High- and low-impact strategies for retrofit · High- and low-impact strategies for retrofit...
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High- and low-impact strategies for retrofit Comparing two strategies for insulating traditional masonry walls internally
3rd EWCHP, Bolzano / Bozen, 16-18 Sep. 2013
Carsten Hermann Senior Technical Officer
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Contents
• Introducing two strategies: high- and low-impact retrofits
• Case studies:
• Hawthorne Road, London – A high-impact retrofit
• Historic Scotland’s low-impact retrofit trials
• Tenement in Sword Street, Glasgow
• Cottage in Holyrood Park, Edinburgh
• Tenements in Edinburgh
• Planned EFFESUS case study in Glasgow
• Discussion:
• Comparison of retrofit strategies
• Governmental context
• Moisture-related risks
• Conclusions
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High- and low-impact retrofit strategies
High-impact retrofit
New insulation to existing wall faces
100 mm glass-fibre insulation
finished with plasterboard
Low-impact retrofit
Insulation injected into cavities
cellulose fibres injected into
30 mm cavity behind existing
plaster on laths finishes
High-impact retrofit
New insulation to existing wall faces
100 mm glass-fibre insulation
finished with plasterboard
• Significant thermal improvement
• Significant financial costs
• Significant occupants’ disruption
Low-impact retrofit
Insulation injected into cavities
cellulose fibres injected into
30 mm cavity behind existing
plaster on laths finishes
• Some thermal improvement
• Some financial costs
• Minimised occupants’ disruption
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High- and low-impact retrofit strategies
High-impact retrofit
• Reduces floor-space area and
changes room proportions
• Results in loss of existing wall
finishes
• Results in complicated and
complex detailing
• Impacts on the rooms’
appearance by covering visually
important wall features
• Results in thermal bridging
• Minimised condensation risk as
vapour control layer installed
Low-impact retrofit
• No changes to floor space-area
or room proportions
• No loss of existing wall finishes
• No complex detailing
• No impact on room’s appearance
• No new thermal bridging
• Potentially condensation risk as
no vapour control layer installed
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High-impact retrofit: Hawthorne Road, London
Image © Anne Thorne Architects
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High-impact retrofit: Hawthorne Road, London
• Refurbishment designed by Anne Thorne Architects, London
• Funded by Technology Strategy Board, a UK public body,
through their Retrofit For The Future programme
• to produce “exemplar retrofitted properties with radical and realistic solutions”
• to deliver “deep cuts in energy use and carbon emissions”
• 80% reduction in CO2 emissions on UK average housing
• Construction works carried out 2010-11
Image © Anne Thorne Architects
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Image © Anne Thorne Architects
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High-impact retrofit: Hawthorne Road, London
• U-values of 0.21 and 0.15 W/(m2∙K) for front and rear facades respectively in lieu of approx. 2.1 W/(m2∙K)
• Cost of complete refurbishment £150,000, “of which £89,000 covered retrofit build works”
• No detailed cost-breakdown is easily available
• Work could have not been carried out if the flat would have been occupied.
• Post-intervention monitoring by Bartlett School of Graduate Studies at UCL is on-going.
Image © Anne Thorne Architects
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Retrofit trials at Sword Street, Glasgow
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Retrofit trials at Sword Street, Glasgow
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Retrofit trials in Edinburgh tenements
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Retrofit trials in Edinburgh tenements
Polystyrene bead insulation injected into
cavities behind existing wall finishes
Overall wall thickness: 590 to 700 mm
Cavity thicknesses: 30 to 50 mm
Before U-values: 1.3 to 1.4 W/(m2∙K)
After U-values: 0.7 to 0.8 W/(m2∙K)
Areas: 4.75 to 25 m2
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Retrofit trials in Edinburgh tenements
Polystyrene bead insulation injected into
cavities behind existing wall finishes
Costs: 40 to 50 £/m2
Cost comparisons:
• 50mm expanded poly-
styrene bead injected
into cavity 6.3 to 7.2 £/m2
• 50mm insulating plaster-
board with slurry coat to
surface 85.0 to 95.6 £/m2
“it is anticipated that an increase in the
scope of works would result in a
commensurate reduction of costs”
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Retrofit trials at Wells O’Wearie, Edinburgh
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Retrofit trials at Wells O’Wearie, Edinburgh
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Retrofit trials at Wells O’Wearie, Edinburgh
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Researching energy efficiency for
European historic urban districts
The EFFESUS research project is receiving funding from
the European Union Seventh Framework Programme
(FP7/2007-2013) under grant agreement no. 314678.
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EFFESUS case study in Glasgow:
Injected aerogel insulation
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Why aerogel insulation? • Aerogel is a high-performance insulating product, developed for the
space industry
• Limited application in the construction industry as insulating board to date, due to the high cost to produce the material
• EFFESUS partners A. Proctor Group, UK, & Active Space Technologies, Portugal, will be developed aerogel further to make it suitable as injection material
• Aerogel could deliver the best of both high- and low-impact retrofits:
• High thermal performance
• Minimal impact on existing fabric
• Minimal disruption to building occupants
• if production costs were to come down
EFFESUS case study in Glasgow:
Injected aerogel insulation
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Discussion
Comparing high- and low-impact retrofits • High-impact retrofits deliver a better thermal performance, but only at
higher financial costs and increased disruption to occupants
• Comparison though are difficult because
• Detailed cost data is not easily available
• Experimental retrofit projects do not deliver mainstream construction costs
• Full life-cycle assessments are not generally conducted
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Discussion
UK governmental policy context
• UK government has introduced the Green Deal, a financial instrument
allowing “householders to pay for energy efficiency improvements
through savings on their energy bills”
• “significant subsidy is needed if traditional properties are to be
retrofitted to make significant CO2 and running cost savings”
• “Solid wall insulation is only eligible for ECO funding [the associated,
governmental subsidy programme] if it achieves a U-value if 0.3 or less.”
• “relaxing the maximum U-value for solid wall insulation would allow
more [insulation] systems to qualify for ECO, including the less
disruptive and lower-cost options such as blown bead insulation.”
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Discussion
Moisture related risks
• Traditional walls are constructed using materials and techniques that
allow the penetration of air and moisture, but constructed to a thickness
substantial enough to generally prevent moisture from reaching the
internal wall faces.
• High-impact retrofits are generally installed with vapour control layers,
reducing the risk of interstitial condensation, but potentially also
impeding room-side moisture evaporation
• Liquid moisture transport is generally not considered when assessing
retrofit options, e.g. in the form of ‘rising damp’ or wind-driven rain
• Low-risk retrofits are generally installed without a vapour control layer,
potentially increasing the risk of interstitial condensation
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Conclusions
Conclusions
• High-impact retrofit is more suitable where major works are planned and
occupants will be decanted anyway
• Low-impact retrofit is more suitable where no other works are planned
and costs and disruption to occupants have to be minimised
• Low-impact retrofit can be of particular interest for buildings where
interiors are of heritage significance, because such retrofits have no
impact on the visual appearance of buildings fabric and spaces.
• The moisture risks associated with retrofitting traditional stone walls
need to be better understood, particularly for low-impact retrofits and in
locations with high exposure to ‘rising damp’ and wind-driven rain.