Flat roof on-site inspections – why they are important

Flat roof on-site inspections – why they are important

SIG Design & Technology looks at the importance of flat roof on-site inspections and how they help everyone in the process of roof refurbishment and replacement, using a school refurbishment project to illustrate the benefits.

Flat roof on-site inspections help the client

The client in a school’s project, in this case a Multi Academy Trust, the School Business Manager and the Head, can gain confidence and peace of mind from having their flat roof installation regularly inspected by a specialist during the works. These inspections satisfy the client that the roof has been installed correctly at every stage.

The warranty is key to the success of a flat roof installation or repair. It needs to be genuine; backed up by a credible and solvent provider and based on good practice. Flat roof on-site inspections confirm that the warranty will be met and give the school confidence that they should not have to call in the warranty and the roof will perform correctly throughout its lifetime if the maintenance programme (which usually consists of 6-monthly inspections) is followed.

On-site inspections limit the client’s risk because they won’t have to claim on the warranty, but it also reduces the risk to the supplier and installer of the roofing materials. If the roof is installed and maintained correctly you shouldn’t have any issues with the flat roof for the lifetime of the roof, and so there won’t be any additional costs.

On-site inspections of flat roofs help the contractor

On-site inspections also assist the roofing contractor because the specialist from SIG Design & Technology can provide expert help and support. Many of their contractors have been working on flat roofs for over 30 years so collaborating comes second nature to them.

If they come across any design issues as the project progresses, they can discuss these with the contractor on site. Finding an issue early enough prevents it becoming a problem, whereas if you discover it later it can be very costly.

By their nature flat roofs are sealed in, and it is only when you uncover the build-up that some issues may come to light. An experienced team can identify the correct way to deal with such issues and prevent any mistakes or poor decisions arising from inexperience.

During on-site inspections, SIG Design & Technology can discuss the best way to achieve the details planned in the specification, to ensure that they achieve the most robust detail possible.

SIG Design & Technology act as a constant point of contact, which enables the contractor to resolve any issues they have quickly and avoid delays in the programme.

What does an on-site inspection involve?

SIG Design & Technology normally inspect a roofing project a minimum of once a week during the works and complete an inspection document known as a SIGnature warranty inspection report if SIGnature products are used. Similar inspection processes are applied for other systems as appropriate.

This inspection report is sent to the client, giving a snapshot of what is happening. In this way the client is fully informed about the stage of the work and always knows about any issues that have been identified and how they are being resolved.

Part of the flat roof on-site inspection process is to make sure every layer of the roof is installed correctly. These may include amongst others:
• The deck;
• A primer;
• The VCL (vapour control layer);
• The Insulation (which may be adhered or mechanically fixed);
• An underlay;
• A capsheet;
• Any trims, and
• Rainwater outlets and gutters.

It is particularly important that SIG Design & Technology check that the VCL (Vapour Control Layer) is installed correctly, because incorrect installation of a VCL can cause condensation issues. In many flat roof constructions, the VCL is adhered to the deck and then the layers above are glued to the VCL. These adhered layers are important to the construction as they prevent wind uplift from damaging the roof, particularly at the edges.

SIG Design & Technology usually use a PU (Polyurethane) adhesive to adhere the insulation to the VCL. The role of the VCL is to stop moist air traveling into the insulation, therefore the VCL itself needs to be fully sealed and terminated to the underlay correctly.

During the inspections, they will also check that the insulation is the correct product (as per the specification), is adhered correctly, and that the adhesive is correctly applied. If the insulation forms a tapered scheme (where the insulation is cut to create the falls in the roof,) they will also ensure the tapers are installed correctly to avoid issues with standing water, for example.

The next layer is likely to be an underlay – they check that this is also fully adhered, and that the laps are sealed. In gutters, they check that the end- and head- laps of the membrane have been increased to 150mm to make sure of a more robust gutter detail. They will also inspect all the other layers and check all the details around the works.

Changing details following an on-site flat roof inspection

On occasion the works will uncover aspects of the existing roof which were not possible to see during the survey, and in this case being present for regular inspections is particularly useful. Here’s an example from a primary school in Darlington.

A set of clerestory windows over the existing toilet block had been inspected during the survey. Because the re-roofing could not fit in the required 150mm upstand from the new roof under them (with its increased insulation to meet current building regulations and improve heat retention), the intention was to close off these windows.

The design stage intention was to install a set of new SIGnature flat rooflights in the existing deck to provide natural light to the rear of the toilets, which are also lit to the front with conventional windows. However, when the contractor stripped the roof off, they found that the reinforcement in the concrete deck would not allow their installation safely. This issue was picked up during an on-site inspection shortly afterwards.

SIG Design & Technology discussed the matter with the contractor, client and their surveyors and identified that the best way forward would be to install LED lighting at the rear of the toilet blocks to supplement the natural light coming from the other side. This would allow a robust detail at this point in the roof, keeping proper upstands, and it was a solution that could be implemented within budget.

The late design decision also had other benefits. Whilst there is plenty of natural light in the toilet block on bright days, the LEDs would perform better than rooflights because they could enhance the lighting levels during dark mornings and evenings, as well as being cost effective. The outcome was therefore at no additional cost to the client and provided a better solution overall.

Flat roof on-site inspections are good practice

If you’re carrying out works to the flat roofs on your school or other building, make sure your roofing professionals are working as a team. Ensure that weekly inspections of the work will be carried out to make the most of their professional experience, encourage communication and avoid delays and additional costs.

Find out more about SIG Design & Technology’s free initial survey of your school flat roofs on their school refurbishment microsite here.

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SIG Design Technology

SIG Design & Technology is a part of SIG Roofing, a leading division of SIG plc, a FTSE 250 listed company and the UK's market leading specialist supplier to professionals in the building and construction industry. They design and supply flat roofing...
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