Short answer. On the Therma-Tru configurations addressed by the 2017 troubleshooting pages, damaged or missing weatherstrip and uneven lock-side jamb contact are different findings. source Changing to a thicker gasket is not the manufacturer's diagnosis for every lock-side light gap or closing problem.
Observe contact instead of choosing thickness
Strip condition: look for a section that is missing, painted or physically damaged. Those are listed independently in the air/light table. source
Uneven contact: check whether the door seems to touch the weatherstrip at one end before the other. Therma-Tru identifies lock-side jamb alignment as its separate remedy in the 2017 tables. source
Loose when latched: if the door has noticeable in-and-out travel after latching, the same table distinguishes a strike-plate adjustment pathway. source This is a documented alternative to declaring the weatherstrip undersized; no adjustment is prescribed here without the exact door installation guide.
Small decision table for a homeowner
| What appears most evident | What to write down | What not to assume |
|---|---|---|
| Paint, split or missing area on jamb strip | “Strip condition suspected” | A new profile must be thicker. |
| A stronger contact mark at top than bottom or the reverse | “Uneven lock-side contact” source | Every part of the strip is faulty. |
| Latch catches but slab moves in/out | “Latched play; strike relationship to check” source | Gasket size alone controls movement. |
| Door is hard to close, head margin uneven or strike visibly misaligned | “Possible geometry/strike condition” source | Forcing a larger strip is harmless. |
Documentation route
- Confirm which jamb is the lock side and note swing/handing without buying handed parts.
- Photograph the jamb strip at top, center and bottom with the door open normally; photograph closure gaps without trapping fingers.
- Check normal latching and note any unusual pressure or movement. Do not loosen a strike plate or reshape the frame as a diagnostic experiment.
- Use the 2017 door will not open or close properly table to keep door sag, frame squareness, strike alignment and seal contact as separate candidates. source
- If the door will not latch reliably or is unsafe to operate, stop and seek appropriate installer/qualified service help.
Decision outcome
Verified visible strip defect: identify the exact existing strip and authorized replacement method. Alignment clue without strip defect: document the jamb/strike condition and obtain original installation instructions. Mixed or uncertain: no part recommendation. This page does not specify a universal compression gap, shim sequence or latch adjustment.
Primary sources and claim locator register
- — Therma-Tru original, 2017 Site Manual — SITE 4, US; p.4.3, distinct strip condition/contact causes. Publisher document.
- — Therma-Tru original, 2017 Site Manual — SITE 4, US; p.4.3 and p.4.9, uneven weatherstrip contact / jamb alignment. Publisher document.
- — Therma-Tru original, 2017 Site Manual — SITE 4, US; p.4.3, latched looseness / strike-plate row. Publisher document.
- — Therma-Tru original, 2017 Site Manual — SITE 4, US; p.4.9, frame, door sag and strike causes. Publisher document.
Evidence and safety boundary
Therma-Tru’s 2017 SITE 4 manual (printed pp. 4.3 and 4.9) discusses weatherstrip contact and jamb/strike alignment as different conditions. With the door operating normally, note whether the strip is visibly damaged or whether the closing edge fails to seat consistently. Record any latching problem and request model-specific service guidance; this page does not supply a universal compression dimension or authorize strike adjustment.