Building components · Roof Carcass & Edges
Tilting Fillet
Explains a small member that solves two different geometric problems, and why omitting it is visible later.
Educational reference entry. What this element has to do, and whether any particular arrangement of it is adequate, depends on the whole assembly, the loading, the exposure, local requirements, the manufacturer's instructions and qualified professional design.
Overview
What a tilting fillet is
A tilting fillet is a tapered member used where a covering meets a change in geometry. At the eaves of a tiled roof it lifts the tail of the first course so it sits at the same angle as the courses above, which are lifted by the tiles beneath them.
Under a sheet membrane, a similar member eases the sharp internal angle where a horizontal surface meets an upstand, so the membrane turns through a shallower angle instead of a right one.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a batten. A batten is parallel-sided and carries covering; a fillet is tapered and changes an angle.
- It is not a counter-batten. A counter-batten creates a drainage path; a fillet resolves geometry.
- It is not an upstand. The fillet sits at the base of an upstand to ease the angle into it.
Terminology
Common names and aliases
These names describe the same element. The library keeps one entry per component so that a trade term or a regional name never becomes a second, thinner page.
- tilt fillet
- sprocket
- arris fillet
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- The geometry it is correcting, which differs between the eaves case and the membrane-angle case.
- Being continuous along the edge, since a gap in a fillet is a discontinuity in the line it creates.
- What is laid over it and what that material can tolerate in the way of angle change.
- Its own fixing, given it sits beneath layers that will not be lifted again.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
At an eaves, a first course that sits flat rather than tilted does not shed water the way the courses above it do.
Under a membrane, a sharp internal angle is where the sheet is most stressed and where failures concentrate; the fillet reduces that.
It is installed before the covering and is invisible afterwards, so its omission is discovered only through its consequences.
Materials
Commonly formed from
Material families this element is commonly realised in. This states common practice only — it is not a statement that any of these materials suits this component in a particular building, which depends on the whole assembly and on qualified review.
Assemblies
Building systems this element is met in
The role this component fills inside each assembly. A role describes what the element does there — it is not a statement that this component suits that system in any particular building.
Junctions
Interfaces this element takes part in
Junctions where the condition between this element and another governs how the construction behaves. These name the junction and the subjects it raises; they are not details, arrangements or approved ways of building.
Tilting Fillet at Upstand Base
Where a horizontal waterproofing plane turns up a vertical one, and where a sharp angle is deliberately softened.
Raises: Moisture · Movement · Buildability · Weathering
Where it is met
Application contexts
Building contexts where this element is commonly encountered. Association is not recommendation: appearing here does not mean the component suits every instance of that context, or any particular one.
- Flat Roof
- Pitched Roof
Clarifications
Commonly misunderstood
- That the fillet is a refinement in appearance. It changes how the covering sits and, under a membrane, how the sheet is stressed.
- That the two uses are the same element. They share a shape and solve unrelated problems.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- What geometric problem is the fillet addressing in this position?
- Is it continuous along the edge?
- What does the covering or membrane above require at this change of angle?
- How is the fillet fixed, given it is permanently concealed?
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this element involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this element comes up.
What this entry does not do
- No size, angle or fixing is stated here.
- Membrane and covering manufacturers state their own requirements at changes of angle, and those govern.
Roof Carcass & Edges
The battens, boards and edge elements that finish a roof structure and prepare it to receive a covering.
Browse all roof carcass & edges entries →