Whole Life Performance Research

The benefit of masonry’s thermal mass has long been acknowledged as a positive attribute in increasing the thermal comfort for building occupiers.

With the predictions for climate change pointing towards a hotter climate, it is vital that new homes remain both energy efficient and comfortable throughout their lifespan. Thermal mass, as part of an integrated design strategy, can play an important role in ‘futureproofing’ our homes.

Findings of whole-life CO2 research

 
The thermal mass benefits of masonry products are supported by research (1) commissioned by The Concrete Centre in 2006, which predicts that “some lightweight homes with minimal thermal mass could be experiencing particularly acute problems in as little as 20 years” due to regularly overheating as a result of global climate changes.

The research, carried out by Arup Research + Development, shows that conventional masonry houses that take advantage of their inherent thermal mass can save a significant amount of energy over their lifetime compared to lightweight timber frame housing. The research is the most comprehensive study to date to examine both embodied and operational CO2 emissions. It provides strong evidence that lightweight timber homes may not be as sustainable in the long term as masonry construction. The research takes account of experts’ predictions for climate change and demonstrates that the thermal mass in masonry homes reduces the need for air conditioning. It also highlights the additional savings that can be achieved through using thermal mass to capture solar gains in winter, thereby reducing the consumption of heating fuel.

These savings can offset the slightly higher level of embodied CO2 in a masonry house in as little as 11 years and ultimately lead to the lowest whole life CO2 emissions.

Comparing lightweight homes to heavyweight homes


Comparing lightweight timber homes with medium weight and heavyweight masonry and concrete homes, Arup found the latter can have the lowest total energy consumption and CO2 emissions over their lifecycle. This is achieved through using the thermal mass of blockwork in the walls to optimise the energy efficiency of the structure. Adding further thermal mass from concrete floors saves even more CO2 over the life of the house. The research found that lightweight homes (timber frame) will overheat more frequently during the predicted hotter summers of the 21st century, which could in turn lead to an increase in the use of air conditioning, resulting in greater energy use and CO2 emissions. Homes built using masonry and other concrete products, such as precast flooring, with their inherent thermal mass will be cooler in the summer and so will not suffer overheating to such a degree.

Summary of research assumptions

 
The research was based on the study of a two-bedroom semi-detached house in the South East of England, typical of the type of ‘starter home’ envisaged by the Government for major areas of housing development such as the Thames Gateway. Analysis of lifecycle CO2 emissions was carried out on four ‘weights’ of construction: light, medium, medium-heavy and heavy.

The lightweight class was a timber-frame home with timber floors, exterior brick and internal plasterboard finish. Medium weight was the same but with brick and block cavity walls. The medium-heavy house had a precast concrete first floor, e.g. beam and block, and ground floor partitions of mediumweight concrete blocks such as Hemelite with a plasterboard finish. Finally, the heavyweight class had the highest level of thermal mass with dense blocks, e.g. Topcrete Standard, used for the external walls and internal partitions, together with a precast concrete first floor and loft floor.

The lightweight home was found to need air conditioning by 2021. This compared to 2041 for the mediumweight home and 2061 for the mediumheavy and heavyweight homes. This means that timber homes, and other similar lightweight constructions, being built today could become uncomfortably warm in as little as 15 years. Over the lifecycle of the homes, the increased reliance on air conditioning in the lightweight home will significantly negate its initial marginally lower embodied CO2.  The medium weight masonry home was calculated to have around 1.25 tonnes more embodied CO2 than the equivalent timber house, yet over a 60-year period the timber home was found to emit 9 to 15 tonnes more CO2.

The Report’s finding support the use of masonry products in conjunction with concrete floors in providing the best long-term sustainable building option, especially if the benefits of thermal mass are fully exploited. The results for housing are of relevance to other sectors such as offices where a major design challenge is keeping cool. Here, adequate ventilation, solar shading and use of thermal mass are the three accepted methods of avoiding overheating through passive means. The moderate to high cooling loads associated with office environments enable significant energy savings to be realised if thermal mass and night ventilation are used to help avoid or minimise the need for air conditioning. This will in turn lead to a significant reduction in operational CO2 emissions.

Reference

(1) - Whole Life Performance Research – A Lifecycle Analysis of Carbon Dioxide Emissions from Housing under Climate Change, Examining the Role of Thermal Mass, research commissioned by The Concrete Centre and British Cement Association and undertaken by Arup Research & Development 2006.

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Fact 29

By 2050, 56% of people want cars to be very low carbon and powered by fuel cells or electricity.
Source: Energy Saving Trust 2008