Short answer. Therma-Tru's 2017 SITE 4 troubleshooting table identifies three separate possible causes of water appearing around or under an entry-door sill: a broken seal at the sill–jamb joint, damaged/painted weatherstrip, and an inadequate or failed sill-to-subfloor seal. Treat these as different investigation branches, not as evidence that a new door sweep fixes them all.
Narrow the observed location before selecting work
| What may have failed | What the 2017 document actually supports | What to record |
|---|---|---|
| Sill meets vertical jamb | A broken seal at that joint appears as its own possible leakage cause. source | Close-up of both sides of the visible junction, no hidden-wall assumptions |
| Flexible perimeter weatherstrip | Damaged or painted weatherstrip is a distinct possible cause. source | Photos of the seal's condition and contact edge |
| Beneath sill at floor interface | Improper or insufficient sealant, or breakdown between sill and subfloor, appears separately. source | Where moisture becomes visible relative to the sill and finished floor |
A bounded evidence checklist
- Confirm the installed entry-door system and whether 2017 SITE 4 is the right document for that system; the PDF cannot identify your product solely from a wet corner.
- During routine observation, note where water first becomes visible, which side of the door is affected, and whether the issue occurs at the joint, against the weatherstrip, or apparently below the sill. These are observations, not proof of the concealed path.
- Photograph the open and closed door without dismantling the sill. Keep the same camera orientation and label the jamb, weatherstrip, door bottom and adjacent floor.
- Match what you can see against the three independent rows of SITE 4, printed page 4.4. The same symptom has multiple possible causes in the table.
- If the water path is inside the subfloor, concealed behind trim or connected with structural dampness, stop speculative sealing; obtain a qualified assessment and the current installation guidance for the exact assembly.
What not to conclude
A damp sill corner does not, by itself, establish that the corner pad, a sweep or a gasket is the failed item. The 2017 guide lists both weatherstrip damage and sill/subfloor sealing breakdown apart from the sill/jamb joint. Replacing whichever part looks worn may leave the actual water-entry path unaddressed.
This page is a documentation and triage aid, not permission for unverified sill disassembly, through-fastening, wholesale sealing, or work that could hide water intrusion. Escalate when the source of leakage is uncertain.
Primary source. Therma-Tru, 2017 SITE Manual — SITE 4, printed p.4.4, “Water Leakage Around or Under Sill” cause/solution table (US edition).