When I remodeled my home, I put soundproofing and an inside lock on this room alone.
Literal
Home [object-を] remodel [at-the-time-of-際に], this room [only-にだけ] soundproof-equipment [and-と] inside-lock [object-を] attached-[explanatory-んだ].
~際に ('when, on the occasion of') is a formal alternative to ~時に. 改築 ('remodeling, reconstruction') — distinct from 新築 ('new construction'). この部屋にだけ stacks に (location) + だけ (only) to mean 'only to this room.' 防音設備 ('soundproofing equipment'), 内鍵 ('inside lock' — a lock that can only be operated from the inside).