Last winter the lower hinge side of back door (which faces west and gets lots of wind) was freezing cold during our Northern Illinois winter. So I wanted to fill it with spray foam to seal it up. When I took the interior trim off I noticed a lot of moist wood and saw OSB underneath the door threshold. I’m pretty allergic to mold and was like woa I got to get this out before it gets worse. Soooo I took the threshold out of the door. I bought a new one at Home Depot and wanted to squeeze it into place under the existing jamb. I haven’t found a lot of guidance on this. At work, when I asked the maintenance guy at work he said replace the whole door. I wanted to fix the threshold only I think I have a pretty tight fit and was planning on caulking it well and filling it with spray foam and then adding a storm door. I don’t see why this wouldn’t work. Am I missing something? Why can’t I just replace the threshold? I’m trying to save on costs so I don’t have to buy two doors this fall. Besides that the HOA is super slow and I don’t think I would have an answer by January.
You can replace just the threshold. Sometimes it is difficult because the original threshold is screwed to the jambs as part of a complete assembly, or it lies under the door stop part of the jambs, but it sounds like you already figured that part out.
I would caution you to investigate and fix whatever caused the water penetration (in case there was an additional issue besides the old threshold) and repair any damaged wood underneath before you install it. I assume your new one is aluminum since you mention filling it with spray foam, screw it down well with stainless screws.The screws that come with them are not always the best ones to use.
You can just replace the threshold. However, the "maintenance guy at work" recognizes that to do so is more work for a worse result than replacing the whole door & frame as a unit. I'd say his advice is spot on. Be very careful with spray foam and windows/doors - many people overdo it and end up with stuck windows/doors from foam over-expansion.
I'm unclear what the HOA would have to do with this, but they do run wild some places.