What is roundwood timber frame construction?
Tŷ Pren has developed a unique system inspired by medieval British joinery and the Shaker/Quaker style of timber framing. It has been adapted by us to use with roundwood larch poles and this is what gives our buildings their inimitable style. Our signature method of marking up enables us to make use of unusually shaped poles that would otherwise be used as firewood or seen as waste within contemporary forestry practices.
The joinery we have developed is designed to increase in strength as the wood dries, this means we can do our work with freshly felled timber. The joints are held together with hand crafted oak pegs. There is up to 50% more strength in a roundwood pole, as the fibres have not been weakened through the milling process. Leaving poles in the round makes the building more affordable, with lower embodied energy as milling is not required.
Why use roundwood timber frame construction?
Tŷ Pren’s roundwood timber frame construction has substantial environmental, financial and aesthetic benefits.
As the manufacturing process utilises local woodland and minimum manufacturing our larch roundwood poles are more affordable in most instances than square timber frame equivalents. Our process is zero carbon (often carbon negative) and creates Zero Waste from materials. We estimate than an average property captures 12 tonnes of carbon throughout its lifecycle. The materials used in construction are low impact and natural, meaning they are free of toxic pollutants that have been linked to a range of pulmonary disorders and cancer. Natural materials look and feel beautiful, with strong architectural merit.
What are the differences between roundwood and square timber frame construction?
Roundwood uses the natural tree pole, while square wood creates a frame using sawn sections of timber. While both styles have their advantages in many instances a roundwood frame will cost less to construct, due to less manufacturing and no need for milling. The manufacturing that does take place uses hand tools almost exclusively. This creates less waste and captures more carbon from the environment.
When constructing smaller cabins or structures where it is beneficial to have the framework in the wall we use sawn square frames. Often there will be elements of both roundwood and square timber in a framework and our specialist team are masters of marrying the 2 techniques.
How does timber frame construction capture and lock up carbon?
An average 30 year old larch tree will absorb through its life cycle approx 1.75 tonnes of Co2, through the process of photosynthesis. When the tree is felled this carbon is captured and stored in the body of the roundwood timber frame. As long as the building stands for longer than it takes to grow the trees that replace those taken this is an effective way to store carbon. As there are timber frames in the UK that are over 700 years old we are confident that this form of building is only going to be regenerative for the planet. What’s more our frameworks are often used with other carbon storing methods of construction, such as straw bale construction, Hempcrete or FibreClay.
How much carbon does roundwood timber frame construction capture?
Here is the math: Firstly you need to ascertain the dry weight of a tree (trees are 25% moisture)- half what remains is derived from Carbon. If you multiply that by 3.67 you get the weight of carbon captured by the tree.
Average Dry Weight (DW) Of a mature European Larch= 575KG https://www.wood-database.com/european-larch/
Average Carbon weight (CW)- CW= DW / 0.5
Weigh carbon-dioxide = 3.67 * CW = 3.67 * 575KG = 1.725 Tonnes of carbon captured per tree.
Is roundwood timber frame construction expensive?
Far from it- it is actually one of the cheapest methods of timber frame construction that adheres to modern building standards and controls. Our frameworks have consistently won contracts for those projects on a budget. Often our foundation system and framework will work out cheaper than it can be to pour a concrete slab for a contemporary, industrialised build.
Can roundwood timber frame construction be used alongside conventional building techniques and technologies?
Yes. While we prefer to build using only natural materials, roundwood frames can be integrated with modern building materials if required. However, with the advances made in straw bale and hempcrete technology it is definitely possible to achieve that ‘modern look’ with materials that are healthy to inhabit and that aren’t contributing to ecosystem collapse.
Why is roundwood timber frame construction beneficial for One Planet Development?
As the process of roundwood timber frame construction is carbon negative it allows builders working under the schemes criteria to meet the strict One Planet environmental requirements. In addition to that, our frameworks mean that clients who wish to self build (often with little to no experience) can do so with assurance that the foundations have been done, the structural section of the building is safe and there is a large dry covered space to work underneath.
What are the limits, in terms of scale, of roundwood timber frame construction?
At present it takes us 6 weeks approx to create a large 3 bedroom house frame, with sufficient lead time we can create Three 3 bedroom houses over an 8 week period.
Isn’t timber frame construction a fire risk?
While all buildings have a fire risk roundwood frames do not use combustible petrochemicals or chemical treatments. They are less flammable than many modern buildings, and less of a risk than square frame construction.
Are timber frame properties more damp?
In the UK damp is a risk to all buildings. Therefore it is important to apply best practice to all design of buildings. Our frameworks are designed to have a sufficient air gap underneath a suspended floor and this provides adequate ventilation to prevent damp.
Breathable, natural materials (when applied correctly) work persistently to maintain a good level of humidity within the building. Not only does this control moisture content but also can remove allergens, toxic off gassing and minimise mould growth. In addition to a well designed suspended floor it is also important to design adequate eaves and makes sure that roof maintenance (clearing gutters etc) is complied with.
What other low impact building techniques can be used for roundwood timber frame construction?
We regularly work with hempcrete, clay, lime, and straw bale- and are in the process of establishing the Association of Natural Builders Cymru. Many clients like the allure of green roofs and there is no reason why Thatch would not be a suitable roofing material.
How long do timber frame properties last?
Any building will only last as long as it is well maintained and used by it’s occupants. There are timber framed buildings in the UK that have survived for hundreds of years. The oldest is in Hertfordshire and dates back to 1297. At Tŷ Pren we are committed to building homes that survive generations, we want to leave an inspirational stock of housing for our grandchildren’s grandchildren. What’s more is that unlike modern housing stock, when it is decided that these buildings no longer serve purpose, all of the materials can be reused or just simply left to compost, providing habitat and fertility once more.
Is roundwood construction beneficial for Welsh woodlands?
Yes, roundwood construction could be a component of every Welsh woodland management plan. It can be integrated into the thinning of existing plantation, letting in more light and ensuring that the trees left are given the best possible opportunity to thrive. Astute management of larch woodlands can help manage and prevent the spread of tree diseases and invasive species. There is also the possibility of integrating roundwood timber framing into coppice systems with a species such as sweet chestnut.
How much will roundwood timber framing cost?
We have created 3 bedroom houses, frame, walls, roof, and floors- ready for first fix, for as little as 60K. Cabins for a couple have been built in their entirety for 27K.
What are the best trees for timber frame construction?
Larch is very abundant in Wales, strong, and flexible. Douglas Fir is excellent. Chestnut and Oak can also be used.
Is roundwood construction safe and covered by building regulations?
Yes. And we have helped set the standard for building control of these properties for Welsh county councils.
How long does roundwood construction take compared to more conventional methods?
The frame takes 6 to 8 weeks to fabricate- then 4-5 days to erect. The roof is then erected to create a dry space for the other trades to work. A 3 bedroom house can be completed in 6 months- about 25% to 50% quicker than breeze block construction.
If roundwood construction is so great why are more people not doing it?
The skill required for roundwood frame construction. It takes 6 to 9 months to train an apprentice, and many years before you can work independently and manage projects safely. Large construction firms are adverse to investing in skills that require so long to develop- and would rather use methods that are less skilled- but with a higher environmental footprint.
Won’t roundwood limit the size and strength of my property?
It will not limit the strength of your property- our frames have been loaded and stress tested by structural engineers up to 12 tonnes. More than enough for most house designs. Roundwood timber frame construction is an extremely strong and durable method of building. There is potential to adapt roundwood methods to be suitable for seismic areas. If using straw bale this may affect the size of rooms when compared to modern house building- although modern insulation requirements are diminishing that effect. If using hempcrete there will be no compromise in space. Our frames can sit both in, or inside of, the walls.
Is building with roundwood sustainable?
Yes. The process is carbon storing, zero waste, and replenishes Welsh woodlands while using a resource that would otherwise be pulped for biomass. We train and hire local people and have complete control over our supply chain from woodland to home. This system is free of the exploitation that is rife in all industry. We invest in our employees and we are not importing any material, thus ensuring that all activity associated with Tŷ Pren is something to be proud of.
What are the cost benefits of working with roundwood?
Here is a real world example- for the Fordhall Farm Bunkhouse: Our budget for this project was 33K. The next cheapest tender used square frame timber, and would have cost 70K. That is some saving!
What are the aesthetic and architectural benefits of roundwood?
Yes, we are a Welsh company using Welsh wood and all the profits stay in Wales. You are supporting Welsh jobs and the local economy when working with Tŷ Pren
Do you do apprenticeships or can I volunteer?
From time to time, yes- feel free to get in touch. We also work with the UK Gov Kickstarter scheme.