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2 Roxburgh Street (2nd Floor) Edinburgh

2 Roxburgh Street (2nd Floor), 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 case study details the window and wall upgrades that were carried out on this north corner, second floor apartment accessed off common stair, within a four-storey plus basement, tenement c. 1800. Upgrading works were carried out to the two external walls and five windows.

Approach

Existing Fabric

  • Wall to front (northwest) and front (northeast) elevations of the apartment comprise broached ashlar, with droved margins to window surrounds. Overall masonry thickness is approx. 650 mm.
  • Wall linings to living room and main bedroom in lime plaster on timber lath, with rich decorative cornices.
  • Wall linings to second bedroom and kitchen in plasterboard on timber framing, with plain run cornices.
  • Box skirting and timber dado rail in living room, and plain ogee skirting elsewhere.
  • Open shelved press in north corner of living room, and gas fire / back boiler to east side of room (with natural ventilation provided via an existing circular vent through an upper window pane).
  • 2 no. 6 over 6 sash and case windows in the living room, and 1 no. in the main bedroom, each with working shutters with panelled elbows soffit and back. Moulded architraves with skirting blocks in living room and moulded architraves without skirting blocks in main bedroom.
  • 1 no. 6 over 6 pane sash and case window in the small bedroom and 1 no. in the kitchen, both with plywood lining on timber framing to reveals, and pencil round facings.

 

Wall upgrades - Living Room and Main Bedroom

  •  Shutters, architraves, skirting and soffit panels were removed.
  • The open cavities below cill level were packed with mineral wool insulation, and any gaps around the perimeter of the window opening were also filled to form a continuous seal.
  • Expanded polystyrene bonded bead insulation (Warmfill White) was blown into the wall lining cavity (approx. 40 – 50 mm deep to the NW wall, and 20 – 30 mm deep to the NE wall) through 22 mm diameter holes in the plaster and timber grounds, until a full fill was achieved.
  • Where the length of the walls beyond the window openings were beyond 2.0 – 3.0 m or where there were obstructions in the cavities e.g. former fireplace surround in living room, additional holes were face–drilled, through the lath and plaster, in the top corners of the wall to complete the cavity fill. This was also done in cupboards.

 

Window improvements - Living Room and Main Bedroom

  •  The windows were fitted with double glazed, timber, tilt and turn secondary glazing units with removable handles, to accommodate the shutters in the closed position.
  • The window reveals, elbows and back and shutter pockets were framed out with timber battens.
  • All timbers were held clear from the stonework / plaster ‘on the hard’, and the framing to the shutter pockets was sized to ensure adequate depth for pockets to accommodate shutters.
  • New timber packers were fitted to the window soffits.
  • Rigid insulation was cut and tightly fitted in between the timbers to the new framing and soffit packers as follows: 75 mm thick to window elbows, 100 mm thick to window back, 35 mm thick to shutter pockets, 35 / 25 mm thick to soffit.
  • Window linings were then reinstated.

 

Wall upgrades - Kitchen and Small Bedroom

  • Existing skirting, window cill board, and apron, to small bedroom removed and set aside.
  • The open cavities were packed with mineral wool, and bonded polystyrene bead was blown in behind the plasterboard to fully fill the cavity (approx. 30 – 40mm deep). Elsewhere, exposed plaster lining to former shutter pockets were drilled and injected with bonded polystyrene bead.

 

Window improvements - Kitchen and Small Bedroom

  • Window fitted with timber, double glazed, tilt and turn secondary glazed unit.
  • Rigid insulation was cut and tightly fitted between the existing framing to the reveals, soffits, and window back (small bedroom) and deep cill (kitchen) as follows: 75 mm thick to window back (small bedroom), 50 mm to reveals, 25 mm thick to soffits, 50 mm thick to deep cill (kitchen).
  • Window linings were then reinstated.

Performance

Pre- and Post-intervention U-value testing

Similar components were tested as previous properties with comparable results and circumstances. Significantly, the tested single glazed window with a timber frame gave a high U-value of 5.2 W/m²K, whilst with the double-glazed secondary glazing unit installed internally it was reduced to 0.6W/m²K. This is due to the additional glazed layer being installed and an adequate sealed space between the original glazing and the new layers. The better thermal performance of timber frames has also made a great contribution to this reduction.

 

Outline costs

Living room and main bedroom

Secondary glazing (and associated works)

Timber double glazed (approx. 2.0 m high x 1.00 m wide

£ 1,550 per window

Blown insulation

Total area:

25.00 m²

£ 40 per m²

 

Small bedroom and kitchen

Secondary glazing (and associated works)

Aluminium double glazed (approx. 1.7 m high x 0.95 m wide)

£ 1,300 per window

Blown insulation

Total area:

12.20 m²

£ 40 per m²

Lessons

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.

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