Key specification considerations for box rooflight performance

Glass rooflights provide a fantastic solution for both creating light and space within a building envelope, and converting used space into an extended living area. Due to box rooflights providing access as well as sliding mechanisms, there are a range of factors to consider when specifying for this type of product.

1. Specifying the correct location

Consider the options available when accommodating for these type of details. Some builds require a free standing box in the middle of the terrace, whilst others would best suit a unit that can be positioned in the corner of a terrace, fixed to an adjacent building, or to a parapet wall.

2. Approved Document K and headroom for stairs

Approved Document K states that a minimum 2 mts of clear headroom must be provided measured from the pitch line of the stairs; this measurement will be critical for determining the actual height of your rooflight. It is important that the relationship between the position of the stair and the maximum rooflight height is considered, particularly where planning restrictions are in place for any proposed structures built on the roof.

3. Specify suitable safety measures for access rooflights

Be sure that suitable safety measures are included in the design of the access rooflight. Current override systems will cut power to the rooflight if it senses an increased load on the motors, or you can opt for proximity detectors, which fire an infra-red beam along the closing edge. If the beam is interrupted, then the rooflight stops.

For external decking or paving you may want the ability to have a flush threshold to avoid tripping hazards. In order to maintain easy access to the mechanism for maintenance purposes, without jeapordising water tightness, you will need to specify a design that has removable tread plates. In these type of designs mechanism and track are concealed below which provides free drainage back out onto the roof.

4. Specify the correct opening dimensions of the glass rooflight

Ideally the opening should not exceed the stair width; otherwise a void may be created. Make sure the only vertical section that opens is at the top of the stairs so that the remaining sides remain in place to act as a balustrade.

5. Specify an appropriate drive mechanism

Rack and pinion drive systems are generally considered to be the most reliable and hard wearing. Some manufacturers use belt or chain drive systems which can be subject to stretching over prolonged use and are also vulnerable to attack, with reports of belts being cut to disengage the rooflight and gain access to a building.

6. Consider box rooflight transit to the roof terrace

Although more site than specification considerations, it’s important to consider how the unit is going to be moved onto the roof. Due to the sheer size it is very common for this type of unit to be craned into position, therefore it is critical to ensure that appropriate lifting points are provided so that the crane can be safely attached.

7. Should you specify electric or manual rooflight?

Building regulations stipulate that the minimum headroom allowable, even in restrictive places, is 1.9m. Manual operation requires the user to ascend the stairs to operate the rooflight. If the headroom is less than 1.9m at the point which the rooflight can be operated, then it will not comply with building regulations. The best rooflight systems will function using motors, so that the user can simply press a button at the bottom of the stair-well to engage the unit. By the time you have reached the top the unit would have fully retracted, thus complying with minimum headroom requirements.

8. Specifying modern access rooflights and rain sensors

With these systems, rain sensor overrides will trip the unit closed when detecting rain. If the home owner is out on the terrace when the box closes, secure external override systems such as keypad entry will enable them to re-activate the rooflight to exit the terrace.

9. Protecting against loss of power

The last thing you need in a power cut is an open rooflight. As well as the case of extreme weather this could also be a huge security risk. Look out for battery pack-up as a useful feature; the best access rooflights will operate via battery that is on constant trickle charge. This guarantees that the unit remains operable even when the lights go out.

10. Security specifications

It is essential that the rooflight cannot be forced open, particularly when the terrace is accessible from adjacent buildings. Use designs that feature additional security such as solenoid bolts. These provide electrical locking of a door by driving a bolt into a strike plate to prevent the door from opening. Other features, such as anti-lifting mechanisms, will reduce the likelihood of drive systems being disengaged and units forced open.

To find out more information about specifying glass rooflights, call our technical department on 01379 353 741, or click here to book a CPD.