Project Background

Northwood Primary was re-located from the old school site (North Road Primary School established 1915) in January 2010. It is a larger than average primary school catering for 420 full-time pupils from Reception to year six, with a further 52 part-time nursery places. The school is a fantastic new building built under the Building Schools for the Future, Pathfinder, initiative. It is a wonderfully bright and vibrant environment for teaching and learning.

The design of the building features a striking cedar cladded front wall, which curves over at the top leading onto sedum covered green roof areas. The building was designed with the environment firmly at the forefront of the priorities and the natural wood and vegetation on the building achieved the desired aesthetics. However, the structure underneath the cedar cladding had not been made sufficiently watertight during construction and this area had proved to be a long-standing source of leaks.

The need to provide a guaranteed waterproofing solution led the client to contact Polyroof for a recommendation. Due to the complexity of the structure and detailing underneath the cladding, Polyroof's Protec liquid system was chosen to provide seamless and maintenance free waterproofing. Polyroof's Technical Service, Barclay Roofing Ltd (Polyroof Approved Contractor) and the architect worked closely together to devise a long-term solution for these issues.

Northwood Primary School, Darlington

Before: exposed SIP panel showing signs of water and condensation damage

Meeting the Key Challenges of this Project

1: Lack of an effective waterproofing system beneath the cedar cladding

The existing waterproofing beneath the cedar cladding consisted of loose-laid building paper over a breather membrane. This had proven insufficient to stop water penetration and led to various and persistent leaks. Furthermore, many of the details, such as gutter channels, abutments to louvres and rooflight upstands, had detailing issues such as low upstand heights that further exacerbated the potential for water ingress.

Polyroof Technical Services worked closely with Barclay Roofing and the architect on the necessary modifications to allow the roof to be properly waterproofed. Initial sketches made by Polyroof and Barclays formed the basis of the architect’s amended drawings and were brought together in a bespoke specification document. This was a great example of a manufacturer, installer and designer working together and combining expertise to deliver an optimum solution for the client.

2: The existing SIP panel construction was suffering from condensation

The existing roof construction consisted of an insulated SIP panel construction supported by Glulam beams. Due to the absence of an effective vapour control layer, condensation appeared to be a problem within the roof. Polyroof Technical Services worked closely with the architect to come up with a solution to eliminate the risk of condensation that would also remove the need for any costly and disruptive stripping / replacement works, meaning the school’s operations could carry on unaffected.

The solution was to install a new breather membrane followed by timber battens at regular centres over the SIP panels, with the voids between ventilated at the perimeters to provide a cross-flow of air. A new plywood deck was then fixed to the battens to provide a substrate for the Protec system. This effectively created a ventilated cold roof design, which in accordance with BS5250 Guidelines is proven to help eliminate condensation problems.

3: The need to mechanically fix the cedar cladding in a fully weatherproof condition.

The cedar cladding needed to be re-fixed after the installation of the waterproofing system so the school’s impressive aesthetics would not be affected. The challenge associated with this aspect was that the fixings had to be adequate to ensure a proper attachment to the roof, and also had to not affect the waterproof integrity of the new system. Polyroof Technical Services came up with a solution that allowed fixing through their waterproof membrane, whilst still remaining waterproof.

Following the application of the first coat of Protec, which included the fibreglass reinforcement, timber battens where fixed through the membrane into the plywood substrate as a fixing point for the cedar cladding. The battens were then encapsulated with the full Protec system, also including the fibreglass reinforcement. The length of the weatherproof fixings for the cedar cladding were chosen as to ensure that they did not penetrate the underside of the battens, and for added protection strips of butyl tape were bonded to the membrane through which the fixings were installed - meaning the details where totally waterproof.

Butyl strips in place over Protec-encapsualted battens ready for the reinstallation of the cedar cladding

Cedar refixed and original aesthetics maintained

4: Vertical application and the demands associated with installing the waterproofing system

Most of the refurbishment work was carried out on vertical sections. It was essential that the liquid system had suitable thixotropy to be applied to vertically without sagging, ensuring that a quick installation and even coverage could be achieved. When Protec was developed the need for coating vertical applications was considered in its formulation, and the resulting product provides equally high performance no matter what the angle of the substrate. This allowed the works to be carried out as quickly as possible, meaning the roof/walls were brought to a waterproof state in the minimum amount of time.

5: Other trades working during and after application of the waterproofing system

Due to the complexity of the works and the various phases involved, it was essential that the waterproofing system was able to withstand foot traffic and the potential for damage from other trades. The Protec system is flexible, durable and impact-resistant – reducing the danger of damage by other trades during construction and installation periods, without the need for additional protection.

This project was an excellent example of a manufacturer, installer and designer working together and combining expertise to deliver an optimum solution for the client. The works were completed comfortably within budget and time deadlines whilst fully minimising disruption to the running of the school.