The Government has set itself, and thus we the people, the legally binding challenge of reducing greenhouse gas emissions by 80% by the year 2050. In order to achieve this goal significant changes are going to be required in all aspects of our daily lives. Assisted by Adam James and myself (we worked at Devereux Architects at the time) and mechanical engineer Alan Clarke, the Sunderland based property business Gentoo Group were commissioned to retrofit six homes. The goal was to reduce the carbon emissions from the homes by 80%! The refurbishment project forms a part of the £16m Retrofit for the Future project which is being funded by the Government’s Technology Strategy Board. Out of 600 applicants and 87 successful bids, from across the UK, the team won three projects; three different pairs of semi-detached homes. Importantly each pair of houses was constructed using a range of different building technologies. Application in the Broader Context The homes were chosen because they were built using different construction technologies including traditional (cavity walls) and non-traditional construction (Laing Easiform and Wimpey No-fines). Each construction technology poses a unique set of challenges and obstacles that need to be understood and overcome.
Why is this important? If the Government is to achieve its objectives then most of the homes in the UK will require a radical retrofit using a highly replicable set of solutions. In order to demonstrate how these solutions can be applied they need developed and tested in a range of contexts.
The units constructed using traditional cavity wall construction were built in 1960. There are about 20,000 of this house type within Gentoo's existing stock. Because these homes use traditional cavity wall construction, the fundamental concepts underlying the proposed retrofit could easily be applied to a large proportion of the 16 million cavity wall homes that exist in the UK.
The Laing Easiform units were built in 1954 and use a type of insitu concrete cavity wall construction. There are 240 of this house type or very close derivatives of this within Gentoo's existing stock. Whilst it is realised this is not one of most common house types in Sunderland however we also recognise the wider importance of this house type nationally as there are estimated to be 90,000 Laing Easiform homes in the UK.
The Wimpey No-fines is also a non-traditional construction. These particular units were built in 1954. Whilst there are only 69 of this house types, or very close derivatives, of this within Gentoo’s existing stock there are over 300,000 in the UK as a consequence they have national relevance. With no-fines being a form of solid wall construction the underlying concepts for the proposed retrofit could easily be applied to a large proportion of the 7 million solid walled homes in the UK.
The solution the team has proposed is a design that is sufficiently generic to mean that it can be applied to each construction technology and is as a consequence highly replicable and could be used to reduce the carbon emissions from a vast proportion of the UK's housing stock. In the team’s view a key part of ‘replicablility’ is being able to allow tenants to stay in their homes whilst work progresses. The aim is to minimise disruption to people’s lives and avoid temporarily relocating occupants which is costly, especially if it is to be done for every home in the UK. This constraint also created specific challenges as it meant that we could not insulate the ground floor. We did consider internal insulation, for walls and floors, but concluded that the approach was problematic as it raised concerns about disruption to tenants and the increased risk of needing to temporarily relocate tenants, the loss of space and long term concerns about the impact that this approach could have upon the building physics.
To achieve our goal, our approach relies upon the concept of a tea cosy whereby an external ‘air barrier’ (to prevent energy sapping and uncomfortable cold drafts), and external insulation are applied to the thermal envelope. Additional energy savings are made by introducing a heat recovery ventilation and some supplementary solar hot water. Another key benefit is that the retrofit can be undertaken without requiring the residents to move out – thus allowing people to enjoy their home whilst reducing capital costs and enabling a high degree of replication. In order to assess the success of the projects they are to be monitored for a period of two years.
The importance of this project can not be underestimated
UK carbon dioxide emissions are about 585.71 Million metric tonnes, of which the 25 million homes are considered to account for about 27% of emissions (158.14 Million metric tonnes, or 6.33 tonnes per house). If it were possible to apply this retrofit strategy to the 23 million homes that we have identified it would save 126.52 Million metric tonnes CO2 per annum (the key variable being the ability to install solar hot water). To phrase this slightly differently we could reduce UK emission by 21%.
Health and indoor air quality
Lately I've also been thinking about the possible health benefits of good ventilation. In the UK asthma affects about 5 million people (1.4 million of which are children). Research in Scotland has shown that MVHR helps reduce the causes of asthma - particularly dust mites (research by Stirling G. Howieson). To help control dust mites, balanced ventilation can serve to keep the relative humidity below 40-45% for sustained periods. When you consider that asthma is reported to cost UK Plc £2.3 billion a year it can be recognised that this is a major issue. On the basis that there are about 23 million homes in the UK, we can estimate that asthma costs £100 per household per annum. Currently a heat recovery ventilation unit costs about £2000 and has a life expectancy about 20 years, the cost to the household is therefore about £100 per annum. If balanced ventilation with heat recovery manages to reduce the burden on the NHS, keep people in work and reduce benefit payments then you could be introducing benefits before you even start to think about the energy/carbon savings (a heat recovery unit in a suitably airtight house can save £150 per annum).
Each year around 1100 deaths from lung cancer (3.3% of all deaths from lung cancer) are related to radon in the home. Current policy requiring basic measures to prevent radon in new homes in selected areas is highly cost effective, and such measures would remain cost effective if extended to the entire UK, it has been suggested that the current policy of identifying and remediating existing homes with high radon levels is neither cost effective nor effective in reducing lung cancer mortality. German research, tabled at the Passivhaus Conference in 2010, suggests that ventilation, and airtightness, is key to addressing the health risks associated with radon. Perhaps if a whole systems approach was taken to asthma and radon risks then the results of the cost analysis may change.
Show me the money
Our integrated design approach has optimised the entire system for multiple benefits, rather than optimising isolated components for singular benefits. The consequence of this approach is that lifecycle savings can be incurred by capturing the interactive effects between components. By undertaking measures with the lowest lifecycle cost we have been able to incorporate technologies / concepts without radically increasing the lifecycle cost beyond that of the existing building. This has unique approach has allowed us to retrofit two homes for less than £150,000, as compared to other RftF projects have spent the same sum to retrofit a single house to the same 80% reduction in carbon emissions.
Now £75,000 per property is a very large sum of money, but is has to be remembered that this is a very innovative project with a good deal of design and research time associated with it. The actual materials and labour costs are nearer £40,000 and allowing for overheads and site costs, the cost of the project is nearer £56,000.
If you now allow for these strategies being scaled up to suit a national retrofit program then the costs could tumble significantly - we estimate that the could fall by over 33% - leading to a construction cost of about £47,700. The most important factor in reducing the marginal cost of a retrofit project would be to tie the work closely to the natural household maintenance cycles. This would mean that certain expenses that would have been incurred anyway do not become direct costs associated with the retrofit work. For example this could include site set up costs, scaffold, re-pointing, replacing roofs and windows etc. Further savings could be made by over coming skills gaps through the implementation of suitable training programmes and optimised manufacturing.
In my view another one of the largest stumbling blocks is the fact that refurbishment incurs 17.5% tax compared to new build which only incurs 5% tax. This additional 12.5% tax adds just over £5000 to the cost of the project. Surely one of the biggest moves towards incentivising low energy retrofit projects would be to remove the tax burden if they are shown to be achieving deep cuts in carbon emissions.
When dealing with such large sums of money we have to ask whether such measures are affordable over the lifecycle of the house. The Energy Savings Trust has estimated that the average heating bill for a two bedroom house is £588 - £882 per annum. For the retrofit it has been estimated that the cost of space heating will be about £121 per annum and the domestic hot water £27 per annum; the total being £147 per annum. The saving is a staggering £441 - £735 per annum; which is a 75% - 83% reduction in heating bills! Whilst it is recognised that the lifestyle of the occupants could of course have a major impact upon this; for better or worse, it can be recognised that the implications are huge. The average saving is therefore £588 per annum – which is strangely the same figure as the lower estimate for the average bill according to the EST. In the following discussion we will use the average savings and average bills as a point of reference.
If we consider that the retrofit was to be undertaken upon a large scale then the extra over costs for setting up the construction site could be reduced. Also, given that this is an innovative project there is a learning curve for all involved. If the standards of design and craftsmanship became the norm then further cost savings could no doubt be achieved. With these allowances the costs roughly balance with the simple savings.
The solutions that we have adopted a based upon the concept of energy efficiency as a consequence there is comparatively little maintenance required compared to solutions that rely upon more gadgets. The tea cosy has a life expectancy of over 80 years (the average UK home is over 100 year old and a through refurb will extend the life of a home significantly). The ventilation unit is generally considered to have a life of 20+ years and the solar hot water has a life of 15 years, as does a regular condensing gas boiler. Over 80 years the ventilation unit would be replaced three times and the solar hot water and the boiler five times. This leads to a lifecycle maintenance cost of £14,400.
A simple saving, excluding inflation, of £588 per annum over 80 years adds up to £47,070 (£588 * 80 = £47,070). But this is not the whole story. Fuel prices have been rising far faster than inflation. If we take a conservative view that fuel prices rise at just 1% per annum faster than inflation then in 80 years the average fuel bill will be nearer £1613 – and that’s ignoring the impact of inflation. Taken cumulatively over the lifecycle, whilst ignoring inflation, the total fuel cost is £89,428. It can now be seen that by investing in radical energy efficiency these discrete savings can in the long term provide a significant buffer to future price increases. The lesson here is that we need to remember that this investment has protected us from fuel price inflation and that this also has a value to the household.
So where does all this leave us? Simple lifecycle calculations for energy bills suggest that over 80 years the occupant will spend £89,428. Over the lifecycle our reduced energy bill sums up to £17874, which means that there is a net saving of £71,554. At today’s costs our retrofit costs about £56,000 per house and we think that the future cost of a retrofit could fall to less than £47,700. If we include the maintenance costs of £14,400 then the total retrofit cost is between £62106 and £70,400.
As noted above a national retrofit programme that improved indoor air quality could have an impact upon the incidence of asthma. The savings could be between £0 and £8000 over the lifecycle; however, due to the lack of statistical evidence the magnitude of the benefits can not be determined in any reliable fashion. For these reasons these benefits have been excluded from further cost analysis. So does the home owner save money? Even in the best of scenarios, from our current vantage point, it would seem that the actual savings are marginal, some £1000-£9433 over 80 years or £13-117 per annum (which is a saving of 1-16% on the lifecycle cost). Considering climate change and the Government’s (hence ‘our’) legal commitment to reduce carbon emissions it will be asked whether is this all this effort worthwhile. We think so no one looses and many can gain.
NOTE: This article was originally written when author worked at DEWJO’C Architects (which latterly became Devereux Architects). In 2011 Mark set up his own practice so that he could continue to pursue his interests in developing sustainable, low energy architecture.
Notes on the author:
Mark Siddall, principle at low energy architectural practice LEAP, is an architect and energy consultant specialising in low energy and PassivHaus design. He was project architect for the Racecourse Passivhaus scheme and has a keen interest building performance. In addition to architectural services his practice provides project enabling and education for clients, design teams and constructors.
LEAP website: www.leap4.it