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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Resources
Embodied Carbon Guidance for Welsh Social Housing Developers, their design teams, contractors and suppliers
This guidance has been written for those wanting to both increase their knowledge of Embodied Carbon in the housing sector and to understand how to reduce it. The target audience encompasses key stakeholders within Welsh social housing organisations including development and asset managers, their design teams, contractors and suppliers.
Clear and authoritative guidance is provided on how to procure and undertake an Embodied Carbon assessment, what benchmarks can be set, tools that can be used and how Embodied Carbon can be reduced. Examples are provided to show how others have tackled Embodied Carbon within their organisations and projects, with a focus on housing. Where relevant, other guidance and useful information is signposted.
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Authors: This guidance has been produced for Woodknowledge Wales on behalf of the Home-Grown Homes project. The document was authored by Jane Anderson of ConstructionLCA Ltd together with Katherine Adams, The Alliance for Sustainable Building Products.
Publication date: December 2020
WoodBUILD 2020 Autumn Series – Podcasts
A series of four 60-minute conversations on some of the themes of the Home-Grown Homes Project – Forestry, Manufacturing, Housing and the Foundational Economy. Each podcast features two individuals with a passion for the subject matter and a willingness to share their thinking. David Hedges, Home-Grown Homes Project Manager introduces each podcast and asks the questions.
Our Future Forests
Two chartered foresters in conversation: Jo O’Hara, Managing Director at FutureArk Ltd in Edinburgh and John Healey, Professor of Forest Sciences in Bangor University’s School of Natural Sciences. They discuss our forests, what they look like now, how and why they have changed over time and what the future holds. Plus, forest use, growth and management, culture and history, land use policy, governance and forestry as a career.
| Jo O’Hara | John Healey |
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Jo is a member of the Institute of Chartered Forester’s Council – see details here / And you can follow Jo on Twitter @mrsjo |
John Healey refers to his work in Bangor. You can find out more about the University’s work in forestry here. |
Future Homes and how we build (or make) them
Two timber housing manufacturers in conversation: Jasper Meade, Director of PYC Group in Welshpool and Neil Sutherland, Director of MAKAR in Inverness in the Scottish Highlands. They talk about natural materials, high performing homes, change and the barriers to it, specifications, legislation and regulations, energy and carbon, Passivhaus, collaboration, culture, behaviours and more.
| Jasper Meade | Neil Sutherland |
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| Jasper is a board member of Woodknowledge Wales and for more information about Jasper’s company, PYC Group, see here. | Neil’s company is MAKAR and their website is here. You can follow Neil on Twitter @makarneil |
Better Performing Homes
Two architects in conversation: Fionn Stevenson is Professor of Sustainable Design in Sheffield University’s School of Architecture and Rob Wheaton is Senior Associate Architect at Stride Treglown. They talk about how different the homes of the future will be from the homes we live in now, sustainability, standards, building performance, architecture education and more.
| Fionn Stevenson | Rob Wheaton |
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| Fionn is the author of Housing Fit For Purpose: Performance, Feedback and Learning, published by RIBA Publishing in September 2019. You can read more about Fionn and her work here. You can follow Fionn on Twitter at @fionnstevenson |
Rob is based in the Cardiff office of Stride Treglown which is a multi-disciplinary employee-owned practice working across the UK. He has recently been working with housing associations on schemes under the Welsh Government’s Innovative Housing Programme. See here. You can follow Rob on Twitter at @robwheaton |
The Foundational Economy
Two Housing Association people in conversation: Debbie Green, Chief Executive with Coastal Housing and Steve Cranston, Foundational Economy Lead at United Welsh. They talk about what the foundational economy is, the pandemic, risk aversion, communities of practice, decarbonisation, listening to people, paradigm shifts and a green recovery.
| Debbie Green | Steve Cranston |
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| Amongst other things Debbie, who is based in Swansea, has been chairing the Ministerial Foundational Economy Steering Group. You can find out more about her and her career here and follow Debbie on Twitter at @debbiegcoastal | Steve, who is based in Pontypridd, has been with United Welsh since 2009 heading up their community investment and in the last year, leading their FE work. He’s also had a period of secondment in the Office of the Future Generations Commissioner. You can find out more about Steve here. and follow him on Twitter @stevecr |
Mandatory quality standards for new homes – WKW response
Woodknowledge Wales have responded to a Welsh Government consultation on “Mandatory quality standards for new homes” which closed on 31 October 2020.
Key targets Woodknowledge Wales propose are need are:
- A target for upfront carbon from April 2023. We propose 300kgCO2e/m2.
- A target for embodied carbon from April 2023. We propose 400kgCO2e/m2.
- A space heating demand target by April 2023. We propose 15 kWh/m2/yr.
- A total energy use intensity target by April 2023. We propose 35 kWh/m2/yr.
Read our full response here.
Google Map highlights exemplar timber housing projects in Wales
Explore information on construction, innovative products, use of home-grown timber and Welsh manufacturing, carbon impact and building performance in innovative timber housing projects across Wales.
This map showcases the exemplar timber housing projects Woodknowledge Wales has worked on in some way over the past few years. The Exemplar Housing Project layer contains basic project information. The Whole Life Carbon layer contains data on the carbon impact of those projects for which we have undertaken analyses. The Building Performance layer contains projects where we have undertaken some experimentation into different building performance methods. The Forest Nation Attribute layer attempts to capture the timber story such as the use of innovative products, the use of home-grown timber and the use of Welsh manufacturing.
This map represents our progress to date. We will continue to record the progress of our timber development agenda as well as the progress of Welsh housing in meeting the challenge of Net Zero whole Life carbon over the coming years.
VIEW MAP ON GOOGLE →
Wood Fibre Insulation in the UK
A relatively old report written in 2013 on wood fibre insulation in the UK authored by our now Chief Executive, Gary Newman, when acting as an independent consultant for Forestry Commission Scotland and Woodknowledge Wales. The report was never published but we consider it highly relevant to today’s discussions about how Wales can become a high value forest nation and delivery zero carbon housing (both new and existing) by 2050. Access to the full report here.
Serious about Green?
A report commissioned by Woodknowledge Wales by the Foundational Economy to look at how we can build a Welsh wood economy through co-ordination.
Open document HERE.
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.
Download in pdf
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”.
Coast Redwood Groves in Wales – a planting solution in a changing climate?
Sequoia sempervirens, also known as coast redwood, coastal redwood, Californian redwood, is a species which is increasingly mentioned when considering alternative tree species to cope with a changing climate in Wales. This may come as a surprise to some given that the deep leaf litter it produces decays slowly and deters ground flora causing a lack of biodiversity. In recent years, this has often been used as evidence against its wider planting benefits. At the same time coast redwood is delivering landscape and societal benefits by storing carbon in the leaf litter substrate and standing timber. As Forest Research say “This is a species that could be grown more widely in Britain with climate warming, not least because it produces a high quality timber.”
In early February 2020, Woodknowledge Wales staff Dainis Dauksta and Ceri Loxton visited the Royal Forestry Society’s Redwood Grove at Leighton, near Welshpool, with Dominic Driver of Natural Resources Wales and Anna Dauksta of Tir Coed to see the coast redwood grove and discuss the potential for Sequoia sempervirens and other softwood species in Wales.
In its natural range, Sequoia sempervirens is confined to a narrow coastal belt, mainly in central and northern California. In the UK, coast redwood was introduced in the 1850s and has been planted on a small scale, often for silvicultural demonstration, landscape and amenity purposes by the Forestry Commission and private estates. The redwood grove at Leighton is impressive – tall straight stems, large diameter trunks covered in thick fibrous bark, towering canopies and dappled light throwing patterns on the deep leaf litter.
New Zealand is one of the countries starting to look at the species more closely and to encourage its planting and establishment. Should Wales follow this example?
Mitigating climate risks
Sequoia sempervirens has some natural advantages to reduce risks associated with climate change in our regions:
● Wind: Its root system can reduce the effects of severe wind. Trees join roots with neighbouring trees and form a strong underground link. The bonding with nearby trees enables them to withstand major weather events.
● Fire: It has the unique ability amongst conifers to re-sprout branches after a fire. Tough fibrous bark insulates the trunk from much of the heat of a fire. While existing branches may be burned the trunk remains alive and sprouts new branches. If a forest has been planted for carbon offsetting, this means that the forest will continue to grow and reduce the potential for future liabilities.
● Insects: In its native range in California there are lots of insects. No insect is known to cause economic damage and none is capable of killing a mature tree.
● Vegetative reproduction: It will sprout from old cut stumps and fallen logs. Because the stumps and roots remain alive and because the heartwood is naturally durable coastal redwood carries more carbon forward into the next rotation.
Adaptability and Carbon Storage Potential
The most interesting characteristics of coast redwood reside in its genetic makeup. Its genetic diversity is very high and the highest of all North American conifer species. Sequoia sempervirens is the only hexaploid conifer with a genome size three times that of its near relative, the giant sequoia. This polyploidy (having more than two paired sets of chromosomes) may explain its extreme survival capability and longevity. The species can clone itself from roots, burls and cuttings. The phenotypic plasticity (how of its leaves allow them to adapt to a wide range of light conditions.
New Zealand foresters are confident that they will be able to breed coast redwoods with more desirable traits than their Californian peers, so that the species can be optimised as industrial roundwood. Attractive compact groves could realise an extremely high carbon storage potential which would justify their new role within Welsh mosaic landscapes.
Suitability for Welsh geography
Forest Research (2016) advise that coast redwood is most suitable for mild, moist climates with more than 1250mm of rainfall, such as those found in Argyll, Wales and southwest England. Favourable locations in terms of climate and site quality will be lower slope and valley bottom sites.
Coast redwood is likely to be a high yielding species. Data from the limited trial sites in the UK indicate high productivity with general yield classes of between 24 and 30 being achieved in England and Wales.
Coast redwood is a species to consider where larch crops are being diversified due to Phytophthora ramorum infection and where site conditions are suitable.
Timber quality – suitable for construction and joinery?
A chalet built in 1966, and redeveloped in 2000 using local wood, including redwood thinnings from the site. The Charles Ackers Redwood Grove at Leighton, Nr Welshpool.
At the site in Leighton a small cabin has been built using local timbers including coast redwood cut from the site. In its native range coast redwood is reported to be used as “veneer, construction lumber, beams, posts, decking external furniture and trim (https://www.wood-database.com/redwood/). However, there is a lack of information about wood properties grown under British conditions.
“My own experience as a sawmiller is that coast redwood cuts and dries really nicely. The heartwood is reasonably durable although there’s a lower proportion compared with western red cedar or larch. The thick fibrous bark may offer potential as an insulating material.” Dainis Dauksta.
Future uses: explore and experiment!
There is more to learn about this species, and while there is a lack of information about wood properties, we also do not know precisely what our wood requirements will be in the future and what processing advancements will have been made. Given the diverse and evolving nature of the timber processing sector it is likely that there will be many future uses.
Because of its high productivity and unusual growth characteristics this species will be of increasing interest in British forestry under predicted climate change. If the carbon sequestration potential of different species is to be considered alongside other properties and multiple landscape requirements, then surely it won’t be long before we start to see increasing groves of coast redwood planted here in Wales?
