Optilight (Skylight – Roof window) 55×78

Optilight 55×78 centre pivot roof window

The Optilight 55×78 is a pine centre pivot roof window for pitched roofs, double glazed to a whole-window U-value of 1.3 W/m²K. It costs £164 including VAT. Add the flashing kit for your roof covering at checkout: £51 for tiles up to 45mm or for slate, £66 for tiles over 45mm. The equivalent Velux GZL 1051 in the same 55×78 size is £235 before its flashing. The window fits any roof pitch from 15 to 90 degrees. Delivery is £10 and takes up to 3 days.

What you get in the box

One 55cm by 78cm centre pivot window with the installation kit: fixing brackets, screws, a plastic levelling wedge and the handle. The flashing kit is chosen separately at checkout (TZ for profiled tiles up to 45mm, TH for tiles over 45mm, TL for slate and flat coverings up to 5mm). With the window and the right flashing, nothing else is needed to fit it into an existing opening.

Glazing and heat loss, in numbers

The window is double glazed with an inert gas filled unit. The glass alone has a U-value of 1.1 W/m²K and the whole window, frame included, 1.3 W/m²K. That is the same whole-window figure as the Velux GZL 1051 and GLU 0051 ranges sold on this site. The inner pane carries a heat reflecting low emission coating, which cuts heat loss in winter and overheating in summer. The outer pane is toughened glass. Sound reduction is 31 dB.

Size and where it fits

55×78 is the smallest size in the Optilight centre pivot range, which runs up to 134×98. It is the same nominal size as the 55×78 Velux, so it is the usual choice for replacing an old window of that size, or for a first window in a small loft room or landing.

How it opens

The sash pivots on hinges at the centre of the frame and turns through 180 degrees, so the outside of the glass can be cleaned from inside the room. The handle is at the bottom of the sash, which keeps it reachable when the window is fitted high. It closes tight and locks in two micro-ventilation positions for background airflow. The VB version (a £15 option) adds an air inlet in the top rail.

Materials and finish

The frame and sash are pine, bonded in layers, impregnated and coated with an acrylic finish. Everything exposed to the weather is covered by weather and UV resistant aluminium profiles, so there is no exterior timber to paint. For kitchens, bathrooms and laundry rooms, the same window is sold with a white PVC interior (Optilight PVC 55×78, £209).

Roof pitch, planning and fitting

The window and its flashings are made for pitches from 15 to 90 degrees. Adding a roof window to an existing roof slope is usually Permitted Development in England, so no planning application is needed, provided it projects no more than 150mm beyond the roof plane and sits no higher than the ridge. Listed buildings and conservation areas are the exception. Building Regulations still apply if rafters are cut: fitting into an existing opening is a job a confident DIYer can do, and a new opening is structural work.

Guarantee

AK Roof Windows gives a 10 year warranty on this window, as on every roof window we sell.

Optilight or Velux?

Both are pine centre pivot windows with the same 1.3 W/m²K whole-window U-value in the same 55×78 size. The Velux GZL 1051 is £235 and the Optilight £164, so the Optilight is about £70 less before flashing on either. Choose Velux if you want the top-operated control bar (Velux GZL and GLU open from a bar at the top, Optilight from a handle at the bottom) or the Velux name. Choose Optilight if the specification is the same and the price matters.

Blinds and accessories

Three blinds fit this window and can be added at checkout: AUB (transparent fabric, £42), ORF blackout (£57) and ARF blackout (£84). Sold separately, the ZST telescopic rod operates the window when it is out of reach, and the ZBB restrictor limits how far it opens for child safety.

Frequently asked questions

Is an Optilight window as good as a Velux?

On the figures that matter for heat loss and glazing, yes: both are double glazed pine centre pivot windows at 1.3 W/m²K. The differences are the handle position (bottom on Optilight, top bar on Velux), the brand, and the price, £164 against £235 in the 55×78 size.

What size opening do I need for a 55×78 roof window?

The window’s outer frame is 55cm wide by 78cm high. Check the rafter spacing before you order: if the rafters are further apart than that, the flashing kit closes the gap; if they are closer, a rafter has to be trimmed, which is structural work.

Which flashing do I need?

TZ for profiled tiles and sheet up to 45mm thick, TH for profiled coverings over 45mm, TL for slate, plain tiles and flat coverings up to 5mm. Choose it at checkout.

Do I need planning permission?

Usually not in England. A roof window on an existing slope is Permitted Development if it projects no more than 150mm above the roof plane and sits no higher than the ridge. Listed buildings and conservation areas are the exception.

Can it go in a bathroom?

Yes. AK sells a white PVC interior version of the same window for kitchens, bathrooms and laundry rooms, where humidity is higher.

Installation video