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Question DetailsAsked on 5/26/2016

Typical cost for a 500 square foot attic conversion into apartment?

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I would doubt one could peg a specific number as "typical" - because of variations in each case in how high-end the remodel goes, how much modification to the attic framing (and potentially roof) and insulation/ventilation is needed, particularly whether the roof height needs to be raised, and so a significant extent if you mean a true apartment - so requires full bath and kitchen and probably laundry facilities.

A low-end conversion to "apartment" living space only can run as low as about $50-100/SF for a low-end minimalist "in-law" type apartment without any roof framing modification or raising, probably more in the $100-150/SF ballpark in all but lowest cost areas if roof reframing or raising is needed and with standard grade construction, and in high-cost areas or with high-end design and finishes or dramatic roof reconstruction can easily reach $200-250/SF. Of course, in very high cost and regulation-heavy inner city/downtown areas like NYC, Boston, Frisco, Chicago some DC areas, etc those numbers can double or more - some higher end attic/loft apartment conversions in NYC have exceeded $1000/SF.

If the HVAC system has to be resized (other than connecting into and adding some ducting and maybe upsizing the fan) because of the larger conditioned air space that can easily add another $5-10,000 to the total - either for replacing existing whole-house HVAC units with larger ones, or adding supplemental units for the apartment.

Also, if the DWV (drain, waste, vent) system is sized small in rare cases that needs some reworking too for several thousands of $ - typically only for much older homes (pre 1970's or 60's usually) with 3" or smaller DWV stack and street run piping rather than 4 inch. However, if the added bedrooms or bathrooms (how septic systems are typically "sized" or rated) mandates upsizing the septic/leach field capacity that can easily add a couple or few to as many as twenty thousand additional $, depending on availability of suitably permeable ground at legal distances from houses, adjacent properties, wells, and other septic systems.

This assumes no major permitting hassles are needed because the apartment is contrary to Planning and Zoning regs on square footage, prohibitions or restrictions on apartments in residential areas, total building height, attic bedrooms in tornado/hurricane zones, etc. Ditto to cost of any required additions to parking spaces for the house or other modifications required for adding additional living unit to the house.

Typically, your Architect can help with advice and information on those type of issues before you commit to the project, and help you with conceptual design and a preliminary cost estimate so you are sure not to get too far into the project before you knopw what it is costing.

Answered 3 years ago by LCD

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