How do you calculate project costs?

We use current market rates for high-quality materials and skilled labour in Durham Region. Every estimate includes a detailed breakdown of tasks so you know exactly where your money is going.

Is the initial consultation free?

Yes. We offer a free first meeting to look at your space and talk about your goals. After that we provide a clear price range for your specific project.

Do you offer fixed-price contracts?

Most of our projects use fixed-price contracts. This means the price we agree on is the price you pay, unless you decide to change the scope of work later.

What happens if material prices go up?

Once we sign a contract, we lock in the material prices for you. We order supplies early to make sure your budget stays safe from market changes.

How long will my renovation take?

Small jobs might take two weeks, while large additions can take months. We give you a full schedule before we start so you can plan your life around the work.

Will I have a dedicated project manager?

Yes. You will have one main person to talk to. They will be on site often to check quality and keep you updated on our progress every day.

How do you keep the job site clean?

We clean up at the end of every single day. We use floor protection and dust barriers to keep the rest of your home safe and tidy while we work.

Do I need to move out during construction?

For most room renovations you can stay home. For very large projects like whole-home guts, we might suggest staying elsewhere for a short time for your comfort.

What areas do you serve?

We serve all of Durham Region including Oshawa, Whitby, Bowmanville, Ajax, Pickering, Newcastle, Clarington, Scarborough, Stouffville, and Peterborough.

Do you handle permits and inspections?

Yes. We submit the plans to the municipality, get the permits, and schedule all required inspections to ensure your home is safe and the work is done to code.

Can you help with the design phase?

Yes. We work with designers and architects to help turn your ideas into professional drawings before we start building.

Do you do commercial construction?

Yes. We offer commercial services for offices, retail spaces, and restaurants alongside our residential renovation work.

What kind of warranty do you provide?

Every Cornerstone project is backed by a 5-year written workmanship warranty. If something we built fails because of how it was installed, we fix it at no charge.

What if I find a problem after you leave?

Contact us directly. We respond to warranty concerns within 1 to 2 business days and will schedule a site visit to assess the issue at no cost to you.

Are you insured and WSIB compliant?

Yes. Cornerstone Construction carries full liability insurance and all our workers are covered by WSIB. This protects you and your home completely.

Do you offer maintenance tips?

Yes. At the end of every project you receive a full Owner's Manual with care and maintenance instructions for every material and system we installed.

Additions & Garages Whitby · Additions & Garages

Home Additions & Garages in Whitby

Whitby currently runs three separate zoning by-laws depending on when your area was developed, and updates on Additional Dwelling Units have changed what's allowed on many lots. We confirm which rules apply to your property before we design anything.

Start Your Construction Diagnostic Call 1-888-404-7383

Whitby at a Glance

0.6mMin. setback for garages & accessory buildings (side & rear)

4.5mMax height for sheds & accessory structures (14'7")

10m²Threshold above which an accessory building needs a permit

4-6Weeks, typical permit review for a standard residential addition

Before We Design Anything

The Rules That Actually Matter

Whitby currently operates under three separate zoning by-laws — 1784, 2585, and 5581-05 for lands on the Oak Ridges Moraine — depending on when your area was zoned. The Town is combining all three into one updated by-law, but until that's finished, we confirm exactly which one applies to your property.

Setbacks & Lot Coverage

A detached garage or accessory building needs a minimum 0.6m setback from interior side and rear lot lines. Eaves and roof overhangs can encroach up to 0.3m into that setback.
Most accessory structures cap out at 4.5m (14'7") in height.
An attached addition follows your base zone's setbacks, which depend on which of Whitby's three zoning by-laws applies to your specific property.
Fences need a minimum 1.0m setback from the property line — worth knowing if your project includes new landscaping or a boundary fence.

What Needs a Permit

Accessory structures over 10m² (other than sheds) need a permit. Sheds need one if over 15m² or more than one storey.
Additions, basement finishing, decks, fences, and pools all require a permit in Whitby — the Town is explicit that even smaller projects aren't exempt.
Standard residential permits typically clear in 4 to 6 weeks; more complex applications can run 2 weeks to 3 months.
Whitby's Committee of Adjustment can grant a minor variance if your project falls just short of a setback rule.

If your addition includes a basement or a secondary suite, see our legal basement apartment guide for Whitby — the parking and unit-count rules there are separate from what applies to a straight addition or garage.

Building Up

What a Second-Storey Addition Actually Requires

Adding a full floor on top of your existing home isn't just framing walls — it changes the structure underneath it too.

What's Involved

Full roof removal down to the existing top plate before the new floor goes on.
A new engineered floor system spans where the roof used to be — this becomes your new upper floor.
The ceiling on your existing main floor gets disturbed by this work and needs refinishing once the new floor system is in.
Structural engineering confirms your existing walls and foundation can actually carry the new load — not optional, required on every second-storey build, and covered under our BCIN design & permit drawing services.
Most Whitby homes built between 1980 and 2005 have a straightforward second-floor framing profile to work with — we confirm your home's specifics at the site visit before finalizing a design.

See real pricing for second-storey additions in our investment calculator

How It Works

Zoned, Designed, Permitted, Built

An addition isn't just built — it's checked against your specific zoning by-law, engineered, permitted, and inspected. We carry all of it.

Confirm Your Zone

We identify which of Whitby's zoning by-laws applies to your property and check setbacks, coverage, and height limits before we design.

Design & Engineered Drawings

Scaled plans plus structural engineering where required — mandatory for any second-storey work.

Building Permit

Filed through Whitby's E-Portal. Standard residential additions typically clear in 4 to 6 weeks; we track it so you don't have to.

Build & Inspections

Framing, structural, electrical, and plumbing inspections through to final sign-off.

$300

Our on-time guarantee. If we miss the agreed completion date for reasons within our control, you're compensated $300 for every day past it — part of the Certainty Stack on every Cornerstone build.

Why Build It Permitted

A Permitted Addition Is Worth More

Resale Confidence

A permitted addition shows clean on a title search. An unpermitted one can hold up your sale or force disclosure to buyers.

Insurance Stays Valid

Unpermitted structural work can void your coverage if something goes wrong down the line — permitted work protects your policy.

No Forced Teardown Risk

The Town can order unpermitted additions removed or brought up to code after the fact. Done right the first time, that risk doesn't exist.

Built to Carry the Load

Proper engineering means your addition holds up for decades — not just long enough to pass a first inspection.

Common Questions

Whitby Addition & Garage FAQ

Do I need a permit for a home addition in Whitby?

Yes. Whitby requires a permit for almost any structural, renovation, or new construction project — additions, basement finishing, garages, decks, even fences and pools. We handle the application and coordinate every inspection.

What's the setback if I want to build a detached garage?

A detached garage or other accessory structure needs a minimum 0.6m setback from interior side and rear lot lines, with a height cap of 4.5m (14'7"). A permit is required if the structure exceeds 10m² in floor area. Your specific zoning by-law may carry additional requirements, which we confirm before designing.

How long does a Whitby building permit actually take?

Standard residential additions typically clear review in 4 to 6 weeks. More complex or non-standard designs can take longer — up to a few months in some cases. We build realistic timelines into your project plan from the start.

Why does Whitby have three different zoning by-laws?

Whitby's three zoning by-laws (1784, 2585, and 5581-05 for Oak Ridges Moraine lands) predate the Town's current Official Plan and each cover different areas. The Town is working on combining them into a single updated by-law, but until that's complete, we confirm which one governs your specific property.

Can I convert my existing garage into living space instead of building new?

Yes — this falls under Space Conversion rather than new construction, since there's no new foundation or exterior envelope to build. It's a genuinely different scope and cost than a new addition or a new garage build.

What happens if my addition doesn't fit my zone's setback rules?

Whitby's Committee of Adjustment can grant a minor variance if your project falls just short of a setback or coverage rule. We flag this early rather than after drawings are done, so you know your real options before committing to a design.

Zoning and permit information last reviewed September 2026. Municipal requirements can change — Cornerstone confirms current Town of Whitby requirements with Building Services on every project. Sources: Town of Whitby Accessory Structures and Building Permits pages; Whitby Zoning By-laws 1784, 2585, and 5581-05.

Part of Our Durham Additions & Garages Guide

See our full investment calculator, garage attached vs. detached breakdown, and FAQ

Back to Additions & Garages →

Also building additions and garages in Oshawa, Ajax, and across Durham Region.

Thinking About an Addition or Garage in Whitby?

Start with a free project diagnostic. We'll check your zoning by-law, run the real numbers, and give you a clear, locked price. Built once, built right.