Building components · Frame Members
Valley Rafter
Explains why a valley rafter carries both a structural and a water-management significance that a hip does not.
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 valley rafter is
A valley rafter runs diagonally where two roof slopes meet inward, forming the internal corner. Like a hip it collects shortened rafters from both sides, and like a hip it spans a longer diagonal than a common rafter.
Unlike a hip, it lies beneath a line where water from both slopes converges. Everything that falls on two roof planes arrives at the valley, which makes the covering arrangement above it as significant as the member itself.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a hip rafter. The geometry is inverted, and the consequence is that a valley collects water while a hip sheds it.
- It is not a gutter. The valley rafter is structure; what carries the concentrated water above it is part of the roof covering arrangement.
- It is not an ordinary rafter, for the same reasons a hip is not: more load, longer span.
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.
- valley
- valley rafters
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- Support at its foot, where load from two slopes arrives at an internal corner.
- Whether it is supported along its length, given the diagonal span.
- What sits above it to deal with concentrated water, since a valley is where roof leaks most commonly appear.
- How the jack rafters from each slope frame into it.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
Water from two roof planes converges here, so the covering arrangement above a valley is under more demand than anywhere else on the roof.
The member carries load from two slopes to an internal corner of the structure beneath.
Valleys collect debris as well as water, and a blocked valley redirects water into the construction rather than off it.
A structural member beneath a line where leaks concentrate is at elevated risk if the covering above ever fails.
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.
Jack Rafter to Valley
Where shortened rafters frame into a valley, beneath the line at which two roof slopes concentrate their water.
Raises: Structural transfer · Moisture · Weathering · Buildability
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.
- Pitched Roof
Related elements
Neighbouring components
Typed relationships to other elements. There is deliberately no generic “related” category: an edge that cannot be classified does not exist.
A narrower form of
Clarifications
Commonly misunderstood
- That a valley is structurally the same as a hip inverted. The load path is comparable; the water regime is not, and the water is what causes most valley problems.
- That valley problems are covering problems only. Prolonged water reaching the structure affects the member beneath.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- What supports the valley rafter, and can the internal corner beneath accept the load?
- How is the concentrated water from both slopes handled above this member?
- Is the valley accessible for clearing debris?
- What is the condition of the structure beneath, given that valleys are where leaks concentrate?
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 section, span, angle or covering arrangement is stated here.
- Roof structure and roof covering at valleys are both design matters; this entry describes the element, not how to build or repair one.
Structural Frame Members
The columns, beams, joists, rafters, plates and bracing that make up a load-carrying frame, identified by the position each occupies.
Browse all frame members entries →