Short answer. In the 2017 Therma-Tru adjustable sill repair pages, the sill gasket is shown in an aluminum channel associated with the threshold; it is not the same illustrated piece as a door-mounted bottom seal. source The same pages also name an adjustable saddle and corner seal pads as different components. source
Name three pieces before comparing fit
Sill gasket: the manufacturer describes carefully taking it from, and returning it to, the threshold's aluminum channel during adjustable-threshold service. source
Adjustable saddle: a separately labeled part in that threshold assembly. source
Door bottom: the flexible door-mounted item in the troubleshooting discussion, which can be torn or wrinkled independently of saddle condition. source
A photo of the lower edge alone is therefore insufficient to declare which part should be purchased. Make a location map before discussing replacement.
A do-not-disassemble classification table
| Your observation | Candidate | What to verify |
|---|---|---|
| A channel-held component on the stationary adjustable sill appears absent | Sill gasket | Whether the installed threshold matches SITE 5 pp.5.22–5.23. source |
| A surface on the adjustable threshold appears damaged | Saddle | Original adjustable-threshold assembly detail, not a jamb strip catalog. source |
| Flexible material on the moving bottom is visibly torn, folded or worn | Door bottom | Door-bottom service documentation; the 2017 fault guide separates this from saddle replacement. source |
Four checks that preserve the evidence
- Identify the actual adjustable sill variant by the manufacturer's original documents, if available.
- Take a stationary-sill close-up with its long axis visible. Draw a simple arrow to the suspected aluminum-channel component; do not remove it for identification.
- With normal door operation only, photograph the moving bottom and compare its condition with the stationary gasket. Avoid adjusting screws, cutting vinyl or raising the sill during this check.
- Read the weatherstrip and adjustable threshold sections as separate repair sections in SITE 5. source If a cause remains unclear, use SITE 4's separate saddle, bulb and sealant-joint headings to plan further inspection. source
Outcome and limits
If you can document a channel-held gasket and the matching edition, request its precise issuer identification. If you only know that a bottom “sweep” leaks, report unresolved component. A generic door-bottom gasket may look close but this document contains no universal substitutability claim. Refer any threshold adjustment or disassembly to the model-specific installation document or qualified service.
Primary sources and claim locator register
- — Therma-Tru original, 2017 Site Manual — SITE 5, US; pp.5.22–5.23, aluminum channel and sill gasket. Publisher document.
- — Therma-Tru original, 2017 Site Manual — SITE 5, US; pp.5.22–5.23, saddle and corner pads identified separately. Publisher document.
- — Therma-Tru original, 2017 Site Manual — SITE 4, US; p.4.4, distinct sill leak rows. Publisher document.
- — Therma-Tru original, 2017 Site Manual — SITE 4, US; pp.4.4–5, damaged bulb vs saddle rows. Publisher document.
- — Therma-Tru original, 2017 Site Manual — SITE 5, US; pp.5.21–5.23, separate jamb and adjustable threshold sections. Publisher document.
Evidence and safety boundary
Therma-Tru’s 2017 SITE 5 (printed pp. 5.22–5.23) illustrates the adjustable saddle and its gasket as threshold components. Inspect whether the observed seal is retained in the sill or attached to the door bottom; capture the location without changing saddle height. Ask for the matching threshold system and service document. This illustration is not permission to adjust or substitute an unknown threshold.