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Community and Q&A

Exterior door thresholds for thick walls

David Meiland | Posted in General Questions on

I need to hang an exterior door in a wall that’s a total of 10-3/4″ thick, from face of drywall inside to face of exterior trim outside. I need a threshold that spans 11″ or maybe a bit more. The door swings in. I usually use Pemko residential thresholds, but the widest I can get is about 8-3/4″, using a 5-3/4″ threshold and a 3″ extender. I have considered making my own, out of rift white oak, or modifying one of the Pemko models that is wood/aluminum by adding more wood to it. Any other ideas? Products out there?

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  1. Expert Member
    Malcolm Taylor | | #1

    David, I know there is little more annoying than people suggesting alternatives rather than answering a question but... have you considered placing the door closer to the exterior - either half way so that the wide threshold would work or all the way so you could use a stock one? Other options are tapering the walls at the door or reducing their width for a short space on either side.

  2. Jin Kazama | | #2

    I've ran into the same kind of problem when workign with ICF ...only larger
    have to cover a wall thickness of ~ 14" with exeterior finish ( ~12.5" without )

    The only threshold i would consider buying in the late years are from Endura ( usa )
    thermally broken, adjustable height sill , quality product and their not even expensive.

    Unfortunately, their longest combination only goes to 8.625" i blieve.

    I've set the doors where i could using their longest threshold.

    So the only solution to your problem is getting a extra extender and be creative.

    If you need to glu aluminum together my i suggest Loctice Speedbonder
    ( u'll probably have to tear the alum before the bond would let go )

    I'd glue it right under the regular extender, or at the end maybe ...
    BE sure to make a water safe box/membrane and proper flashing, under the sills.

  3. Don Purington | | #3


    Brosco sells an aluminum sill extender:
    Extra Wide Wall Aluminum Sill Extender (not applied): 12'-0" piece only
    3/16" thick aluminum to extend a 6-9/16" wall sill up to 11-1/2". Field application is required.
    Mill Finish - $106, Bronze Finish - $142.

    Information is on page 4 of this pdf file:

    Brosco has dealers in MA, RI, CT, VT, NH, NY and NJ.:

    My builder installed one for an in-swing exterior door in our 11" thick wall two years ago. In the photo below the sill extension starts at 6 1/2" and ends at 12". There is a 1/4" "step-up" where the extension joins the original sill. You only notice it if you step on it with bare feet.


  4. Jin Kazama | | #4

    Don : thanks for the info, i dind't know about this company...will keep in file for future projects!!
    Though 12" of alum treshold doesn't look that good :p

  5. Kevin Dickson, MSME | | #5

    Typically you want to keep any inswing door close to the interior wall. Otherwise, it won't open more than 90 degrees. Then the doorknob is in the way of couches. You want the door to open flat against the wall.

    By the same token, outswing doors must be mounted as "outie" doors so they can open flat against the wall and not get caught by a gust of wind.

  6. Jin Kazama | | #6

    Kevin: unless u use pivots instead of hinges ... then you can move the door somewhat inside the frame/wall with calculated geometry.

    I have yet to see an outswing front door here in QC ...can't think of a single one on any houses i've been to ... only public buildings have those !

    But nice input about the wind ..never thought of it that way !!

  7. Lucas Durand - 7A | | #7

    I'm having some thresholds made by a local metal shop.

    The problem I had with all the "off-the-shelf" extensions I looked at was that they don't seem to be designed to integrate with the WRB or cladding to keep water out.
    The thresholds I'm having made will include vertical flages at the jamb so that I can shingle over them with my cladding.

  8. David Meiland | | #8

    Thanks for the ideas. I don't want to make this a "middie" door--it needs to hang flush with the interior side of the wall, as usual. As far as I can imagine, a "middie" door would need a wider R.O. and a stepped jamb, so that the door could open fully.

    I looked at Pemko's commercial thresholds. A lot of them are basically flat aluminum extrusions. I may install one of these first, and then place a regular residential threshold on top of it, in the normal position. A small section of the commercial threshold could project out from under the residential, to the exterior, covering the top of the concrete that would otherwise be exposed.

    I may also get a piece of steel made for this purpose, something like 16 gauge plate with a small 90-bend along one edge, to turn down at the outside wall line.

    Lucas, post some photos when you get done. On my install, only the jamb is in the R.O. Sounds like you are turning your cladding in towards the door.

  9. Lucas Durand - 7A | | #9

    Sure, I'll post some photos after I get them bent.

    Sorry if my earlier description was a bit confusing - I'm suffering from a head cold that seems to be making me a bit cotton-headed.

    I have "innie" doors and decided to return the cladding into the R.O. towards the door.
    I flashed the bottom (and up each side 8" or so) of each R.O. with a waterproof membrane, then pulled the WRB inside so that it laps over the membrane below.
    The threshold extensions I'm going to have made will have vertical flanges at each side of the R.O. so that the cladding can shingle over the flanges.

  10. David Meiland | | #10

    Here's what I ended up doing. I bought a Pemko 85514 threshold with EXT3D extender, and installed them so that the exterior edge of the extender lined up with the exterior trim the way I wanted it to. I added a piece of white oak against the inside edge of the threshold, milled to the same elevation as the top of the threshold, then capped that with a Pemko 151 commercial threshold. The door shoe seals against the 151. It works well.

    The jamb is typical 6-9/16" jamb stock with a 2-5/8" extension jamb added to the outside. Interior trim is 3/4", exterior trim is 1-1/2".

    It would be easier if someone made thresholds wide enough for these thick walls, but they don't as far as I can tell.

  11. Lucas Durand - 7A | | #11

    Yeah, I've also wondered why there aren't more options out there...
    I still haven't gotten around to dealing with my thresholds.
    Yours look great.

  12. Kevin Dickson, MSME | | #12


    That looks great. My wall was a bit fatter so I bent a piece of scrap sheet metal:

  13. Lucas Durand - 7A | | #13

    I'm thinking of doing something similar...
    What gauge sheet metal did you use?

  14. User avatar
    Ethan ; Climate Zone 5A ; ~6000HDD | | #14

    All of these options, except maybe the Endura, seem like major thermal bridges...

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