Channel drain, next to, or underneath Door threshold?

9 Nov 2021
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United Kingdom
I have a bifold door with a DV14 threshold. I am planning to run a channel drain, but do I butt it up next to the threshold, or place it underneath. I plan to run somedecking to to the doors, but would this then butt up to the drain or go over the top? I have created a sketchup to try to illustrate. i coloured the door red, it isnt really going to be red..
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Why does it need a surface drain if you are decking it?

i want to make sure all water is carried away from the door. I thought it was the done thing to put a channel drain between the doors and the decking . It seems sensible to have the drain underneath the catch any water then some sort of mesh to cover the gap above the threshold bit that sticks out. Then the decking can run to the mesh and it will look like a continuous level into the room .
The rain will be going straight through any decking and into the ground below, so I can't see any point in fitting a surface drain with decking as it just wont do a thing, nothing.
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You only use drain channel where you can’t drain away from the property and have solid surface ( tile etc) preventing drainage.
Unless the surface is self draining (like decking here) you should always have a threshold drain if the external finishes are flush with the threshold.

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