How to Build a Room Addition in 8 Steps

Know what’s involved in room addition construction

Deane Biermeier
Written by Deane Biermeier
Updated July 14, 2022
Mother in the nursery room holding her child
Photo: Cavan Images / Cavan / Getty Images


This one takes some serious know-how.

Time to complete

2920 hours



Only take it on if you have past experience.

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What you'll need:


  • Measuring tools
  • Various saws
  • Carpentry tools
  • Hand tools
  • Ladders or scaffolding


  • Concrete and block
  • Lumber
  • Roofing materials
  • Insulation materials
  • Drywall
  • Paint and finish materials
  • Trim lumber
  • Flooring
  • Windows
  • Door(s)
  • Siding
  • Electrical and other mechanical materials

Building a room addition is a big job, and most homeowners hire professionals to get it done. However, understanding how to build a room is a huge plus when searching for local contractors. It’s also necessary if you plan to be your own contractor or wish to perform some tasks yourself to save money. In most cases, your contractor will be performing all of these steps.

  1. Plan Your New Room 

    Architect in her studio is sketching floor plan
    Photo: Jose Luis Pelaez Inc / DigitalVision / Getty Images

    Every large remodeling project needs to start with a plan. Many homeowners choose to hire the help of a local architect or a design-build contractor before making any plans. Here’s what to do.

    Create several drawings, including a floor plan and interior and exterior elevation plans. Submit those drawings and an application at your local permitting office so you can obtain a building permit and, if necessary, other needed permits. 

    You’ll also need to call 811 to have your utility companies perform an underground survey.

  2. Build a Foundation

    New home concrete foundation
    Photo: graja / Adobe Stock

    Your builder (or foundation contractor, if you’re acting as your own contractor), will bring in some heavy equipment for this step.

    Dig a hole to accommodate the frost-depth footing or concrete slab, and pour the concrete foundation or slab. Install concrete blocks onto the new foundation, if necessary. Then, have the inspector sign off on the foundation.

  3. Build Walls and Roof

    Wall installation in a new room
    Photo: JamesBrey / E+ / Getty Images

    Speed is your friend during this step to make the project weather-tight and avoid water damage that can happen during delays.

    Install the floor joists and subfloor sheeting. Frame the exterior walls, the roof rafters, and install roof trusses. Cover the exterior of the walls and roof framing with sheeting (plywood or other similar material).

    Next, install roofing shingles or other roofing material, and an exterior moisture barrier and seal with sealing tape. Add windows and an exterior door, if they’re part of the plan.

    Have the inspector perform a framing inspection. Install exterior siding at any time after the previous steps.

  4. Add Mechanical Equipment

    Engineer installing new air conditioning duct
    Photo: sturti / E+ / Getty Images

    Your room addition needs electrical and HVAC components, and depending on the addition, you may need plumbing as well. 

    Install heating and cooling ductwork and the rough-in plumbing, if necessary. Put electrical wiring in place last behind the first two mechanical systems. Have the inspector perform rough-in mechanical inspections. 

  5. Add Insulation and Vapor Barrier

    Construction with insulation and vapor barrier
    Photo: gen1607 / Adobe Stock

    Insulation is a requirement in every living-space addition. To install it, use spray foam insulation or install batt insulation below the roof rafters. Also use spray foam insulation or install batt insulation into exterior wall cavities.

    Create a vapor barrier envelope with plastic sheeting, sealing tape, and caulk throughout the room, then have an inspector give the OK. 

  6. Install Drywall and Paint

    Workers applying mud to drywall
    Photo: GeorgePeters / E+ / Getty Images

    Now it’s starting to look like a room. Install drywall on the ceiling and walls. Finish the drywall by mudding it, and then five it a coat of paint. 

  7. Finish Mechanical Installations

    Electrician installing wires in a new house
    Photo: Antonio Garcia Recena / Moment / Getty Images

    Now, the mechanical technicians can return to complete their work.

    They should install any HVAC components such as duct grilles or radiant heaters. If plumbing is part of the project, install the plumbing fixtures now. Put electrical outlets, switches, covers, and lighting components in place.

  8. Install Floor and Trimwork

    Woman installing new laminate flooring
    Photo: Mint Images / Mint Images RF / Getty Images

    This part always seems to take the longest out of the sheer anticipation of getting to use your new room. 

    Install the flooring material. If you plan on having carpeted floors, this step can wait until after the trim work step. Set the interior door or doors. Apply a coat of finish to the trim boards and install the trim work. Apply a final coat of finish to the trim. 

    Call the inspector to perform the final inspection and sign off on the project as complete. 

Building a Room Yourself vs. Hiring a Pro

Building a room takes several months to get from the planning stage to the relax-and-enjoy stage and is a significant investment no matter how big or small the project is. Choosing to be your own contractor or performing some of the steps yourself can save some money on labor, but often not enough to make it worthwhile. 

The project costs range from $80 to $200 per square foot to hire a contractor. You may be able to negotiate a lower overall price with some contractors if you would like to do some of the work.  

Additional Questions

What is the most affordable room to build?

Other than simply building a divider wall to turn one room into two rooms, the most cost-effective way to add a room to your home is to finish the attic. In many houses, the attic is ready-made for a simple renovation to turn it into a bedroom or home office for around $30 to $60 per square foot.

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Get quotes from top-rated pros.