high- and low-impact strategies for retrofit · high- and low-impact strategies for retrofit...

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

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

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


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

High- and low-impact retrofit strategies


• 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

High-impact retrofit: Hawthorne Road, London

Image © Anne Thorne Architects


• 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



• 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.


Retrofit trials at Sword Street, Glasgow

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


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”

Retrofit trials at Wells O’Wearie, Edinburgh

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.

EFFESUS case study in Glasgow:

Injected aerogel insulation

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

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

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.”

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

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.

high- and low-impact strategies for retrofit · high- and low-impact strategies for retrofit...

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