The Bale House, Hastings Country Park - Timber Frame and Roof

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. 

The Bale House, Hastings Country Park - Groundworks and Foundations

In our latest blog, we take a step back - right to the beginning of the project to build a new, straw-bale Hastings Country Park visitor centre - now called The Bale House. In this post we’ll explain and explore how the groundworks and foundations took shape for this exciting new building.

The new Visitor Centre is located next to the old one in the Hastings Country Park. The park itself is an Area of Outstanding Natural Beauty (AONB) and a Site of Special Scientific Interest (SSSI) and its position is perfect to take in the glorious views across this beautiful landscape. Although the site might be considered a challenging choice for some, in that it’s near a cliff edge with horizontal wind and rain likely at times, the design of the Visitor Centre eliminates any concerns of the possible ‘wetness’ of the site, principally through the use of timber rain screen cladding on the side of the prevailing wind (the south and west).

Groundworks, simply put, involves excavating material from the building site to the point where the foundations of the building and surrounding area can begin. Once Huff and Puff Construction had cleared the site and completed the groundworks our attention turned to building its foundations. 

Focus on Foundations:

The site of the Visitor Centre is a mix of heavy clay and sand through to mudstone and sandstone. Areas of the site under the building had to be excavated to different depths to find good bearing ground. Deeper areas were filled and compacted with recycled crushed materials and compacted to create a level surface. A limecrete (the lime version of cement-based concrete, using hydraulic lime, sand and aggregate) base was then poured. Ashlite concrete blocks were then used to create plinth walls (low walls for the rest of the structure to sit on). These blocks are made from 100% recycled concrete and these blocks took us up to ground level.

On top of this, two courses of ebony bricks, were laid using NHL 3.5 hydraulic lime mortar, which took us 200mm above ground. (NHL 3.5 lime is slightly softer and accommodates movement). 

Huff & Puff Top Tip: The mortar should always be softer than the bricks - because then any movement cracks the mortar and not the bricks (which would cause structural failure).  Although we would try to eliminate movement by design (with good foundations) straw bale buildings can naturally accommodate a very large amount of movement - unlike masonry where movement could cause serious structural damage.

Floor buildup:  

The most common solid floor construction, in standard non-straw building projects, uses a plastic damp proof membrane, a lot of petrochemical foam (for insulation) and cement-based concrete.  Instead Huff and Puff Straw bale Construction methods ensure the use of a product called foamed glass gravel (made from recycled glass from bottle banks) for the main floor substrate.  This is insulating and hydrophobic, so it creates an insulated floor that will not absorb moisture (it creates a capillary break) - all without using petrochemical products.  On top of this is a 100mm limecrete screed.  This creates a completely breathable (vapour permeable) floor, just like our walls.

There have been some challenges encountered during the foundation stage of the build, and we did encounter a seam of fine silica sand on the site. This was interesting because historically, very close to the site, there was a quarry that extracted this sand.  For those interested in the history of this site, it was the Fairlight Mining Company back in May 1939, who leased land from a Major Sayer between the top of the Warren Glen and Fairlight Church to dig for this silica sand (used for making optical lenses etc.). It created the large quarry at the top of the glen and a smaller one nearer the church, which today is the site of the Hastings Country Park car park. Overall, the sand itself was less of a concern than the amount of clay that we also encountered at the site. Clay is prone to movement through a freeze/thaw action.  So, most of our excavation work, therefore, aimed to remove the clay down to mudstone or sandstone, which is much more stable.

Huff and Puff Construction would like to thank all those who worked so hard on the foundation stage of this build, including the team at Red Kite Design and Build. 

In the next blog we’ll take a look at the next stage of The Visitor Centre’s build – as we focus on the timber frame and roofing aspects of this exciting project.