Single ply overlay to an existing metal roof

What should be considered when an old metal roof is causing problems?

A key element is to identify whether water appearing inside the building from the roof is because the roof is leaking or suffering from a build-up of condensation.

A roof survey is required to accurately ascertain the existing assembly; is it a composite panel, a built-up standing seam roof, or a fully supported system? Once an assessment of the full build up has been completed, options for potential renovation can be considered. An essential part of the roof survey is a pull-out test to determine the mechanical strength of the existing roof structure and deck. This will identify if an overlay renovation is feasible, and if so, the correct type of fastener to be employed.

Access to the roof during these preliminary stages could be required, therefore it is vital that the correct safety measures are considered from the outset.

Rooflights can become fragile after years of UV degradation. It should be identified if the existing rooflights need to be replaced or removed prior to the renovation (in-plane rooflights are not suitable to be retained in a warm roof membrane assembly). Old rooflights should not remain in place when a new waterproofing is installed over the existing because they cannot provide a suitable support.

What are the client’s requirements?

The primary concern is to identify and remove the water ingress, whether that’s condensation or leaks. From there, what are the requirements for a thermal upgrade of the roof to meet current building standards by the client or building control and in some cases, because of a condensation risk analysis test?

The condensation risk analysis test is completed prior to producing the re-roofing specification because adding further insulation to the roof, if there is existing insulation within the metal roof assembly, can impact the location of the dew point. An additional thickness of insulation may need to be specified over and above the initial client target U-Value to ensure that the new installation is not compromised.

For this type of overlay to an existing metal roof, a Bauder single ply membrane is usually specified due to its lightweight nature (circa 6kg/m² with 140mm PIR flatboard insulation) coupled with the ease and speed of installation. Also, the installation method ensures minimal interruption to the internal workings of the building.

How does Bauder PIR Infill Single Ply overlay system work?

Bauder Profiled Overlay System provides PIR support to the height of the existing crown, then a new built-up system can be installed on top of this comprising an air and vapour control layer, BauderPIR FA flatboard insulation, and Thermofol (PVC) or Thermoplan (FPO) membrane which can be adhered or mechanically fastened.

Existing metal roof systems typically achieve B_ROOF (t4). Bauder ensures the overlay assembly specified can have a current B_ROOF (t4) fire report for full compliance with building regulations.

Often clients require simulation of the existing metal roof aesthetics. Bauder decorative profiles can be added to the finished waterproofing, providing a visually seamless finish.

A future-proofing benefit of renovating with Bauder PIR Infill overlay system is BauderSOLAR F photovoltaic solution can be retrofitted to the roof without penetrating the waterproofing (subject to confirmation from a structural engineer). BauderSOLAR has a lightweight design, between 9-12kg/m², suitable for installation on roofs with a pitch of up to 10 degrees.

University of West England W Block case study

The existing single ply waterproofing and composite panels on the roof of University of West England, W Block were aged and failing, therefore the specifier’s main objectives with this refurbishment project, were to source a lightweight waterproofing solution and thermally upgrade the roof.

Bauder Thermofol single ply system was chosen to overlay the existing single ply and pitched composite panels due to its lightweight properties and versatility. At the specification stage, U-value calculations were carried out to determine the minimum thickness of insulation needed to ensure that the roof satisfies the current building regulations.

Read the full case study to find out more of the project’s specification, client benefits and challenges that were overcome.