Wood and building performance

1 Introduction
2 The Future Homes Standard
3 A fabric first approach
4 Whole life carbon
5 Which products to use
6 Building performance evaluation
7 Addressing the gap
8 Design to eliminate overheating
9 The way forward
10 Related articles on Designing Buildings Wiki

[edit] Introduction

Against the backdrop of a chronic lack of high-quality, affordable housing, coupled with the unprecedented challenges of the climate emergency, delivering record numbers of well-designed, better performing homes has become an urgent priority.

Despite successive governments pledging to make housing a priority, the National Housing Federation estimates that 8.4 million people in England—more than 15% of the population—are living in unaffordable, insecure or unsuitable homes.

The housing crisis not only reflects the lack of social and affordable housing in the UK, it is also a crisis of quality: old housing stock, badly planned refurbishments and low-quality new homes are contributing to the problem. Unhealthy buildings with poor ventilation are adding to the increase in asthma, while the rising costs of heating our poorly insulated homes is leading to fuel poverty.

Meanwhile, the climate crisis is upon us. According to the UN Intergovernmental Panel on Climate Change (IPCC) we have just over a decade to limit global warming to a maximum of 1.5°C above pre-industrial levels to avoid climate breakdown.

Against this backdrop of a chronic lack of high-quality, affordable housing, coupled with the unprecedented challenges of the climate emergency, delivering record numbers of well-designed, better performing homes has become an urgent priority.

[edit] The Future Homes Standard

The Government has committed to achieving net zero greenhouse gases by 2050. This means that emissions from homes, transport, farming and industry must be completely avoided or where that is not possible, offset by planting trees. Around 15% of all carbon emissions in the UK come from housing. The UK Climate Change Committee has said that all existing and new UK homes must be low carbon, low-energy and resilient to climate change.

To help meet these aspirations, the UK Government recently committed to a new ‘future homes standard’ (2019), which states that from 2025 at the latest, no new homes will be connected to the gas grid. Instead they should:

Be heated through low-carbon sources such as air source heat pumps.
Have ultra-high levels of energy efficiency alongside appropriate ventilation.
Where possible, be timber framed.

Together with the Government’s Industrial Strategy Clean Growth Grand Challenge mission to halve energy use in all new builds by 2030, this will set a path towards decarbonisation of all new homes and will support the scaling up of low carbon technologies to improve energy efficiency in existing homes.

[edit] A fabric first approach

To meet the aims outlined above, all new homes should be built to very high fabric standards. Adopting a fabric first approach to building design means considering the impact of the performance of every component and material that makes up the building itself. This can help to improve energy efficiency, reduce carbon emissions, lower operational costs and reduce the need for maintenance. It is expected that the average future home will be responsible for 75-80% less carbon emissions than one built to current standards.

According to George Martin of the Building Performance Network, the role of building fabric and the choice of materials is critical to the performance of the home. Materials have an effect on energy efficiency, indoor air quality, thermal comfort and moisture control. He recommends urgent change to the way homes are procured and specified.

Adopting a fabric first approach means opting to build with sustainable, renewable materials such as timber, choosing natural insulation materials such as wood fibre, maximising air-tightness and optimising natural ventilation.

[edit] Whole life carbon

A fabric first approach also considers the whole life carbon emissions of the building. These are directly related to the type and quantity of resources used to create, maintain and use a building. Whole life carbon assessments consider resource efficiency and carbon emissions and with this in mind the Royal Institute of British Architects (RIBA) has produced a comprehensive guide for architects providing advice and guidance through the RIBA work stages. Whole life carbon is expected to become more important as a way of saving resources and enabling residents to lead lower carbon lives.

In his new book Designed to Perform: An Illustrated Guide to Providing Energy Efficient Homes, Tom Dollard provides practical design guidance on how to deliver better energy performance in all types of new build homes.

[edit] Which products to use

A fabric first approach lends itself well to timber frame buildings. In particular, closed timber panels, which are manufactured offsite and leave the factory ready-insulated, have intrinsically high levels of thermal performance.

Options for rendering or cladding a property built with timber panels include preserved timber cladding, or other natural materials such as lime render. Any timber products should come from sustainably-managed sources.

By ensuring high levels of insulation and air-tightness in the building’s design and combining that with ground source or air source mechanical ventilation and heat recovery systems, there is less reliance on generating electricity. However, if extra energy is required, sustainable methods such as photovoltaic panels or wind turbines are a good option.

Triple glazed windows reduce the amount of heat lost and placing windows on the south side of a home helps to maximise solar gain and reduces the need for heating. To keep the building cool in the summer, extended eaves or blinds reduce the heat from the high summer sun.

[edit] Building performance evaluation

Unfortunately, new buildings often underperform when it comes to energy efficiency in comparison to the expectations defined at the design stage. This is known as the ‘building performance gap’. On average, traditional new-build homes use 60% to 80% more energy for heating than their design target.

Evaluating a building’s performance is essential to ensure that the targets set are in fact met, and as a way of ensuring continual improvement in building methods.

To meet this demand, as part of the Home-Grown Homes project in Wales, Cardiff Metropolitan University is testing a range of practical solutions for building performance evaluation (BPE) with the aim of encouraging developers and housing associations to use BPE on all their builds.

Post occupancy evaluation should be incorporated into every project with the results built into the next project brief to ensure continual improvement.

One example of building performance and post occupancy evaluation in action is at Ty Newidiadau in Cardiff. The project features properties built using three different construction methods and aims to assess their performance over time to inform design and material decisions for new affordable and social housing.

[edit] Addressing the gap

One approach to help address the building performance gap is Passivhaus, which, according to the Passivhaus Trust, achieves a 75% reduction in space heating requirements, compared to standard practice for UK new builds.

The benefits of Passivhaus performance include:

Improved indoor air quality.
Thermal comfort.
Self-maintained moisture and humidity levels.

Passivhaus is about airtightness and breathability, so choosing the right insulation material is key. Wood fibre insulation is a good option as the natural fibres help to prevent overheating in summer.

Homes built to Passivhaus standards use heat recovery ventilation systems to heat the incoming fresh air with heat from the outgoing stale air. Due to their design, they stay warm in winter but remain cool in summer. Homes designed to Passivhaus standards often benefit from increased space and daylight, too.

[edit] Design to eliminate overheating

While building to Passivhaus standards is one way to prevent poor ventilation and overheating in new homes, there is a raft of design, material and planning considerations which can also help to reduce these problems.

With this in mind, in July 2019, the Good Homes Alliance launched a new tool and guidance for those involved in the early stages of designing and developing new homes. The tool offers comprehensive guidance and enables the project team to estimate the likelihood of overheating in the future, and suggests ways to mitigate the risk

[edit] The way forward

A chronic lack of affordable and social homes is no excuse to house our most vulnerable people in unsuitable bed and breakfast accommodation, badly converted office blocks and poorly designed new builds.

Instead, a fabric first approach to thoughtfully-designed new builds and renovations, using sustainable, locally sourced materials where possible and implementing passive methods of heating and ventilation will result in housing for future generations that we can be proud of. Let’s hope the latest Stirling Prize winner sets a precedent for change.