F, T, L and W ratings: what each letter on a firestop system measures
A laboratory floor penetration submittal carries an F rating. The specification also asks for a temperature-related performance rating at that location. A reviewer highlights the missing entry, and the foreman asks whether the product’s fire rating is already enough.
Read each rating as a different measured characteristic, then check what your location actually requires. In the cited UL framework, F concerns fire passage over time, T temperature rise over time, L measured air leakage and W water passage under its test conditions. One letter does not establish the others. Confirm the project’s governing test basis and required designation; Canadian listings and requirements must be read in their own applicable framework.
Compare the required and offered performance
- Record the requirement first. Identify the opening’s assembly, location, specified ratings and applicable test reference. Ask the responsible professional to resolve missing or conflicting requirements. Do not infer the need for a temperature or leakage rating from a colleague’s last project.
- Read the complete listing entry. Obtain the actual accepted system, including the construction, penetrating service and stated ratings. Keep a blank rating distinct from a documented value. A brochure describing a product family is not the same record as the specific system proposed for this opening.
- Separate time and leakage measures. Read F and T on their stated time basis and L with its actual units and test conditions. Keep the values in separate fields. A smaller or larger number can mean something different across those measures; do not compare an air-leakage result with an hourly fire requirement.
- Check the water designation within its scope. Confirm whether W is required and what the offered system records. Keep the stated test conditions with that result. A water-passage rating does not establish the design or performance of the building’s whole waterproofing assembly.
- Compare the field condition as well. Have the installation team check the assembly, services and relevant dimensions against the accepted system. Matching rating letters cannot cure an opening that falls outside the listed arrangement. Keep any mismatch on the technical review route before work depends on it.
- Close the missing entry properly. Obtain a suitable reviewed system or the authorized disposition for the actual condition. Preserve the original submittal and response history. Do not write a desired value into a blank cell or substitute an assumed equivalent result to clear the programme.
Common mistakes
- Reading one rating as proof of every performance requirement.
- Treating a missing value as zero or as an acceptable exception.
- Ignoring the construction and service behind the rating.
Checklist
The rating comparison sheet
- Location and actual required designation.
- Applicable test basis.
- Complete system reference.
- Separate values, units and conditions.
- Field-condition match.
- Reviewed resolution of missing entries.
Check your understanding
The offered system has a strong F result but no stated L result. Does that answer a specified leakage requirement?
