The Top Mistakes People Make When Designing an Addition

Home additions can be the perfect solution for growing families, home-based businesses, or simply the need for more functional space. But without the right planning and design, an addition can quickly turn into a costly regret. In Ontario—where zoning regulations, climate, and resale value all play key roles—getting it right the first time is critical.

Here’s a breakdown of the most common mistakes homeowners make when planning a home addition and how to avoid them with the help of experienced professionals.

Mistake #1: Underestimating Scale and Proportion

One of the most common design blunders is building an addition that doesn’t blend well with the original structure. Oversized extensions can dwarf the existing home, while undersized ones may not add meaningful function or value.

Why it matters:

• Poor proportions can negatively impact curb appeal and resale value.

• An imbalanced layout can cause traffic flow and functional issues inside the home.

Design tip: A well-designed addition should feel like a natural extension of your home—visually and functionally. That includes matching rooflines, exterior finishes, and window styles. At De Simone Designs, we specialize in creating additions that look like they were always part of the home.

Mistake #2: Ignoring Local Zoning and Permit Requirements

In Ontario, each municipality has unique bylaws governing lot coverage, setbacks, height limits, and the use of space. Overlooking these requirements can lead to expensive redesigns, delays, or even removal orders.

Common issues:

• Exceeding the maximum lot coverage

• Building too close to property lines

• Adding units that are not compliant with zoning for secondary dwellings

Avoid it by: Consulting with a BCIN-certified designer early in the planning stage. At De Simone Designs, we conduct detailed zoning reviews and coordinate directly with municipalities across Niagara and Ontario to ensure compliance before construction begins.

Mistake #3: Overlooking the Permit Timeline

Permits aren’t just a formality—they’re a legal requirement in Ontario, and the process can take time. Many homeowners fail to account for this in their project timeline, which leads to delays or conflicts with contractors.

What you need to know:

• Building permits can take 2–6 weeks (or more) depending on the scope of work and the municipality.

• Additions that include plumbing, electrical, or secondary units require additional documentation.

Pro tip: Work with a firm that manages the permit process for you. De Simone Designs handles all required drawings, submissions, and correspondence so your project moves forward smoothly.

Mistake #4: Mismatched Architectural Style

While the interior function of an addition is important, the exterior design must respect the character of the existing home—and in some areas of Ontario, even the surrounding neighborhood.

Common missteps:

• Choosing modern materials that clash with traditional homes

• Creating awkward rooflines or incompatible facades

• Neglecting symmetry, window lines, and scale

Design rule: Great additions blend new functionality with architectural harmony. Our team ensures that each element—from siding to slope—is thoughtfully integrated to preserve your home’s identity.

Mistake #5: Poor Planning of Interior Flow

Adding a room is more than just adding square footage—it’s about how the new space connects with the rest of the home. Poor planning can create awkward transitions, dark hallways, or unusable spaces.

Layout issues we often see:

• Isolated additions with no connection to key living areas

• Conflicts with existing plumbing or HVAC

• Blocking access to natural light or creating dead zones

Design solution: Before we draw a single wall, we look at your entire home’s flow and how the addition enhances functionality. Whether it’s expanding a kitchen, adding a main-floor bedroom, or creating a home office, we focus on seamless transitions and natural movement through the space.

Mistake #6: Skipping the Budget Contingency

Even with the best planning, renovations and additions can uncover surprises—especially in older homes. Failing to set aside a contingency fund often results in cut corners or incomplete features.

Typical unexpected costs:

• Structural upgrades for load-bearing walls

• Electrical or plumbing modifications

• Insulation or waterproofing upgrades to meet code

Recommendation: Plan for a 10–20% contingency within your renovation budget. It’s better to finish strong than to have to compromise late in the project.

Mistake #7: Going DIY Without a Design Pro

Online inspiration can make a DIY addition seem doable—but the reality is that most additions require professional planning to ensure safety, functionality, and code compliance.

Why professionals matter:

• You gain expert insights on space planning and building codes.

• You avoid costly rework from incorrect measurements or design flaws.

• You protect your investment with documentation that satisfies lenders and insurers.

Working with an architectural technologist like Thomas De Simone means you’re not just adding space—you’re adding long-term value and peace of mind.

Ready to expand with confidence? Avoid costly design mistakes and partner with De Simone Designs to get your home addition done right the first time. From concept to permits to execution, we ensure your space is beautiful, functional, and compliant with Ontario’s building regulations.

📞 Contact us today to schedule your addition consultation!