I am replacing an entrance with one like this three-pane design with a door in the middle and two side panels:

enter image description here

The door will swing over a concrete slab inside, requiring about a 1 inch raise above the slab to provide space to clear a foot mat and tiles. The entire assembly is about 6ft wide.

Currently there is a piece of 1x6 to provide some of the raise. I used thinset to fill the unevenness of the slab, applied a sill guard and then the 1x6. There is no vertical room for a 2x6.

There is also about 0.5in of additional horizontal shimming needed to level the threshold. That gap and shim is currently between the 1x6 and the door's threshold.

The studs in the opening are anchored sideways into concrete foundation, and the jamb will be screwed & shimmed to these studs.

  1. The threshold is aluminum. At how many spots does it require shimming (between the threshold and the 1x6), and does it require cement / thinset between shims to prevent bending?

  2. Should the threshold be anchored to the foundation under it, and if so, how? Or is the sideways fastening of the jamb into the studs sufficient for the threshold?

I am concerned that door slamming may put too much lateral force on the threshold and too much stress on the lower jamb fasteners.

I could anchor the 1x6 with anchor screws, but the threshold can still move freely. I don't believe the adhesion of thinset or cement is the appropriate remedy for these lateral forces. But maybe it is?

The opening over foundation is much like this one

enter image description here

from Threshold for pre-hung exterior door

Except that the inner jambs for the door obviously cannot be fastened to the studs, and so lateral slamming forces transfer through the treshold and the top jamb sideways into studs and into the header.

  • Is the foundation you're referring to the one that the entire house is built directly upon? Or is the house on a crawlspace and there is a raised concrete slab porch/step "attached" to the house (a photo may help here...)? Also, why do you think normal operation of the door will cause strain on the threshold? The two are not attached in any way.
    – TylerH
    Jun 14, 2021 at 18:48
  • @TylerH: under the threshold is slab, inside too. On the sides there is 4ft of foundation wall. I am concerned about the door slamming and the forces on the two inner vertical jambs of the door slab transferring to the threshold and eventually to the outer jambs of the assembly and into the studs. Can the threshold take it? Does it need to be anchored somewhere in the middle?
    – P2000
    Jun 14, 2021 at 18:55
  • Wait, you have a concrete slab on top of a (CMU, I'm guessing) crawlspace? I really think a photo of your actual, current setup is necessary to understand what we're dealing with. I can't really tell from your descriptions. Anyway, regarding the threshold, there shouldn't be much, if any, force on a frame by the normal operation of a door. Normally you would use screws or bolts of some kind to fasten the threshold to the subfloor, but it's not clear what you have to work with here (that photo would help).
    – TylerH
    Jun 14, 2021 at 19:03
  • @TylerH, there's no crawlspace. Slab on ground. There's foundation under the door opening. Threshold is over foundation. No subfloor.
    – P2000
    Jun 14, 2021 at 19:07
  • OK, the "4ft foundation wall" bit was throwing me off.
    – TylerH
    Jun 14, 2021 at 21:03

1 Answer 1


You should fasten the threshold to the concrete using screws/anchors designed for concrete fastening. See How can I fasten a threshold to concrete? for more info on that. Otherwise, the threshold won't be attached to anything and will move all over the place, based on your description.

I still don't see any cause for concern about force from lateral movement or whatever on the door or threshold. The two sides and top of the jamb should be fastened to the framing studs, through any shims that were used for getting the jamb aligned. That should be enough to allow your door to operate normally.

  • Ok so would you drill a new hole through the threshold? If this is common practice, why is there no hole for these anchors? BTW the linked answer is for a question where the holes and screws are provided, making it a question of how to drive the screws into the concrete, not (as in my case) how/whether to drive a screw through the threshold. I'll be stuck with a visible head that I'll have to counter sink or otherwise hide. Thoughts?
    – P2000
    Jun 14, 2021 at 21:15
  • @P2000 It probably wasn't done before because of cost. Most houses are built just to be code compliant, which is another way of saying "the bare minimum", because that's how builders make the most money. You can drill holes into the concrete with a masonry bit; you don't need particularly deep ones for a threshold. Many thresholds have fastener heads on them. Can you update the question to include the specific brand and model of the threshold you bought? I imagine the manufacturer provides instructions on how to fasten it.
    – TylerH
    Jun 14, 2021 at 21:24
  • @P2000 One reason I suggest fastening it into the concrete is partly because it sounds like the 1x6 is not currently fastened/attached to the foundation, and it absolutely must be, with the gaps sealed ideally, and this will accomplish that. Another reason is that you could just fasten the threshold to the 1x6, but then you would need fasteners that are less than an inch long and that little purchase into a material is not going to provide much strength; the threshold is likely to move or warp over time just from people stepping on it.
    – TylerH
    Jun 14, 2021 at 21:27

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