Summary

Roof access and fixing systems for solar PV are closely linked. The fixing method must be appropriate for the roof covering type, and the access method must allow safe installation of that fixing without risk to the operative or damage to the roof. Both are governed by practical standards (MCS MIS 3002 for solar; NASC guidance TG20:21 and the Work at Height Regulations 2005 for access).

This article covers the practical aspects of roof access and panel fixing for the main UK roof types: interlocking concrete tile, clay tile, natural slate, and flat roof.

Key Facts

  • Roof hook — the standard fixing for interlocking tile (concrete and clay) roofs; hooks under the tile, bolts to the rafter; aluminium or galvanised steel; adjustable height to suit tile profile
  • Rafter fixing requirement — fixing must go into the rafter, not just the batten; battens are typically 38mm × 19mm or 38mm × 25mm and cannot resist the uplift loads specified in the mounting system design guide
  • Rail system — aluminium mounting rails run across the rafter hooks; panels mount to the rail via mid-clamps and end-clamps; the rail carries loads to the hooks
  • Natural slate fixing — S-hooks (slate hooks) or dedicated slate adapters replace the standard roof hook; slates must be lifted carefully to avoid cracking; broken slates during installation are a common callback issue
  • Plain clay tile — older clay plain tiles can be fragile; take care when lifting to insert hooks; use purpose-made plain tile hooks
  • Interlocking tile profile hooks — different roof hook profiles suit different tile profiles (low, medium, high profile); confirm the hook is rated for the tile profile before ordering
  • Standing seam metal roof — non-penetrating clamps grip the standing seam; no holes drilled; no sealant needed; rail and panel attach above; used on Colorbond, Lindab, Kalzip, and similar systems
  • Ballasted flat roof — aluminium or stainless steel frames with concrete ballast blocks; no roof penetration; panels tilted at optimal angle; ballast calculation per BS EN 1991-1-4 wind uplift requirement
  • Penetrating flat roof fixing — frames fixed through the roof membrane into the structural deck or purlin; require sealant boots around each penetration; only where permitted by the roof membrane manufacturer
  • Work at Height Regulations 2005 — any work above 2m requires a risk assessment and appropriate fall prevention or protection; full scaffold required for work on pitched roofs above two-storey eaves height
  • Roof ladder (cat ladder) — a roof ladder hooked over the ridge, resting on the roof surface; provides limited purchase for single-storey work; operatives should still wear a harness clipped to the ridge or roof anchor
  • Anchor points — roof anchors (BS EN 795 certified) can be installed on the ridge or adjacent structure; allow fall-arrest lanyards to be used; required where full scaffold is not in place

Quick Reference Table: Fixing Types by Roof Covering

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Roof Type Standard Fixing Key Consideration
Interlocking concrete tile Tile hook into rafter Confirm hook profile matches tile type
Interlocking clay tile Tile hook into rafter Older tiles: lift with care to avoid cracking
Natural slate Slate hook (S-hook) or slate adapter Easily cracked; experienced slater preferred
Plain clay tile Plain tile hook Fragile; check condition before lifting
Standing seam metal Non-penetrating seam clamp Confirm clamp is rated for the seam profile
Flat roof (EPDM/felt/GRP) Ballasted aluminium frame Ballast calculation required; structural check
Flat roof (concrete deck) Penetrating frame with sealant boots Membrane warranty may be voided; check

Detailed Guidance

Interlocking Tile Roofs

Roof hooks: Standard aluminium roof hooks have an adjustable stem height to match the tile profile (typically 40–80mm head height). The hook head sits under the tile on the tile batten, while the fixing bracket bolts through the top of the hook into the rafter below.

Finding rafters: Before ordering hooks, confirm the rafter spacing (typically 400mm or 600mm centres). Measure from inside the loft if accessible; alternatively use a rafter finder (magnetic) or probe with a small drill bit in a mortar joint area. Mark rafter positions on the felt with chalk before going on the roof.

Hook installation sequence:

  1. Identify the tile to be lifted — it must be directly above a rafter
  2. Lift the tile using two flat pieces of thin slate or tile lifters; the tile interlocks and requires careful lateral movement to release
  3. Position the hook bracket on the batten; ensure the hook head is flush with or slightly above the batten surface
  4. Drill through the batten and into the rafter (typically 4–5mm pilot, then 6mm or 8mm fixing bolt)
  5. Bolt the hook through the batten into the rafter; torque to specification
  6. Replace the tile; confirm it interlocks fully and there is no visible gap
  7. Apply a bead of appropriate sealant (butyl, or as specified by the mounting system supplier) around the hook stem exit point

Rail installation: Aluminium mounting rails (typically 40mm or 60mm C-section) attach to the hook brackets via appropriate connectors. Rails run horizontally across the roof; span between hooks must not exceed the rail manufacturer's maximum unsupported span (typically 1.2–1.5m for residential panels). Rails must be cut to length to allow drainage between rail ends (typically 10–15mm gaps).

End and mid clamps: Panels are secured to the rails by end clamps (at the outer edge of the first and last panel in a row) and mid clamps (between adjacent panels). Torque clamp bolts to the manufacturer's specification — under-torqued clamps can release in high wind; over-torqued clamps can crack the panel frame.

Natural Slate Fixing

Natural slates are more fragile than concrete tiles and require more care. Old slates (Welsh or Westmorland) can be over 100 years old and may crack under the slightest lateral force.

Slate hooks: S-shaped galvanised or stainless steel slate hooks are inserted under the slate above, passing through the nail hole or a drilled hole in the lower slate, and hooking over the batten. No tiles are lifted — the hook is inserted from the front face.

Alternatively, purpose-made slate adapters clip under the slate and attach to the rafter via a bracket below — the slate is lifted, the adapter positioned, and the slate replaced. This provides a more secure fixing but requires lifting the slate.

Sealant and waterproofing: Where any fixing penetrates the slate, a sealant boot or lead flashing is required to maintain the waterproof envelope. Do not rely on silicone alone on natural slate — use a purpose-made sealant boot.

Replacement slates: Have matching replacement slates available on site. Natural slate varies by age and quarry; carry a selection of sizes to cover breakages. Broken slates during installation are a cost to the installer, not the customer — include a contingency for this.

Standing Seam Metal Roofs

Standing seam metal roofs (common on agricultural buildings, garden rooms, garages, and modern homes) require non-penetrating mounting clamps. These clamp to the raised seam that runs down the roof pitch, without any penetration of the metal panel.

Clamp selection: The clamp must be specified for the exact seam type (single or double lock, height, and width). Common seam types: Kingspan, Kalzip, Orion. Confirm the seam profile before ordering — wrong clamps will not provide the required holding force.

Structural check: On agricultural standing seam roofs, check that the purlins beneath can take the additional dead load of the panel array. Agricultural steel roofs may be designed for a minimal snow load and may not have adequate capacity without engineering assessment.

Flat Roof Ballasted Systems

For flat roofs (EPDM rubber membrane, felt, GRP/fibreglass, or liquid membrane), a ballasted frame avoids any penetration of the waterproof membrane.

Frame design: Ballasted frames are typically aluminium or stainless steel, supporting panels at a tilt angle (typically 10–15° for flat roof UK installations — a compromise between optimal tilt and wind load). Ballast blocks (concrete paving slabs or purpose-cast weights) hold the frames down against wind uplift.

Ballast calculation: The ballast weight must be sufficient to prevent the frame from being lifted or overturned by the design wind speed for the location (BS EN 1991-1-4). Most mounting system suppliers provide a ballast calculation tool taking site postcode and installation geometry as inputs. Always use the manufacturer's calculation and retain it in the design file.

Flat roof structural load: The combined weight of panels (approximately 20kg/m²), mounting frames (~5kg/m²), and ballast (15–30kg/m² depending on calculation) adds 40–55kg/m² to the flat roof structure. Check the roof structure can take this before proceeding. For concrete deck flat roofs, this is generally fine. For cold-roll steel deck roofs on commercial buildings, a structural check with the building's structural engineer may be required.

Access to flat roofs: Flat roof solar installations generally allow operative access on the roof surface during installation. Operatives must still follow Work at Height Regulations: if the roof edge is not protected, perimeter edge protection (Heras fencing or scaffold edge rail) is required for any work within 2m of the roof edge.

Work at Height Requirements

For all roof work:

  • Risk assessment before work commences
  • Fall prevention (scaffold, edge protection) or fall protection (harness, lifeline) in place
  • Equipment checked before use
  • No working alone on a roof

Roof ladder (for single-storey work only): A roof ladder must be:

  • Long enough to project 1m above the roof ridge
  • Equipped with a ridge hook that engages fully over the ridge
  • Positioned to reach the work area without overreach

Operatives using a roof ladder should also wear a fall-arrest harness with a lifeline clipped to a roof anchor (BS EN 795 Type A anchor bolted to the ridge or adjacent structure). Roof ladders alone provide limited fall protection — they are a means of access/footing, not a fall prevention system.

Full scaffold (recommended for two-storey and above): For any domestic install where the eaves height is more than approximately 6m (two full storeys), a properly erected scaffold system with guard rails at working level is the appropriate access solution. The scaffold should be designed and erected by a competent scaffolder (CISRS-carded). The solar installer is responsible for pre-use inspections and ensuring the scaffold is within its safe working period.

Frequently Asked Questions

A tile broke when I lifted it to insert a hook. What should I do?

Replace it immediately. Source a matching tile from the customer's spare stock (ask at the start of the job if they have any; many homeowners do). If no spares exist, source a matching replacement — most manufacturers produce matching tiles for decades. Do not leave a cracked tile in situ hoping it won't cause a leak; leaks cause significant damage and installer liability.

Do I need to apply sealant around every hook?

It depends on the hook type and the mounting system specification. Many modern roof hooks are designed so that the tile re-seats fully around the hook stem, maintaining the water-shedding path without sealant. However, where a gap could allow water to sit against the hook (particularly on profile hooks where the tile cannot close flush), butyl mastic sealant or a purpose-made boot seal should be used. Follow the mounting system installation guide.

How many hooks do I need per panel?

The number of hooks per row (and per panel) is specified by the mounting system's structural design guide. Typically: a 1.7m × 1.1m panel is supported by 4 hooks (2 rails × 2 hooks per panel, i.e., 4 rafters engaged per panel). For high wind exposure zones (coastal, highland), the fixing frequency increases. Always use the manufacturer's structural calculator for the specific location.

Regulations & Standards