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Light Wells and Clerestories

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Light Wells & Clerestories

A light well is a vertical shaft from the surface to the interior, with a glazed or open top and white-painted or mirrored walls to bounce light deeper, while a clerestory is a raised section of roof with vertical windows that lights a deep room and keeps earth cover on the main roof. Both must shed rain and meet the waterproofing of the roof.

Part of Underground & Earth-Sheltered Buildings

Light wells and clerestories bring daylight in from above where a side window cannot reach.

Light From Above Reaches Where The Front Wall Cannot

A south-facing glazed wall lights the front of the room. Deeper in, the room is dark. A light well or clerestory fills the gap. Each is an opening in the earth roof, and every opening in an earth roof is a place where water can get in, so each needs its own upstand, drainage and membrane lap.

What You Need

  • For a light well: a shaft lining of stone, earthbag, timber or brick; a glazed or open top; light-coloured or reflective lining, such as white paint or salvaged mirrors.
  • For a clerestory: a raised wall on the roof structure with glazing set in vertical frames; see Flat Glass or Window Design for glazing before glass.
  • Waterproofing details to turn the roof membrane up the shaft or the clerestory wall.
  • Drainage for the base of an open well.

Method: Cut, Line, Seal, Glaze

Step 1: Locate the opening where daylight is needed and the roof structure allows; a hole in a roof beam line needs a trimming beam to carry the cut ends.

Step 2: Build the shaft or upstand with its top above the surrounding soil so earth and water do not spill in.

Step 3: Run the membrane up the outside of the shaft and over its top edge.

Step 4: Line the inside with a light, reflective surface.

Step 5: Glaze or cover the top with a cap that sheds rain but admits light; if left open, drain the bottom.

Common Mistakes

  • Membrane stopped at the roof surface. Water runs down the shaft wall.
  • Open well with no drain. It fills with rain.
  • Dark lining. It absorbs the light you want.
  • An opening cut in a loaded beam line. It weakens the roof; see Roof Structures for Earth Loading.

Safety

Open shafts are fall hazards

An open light well is a hole in the ground. Fence or cover it so people, children and animals cannot fall in, and never walk on a glazed cap.

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