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FS42 - Co-heating test for Alternative Refurbishment Strategy on Hard to treat House on Uist

Written by: CIC Start Online

"Co-heating test for Alternative Refurbishment Strategy on `Hard to treat` House on Uist" by Glasgow Caledonian University and Locate Architects


Sustainable Uist ( is a community organisation formed in 2009 to combat climate change on the Uists and the Western Isles. It has attracted funding from Climate Challenge Fund, BLF and CnES (Western isles Council) and Historic Scotland to support a number of environmental initiatives, only some of which are energy and refurbishment related.

One project involves research into ‘Hard to Treat’ housing, which accounts for about half of the housing on the Island’s housing stock and as such is ineligible for the Government funded insulation schemes. The aim is to get a better understanding of the issues through extensive survey work across the Islands, to study potential domestic heating and micro-renewables option, but importantly, to construct and monitor three alternative refurbishment strategies to assess different energy efficiency models. This feasibility study will provide support for the ‘real-world’ testing of these strategies via a ‘Co-heating’ test ( which is to be carried out by GCU.

There is existing research on various aspects of the work undertaken, such as the airtightness measures, the co-heating test methodology, the hygrothermal modelling-derived external treatment of the solid walls, the thermal bypass reductions and the thermal mass, but as far as we know, there is no research which looks at all of these aspects together, nor in a refurbishment context.

Locate Architects have devised an alternative refurbishment strategy which has been supported by Sustainable Uist due to its potential to provide much more cost effective energy efficiency. A single storey derelict house has been identified which has been split to allow different strategies to be applied to either (identical) half.

The strategy devised by Locate Architects consists of fairly conventional ceiling and floor insulation, however the following aspects are unusual:

  • No wall insulation, instead dry lining has been removed and the wall plastered using lime plaster, with well sealed junctions
  • Great care given to airtightness across the whole fabric including use of imported specialist tapes to seal all junctions
  • Care given to reduce thermal bypass through additional membranes and specific detailing
  • Treatment of the outer face of the walls to prevent rain penetration keeping the walls dry
  • Exposing and connecting the thermal mass of the wall with the indoor air.

SAP does not include the above issues in its assessment parameters, so it is anticipated that whilst the SAP analysis will award the strategy with a fairly poor result, based on the high / poor U value of the wall, the co-heating test will enable the benefits of the above measures to be accurately assessed. If the strategy is successful (and can be shown to be representative), then the implications for refurbishment and energy assessment generally would be significant.

The potential for collaboration between Locate and GCU in undertaking further studies related to these and related issues of cost effective, airtight, vapour permeable and dry-wall solutions is high.

If the outcome of the monitoring is successful, then the next objective would be publicise and find another study in which to establish how representative the initial results are. If the approach proves to be generally representative, the benefits should include: reduced costs for householders / owners for providing effective energy efficiency greater potential uptake by households due to non-specialist requirements of installation reduced energy use overall reduced fuel poverty improved performance of buildings generally, longer service lives / reduced risk of failure

Key words: pre-1919 buildings, domestic buildings, refurbishment, energy efficiency


Dr Paul Baker, Glasgow Caledonian University

For Locate Architects

The outputs of this study will be disseminated in due course.


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