A building’s thermal performance is now as important an aspect of the building’s design and construction as its structure. Energy prices and climate change are often cited as the principal reasons for the increased energy and CO2 reduction standards required of our built environment. Less known is the fact that insulation can also play a major role in our health, safety, comfort and wellbeing.
When higher levels of thermal performance are required, this has a significant impact on building physics and other dynamic elements of a building’s performance.
Woodfibre insulation has a number of properties that enables it to provide a multifunctional role within the construction of a home. When specified and installed correctly, woodfibre provides protection against summertime overheating, enhanced acoustic performance and moisture control. The latter provides a building fabric with additional insurance against potential moisture problems that could otherwise undermine the integrity of the building and the health of the occupants.
Woodfibre is highly sustainable, locking up considerably more CO2 than is produced in manufacture. It can therefore play an essential part of a strategy for mitigating climate change.
This document provides information for specifiers and procurement specialists working on social housing projects. It is designed to help with the specification of wood fibre insulation within a social housing context. It provides performance criteria and indicates what needs to be considered when specifying woodfibre insulation.
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Building Performance
Wooden Windows-Specification guidance for timber windows
Windows provide an outlook on the world. They help set the tone and character for a building and the area in which it stands. Windows define natural lighting levels and thermal comfort essential for the wellbeing of residents. They offer sound protection and keep homes safe from intrusion. Windows are an essential part of the building fabric and as such contribute to a development’s overall energy performance.
Modern factory-finished timber windows have a better environmental performance than any other window material. They have a longer service life and lower whole life costs than uPVC windows. Wooden windows can be repaired and recoated throughout their lifetime and are the best option for achieving zero carbon buildings. They can be sourced from local manufacturers using home-grown timber and support economic recovery in Wales.
The multiple benefits wooden windows deliver over their life-span in terms of maintenance, durability, embodied carbon, and other social and environmental aspects make them excellent value for money.
This document provides information for specifiers and procurement specialists working on social housing projects. It is designed to help with the specification of low-carbon timber windows in a social housing context. It provides performance criteria and indicates what needs to be considered to achieve these in practice. Windows are an essential element of the building fabric and should not be discussed in isolation. They should be considered very early in the design process when deciding what build system to use.
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Building Performance Evaluation Guide
New homes often fail to meet low-energy targets, and to satisfy residents with fundamental issues such as ease of use, summer comfort and energy costs. There is little Building Performance Evaluation (BPE) happening routinely on projects to close the performance gap. A step change is needed to transition to net zero carbon while making our homes comfortable, healthy and enjoyable.
This guidance is aimed at housing clients, and anyone interested in Building Performance Evaluation (BPE) who want to evaluate and improve the performance of homes.
Its purpose is to provide an introduction to applying BPE in practice on projects, with:
- Information for clients and project managers to gain an overview of the benefits of BPE, what the main BPE techniques can do, how to procure it, and the main activities to plan throughout a project from design to occupancy
- Guidance on the main BPE techniques available
- Tools for day-to-day use on projects, complemented by more detailed guidance, examples and references.
This guidance recommends a “core” BPE scope for clients and project teams wanting to understand and improve the performance of their homes. This provides a holistic look at performance, including people, the indoor environment, fabric performance, energy use and water use. It highlights how BPE techniques can work together, and the interactions between energy performance, people, and the indoor environment. It limits the involvement of experts and expensive equipment. Instead, the aim is to embed building performance throughout the project stages and empower project teams to deliver high performance.
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Cover image: © shutterstock.com / NDAB Creativity
Making the Right Choices—A Guide to Improving the Build Quality of New Build Timber Frame Social Housing
Making the right decisions for the benefit of a building’s long term performance and user experience can be compromised by cost, lack of experience, and poor understanding of timber frame construction.
This guide aims to highlight some of the key points to consider along the pathway of designing, constructing and maintaining timber frame housing.
These points have been compiled reflecting on experience gained by delivering BMTRADA’s frameCHECK on-site quality consultancy service.
By helping the reader understand more about the consequences of some of the decisions to be made during construction.
This report has been compiled as part of the Home-Grown Homes Project, which looked into the way that timber is specified and used in construction, with its focus being on manufacturing. The aim of this document is to help all those involved with timber frame construction to deliver better performing and longer lasting homes.
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Net-Zero targets for Wales
Building on the work of the UKGBC and LETI, the Home-Grown Homes Project have developed a graphical net-zero guide with a set of targets & principles that we believe are achievable within a Welsh context. The guide is aimed at helping developers, designers and manufacturers achieve net-zero whole life carbon. This means tackling upfront carbon, energy demand, use of renewables and embodied carbon in order to reduce the overall emissions associated with any proposed development.
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Later this year we will publish a set of additional supporting guides that run alongside this graphic, describing, for example how to measure and reduce embodied carbon, a zero-carbon design guide using typical Welsh timber frame systems, and a guide to support building performance evaluation to address the energy performance gap.
Demonstration of Practical Building Performance Measurements
Woodknowledge Wales (WKW) believes that we can only improve the performance of housing and really deliver zero carbon through the measurement of whole life carbon and testing of building performance. Otherwise we live in the dark.
How do we make building performance measurement practical and affordable?
Woodknowledge Wales and Cardiff Metropolitan University recently carried out detailed performance measurements on two newly built timber frame low rise blocks of flats as part of our Home-Grown Homes Project. The purpose of the work was to test out novel methods of building performance evaluation being pioneered by Build Test Solutions (BTS), who specialise in making practical building performance measurement technologies.
The two building projects participating in the testing were:
- Pentland Close, Cardiff, a development for Wales and West Housing Association. Built by Hale Construction who procured Sevenoaks Modular as a specialist timber structures supplier using their Trisowarm system.
- Croft Court, Welshpool, a development for Mid-Wales Housing Association. Built by Mid Wales Properties Ltd, who contracted AC Roof Trusses to provide the timber frame.
Both projects were designed with high thermal performance aspirations, and the measurements have shown that this high performance was delivered in practice. WKW hope that these measurements could provide the template for as-built performance measurement testing in the future.
Testing equipment in place at Croft Court.
The performance testing enables the contractors to demonstrate the quality of their work and providing quality assurance to their clients.
The Clients Perspective
Grant Prosser from Wales and West Housing Association commented that
“these measurements for the first time allow us to quantitively assess the energy performance of the built product at completion, as the performance gap is a significant concern for us as it negatively impacts on our residents this is fantastic quality assurance on this project and could be a great way for us to inform our product selection and work with contractors to provide high quality, low carbon new homes.”
The Manufacturers Perspective
Matt Hall from Hale Construction said that
“it’s been great to be involved in the project and get assurance of the quality of our work. We pay close attention to detailing to achieve the design airtightness and limit thermal bridging and it’s great to see the proof that this pays off”.
Thermal Performance and Buildings
Thermal performance refers to building’s ability to retain heat, so that when the performance is higher the dwelling can be heated inexpensively and with lower consequent emissions. It is measured by the Heat Loss Parameter (HLP), which is a measure of the rate of heat loss per degree of temperature difference between inside and out per m2 of floor area.
The performance gap is a much-researched phenomena in buildings, where the actual thermal performance is typically worse, and sometimes much worse, than the design expectation. For example, the Building Performance Network’s recent State of the Nation report which was part funded by Woodknowledge Wales found that in their sample of 29 buildings measured, 20 performed worse than expected by an average of 18% with an extreme case 100% worse than predicted.
Heating buildings accounts for around a third of all emissions in the UK, and addressing these emissions is therefore a key part of any national decarbonisation plan. At present all policy in this area is based on predicted, rather than measured performance, this is largely driven by a lack of practical methods to measure building performance.
The Pulse air permeability testing equipment.
How to Test Thermal Performance in Buildings
Currently the most widely used method to measure building thermal performance is called the co-heating test, it has been a crucial tool in revealing the performance gap but at a cost of thousands of pounds per test and requiring a building to be empty for two weeks it is not practical on a wide scale.
Build Test Solutions make building performance measurement equipment and methods to address this gap, which they applied alongside traditional methods on these two demonstration projects. The measurements included airtightness using BTS’ Pulse equipment and a blower door test, whole building thermal performance using BTS’ SmartHTC and a co-heating test and the thermal performance of the external walls using BTS’ heat flux plate kit. Richard Jack, a product manager at BTS, said that
“this project is an excellent demonstration of a full range of thermal performance measurements, and an excellent opportunity to engage with clients, manufacturers and contractors to understand how the measurements can help inform their processes”.
Croft Court, Welshpool
In Croft Court, the performance measurements were carried out in a top floor flat, for each measurement the measured performance was very similar to the design value.
This suite of measurements allows not just a judgement of the overall thermal performance, but also allows sources of heat loss to be further broken down through different heat loss paths.
Pentland Close, Cardiff
In Pentland Close, measurements were carried out in a top and bottom floor flat and for each showed close agreement with the design values. Data collection for the SmartHTC measurements in these flats was interrupted by the movement restrictions imposed by COVID-19 which means these results can’t yet be calculated.
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| Pentland Close. Ground Floor Flat | Pentland Close. Top Floor Flat |
The difference in performance between the two flats is caused primarily by the adjacency of the ground floor flat to an unheated buggy store. By comparison, the top floor flat (which is of the same dimensions) is next door to another heated flat and hence assumed to have no heat loss through the equivalent wall. This results in an extra source of heat loss through the internal wall between the two and also a higher calculated thermal bridging due to larger exposed area. The breakdown in heat loss for the two flats shows this additional heat loss to the buggy store.
Comparing different Build Projects
Beyond the comparison with the design figures for each flat, it’s also possible to consider what level of performance the flats reach in comparison with others.
At present, fabric performance metrics are not common measures of the energy performance of dwellings, with the Energy Efficiency Rating from the Energy Performance Certificate the most commonly used metric. The Energy Efficiency Rating is based upon the expected cost of fuel consumption to heat a dwelling, calculated using the Standard Assessment Procedure (SAP). This calculation is based upon the thermal performance of the dwelling, but also an assumed occupancy pattern, the efficiency of the heating system and the assumed cost of energy (gas and/or electricity). The Croft Court flat has solar PV panels which significantly offset the cost of electricity, and hence result in a higher (better) EPC rating.
| Flat | EPC Rating |
| Croft Court | 92 (A) |
| Pentland Close ground floor | 81 (B) |
| Pentland Close top floor | 82 (B) |
Measuring fabric performance
A building’s thermal performance is key to its energy performance and thermal comfort, it is fundamentally important because the building will likely last longer than its systems or occupants. As such it makes sense to consider a specific fabric performance metric such as the Heat Loss Parameter, alongside the EPC rating, promoting a fabric-first approach. The HLP has previously been used as a key performance indicator in the Code for Sustainable Homes.
All three flats measured display high levels of thermal performance, with insulation levels similar to those recommended in schemes such as Passivhaus (though with higher air permeability). This is clear when comparing the measured HLPs in these flats, which ranged from 0.65-1.00, with the HLP scale produced by BTS.
The performance measurement demonstrations provide quality assurance on these three flats, and a demonstration of what’s feasible using performance measurement. Diana Waldron from Cardiff Metropolitan University, project partners on the Home-Grown Homes project, summed up the project as;
“a unique opportunity to gain further understanding in the area of building performance evaluation methods, aiming to find ways to make them more approachable to all relevant actors in the building industry. All the learning captured during this investigative work will be further disseminated, put into practice and re-tested, in tandem with our main aim: to achieve better quality homes in Wales”.
