House Expansion: home extension, basement or second storey addition

Since purchasing your home, planning for its extension or second storey addition has probably been your most ambitious project. How much does a home extension or second storey addition cost? Do I need a permit? Where to find a trusted contractor? How to avoid being misled? Do I need an architect? These are all questions you ask yourself, and if you don't know where to start, we built an exhaustive guide for you!

This guide will allow you to discover all the stages of a second storey addition or home extension project, from its initial definition to its final completion. In addition, this guide provides you with valuable advice in order to make each stage of your project a success!

Guide Plan

home extension

Photo Credit: Hanson Fine Building

Move or expand your house?

Does your house no longer meet your needs due to lack of space and you’d like a change? You then have two choices: move or transform your house to increase its surface area.

There are many motives for undertaking a transformation work. It is very common to see new buyers undertake home renovation work as soon as they receive the keys to their new house in order to adapt it to their needs, whether it be to transform a room into a bathroom, open walls, modify the kitchen.

If for you, moving is not an option because you love your neighborhood so much that you rather invest in your heritage, and so to increase its value, you can opt to transform your home! This is your most ambitious home renovation project and quite possibly your biggest investment after buying the home, but where to start?

What are the types of house expansion?

For the expansion of a house, several options are possible which can be dependent on your present and future needs (or those of a future owner), the existing configuration of the building, the land area, or the city requirements in your neighborhood.


Average price: $225/sq.ft

Photo Credit: Ryan Duebber Architect, LLC

Basement addition

Adding a basement is a popular expansion option, especially for townhouses in Montreal. From a technical point of view, there are several construction options that emphasize safety much more than other types of expansions. In fact, before starting any excavation work, if the existing building is a single-family house, it must be stabilized with the house lifting.

It is also possible to transform your crawlspace into a liveable space by doing underpinning work. This means carrying out the expansion by digging under the foundations, then constructing the new foundations, wall and footing, under the existing ones as the excavation progresses. The minimum height required for a liveable room in a basement is 6 feet 11 inches.

second level home addition

Average price: $200/sq.ft

Photo Credit: Studio MMA Architecture + Design

Second storey addition

If your home is a single family, adding a storey is definitely an option to consider. It allows you to increase your living space without reducing the space in your yard. From a work complexity point of view, it is less challenging than a basement addition, especially if you decide to replicate the layout of the existing floor onto the new one. However, your architect or architectural technologist will need to ensure harmony between the existing building and the expansion.

garage home extension

Average price: $135/sq.ft

Photo Credit: Birdseye Building

Garage addition

Adding a garage also counts as a type of home expansion. We see more and more garages with extensions in order to create additional rooms such as a powder room or even a family living room.

garage home extension

Average price: $160 to $195/sq.ft

Photo Credit: 51 Architecture

Extension on piles or foundation

If you have a garden in the backyard or back of the house, expanding by adding an extension is definitely an option. It will allow you to create more open space and give your home a more modern face. There are 2 types of foundation for this type of expansion:

Extension on a concrete foundation:

this is the option to choose if you wish to make your extension by including a room in the basement (under the extension) or an extension on several floors (for example, basement and ground floor)

Extension on piles:

it is cheaper. However, it is not possible to use this option if you want to add a basement room or an upper floor on your extension, now or in the future.

How much does a house expansion cost?

The first question that usually comes to mind before starting your home expansion project is: how much does it cost?

At this stage, it is important to have an idea of the cost of the work to know the scope of such a project. It varies according to several factors such as: the type of finishes (flooring, windows, plumbing equipment, etc.), the type of room in your extension (bathroom, kitchen, living room, etc.), the location, the work schedule.

Here is the average cost schedule of a house extension in Montreal including finishing, depending on the type of extension:

House extension price

Example with 800 sq.ft

Garage addition

$135/ sq.ft


Basement addition



Second storey addition



Extension on piles



Extension on foundation



These prices are market averages based on standard expansion projects of 400 sq.ft and greater floor surface. For a smaller expansion, the smaller the area, the higher the cost per sq.ft. It is indeed more difficult to have economies of scale in small quantities, both for construction materials and for labor.

The smaller the area, the higher the cost per sq.ft.

Think long term! Expanding or modifying your home is a great investment on your property! It is therefore necessary to project 20 years in time and adjust the scope of the work accordingly in order to be able to optimize your investment as much as possible.

What are the steps to carry out a house expansion?

home addition kitchen

Step 1

Definition of the scope of work


Desire to carry out a home expansion

Tools and Technique

Brainstorming, looking for inspiration, reading building guides;

Expert judgment


High level description of the scope of work;

List of requirements

This is the most important step in your project. The work and time invested in it will have a direct effect on the likelihood of your project being successful! Take the time to define your needs on your own.

It is important to clearly describe the problem you are trying to solve in order to define the project’s objectives. In other words, you must compile all the data that allows you to understand the existing situation and the desired situation (through a text description, sketches, photos of the existing space, photo inspirations, etc.). Essentially, you must answer these questions:

  • What type of home expansion do you want: home extension, second storey addition, basement addition, garage addition?
  • What is the total surface area of the home expansion? How many floors are there?
  • How many rooms do you want and what are they (kitchen, bedroom, bathroom)?
  • Do you need a centralized HVAC (heating, ventilation and air conditioning) system?
  • What is your budget?
  • When should the work be done?
  • What is the existing situation (before the work)?
  • What is the projected situation (after the work)?

This preliminary document describes, at a high level, the scope of the work. It is the basic document that you will give to a building expert, for example an architect or architectural technologist, an engineer, or an interior designer. It collects all your needs and requirements.

Think long-term

Think long term! Expanding or modifying your home is a great investment on your property! It is therefore necessary to project 20 years in time and adjust the scope of the work accordingly in order to be able to optimize your investment as much as possible.

Billdr guides you in defining your project and provides you with the necessary documentation to help you collect your needs.

Speak with an advisor
farm house addition

Photo Credit: Wyant Architecture

Step 2

Information from the City


High level description of the scope of work

List of requirements

Tools and Technique

Expert judgment (City)


Informal approval of the project (no document will be submitted by the City at this stage!)

Please note, this step does not pertain to the building permit application! It allows you to get information from the City to check the acceptability of your project.

By going to the permit counter, you can present your project to a city official to find out if it is eligible or if it needs to be corrected by adjusting the definition of the work. For example, in your district, there could be a limit on building height. Therefore if you want to expand your home, you will probably think of an extension to the side of the house or to the garden.

To carry out house alteration work, you will need a building permit granted by the City before starting the work. From one district to another, the municipal rules may differ in terms of modifications, second storey additions or house extensions. Here are some examples of questions you can ask:

  • Am I allowed to modify my home (as described in step 1)?
  • What is the time required to obtain a building permit for this type of project?
  • What documents will I need to obtain the building permit?

Here are some examples of documents that may be requested by the city for the granting of a building permit:

  • Architectural plans (produced by architect or technologist)
  • Plans of a structural engineer
  • Concept plan in 3D
  • Shop drawings or photos of elements visible from the outside such as the exterior siding, doors, windows
  • Certificate of localization
  • Survey plan
  • Building sheet
  • Proof of insurance from the contractor performing the work
  • etc...

backyard home extension

Photo Credit: Go building

Step 3

Stakeholder identification


High level description of the scope of work

List of requirements

Tools and Technique

Expert judgment


List of stakeholders

Typically, for a standard home expansion project (construction budget around $ 100,000), you will need an architect (or architectural technologist) and a structural engineer. Also, we often get to observe the interior designer’s involvement in projects

The list of stakeholders kits all the people who will be involved in your project, regardless of their area of expertise. In general, here are the stakeholders most often involved in a house expansion project:

  • Client / Owner
  • Architect (or architectural technologist)
  • Interior Designer
  • Engineer
  • City
  • Insurer
  • General contractor, his subcontractors and suppliers
  • Owner's suppliers

An expert’s primary goal (here the term expert refers to an individual member of a professional order, such as an architect, technologist, engineer, doctor, etc.) is to ensure the safety of the public. Similar to the healthcare sector, there are several different experts with diplomas, fields of expertise, each with different reserved acts. Building construction operates the same way, where experts hold different responsibilities.

In a new construction, building expansion, or extension project, several disciplines are involved: architecture, building services (ventilation, air conditioning, plumbing), electricity, structure, foundation, soil study, vertical transportation, fire safety, etc. As a general rule, the larger the project, the more stakeholders are involved.

Billdr walks you through this stage by evaluating the different options available to you for the work you plan to undertake as well as by identifying the needed resources.

Speak with an advisor
kitchen home addition

Photo Credit: Go building

Step 4

Project planning

Planning your project is an important step. This step is to educate yourself and prepare for the upcoming adventure. It consists of having a "game plan" for each aspect of the project such as: scope of work, budget, schedule, list of stakeholders, and risks.

This guide offers several tools to prepare and help you with your project management. However, each project is unique and must be managed on a personalized basis.

The goal of your dedicated renovation advisor is to make your project a success and this involves giving tailor-made assistance according to the needs of your project.

Speak with an advisor
home addition individual

Photo Credit: Dana Webber Design Group

Step 5

Hiring an architect (or an architectural technologist)


High level description of the scope of work

List of requirements

Tools and Technique

Meeting, brainstorming, data gathering


Expert judgment


Architect (or technologist) contract

High level estimate of the cost of the works

The architect or architectural technologist’s role is, through the realization of plans, to materialize your vision in order to make it tangible. The architect or architectural technologist should discuss with you in order to fully understand the motivations of your project, your tastes, but also take into account the design of harmony between the existing house and the new layout.

What should the mandate (or contract) of the architect or architectural technologist contain?

The architect's mandate consists of the agreement you have with them, where they define, among other things, the terms of your contract, deliverables, and fee costs. This is their service offer or contract in which you both agree to. Here are some recommendations concerning the content of the architect or architectural technologist's contract:

Payment method

Go with a flat rate mode instead of the hourly mode. If you have accordingly defined your needs beforehand, the architect is able to estimate the time needed to fulfill their commitments. Please note, if you make changes in the description of your needs along the way, additional costs may be charged on an hourly basis.

Payment terms

Billing for the architect should be based on the progress of their work. If the deliverables are defined and detailed, they should send an invoice only after the deliverable is issued, therefore according to the value of the work provided to date.

Hourly rate

Even if you are in flat-rate mode, ask the architect to include his hourly rate in his service offer. This is useful in the event that there are changes in their contract along the way (for example, change in your needs, widening of the scope of work, consultation during the construction period).


Ask the architect to clarify the scope of their work and clearly list the deliverables of their mandate. Depending on the complexity of the work, it is recommended to have several deliverables depending on the development and progress of work:

1 - Concept(s): We recommend that you first ask the architect for several concepts (1 to 3) depending on the complexity of your project. This deliverable allows you very quickly to see if you and the architect are lining up in the same direction. If necessary, it will allow the aim to be rectified.

2 - Plans at 30%: Completing plans at 30% complete allows you to quickly integrate your comments.

3 - Plans at 75%: Completion of plans at 75% complete allows you to integrate your comments for the final version of the plans.

4 - Plans for permit: These are 100% plans, with the mention of “for permit” on each page. This version of the plans that will be used to apply for the building permit from the city. Permit plans are also used by contractors during the bidding period. They contain all the information a contractor needs to provide you with the price of the work.

5 - Plans for construction: These are 100% plans and authorize the execution of the works following the acceptance of the plans by the city. In good practice, a contractor will not carry out the work if the plans do not mention "for construction". It may happen that the architect has to modify the version for permit following the comments of the city. The changes will be reflected in the plans for construction and the general contractor will have to adjust their prices accordingly and as needed.


You need to come to an agreement on the due date of the deliverables. This will allow you to plan in advance a good amount of time to read the documents but also for the architect to meet their commitments.

Work supervision

Work supervision is not necessarily included in the architect's mandate. In fact, the architect has no obligation to monitor the work or visit the premises (during or after the work). It is a separate mandate, distinct from that of carrying out plans. If you want the architect to be present during the construction phase, you can come to an agreement on the number of site visits to be made or remote involvement in project management. However, additional costs will then be expected (around $400 per visit and costs billed per hour for project management).

What is the difference between a technologist and an architect?

The technologist and the architect all operate in the architectural field with one main difference in responsibility.

According to the Architects Act (article 16 and 16.1), a technologist can only carry out and sign plans for residential, commercial or industrial construction and renovation projects with an area less than 3,200 sq.ft whereas an architect has no restrictions on architectural plans

Depending on the municipalities and the type of work, plans made by an architect may be required by the city for the issuance of the building permit. Where applicable, plans made by a technologist are accepted.

home addition individual

Photo Credit: Studio MMA Architecture + Design

Step 6

Design of architectural plans

The process of carrying out construction plans begins with a meeting with the expert (architect or architectural technologist). First, it is a question of taking the house’s measurements.

The expert will then base on the existing to draw the demolition plans (if necessary) as well as the plans of the new layout, known as the “construction plans”.

Construction plans are important for the following reasons:

  • Plans are first and foremost a means of communication; they are the best way to describe your construction work! In a plan, you’ll find: drawings of the premises’ current state before the work, the demolition work, the construction work with details concerning the dimensions of the rooms, the materials, the finishing specifications, the siding, flooring, foundation, sound and thermal insulation, etc.
  • The plans allow contractors (as well as their subcontractors and suppliers) to estimate costs and make quotes. They are an essential tool for any work carried out, because they compile all the information concerning the scope of the work in a single document, without ambiguity, misunderstanding or risk of interpretation. They may be mandatory as it is a legal requirement that for certain given work, the design must be made through plans signed by a designated professional.
  • The plans are necessary for obtaining the building permit.

Receiving the architectural plans and depending on their progress, Billdr will assist you in reading and understanding the content of the documents.

Then we make comments and recommendations to challenge the designer for optimization purposes.

Our detailed cost estimate throughout the plan progression allows us to better control the budget and your expectations when receiving quotes from contractors.

Speak with an advisor
garden home addition

Photo Credit: Studio MMA Architecture + Design

Step 7

Hiring a structural engineer


Architecture plans

High level description of the scope of work

List of requirements

Tools and Technique

Meeting, brainstorming, data gathering



Engineer contract

In Quebec, the title of engineer is reserved for members of the Ordre des Ingénieurs (OIQ). Like the architect, the engineer is a member of a professional order whose mission is to ensure the safety of the public. Contact information for all members of the order is available to the public on the OIQ website. You can therefore verify the identity of your engineer by entering his name in the OIQ directory.

What is the difference between architectural plans and engineering plans?

Usually, for your home expansion project, you will need an architect (or architectural technologist) and a structural engineer. While the architect is responsible for designing the new layout and choosing the types of construction materials, finishes, etc., the structural engineer is responsible for designing and sizing the structural elements (which ensure that your house holds up), whether they are wood, steel or concrete.

For example, during the design of your project, the architect can choose a reinforced concrete foundation. However, in the architectural drawings, there will be no specifications regarding the selected concrete, no plan of reinforcement within the poured concrete, nor will there be walls and footings dimensions.

Indeed, the architect does not have the expertise to give these directives, therefore it is not his professional responsibility. According to Quebec law, the design and sizing of structural elements is an act reserved strictly to engineers, members of the Ordre des ingénieurs of Quebec. To determine if something is structural, think about whether the house would collapse if you remove that element.

Did you know ?

According to Quebec law, the design and sizing of structural elements is an act reserved only for an engineer, member of the Ordre des ingénieurs du Québec.

To determine if something is structural, think about whether the house would collapse if you remove that element.

What should the engineer's mandate (or contract) contain?

Compared to that of the architect, the engineer’s mandate is generally smaller and often involves providing detailed drawings of structural elements. The engineer should provide the plans for permit and the plans for construction. We recommend that you include site visits in the engineer's mandate (additional cost of approximately $ 500 per visit to be expected) for the supervision of the project.

How much does an engineer cost for a house expansion or extension?

The hourly rate for a building engineer is between $95 and $120. As a general rule, for the size of such a project (around $100,000), engineer fees can vary between 1,000$ and 5,000$ (before taxes), depending on the complexity of the structural work.

home extension kitchen

Credit: Affleck Property Services

Step 8

Design of structural plans


Architectural plans (base plans)

Tools and Technique

Meeting, brainstorming, data gathering

Engineer expertise


Structural plan sealed and signed by the engineer

The structural engineer's plans consist of defining the structural elements of your extension or expansion. These elements include, among others: foundation, concrete slab, load-bearing walls, columns and beams, lintels above doors and windows, etc.

Structural plans are required so that the general contractor has precise information on how to build the structural elements of your extension. According to the Law on Engineers, the opinion of an engineer is mandatory for any construction work on a building’s structure.

Often general contractors can recommend a structural engineer they are used to working with. However, we recommend that you hire a structural engineer independent of the general contractor to avoid conflicts of interest. In addition, a contractor needs to receive the engineer's recommendations on structural work before providing you with the final price of his quote


However, we recommend that you hire a structural engineer independent of the general contractor to avoid conflicts of interest.

In addition, a contractor needs to receive the engineer's recommendations on structural work before providing you with the final price of his quote.

backyard home extension

Credit: Martyn Clarke Architecture

Step 9

Request for a building permit


Plans (architecture, structure)

Building sheet

Certificate of location

On demand technical sheets (window, door, exterior cladding)


Tools and Technique

Data analysis, expert judgment



Building permit issued by the city

A building permit is an authorization from your municipality to undertake specific renovation work including extensions and expansions. For more information, consult our building permit guide.

As part of your expansion project, we suggest that you start your process of obtaining a building permit from the City upon receipt of the architectural plans. Some municipalities may also require structural engineer plans. If this is not the case, you can begin your dealings with the City at the same time as the preparation of the structural plans

How much does a building permit cost?

The cost of a building permit varies from city to city. In general, in the city of Montreal, the cost is $ 9.8 per $ 1,000 of work, or 0.9% of the value of the cost of the work.

This cost may be lower in another municipality. For example, in the City of Mercier, the cost of a building permit is only $ 60 for major residential renovation, transformation or expansion work.

How long does it take to get a building permit?

In general, you should allow between 2 and 3 months to obtain your building permit, depending on the municipality and the type of work you plan to carry out.

Depending on the municipality and or the district in which your house is located, your permit application may go to the CCU (Urban Planning Advisory Committee), which has the final say on the issuance of building permits for certain projects.

In general, these are projects for which there is a visible modification of the premises from the public space. In these cases, your project may be subject to the AIIP (architectural implementation and integration plan), i.e. specific district planning regulations which aim to regulate the construction or modification of a house, taking into account the aspects that are specific to the building and its integration into the heritage of the district where it is built.

backyard home addition

Credit: Obespoke & Obbard Design & Development

Step 10

Call for tenders with general contractors


Plans (architecture, structure)

Tools and Technique

Site visits

Reading plans, consulting clients and professionals

Cost calculation, consultation of subcontractors and suppliers


Quotes from general contractors

Quotes from general contractors

Once the architectural plans (designed by an architect or a technologist) and the structural plans (designed by a structural engineer) are set, you have all the technical information you need to start calling for tenders with general contractors. It is important to provide contractors with all the necessary project information to enable them to quote effectively. For instance, if a part of the plans is missing and you decide to involve the contractors at this stage, you risk making them work double-time since they will have to revise their quotes once the call for tenders is updated. This is certainly a non-efficient practice.

Once the documents received, contractors interested in your project will want to visit the property to ensure they fully understand the project, assess and visualize the environment of the project (entries, exits, general condition of the house, etc). These elements are important because they have an impact on the cost of the work. Moreover, when talking to a contractor, make sure that the contractor has understood your project’s objectives. It often happens that contractors question the plans of architectural and/or engineering professionals, offering other alternatives that may reduce the cost or improve the quality of the work. This is welcome and a good sign that the entrepreneur’s vision lines up with yours.

Should I reveal my budget to a contractor?

"What is your budget?" is a question that entrepreneurs often ask customers.

Mainly because they want to make sure they don't “work for nothing”, since their time is very precious. Preparing a quote for a home expansion project can take an entrepreneur up to 1 week of work time from reading the plans and specifications, meeting with the client, communicating with professionals, requesting prices from suppliers and subcontractors, all the while knowing they are not paid for this job. Before starting a quote, it is important for a contractor to know if the client has the budget to complete the work.

In your budget, it is important to keep a contingency of at least 15% to cover all the unforeseen and/or additions to the scope of work. It is very common to see a project shift between the design of the plans and the actual execution of the work.

At Billdr, all partnering entrepreneurs have their RBQ license(s) and civil liability insurance. We make sure to work with the best. To learn more, consult our guide to finding a good contractor.

Billdr shares with you the portfolio of each of the entrepreneurs who are interested in your project. In these portfolios, you will have information about the entrepreneur such as his license number, his areas of expertise and photos of projects he has carried out.

To help contractors during the bidding period, we provide everyone with a report that lists all the information about your project with regards to your needs as well as your project’s architectural and engineering plans. This helps ensure that the contractors can fully understand your project as a whole. This report also helps them to provide a detailed quote, something barely seen today among contractors!

Speak with an advisor
second level home extension

Credit: Zugai Strudwick Architects

Step 11

Hire the general contractor


General contractor’s quote

Tools and Technique




General contractor’s contract

At this point, you will have met with several general contractors and received their quotes. A specific contractor will especially stand out because he is competitive and inspires you with confidence. Hence, you want to hire him to carry out the work.

Before signing the quote, you should make sure that the contractor understands the scope of work and that their quote is clear and complete. The contractor's quote, once signed, becomes the contract: it is the contractual document that binds you with the contractor. It is therefore important to ensure that it is complete. For instance, it should specify:

  • The name of the general contractor
  • The RBQ license number of the general contractor
  • Customer's name
  • The project’s address
  • The scope of the project (in addition, the contractor must mention the work will be done "according to the architectural and engineer plans")
  • The deadlines
  • The cost
  • The payment terms
  • Any specific conditions of the contract (these are elements not yet included in the contract or additional details)

Additional tips

In addition, here are some tips to consider before selecting your general contractor:

  • Make sure that the general contractor has a valid RBQ license and liability insurance of at least $ 2,000,000 to protect your property and that of your neighbor during the work
  • Check the experience of the general contractor via his project portfolio
  • Check the contractor's availabilities for when to begin the work process
  • Verify payment terms
house extension kitchen

Credit: Fine House Photography

Step 12

Construction work execution

Executing a home expansion project: stages, stakeholders, civil liability The first days in commencing the project consist of doing mobilization on the site. This is a step that allows the contractor to install protective measures to secure the site, install access, temporary services (for example temporary lighting on the site), protective measures for the existing installations (e.g. covering existing floors to protect them), a waste container, etc.

Then, the second step is to carry out the demolition work before starting the new construction.

Building a house extension or second storey addition involves several different stakeholders. It must therefore be understood that the general contractor does not do all the work himself with his employees. Indeed, he may have to do part of the work because it is his primary specialty, otherwise, he works with specialized contractors (such as an electrician, a plumber, an excavation company, etc.) to whom he subcontracts part of the work.

The general contractor has several responsibilities towards his subcontractors: he must coordinate the work of all stakeholders on the site, plan their work schedule, manage deadlines to avoid delays, and monitor the quality of the work. In practice, as a client, you do not have to communicate with a subcontractor, the general contractor should be your point of contact at all times for the work in progress. For example, you have decided to add additional lights. You should not call the electrician to ask him the cost of this addition, but rather the general contractor.

The general contractor is responsible for the construction site, he is the prime contractor. He is solely responsible for ensuring that all work is carried out in accordance with laws, regulations and building codes. He is also responsible for the health and safety of any person on the site.

Its site is covered by its civil liability insurance. Thus, as a project manager, the general contractor is within his rights to refuse access to his site to anyone. For example, even if as the owner you are the owner, you cannot make a unilateral decision to bring in your cousin or friend, an electrician and have him do work within the scope of the general contractor. without the agreement of the latter, because the site is under its civil responsibility.

If he does not carry out part of the work for which he is responsible, the general contractor can effectively relinquish his responsibility in relation to the guarantee of the work or part of the work.

Monitoring communications

Communication is a major element in any project meaning you can never communicate too much! As soon as the contract is signed, immediately identify with your general contractor the most effective communication channel for you.

It will allow you to exchange and coordinate regularly the progress of the work, plan the next steps, make site visits, follow up on invoicing and payment and, most importantly, manage changes. You will also have a lot of verbal communication with your contractor. Despite the trust and the good relationship that binds you with your contractor, it is important to keep a written record of all your communications, especially any decisions taken along the way.

Important Note

You will have a lot of verbal communication with your contractor. Despite the trust and the good relationship that binds you with your contractor, it is important to keep a written record of all your communications

Managing change orders

It often happens to see changes in the scope of work in a construction project, but that is not to say it happens all the time! Change orders include any additional work and the general contractor may charge you additional costs. They also include any tasks canceled which will lead to a credit to the contract value. These change orders can come from 3 different sources:

They also include any tasks canceled which will lead to a credit to the contract value. These change orders can come from 3 different sources:

1 - Site condition: These are change orders that appear most often during demolition work, for example, the unexpected discovery of ceramic tiles under the floor that need to be demolished or the discovery of a load-bearing wall. It was impossible to foresee this information when making the plans or quotes. This now becomes a concern of unexpected and unforeseeable events.

2 - Error or omission: These are inconsistencies in the plans made by professionals (architect, technologist or engineer). When carrying out the work, the contractor may find that what is requested on the plans is not achievable and adjustments are necessary. This now becomes a concern of unexpected but foreseeable events.

3 - Customer request: You have decided, for example, to add a window even though this was not scheduled for in the plans. Owners often have to widen the scope of the work. Some opportunities for change are good, but beware! “While we're at it, we want…” is a phrase we hear often. This is a bad practice in project management because it causes significant risk for scope creep and in losing control of the budget.

Managing change orders or “extras” is very important in a construction project. This is the main source of conflict during the construction phase.

It can generate frustration and tension due to the lack of clear communication. We advise you to have an agreement with your contractor, namely not to carry out any change in the scope of work without your prior agreement. This means that he will first have to give you the price of the change order before starting the work.

In reality, things can be more complex than one might think: to assess the value of a change order, the entrepreneur often needs to receive a price from their supplier or subcontractor. At the same time, he risks falling behind (which means a loss of income for him) if the change order is on the critical path (this is the shortest path to complete the work). Change orders should be documented in writing and an out-of-court negotiation remains the best option for everyone.

Controlling scope

The scope of work is the baseline of your project and may change over time. As the project develops, changes may be required, new ideas may emerge or opportunities to be seized may arise and as a result, modify the scope of work.

It is therefore important to constantly update the scope of work as it forms the basis of your contract with the general contractor.

Controlling schedule

Schedule tracking is monitoring the project schedule to measure the progress of work over time. It makes it possible to identify and document the causes of the delay on the construction site. It also allows you to plan site visits, including those of the engineer or architect. Finally, monitoring work schedules allows you to maintain control over the contractor's invoicing, according to the terms defined in the contract.

Controlling cost

Tracking costs allows you to control your budget and account for expenses. At this stage of the project, in your budget, there is the amount allocated to the general contractor’s contract and the construction contingencies.

You should be able to know by now the total amount invoiced by the general contractor, the total value of the changes and therefore the balance of construction contingencies. For more information, consult our guide on payment terms.

Controling quality

Quality control consists of evaluating the quality of the work which is carried out during a site visit. It is good practice to carry out a site visit on a weekly basis at least.

It is always recommended to ask professionals to make a site visit at the appropriate time to inspect the work, especially before the walls and ceilings are closed. This stage pertains to the structure, the electrical installation, the thermal insulation or the waterproofing against moisture and water. For concrete work, the engineer could visit the site at the end of the formwork, just before the concrete is poured.

Billdr is involved at all levels during the construction phase. Written communications between you, the general contractor and your renovation advisor (Billdr) are done through a group discussion to allow everyone to share information.

Through weekly site visits, your dedicated advisor follows up on the progress of the work and ensures that your project is on time and on budget.

With photos of the site’s progress, a report that also compiles up-to-date project information tracking the work done, changes, budget, payments, etc. is sent weekly.

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basement home extension

Credit: Fine House Photography

Step 13

Work acceptance

At the end of your home expansion project, final approval of the completion of the work is generally carried out in 2 stages.

The first step is to carry out the deficiency visit: your task is to visit the construction site with the general contractor in order to detect any irregularities and uncompleted work also known as deficiencies. It is important for the contractor to note and document all deficiencies for the work under his responsibility. Once the deficiencies have been corrected, you can take possession of the premises.

Taking possession of the premises also corresponds to the transfer of responsibility for the premises from the entity in charge of the project (general contractor) to the owner. This is the time for you to call your insurer to update your home insurance, namely to add the new extension to your home since it was under the cover of the general contractor's insurer until now. To learn more, consult our guide on insurance.

Billdr supports you in this phase by first making sure that all construction work tasks have been completed.

We prepare the list of deficiencies for you and ensure that they are all corrected by the general contractor.

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home extension backyard

Credit photo: Construction Precellence

Step 14

Project closure

With the work completed and all deficiencies corrected, the contractor has fulfilled almost all his contractual obligations. Finally, he must actually give you the letters of guarantee

For more information, consult our guide on warranty and guide on risks of undeclared work. You are therefore now able to release the withholding payment by paying your last invoice. This marks the end of the project.

At Billdr, we provide you with an end of project report (see example by clicking here).

This is a deliverable in which is listed all the information pertaining to your project: the scope of the work, the professional plans and specifications, the contact details of the stakeholders who participated in the project, the site visit reports, the photos taken throughout the work, cost tracking and shop drawings for materials and equipment installed during the work!

This is very valuable information to you as it contains proof of the quality of the work and its compliance. This is the manual you sell the day your home goes up for sale!

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Average cost of a house extension

Example with 800 sq.ft

Garage addition

$135/ sq.ft

Basement addition


Second storey addition


Extension on piles


Extension on foundation