Reducing costs & risk on school roofing projects

Reducing costs & risk on school roofing projects

SIG Design Technology look at a schools project from the perspective of its roofing challenges and show how a collaborative, integrated approach to the full process of product choice, design and implementation kept down costs whilst reducing risk.

School Roofing: The Project
The client, a main contractor, undertook a major building programme at a girls’ school in London. Part of the Priority Schools Building Programme (PSBP), the project included a dedicated sixth form building, new sports hall and dining room.

The project was a legacy project; so cost effectiveness was absolutely paramount. Nevertheless, the solutions would have to be robust and long lasting, and as part of the PSBP, would have to satisfy challenging performance criteria.

There were four roofs on the project, totalling over 2000m2. To meet the criteria in the most cost effective way, they would require two different finishes and three different build-ups. Crucially, the client was looking for one single guarantee to cover all four.

Guidance from the 8 Steps
To make sure your roof performs correctly, SIG Design Technology developed a set of guidance called ‘8 Steps to a Perfect Roof’. In the case of this school roofing project, these steps were particularly important:

Step 1: The Right Products – understanding the contractor’s protocols;
Step 2: Design Expertise – a single design team from the deck up would manage the risk whilst developing innovative solutions;
Step 3: Meeting the Regulations – under the PSBP acoustics were particularly challenging;
Step 5: Experienced Contractors – one single multi-disciplined contractor would be required to install three different finishes;
Step 7: Full Guarantees – A system warranty was required to cover all the roof components at one single source.
Step 8: Planned Maintenance – Designing for maintenance was to be essential to ensure the guarantees were valid, and keep costs down long term.

Four Different School Roofs – Three Different Solutions
Each of the four roofs represented a different challenge.

1. The Sports Hall Roof would be built on a metal deck and was to have PV installed. The roof PV installation would require regular maintenance. There would be no ceiling, which would save in cost, but the roof still had to comply with the latest acoustic regulations on rain noise (aka BB93) and reverberation, so it would be suitable for both noisy sports and exams.
2. The Dining Hall Roof would also be built on a metal deck, but unlike the Sports Hall, the dining hall had no PV or roof mounted plant so would not be regularly trafficked. Nevertheless, acoustics were again an issue for this flexible space.
3. The Changing Rooms Roof was to be built on flat concrete planks with roof-mounted plant, so needed to be robust to withstand regular foot traffic.
4. The 6th Form Block Roof was also on flat concrete planks but with only a little plant, so less need for frequent traffic.

The Right Products – Changing Rooms and 6th Form Block
The two concrete plank roofs were to be put to falls using screed, however the screed was omitted and instead used Cut to Falls insulation which provided a cost saving through a reduction in weight.

The considerable amount of plant on the Changing Rooms Roof led to recommend a robust built up felt roofing system, with a slip resistant, granular finish. The result was a cost efficient, robust and well-drained roof with no ponding water, well suited to future needs.

Meeting the Regulations: Dining Hall Roof
A metal deck with no ceiling creates the opportunity for reverberation and a very noisy dining hall. However SIG Design Technology wanted to maintain the cost saving of not installing an expensive ceiling, so recommended a perforated deck with trough infills to enable the roof to meet sound absorption class C more cost effectively. However, this isn’t the whole story.

The metal decks on the dining hall and sports hall put them at risk of problems with rain drumming noise. SIG Design and Technology have developed a range of tested, certificated build ups for use with schools in the PSBP.

One of these solutions was ideal for the Dining Hall Roof as well as being the most economical:
• Perforated Deck and Trough infills;
• A Polyethylene Vapour Control Layer;
• Our own developed 10mm acoustic mat;
• Mechanically fixed PIR insulation, and
• Armourplan PVC single ply membrane, again mechanically fixed.

Planned Maintenance: The Sports Hall Roof
The sports hall roof is similar to the dining hall, but with a roof mounted PV array, heavy traffic was going to be an issue.

Where there is to be heavy traffic, the contractors’ protocol is not to use single ply membranes, and the preference is for a built up felt roof instead. However with a perforated deck the bitumen primer required for the felt vapour control layer would stain the decking webs and with no ceiling this would be unsightly.

A hybrid system was negotiated with the manufacturers. This system, which used a built up felt roof with a polyethylene vapour control layer, dealt with both the acoustic and aesthetic requirements, and was robust for high traffic and cost effective.

What is more, despite being innovative, the complete system would still be covered under our PI Insurance, like all the roofs in this project.

Delivering a Single Guarantee
The ultimate objective of this school roofing project was to deliver the roofs under a single guarantee, and for this the quality of installation was essential. The 1300 trained installers in 397-company DATAC contractor network provide the installation expertise. SIG Design and Technology monitor all installations, reporting on visits and ensuring the roofs are all installed as specified.

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SIG Design & Technology is a part of SIG plc a FTSE 250 listed company. We are committed to supporting the construction industry through the provision of exceptional roofing solutions to aid design, performance and aesthetic considerations. SIG plc is...
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