How to: Install a Velux flat roof window in conjunction with Cure It GRP waterproofing system.

Watch the demonstration now

The problem: Is it beneficial to add a flat roof window to a new or existing flat roof?

There are many reasons as to why adding a flat roof window to a new or existing property can be beneficial. Whatever the case may be Cure It GRP has got you covered.

 A flat roof window makes it easy to bring daylight and fresh air into your flat roof home. Most flat roof windows are available in several sizes as venting or fixed installations with manual or electrical operation. You can choose between a classic model with a convenient dome or the stylish flat glass version with discrete profiling.

Many living spaces in flat roof buildings – including kitchens, living rooms and offices, these typically get very little natural light. By adding a flat roof window, you can transform and improve virtually any space.

The solution: How to install the Cure It system in conjunction with a Velux roof window.

Please view the step by step guidance provided in our VELUX/Cure It instructional video.

The video will only include the initial steps needed to install the Cure It system in conjunction with the VELUX flat roof window. For full instructional use of the Cure It system please refer to our installation manual. Training is also recommended before first use. By following this procedure, you will find the process quick, easy and hassle free. Whilst leaving a finish you and your customer can be proud of, plus provide a fully sealed waterproof membrane that will last a life time.


Step by step guide:

  1. First the joists of the roof must be configured to the correct aperture of the roof window, you may require guidance from a structural engineer to insure the construction of the roof is satisfactory if alterations have been made to the joists.

  2. The OSB3 18mm T&G (tongue and groove) boards can then be fixed to the deck, cutting the boards to the outline of the joists to allow a flush interior finish. The boards must be fixed using galvanised ring-shank nails or screws, with fixings every 200mm centers across the width of the board, plus achieving a minimum 40mm penetration into the joists. A 25mm expansion gap must also be left between any fixed structure i.e. Parapet wall. Please refer to our installation guide if the addition of insulation is required.

  3. Once the decking is finished the flat roof window should be positioned so that it is straight and flat on the deck. Pilot holes should be drilled around the curb at 300mm centers, using a 4.5mm drill bit. The galvanised screws provided with the Velux roof window should be used to fix the curb to the deck. The roof window is now fixed in place, and the Cure It roof can be installed to make It watertight.

  4. When applying the GRP edge trims, use D260 fillet trims to form the up-stand around the roof window. Making sure they reach as far up the sides as possible.

  5. Using an angle grinder or snips to miter the corners following the contour of the roof window edge. The trims can then be fixed to the deck using staples or clot nails. Use masking tape to cover any gaps between trims.

  6. Refer to our installation manual for installing all A, B and C trims where needed.

  7. Cut the 75mm bandage to cover all edges around the perimeter of the roof light and any mitered corners. This procedure will need to be applied over any other GRP edge trims. The bandage should then be laminated using the correct procedure as specified in the Cure It installation manual.

  8. Once the bandage has been completed, the CSM (chopped strand matt) can be cut to size over the entire roof area and around the perimeter of the roof window. Make sure there is a minimum 50mm overlap of the CSM pacing the feathered edge over the straight edge.

  9. The main waterproof laminate can then be applied to the roof area. Take extra care to avoid spray from the roller when laminating in close proximity to the roof window.

  10. Hardener must be applied to the resin to allow the material to cure, working on a 1%-4% ratio of hardener dependent upon weather conditions.  For further in depth laminating information use the Cure It installation manual.

  11. Once the roof area has cured and can be walked on, the addition of the rain censor or correct flashings can then be clicked in place and fitted to the roof window.

  12. The colour topcoat can now be applied over the entire roof area. Make sure the same percentage of hardener has been applied to the mix (topcoat requires hardener to cure). The topcoat is available in a graphite grey as standard.

Related Products

Download the catalogue from AJW

Product Catalogue

Download the latest AJW Distribution catalogue…