How Much Does It Cost To Add a Room Onto a House? Additions and Alterations

Spread the love

How Much Does It Cost To Add a Room Onto a House?

How Much Value Does a Room Addition Add?

How Big of an Addition Can I Build?

Adding a room in your house is classified under renovations (alterations and additions) and the cost should be way smaller than a standalone construction. How much you will pay depends on the method of construction and type of materials used. Alterations are less costly than extensions which need their own foundations and floors.  But you might be asking, what is the difference between alterations and extensions?


In construction, alterations are adjustments and modifications to the existing structure of the house.  Elements such as floors, walls, ceilings, doors, windows, roof, finishes and fittings are altered, replaced, removed and refurbished without necessarily changing the gross floor area of the house. The square footage of the house is maintained throughout the alterations as well as the overall building superstructure (shell or envelope). According to the architectural renovations plan and needs of the homeowner, alterations can be done on the internal and external side of the house. Thus, without increasing or decreasing the gross floor area of your house, you can undertake major alterations as well as minor alterations. What percentage of your house is going to be altered? The higher the percentage, the higher the costs of renovation. Therefore, major alterations will be more expensive than minor alterations. Cost is usually determined by the type of replacement materials used as well as the type of skilled labour required to alter, remove, replace and install new material. Removing existing floor and wall tiles is a much harder job and more time consuming than removing laminated plank floors. This is due to the fact that floor tiles are adhered to the subfloor substrate with glue or cement, creating a very strong bond that makes it harder to remove without tools. On the other hand, laminated floor boards are easy to remove because they aren’t fixed to the subfloor, which allows them to float and expand as needed.

In alterations, existing rooms can be divided with partition walls to create an extra room. Alternatively, existing rooms can be converted into more spacious rooms by shifting and removing walls. In this case, two smaller rooms can be combined into one or the partition wall can be shifted to change the room dimensions. The positions of existing doors may need to be changed as well as the positions of existing windows. New doors might be necessary and a new window may be required for the additional room to comply with daylighting building codes. However, in most cases, when renovating a house, existing doors and windows are usually reused and repositioned as this will save you some money.

Alterations and Additions - Existing House Before Renovations CUT STAMPED

Existing House Before Renovations

Alterations and Additions - Existing House After Renovations_2 CUT STAMPED

Existing House After Renovations

Extensions / Additions

Extensions are also known as Additions in construction, and just like alterations, they fall under renovation works. Unlike alterations, extensions will increase the gross floor area of your house. Extending a house means the additional room will have its own substructure (foundations and floor) since you are building outside the existing square footage of the house. The additional room is treated as a new building so you will be required to excavate trenches for the foundations and build the substructure up to floor plinth level. Complete the new addition by building the superstructure and roof, and then installing the ceiling, doors, windows and finishes.

Alterations and Additions - Existing House Before Renovations 3D_3 STAMPED

Existing House Before Renovations


Alterations and Additions - Existing House After Renovations 3D CUT STAMPED

Existing House After Renovations – Alterations and Additions

The difference between alterations and additions is defined clearly by ADA and the City of Grande Prairie.

How Much Does It Cost To Add a Room Onto a House?

Cost of Alterations

In case you are planning to add a new room in your house, alterations are always cheaper than extensions. To give you an idea of the comparative costs, imagine a room in your house, for example a living room. It’s basically a rectangular shape or box. If you want to add a new room, say a study room. You have the option of dividing the living room into two parts, which involves installing a partition wall.  The new partition wall is all you have to pay for. If you have two small rooms next to each other, and you want a much bigger room, all you need to do is break down and remove the wall separating the two rooms. Your only costs here are for removal of the existing wall. Depending on the condition of your house, you should expect additional costs for refurbishing your room/house if the floor, walls and ceiling are in bad condition. This includes refinishing the walls, replacing floor tiles/finishes and painting the ceiling.

Altering existing rooms (breaking down walls) to make way for partition walls ranges from $1.23 to $1.32 per SF for stud walls, $3.12 to $5.69 per SF for brick/block walls, and $21.25 to $28.23 per SF for concrete walls. Installing new partition stud walls ranges from $2.00 to $3.70 per SF. A standard sized bedroom is 14×16 feet and if two sides are new walls, that will be $480 to $888 per room. Refinishing the walls will add an extra $0.39 to $5.26 per SF, and new vinyl tiles will cost $2.17 to $3.77 per SF. This converts to $187.20 to $2524.80 for wall refinishing, and $486.08 to $844.48 for new floors. The total sum of renovation costs will be $1153.28 to $4257.28 per room. The total renovation costs per square foot for adding a new room through alterations is therefore $5.15 to $19 per square foot.

Cost of Additions/Extensions

Additions as you will see in the calculations below are way more costly than alterations. The cost of building a house extension is comparable to that of a semi-detached or detached outside room, for example, a studio, guest house, garage or servants living quarters. The costs are closer to any of these mentioned structures which are attached to the house. Basically it’s like building a new detached room minus one side or two if the room is built in an enclosing corner of the house exterior. The elemental costs of building an extension for a wood-framed house are shown below:

The estimated building costs below are for a 14×16 feet room extension with low-cost material specifications:

  1. Exterior stud walls (includes drywall interior, wood siding exterior, gypsum drywall inside face ready for painting, R-19 insulation and rough sawn T-1-11 exterior grade plywood siding on the outer face)  – $3064.80
  2. Floor Framing (Includes Joists, Subflooring, Blocking & Fibreglass Insulation) – $1328.32
  3. New vinyl floor tiles – $526.40
  4. Drywall painting (exterior siding) – $595.20
  5. Drywall painting (interior) – $542.40
  6. Panelized wood roof system – $605.33
  7. Reinforced concrete strip foundations with stem wall, including excavation, backfilling, formwork, ground treatment, compaction and reinforcement – $3375
  8. Prehung solid core hardwood door – $250.86
  9. Vinyl-clad wood window – $313.11

Total Cost of Building a 14×16 Room Addition – $10,601.42

Room Addition Total Construction Cost Per Square Foot – $47.33 per sqft

The cost estimate above is for Class 6 minimum standard material specifications for an economic dwelling. Class 1 dwellings (luxury homes) will as expected make use of expensive high-end materials, so the building cost per square foot will be much higher for the same room size.

We can produce a Measuring List (Cost of Additions) like the one above for higher classes of material specifications, but to make it easier, we will use quality cost factors to estimate the cost of adding a room:

Average Cost Per Square Foot of Adding a Room Onto a House (USA)

Class 1 Luxury room addition – $258.82 per sqft

Class 2 Semi luxury room addition – $156.86 per sqft

Class 3 Best standard room addition – $100.55 per sqft

Class 4 Good standard room addition – $73.93 per sqft

Class 5 Average standard room addition – $60.11 per sqft

Class 6 Minimum standard room addition – $47.33 per sqft

Average Cost of Adding a 14×16 Feet Room (USA)

The cost of building a 14×16 feet room addition will be as follows:

Class 1 Luxury room addition – $57,975

Class 2 Semi luxury room addition – $35,136

Class 3 Best standard room addition – $22,523

Class 4 Good standard room addition – $16,561

Class 5 Average standard room addition – $13,464

Class 6 Minimum standard room addition – $10,602

Cost of Adding a Room Onto House - Extensions - Copy

Cost of Adding a Room Onto House – Extensions

As you can see, room additions (extensions) always cost a lot more than alterations for the same gross floor area. If you are on a tight budget, you should divide an existing bigger room into two, rather than building an addition.

Since wood-framed houses are the most common type of dwelling in the USA, it should be cheaper to build an addition because wood is cheaper than bricks and concrete walls. Concrete wall dwellings are the most expensive followed by stone and brick walls. Obviously, if your house is built from bricks, you should use bricks to build an addition to maintain structural/architectural consistency.

How Much Value Does a Room Addition Add? Financial Pros & Cons Of Adding A Room

Adding an extra room increases the value of your home whether it be a bedroom, living room, guest room or conservatory, allowing you to sell your home by as much as 15% depending on the finishes and fittings. Alterations and conversions will not increase the value of your home in most cases, but extensions will increase the property value because of increased floor square footage. To get every penny’s worth out of your home, focus on major visible elements which will be readily appreciated by the client on sight. This includes features such as built-in cupboards and closets, wall finishes, floors and landscape.

How Big of an Addition Can I Build?

As we said earlier, alterations do not change the gross floor area of the existing house, but extensions (additions) will. To calculate the appropriate size of the required addition, you should first make sure that the additional room meets the minimum standard size according to building codes. The minimum standard size of a room depends on its usage and location on the site plan.

According to IRC Code R304.1 (2015), the required minimum floor area of any habitable room is 70 square feet or 6.5 square metres, and the minimum horizontal length of each side of the room is 7 feet or 2134mm in metric units. However, these rules don’t apply to kitchens, which can be less than the stipulated minimums. Previously, the IRC code made provisions for one habitable room with a minimum size of 120 square feet, but the code was amended resulting in the removal of this requirement.

Now that you have the codes right, you can build an addition with the following dimensions: 10×10 room, 12×12 room or 14×16 room. As long as the minimum dimensions are met, you can have various sizes for your rooms. Think about what will go into that room as well, the furniture, fittings, equipment and other installations. Make the necessary adjustments to get the right space for your needs. Living rooms, dining rooms, bedrooms, family rooms, recreational rooms, eating rooms and garages are usually larger than 70 square feet, exceeding the minimum floor area required for any habitable room. Pantries, laundries, bathrooms, saunas and utility rooms are usually smaller than the minimum.

So you have gotten your tools and you are ready to build? Not yet. There are other codes waiting for you. Before you start any excavations or building, you must locate and identify the setback line (aka building line) on your private property. Setback lines are prescribed by the local municipality in your town or city. The offset for a setback line is measured from the property boundary line. You are not allowed to build within the offset area also known as the setback area.

Once you have measured the setback line inside your yard and around the house, you should transfer the measurements onto your CAD program site plan. Draw the setback line on your site plan using dashed lines. Thus, when you are planning and determining the size of your extension/addition, you should make sure the drawing doesn’t encroach the setback line.

Spread the love