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Ex-Miners Cottage, Newtongrange

Ex-Miners Cottage, Newtongrange

Installation of roof and coom insulation and secondary glazing

Overview

This project focused primarily on coom ceilings, areas which have previously been difficult to insulate without stripping out internal linings, often leading to loss of historic fabric, disruptive building work, and the expense of new materials and labour.

Approach

The cottage was built in 1872 and sits in a row of properties which were originally built for miners working at the nearby Lady Victoria Colliery.

It is constructed of red brick, with cream brick detailing and is 1 1/2 storeys, having dormers at the front and rear, to accommodate bedrooms. The roof is Scottish slate, internally the walls are finished with plasterboard and all windows are timber, sash and case, single glazed.

Improvement measures

The upgrades were carried out on the upper floor and roof only, involving:

  • the installation of secondary glazing to the windows,
  • blown polystyrene bead insulation behind the plasterboard linings of the coom,
  • replacement of degraded mineral wool with sheep’s wool insulation in the loft space.

 

Secondary Glazing

Double glazed secondary glazing units, with integral trickle vents were manufactured and installed, ensuring that access was still possible to the existing windows to allow them to be cleaned safely. Ventilation was increased by removing the damaged draught-stripping from the original windows, thus reducing the condensation risk.

Coom Ceilings

Existing insulation was removed, carefully, due to the slate nails sticking through the sarking, and bonded polystyrene beads were blown in between the rafters from the roof space, avoiding the need to remove linings or decoration in the bedrooms below.

Roof space

Breathable sheep's wool insulation (140mm between the roof ties, and 100mm on top) was installed in the roof space, replacing the existing mineral wool. The cold water tanks, pipework and ceiling hatch were all also insulated.

It was decided to not increase the roof space ventilation (as is often required when a 'cold roof' is created through refurbishment works), but rather assess whether the blown polystyrene beads in the cooms allowed enough air to penetrate to ensure the roof space was adequately ventilated.

Performance

The thermal performance of the unimproved ceiling was measured before the new insulation was installed. In-situ U-value measurements were taken of the coom and the ceiling, to derive a pre-intervention performance. The measured values are shown below.

Pre-intervention:

Ceiling - 1.6 W/m2K

Coom ceiling - 1.9 W/m2K

Following the insulation works, the U-value tests were undertaken again to identify the thermal improvements made.

Post-intervention:

Ceiling - 0.4 W/m2K

Coom ceiling - 0.3 W/m2K

Full analysis of the monitoring undertaken in the cottage can be viewed in Historic Scotland's Technical Paper 19.

Lessons

Following the improvement works, the tenants reported improved temperatures in the bedrooms. However, the following winter, the tenant noticed white mould on the underside of the sarking boards. Investigations by the architect and Historic Scotland indicated that this was a result of high humidity levels in the roof space, due to insufficient ventilation.

While checking for further defects (requiring the removal of the blown bead insulation from the cooms), it was discovered that not all the mineral wool insulation had been removed, and some was left at the base of the coom, preventing air movement.

Edinburgh Napier University installed monitors to continually measure the relative humidity to ensure that acceptable levels were reached, and mould growth would not continue.

As the bead insulation had been removed, it was decided to install wood fibre board insulation in the cooms, with a 30mm air space below the sarking. This work is due to take place in Spring 2014.

 

Despite the need for this remedial work, the tenants have experienced improved thermal comfort, reduced energy bills and improved acoustic performance, from the secondary glazing units.

The tenants were also able to remain in their home whilst the work was undertaken.

This case study shows that a full understanding of the building must be achieved before any interventions are carried out, and that post-intervention monitoring is worthwhile to early identify any problems. 

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