Question on Converting SFR into a Duplex

2 Replies

Hello BP community,  

I’m helping orchestrate converting my parents rental property into a duplex and would like some insight since this is the first time attempting this. 

The house is in a smaller town in Colorado. Population: 8200 (and growing rapidly). 

Lot size: 9,365 

House size: 760sqft (2bed 1 bath)

Zoned: R2 for Duplex 

Owned Free and Clear 

Possibly have to fix foundation

I have already contacted an architect to give me an idea about pricing but I had a few questions before I send him info. 

1) how do I determine what size I would want the duplex to be. 
- based on other duplexes around?

- based on how many rooms wanted?

- based on the size of the lot?

- all the above? 

Any advice or suggestions about anything to do with converting a house into a duplex would be much appreciated!


Chris Reyes 

Hi Chris! Sorry this response is a little delayed.  The piece of information that you've stated, Zoning as R2 for Duplex, is the best item to help answer your questions. In the City's Zoning code, you can look up the R2 and find what is required and/or what is allowed with this zoning.  

Your zoning will have required setbacks for your front yard, side yards, and back yard lot lines. Plus, there will be a min/max size of your building (the minimum will be a SF and the max may be a percentage of the lot).  If the nearby lots are also R2, you'll likely have a similar size duplex.  There will also be a min/max height that your building can be.  But the size of your duplex will have to fit into the requirements of your zoning, so that is already laid out.  

Now, if you're asking a deeper question on the size of your duplex as it relates to cost of your duplex plus what you can rent it for and how you can get the best rate of return for your investment, that's beyond my experience!  I do engineering for developers, so I do not have much familiarity with the finances part of the investing. But I hope some of that info helps you!

Hi Chris,

Adding to what Jamie said just because you can build a larger duplex does not mean it is the most efficient use of that foot print within the setbacks.  There is a reason on a sq ft basis that bachelors usually fetch a higher rent per sq ft. over a 2 bedroom. Pay close attention to your setbacks, build what you're allowed to build by right in the zoning code and then determine how much it will cost per sq ft. (Keep in mind that building vertical is cheaper then building out) so pay attention to your height restrictions and your ability to possibly dig down a bit too.  Once you know how much it will cost to build, what it will likely appraise for and what you'll likely get in rent (, rentometer, agent market report), you can really start adjusting the size of the unit within the footprint and sharpen your pencil even further to see if you have a viable project.

Some tricks to help people out that are looking at infill opportunities:

1. Always go to the planning website for the local town or city and look up the code.

2. Google Interactive GIS Map "CITY NAME HERE" and start browsing the area.

3. Pay close attention to items that will make your project difficult, waterways, water courses, ditches, canals etc these are either easy obstacles or deal killers.

4. Check FEMA flood maps on their website for the property

5. Once everything checks out, contact a planner and do exactly what Chris posted above to the BP community.  Ask that planner to go through the property with you on a call or a zoom call where they can share their screen and talk you through what they see. These folks are amazing to work with and they want YOU (the reader) to do things properly.  They are there to help everyone! From the largest experienced local developer to an old  man who wants to sever a chunk of land off his farm and still pays his bills at the bank because he cannot use a computer.

6. Look at other development applications in the area on the city website.  Get a sense of what kind of projects are in the pipeline and then see if they are pushing the rules in the zoning.  if they are find out why -- is it the official plan, the secondary plan, is it an opportunity zone, a hamlet? 

7. Start talking to people who do development.  The ones who do it, love to talk about it ;)