Overheating in homes

This post was written by BSRIA's Saryu Vatal

This post was written by Saryu Vatal, Senior Consultant of BSRIA’s Sustainable Construction Group

BSRIA’s Residential Network organised an event on the 22nd of July focussing on the issue of overheating in homes with an excellent line up of speakers. Nicola O’Connor started the day summarising an extensive research project by the Zero Carbon Hub that brought together input from government, industry and academic experts to understand the challenges around tackling the risk of overheating in homes (http://www.zerocarbonhub.org/current-projects/tackling-overheating-buildings). Chris Yates from Johnson and Starley made an appraisal of the assumptions and requirements within the Building Regulations and associated guidance as well as the implications for mechanical ventilation system manufacturers. Neil Witney from DECC explained the challenges around defining and regulating of overheating within homes, current policies and mechanisms that may be introduced in the future in response to the growing body of evidence highlighting the issue. Paul Ciniglio from First Wessex shared the organisation’s findings from several research projects and experience from their own developments, which resonated with issues highlighted by members of the audience. Bill Gething of Sustainability + Architecture and professor at the University of West England brought into perspective how changes in the way homes have been designed and built over the recent years has led to a shift in the performance of homes. James Ford, partner at Hoare Lea discussed some key considerations for designers to address the issue at early stages, to help minimise risk and dependence on active cooling solutions.

Extent of overheating

Evidence indicates that up to 20% of homes in England may already be overheating. Areas where additional risks have been highlighted include:

  • Common areas in apartment blocks, especially where community heating is installed – these areas are not assessed using SAP as they are outside the dwelling envelope. In reality, being unoccupied spaces these are often not modelled for their thermal performance (and energy use) at all. Community heating is being incorporated in an increasing number of projects and the supply network remains live even in the summer to meet the domestic hot water demand. Ensuring that the specification and installation of insulation for the distribution pipework is adequate is becoming increasingly important as buildings are made more airtight. Often stairwells and circulation areas have a high proportion of glazing and, with recent improvements in the general standard of construction and materials, tend to retain a large proportion of the heat gains. It is now important to incorporate a ventilation strategy for these spaces so that the accumulated heat can escape.
  • Urban areas – the average temperatures in city centres can be more than 4°C higher than rural areas. Flats are more common to city centres and these are often close to sources of noise and air pollution and have limited, if any, potential for cross ventilation. All these factors can combine to limit the effectiveness of natural ventilation in addressing the build-up of heat and not just in the summer. Building designs that incorporate large proportions of glazing in their facades, such as penthouses, if not carefully designed, can require air change rates that are unrealistic to achieve, using natural or mechanical ventilation systems.

Need for a definition

A number of sources and definitions are being referred to currently when evaluating for the risk of overheating in homes. These include CIBSE’s Environmental Design Guide A (2006) which sets standards for comfort, although it is not mandatory to use this to demonstrate compliance with the Building Regulations. Dynamic modelling through tools such as TAS and IES offer the opportunity of making a more comprehensive evaluation than SAP, but this option is skill, time and cost intensive. Building Regulations do not relate to limiting overheating for thermal comfort, just limiting the use of fuel and power for air-conditioning. The minimum evaluation for demonstrating compliance with Criterion 3 of Approved Document Part L of the Building Regulations needs to be carried out using SAP. While SAP is not intended to be a design tool, it is accepted that it is the default tool the industry uses widely.

Research projects have highlighted that dwellings can demonstrate a risk of overheating when evaluated against the CIBSE standard but not when modelled in SAP. Surveys from the Zero Carbon Hub study showed that nearly 60% of the housing providers surveyed had checks in place to assess the risk of overheating. However, only 30% of these housing providers explicitly included the requirement for considering the risk of overheating as part of their employees’ requirements to architects and designers. This suggests a missed opportunity for the issue to be addressed early on in the process, when cost and energy efficient measures may be effectively incorporated.

There are several challenges around the definition of conditions under which overheating can be said to occur as several factors contribute to this, including but not limited to air and radiant temperatures, humidity, air velocity, level of activity the adaptability of the individual. There are several checks that can be built into the design process which can help identify the risk at an early stage and allow for a method for mitigating these to be set up and followed through.

Contributing factors
The energy efficiency of homes in the UK has improved significantly in terms of reduction of space heating loads. This has come about in new homes through Approved Document Part L 1A of the Building Regulations and in existing homes through schemes such as the Green Deal. Homes are now less leaky and better insulated to keep warmth in but attention and emphasis is needed on measures to facilitate the expelling excess heat adequately when temperatures rise.

Homes are expected to provide comfortable conditions for occupants all year round and through a range of different occupancy patterns, which may in reality be considerably different to the standard assumptions made in modelling tools like SAP. It is possible that if modelling for thermal comfort is carried out assuming worst case assumptions for occupant density, external conditions and hours of occupancy, many homes would require mechanical cooling. There are, however a number of common sense measures that can be applied to ensure the impact of key contributing factors are minimised. These include controlling solar gains from south and west facing glazing and making provisions for adequate, secure ventilation especially when thermal mass has been incorporated in the structure.
The current extent of overheating in homes must be seen in the context of the anticipated changes in climate. With external temperatures expected to rise with an increased frequency of extreme weather conditions, homes built today must be fit for purpose for warmer summers.

Mechanical cooling?
There has been a rise reported in the installation of mechanical cooling systems in homes in the UK, more noticeably so in the south. While this may be an expected feature in high end homes, the cost of running these systems can be prohibitive, or at least perceived as so, for households where minimising expenditure on energy and fuel is a priority.
There is potential to develop low carbon mechanical cooling systems such as reversible heat pumps. The large scale uptake of these can however have some serious implications for energy supply and the capacity of the grid to accommodate a draw in peak summer months.

Way forward
In addition to affecting comfort, exposure to high temperatures over prolonged periods can have a significant impact on the health and well-being of residents. It is critical therefore to agree on a set of parameters that can help define overheating in homes and this should be carried out with input from bodies such as Public Health England.
Until a definition and modelling strategy is developed, designers and housing providers can refer to several good practice guides and research studies that help embed a common sense approach to design. There is significant potential to mitigate the risk of overheating in homes if early stage design decisions are taken with due consideration for the issue. The limitations of mechanical ventilation systems to help achieve comfort in homes must be acknowledged so that the final burden of an ill-considered design does not rest with the occupants.

References and further reading
http://www.zerocarbonhub.org/sites/default/files/resources/reports/ZCH-OverheatingInHomes-TheBigPicture-01.1.pdf
Design for Climate Change, Bill Gething and Katie Puckett, RIBA Publishing Feb 2013
http://www.arcc-network.org.uk/wordpress/wp-content/D4FC/01_Design-for-Future-Climate-Bill-Gething-report.pdf
http://www.zerocarbonhub.org/sites/default/files/resources/reports/Understanding_Overheating-Where_to_Start_NF44.pdf

To find out more about our Residential Network and to download the presentations from this meeting check out BSRIA’s Network pages.  To find out more about all of BSRIA’s networks contact tracey.tilbry@bsria.co.uk.

BSRIA Residential Network launch

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This blog was written by Saryu Vatal, Senior Consultant and Researcher for BSRIA Sustainable Construction Group

The BSRIA Residential Network was launched on the 11th of September, kindly hosted by the Wellcome Trust and well attended by over 50 delegates, comprising of both members and invited guests.  Ian Orme Business Manager for the Sustainable Construction Group welcomed the delegates and introduced briefly the intention of the network and how BSRIA would like to engage with all stakeholders to help make residential development better.

The event was chaired by Richard Partington of Richards Partington Architects, architect advisor for the Zero Carbon Hub and co-chair of the steering group for their Performance Gap project.

The day started with a summary of the current policy context for energy efficiency standards in new homes and challenges and opportunities for low energy retrofits.

The recently concluded Performance Gap project for the DCLG provided a starting point for discussing issues that impacted new build residential developments. For this project, an extensive evidence gathering and review exercise was carried and over 60 issues were identified as contributing to the gap between the designed and measured energy use in homes.  Of these the ones prioritised for action and further research, along with the shortcomings in skills and knowledge highlighted through the end-to-end process review of over 20 new developments,  formed the core of the Hub’s recommendations to the Government.

Rick Holland was present to give an update on the Government’s continued support for funding research into construction processes via Innovate UK (previously Technology Strategy Board), both for domestic and non-domestic buildings.

A major programme from this funding stream looking at Building Performance Evaluation is coming to a close at the end of September and early stage findings from meta-data analysis were presented by Ian Mawditt of Fourwalls.  This focused on the common issues found with the design, installation and operation of MVHR systems and data from whole house co-heating tests. The final findings will be disseminated via Innovate UK and will include information from all projects across the seven funding tranches.

The analysis of key design specifications that would impact the performance of the mechanical ventilation systems raised some interesting observations about common assumptions made at early design stages.  Common themes from the commissioned air flow rates were also discussed.  The performance of homes built to Passivhaus standard was notably better, which emphasised the importance of process control on site, but also highlighted the fact that, when needed, the industry was able to deliver a high quality product (homes).

The presentations of the day concluded with a summary of how BSRIA would like to engage with its members to try and address various shortcomings identified through research.  Members are invited to put forward areas where there is a need for additional support, in the form of training, guidance and impartial technical expertise.

Calculator leaned on a little house with red roofA panel discussion was facilitated by the event chair in which a range of topics were discussed.  These included issues around the effective design, installation and modelling of district heating in residential and mixed use schemes and variations in standards and assumptions between the EU and the UK.  Ashley Bateson was able to provide an update on standards being developed by CIBSE.

The conflict between supporting innovative technology and the confidence in product and performance data to allow these to be accepted into mainstream and within compliance tools was also highlighted as an area of concern.

The impact of users on the actual energy performance in homes has not been included in some key research projects although in reality this has significant impact.  While this lies beyond the scope of a developer’s influence, key decisions about the complexity of services, controls interface and handover procedures all contribute towards the usability of homes.  Instances of how internet based tools and were successfully employed in some projects to engage with occupants to develop a feedback and learning mechanism were highlighted.

There were concerns voiced about the problem of overheating in new and newly refurbished homes, especially when dealing with vulnerable occupant groups like the elderly.  The Zero Carbon Hub are working on a project looking at the evidence and aim to help develop the assessment standards and methods for evaluating and mitigating risks in new homes.

BSRIA sees itself well-placed to engage with its members and the wider industry to help address the various shortcomings and areas of concern highlighted.  Subsequent network events have been planned to focus on specific topics in detail and we are seeking feedback from members to help structure our efforts in the most effective and useful manner.

Presentations from all speakers can be found on the networks page of the BSRIA website.

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