SPECIFICATION
What a rooflight specification has to pin down
Six decisions. Leave any of them open and the contractor makes it for you on site, usually on price.
| Decision | Why it cannot be left open |
|---|---|
| Product line | Frame and glazing build-up differ between lines, and so do the declared values |
| Nominal size | The opening the unit suits, short side first. Not the outside dimension of the unit |
| Glazing | Clear or Opal, and the shell build-up. Drives Ut, LT and g together |
| Upstand type and height | PVC, steel or thermally broken, and the height your build-up needs. Available heights differ by type |
| Frames | SR is a weathering frame. Fall-through protection is a separate range — RSM LK, HDS LK, EAD LK and others, depending on the application. These are not interchangeable |
| Ventilation | Fixed or opening, and the actuator if opening |
Every one of these maps to a Kingspan article number, which is what the factory and the contractor both work from.
WRITING IT
A clause that leaves nothing to interpretation
Specifications that reach us in this shape get priced same-day and built without a single clarification request:
Rooflight: Kingspan Light + Air [product line], nominal size [short/long, cm], [Clear / Opal] glazing, [shell build-up]. Upstand: [AK PVC / AK ST / AK ST-TG], [height] cm. Frames: [SR weathering frame / RSM LK or HDS LK fall-through protection / NSHEV], as applicable. Ventilation: [fixed / opening, actuator type]. Article numbers: [as scheduled].
Two habits are worth more than any other on a rooflight schedule. Specify by article number wherever you can — it removes ambiguity entirely, and the article number is the handle on every product page here, so it is quick to look up. And state the roof build-up alongside the upstand height, because the height only makes sense in relation to the finished surface. A schedule giving the upstand height without the build-up is one that gets queried.
DECLARED VALUES
Reading the performance data
Published figures come from Kingspan Light + Air. Four distinctions matter when you transcribe them into a schedule.
| Symbol | What it is | Watch for |
|---|---|---|
| Ut | Thermal transmittance of the transparent element | Not the whole opening |
| URC | Thermal transmittance of the whole rooflight construction, including upstand | This is the figure an opening-level calculation needs |
| LT | Light transmission | Falls with Opal glazing and with shell count |
| g | Total energy transmission, including heat | Moves against LT — the trade-off is the design decision |
| Rw,p | Weighted sound reduction | Often declared as a minimum, and the qualifier is part of the value |
Ut and URC sometimes coincide on a given build-up. That coincidence is exactly why the labels have to be carried through correctly.
Declared values sit under Specifications on every product page, with the manufacturer's datasheets under Downloads. Where a figure on this site differs from current Kingspan documentation, the documentation governs — and if a value your calculation needs is not published, ask rather than interpolate. We will get it confirmed by the manufacturer instead of estimating.
[TBC-A42]
COMPLIANCE
Standards and regulatory context
[TBC-A43]
[TBC-A44]
Where your project is pursuing a sustainability assessment, the rooflight contributes through the daylight and thermal routes rather than as a product credit in its own right. [TBC-A45]
RESOURCES
What you can take away
Product datasheets
PER PRODUCT
Declared values, dimensional data and construction detail, as published by the manufacturer.
- Under Downloads on every product page
- No account needed
- Always the current revision
Use it when you are transcribing figures into a schedule.
Installation documentation
PER PRODUCT
The manufacturer's instructions, which also tell you what the detail around the opening has to do.
- Under Installation on every product page
- Useful at design stage, not just on site
Use it when you are drawing the junction between the unit and the roof build-up.
BIM and CAD
[TBC-F28]
[TBC-F29]
- Ask and we will tell you what exists for the line you are specifying
Use it when you are modelling the opening rather than scheduling it.
Specification support
BY ENQUIRY
Send a drawing, a schedule or a set of performance requirements and we will come back with what meets them, and what the alternatives cost.
- Works from a specification, not just a product code
- Alternatives priced alongside, so value engineering happens now rather than on site
Use it when the performance requirement is fixed but the product is not.
Send a specificationEARLY STAGE
Worth asking before the drawings are fixed
Three things are cheap to change at design stage and expensive afterwards.
Opening sizes. Standard nominal sizes are stocked and priced accordingly; anything outside them is made to order, with a different lead time and a different cost. If a 5 cm adjustment to a proposed opening brings it onto a standard size, that is usually worth knowing before the drawing is issued.
Upstand height against the build-up. The specification sets the build-up; the build-up sets the upstand height; the upstand type limits which heights exist. PVC comes in 15, 30 and 50 cm, steel in 30, 40 and 50, and the thermally broken version in 50 only. A detail drawn to a height that does not exist gets resolved on site, badly.
Whether the opening ventilates. Adding opening gear later means a different unit, not an accessory.
QUESTIONS
Common questions
Can you review a specification before it is issued?
Yes, and it is the most useful thing we do. Send the draft schedule and the roof build-up. We will flag anything that cannot be supplied as written, anything that is going to be queried by a contractor, and anywhere a standard size would do the same job for less.
A performance figure I need is not published. What now?
Ask. We will get it confirmed by Kingspan rather than estimating it. Where a value genuinely does not exist for a particular build-up, we will tell you that too — which is more useful than a figure with no source behind it.
Can you supply outside the standard sizes?
Yes. Made-to-size is routine rather than exceptional — it is quoted rather than ordered online, and the lead time differs. Send the opening dimensions and we will price it.
Do you work directly with the contractor once the project is on site?
We supply whoever is placing the order. Where a specification has been developed with us at design stage, we hold that detail against the project, so a contractor ordering later gets the specified product rather than an approximation of it. Tell us the project name when you enquire and it stays attached.
Do you supply the roof detail, or just the product?
The product and the manufacturer's documentation for it. The junction between the rooflight, the upstand and the roof build-up is a design decision for the project, and the roofing specification governs it. We will tell you what the unit requires; we will not design the detail.
Send us the drawing.
A draft schedule, a section through the roof, or just the performance requirement. You will get back what meets it, what it costs, and where a standard size would do the same job.
Technical data published on this site is as declared by Kingspan Light + Air. Where it differs from current manufacturer documentation, that documentation governs. Guidance here does not constitute design advice for any particular project.