stove provides top-up heating and hot water for the whole house on a cloudy winter day. We expect it will only be needed for the coldest five or six weeks of the year. 80% of the heat it generates goes to our hot water cylinder store upstairs. We have not had to light the stove since 23 February, when there was still snow on the ground – ie. all our hot water has been generated from our solar panels since then, although external temperatures have been as low as -6 degrees centigrade.
Consolar UK vacuum tube solar panels are installed on the roof. They will provide at least 70% of our annual hot water. The hot water store has a capacity of 850/1000 litres, which is about five times the size of a normal domestic hot water cylinder. In the colder months this means that the hot water generated on one sunny day can be stored to tide us through quite a few cloudy days without requiring top-up heating from the wood stove.
This cylinder (5x average UK domestic size) takes hot water from the solar panels on the roof and from the wood-burning stove, and stores it for several days. The water is used for both hot water and also to add extra solar heat into the house through towel rails in the bathrooms.
The original roof slates, battens, roofing felt, timber joists and purlins are all intact above your head. We have removed the old flat plaster ceiling and added a new sloping lining following the line of the roof, but set 400mm (16 inches) below the original level to create space for lots of insulation. Even though the wall line has moved in a bit there is a greater feeling of spaciousness than before.
The triple-glazed rooflight allows extra natural light to animate the bedroom.
The blackened reminder of the 170 years of coal fires used to heat this house.
Our slate hearth was once part of a billiard table – can you see where the corner pockets were?
Mirrors intensify the natural light in many of our rooms. Here our nephew counted his reflection 28 times!
The recessed picture rails mean we don’t have to bang nails into our walls – no mess, but also no compromise on our airtightness layer.
This projecting oriel window adds space to our smallest bedroom/study. The mirror helps to intensify the natural daylight and bounces extra morning sun-shine deep into the room and across the landing.
Warmcel 500 insulation is used to line inside the existing front elevation of the house. It was blown in dry under pressure through a tube. Warmcel is manufactured from 100% recycled waste newspaper and has extremely low embodied energy, requiring far less energy to produce than other mainstream insulation materials. It does not contain any added formaldehyde and is free from CFCs, volatile organic compounds (VOCs) and other toxic substances. Our walls now have a U-value of 0.11 W/sqm/degC, which is about 16X better than before.
The thicker wall construction gives two nice extras: the angled reveals, like many Georgian houses, which help natural light into the room; and also the window seats, made using the same reclaimed timber as the staircase.
The external and side walls, both original and new, are insulated on the outside and then rendered over.
This material is called Neopor. It is the insulation used on the outside of our original 9 inch brick walls at the rear and side, and also on the outside of our new solid clay block walls. It is fixed with special adhesive and no metal or plastic fixings that would compromise its thermal performance. It is dark grey in colour because it is made with graphite. This reflects back radiant heat into the house. Its foam structure, which traps air, also reduces conduction and convection heat losses.
The external face of the insulation is finished with a waterproof but vapour-permeable reinforced render. Mostly white – but with some zaps of colour!
Magmatec TeploTies made from basalt fibre have been used to tie the structure together. Wall ties stop the inner and outer brick skins of a cavity wall construction from parting company and are usually made of stainless steel. The basalt wall ties we have used conduct much less heat than steel.
Warmcel 500 insulation has also been used to line the inside of the original roof of the house. It was blown in dry under pressure through a tube. Warmcel is manufactured from 100% recycled waste newspaper and has extremely low embodied energy. The old slates, battens, rafters and roofing felt were kept, and a new light timber framework was constructed below to support the “Intello Plus” airtight membrane, battens and ceiling. Our roofs now have a U-value of 0.08 W/sqm/degC, about 25X better than before.
Water from the bath goes to a barrel in the garden, to be used for watering the garden.
Low flow taps are used throughout to help us save water.
The original front door is now a window that opens to our front garden.
In the former coal cellar is a 2,500L rainwater harvesting tank from Rainharvesting Systems. We filter and store rainwater collected from our roof for flushing the wcs, washing clothes in the washing machine, and for a rainwater tap in the kitchen. We expect this will reduce our water consumption (which is metered) by approximately 50%. It will also reduce the amount of rainwater discharged into the drainage system.
All our windows are triple glazed with a U-value of 0.65 W/sqm/degC, which is approximately 14X better than the original single glazed windows. Every room has at least one opening window (Enersign range from the Green Building Store) for natural ventilation in summer. In this year’s cold winter we had beautiful ice crystals growing up the outside of our windows while we were snug inside!
Walls are finished with Glaster, a traditional lime plaster using ground up recycled glass in place of sand.
The house has been sealed to a level 28 times better than the original using “Intello Plus” airtight membranes. These allow vapour permeability so that condensation is minimised. Research shows that limiting warm air leakage, even through concrete walls is an essential element in reducing heating needs.
An special air-blowing machine was used on site to test work as we went along, and at completion an independent test was undertaken. This pressurised the whole house and measured the air leakage rate. The achieved Q50 airtightness rating was 0.97 m3/m2/hr – more than ten times better than the new building regulations.
The construction stores heat to keep the house warm in winter and cool in the summer. This works like a night storage electric heater, and is called “high thermal mass” construction. Lightweight (timber) construction can overheat dramatically in hot summers.
Dual flush toilet uses 2.6/4 litres (rather than up to 13 litres in some UK wcs). This is important as there is a large hidden energy cost in cleaning, purifying and pumping water to our homes. And here we are using rainwater collected from our roof to flush the toilets. These Ideal Standard wcs are the first seriously low water usage ones to be made in the UK.
Views framed up into the ash tree, which gives us our summer solar shading, and over the rooftops out to the skyline of leafy Edgbaston. You can’t see it but up to your right outside is a bat box, facing north so that the nocturnal bats are not woken up too early by sunlight!
These shutters can be closed for privacy and quiet. Or they can open to connect the space with the rest of the house, allow light in from the top-lit staircase.
This shutter can be closed for privacy and quiet. Or it can open to connect the bedroom with the rest of the house, allowing light in from the top-lit living room and helping especially in summer to ventilate the house and keep us cool (which will be increasingly important with global warming…)
South west facing glass, triple-glazed, allows useful solar gains in the winter when the sun angle is low. In the summer the higher angle of the sun, and the leaves on our old ash tree, will shade the glass enough to prevent overheating. Above the windows in the recess there will be insulating blinds,
In place of tiles we used pebbles we collected on holiday on the Gower peninsular in Wales.
This second kitchen tap is for rainwater harvested from our roof. We use it for washing down, scrubbing carrots, etc.

Zero Carbon House, Birmingham UK » Open Day

Design notes on the Zero Carbon House