EPDM DPM to DPC - How best to complete....?

[Mulberry View]

This is an external door installed onto XPS with EPDM as the DPM. The EPDM was left long on the inside. I turned it up at the sides in case it was needed. It's an ICF build with Waterproof concrete and no conventional DPC. It's an RK door with a skimpy low threshold, almost non existent upstand.

 

The floor is Block & Beam, there is a 1200ga DPM under the PIR, this is what you can see in the image laying back onto the PIR.

 

 

This is with the EPDM lifted. The inner threshold is 50mm below the door threshold, but still XPS. The screed needs to come up almost to the underside of the threshold, with 3-4mm Microcement as the final finish.

 

 

How should this detail be finalised? Should these membranes just be taped together? Any expansion joint along the threshold?

 

There's another 80mm of PIR to go on yet, this will bring it level with the blue XPS, with everything 50mm below final FFL. I have 2 more Norrsken doors following roughly the same principle.

 

As always, your help is invaluable to me, and I'm procrastinating on it at the moment!

[JpManning]

I'd treat the EPDM and the 1200g DPM as one continuous layer and lap them rather than just butting them up and taping the edge. Give it a good lap, 150mm or more, bonded with double sided butyl tape or the EPDM primer and seam tape, with both surfaces clean and dry and the lap rolled down firmly. The aim is a continuous tray from under the threshold right across the floor.

At the sides, keep your EPDM upstands and bring the DPM up behind them, then carry both up the reveals to at least finished screed level so the screed is fully contained.

Under the threshold I'd bond the EPDM to the sill support or the underside of the frame rather than leaving it loose, and seal the frame to the membrane with a compatible sealant. With an almost non existent upstand that joint is your main defence against wind driven rain, so a fall away from the door or a drainage channel outside is well worth having too.

On the expansion joint, yes. I'd run a strip of perimeter edge foam (5 to 10mm) along the threshold and round the reveals before screeding. It stops the screed bonding to the frame, takes up movement and gives the microcement a clean line to finish against, so it's less likely to crack at that junction. Trim it flush afterwards and finish with a flexible sealant once the microcement is down.

Also worth checking the screed and microcement makers' moisture limits before finishing, as 50mm of screed over PIR can take a fair while to dry out.

[Nickfromwales]

16 hours ago, Mulberry View said:

This is with the EPDM lifted. The inner threshold is 50mm below the door threshold, but still XPS. The screed needs to come up almost to the underside of the threshold, with 3-4mm Microcement as the final finish

Inward or outward opening?