The Side by Side duplex is one of the most common small multi-family units. It makes up a big part of the “missing middle” of housing types. A side by side duplex is a great project type and this document looks to explain some of the ideas behind the type and how to implement it.
pictured above: a historic duplex in Annapolis
The Side by Side is an older type, being found early in Colonial cities, then known as a double house, twin house, or attached house. You can find examples in urban areas that are essentially paired rowhouses and more relaxed types that appear as a larger single home. The Side by Side was substituted by The Over Under Duplex (click to revisit the BDS post) in many cities as the Over Under would plug into a more typical single family lot size. During the late 60’s and 70’s the side by side returned as a popular unit type. These types are often suburban in character and not especially note worthy.
Today, this is a great product type. Duplexes in general are great houses for young people looking to buy or build a first home. They provide income and help that first time home buyer get into wealth building. Duplexes also fall under the One and Two Family Building Code (International Residential Code in most states) which allows typical construction methods and use of residential trades.
Advantages of the Side by Side Duplex:
Simplifies Privacy: There is clear front and rear yard privacy for these units and a rear yard fence can be easily added for additional outdoor space privacy.
Simplifies Separation: Fire and sound separation is generally very simple in a single continuous wall. This is more so than the Over-Under Duplex type which involves methods that most residential builders may not be familiar with.
Residential Building Code: These units are always covered under the International Residential Code which allows typical residential construction methods and materials. Your builder or sub-trades will not require a commercial license.
Corner Lots; a corner lot can really be a special unit type here. We like to shift the entry of the side unit over to the side street which really enhances the privacy of the units.
Challenges of the Side by Side Duplex:
Sound is always one of the main issues in any multi-family project. Although this unit simplifies the sound & fire control wall into a single wall, care must be taken to address the sound control. This is the area to invest in solid system and not rely on the code minimums. The typical mode minimum wall system will allow some sound to be heard. Care should also be taken towards which rooms are adjacent to the separation wall. We recommend a physical separated double stud wall with an internal airspace and drop in fire partition. Sound insulation batts and acoustic gypsum board complete a very good system.
Design Concerns: There are some unique challenges to a side by side duplex. Generally, the lots are tight and that makes it difficult to design a master down plan unless your lot width is approaching 70’ in width. Typically you end up with bedrooms on the second level.
Where to use the Side by Side Duplex:
These work best in the T-3 to T-4 transect zone and blend in well with the typical single family streetscape in scale, form and mass.
Great infill units in most cities.
In Greenfield Development, typical units make great transitional streets from a single family neighborhood to the town center or multi-family blocks.
What kind of lot do I need? Side by Sides tend to need more width than the Over Under type. Some of our smallest units are 16’ wide which make the whole unit 32’ wide. You typically will want 5’ on each side (more if you need a drive on one side) so you are in the 45’ wide lot range for a small unit and larger ones fit best on a 50-60’ wide lot. Depth depends on the available access to an alley but a typical 100’ deep lot works in most cases. Keep in mind, a wider lot allows more side/rear yard private space, which becomes more valuable as your unit moves up the economic scale.
We have designed and built these units for twenty-plus years and have found them to be accepted well in the market with a modern update to the design of course. These can be smaller units that function as great starter homes for a young person or family that helps cover the mortgage, or we have also built larger high-end market homes that are popular with the older retired crowd or retired singles.
Above you'll see images of our own built units, as well as a historic example of the type in Annapolis. Brown Design Studio offers 20 years of experience building great places and the buildings that are the fabric of those places. Duplex and other unit types plans can be found at our website or by contacting us directly.