Building components · Substructure & Ground
Light Well
Explains the well as an open void within retained ground whose defining problem is that it collects water and has to be drained.
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 light well is
A light well is a void formed outside a below-ground wall and open to the sky, so that a window or door in that wall faces open air rather than earth. It is bounded by retaining structure on the ground side and by the building on the other.
Being open to the sky is what makes it useful and what makes it a problem. Rain falls into it, water moving through the surrounding ground arrives at its walls, and its lowest point sits below the level of the ground around it with a habitable space immediately behind. A light well that does not drain is a tank against the side of a building.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not a basement. The basement is the enclosed space; the light well is the open void outside it that lets that space have a window at all.
- It is not a drained cavity. A drained cavity is a concealed void within a waterproofing build-up, collecting water that has passed the structure; a light well is open, is walked in, and sits outside the building envelope entirely.
- It is not a drainage sump. A sump is the low collection point from which water is removed; a well commonly contains one, but the well is the open space and the sump is a point within 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.
- basement area
- sunken area
- area well
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- Its drainage, since everything that falls into it or arrives at its walls has to be removed from a point below the surrounding ground level.
- The waterproofing of the wall behind it, which is continuous with the rest of the below-ground envelope and is interrupted by the very opening the well exists to serve.
- Its retaining structure, which is holding ground back over the height of the well.
- Being reachable, because a well that cannot be entered cannot be cleared, and a blocked outlet in a well fills it.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
The opening a well serves is a hole in the below-ground envelope at a level where water is present, which makes the junction around it among the most demanding on a basement.
Water can only leave a light well by being taken away from a level below the ground around it, which commonly means it cannot simply run to a drain by gravity.
Leaves and grit collect in a well and arrive at its outlet, and a well that is awkward to get into is one where that is discovered by flooding.
A well is wet, shaded and poorly ventilated, which shortens the life of finishes, fixings and anything organic left in it.
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.
Materials
Commonly incorporates
Materials this element commonly contains as a distinct constituent part, rather than being made of.
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.
Clarifications
Commonly misunderstood
- That a light well is a landscape feature. It is part of the below-ground envelope and part of the water management of the building.
- That a grating over a well makes it self-maintaining. A grating keeps larger debris out and hides whatever has collected beneath it.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- How does water leave this light well, and does that route depend on a pump?
- What happens if the well's outlet blocks, and how deep can water become before it reaches the opening behind it?
- How is the waterproofing of the wall carried around the opening the well serves?
- How is the well entered and cleared?
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
- This entry describes a position. It states no size, depth, drainage arrangement, pump provision or escape requirement, and none can be inferred from it.
- Basement design, waterproofing, and any means-of-escape function an opening into a light well may carry are regulated matters requiring qualified design.
Substructure & Ground Elements
The prepared surfaces, layers and buried members between undisturbed ground and the first structure above it.
Browse all substructure & ground entries →