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16 Roxburgh Street Edinburgh

16 Roxburgh Street, Edinburgh

Wall and window upgrades

Overview

This case study is part of a new Historic Scotland publication series which presents examples of refurbishment projects of pre-1919 buildings designed to improve their energy efficiency.

This Refurbishment Case Study presents an energy-efficiency upgrade project which was carried out in five tenement flats owned and managed by Castle Rock Edinvar Housing Association. 16 Roxburgh Street is a main door, ground floor flat, within a three-storey and basement terrace, built around 1840. This project trialled a way of integrating secondary glazing with insulation behind the wall linings and around the window openings in tenement buildings, to improve the thermal performance of the entire external elevation. External doors were also upgraded.

Approach

In the Living Room, Bedroom, Kitchen and Hallway the following technical interventions were made to improve the energy efficiency of the property:

Improvements in the living room

  • Shutters, architraves, skirting blocks and soffit panels were all carefully removed as were the window elbows and backs to expose the wall cavities. The open cavities around the perimeter of the window openings were packed with mineral wool insulation to form a continuous seal. Expanded polystyrene bead insulation was blown into the wall lining cavity (approx. 30 – 40 mm deep) through the mineral wool packing, until a full fill was achieved.
  • The window reveals, elbows and shutter pockets were framed out with timber battens. All timbers were held clear from the stonework. Rigid insulation was then cut and tightly fitted in between the timbers.
  • The shuttered windows were fitted with double glazed, aluminium, tilt and turn secondary glazing units.
  • 12 mm timber cover plates were fixed to the face of the secondary glazing case and scribed to new shutter pocket lining, with all voids behind also filled with rigid insulation.

 

Improvements in the bedroom

  • The plasterboard linings to the window reveals were removed, leaving the cavity around the opening exposed in places. The removal of the linings exposed large, structurally unsound voids in the inside face of the stonework to the base of the reveals and window back, which had to be made good.
  • The open cavities in the walls were packed with mineral wool, and bonded polystyrene bead was blown in behind the plasterboard to fully fill the cavity (approx. 70 – 80 mm deep).
  • The window opening was fitted with an aluminium, double glazed, tilt and turn secondary glazed unit.
  • Rigid insulation was cut and tightly fitted between the new framing to the window back and the existing framing to the reveals and soffit.

 

 Improvements in the kitchen and hallway

  • 10 mm thick Proctor Spacetherm insulation blanket fitted to external walls and to the inside face of the external front door.
  • 12 mm bonding coat of Limelite plaster applied to the metal lath, and finished with a 3 mm Limelite skim coat
  • Existing, non-original glass to plain fanlight above external kitchen door removed, and replaced with 4 mm toughened glass, 4 mm argon-filled air gap, 4 mm low-e toughened glass

 

Following the wall and window upgrades, the properties were completed by the finishing of window surrounds, cill boards, woodwork painting and fitted carpets were trimmed to fit and re-laid. Other improvements were also made (e.g. plastering, electric work), for more information and details of the cost of this work, see the published document which can be downloaded from the top right hand corner of this page.

Performance

Pre- and Post-intervention U-value testing

In order to quantify the energy-efficiency improvements, the thermal performance, or U-value, of all components was tested before and after improvement works. Heat flux sensors were used to measure heat flows through the selected walls and windows. The sensors were mounted on the inner face of the component for 14 days so that an average value could be measured. Sensor locations were chosen to avoid thermal bridging near windows and corners as well as probable stud locations of plasterboard linings. 

U-value measurements results
     

Pre- Intervention

Post- Intervention

Location of measurement

Thickness (mm)

Improvement type

Monitored U Values (W/m2K)

Monitored U Values (W/m2K)

Wall (living room)

590

40mm "warm Fill" poly- bead in cavity

1.4

0.8

Side wall inner window elbows

590

75mm "Kspan Kooltherm K12"

1.9

0.4

Plaster on hard (hall wall)

590

10mm Spacetherm w/  ‘Limelite’ plaster

-

0.8

Front Door (solid & Spacetherm)

40

10mm Spacetherm + 4mm Ply

3.0

0.7

 

Outline costs

Living room

Secondary glazing (and associated works)

Aluminium double glazed (approx. 2.2 m high x 1.0 m wide)

£ 1,400 per window

Blown insulation

Total area: 4.75 m²

£ 50 per m²

 

Bedroom

Secondary glazing (and associated works)

Aluminium double glazed (approx. 2.0 m high x 1.0 m wide)

£ 1,250 per window

Blown insulation

Total area: 6.00 m²

£ 40 per m²

Lessons

Prior to improvements, tenants across the five tenement flats rated their windows as ‘poor’ with reference to security, ease of cleaning, thermal performance and acoustic performance. Tenants’ annual energy costs in 2009/10 ranged from £569 to £1597 – all amounting to a little over or substantially more than 10% of the residents’ predicted annual income. This put some of the tenants in ‘fuel poverty’.


Post-completion feedback indicated that the outcome is seen as beneficial by the tenants, although there were a number of issues raised. As the specification was non-standard, and some elements were experimental, the level of site supervision required was beyond that of a normal window replacement contract. The duration of works was a major concern and all tenants would have preferred that the work could have been coordinated more tightly.

 

The work was conducted whilst the homes were still occupied. This presented challenges for all involved and was quite disruptive for residents. Areas which had been previously undisturbed for over a century were opened up causing issues with dust. The surface insulation that was used caused very fine dust and created problems for both the installer and the tenant. Controlling the spread of dust and the lack of clear areas to work created friction between tenants and contractors.

 

Some tenants highlighted that the ‘tilt and turn’ timber secondary glazing was heavy and difficult to operate. However, overall feedback from the residents was that the pilot was a good idea. Tenants commented that the properties were much warmer and that aesthetically – the solution ‘was beautiful’.

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