Cost to Build a Duplex

Hi Carl,

I was wondering if you could comment on the cost to build comparison between a twin (duplex) per sq ft vs. a single family house per sq ft.

For instance, a 2-story, 3,200 sq ft single family house should be cheaper to build per sq ft than a 1600 single family house with the same quality standards,

So, I'm curious how the overall cost per sq ft would compare if a 3200 single family house was split in two to make a duplex.

The footprint would be nothing fancy, 40 feet x 40 feet (4 corners).

If it helps, I'm in Pennsylvania. Thanks for weighing in!

1645 sq ft per unit Duplex from Building Designs by Stockton

I believe the following quote, taken from my blog of Monday, February 9, 2009 on Plex Building should answer your question.

"A four unit house (4 plex) will cost at least 4 X the price of 1, maybe more.
A three unit house (3 plex) will cost at least 3 X the price of 1, maybe more.
A two unit house (duplex) will cost at least 2 X the price of 1, maybe more.

The “economy of scale”, that is, the price per sq ft drops as the house gets larger, is mostly overridden in “plex” building, by increases in the number of kitchens, baths, HVAC units, parking, garages (if any), etc., as well code compliance for multi-family (fire walls, sound proofing, visitor parking, etc.), as well as permit costs."

Hope this helps,