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22 Drummond Street, Edinburgh

22 Drummond 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. 22 Drummond Street is a rear second floor flat, accessed from a common stair, within a five-storey tenement block built c. 1790. Upgrading works were carried out to the rear wall and window in a single room (bedroom).

Approach

Existing Fabric

  • South west elevation of apartment (wall to rear) comprising random rubble stone with broached ashlar window surrounds. Overall masonry thickness approx. 750 mm.
  • Wall linings in plasterboard on metal studwork (with original plaster ‘on the hard’ behind) and pencil round skirting. No cornice.
  • 1 no. 6 over 6 pane sash and case window. Plasterboard on metal framing to window reveal. Taped corners to leading edge of window reveal / soffit.

 

Window improvements

  • Window fitted with an aluminium, double glazed, tilt and turn secondary glazed unit.
  • New timber framing was fixed to the window reveals and the window back.
  • Rigid insulation was cut and tightly fitted between the new framing to the window back and reveals, and to the underside of the RSJ’s at the window head, with timber grounds to take the new soffit lining.
  • Window linings were reinstated.

 

Improvements to external walls

  • The open cavities were packed with mineral wool, and bonded polystyrene bead was blown in behind the plasterboard to fully fill the cavity (approx. 100 mm deep).

Performance

Pre- and Post-intervention U-value testing

U-value testing was carried out before and after the interventions were made. The pre-intervention U-value results from this property were unusually low. This may be due to the large void behind the existing plasterboard, approximately 100 mm deep, which acted as a thermal resistance barrier, lowering the overall U-value of the wall. With the insulation installed, the U-value of the wall was only marginally reduced, suggesting that the air space behind the linings was unventilated in this instance, and was therefore providing a degree of insulation. This is unusual as generally these cavities are slightly ventilated with lower thermal resistances influencing the passage of heat.


The monitoring of the window demonstrated a substantial improvement in U-value following the upgrade works. The double glazed secondary unit with aluminium frame gave a 4.4 W/m²K decrease.

 

Lessons

Carrying out the trial improvements without decanting the residents proved problematic, especially where all of the external wall/window elements were treated in a single operation. In these instances, it soon became clear that the treatment required to be phased if the properties were to remain occupied, possibly by treating each property in two halves to minimise the disruption. Also, by managing the tenants’ expectations and carefully co-ordinating the works, further cost reductions should be possible.


The pilot demonstrated that the solution for installing secondary glazing where shutters are present can deliver a substantial thermal and acoustic improvement to the windows without impacting on the appearance or functionality of the existing window features. In addition, the thermal performance of walls and external doors was also improved considerably while retaining existing elements.

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Case Study

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