Non-Traditional (Crosswall) Properties, Reading

Project Overview

Background

In May 2022, at the request of Reading Borough Council, Permarock produced a specification for the treatment of multiple two-storey flats at Bamburgh Close, just over 2km south of the town centre.

The properties featured walls of varying designs but their overall effect was not thermally efficient. Consequently, the client required a design solution that would improve the energy efficiency of the homes while also delivering good weather protection and producing an attractive, uniform external appearance.

Brief:

The walls featured a range of construction types:

  • Front and rear walls: timber frame panel infill to a brickwork crosswall construction.
  • Timber frame walls: clad with a mixture of Steni panels and vertically hung tiles.
  • Flank end walls: brickwork cavity construction with cavities approx. 50 mm wide and partly filled with insulation.
  • Load-bearing cross walls to communal areas and elsewhere: solid brick construction.

The variety of wall designs within a single project called for close stakeholder collaboration from the outset. Ultimately, it was agreed that the best solution would comprise the installation of a Permarock mineral fibre external wall insulation system to all external wall types above DPC level, and a Permarock EPS-Plinth system, to be applied to wall bases (concrete slab edges) to a depth of at least 200 mm below DPC level. The Permarock Technical Hub Team were asked to supply a separate specification for the EPS-Plinth System.

Additional weather protection, airtightness and aesthetic improvements would be provided by means of a flexible, through-coloured render.

Design and Specification:

The proposed solution comprised a combination of Permarock Mineral Fibre Insulation, supplied in various thicknesses, and Permarock Silicone Ultra K-Finish as the decorative render.

Permarock Mineral Fibre external wall insulation is non-combustible (Class A1 to EN 13501-1) and suitable for use on buildings of any height. It is supplied in boards measuring 1200 mm by 600 mm and affixed using a mineral polymer-modified adhesive and mechanical fixing pins. It has low embodied energy, a thermal conductivity of 0.036 W/mK, and an Ecopoints score of 0.10 (m2), which is an ‘excellent’ rating. The insulation has zero ozone depletion potential (zODP), it is CFC- and HCFC-free, and it has a Global Warming Potential (GWP) of less than 5.

Permarock Silicone Ultra K Finish is a solvent-free, through-coloured render that affords excellent weather protection and produces a long-lasting, colour-stable finish. It helps resist the accumulation of dirt and the growth of unsightly mould, algae and other organisms longer than traditional renders.

Technical Support

Permarock has over 40 years’ experience of developing EWI designs for British properties, including many non-traditional archetypes. It’s technical team was therefore more-than-able to support the project design team, retrofit coordinator and installers. Its support included:

  • Assisting with property visual surveys.
  • Providing U-value calculations.
  • Producing material samples.
  • Supplying detail drawings and method statements.
  • Conducting pull-out tests to help determine the suitability of the various substrates to accept the EWI system.
  • Providing ongoing technical support pre, mid and post-tender, as well as for the duration of the installation, both remotely and on site.

The specification called for:

  • The removal of existing claddings (Steni panels and tiles), building paper and/or breather membranes (if present) from front and rear walls to expose the timber frames.
  • The removal of any existing insulation.
  • The installation of a new vapour control layer into the timber frame.
  • Packing new mineral fibre insulation, 100 mm thick, into the spaces between the timber studs
  • Fixing new 12 mm sheathing board to the timber stud framing to provide a base for the subsequent application of external wall insulation. Fixings to be non-corrodible.
  • Sealing the sheathing boards to the load-bearing structure at all abutments, sealing the new windows to the sheathing, and making all penetrations through the wall panels air-tight.

Permarock’s support also included drawings and advice for general installation, and for managing the interfaces with new doors and windows, which other stakeholder team members would install.

Result:

The scheme reached completion in June 2024. The accompanying photographs show the results of the work.

Project
Retrofit / Non-Traditional Property
Client
Reading Borough Council
Specifier
Reading Borough Council
Substrate
Mixed: Crosswall / Timber Frame / Steni Panel / Brick Cavity Wall
System
Permarock Mineral Fibre Dual Density External Wall Insulation
Finish
Permarock SiliconeUltra K Finish