If timber floor structure face fix the handrail to the front of the floor structure with EPDM washers where the fixing meets the cladding. Bolt fixing through the boundary joists into a L Bracket which bolted to the joist beside. Have 4 baluster paosts, wih the end ones finishing 50mm away from the building. This way the handrail does not penetrate the wall cladding. Only the bolts penetrations require flashing with the EPDM washers mentioned.
If timber floor structure face fix the handrail to the front of the floor structure with EPDM washers where the fixing meets the cladding. Bolt fixing through the boundary joists into a L Bracket which bolted to the joist beside. Have 4 baluster paosts, wih the end ones finishing 50mm away from the building. This way the handrail does not penetrate the wall cladding. Only the bolts penetrations require flashing with the EPDM washers mentioned.
One way with steel is to powder coat it.
https://en.wikipedia.org/wiki/Powder_coating