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

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.

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