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Before You Design Your Addition

Before you design your addition/renovation, become familiar with these basic code issues and design considerations.

If you’re designing your addition or renovation yourself, there are basic code issues and design considerations that you need to keep in mind. Look to the International Residential Code for specifics (Building Planning, chapter 4) and to the Massachusetts amendments. 

The following is a list of basic code issues that come up in the course of a typical project:

  • Hallways must be at least 3 feet wide and 7 feet high.
  • Stairs in Massachusetts must have a minimum tread of 9 inches and an 8 ¼-inch riser.  The headheight over the entire stair must be 6’8” minimum.
  • The minimum size of a bedroom is 70 square feet, with a minimum of 7 feet in one direction. 
  • A room under a sloping ceiling must have all of the required floor area with a ceiling height of 5’, and at least 50% of the required floor area must have a ceiling height of 7 feet or more.
  • A loft accessed only by a ladder cannot be considered anything other than storage.
  • Habitable rooms must include windows. The area of the windows must equal 8% of the floor area for light, and 4% of the window area must be operable or mechanical ventilation will need to be incorporated.  


  • Every bedroom in a single or two-family home must have a secondary means of egress. This could be a door or a window.  Massachusetts code allows a window with a 5 square foot opening, 21” x 24” minimum clear opening. The maximum sill height of this window is 42 inches. This is to allow the firefighters to access the room with their equipment in case of emergency.  In most cases, a non-compliant window will be allowed to remain in an existing bedroom, but check with the inspector to be sure. 
  • Bedrooms in a basement are tricky due to egress requirements, see above.  The required window must have a window well that is big enough for the firefighters to use in case of emergency.  If a basement is mostly below grade you will likely need to dig out around the bedroom window.  

Third Floors

  • Third floor renovations can be complicated and the regulations vary from town to town. There are restrictions on what can be built on the third floor — usually, 50% of the area of the second floor may be developed on the third floor. The area is calculated using space of a certain height, which varies from 5-7 feet to all useable space. 
  • Restrictions on dormers vary from one town to another, so check local zoning before planning. 

A bathroom CAN open onto a kitchen, but it just feels gross. 

In my interactions with people designing their own spaces, I’ve heard all of those issues come up.

Besides being aware of all these rules, here are some bigger picture questions to ask yourself as you’re beginning to design your addition:

1. Think about your furniture and where it will be able to fit in your renovated rooms. Be sure to examine bed placement in a bedroom, including the width of the bed and the nightstands.  Ideally, you will be able to fit a king-sized bed and two nightstands against at least one wall in the room.  

2. Think about the adjacency of rooms and their uses. How will you and your family be using the spaces? People dream about open plans, but what are they like in reality, and how well would they fit your situation? Keep in mind that life can change a lot in five or ten years. Kids get older, for example. 

3. Speaking of getting older, if you plan to stay in your house for a long time, think about making it easy for people with limited mobility to live in or visit your home. Look into Universal Design, a process of inclusive environmental design that strives to make spaces as accessible as possible to as many people as possible, without the need for special modifications or assistive devices.

4. Finally, if your home is a condo, your project may be more complicated, or not allowed.  For example, you are probably not going to be able to build an addition onto your space. Making structural changes or moving a toilet may impact other units. Check your condo rules before you start planning your project.

When you consider all these basic code issues before you start designing, you will have a smoother, happier renovation.

Not sure how to add all these codes into your dream renovation? I offer a free Project Coaching Call! Contact me to set up a time for our call: