Flat Roof Skylight Guide - with our Timber Kerb

A step-by-step guide to installing your Custom Flat Roof Skylight, when supplied with your timber rebated kerb.

When you are installing your Custom Flat Roof Skylight, there are some things to first consider.

1) Ensure your roof is prepared correctly (more info in Roof Preparation Tips for you Rooflight), & double check your structural opening vs the skylight size you order.

2) Your skylight must have a gradient for water run-off. This is 40mm for every 1000mm of skylight run - ideally across the shortest side.

3) Consider the weight of your skylight unit. You may need several people to assist the manual lifting & positioning of your roof light. Additionally, suction cups or mechanical lifting assistance may be required (trained operatives only). 

Step 1: Firstly, check above advice & consult Roof Preparation Tips. If installing a Firestone Elevate EPDM rubber roof covering (or any EPDM) - ideally ensure the membrane is bonded to your deck first, then cut to fold back, ready for skylight kerb installation.

Check the internal dimensions of your roof opening, are the same as the dimensions on the product ordered. See the picture (right) for assistance on correctly measuring the opening.

Step 2: Position your own base kerb (80mm x 80mnm), still ensuring the correct fall of 1 in 40 across the shortest run. The shortest run should ideally be towards to your gutter run for best results.

The internal face of your kerb, should be flush with the face of your structural opening (joists/upstand). Secure in place with appropriate fastenings (no proud fixings).

Step 3: Now, place your supplied timber rebated kerb (70mmx80mm), on your base kerb, with the internal face flush as previously stated.

Plan, pilot & counter sink drill your timber rebated kerb, at 400mm centres, & 150mm from any corner.

Using the appropriate fastenings, fix your rebated kerb into your base kerb, ensuring you have no proud screw heads. Your total kerb height will now be a minimum of 150mm.

Step 4: Proceed to dress your roof covering (Firestone Elevate EPDM preferably) to the top of your kerb. Ensure strong adhesion. 

You will need to flash/seal your external corners of your skylight. For your Firestone Elevate flashing, you will need youf Quick Seam Flashing, see here for your guide on flashing external corners.

Step 5: Apply a continual bead of quality, low-modulus sealant to both top flat surfaces of your rebated kerb, as well as the corner of the rebated glass unit.

We advise clear CT1 sealant as an example of the type of sealant required.

Step 6: Carefully & safely position your triple glazed unit into position.

As mentioned previously, depending on the size of your skylight, you will need to consider its weight & use multiple peoples to assist in safe lifting.

Step 7: Using the palm of your hands, push down around the edge of the skylight, evenly compressing your sealant (don't force over pressing on the glazing overhang).

Step 8: Once the glazed unit is in place, apply a final bead of sealant to the underside of your skylight overhang, where it meets the top of your kerb and roof covering.

This will help defend against any capillary action of ingress & pulling away of your roof covering. You can now, gently clean your glass if needed (no harsh chemicals).

Well done, you've installed your triple glazed flat roof skylight!