EPDM Internal Drains

A step-by-step guide to installing and water-proofing your EPDM flat roofs internal drains.

Firstly, there are 2 key things to set-up, which will greatly improve the end result of your internal drain!

Set-up tip 1: Ensure the internal drain feed is just shy of being flush to the top of your finished roof deck. This will ensure when you slide your drain in, there will be a maximised overlap of pipe – no water backtracking in the future!

Set-up tip 2: This is a neat step our team included after many installations. Due to the natural thickness of the internal drain and the subsequent flashing, even with a good roof slope, this will create a mini β€˜kick’ & some sitting water. 

To eliminate this, where possible, install 11mm timber (preferably OSB) instead of 18mm OSB to the area where your drain and flashing will sit. Use a planer or sander to gently slope the step.

This way, once your drain and flashing are applied, they will be back β€˜flush’ with the rest of your EPDM, allowing better drain-off.

Step 1: Where possible, follow set-up tips 1 & 2. Next, ensure your EPDM is fully adhered to your decking – then cut out the hole for the drain. Be sure to use the most appropriate diameter drain for your sized outlet.

Step 2: Next, apply a continuous bead of Bond & Seal sealant to the underside of your drain, at least 20mm from the edge. Push your drain into position, compressing the sealant.

Step 3: Using appropriate sized fasteners & washers, secure your drain in position.

Step 4: You now need to flash over the area. Your flashing must lap onto your EPDM at least 75mm, & cover the entire top of your drain.

Cut your piece of flashing to suite this area, a piece of 18’’ wide flashing would be most suitable here. 

If you must do in 2 or more pieces, allow for overlap of each piece by 75mm.

Step 5: Chalk around your piece. Then using your Quickscrub pad & handle, apply your Quickerprimer Plus to the area, plus an additional 20mm.

Step 6: Once touch-dry & tacky, mate your quick seam flashing, starting at one side and smoothing into place. Keep flashing taut without stretching to help stop air pockets. Work in using your Silicone Rubber Roller and Penny Roller.

Step 7: Cut out the hole in your flashing. Don't accidentally cut the drain itself.

For extra precaution, you can apply a bead of Firestone Elevate Lap Sealant to your exposed flashing edges. Note though, not to have a too proud bead which will cause sitting water.

Step 8: As a precautionary measure, slide a Universal Leaf Guard into the drain hole, to defend against blockage - keeping the pipe feed clean.