1. Executive Summary

This report presents the findings of a visual drone inspection of the flat roof and rooftop solar photovoltaic (PV) installation at the above-referenced residential apartment block. The survey was conducted on 23 November 2025 using an unmanned aerial vehicle (UAV) equipped with a high-resolution camera system, operating in clear, bright winter sunshine conditions.

The building is a modern, multi-storey residential block of approximately four to five storeys with a large flat roof area. The roof is finished with a light-grey single-ply or torch-on membrane and accommodates a solar PV array of an estimated 50 panels arranged in an east-west back-to-back configuration across three zones, together with multiple HVAC units, rooflights, and associated plant and equipment.

Overall, the roof membrane and solar installation appear to be in satisfactory condition for the age and type of construction. Several items warranting further investigation or preventative action have been identified, and these are detailed in Sections 6 through 8.

Summary of Key Findings

• Roof membrane: Generally sound with no large-scale visible blistering or standing water observed at time of survey.
• Solar array: One installation across three zones — a wide full-width strip, a central box section, and two small end groups — totalling approximately 50 panels in an east-west back-to-back mounting configuration. General condition appears acceptable.
• Cable management: DC cable routing visible across roof surface; compliance with containment best practice requires verification.
• HVAC plant: Multiple units identified; maintenance access pathways appear limited in areas.
• Rooflights: Two rooflights visible; upstand heights and flashing integrity require physical verification.
• Drainage: Four corner drainage outlets identified; leaf/debris accumulation risk noted given adjacent trees.
• Edge/parapet: Parapet copings visible; coping joints and drip details require closer inspection.

2. Property & Survey Details

2.1 Building Description

The property is a modern multi-storey residential apartment block, constructed to a standard reinforced concrete or steel frame with masonry infill panels — typical of UK residential construction from the 2000s–2020s. The building comprises four to five storeys above ground level, with a large flat roof of approximately rectangular plan form, bounded by a continuous parapet wall with metal or pre-cast coping stones.

2.2 Survey Methodology

The survey was carried out using a DJI drone platform operating under CAA Operational Authorisation. Three high-resolution still images were captured from multiple perspectives including near-vertical (plan view) and oblique angles at approximately 30–45 metres above ground level. The low winter sun angle at the time of survey (23 November) cast shadows that assisted in identifying surface undulations and upstand heights.

2.3 Limitations of Drone Survey

• No physical access was made to the roof surface during this inspection.
• Internal roof construction, including insulation, vapour control and deck condition, cannot be assessed from aerial imagery.
• Membrane lap joints, upstand heights, and drainage outlet details are not verifiable without physical inspection.
• Electrical installations (inverters, fusing, earthing, string configurations) were not assessed.
• Thermal imaging was not conducted; moisture ingress within the membrane cannot be ruled out or confirmed.

3. Roof Construction Overview

3.1 Roof Type & UK Construction Context

The roof appears to be a warm flat roof construction, the most common specification for commercial and residential flat roofs in the UK since the 1990s, consistent with guidance in BS 6229:2018 (Flat roofs with continuously supported flexible waterproof coverings) and NHBC Standards Chapter 7.1. In a warm flat roof, insulation is positioned above the structural deck and below or within the waterproofing layer, meaning the structural elements remain at or near internal temperatures and are not exposed to condensation risk.

3.2 Typical Warm Flat Roof Construction Sequence

Based on the building’s apparent age and the observed roof finish, the following construction is considered most likely:

• Structural deck: reinforced concrete slab or profiled steel decking.
• Vapour control layer (VCL): foil-faced bitumen layer or polyethylene sheet, preventing moist internal air migrating upward into insulation.
• Rigid PIR insulation boards: typically 100–150 mm minimum thickness to achieve U-value ≤ 0.18 W/m²K (Approved Document L).
• Waterproofing membrane: single-ply TPO, PVC, or EPDM, or a reinforced bitumen membrane. The light grey colouration is consistent with a TPO or glass-reinforced bitumen cap sheet.
• Protection layer: fleece protection mat laid beneath panel frames and ballast blocks to protect the membrane from puncture and abrasion.

3.3 Parapet & Edge Details

Parapet walls are visible on all four sides of the roof, appearing to be approximately 600–900 mm in height. UK best practice (BS 6229, NFRC guidance) requires membrane upstands to extend a minimum of 150 mm above finished roof surface level onto the parapet face, with terminations protected by a counter flashing. Parapet copings appear to be metal or pre-cast concrete with joints that require physical inspection — coping joint failure is the leading cause of water ingress in UK flat-roof residential buildings.

4. Roof Plan & Features

4.1 Key Roof Features Identified

5. Solar PV Array Analysis

5.1 Array Configuration

The solar installation forms a single array distributed across the roof in three zones: a wide two-row strip running near the full width of the roof, a box-like cluster of rows centred above the strip, and two small two-panel groups positioned above the far left and right ends of the strip. Based on close analysis of the drone imagery, the following characteristics are observed:

• Panel technology: Bifacial half-cut monocrystalline silicon modules, consistent with the cell pattern and orange-brown tint visible under direct sunlight — increasingly common in UK installations from 2022 onwards due to improved yield in diffuse light conditions.
• Mounting system: East-west back-to-back configuration. Each mounting unit consists of a pair of panels sharing a central ballast foot, with one panel tilted to face east and the paired panel tilted to face west, forming a ridge or inverted-V profile. This is clearly visible in the drone imagery as alternating lighter and darker rows across the array. Tilt angle is typically 10–15 degrees.
• Orientation: East-west mounting produces a broader, flatter daily generation curve — east-facing panels generate during morning hours, west-facing panels during afternoon hours — well-suited to residential apartment blocks with sustained all-day electricity demand.
• Panel density: No inter-row shading gap is required between pairs as each panel faces away from its neighbour, allowing significantly higher panel density per m² and lower wind loading compared to south-facing tilted arrays.
• Estimated capacity: Approximately 50 panels at 400–450 Wp per module gives an estimated system capacity of 20–22.5 kWp.

5.2 UK Best Practice for East-West Flat Roof Solar Installations

East-west back-to-back mounting is an established and increasingly prevalent system type for UK flat-roof solar installations. The following standards and guidance documents apply:

• MCS 012 — Primary UK standard for solar PV installation. East-west systems must include specific shading and yield assessments. Required for Smart Export Guarantee (SEG) eligibility.
• BS 7671:2018 + Amendment 2 (2022) — IET Wiring Regulations. All DC wiring, inverter connections and AC connections must comply, including DC arc fault protection (AFDD) requirements introduced in Amendment 2.
• BS EN 1991-1-4 — East-west systems have lower wind uplift than south-facing arrays but ballast must still be formally designed for site wind exposure. Minimum 500 mm edge setback from parapet required.
• Building Regulations Part L & Part P — Systems above 3.68 kW per phase require G99 application to the Distribution Network Operator (DNO).
• System yield assessment — East-west mounting typically produces 10–20% less annual yield per panel than an optimally south-facing system but higher panel density often results in greater total output from the same roof area. PVsyst modelling with east-west bifacial configuration is recommended.
• Fire safety — NFPA 1 and NHBC guidance require DC cabling to be kept away from roof penetrations and escape routes, with appropriate DC isolators installed.

5.3 Observed Compliance Indicators

• East-west configuration confirmed from drone imagery: characteristic alternating tonal rows of panels reflect the differing sky angles of east and west-facing panels under low winter sun.
• Panel setback from parapet edges appears generally adequate; precise measurement requires physical survey.
• Mounting pairs appear consistently oriented with no visibly displaced or mis-angled frames.
• DC cabling visible on roof surface; UV-stable conduit or cable tray containment cannot be fully verified from aerial imagery.
• No visibly cracked, displaced, or delaminated panels identified; micro-cracks, hotspots and cell degradation require infrared thermal drone survey to assess.

6. Condition Assessment — Roof Membrane & Envelope

6.1 Roof Membrane

The exposed membrane surface appears light grey and generally uniform in colouration, consistent with a TPO or bitumen cap sheet in serviceable condition. There is no obvious evidence of large-scale blistering, splitting, or ponding at the time of survey. However:

• Lap joint integrity cannot be confirmed from aerial imagery — single-ply membrane lap joints are the most common failure point and require physical inspection including probe testing.
• Solar panel frames create shadow zones beneath which membrane deterioration, moss growth and debris accumulation can occur undetected.
• Minor debris (leaves, bird deposits) is likely given the proximity of mature trees in adjacent garden areas — organic debris retains moisture and accelerates membrane degradation.

6.2 Drainage

Four drainage outlets are visible at the approximate corner positions of the roof. The membrane appears to fall toward these outlets, consistent with BS 6229 minimum fall requirements of 1:80. However:

• Outlet grilles and debris guards cannot be confirmed as installed or clear from imagery.
• Partial blockage during heavy rainfall could lead to temporary ponding with risk of water ingress at membrane laps and perimeter upstands.
• UK climate change projections (UKCP18) indicate increasing intensity of short-duration rainfall events; drainage adequacy should be assessed against current hydraulic design standards (BS EN 12056-3).

6.3 Parapet & Coping

Parapet walls and coping stones are visible on all elevations. Coping condition appears satisfactory at the resolution and angle of survey; however, joint sealant condition, DPC presence, and drip overhang detail cannot be verified. Physical inspection of all coping joints is strongly recommended — parapet coping failure is statistically the most common cause of water ingress in UK flat-roof residential buildings.

6.4 Rooflights

Two rooflights are visible in the imagery, appearing to be kerb-mounted or upstand-type units consistent with modern construction. The minimum recommended upstand height is 150 mm above finished roof surface level, with the waterproofing membrane dressed up and over the upstand and covered by a counter flashing. Compliance cannot be confirmed from drone survey.

7. Solar PV Array — Condition & Issues

7.1 Panel Condition

Based on visual inspection of the drone imagery, the solar panels appear to be in generally acceptable condition. The east-west back-to-back configuration is clearly identifiable throughout all zones of the array. Specific observations:

• Box section (central upper zone): Multiple rows of back-to-back pairs with characteristic tonal alternation between east and west-facing panels, confirming consistent mounting orientation throughout.
• Wide strip (lower zone): Full-width two-row strip of east-west pairs. Appears continuous and evenly installed. No missing or displaced panels observed.
• Two-panel groups (left and right ends of strip): Small paired units at each end, consistent with the main array mounting system.
• Soiling: Some differential soiling (dust, bird droppings, moss) visible. In east-west systems, west-facing panels tend to accumulate more soiling as they face the prevailing weather direction. Soiling losses of 2–5% annually are typical without regular cleaning.

7.2 Mounting System

The east-west ballasted mounting system appears intact with no visibly displaced frames, separated pairs, or collapsed mounts. However:

• Protection matting: Cannot be confirmed from aerial imagery. In east-west systems the shared central foot carries the load of two panels — without protection matting the risk of membrane puncture is elevated and must be verified by physical inspection.
• Pair integrity: Each back-to-back pair shares a central mounting structure. Loosening of the central connection could allow one panel of a pair to move under wind loading. Mechanical fixing torque cannot be confirmed from visual survey.
• Cable management: DC cables typically emerge from the ridge of each pair and run along the base of the array. Loose or unsecured cables present a trip hazard and abrasion risk to both cable and membrane.
• Edge setback from parapet: Appears reasonable but precise measurement is not possible from drone survey.

7.3 Issues Not Assessable from Visual Survey

• Hotspots and cell degradation — requires infrared (IR) drone thermal survey at peak irradiance on a clear day.
• String performance — voltage and current measurements per string require access to the inverter or a portable I-V curve tracer.
• DC arc fault risk — post-Amendment 2 BS 7671 compliance for AFDD cannot be determined from visual survey.
• Inverter condition and data logging — inverter location not visible in drone imagery; output data review is recommended.
• Earthing and bonding — electrical continuity of frame earthing is a critical safety requirement and requires physical testing.

8. Defects & Observations Register

The table below summarises all observations from the drone survey. Severity ratings are indicative only based on visual evidence; physical survey is required to confirm.

9. Recommendations & Maintenance Schedule

9.1 Immediate Actions (within 3 months)

• Arrange a physical access roof survey to assess coping joints, drainage outlets, rooflight upstands, and solar panel mounting details including confirmation of protection matting under all ballast feet.
• Commission an independent electrical inspection of the solar PV system by a NICEIC or NAPIT registered engineer. Verify compliance with BS 7671:2018 + AMD2 including arc fault detection, earthing, and DC isolator provision.
• Confirm the presence of membrane protection matting under all east-west mounting feet. If absent, this must be rectified immediately to prevent membrane puncture.

9.2 Short-Term Actions (3–12 months)

• Commission an infrared (thermal) drone survey of the solar arrays during peak irradiance conditions to identify hotspots, shading losses, and cell-level defects.
• Clean all solar panels using deionised water. Establish a 6–12 month cleaning schedule; pay particular attention to west-facing panels which accumulate more soiling.
• Inspect, clear and where necessary upgrade all roof drainage outlets with appropriate debris guards. Carry out hydraulic check against BS EN 12056-3.
• Review and improve DC cable containment and fixing throughout all array zones to comply with BS 7671 and MCS 012.

9.3 Ongoing Preventative Maintenance Schedule

10. Disclaimer & Limitations

Standards Referenced

• BS 6229:2018 — Flat roofs with continuously supported flexible waterproof coverings
• BS 8217:2005 — Reinforced bitumen membranes for roofing
• BS 7671:2018 + Amendment 2 (2022) — IET Wiring Regulations
• BS EN 1991-1-4 — Eurocode 1: Actions on structures — Wind actions
• BS EN 12056-3 — Gravity drainage systems inside buildings — Roof drainage
• NHBC Standards Chapter 7.1 — Flat and low-pitched roofs
• MCS 012 — MCS Installation Standard for Solar PV Systems
• BRE Digest 312 — Flat roof design — The technical options
• NFRC Technical Guidance — Single-ply roofing
• Approved Document L (2021) — Conservation of Fuel and Power
• Approved Document P — Electrical Safety in Dwellings
• CAA Air Navigation Order — UAV operational requirements
• UKCP18 — UK Climate Projections 2018

END OF REPORT
Visual drone inspection only — see Section 10 disclaimer