Guide: How to Specify Rooflights for High-Spec Projects

Rooflights can transform a project, but in high-spec work they need to do more than bring in daylight. The right specification balances aesthetics, thermal performance, safety, weathering, and installability so the product performs as well as it looks.

What to specify

Start with the project intent:

Next Gen Rooflights deliver a made-to-order, multi-purpose solution to architectural developments. It’s a perfect fit for:

• Potential daylighting strategies.
• Accessing outdoor space.
• Fitting a solely architectural role.
• Acting as part of the ventilation, access or maintenance strategy.

When establishing why a rooflight is vital to the project, make it clear that a Next Gen Rooflights system offers thermal performance, solar control, safety glazing, non-fragility, load resistance, waterproofing, and key industry certification awarded after rigorous testing. 

Core technical checks

Over the years, we’ve gained a thorough understanding of our architectural partners’ design processes and the considerations they need to make when choosing technical products. When choosing a rooflight, know that ours offer:

• Inner pane safety. Laminated glass in the inner pane is our default for overhead glazing. It’s vital for occupant safety, as it helps retain fragments in the event of breakage.
• Non-fragility. Our rooflights are CWCT Class 2 certified, the highest classification for rooflights. After extensive product testing, our rooflights maintain excellent damage resistance, withstanding loads equivalent to an adult, tools, and equipment.
• Thermal performance. Key to any development, we can promise our rooflight solutions deliver in maintaining and regulating the building’s temperature. We prioritise solar-controlled glass, which boasts a U-value of 1.0-1.2 W/m²K, offering greater insulation than the UK standard. Warm edge spacers are used to minimise further external heat transfer, which is conducted to an insulated upstand/kerb system.
• Rooftop terrace access. Rooflights can do more than just let light in. If your development includes plans for an external terrace area, our rooflights can serve as an access point.
• Solar control. With temperatures rising, solar control is becoming an increasingly valuable feature in building specs. If overheating is a major risk for people and equipment in the building, our solar-control-glazed panels reflect and absorb infrared heat without compromising access to natural daylight. If required, this can be downgraded to Low-E.
• Dimensions. As made-to-order systems, you will need to define specific measurements of the structural opening or the overall weathered stand size. We will specify the correct thickness of the IGU’s panel. This will all be vital for the pricing quotes and daylighting.

Detailing that matters

When looking at details like roof pitch and water runoff, it’s vital to include explicit outlines in your spec and any drawings. Our rooflights are mostly designed at 3 degrees for flat-glass rooflights to help prevent ponding and ingress. They will be 1 degree for full Class 0 walk-on units. The framing and retention system is just as important as the glass, so the spec should reflect this. Don’t just detail the glass pane; the full system adds extra measurements that must be accounted for. For profiled-sheeted roofs, manufacturers’ installation details should govern fixing pattern, sealants, lap details and thermal movement allowances.

Risk and compliance

For rooflights used above circulation spaces, over water, or where the falling-glass risk is unacceptable, include a safety strategy in the spec and coordinate it with the project risk assessment. If a unit can be walked on, you must treat it as a specialist walk-on product; this means specifying:

• Load ratings,
• Need for any anti-slip treatment,
• It is not a standard rooflight. 

For higher-end projects, also ask for CAD/BIM objects, technical data sheets and installer documentation up front so the design team and contractor are working from the same system definition.

Example spec line

A strong spec note provides succinct yet clear outlines of the exact product needed, so the person in charge of procurement knows what to buy.

It should read along the lines of:

 “Thermally broken aluminium rooflight system with laminated inner pane, 1.0-1.2 W/m²K insulated glazing, warm-edge spacer, manufacturer-approved insulated upstand, minimum 1-degree installation pitch, and CWCT Class 2 glass, to the applicable roof assembly standard, complete with manufacturer-certified installation details”.

Practical procurement advice

From a QS or contractor perspective, the biggest commercial risk is replacing a visually similar product with a weaker-performing one or incorrect dimensional references. Tie the performance schedule to the specific manufacturer’s system. Proper performance, such as non-fragility, minimal weathering, high load resistance, and warranty coverage, can all change if the assembly and installation methods are altered.

Rooflight spec checklist

Use this as a one-page checklist for architects, QSs and contractors when specifying rooflights on high-spec projects.

• Project role defined: daylighting, ventilation, access, or feature element.
• Rooflight type confirmed: fixed, opening, walk-on, conservation, or made-to-order.
• Opening size confirmed: structural opening, kerb size, and visible glass area all stated. Include size of weathered upstand if necessary.
• Roof pitch checked: minimum slope and drainage direction noted to prevent ponding.
• Thermal target set: required U-value and warm-edge spacer specified.
• Solar control considered: overheating risk assessed and solar gain target defined.
• Safety glazing specified: laminated inner pane as standard for overhead use.
• Non-fragility required: performance in accordance with the relevant assembly standard confirmed.
• Load requirements defined: snow, wind, maintenance, and walk-on loading where applicable.
• Frame system specified: thermally broken construction and compatible upstand/kerb included.
• Waterproofing detail issued: upstand height, membrane interface, flashings, and seals detailed.
• Ventilation requirements stated: manual, electric, or smoke-vent function if needed.
• Acoustic performance checked: where relevant, airborne sound target included.
• Requested compliance evidence: product data, test reports, warranties, and installer certification.
• Coordination complete: structural, fire, waterproofing, and MEP interfaces resolved before order.

QS and contractor checks

• Confirm the unit is priced on the same basis as the drawings.
• Check lead time, access requirements, and crane/installation constraints.
• Verify whether the quote includes kerb, flashing, fixings, controls, and certification.
• Reject substitutions that change glass make-up, frame system, or tested performance.

If you need any additional assistance at any stage of the specification process, please get in touch with our team. We’d love to hear about your project and answer any burning questions you may have about our rooflight systems.