Cuttens Barn is a timber frame, self-build dwelling on the outskirts of Tonbridge, Kent. The project aim for Cuttens Barn was to achieve Passivhaus standard envelope with use of high performance sustainable products.
Self Build Project
For this self-build project, NBT were heavily involved with the client, contractor and other members of the project team from the specification stage right through to site support. Some of the key areas were:
- Wall and roof build-ups specifications to achieve high standards. SAP calculation was performed.
- Analysis, design and details of the critical junction for the thermal performance and condensation risk.
- Analysis, design and details of the unvented warm flat roof to minimize moisture accumulation risk.
- Design and detail for an airtight envelope.
- Assisted on CAD construction detail drawings.
- Detailed quantity take-off for the PAVATEX products to minimize wastage.
- Site training for the contractors and continuous support throughout the project.
Challenges
The biggest challenge was to deliver the high performance. This was achieved by providing distance support with drawings and details, and also providing stringent site training to the contractor/sub-contractor and visited the site at regular intervals to approve the correct installation.
The curved roof has an over rafter insulation system which was a new concept. Experiments and physical calculations were carried out to conclude that best flexibility is achieved by vertical placement of the insulation boards. Air-tightness was another challenge with several complicated junctions, like the cantilever of the first floor. In an effort to deliver the best air-tightness possible, every detail was analysed and appropriate methods specified to attain Passivhaus air-tightness. We finally achieved 0.49 m3/m2h at 50Pa.
We also had to reduce the thermal bridging through steel section and at the same time maintain air-tightness with ease of installation. Detail thermal bridging analysis of the junctions was carried out to determine the dew point temperature and recommended optimum thickness of the insulation to wrap the steel beam. For air-tightness, a breathable yet airtight membrane was recommended to be fixed under the cantilever beam and dressed to the internal airtight layer of the ground floor wall.
Project Statistics
Floor Area – approx. 200m^2, Family house.
EPC rating Achieved – ‘B’ without the inclusion of Photovoltaic Panels (PV). Exploited Pavatex systems low Y-value (Thermal Bridging)
Airtightness Level Achieved – 0.49 m3/m2h at 50 Pascal (Blower Door Test)
CO₂ locked into the building (Carbon Sequestration) by using Pavatex systems (deducting CO₂ emissions from manufacture and delivery) – 6.34 Tonnes
Build Ups
Wall – Pavatex Timber Frame Clad System, U-value = 0.15 W/m2K.
Roof – Pavatex Pitched Roof System, U-value = 0.12 W/m2K