100 year old brick house with a new front door. The door is awesome at stopping the cold, but there is a space under the door where cold still comes in. I originally put some fiberglass pink insulation in there, but that didn’t do much. I think I need to stop the air flow better.

One option is to fill it with spray foam. But I’m not sure if I want everything glued together for all eternity. And I believe you should only fill cracks, not voids.

Another is to cut a piece of plastic and glue/caulk it along the front (so the insulation is behind).

Any other ideas?

Space under front doorenter image description here

  • Can you clarify where the cold is coming in? Is there actual cold air, or the floor in the area is cold and you think it's because of the outside gap? If there's cold air, exactly where do you detect it?
    – fixer1234
    Jan 20, 2018 at 22:40
  • I can feel cold air with my hand at the base of the door, closer to the sides. The door trim is not tight to the wall, and i can feel cold air coming in. On some particularly cold nights (-20C) I measured with an infrared/laser thermometer, and the temps on the floor in the trim crack were close to freezing. Jan 21, 2018 at 2:46
  • Where you're trying to insulate is below where the air is coming in (even below the floor). Check the door bottom and threshold to see if there is an adjustment to close the gap. It sounds like you need to better seal the bottom gap and maybe add or replace weather stripping on the door jamb. You may need to adjust how the door hangs, or adjust the striker plate(s) so that the door is held tighter against any existing weather stripping.
    – fixer1234
    Jan 21, 2018 at 2:54
  • Another thing to check: feel around the door trim for drafts. You may need to remove the trim and caulk or fill the gap between the door framing and the jamb, then replace the trim.
    – fixer1234
    Jan 21, 2018 at 2:58
  • The door has a 4-side compression seal. It’s not the door that leaks - i initially thought it was the door as well, but it’s the space under the door is 100 year old framing - and has no air/vapour barrier at all. Cold air blows in underneath the entire door frame. Jan 21, 2018 at 4:04

3 Answers 3


Go with both. If it needs to come apart in 10 yrs' time, you'll have to wreck it anyway. Gently push the fibreglass towards the back of the void, then use spray foam for the final 3 or 4". When it's all cured, use a stip of wood or plastic as a finisher to cover it all up - after of course, you've trimmed the foam.

  • This makes a lot of sense. You want the foam to fill every little gap, but spraying that much foam will go through a couple of cans. Using the fiberglass as "filler" (as well as insulation) will fill most of the space, then the spray foam will ensure the little gaps are sealed up, preventing air infiltration.
    – FreeMan
    May 6, 2022 at 11:36

That opening will be sealed off with a riser. Make sure it's a tight fit with no gaps. The horizontal pieces extend farther than the framing, so add wood to extend the vertical framing to make a 4-sided box that the riser mounts against. Caulk between the riser and that threshold "box" to seal it.

Beyond that, fiberglass batting like you show should be fine to fill the space.


Maybe try solid foam insulation. Sheet foam. Get a piece cut to fit tight, then silicone caulk around that. Once that cures, cut a piece of wood to cover that and make it look good. Attach this wood with more caulk and screws.

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