I work in MEP and our emails are always considered legal documents as they can be used as evidence if ever we are taken to court. So we always treat them very technical and try to over explain everything so clients/plan reviewers/contractors can’t misinterpret. It’s kind of an old school thing, but the head of our department is an old school guy.

Engineer here.

Typically when I type out professional emails or documents that contain numerical values, I write out the number followed by the digits in brackets if it is ten [10] or below for cases of amount, unless I am listing out the counts of items, then I only use digits.

“The updated electrical design will require three [3] new, pad-mount 500kVA transformers to replace the three [3] existing 225kVA transformers,each located on floors four, five, and six.”