The Hidden Costs of Building a Detached Garage in Ontario

Detached garage construction in Ontario — permits and planning matter just as much as lumber and nails.

When most homeowners in Ontario think about building a detached garage, they focus on the obvious costs: concrete, lumber, roofing, and labour. But what often catches people off guard are the hidden costs—fees, design requirements, and municipal rules that can add thousands to the project if you’re not prepared.

As a former municipal building inspector, I’ve seen homeowners blindsided by these expenses. Here’s what you should know before you start planning.

1. Building Permit and Design Fees

Every detached garage in Ontario requires a building permit. Most municipalities calculate fees based on the garage’s floor area. For example, many cities charge between $11–$18 per square metre. That means a 40 m² garage could add $500–$700 in permit fees alone.

On top of that, you’ll need permit-ready drawings prepared by a BCIN-qualified designer. Most straightforward detached garages (single-storey, standard construction) can be fully designed and submitted without engineering.

However, certain situations do trigger engineering costs:

• Slab-on-grade or unusual foundations may require an engineered design.

• Lofts or habitable space above the garage often need additional structural review.

• Custom spans or beams may also require stamping.

  
  

👉 Truss shop drawings are usually included in the cost of your trusses from the lumber supplier (e.g., Turkstra), stamped by a P.Eng. at no additional charge. This covers most typical garages, but unusual roof designs can mean extra engineering fees.

✅ The Building Permit Guy acts as your one-stop shop — we prepare all drawings in-house and, when engineering is needed, we coordinate directly with our trusted engineers so everything is handled seamlessly.

2. Zoning, Setbacks, and Surveys

Ontario municipalities strictly regulate setbacks—how close your garage can sit to property lines. If your proposed garage doesn’t fit the bylaw, you may need a minor variance application, which typically costs $1,000–$2,000 and adds months to your timeline.

Some cities also require a lot grading plan or a fresh survey to confirm drainage won’t impact neighbours. Surveys can cost another $1,000–$2,500, a hidden cost many homeowners overlook.

3. Hidden Construction Costs

Beyond design and permits, several Ontario-specific construction rules can affect your budget:

• Foundations: Detached garages must meet Ontario Building Code frost-depth requirements. If a simple slab isn’t allowed, an engineered frost wall will add costs.

• Electrical: Running power to your garage may trigger a service upgrade or ESA inspection fees.

• Drainage: If your lot slopes, municipalities may require drainage controls, which can mean excavation, swales, or extra grading.

  
  

4. Retroactive Permit Penalties

Thinking of skipping the permit? In Ontario, the cost is steep. Many municipalities charge double fees for retroactive permits (while others apply flat surcharges), and you may need to hire an engineer to confirm the structure meets code. In the worst case, you could face orders to modify or even remove the garage.

It’s always cheaper—and far less stressful—to design it right from the start.

5. A Former Inspector’s Perspective

During my years as an inspector, I saw homeowners caught off guard by costs they didn’t budget for. One family built their garage too close to the lot line and had to spend over $10,000 on drainage and grading changes just to keep it. On top of that, they were charged double the normal permit fee because the garage had been built without prior approval. Situations like that are avoidable when you start with proper drawings and approvals.

This is why our clients value us as a one-stop shop: from drawings to permits to engineering coordination, we make the process simple and stress-free.

Ready to start your garage project? 

The Building Permit Guy prepares BCIN-certified garage drawings that meet Ontario’s code and local requirements. When engineering is needed, we coordinate directly with trusted professionals to provide stamped designs.

📩 Contact us today at info@thebuildingpermitguy.ca to get started.