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Confusion on Exterior door – One or two slopes?

NewTinyBuilder | Posted in General Questions on

New builder Evan here, getting ready to put an exterior door on my 8×10 tiny cabin in Vermont. With your help I got the floor, walls, and roof built and I will install the final window tomorrow! 

I have read as much as I can find about the proper way to flash my exterior door, which will be highly exposed to rain/snow. This 2018 article by Martin ( led me to the following plan:

Create and install a sloped sub-sill from 1x pressure treated lumber on top of my subfloor. Will be installed with exterior screws over 3 beads of sealant. Then I will use 3M All Weather flashing tape to flash that sub-sill similar to my windows. After the sill and rough jambs are flashed I will install my door frame (jambs and header), with the bottom of the jambs cut on a slight angle to match the sub-sill angle. Then I will install a sloped metal threshold in between the jambs, something like this: Then I will install the door. 

The reason Im confused is because, in this set up, which appears to be recommended in Martin’s article, I am installing two sloped items – a sloped sub-sill/sill pan and the sloped threshold. Is that correct? Do there need to be shims to create a level surface for the threshold to sit on? Elsewhere, like in this Q&A ( post, Martin shared a photo where the sub-sill does not appear to be sloped and only the threshold is sloped. Most sources I see online include either a sloped sub-sill or sloped threshold, but I havent seen both. Any advice you can offer would be really helpful, I hope to install the door in the next 48 hours (after the final window). 

Thank you!

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  1. Expert Member
    1. NewTinyBuilder | | #2

      Thank you Malcolm! Very interesting, it looks like they create a flashed back dam with L metal and install the threshold directly on that - basically right on the subfloor. So only one sloped at the sill/threshold level, and no subsill. Sounds different from what I'm reading here on GBA. I'll look into the L metal idea and see what I learn. Just installed the last window today!

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