What is a rooflight schedule?

A schedule turns a scatter of rooflights across a roof plan into a numbered list that nobody can misread. Each unit gets a reference, usually something like RL-01 or SL-12, and that reference appears on the roof plan next to the opening it belongs to. Read the plan and the schedule together and there is no ambiguity about which piece of glass goes where.

The columns vary between practices, but a schedule worth the name will give you most of the following for every unit:

• Reference. The unique tag that ties the row to a position on the roof plan.
• Structural opening size. The hole in the roof, width by length, not the glass size. This is the figure the roofer and the frame supplier both work to.
• Rooflight type. Fixed or opening, flat glass or a domed unit, a walk-on panel, a continuous ridge run, or a lantern. On a commercial roof it will also say whether the unit sits on a builder’s kerb or a proprietary upstand.
• Glazing specification. The full build-up: number of panes, the U-value, the G-value and the light transmittance, plus any safety and acoustic requirements.
• Opening and control. Manual, electric or actuator-driven, and whether the unit forms part of a smoke ventilation system, which changes the whole specification.
• Finish and framing. Frame material and colour, kerb height and any weathering detail.
• Quantity and location. How many of that exact unit, and which roof, bay or grid line they land on.

Get those columns filled in properly and the schedule answers almost every question a supplier or an inspector can ask without anyone reaching for a phone.

On a small domestic loft conversion the rooflights might be scribbled onto the section drawing and that is the end of it. On anything commercial, warehouse, school, retail unit, office refurbishment, the rooflights are pulled out into their own document precisely because there are too many to annotate cleanly on a plan.

The schedule usually lives alongside the window and door schedules as part of the architect’s or specifier’s tender information. It cross-references the roof plan, the sections that show the upstand and kerb details, and the specification clauses that spell out performance standards. A contractor pricing the job reads the schedule first, because it is the fastest way to count the units and total the glazed area. A supplier quotes from it. The site team orders from it. Building control reads it to confirm the units meet Part L for thermal performance and Part K for safety glazing.

Because so many trades draw from the same table, an error in one row propagates. A wrong opening size ordered from the schedule turns into a frame that does not fit the hole the roofer has already formed. That is why the schedule is checked and reissued with revision letters rather than quietly edited, so everyone can see they are working to the current version.

Most people scanning a rooflight schedule count the units and check the sizes. The column that actually governs how the finished building feels is the glazing specification, and on a commercial roof it is easy to get wrong at scale.

Commercial roofs are mostly flat or low pitched, which means the glazing faces the sky rather than any compass direction. Horizontal glass sees the high summer sun almost square on, so it collects solar heat all day regardless of which way the building is turned. Put a run of clear double-glazed rooflights at a G-value near 0.6 over an open-plan office or a south-facing retail space and you have specified a solar collector across the whole roof. The heat load lands on the cooling system, the running cost climbs every summer, and the people underneath ask why the air conditioning cannot keep up.

The fix is written into the schedule, not bolted on afterwards. Specify solar-control glazing with a G-value around 0.3, and the same openings deliver roughly half the summer heat while still flooding the floor with daylight. Here in Southend the point is sharper still, because the city faces south across the Thames Estuary with an open horizon and reflected light off the water, so a south-facing commercial roof gathers more sun than the same building would inland. That physics, orientation first, then glass specification, is exactly what our commercial skylight installation work is built around, and it starts with the numbers in this one column. Our energy-efficient glazing page sets out the G-value argument in full.

The schedule is normally drawn up by the architect or a specialist rooflight specifier during the design stage, then handed out with the tender pack so contractors price like for like. It is a living document. As the design firms up, the fabric build-up changes, or building control comes back with a comment, the schedule is revised and reissued rather than replaced.

On a design-and-build contract the responsibility can shift to the contractor or the rooflight supplier, who completes or refines the schedule against a performance specification the client has set. Either way, the schedule should be signed off before any rooflights are ordered, because the openings the roofer forms are cut to the sizes it carries. Change a unit after the kerbs are built and you are altering the roof, not just the glass.

If you are pricing or specifying a commercial roof, treat the schedule as the place to get the performance right, not just the sizes. Fill in the G-value, U-value and light transmittance for every unit, and go lower on the G-value for any large expanse of glass over a room that runs hot.

If you have a schedule already drawn up and want a second read on the glazing before it goes out to tender, or you would like us to complete the specification against your roof plan, send it over. Ring 01702 898232 or request a quote, and we will look at how the whole roof will perform rather than just the openings in it. You can also see the wider range of units we fit on our services page.