An Ottawa homeowner called us in February. They wanted to add 600 square feet to the back of their bungalow. Their first quote, from another contractor, came in well under ours. The difference, almost line for line, was the energy code.
The other contractor had priced an exterior wall at R-19 with single-pane windows and standard exhaust fans. None of those numbers meet the current Ontario Building Code. The drawings would have been rejected at permit review, and the work, if it ever got built, would have failed final inspection.
OBC Section 9.36 is the energy efficiency code. For renovations and additions in Ottawa (climate zone 6), it sets minimum R-values for every assembly, U-values for windows, and ventilation rules. After the 2024 update, those numbers got tighter. Here is what that means for your project.
The R-Values You Have to Hit
Section 9.36.2 of the OBC sets prescriptive insulation values for new construction and additions in climate zone 6, which covers all of Ottawa. The current minimums for a heated, occupied space:
- Above-grade walls: R-22 effective
- Roof or ceiling: R-40 effective for an attic with venting, R-31 for cathedral or flat roofs without vent
- Floors over unheated space (bonus rooms over garages, cantilevers): R-31 effective
- Foundation walls below grade: R-12 effective full-height
- Slab on grade with integral footing: R-10 around perimeter, 1.2 m horizontal or vertical
- Heated slab: R-20 under the slab and at the perimeter
The word "effective" is important. Effective R-value accounts for thermal bridging through the studs and framing, not just the value of the insulation itself. A 2x6 wall stuffed with R-22 batt actually delivers R-17 to R-19 effective, depending on framing factor, so to hit R-22 effective you need to add continuous exterior insulation or upgrade to a higher-performing cavity insulation.
Windows and Doors: U-Values, Not R-Values
Windows are rated by U-value (heat loss) rather than R-value. The lower the number, the better. Section 9.36.2.7 sets the maximum U-value for fenestration in climate zone 6 at U-1.6 (in W/m²·K), which translates to roughly U-0.28 in imperial units, or an Energy Star rated triple-pane unit with low-e coating and argon fill in most product lines.
You cannot put a builder-grade dual-pane window in a new addition in Ottawa and pass code. The cheapest options that meet U-1.6 today are:
- Triple-pane vinyl with two low-e coatings and argon: the common code-compliant choice in most Ottawa product lines
- Dual-pane with high-performance low-e and argon, in some specific Energy Star Most Efficient lines: a narrower set of units that still clears U-1.6
- Fibreglass triple-pane: the highest-performing option, with frame durability that suits Ottawa freeze-thaw cycles
For doors, the U-value rule applies to the door system, including the slab and the frame. A solid wood door rarely makes it; insulated steel or fibreglass slabs are the practical choice.
Heads up
Replacement windows in an existing house are usually not held to U-1.6 unless you are also enlarging the rough opening or making structural changes. Like-for-like swaps fall under the renovation exemption. The minute you cut a new opening or increase the area, full code applies.
The 2024 Code Update: What Changed
The 2024 OBC update made three changes that hit Ottawa renovations directly.
First, the airtightness requirement. New construction and additions are now required to achieve a measured air-change rate, verified by blower-door testing. Most builders are targeting 2.5-3.0 ACH50 to comfortably pass. Older houses are typically 6-10 ACH50, so an addition has to be tighter than the house it attaches to.
Second, heat-recovery ventilation. The previous code allowed bathroom and kitchen exhaust fans as the primary ventilation strategy. The current code, in most scenarios, requires an HRV (heat recovery ventilator) or ERV (energy recovery ventilator) for any new dwelling unit or major addition. We will get into the difference below.
Third, thermal bridging. Continuous insulation outside the framing is no longer optional in many wall assemblies. The math forces it: hitting R-22 effective in a 2x6 wall without continuous insulation only works with high-density spray foam, and that has its own carbon footprint and cost.
HRV vs. ERV: Which One You Need
Both are mechanical ventilation devices that exchange stale indoor air for fresh outdoor air, while recovering most of the heat from the outgoing air.
An HRV recovers heat only. It works best in dry climates and homes with occupants who run a lot of moisture (showers, cooking) because it dumps that moisture outside.
An ERV recovers heat and moisture. In Ottawa winters, a properly sized ERV keeps the indoor humidity in the 35-45% comfort range without a humidifier; in summer, it keeps humid outside air from overwhelming the AC.
For most Ottawa homes built tight to current code, an ERV is the better fit. The cost difference at install is modest relative to the unit. The comfort and equipment-life difference over 15 years is significant.
Sizing follows OBC 9.32: total continuous ventilation rate is 0.3 air changes per hour for the principal living area, plus specific exhausts. A 2,000 sq ft house with 9-foot ceilings needs approximately 90 CFM of continuous balanced ventilation. The unit you install has to deliver that rate at the lowest fan speed, not the highest.
Passive House Adders for Ottawa
If you want to go beyond code, the Passive House standard is the most rigorous voluntary spec. The "Passive House adder" we use on Ottawa projects when clients want net-zero performance:
- Walls: R-40 effective, double-stud or exterior continuous
- Roof: R-60 effective
- Slab: R-30 with thermal break at footing
- Windows: U-0.85 (triple-pane fibreglass with warm-edge spacer, krypton fill)
- Airtightness: 0.6 ACH50 verified by blower-door
- HRV/ERV: 80%+ sensible recovery efficiency
The cost premium over code-minimum runs 8-15% of total construction. The operating-cost savings, in Ottawa, are roughly 70-80% versus a code-minimum house. If you plan to live in the home for 15+ years, the math works.
"Code minimum is exactly that: the worst legal house. Anyone building to code in Ottawa today is signing up for tomorrow's renovation in 25 years."
How the Energy Code Shows Up in Permit Drawings
Your BCIN designer has to demonstrate energy compliance on the drawings before the City stamps the permit. There are two paths:
- Prescriptive path. Each assembly meets the R-value and U-value table directly. Easiest, but inflexible.
- Performance path. Use HOT2000 or similar software to model the whole-building energy use. You can trade lower R-values in one assembly for higher in another, as long as the total energy use beats the reference house.
The performance path is what we use on most additions, because it lets us optimize cost. For example, going to triple-pane windows lets us reduce the wall R-value back to a standard 2x6 batt, saving on wall thickness and labour while improving overall performance.
The drawings need an SB-12 compliance summary in the title block of every page, calling out the path used, the assembly values, and the ventilation rate.
Costs: What This All Adds to Your Budget
For a typical Ottawa home addition of 400-600 sq ft, the energy code requirements show up as distinct line items in a written estimate. The cost drivers to plan for:
- Continuous exterior insulation across the wall area
- The upgrade from dual-pane to triple-pane windows at each opening
- An HRV/ERV unit plus its dedicated ducting
- The required blower-door test
- Energy modelling when you take the performance path
These items form a real energy-code premium on a typical addition, and we itemize each one in a detailed written breakdown so you can see exactly what the code is driving. That premium pays back in heating and cooling savings over 8-12 years and is recoverable on resale. The contractor who quotes without it is not doing you a favour. They are setting you up for a permit failure.
If you are weighing addition options for your Ottawa lot, the right path starts with a feasibility check. Call 613-862-4555 or read more about the Ottawa permit process and the documents your designer has to submit.
Frequently asked questions
What insulation R-values does an Ottawa addition need?
Ottawa sits in climate zone 6, where OBC Section 9.36.2 sets effective minimums of R-22 for above-grade walls, R-40 for a vented attic ceiling, R-31 for cathedral or flat roofs and for floors over unheated space, R-12 full-height for foundation walls, R-10 at the perimeter of a slab on grade, and R-20 under and around a heated slab.
What does effective R-value mean?
Effective R-value counts heat lost through studs and framing, not just the rated value of the insulation. A 2x6 wall filled with R-22 batt delivers only R-17 to R-19 effective, depending on framing factor. To reach the R-22 effective an Ottawa addition needs, the wall needs continuous exterior insulation or a higher-performing cavity insulation such as high-density spray foam.
Do replacement windows have to meet the energy code U-value?
Usually not. Like-for-like replacement windows in an existing house fall under the renovation exemption and are not held to the U-1.6 maximum. The full code applies the moment a new opening is cut, a rough opening is enlarged, or structural changes are made. In a new Ottawa addition, windows must meet U-1.6 W/m²·K, which in most product lines means triple-pane with low-e coatings and argon.
Should an Ottawa home have an HRV or an ERV?
For most Ottawa homes built tight to current code, an ERV is the better fit. An HRV recovers heat only and dumps moisture outside. An ERV recovers heat and moisture, keeping winter indoor humidity in the 35 to 45 percent range without a humidifier and keeping humid summer air from overwhelming the AC. The current code requires one or the other for most new dwelling units and major additions.
How airtight does a new addition have to be under the 2024 code?
The 2024 Ontario Building Code update requires new construction and additions to reach a measured air-change rate, verified by a blower-door test. Most builders target 2.5 to 3.0 ACH50 to pass comfortably. Older houses typically test at 6 to 10 ACH50, so an addition has to be tighter than the house it attaches to. The voluntary Passive House standard goes further, to 0.6 ACH50.
Official references
- Keeping the Heat In, Natural Resources Canada