# Multiplex Additions Toronto | Multiplex Toronto Builders

URL: https://multiplextorontobuilders.ca/multiplex-additions/

![Two-storey rear addition on a Toronto brick house with large casement windows](/images/misc/two-storey-rear-addition-on-a-toronto-brick-house-.webp)

Design \* Build \* Deliver - Multiplex Additions

# Multiplex Additions in Toronto, ON | For Owners Adding Units or Floor Area

Last updated: October 21, 2026

Rear, side and storey additions that create or enlarge units, with an engineer's foundation assessment and a setback and coverage check before design starts.

Price band (CAD)

$180K-$600K

Timeline

5-8 months construction (typical, confirmed at feasibility)

Built for

Owners Adding Units or Floor Area

-   Engineer Check First
-   Setback & Coverage Tested
-   WSIB Compliant
-   Insured & Bonded
-   15 Years Toronto

## Request Written Feasibility

Zoning check + CAD estimate before any deposit.

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We reply within one business day to book your feasibility review.

-   ★5-Star Multiplex Construction Rating
-   ◆15+ Years of Toronto Infill Construction Experience
-   ◆40+ multiplex projects coordinated
-   ◆Free in-home feasibility with written zoning verification

Multiplex Toronto Builders

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 designs and builds multiplex additions across Toronto, East York, Scarborough, Etobicoke, North York and the GTA: rear, side and storey additions that create a new unit or enlarge an existing one. Every addition starts with a structural engineer’s assessment and a setback and coverage check, and runs under HCRA registration where it applies, WSIB and a $5M CGL policy. Scope is written in CAD and checked against the Ontario Building Code, and we coordinate with the Toronto Committee of Adjustment, Toronto Building, Toronto Water, Toronto Hydro and your insurer so the new space is legal from day one.

Additions fail when the planning is skipped. Owners are told an addition makes a sixplex possible where only a fourplex is as-of-right, mix up severance with multiplex approval, assume EHON setback math works for a side addition on a 25-foot lot, or are promised a parking variance that never gets filed at the CoA. Then the foundation turns out to be too small for a new storey. We confirm OBC Part 9 scope, check footing capacity before design, spec insulated glazing, use 316 stainless fasteners within 500 metres of the lake and verify zoning through GeoWarehouse before signing.

Rear additions typically cost **$180K-$400K CAD** and side additions **$220K-$600K**, with 5-8 months of construction. We build in Toronto, East York, Scarborough, Etobicoke, North York, York, Vaughan, Markham, Richmond Hill, Mississauga, Brampton and Pickering, with a written workmanship warranty on every project.

![Rear addition framing tied into an existing Toronto brick house with new foundation walls below](/images/content/rear-addition-framing-tied-into-an-existing-toront.webp)

Additions often pair with a 

multiplex conversion

[/multiplex-conversion/ →](/multiplex-conversion/)

 of the existing house. Before building up, read 

can your foundation support a storey addition

[/guide/foundation-storey-addition-structural-checks/ →](/guide/foundation-storey-addition-structural-checks/)

.

## Types of Multiplex Additions

### Rear Addition

A rear addition extends the house into the backyard, usually one or two storeys. It is the most common way to add a unit or enlarge one, because rear yards often have room to grow within the rear setback and lot coverage limits. The trade-off is soft landscaping: Toronto’s by-law requires a share of the rear yard to stay landscaped. We model the footprint against those rules, design the addition as its own unit or as an extension of an existing one, and tie it into the existing structure with new footings. Rear additions typically cost $180K-$400K.

### Side Addition

A side addition builds into the side yard, which can give a new unit its own street-facing entrance. On wider suburban lots in North York, Scarborough and the GTA, side additions often fit within setbacks. On narrow Toronto lots, they usually need a side-yard variance, which adds 4-6 months. Side additions cost more, $220K-$600K, partly because they often involve more facade work, roof tie-in and utility relocation.

### Storey Addition (Top-Up)

Adding a storey, often called a top-up, is a strong option for bungalows that sit on wide lots. A new second storey can become a separate unit with its own stair, or enlarge the main unit while the basement becomes a rental. The key is the foundation. Most bungalow footings were sized for one storey, so a structural engineer must confirm capacity, and reinforcement is often needed. Height limits under the by-law also cap how high you can go.

### Structural Tie-In and Foundation Reinforcement

Every addition joins new structure to old. That means engineered beams where walls are opened, new footings or helical piers for the added load, careful flashing and waterproofing at every junction, and fire separation if the addition is a separate unit. Our engineers design to CSA O86, and we check the existing framing for rot, undersized joists or past alterations before closing anything in. Getting the tie-in right is what keeps an addition from cracking or leaking years later.

## Common Multiplex Addition Problems in Toronto

### Foundation Cannot Carry a New Storey

**Symptom:** Your plan is a second storey on a bungalow, but the engineer finds shallow, narrow footings or cracked foundation walls. **Immediate action:** Get an engineer’s assessment with test pits before design or pricing. **Scope:** Options include underpinning, helical piers, new interior footings or a lighter structural design. Each changes cost and schedule. **Qualified contractor response:** We bring the engineer in at feasibility, price the reinforcement in the first quote and design the addition around what the foundation can carry once reinforced. Our Cliffcrest client’s top-up needed helical piers, and the price included them from the start.

### Rear Addition Breaks Soft Landscaping Rules

**Symptom:** The rear addition you want leaves too little landscaped area in the backyard, and the zoning review flags it. **Immediate action:** Check the soft landscaping percentage and rear-yard setback for your zone. **Scope:** A smaller footprint, a second storey instead of a wider first floor, or a variance can fix it. **Qualified contractor response:** We model the addition against soft landscaping and coverage first. Often a two-storey addition with a smaller footprint delivers the same floor area without a variance. If a variance is still the best route, we file it and represent you.

### Height Limit Caps the Top-Up

**Symptom:** You planned a full second storey with a pitched roof, but the zone’s height limit cuts it short. **Immediate action:** Confirm the height limit and how it is measured for your lot. **Scope:** Flat or low-slope roofs, lower floor-to-ceiling heights or a partial storey can keep the design within the limit. A height variance adds time and is not guaranteed. **Qualified contractor response:** We design the addition inside the height envelope from the start, using roof forms and ceiling heights that keep the space comfortable and legal. If a small height variance would add real value, we show you the trade-off before filing.

### Addition Blocks the Basement Unit’s Light and Egress

**Symptom:** A rear addition is designed to enlarge the main unit, but it covers the basement windows that provided light and egress for the basement unit’s bedrooms. **Immediate action:** Review how the addition affects every existing window and exit before finalizing the design. **Scope:** Basement bedrooms need compliant egress windows, and covering them with an addition can make those bedrooms illegal. Fixing it later may mean new window wells, relocated bedrooms or a redesigned addition. **Qualified contractor response:** We design additions around the whole building, not just the new space. Basement egress windows are kept clear or relocated into the addition’s design, window wells are planned with drainage, and fire separation between units is maintained across the old and new structure. The result is an addition that adds floor area without taking away the legality or livability of the units around it, which matters both for tenants and for the building’s value when you refinance or sell.

Why Owners Pick Us

## Why Choose Multiplex Toronto Builders for Multiplex Additions?

Six things we do on every project, written into the scope before you sign anything.

### Foundation Checked Before Design

A structural engineer assesses footing and wall capacity before we draw a storey addition. No designing a second floor your house cannot carry.

### Setbacks and Coverage First

We test rear and side setbacks, lot coverage, soft landscaping and height limits so the addition fits the by-law, or we tell you plainly which variance it needs.

### Additions That Become Units

When the goal is a new unit, we plan separate entrances, egress, fire separation and utilities into the addition so it qualifies as a legal self-contained unit.

### Clean Structural Tie-In

New and old structure joined properly, with engineered beams, footings or helical piers to CSA O86 and waterproofing at every junction.

### Phased So You Can Stay

Where it is safe, we phase rear and side additions so you can keep living in the house, with dust control and a clear schedule.

### Fixed Price After Feasibility

Once the engineer's assessment and feasibility are done, you get a fixed-price contract with allowances listed. No open-ended cost-plus.

Execution Roadmap

## How Does Multiplex Additions Work With Us?

Four steps from the first zoning check to keys. Typical timeline: 5-8 months construction (typical, confirmed at feasibility).

1.  1
    
    ### Step 1: Feasibility & Structural Check
    
    GeoWarehouse zoning pull, setback and coverage test, and an engineer's review of footings and walls.
    
2.  2
    
    ### Step 2: Addition Design
    
    Rear, side or storey addition design with unit access, egress and fire separation, plus stamped drawings.
    
3.  3
    
    ### Step 3: Permits & Variances
    
    Building permit, any Committee of Adjustment variance and utility applications if a new unit is created.
    
4.  4
    
    ### Step 4: Build & Tie-In
    
    Foundations or reinforcement, framing and tie-in, envelope, MEP and finishes, typically 5-8 months.
    

Published CAD Pricing

## How Much Does a Multiplex Addition Cost in Toronto?

Multiplex additions typically cost **$180K to $600K CAD**:

-   **Rear addition:** $180K-$400K
-   **Side addition:** $220K-$600K
-   **Storey addition (top-up):** priced after the engineer's assessment, because foundation reinforcement can range widely

What drives the number:

-   **Foundation work:** underpinning, helical piers or new footings for the added load
-   **Unit creation:** a new self-contained unit needs separate entrance, egress, fire separation and utilities
-   **Size and height:** two-storey additions cost more but add more floor area per dollar of foundation
-   **Variances:** a side addition on a narrow lot often needs one, adding 4-6 months
-   **Finish level:** luxury finishes add $80-$150 per sqft

Construction typically runs 5-8 months, confirmed in your feasibility report. The fixed price follows the engineer's assessment.

| Unit Type | Price (CAD) | Project | Timeline |
| --- | --- | --- | --- |
| Triplex New Build | $400K-$1.1M | 3 units, Part 9 | 8-10 months |
| Fourplex New Build | $500K-$1.4M | 4 units, as-of-right citywide | 9-12 months |
| Sixplex (Approved Zones) | $800K-$2M | 6 units, Part 3 likely | 12-16 months |
| House-to-Multiplex Conversion | $250K-$900K | 2-4 units in existing house | 6-9 months |
| Architectural Design (Stamped) | $15K-$60K | Permit drawing set | 6-10 weeks |
| Permit Coordination | $5K-$18K | Toronto Building + CoA | 9-14 weeks |
| Feasibility Assessment | $1,500-$4,500 | Written zoning + budget report | 1-2 weeks |

Priced rear $180K-$400K, side $220K-$600K.

Straight Answer

## Is an Addition Cheaper Than a Full Rebuild?

Often, yes, but not always. In our opinion, an addition makes the most sense when the existing house is structurally sound, the layout works, and you need one more unit or more floor area for an existing unit.

An addition gets expensive when the foundation needs major reinforcement for a new storey, when the existing house has deep problems you would fix in a rebuild anyway, or when the addition needs several variances to fit. At that point, the per-square-foot cost of a new fourplex can be better value, especially if the lot can carry four units.

The feasibility report compares both routes for your property. Our guide on 

rear vs side additions

[/guide/rear-vs-side-addition-multiplex/ →](/guide/rear-vs-side-addition-multiplex/)

 covers which addition type usually adds a unit more easily.

Our Work

## Multiplex Additions Project Photos

Finished exteriors, interiors and site stages from Toronto and GTA projects. Click any photo to enlarge.

 

![](data:image/gif;base64,R0lGODlhAQABAAAAACw=)

Client Feedback

## What Owners Say About Our Multiplex Additions

> "They were upfront that EHON doesn't apply in Vaughan and worked within the city's own unit rules instead. Rear addition for my parents was done for $265K."

Anita D., Woodbridge Rear addition $265K

> "Side addition in Springdale to make room for a second unit. They checked the foundation before quoting, which saved alot of guesswork. On schedule and on price."

Harpreet S., Springdale Side addition $340K

> "Our Cliffcrest bungalow needed helical piers before the second storey could go on. The engineer explained it on site, the price included it, and the new upper unit was rented within a month."

Derek T., Cliffcrest Storey addition

Guides

## Multiplex Additions Guides

Plain-language answers to the questions owners ask before they commit. Each guide links back here when you are ready for numbers.

Can Your Foundation Support a Storey Addition? Structural Checks FirstExplainer

[/guide/foundation-storey-addition-structural-checks/ →](/guide/foundation-storey-addition-structural-checks/)

Rear Addition vs Side Addition: Which Adds a Unit More Easily?Decision guide

[/guide/rear-vs-side-addition-multiplex/ →](/guide/rear-vs-side-addition-multiplex/)

Browse all multiplex guides

[/guide/ →](/guide/)

Toronto Zoning FAQs

## Multiplex Additions FAQs

### How much does a multiplex addition cost?

Rear additions typically cost $180K-$400K CAD and side additions $220K-$600K. Storey additions are priced after a structural engineer assesses the foundation, because reinforcement varies widely.

### Rear or side addition: which adds a unit more easily?

Rear additions usually, because rear yards have more room and fewer setback conflicts. Side additions on narrow lots often need a side-yard variance. Rear additions also tend to cost less.

### Can my foundation support another storey?

Only a structural engineer can say for sure. We open up the foundation, check footing size and wall condition, and if needed reinforce with underpinning, helical piers or new footings before building up.

### Do additions need a minor variance?

Some do. Side additions on narrow lots and additions that push rear-yard setbacks, lot coverage or height often need one, adding 4-6 months. We test this during feasibility.

### How long does an addition take?

Typically 5-8 months of construction after permits, depending on size, foundation work and whether a new unit is created. Your feasibility report confirms the timeline for your house.

### Can I stay in the house during an addition?

Often, yes, for rear and side additions, with phasing and dust control. Storey additions usually require moving out for part of the work because the roof comes off.

### Do you build additions in Brampton and Markham?

Yes. We build additions across the GTA under each city's own zoning and additional residential unit rules. EHON applies only within the City of Toronto.

### Does an addition count toward EHON unit limits?

Yes. In Toronto, any unit created by an addition counts toward the four-unit as-of-right maximum, or six in the approved sixplex areas. Garden and laneway suites follow their own permissions.

Related Services

## Related Multiplex Services

### Multiplex Construction

Ground-up triplex, fourplex and approved-zone sixplex builds on Toronto infill lots, scoped to OBC Part 9 or Part 3 by unit count and height.

$400K-$2M

View multiplex construction

[Multiplex Construction →](/multiplex-construction/)

### Multiplex Conversion

Existing Victorians, semis and bungalows reworked into 2-4 legal self-contained units, with underpinning, fire separation and separate meters planned up front.

$250K-$900K

View multiplex conversion

[Multiplex Conversion →](/multiplex-conversion/)

### Architectural Design

Concept, zoning review, BCIN or OAA stamped permit drawings, structural and MEP coordination and SB-12 energy compliance.

$15K-$60K

View architectural design

[Architectural Design →](/multiplex-architectural-design/)

![](/images/misc/finished-brick-and-oak-toronto-multiplex-exterior-.webp)

Start With Certainty

## Get a Fixed Number for Your Multiplex Additions

Send us your address and we come back with a zoning read, an honest unit count and a CAD budget range in writing, before you spend on drawings.

Get a Written Feasibility Assessment

[/contact/ →](/contact/)

 

See All Services

[/services/ →](/services/)

-   Written zoning verification
-   CAD price bands before deposit
-   Licensed Ontario Builder, Insured & Bonded