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Ballindalloch Drive Flats, Glasgow

Ballindalloch Drive, Glasgow

Glasgow’s Tenements to Passivhaus Standard

Overview

This case study is evidence of Milnbank Housing Association's refurbishment of tenement housing with the aim of reducing energy use, energy bills and exploring the possibility of meeting the internationally recognised Passivhaus standard.

This study has outlined the implications of three standards for tenements, investigated the technical constraints, proposed solutions and prepared budget costs. 

Further to this, the strategies considered physical upgrades which included: heating systems, window replacement and draught proofing.

Approach

Existing Fabric 

  • This case study involves three tenement mid-terraced flats - one at ground floor, one first floor and a third upper floor flat.
  • The wall to the front (north east elevation) of the tenements is comprised of sandstone.
  • The lining of the walls includes 15mm bead insulation behind the plasterboard and sandstone. The overall thickness is approximately 695mm.
  • There had been significant leakage detected around bathroom fittings, light fittings, sockets, skirting boards and through walls.
  • The flats have un-insulated doors and fan lights in addition to problems of leakage in double glazed UPVC windows.

The following subsections display the three proposed upgrades (Gold, Silver and Bronze) and their main features.

 

Wall upgrades

Bronze Standard:

  • Walls stripped back to stonework.
  • Plaster parge coat applied, 100mm wood fibre board fitted with mechanical fixings.
  • Finished internally with 10mm insulated plaster and organic paint.
  • The wall underneath the window was stripped back to stonework, and 20mm plaster applied.  

 

Silver Standard:

On top of the Bronze additions the Silver standard displays:

  • A plaster airtightness barrier.
  • 20 mm of insulating plaster applied and externally 250mm of polystyrene is applied. (Newton Diathonite insulation plaster)
  • Dry lining (where present) was stripped from party walls, gaps were sealed and the walls re-plastered.
  • Plaster was tied into walls in flats above and below along with being sealed to new plaster work at external walls.

 

 Gold Standard:

 In addition to the Bronze and Silver upgrades, Gold includes:

  • Airtightness tape between windows and new plaster.

 

Window improvements

Bronze and Silver Standard:

  • Current UPVC double glazed windows remain with the addition of airtightness tape and new plaster.

 

Gold Standard:

  • Passivhaus certified triple glazed windows (suggested U-value 0.69W/m2K installed and taped into airtight barrier.
  • The windows will have an airtightness membrane fitted and this is lapped into the plasterwork surrounding the windows.

 

Additional Improvements

Heating:

For the Silver and Gold standard, the heating demand of the block would drop to a level suitable for communal heating. A gas-fired communal heating system is proposed which would be installed in the roof space. This could be linked to solar panels to pre-heat the water.

Calculations illustrate that a standard 30kW boiler should provide the heating output required for the improved flats. For the purposes of costing, two 30kW boilers mounted in tandem, connected to 10m2 of solar thermal are proposed.

P.V. Panels:

An 88m­2 array with a 10kWp rating would offer the best return. The capital cost for the system would equate to around £13,000, which with the current feed in tariff of 14p/kWh would give a payback period of 9 years and a total profit over 20 years of more than £19,000.

MVHR System:

This study is based on the assumption that the airtightness of the flats can be improved up to EnerPHit levels. As such an effective ventilation system must be installed to ensure a healthy indoor environment. A Passivhaus certified system was proposed in each case.

Performance

Pre and Post-intervention U-value testing

U-value tests were carried out before and after the improvements were made. Testing the Sash & Single Glazed Window gave U-value results of 5.2W/m2K before and 1.5 after.

Thermographic Testing

An infrared survey was undertaken during the early hours of 2 May 2012, between the hours of 3:00am and 5:00am. The ambient temperature was around 5ºC. Thermographic testing can show up areas of heat loss by measuring surface temperatures. The higher the temperature on the surface, the more heat is escaping.

Pre-analysis of the building estimated that most of the losses in heat would be from the stonework. However, after the infra-red images were taken it was evident that the UPVC windows showed an inherent weakness, possibly due to the lack of seals or insulation between the window frame and the surrounding stone.

It has been suggested that airtightness tape is used in future to minimise the air losses around these areas.

40ballindalloch Drive

Image: © John Gilbert Architects Team.

Lessons

The key outcomes are as follows:

  • Retrofitting of tenements is better undertaken on a close-by-close basis than a flat-by-flat basis.
  • A strategy of improving airtightness, whilst ensuring sufficient ventilation, has a more significant effect on energy use than insulation alone.
  • Communal heating has an effect on the cost of heating for tenants rather than necessarily an impact on reducing energy usage. There are however, additional management and charging issues to be addressed when using communal heating.
  • It is theoretically possible to meet the EnerPHit standards in a tenement close offering significant reductions on energy bills and increased comfort for residents.
  • Given the predicted raise in energy prices over the next decade, the silver and gold standard offer comfortable indoor temperatures with energy usage that significantly reduce the risk of fuel poverty.
  • The costs of any upgrades can be significant.

 

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