Asbestos Valley Trough
V-shaped asbestos cement troughs installed in roof valleys to channel rainwater between roof slopes.
Description
Asbestos valley troughs are V-shaped or U-shaped channels manufactured from asbestos cement, designed to be installed in the valleys of pitched roofs where two sloping planes meet. Their function is to channel rainwater from the converging roof surfaces down to the gutter system. They were produced from the 1930s through to the late 1990s and installed on residential, commercial, and institutional buildings alongside various types of roof covering.
The asbestos content in valley troughs is typically 10 to 15 per cent, using chrysotile asbestos fibres bound in Portland cement. The profile was either formed by pressing or by bending a flat sheet to the required angle. Valley troughs were preferred over lead or zinc valley liners in many mid-century construction projects because they were cheaper, lighter, and easier to install.
Asbestos valley troughs are one of the more frequently overlooked asbestos-containing materials on buildings because they are concealed beneath overlapping roof tiles or slates. They are only visible from inside the roof space (where the underside may be exposed) or when roof coverings are stripped during re-roofing. This hidden nature means they are often discovered unexpectedly during roof renovation projects.
When intact, asbestos valley troughs are non-friable and present a low risk. They are protected from direct weathering by the overlapping roof coverings and often remain in remarkably good condition even after decades. The risk arises primarily during re-roofing work, when the valley troughs are exposed and must be removed to allow new valley liners to be installed. Breaking, cutting, or carelessly handling the troughs during removal releases asbestos fibres.
Roofing contractors and building owners should be aware that valley troughs on pre-2000 buildings may contain asbestos. Before commencing any re-roofing project, valley liners should be inspected and, if suspect, sampled and tested. If asbestos is confirmed, the troughs must be carefully removed whole or in large sections, without breaking, and disposed of as asbestos waste. Replacement valley liners are available in lead, GRP (fibreglass), or modern fibre-cement.
Countries where commonly found
Commercial brands
How to identify
Asbestos valley troughs are grey, V-shaped or U-shaped channels visible either from inside the roof space or when roof tiles are stripped. They are typically 300 to 450 mm wide and 4 to 6 mm thick, with a smooth or slightly rough surface. They are rigid, heavy, and brittle — snapping rather than bending when forced. The material looks and feels like asbestos cement. They may be partially hidden by mortar bedding or roof tile overlaps.
Health risk & friability
This material has a risk level of 2 out of 5.
It is classified as non-friable, meaning the asbestos fibers are tightly bound within the material matrix. When in good condition and left undisturbed, the risk of fiber release is low. However, cutting, drilling, sanding or breaking the material can release dangerous fibers.
What to do if you find this material
Do not break, cut, or prise out valley troughs without first testing for asbestos. If they are concealed beneath intact roof coverings and not being disturbed, they present no immediate risk. When re-roofing, have valley troughs assessed and tested before stripping begins. A contractor experienced in asbestos cement removal should lift the troughs out whole, using wet methods to suppress dust, and package them for disposal at a licensed waste facility.
Frequently asked questions
How do I know if my roof has asbestos valley troughs?
Can roofers remove asbestos valley troughs themselves?
What should I replace asbestos valley troughs with?
Related materials
Other asbestos-containing materials you might encounter.
Asbestos Ridge Tile
Moulded asbestos cement ridge capping tiles used to seal the apex of pitched roofs.
Asbestos Roofing Slate
Artificial roofing slates made from asbestos cement, designed as a cheaper alternative to natural stone slate.
Asbestos Cement Corrugated Sheet
Corrugated roofing and cladding sheets made with chrysotile asbestos fibres bound in Portland cement.
Asbestos Roofing Felt
Bituminous roofing felt reinforced with an asbestos fibre mat, used on flat and low-pitch roofs.
Need professional help?
Browse verified asbestos professionals near you. Testing, surveys, removal — direct contact, no middleman.
Browse the directory