SIG Design & Technology looks at the importance of getting an accurate picture of the state of a flat roof before carrying out repairs. A good survey will help inform a detailed maintenance, repair and reroofing strategy.
The article will use examples from a primary school in the North of England that SIG have been working with for over three years, implementing an ongoing strategy to look after their flat roofs. The original work began when SIG were contacted by a partner surveyor to identify the causes of a leaking flat roof.
Phase 1 of the work, which was completed last year, allowed classes to be decanted into repaired areas in preparation for Phase 2, which has just received Condition Improvement Fund (CIF) for 2019-20.
Four core samples were taken during a detailed survey in preparation for Phase 2 of the works. Three were taken from one roof area and one from a second roof. Both roofs were part of the successful CIF funding bid for this work.
The school was experiencing leaking under each of the core sample areas.
The first core sample showed that the roof was a bitumen flat roof laid over insulation onto a chipboard deck. There was a Vapour Control layer however the insulation was saturated and visible water within the roofing system. The chipboard deck was exposed at the bottom, but it appeared to be unaffected by the moisture at this point.
The second sample was taken from the same roof but in a different position and showed visible water and saturated insulation, and the deck here is also dry.
The third core sample was taken on the same roof but in a different place. The sample showed a complete deck failure – a chipboard deck in this area had completely rotted away and you could see a hole at the bottom of the core sample.
The fourth core sample was taken in another roof area, a Single Ply roof membrane over insulation and a plywood deck. Everything here was dry and the deck in good condition. However, there was no Vapour Control Layer in the build-up. Whilst water was displaying inside the school in this area, this water was caused by Interstitial Condensation, not by a leak – not all water ingress is caused by leaking roof membranes.
The core samples revealed areas of saturated insulation, areas of failed deck and a single ply roof without a vapour control layer.
The core samples taken led to an estimate that 75% of the deck had failed. As a result, the budget and the successful school funding application allowed for all roofs to be stripped back to deck and a 75% deck replacement.
If this informed calculation hadn’t been made and the bid was successful, the school would have had to find funds from elsewhere to replace any failed deck, or even make a new grant application. The cost a new deck over this whole roof would have been over £20,000.
SIG’s advice about intrusive surveys for school roof repairs
In order to make an accurate application for funding and for a successful project to follow SIG recommends that a school takes the following steps:
1. Use a specialist roofing design company to make the survey and support the funding application, including informing any phasing decisions.
2. Ensure the surveyor looks at the whole roof, not just one small section. Make sure their proposal includes for the time required.
3. Have your surveyor carry out sufficient core samples and inspections to gain an accurate view of the condition of the roof, not just its saturation level. Remember core samples should not be taken if the roof is under warranty.
4. Ensure that a specialist roofing contractor carries out the repair and replacement works and that these are inspected by the design team who carried out the survey and made the application.
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