A section value and an assembly result answer different questions
DASMA distinguishes calculated section R-value from tested whole-door U-factor. Higher R-value and lower U-factor indicate greater thermal resistance in their respective measurements, but the two published figures are not interchangeable by taking a reciprocal. Ask which measurement supports the exact door in your proposal.
Request evidence for the configuration being quoted
Ask the supplier to identify the model, section construction and glazing arrangement attached to a claimed result. DASMA’s thermal verification program provides independently checked U-factor information through ICC-ES. A logo on a brochure should lead to a relevant listed product rather than stand in for the data.
Make the purchase comparison useful
Create a short comparison with installed price, specified construction, windows, thermal evidence and service coverage. A thermal test is not a promise of a particular indoor temperature or utility-bill reduction. Garage use and the rest of the enclosure also matter; avoid buying solely from a headline number.
Your questions
Can I calculate whole-door U-factor by dividing one by the advertised R-value?
No. A section calculation and a whole-door test do not describe the same assembly. Request comparable published measurements instead of converting marketing figures.
Does a verified thermal rating also certify sound reduction?
No. Thermal evidence does not establish acoustic performance. Ask for separate relevant sound data if outside noise is part of the buying decision.