Sealing and reinforcing underneath existing enclosed sunroom porch.

House Repair Talk

Help Support House Repair Talk:


New Member
Mar 1, 2023
Reaction score
Dayton, OH
I am looking for recommendations on what to do with this situation. I am in the process of sealing the underside of my existing 12’ x 20’ sunroom. It is a finished part of my house that is open to the elements underneath. Old insulation is long gone and the 12’ double glass wall slider failed because they didn’t properly support a 20’ span. I have dug out around the foundation and plan on building up a small block wall to the existing rim joist while adding a pt sill plate. My plan is shown in the diagram. The room is on 4x4 posts with footers so the new foundation is more to seal and insulate rather than act as support but will shore it up in case the current posts some day fail. Once sealed on outside, I plan on tearing up the floor to insulate and install a vapor barrier. Also removing large 4 panel sliding patio door and replacing with 2 panel 72” sliding door. I am looking for any techniques or suggestions on how to build up and meet the underside of the existing rim joist. I may just need to shim it several places and then seal it in with mortar and foam. Any links or thoughts would be appreciated. My plan is to pour a 6x6 footer then use 4x8x16 solid blocks to build up. My concern is that I won’t meat the rim joist and will have a gap to make up for.


  • 547E39B3-E475-484D-B653-97CFC645B045.jpeg
    2.9 MB · Views: 0
  • 4F710117-874A-4F8C-A738-752DF4E10685.jpeg
    2.7 MB · Views: 0
  • 59DFD785-D6AE-44B8-B465-65251DC77258.jpeg
    2.8 MB · Views: 0