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Code guide

Attic Insulation Requirements in Ontario

Attic insulation in the 2024 Ontario Building Code: R60 or R50 by SB-12 package, R20 minimum at hatches and eaves, baffles, vents and the attic hatch size.
attic in most Zone 1 high-efficiency packages (RSI 10.56)
R60
attic in most Zone 1 high-efficiency packages (RSI 10.56)
attic in the other packages (RSI 8.80)
R50
attic in the other packages (RSI 8.80)
minimum over hatches and at the eaves (RSI 3.52)
R20
minimum over hatches and at the eaves (RSI 3.52)
attic vent area to insulated ceiling area
1/300
attic vent area to insulated ceiling area

Last updated

Under the 2024 Ontario Building Code, the attic insulation in a new house comes from Supplementary Standard SB-12. In Zone 1 with a high-efficiency furnace, a ceiling with an attic needs nominal RSI 10.56 (R60) in most compliance packages and RSI 8.80 (R50) in the rest (SB-12 Table 3.1.1.2.AOBC SB-12 Table 3.1.1.2.A. (SI) — Zone 1 — Compliance Packages for Space Heating Equipment with AFUE ≥ 92%Table 3.1.1.2.A. (SI) — Zone 1 — Compliance Packages for Space Heating Equipment with AFUE ≥ 92% Forming Part of Sentence 3.1.1.2.(1) Component | Thermal Values[8] | Compliance Package A1 | Compliance Package A2 | Compliance Package A3 | Compliance Package A4 | Compliance Package A5 | Compliance Package A6 Ceiling…). Near the eaves and over the hatch it can be thinner, but never below RSI 3.52 (R20) (SB-12 3.1.1.8.OBC SB-12 3.1.1.8. Thermal Resistance Values for Roof Access Hatches and Eaves(1) Except as provided in Sentence (2), the thermal resistance values for insulation required by Articles 3.1.1.2., 3.1.1.3. and 3.1.1.11. for exposed ceilings with attic spaces are permitted to be reduced (a) directly above access hatches, and (b) near eaves to the extent made necessary by the roof slope and required…).

This page pulls together the attic rules: the R-values, the eave and hatch allowances, venting and baffles, the attic hatch, and the air and vapour barrier below the insulation. Your building department decides how the code applies to your house and permit.

Attic insulation rules at a glance

Item Rule in short Where to look
Attic, Zone 1, 92% AFUE or more R60 (A1, A2, A4, A6) or R50 (A3, A5) SB-12 Table 3.1.1.2.A
Attic, Zone 1, 84% to 92% AFUE R50 in most packages; R60 in B6; R60 + HH in B4 SB-12 Table 3.1.1.2.B
Attic, Zone 1, electric heat R60 + HH (C1, C2) or R50 (C3, C4) SB-12 Table 3.1.1.2.C
Ceiling without an attic (cathedral, flat) R31 (RSI 5.46) in every Zone 1 package SB-12 Tables 3.1.1.2.A to C
Over hatches and at the eaves reduced, but not below RSI 3.52 (R20) SB-12 3.1.1.8.(1)
High heel (HH) 250 mm heel; fully insulate the wall face below the vent space SB-12 3.1.1.8.(2)
Attic venting 1/300 of the insulated ceiling area 9.19.1.2.
Baffles 25 mm air space, 50 mm above the insulation 9.19.1.3.(2)
Attic hatch 550 × 900 mm, or 0.32 m² for one dwelling unit 9.19.2.1.
Air barrier continuous under the insulation 9.25.3.1.
Vapour barrier on the warm side of the insulation 9.25.4.3.

This is our summary of the articles and tables, not a copy of them. Read the full text before you size real insulation.

Where the attic R-values come from

Part 9 does not hold the energy numbers for houses. Part 12 sends Part 9 houses to SB-12, which gives prescriptive compliance packages by climate zone and heating type (OBC Div. B 12.2.1.2.OBC Div. B 12.2.1.2. Energy Efficiency Design(1) Reserved. (2) Except as provided in Sentence (3) and Sentence (4), the energy efficiency of all buildings shall (a) be designed to exceed by not less than 13% the energy efficiency levels required by Sentence 12.2.1.1.(2) of O. Reg. 332/12 (Building Code) as it read on December 31, 2024, or (b) conform to Division…). Each package is one column of a table: pick one column and meet every row in it, from the attic to the windows and the furnace. Our insulation requirements guide explains the packages and the difference between nominal and effective values.

For the attic row in Zone 1:

  • 92% AFUE or more (Table 3.1.1.2.AOBC SB-12 Table 3.1.1.2.A. (SI) — Zone 1 — Compliance Packages for Space Heating Equipment with AFUE ≥ 92%Table 3.1.1.2.A. (SI) — Zone 1 — Compliance Packages for Space Heating Equipment with AFUE ≥ 92% Forming Part of Sentence 3.1.1.2.(1) Component | Thermal Values[8] | Compliance Package A1 | Compliance Package A2 | Compliance Package A3 | Compliance Package A4 | Compliance Package A5 | Compliance Package A6 Ceiling…): RSI 10.56 (R60) in packages A1, A2, A4 and A6, RSI 8.80 (R50) in A3 and A5.
  • 84% to less than 92% AFUE (Table 3.1.1.2.BOBC SB-12 Table 3.1.1.2.B. (SI) — Zone 1 — Compliance Packages for Space Heating Equipment with 84% ≤ AFUE < 92%Table 3.1.1.2.B. (SI) — Zone 1 — Compliance Packages for Space Heating Equipment with 84% ≤ AFUE < 92% Forming Part of Sentence 3.1.1.2.(2) Component | Thermal Values[8] | Compliance Package B1 | Compliance Package B2 | Compliance Package B3 | Compliance Package B4 | Compliance Package B5 | Compliance Package B6…): RSI 8.80 (R50) in B1, B2, B3 and B5, RSI 10.56 (R60) in B6, and R60 with a high heel in B4.
  • Electric space heating (Table 3.1.1.2.COBC SB-12 Table 3.1.1.2.C. (SI) — Zone 1 — Compliance Packages for Electric Space HeatingTable 3.1.1.2.C. (SI) — Zone 1 — Compliance Packages for Electric Space Heating Forming Part of Sentence 3.1.1.2.(3) Component | Thermal Values[8] | Compliance Package C1 | Compliance Package C2 | Compliance Package C3 | Compliance Package C4 Ceiling with Attic Space | Minimum Nominal RSI[1] | 10.56 + HH | 10.56 + HH…): R60 with a high heel in C1 and C2, R50 in C3 and C4.

Ceilings without an attic space, such as cathedral ceilings and flat roofs, need RSI 5.46 (R31) in every one of those packages. Zone 2 (the colder north) has its own tables starting at Table 3.1.1.3.AOBC SB-12 Table 3.1.1.3.A. (SI) — Zone 2 — Compliance Packages for Space Heating Equipment with AFUE ≥ 92%Table 3.1.1.3.A. (SI) — Zone 2 — Compliance Packages for Space Heating Equipment with AFUE ≥ 92% Forming Part of Sentence 3.1.1.3.(1) Component | Thermal Values[8] | Compliance Package A1 | Compliance Package A2 | Compliance Package A3 | Compliance Package A4 | Compliance Package A5 | Compliance Package A6 Ceiling….

Eaves, hatches and high heels

Full-depth insulation rarely fits at the eaves, where the roof comes down to the wall. SB-12 lets the attic value drop near the eaves, to the extent the roof slope and the required vent space make necessary, and directly above access hatches, but the insulation over the hatch and over the inner face of the exterior walls must stay at RSI 3.52 (R20) or more (SB-12 3.1.1.8.(1)OBC SB-12 3.1.1.8. Thermal Resistance Values for Roof Access Hatches and Eaves(1) Except as provided in Sentence (2), the thermal resistance values for insulation required by Articles 3.1.1.2., 3.1.1.3. and 3.1.1.11. for exposed ceilings with attic spaces are permitted to be reduced (a) directly above access hatches, and (b) near eaves to the extent made necessary by the roof slope and required…).

Some packages are marked HH, a 250 mm high heel: a truss raised at the wall so more insulation fits over it. Where a high heel is required, the space on the inner face of the wall below the roof vent space must be fully insulated (SB-12 3.1.1.8.(2)OBC SB-12 3.1.1.8. Thermal Resistance Values for Roof Access Hatches and Eaves(1) Except as provided in Sentence (2), the thermal resistance values for insulation required by Articles 3.1.1.2., 3.1.1.3. and 3.1.1.11. for exposed ceilings with attic spaces are permitted to be reduced (a) directly above access hatches, and (b) near eaves to the extent made necessary by the roof slope and required…).

Venting and baffles

Attic insulation must not block the attic ventilation. Where insulation sits under the roof sheathing, a vented space is required between the two (9.19.1.1.OBC Div. B 9.19.1.1. Required Venting(1) Except where it can be shown to be unnecessary, where insulation is installed between a ceiling and the underside of the roof sheathing, a space shall be provided between the insulation and the sheathing, and vents shall be installed to permit the movement of air from the space to the exterior. (See Note…), with an unobstructed vent area of at least 1/300 of the insulated ceiling area, or 1/150 for low slopes and roof joists (9.19.1.2.OBC Div. B 9.19.1.2. Vent Requirements(1) Except as provided in Sentence (2), the unobstructed vent area shall be not less than 1/300 of the insulated ceiling area. (2) Where the roof slope is less than 1 in 6 or in roofs that are constructed with roof joists, the unobstructed vent area shall be not less than 1/150 of the insulated ceiling area. (3)…).

At the eaves, preformed baffles hold the insulation back from the vents. They must leave an air space of at least 25 mm between the insulation and the sheathing, large enough to meet the vent area rule, and extend at least 50 mm above the top of the insulation (9.19.1.3.(2)OBC Div. B 9.19.1.3. Clearances(1) Except as provided in Sentence (2), where venting is provided to a roof joist space, not less than 63 mm of space shall be provided between the top of the insulation and the underside of the roof sheathing. (2) Where venting is provided at the junction of sloped roofs and exterior walls and where preformed baffles…). In vented roof joist spaces, keep at least 63 mm clear above the insulation (9.19.1.3.(1)OBC Div. B 9.19.1.3. Clearances(1) Except as provided in Sentence (2), where venting is provided to a roof joist space, not less than 63 mm of space shall be provided between the top of the insulation and the underside of the roof sheathing. (2) Where venting is provided at the junction of sloped roofs and exterior walls and where preformed baffles…). See the attic ventilation guide for the full venting rules.

The attic hatch

An access hatch is required where the attic is at least 10 m² in area, 1,000 mm in length or width, and 600 mm high over that area, or where it contains a fuel-fired appliance. The hatch must be at least 550 × 900 mm, or for a hatch serving only one dwelling unit, 0.32 m² with no dimension under 500 mm, and it needs a door or cover (9.19.2.1.OBC Div. B 9.19.2.1. Access(1) Every attic or roof space shall be provided with an access hatch where the attic or roof space (a) measures not less than (i) 10 m² in area, (ii) 1,000 mm in length or width, and (iii) 600 mm in height over at least the area described in Subclauses (i) and (ii), or (b) contains a fuel-fired appliance. (See Note…). The insulation over the hatch can be thinner, but not below R20.

Air and vapour barrier under the insulation

The ceiling below an attic separates heated space from unheated space, so it needs a continuous air barrier to stop warm, moist air leaking into the attic, where it would condense in winter (9.25.3.1.OBC Div. B 9.25.3.1. Required Barrier to Air Leakage(1) Wall, ceiling and floor assemblies that separate conditioned space from unconditioned space or from the ground shall be constructed so as to include an air barrier system that will provide a continuous barrier to air leakage (a) from the interior of the building into wall, floor, attic or roof spaces sufficient to…). It also needs a vapour barrier on the warm side of the insulation (9.25.4.3.OBC Div. B 9.25.4.3. Installation of Vapour Barriers(1) Products installed to function as the vapour barrier shall protect the warm side of wall, ceiling and floor assemblies. (2) Where different products are used for the vapour barrier and the insulation, the vapour barrier shall be installed sufficiently close to the warm side of the insulation to prevent…). Seal around light boxes, pot lights, the hatch and plumbing stacks. Our vapour barrier guide explains both.

Common mistakes

  1. Mixing packages, such as the attic from one SB-12 column and the windows from another.
  2. Insulation blocking the soffit vents. Use baffles with a 25 mm air space.
  3. Thin insulation over the walls. At the eaves and over the hatch it can drop, but not below R20.
  4. Forgetting the high heel in an HH package.
  5. Leaky ceilings. Without a sealed air barrier, moist air reaches the attic and frosts the sheathing.

How to look it up yourself

The attic values are in Volume 2 of the Compendium, in SB-12. The venting and hatch rules are in Division B, Section 9.19. Search terms that appear in the text:

  • "Ceiling with Attic Space" (the SB-12 package tables)
  • "Roof Access Hatches and Eaves" (SB-12 3.1.1.8.)
  • "Required Venting" and "Clearances" (9.19.1.)
  • "access hatch" (9.19.2.1.)

Read the venting article in the code viewer alongside the hatch article.

BCIN exam angle

Attic vent area, baffle clearances and the attic hatch size are common House exam questions, and the SB-12 packages are tested on the HVAC House exam. Study the House chapter on heat transfer, air leakage and energy efficiency, then try the free quiz on the House exam page.

Based on the official 2024 Building Code Compendium on ontario.ca.

© King's Printer for Ontario, 2024. Reproduced with permission.

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Frequently asked questions

What R-value is required in an attic in Ontario?
For a new house in Zone 1 with a high-efficiency furnace (92% AFUE or more), SB-12 Table 3.1.1.2.A calls for nominal RSI 10.56 (R60) in packages A1, A2, A4 and A6, and RSI 8.80 (R50) in packages A3 and A5. Other heating types and Zone 2 have their own tables. You choose one package and meet every line in it.
Can attic insulation be thinner at the eaves?
Yes. It can be reduced near the eaves where the roof slope and the required vent space leave no room, and directly above the access hatch, but never below RSI 3.52 (about R20) over the hatch and the inner face of the exterior walls (SB-12, Article 3.1.1.8.).
Do I need baffles in my attic?
Where baffles are used at the eaves, they must leave an air space of at least 25 mm between the insulation and the roof sheathing and extend at least 50 mm above the top of the insulation. Ceiling insulation must never block the vents (Division B, Article 9.19.1.3.).
How big does an attic hatch have to be in Ontario?
At least 550 mm by 900 mm, or for a hatch serving only one dwelling unit, at least 0.32 m² with no dimension less than 500 mm. A hatch is required where the attic is at least 10 m² in area, 1,000 mm in length or width and 600 mm high, or contains a fuel-fired appliance (Division B, Article 9.19.2.1.).
What does R60 + HH mean in SB-12?
HH stands for a 250 mm high heel at the eaves (a raised heel truss), so the full depth of insulation can reach over the exterior walls. Some packages require it, and where it is required the wall face below the vent space must be fully insulated (SB-12, Article 3.1.1.8.(2)).