Project team

Architect – Rocket Architects | Design consultant – Hartwyn | Engineer – Structural Solutions | Contractor – Hartwyn

  • Foundations – recycled compacted concrete aggregate.
  • Plinth walls – local random field stone, hot-lime mortar.
  • Structure – internal roundwood henge, external load-bearing timber frame.
  • Roof – Roundwood reciprocal timber frame and outriggers, Douglas fir boarding, Epdm membrane, intensive biodiverse green roof.
  • Insulation – straw bale walls, foamglas foundation and sub floor, wool and woodfibre thermal bridges and reveals, perlite (roof).
  • Airtightness – built tight with high attention to detail, membrane to the roof, fully plastered inside and out for main structure.
  • Finishes – reclaimed hand-built joinery, cob bench, earth floors, clay paint, limewash, linseed oil and beeswax.

The Brief

Hobbit Hideaway is a guest house that offers self-catering holiday rentals and uses some of the income to offset the cost of respite holiday stays for people from the care and neurodivergent communities.

The client had already self-built a straw bale home on the property and is passionate about opening up the world of low-cost housing to self-builders in Scotland, as well as being an advocate for natural materials and sustainability.

The initial design was heavily informed by A Pattern Language by Christopher Alexander et al. and the client’s interactions with various natural materials. The brief was very detailed and based on an initial aesthetic which closely replicates Tolkien’s fictional Hobbit houses – turf-roofed, round door – whilst also demonstrating as many different natural materials choices as possible.

Inspiration comes from many places

This showcase element was very exciting at the design stage as it was an excellent opportunity to demonstrate what can be achieved with natural materials. However, we knew it would be a challenge to build as we had designed easy yet high impact solutions. No cement was used in the build, and very little in the way of plastics were included, just one membrane in the roof. Despite this, high airtightness levels were obtained by thorough detailing and rigorous quality control.

The design was collaborative between Sam Edge from Rocket Architects and Hartwyn, with detailed input from the client and the engineers. This level of involvement from such an early stage pays dividends throughout the process as all the elements intentionally work together, from the core aesthetic to complex engineering solutions and specific material choices.

Specs

Footprint: 54 m2

Wall u-value: 0.11w/m2k

Roof u-value: 0.22w/m2

Airtightness: 3.2m3/h.m2

Build cost: £1500/m2

A Pattern Language

Challenges > Problems

Once we had the basic concept – a roundhouse – we could start to integrate the two ends of the materials spectrum; exploring what was available locally, and what the client preferred. This stage is where the biggest compromises happen as we consolidate the design to maximise our resources, our budget, the brief and the performance we’re aiming for.

It’s at this point where we air one of our cheesy but effective design maxims:

“There are no problems, only challenges.”

We find this to be a useful tool for assessing materials or technologies. Challenges can often lead to creative solutions, but endlessly chasing a solution can be inefficient. Knowing when to move to a different starting point or dismissing what looked like a favourable choice earlier can be as useful a solution as any other.

Reciprocal rafters & oculus

The budget for this build was ambitious, so a lot of creative thought went into realising some of the more complex requirements. Maximising natural light whilst also maintaining the thermal envelope, on a budget, was probably one of the thorniest challenges we faced. Our solution was to hand build our windows on-site and place a large 2m triple glazed roof dome above the central space, flooding it with light and enabling superb star viewing.

Foundations

The foundations were simple to construct but complex to design. The perimeter walls were laid out in relation to concentric overlapping circles defined by the position of the inner roundwood frame. This required detailed and repeated mapping onsite to realise the non-geometric organic footprint.

Post setting out

The house was dug into the bank and is partially earth-sheltered to the rear. Upon excavation, we discovered a spring that we needed to divert before stabilising the soil with lime (a traditional remedy for waterlogged soil). Once that was taken care of, we could get the foundations consisting of compacted recycled concrete aggregate in place and begin our plinth walls.

As part of our drive to source as many of our materials from the immediate locale, we managed to find a supply of fieldstones from a neighbouring farmer. These stones were random with variations in sizes, from smaller brick-shaped stones to huge irregular tombstones. We bedded them in a hot-lime mortar, creating a cavity wall and several individual plinths for our main loadbearing roundwood posts to sit on.

HH eng drawings

Superstructure

The main loadbearing structure was split between two elements: an internal roundwood henge with a reciprocal framed roof and an external dimensioned timber frame with roundwood outrigger rafters. The overlapping circles of the footprint defined a loose ‘roundhouse’ shape with organic gentle curves. This was one of the biggest challenges to put down and remain faithful to, which was important as all the engineering relied on accuracy. The strawbale infill system requires a timber ladder to run along the top of the plinth wall, to spread the load and provide protection for the base of the bales. Following this inconsistent wonky path was engaging but not one I’d like to repeat!

Load-bearing timbers set at regular intervals carried a wall plate to support the Roundwood rafters, each of which was a bespoke cut at each end, allowing a generous overhang to protect the walls.

Load-bearing timbers set at regular intervals carried a wall plate to support the Roundwood rafters, each of which was a bespoke cut at each end, allowing a generous overhang to protect the walls.
The complete build is very beautiful, a testimony to their [Hartwyn’s] natural build knowledge, skills and practical application.

Kim Siu – Hobbit Hideaway

The roof

As with the rest of the structure, the roof followed the natural curves of the roundwood framing with beautiful boarding using rough sawn Douglas fir straight from the sawmill. Detailing the two-meter oculus was tricky as the reciprocal roundwood framing came to a point and required careful trimming back to create a uniform platform. Breather membrane, insulation and Epdm membrane completed the buildup, with spoil from site and turf removed from the building footprint finishing the exceptionally beautiful roof structure, helping it settle into the landscape almost immediately.

Roof boarding
Kirk

Insulation

One of the most important elements of any build, and no less so in this instance. We used straw infill for the walls, with woodfibre detailing to the reveals of doors and windows. We used light clay straw for the transition from wall to roof as this is a flexible medium, able to form around the roundwood rafters and create a tight consistent envelope.

The roof used perlite, still in the bags, and tessellated to provide an overlapping consistent covering. We also used wool around the oculus to plug smaller inconsistencies.

Straw

Finishes

The entire building was fitted out using leftover building materials that would otherwise have been scrap. Everything was handmade and bespoke owing to the complex curved walls. Buildings like this cannot rely on big box stores and mass-produced solutions which are designed for conventional boxes.

We used clay plaster internally and lime stabilised clay render externally, with several coats of hot lime limewash to protect the building from the Scottish weather.

We laid an earth floor throughout (apart from the tiled bathroom). Natural clay paints, linseed oil and beeswax all contributed to muted natural tones that complemented the materials palette used.

The client also managed to forage a great deal of reclaimed items.

This project was incredibly complex to deliver but was nevertheless very satisfying to complete and is a real showcase for what is possible with natural materials – building to high thermal efficiency standards using a vernacular design approach.
This project was incredibly complex to deliver but was nevertheless very satisfying to complete and is a real showcase for what is possible with natural materials – building to high thermal efficiency standards using a vernacular design approach.