House, Sussex

Introduction

This elegant house stands on a ridge in Sussex looking out over the South Downs, whose distant hills are reflected in the undulating surfaces of the cross-laminated timber (CLT) roof. Its clean modern lines and muted palette of materials have generated a tranche of awards including a Regional and National RIBA Award, for which the citation reads:

‘A lack of decoration and ornament gives this modern house a functional feel, but one that is cleverly considered to the very last detail… Internally the double-height void and staircase orchestrate the house effortlessly, organising a contiguous open-plan and cellular spaces into a simple but elegant arrangement. The oversailing first floor produces the feeling of a quiet monastic cloister with sun-filled spaces and carefully framed views’.

Designed by Wilkinson King Architects, the house replaces a 1950s cottage and is a country retreat for its London-based owners. ‘The clients were passionate about creating a contemporary building that truly engages with and responds to the rural landscape, using materials that are natural and sit well in this context’ explained architect Julian King. Although it occupies a 12 hectare site, the design was constrained by the requirement to maintain the original residential curtilage including its height.

The main entrance lobby of the house opens to a double-height hall / reception space which rises to the roof, an origami-like series of folded timber planes, while its glazed walls frame the magnificent view. To one side is an enclosed en-suite master bedroom; to the other side is a large open plan living / dining / kitchen, with floor to ceiling glazed walls. They are shaded by the overhanging first floor, supported at the perimeter by a series of light steel columns.

From the reception a timber staircase rises to the first floor, where a generous landing / corridor space acts as a study and leads to three bedrooms, each with an en-suite bathroom within a timber enclosure. The landing and bedrooms are all set beneath the folding planes of the CLT roof which is inset with large triangular rooflights, creating a dynamic pattern of light and shade.

The staircase has a metal frame and is clad with spruce to match the CLT panels. The treads are open and cantilevered to make the staircase as transparent as possible. 

Externally the first floor is clad with a rainscreen of cedar boards. The windows are fitted with horizontal louvered shutters which slide behind the cedar boards; the shutters shade the windows from unwanted solar gain in summer and allow the lower winter sun to warm the interior. The first floor is lined with oiled engineered oak floorboards.

 

The use of cross-laminated timber (CLT)

The first floor walls and roof structure are selfsupporting and fabricated entirely from CLT panels. A total of 143 panels were used for the first floor superstructure. The CNC cutting technologies used in CLT production resulted in excellent dimensional stability, both in overall panel size and for structural openings. This allowed individual panels to be shaped and for edges to be chamfered so that they came together to form a continuous ceiling soffit with no visible joints. The wall panels are made of three layers of solid spruce boards (94mm overall thickness) and the roof panels are 117mm thick and made up of five layers. The CLT spruce panels also act as the finished surface of the interiors and give a warm and a tactile quality to the bedrooms and circulation spaces. The highest available visual quality of panel - domestic visual grade – was selected. The surfaces were treated with a site applied surface spread of flame coating and transparent white lacquer finish to prevent them degrading over time due to UV light.

The use of the CLT panels allowed this very complex element of the design to be built very cost effectively and also extremely fast; they were assembled on site in only ten days. The solid timber structure acts as a heat sink, evening out the internal temperature and the moisture content of the air.

 

The CLT structure

Rachel Betts, structural engineer of Price and Myers writes: ‘The structural properties of CLT lent themselves to this project and in particular to the geometry of the roof, which is formed of triangulated pieces of CLT. The CLT roof panels span one way onto loadbearing CLT walls below, which in turn are supported off a steel frame at ground floor level. The valley which is formed between the roof panels naturally provides a stiffened section due to the increased depth of the panel, which helps reduce the deflection of the roof.

The panel joints are mitred and skew screwed together from the top with partially threaded screws, allowing a quality finish on the exposed underside of the panel. The junction at the top of the roof pitch needed a bit more thought as four triangulated pieces of CLT met at one point. A shaped timber packer and a cranked steel angle were used to tie these pieces of roof panel together and stop the roof from spreading. The manufacturing process of CLT suited this roof geometry as the CNC cutting of the panels led to an accurate panel shape and the threaded screws helped pull the panels together to ensure a gap was not formed’.>

 

The cladding

The entire first floor of the building is clad with western red cedar, selected primarily for the way it ages naturally, as it was important that the building would sit well in its rural setting. Untreated cedar ages over a short period of time to achieve a silver colour, one which matches the colour of the bark of trees close to the building; the appearance is especially impressive in winter. The durability and weathering of cedar was also a very important factor when choosing the species.

The best visual grade of cedar was selected to avoid knots. The 145 x 18mm boards are tongue and grooved and fixed horizontally in 2.4 metre lengths, stacked one above the other. There is a 10mm gap between them, giving a rhythm to the facades and allowing for expansion and easy maintenance as necessary. They are nailed to treated battens with stainless steel annular ring nails.

The first floor is clad with horizontal western red cedar boards. A view from the first floor landing; the double-height space is lit by triangular rooflights. CLT wall and roof panels give a warm and tactile quality to the first floor. The facade was very carefully detailed to avoid any protruding elements such as window sills, where rainwater run-off might stain the cedar. The sliding windows and the louvered shutters are designed to slide behind the cladding. The shutters are made of the best visual grade cedar to match the cladding and the boards are held in place by a stainless steel frame.

 

Sustainability

The structural timber CLT from KLH is highly sustainable. A cubic metre (480-500kg/m³) of KLH panels will remove approximately 0.8 tonnes of CO2 and will have approximately 240-250kg of 'lock-in' carbon. (In comparison, the production of Portland Cement results in around 870kg of CO2 emissions per tonne of cement).

All KLH timber is PEFC certified and the raw material used to manufacture the panels comes from sustainably managed forests. The adhesive used in the cross-lamination process is completely solvent and formaldehyde free ('o' class emission class). KLH Massivholz has a zero-waste policy with sawdust, shavings etc reconstituted into biomass pellets and used to heat/power the factory. KLH Massivholz is ISO14001 accredited.

The western red cedar cladding is legally, responsibly and sustainably harvested in publicly managed forests of British Columbia, Canada. Vincent Timber's Chain of Custody is monitored by BM TRADA which currently covers CSA, SFI, FSC and PEFC.

The engineered oak floor boards are FSC Certified by Rainforest Alliance. The 6mm veneer was bonded to 15mm birch ply substrate by a cold press method.

Completion Date:

August 2014

Year Published:

July 2016

Building Type:

House

Location:

Sussex

Client:

Private

Architect:

Wilkinson King Architects

Structural Engineer:

Price & Myers (CLT), Packham Lucas

Main Contractor:

Westbridge Construction

CLT Manufacturer:

KLH UK

Joinery:

SM Carpentry (external cladding and deck, staircase)

Timber Supplier:

Vincent Timber

Timber Elements:

first floor wall and roof structure, internal walls, staircase, external cladding, floor

Timber Species:

Spruce, western red cedar, engineered oak

Register to download the full case study with images and architectural drawings

Register

Suggested Reading

Timber design pioneers: tackling the sustainability challengenavigation-arrow

Timber design pioneers explores how collaboration can drive innovation in design and construction.

 

Chapter 4, Tackling the sustainability challenge, features three very different and remarkable projects:

  • Cowan Court, Churchill College
  • Rievaulx Abbey Visitor Centre
  • New Islington

 

Chapter 4 includes interviews with:

  • Tom Emerson, 6a architects
  • ...

28/08/2019

Procuring engineered timber buildings: A client's guidenavigation-arrow

Procuring engineered timber buildings: A client's guide highlights the important questions developers and other clients need to consider when reviewing the merits of engineered timber solutions for the structure of their building. The publication will assist TRADA members in providing answers to the following questions and may be shared with...

30/05/2019

Structural fire design: Statement on the design of cross-laminated timbernavigation-arrow

Included on the TRADA website by permission of the Civil Engineering Research Journal, Juniper Publishers and the authors.

 

This document was prepared in response to comments about cross-laminated timber (CLT) in journals, online press and lobby documents that highlighted “inconsistencies” of the product...

24/05/2019