Ashfield Cottage

Built on a tight site, this charming self-build project demonstrates a highly efficient combination of structural solution and insulation system.

About this project

Much Wenlock is a beautiful historic town in Shropshire, perhaps best known for being the birthplace of the modern Olympics. Full of gorgeous period properties and with space at a premium, when an opportunity arose for Sandra and Mike to build on a plot in the centre of the town, they leapt at the chance to create their very own dream cottage from scratch. The site was relatively tight and, with a narrow drive as the only means of access, building on the site was potentially challenging.

Use of Timber

To avoid the noise and disruption of a constant stream of lorries delivering heavy building materials, the couple opted for a timber framed construction, to be built and customised offsite by a local manufacturer. Keen that the property should blend in as much as possible, they chose surface render and a wood fibre based wall insulation system. This combination offered an important additional benefit on a small plot over a traditional masonry build. For the same heat U value the timber framed construction has a smaller footprint leaving more space for the garden.

Technical specification

Consisting of a unique combination of wood fibre boards and special lime render, the insulation system works by enveloping timber frame structures in a complete layer of rigid insulation with minimal air gaps, or ‘thermal bridges’, across which cold can travel inwards. However, because the system leaves walls breathable, damaging moisture won’t get trapped in the structure and a healthier environment will be created inside.

For the timber frame contractor using this insulatoin system was a good solution. The 100mm wood fibre insulation boards were fitted to the outside of the stud framework and a 10mm OSB board on the inside, onto which battens with plasterboard were fitted to form a service cavity and then finished using a decorative one-coat plaster. The joints between the internal OSB racking boards were taped to effectively create an airtight box within the timber frame. A high level of air-tightness was required as a heat recovery system was being installed. The chosen wood fibre & lime render combination also provides excellent insulation for heat and sound.

Small holes were then drilled into the OSB boards through which loose cellulose insulation was blown under pressure to completely fill the void and every potential air gap in the wall. The cottage now had, in effect, solid walls of insulation that were both strong and provided excellent ‘U’ values.

On the exterior walls, base render was applied to the insulation boards, with a glass fibre reinforcing mesh worked into it. The walls were then completed with a top coat of mineral silicate paint.

As well as enhancing the very attractive design of the property, the inclusion of oak windows throughout, a green oak porch and the use of local stone create a strong link with period properties nearby.

Having specified a highly energy efficient home, when tested for air-tightness, Sandra and Mike were delighted to find that their cottage leaked just 3m³ per hour, much less than the 10m³ per hour that Building Regulations demand.  The heat U value achieved was 0.18 W/(m2K)

Not surprisingly, the underfloor heating is only needed a few times in winter, which means that the couple not only have the dream cottage they were looking for, but also a very energy efficient and inexpensive home for their retirement.

Photography: Lime Green Products Ltd.

Key contacts

Architect

A.C. Craig Associates  

Main Contractor

J & D Builders  

Timber Frame contractor

Taylor Lane

Insulation System Supplier

Lime Green Products Ltd.

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