For the next instalment of our recent blog series, where we’ve been looking back our experiences of building the new Hastings Country Park Visitor Centre, we focus on the next stage of the build after the groundworks and foundations have been completed.
This is when the building really comes to life and starts to take shape, as the timber frame and roof go up. Read on to learn more about the timber frame and roofing aspects of this build, and some of the challenges we faced.
The Timber
Huff and Puff Construction try and source UK timber, as local as possible, wherever can. For this job we have used East Brothers Timber in Salisbury, Capricorn Eco Timber in Stafford, as well as suppliers in Sussex such as Copford Sawmill in Heathfield and Balcombe Estate Sawmill.
Timber is a complicated subject and there are lots of factors to consider. If you are considering a timber framed build, we would recommend that a good place to start is a chat with your local sawmill about wood suitability. Huff and Puff’s MD, Phil Christopher, grew up dismissing softwood timber as being inferior to hardwood timber; thinking that surely hardwood timber is better? But, as we’ve discovered in our experience over the years, it’s a lot more complicated than that – especially when considering the environmental aspects and how long timber takes to grow.
Whilst a lot of folk dream of having an oak timber framed house, oak takes a really long time to grow and huge amounts are now imported. All types of wood have their own resistance levels to decay and insect attack. We use a lot of Douglas fir and larch in our framing. These are resilient softwoods that work well structurally. As a rule, Huff and Puff would advise the use of ‘heartwood’ – the older timber in the middle of the tree – rather than the ’sapwood’ – the living timber around the outside. The heartwood is an inky brown colour and the sapwood is white.
Huff & Puff Top Tip: Bigger sawmills (and some smaller ones) will be able to grade timber for you to make sure it is suitable and meets your structural engineer’s requirements.
The Frame
The main building frame, roof timbers and cladding for the Hastings Visitor Centre are all Douglas fir. The posts in and around the building are larch. We also wanted to treat the external timber to preserve it – in the case of the posts, which are structural and exposed, this is the most sensible thing to do. Timber preservatives can be a hideous cocktail of chemicals, but they do not have to be. For example, limewashing timber is cheap and effective. It creates a breathable barrier on the timber that offers substantial protection. It will just need repainting now and again. We have used a Swedish product SiOO:X (pronounced soo-x) which is non-toxic and environmentally friendly and should last for 10 years or so. It’s a bit like a silicate paint on lime render. It’s applied in two stages – a ‘wood protector’ that soaks into the wood and a ‘surface protector’ that ads water repellency. Most wood silvers as it weathers and this product offers that same look very loosely, the silvering effect being hastened by contact with water.
The Hastings Visitor Centre was originally envisaged as load bearing straw bale, where all of the weight of the roof is on the straw, however we now frequently use a method where we erect a lightweight timber frame first and infill the straw. Essentially the framing is identical to robust load bearing methods, just with more posts. This method is a much better fit for our teams and for the site – which is incredibly exposed, being over 130m above sea level and on the edge of a cliff. We have experienced winds of approximately 70mph about six times since the project started and anchoring the building solidly has been imperative. We often refer to the method as a hybrid, as the straw is still a structural part of the walls, both for load and racking. For working ‘hands-on’ with straw on site we find this method works better than load bearing commercially for a number of reasons as follows:
1. Building professionals can do measurements and calculations on timber which makes things easier all round. Straw and mechanical fixings work together, rather than relying on one or the other.
2. We’d estimate that 75% of people don’t ‘get’ load bearing and this method makes them feel safer and more likely to build with straw.
3. It’s safer on site with multiple trades as the framing and a good amount of roofing gets done before the straw work begins.
4. More bales around notches means more regular walls, eliminates snaking and the need for pinning etc.
Commonly, we would build at least parts of the frame off site and then truck them in. As with most timber framing, it’s very helpful to be able to do the fabrication in a workshop and just assemble it on site. However, scheduling issues meant that was not possible for this build and everything was built on site.
The main issue on the building site for the new Hastings Visitor Centre has been the weather and mainly the challenge of keeping the timber dry. We also had huge heavy beams for the roof (some that weighed in at about 300kg), that needed to be moved and manoeuvred into position using post and beam framing methods and a manual, mechanical Genie lift. We were very glad to have Jamie Thomas and Jonathan Kalviac on the crew, both experienced timber framers, who generously shared their knowledge of how to move these heavy roofing beams.
The frame consists of two structural timber box beams – one at the bottom of the wall and one at the top. We build the bottom beam first and then position and fix posts that will support the top beam. Then the bottom be a can be insulated with wool or foam glass aggregate, for example, and then lidded and sealed so no water can get in. We use roofing membrane to stop the timbers getting wet and provide another layer of waterproof but breathable protection.
The top beam is then built in the same way. Temporary bracing is used to make sure the building remains stable and square whilst all the timber elements, and finally the straw, is inserted.
The Roof
The roof of the new Hastings Visitor Centre has an exceedingly shallow dual pitch, it looks almost flat. A single ply membrane has been used, which is common for flat roofs. We did hope for and consider a ‘living roof’ for this project, however because the area in which the building is situated, is so protected environmentally, there were challenges with finding suitable flora that would be in-keeping with the site and also be suitable for a rooftop location.
Our main challenge during the roofing stage was the weather we encountered last autumn that was particularly bad with frequent high winds and incessant rain. It caused us significant issues. The main priority in weather conditions like this is keeping everyone safe and protecting the building as best as possible. Eventually we had to put a scaffold hat over the entire building and in January, when the roof membranes were laid, we had days when the site was so enveloped in cloud that water was condensing on the underside of the scaffold roof, so it was still raining underneath it!
Huff and Puff Construction would like to thank all those who worked so hard on the timber frame and roofing stage of this build. Next month’s blog will take a look at the next stage of the Visitor Centre’s build – as we focus on the timber frame and roofing stage of this exciting project.
