Historic Environment Scotland

Retrofit Project Review

Dr Moses Jenkins MCIOB

Technical Conservation Group

The aims of the review

• To commission an external firm of surveyors to

investigate the condition of 20 case study

buildings which had been refurbished between

2009 and 2016

• To ascertain if any defects had arisen as a result

of the retrofit works we had carried out

• To see what lessons can be learned for the

future and revise guidance if necessary

Conclusion 1: vapour open IWI works

A range of IWI solutions examined with

no detrimental effects to building fabric

• Insulation behind a wall ling including bonded

bead, cellulose and open cell foam

• Surface applied insulation including calcium

silicate board and aerogel

• Board material including wood fibre and hemp

fibre

• All maintain moisture movement as a critical

principle in the retrofitting of traditional buildings

Conclusion 2: Insulating a suspended timber floor between

joists with vapour open insulation also work well

Lime concrete floors can also be very

successful as part of wider refurbishment

Conclusion 3: Secondary glazing works but needs to be

designed around occupants and windows need to be in

good condition

Secondary glazing findings:

• In two cases secondary glazing had been removed as

thermal comfort and condensation still a problem due to

condition of the windows

• Tenants prefer new double glazed sash and case

windows in these cases

• Polycarbonate sheet secondary glazing can be hard to

clean and store

• When bespoke solutions are sought feedback more

positive and the intervention is more successful

Conclusion 4: Roof spaces need a careful

approach especially if roofing felt present

Risks are significantly increased where there

is bituminous felt over sarking boards

Also vital not to leave cold

uninsulated areas...

Roof spaces can be successfully

improved when adequate ventilation is

provided

Conclusion five The functioning and

positioning of extract ventilation is important

Ventilation from bathroom to

roof space

Conclusion Considerable thermal

improvements can be made

• Walls:

• 0mm calcium silicate

board 81

• Wood fibre board 83

• Hemp fibre board 100mm

80

• Roofs:

• Sheep's Wool 8six

• Hemp Fibre 8five

• Floors:

• 80mm wood fibre board

7five

• Lime concrete floor

• Windows:

• Secondary glazing 88

• Insulated shutters 82 2.2

to 0.4

Scottish Building Standards

targets can be met

• Walls: 100mm of hemp insulation U-value of 0.22 and 80mm of

wood fibre 0.19, both well within the Scottish Government’s Building

Standard guidance for maximum U-value of 0.3 for conversion of

heated buildings

• Roofs: 200mm Wood fibre board, 280mm sheep's wool (0.2) and

2five0mm hemp fibre board (0.2) all met the uvalue target of 0.2fvie

• Floors: target uvalue of 0.2 could be met with 10mm wood fibre

board and lime concrete floor

• Windows: The target uvalue of 1.six can be met with secondary

glazing (0.8 to1.) and also with a range of slim double glazed units

Conclusion: Micro Renewables must be well

thought out

Micro Renewables

• Ground source heat pump at Downies

Cottage provided constant low level

heating a worked well for the building

• Air source heat at church along with

radiant panels reported as good for

parishioners but perhaps not enough for

building fabric

• Radiant panels at a domestic level can be

effective supplementary source of heat

Conclusion Significant interventions to improve energy

efficiency can be made with minimal impact on character or

significance

The Outlander test...

Overall Conclusions therefore are:

1. Vapour open IWI works successfully both in terms of

moisture and thermally

2. Insulating floors is a very successful fabric improvement

3. Secondary glazing works but needs to thought through

4. Roof space improvements need careful planning and a

good understanding of building fabric

. Functioning and positioning of extract ventilation important

Considerable thermal improvements can be made

7. Micro renewables can be successful but again need to

be carefully planned

8. This can be balanced with conservation considerations

Technical Paper Coming Soon!

This and more can be found at

www.engineshed.scot/publications/

I can be contacted at

moses.jenkins@hes.scot