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Annat Road, Perthshire

Annat Road, Perthshire

Thermal improvements to an interwar cottage

Overview

This case study describes work undertaken by the Gannochy Trust on a traditional cottage from the interwar period. The measures installed were part of the suite of thermal interventions for traditional and historic buildings developed by Historic Scotland. While most of the property was built in a traditional way, some aspects of the build were different, notably the use of cement in the external walls. This allowed the opportunity to assess how the measures performed with building fabric with a lower level of vapour movement in the walls.

Approach

Existing Property

The property is a detached cottage, built in 1927, comprising three bedrooms, hall, bathroom, kitchen and lounge, with a total living space of 77m².

The construction is red sandstone mass walls approximately 500mm thick, cement bonded and finished with lath and plaster, which has a 40mm cavity. Internal partitions are of colliery brick, plastered on the hard. Ceiling heights are generous, and there is a partially floored attic space. The roof is slated, and has overhanging eaves which gives good protection from wind driven rain. The property was designed to be naturally ventilated, as outlined in the plaque below.

 Ventilation

Ventilation instructions for residents © Historic Scotland

Existing double-glazed timber windows date from the 1990s.

Modest thermal improvements had been made in the past, including mineral wool between ceiling joists in the attic, and insulation in the lowered ceilings of the bathroom and kitchen.

 

Refurbishment Approach

The aim of the refurbishment was to:

  1. Install technically appropriate thermal upgrades to walls, floors and roof space.
  2. Maintain the design of the original cottage, and reduce waste of existing and original material
  3. Produce a specification that can be replicated at scale
  4. Conduct monitoring to quantify fabric improvements
  5. Achieve an improved SAP rating
  6. Disseminate findings.

 

Upgrade Works

  • Existing facings, doors and skirtings were removed to allow for rewiring. These were repaired where necessary and replaced as part of the strategy to reduce waste during the refurbishment.
  • Lowered ceilings in the kitchen and bathroom were removed.
  • The kitchen was upgraded to improve amenity.
  • A water-based expanding foam insulation was blown behind the existing wall linings.
  • 100mm wood fibre board insulation was fitted on the underside of the floor joists. Original floor boards were retained where possible - around 15% new floor boards were required to make good breakages and account for legacy interventions.
  • 100mm wood fibre boards in the underside of the rafters in the attic, creating a 'warm roof'.
  • Improved ventilation including use of existing flures in bedrooms, unblocking existing vents and a new ventilation grille in the lobby area.
  • Redecoration throughout.

Performance

Glasgow Caledonian University conducted pre-intervention monitoring in Spring 2014 on a similar property, and post-intervention work was assessed in February/March 2015 to confirm the performance of the refurbishment works. Details of the U-value and humidity test results can be found in the case study document, available to download on the right.

 

Prior to the refurbishment, an Energy Performance Certificate (EPC) was prepared for Annat Road based on the existing conditions. This gave a SAP rating of 45, putting the property into EPC band F.

Following the refurbishment works a second EPC was produced, and the property achieved an EPC rating of E, having gained five SAP points.

Given the extent of the works, this is a modest improvement, and is likely to be caused by the limited number of upgrade measures available for use, as well as many assumptions of traditional building fabric performance. Historic Scotland are seeking a review of SAP methodology and product assessment to allow SAP assessors to enter more accurate information on historic buildings.

Lessons

The project was considered a success, with most of the objectives being achieved. Lessons were learnt in the use of wood fibre board and new wall insulation techniques. Monitoring is proving that these measures are effective both in thermal terms and in maintaining the important characteristic of vapour open construction in traditional buildings.

Local contractors are now familiar with a greater range of refurbishment materials and techniques, as well as the new refurbishment principles of the Trust.

Following the success of this project the Gannochy Trust is confident in procuring further refurbishment work on their estate with similar materials and techniques.

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Case Study

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