A survey of a flat roof involves more than a visual inspection of the roof surface. Knowledge of the type and condition of underlying substrate of insulation layers, vapour control and deck material are necessary to form a comprehensive survey report. A visual inspection of the surface cannot provide this level of information and since a drone is basically a flying camera, a visual surface inspection of the surface is all that can be provided.
However, sometimes the aerial drone survey is the most effective way forward in assessing the best actions for maintaining or refurbishing a flat roof.
The first matter to consider in carrying out a flat roof inspection is how to access the roof. Some buildings have internal access to their roofs, and provided that all necessary precautions are taken regarding operatives’ proximity to roof edges, voids and rooflights, these are the obvious method of roof inspection.
Without internal access, other means need to be considered.
Ladders are a possibility for access, still allowed under HSE guidance and safety law, for low-risk, short duration tasks, such as access and egress to and from a roof. They have to be used according to various stipulations such as standing on firm level ground, being footed by a second person and being tied off to the building (often the most difficult part). They are unlikely to be considered the best option for roofs beyond two storeys in height however.
A better option is to use a tower scaffold, but as with ladders, must be used according to various safe precautions, particularly ground stabilisation. Obviously, there is additional time and cost involved here in accessing the roof.
A cherry picker can provide access for a visual inspection only since it is not permitted under safety regulations to exit the cradle in order to access the roof. A surveyor using a cherry-picker for a roof inspection also needs to have received the requisite training in the use of harnesses and their use in conjunction with cherry-picker cradles.
Where the access is limited or unsafe an alternative option is to use a drone-camera for an aerial inspection. This will provide a good initial inspection of the roof which can be used to inform the decision on what further action may or may not be required for the future maintenance of the roof.
So what information can the drone provide?
For routine maintenance, which is normally visual;
- Obvious damage. Severe storms can not only cause damage to a flat roof covering, but may dislodge items such as chimney pots, TV aerials/satellite dishes, roof slates or stonework from adjacent parts of the building or other buildings, which can cause impact damage to a flat roof.
- Delaminated membranes or entire coverings, occasionally happens following severe storms.
- Detached upstands, lead flashings or expansion joint coverings.
- Debris build-ups – leaves most commonly. Debris will accumulate in corners and at kerbs and abutments leading to vegetation growth on the roof, which will eventually damage roof membranes
- Gutters/channels – whether running clear or blocked
- Missing cowls/gratings to flues and outlets. Missing gratings from outlets allow debris into the down-pipes the ground level drainage system.
For roof surveys further information can be acquired;
- The type of covering can usually be determined. Bituminous membranes, single-ply membranes, mastic asphalt or liquid-applied waterproofing systems will normally be apparent to the experienced observer. Roofs with stone coverings are more difficult to assess, but perimeter upstands may indicate the type of covering in place.
- The membrane’s surface condition will be apparent. Cracks, splits, blisters and general erosion are noticeable.Â
- Drainage outlets. The type of drainage outlet, whether internal, chute through wall, or drip edge to gutters can be observed. Some roofs have symphonic outlets and these too will normally be apparent. Outlet sizes can often be estimated which gives an indication of the roof’s drainage capacity.
- Surface drainage will be apparent. Areas of ponding, whether standing water or dry staining, indicates the flow of rainwater across the roof. The effectiveness of the surface drainage will be noticeable by relating the areas of ponding or staining to outlet locations. It will often be seen that rainwater run-off is not reaching outlets due to depressions and backfalls in the roof. Membrane lap build-up around outlets and at drip edges often causes ponding, which will noticeable in a drone photo-inspection.
- Perimeter constructions. With the drone we can observe waterproofing dressing to upstands, parapets, expansion joints, door thresholds, window cills and the various items of roof furniture. The condition of any copings, whether stone or metal cappings, can be identified.
- Roof furniture condition – rooflights, vents, extracts, flues, chimneys. The type of support to roof mounted plant will be of interest for any maintenance or refurbishment.
- Gutters/channels –whether blocked or flowing.
- Thermal cameras. Drones provide the ideal vantage point for a thermal survey over a flat roof, and the thermogram image, when assessed by a qualified thermographer, can reveal much about the underlying condition of the roof covering.
For a fraction of the cost of access towers or cherry-pickers, a drone can supply an overview of the roof type and condition, and the imagery obtained will allow facilities managers to determine the most appropriate follow-on actions. It may indicate that a further manual inspection is warranted and that scaffold access is justified. Or the drone imagery may have flagged-up that there are obvious matters of roof maintenance or repair which need to be carried out, and the maintenance contractor will be well informed as to the required materials and resources for the remedial works.
And in future, who knows, drones may well be able to lift the roofing materials to the roof and deposit them directly in the required location for the work.
This article was written by Tony Doyle. You can learn more about Tony and his service here
Tony Doyle is the founder of Seagull Aerial Survey & Photography, a CAA-registered drone operator specializing in aerial imagery for roofing and construction projects. With expertise in aerial inspections, site mapping, and promotional imagery, Tony and his team provide safe, efficient, and economical solutions for clients in the building industry.
