Skip to content
BCIN ExamBCIN Exam

Code guide

Basement Insulation and the Ontario Building Code

Basement insulation under the 2024 Ontario Building Code: SB-12 packages (often R20 ci), the 200 mm floor gap, slabs, rim joists and vapour barriers.
basement walls, the most common package value
RSI 3.52 ci
basement walls, the most common package value
max gap above the basement floor
200 mm
max gap above the basement floor
heated slab, or slab within 600 mm of grade
RSI 1.76
heated slab, or slab within 600 mm of grade
heating degree days that start Zone 2
5,000
heating degree days that start Zone 2

Last updated

For a new house under the 2024 Ontario Building Code, the most common SB-12 prescriptive packages require basement walls to have RSI 3.52 continuous insulation (R20 ci), or the permitted equivalent of RSI 2.11 + 1.76 ci (R12 + R10 ci), installed from the underside of the subfloor to within 200 mm of the basement floor (SB-12 3.1.1.7.OBC SB-12 3.1.1.7. Insulation of Foundation Walls(1) Foundation walls enclosing heated space shall be insulated from the underside of the subfloor to not more than 200 mm above the finished floor level of the basement. (See Appendix A.) (2) The insulation required by Sentence (1) may be provided by a system installed, (a) on the interior of the foundation wall, (b)…, SB-12 3.1.1.2.OBC SB-12 3.1.1.2. Energy Efficiency for Buildings Located in Zone 1(1) Except as provided in Sentences (2) to (5) and (7), the minimum thermal performance of building envelope assemblies and equipment shall conform to Table 3.1.1.2.A. (2) Except for solid fuel-burning space heating equipment and except as provided in Sentence (5), where the space heating equipment efficiency is 84%…). These requirements come through Part 12 of Division B, which points Part 9 houses to Supplementary Standard SB-12 (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…).

Ontario does not use the national energy section for houses: Section 9.36 is reserved in the Ontario code. That is why searches for "9.36 basement insulation" lead people astray. This page explains where the rules really are. Your building department confirms what applies to your house and permit.

Basement insulation values at a glance

Element Typical SB-12 prescriptive value Where to look
Basement walls (most common value) RSI 3.52 ci (R20 ci); some packages require more SB-12 Tables 3.1.1.2.A to 3.1.1.3.C
Permitted swap RSI 2.11 + 1.76 ci (R12 + R10 ci) notes to the SB-12 tables
Gap allowed at the bottom of the wall up to 200 mm above the basement floor SB-12 3.1.1.7.(1)
Heated slab, or slab within 600 mm of grade RSI 1.76 (about R10) SB-12 tables and 3.1.1.7.(5) to (7)
Walk-out basement walls same as above-grade walls (in listed cases) SB-12 3.1.1.1.(10)
Rim joist or header at least the above-grade wall value SB-12 3.1.1.1.(14)
Basement walls in an addition RSI 3.52 ci (R20 ci) SB-12 Table 3.1.1.11.

"ci" means continuous insulation. Values are our summary of the packages; the package you choose for the house sets the actual number.

How the energy rules fit together

12.2.1.2.(3)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… gives a Part 9 house that is occupied through the winter two options: be designed to beat the energy efficiency levels of the 2012 code by at least 15%, or follow Chapters 1 and 3 of SB-12. SB-12 then offers three routes: prescriptive compliance packages, a performance path, or other acceptable methods (SB-12 1.1.1.3.OBC SB-12 1.1.1.3. Compliance Options(1) The energy efficiency of a building or part of a building of residential occupancy that is within the scope of Part 9 of Division B of the Building Code and is intended for occupancy on a continuing basis during the winter months shall comply with (a) Subsection 3.1.1. (Prescriptive Compliance Packages) of Chapter…).

Most builders use a prescriptive package. You first find your climate zone: Zone 1 has fewer than 5,000 heating degree days and Zone 2 has 5,000 or more (SB-12 3.1.1.1.OBC SB-12 3.1.1.1. Energy Efficiency(1) Except as provided in Articles 3.1.1.4. to 3.1.1.11., the building shall conform to (a) Article 3.1.1.2. if the building is located in Zone 1 with less than 5000 heating degree days, or (b) Article 3.1.1.3. if the building is located in Zone 2 with 5000 or more heating degree days. (2) Except as required in…). You then pick a package from the table for your zone and heating equipment (SB-12 3.1.1.2.OBC SB-12 3.1.1.2. Energy Efficiency for Buildings Located in Zone 1(1) Except as provided in Sentences (2) to (5) and (7), the minimum thermal performance of building envelope assemblies and equipment shall conform to Table 3.1.1.2.A. (2) Except for solid fuel-burning space heating equipment and except as provided in Sentence (5), where the space heating equipment efficiency is 84%…, SB-12 3.1.1.3.OBC SB-12 3.1.1.3. Energy Efficiency for Buildings Located in Zone 2(1) Except as provided in Sentences (2) to (5) and (7), the minimum thermal performance of building envelope assemblies and equipment shall conform to Table 3.1.1.3.A. (2) Except for solid fuel-burning space heating equipment and except as provided in Sentence (5), where the space heating equipment efficiency is 84%…). Each package lists values for every part of the envelope, including basement walls and slabs.

Reading the tables: in the Zone 1 package table for high-efficiency furnaces, most packages list RSI 3.52 ci for basement walls, one lists RSI 2.11 + 1.76 ci, and one allows RSI 2.11 + 0.88 ci (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…). The Zone 2 equivalent lists RSI 3.52 ci for every package (SB-12 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…), while the Zone 2 tables for lower-efficiency furnaces and electric heat ask for more in several packages, such as RSI 3.52 + 1.76 ci or RSI 3.52 + 2.11 ci (SB-12 Table 3.1.1.3.BOBC SB-12 Table 3.1.1.3.B. (SI) — Zone 2 — Compliance Packages for Space Heating Equipment with 84% ≤ AFUE < 92%Table 3.1.1.3.B. (SI) — Zone 2 — Compliance Packages for Space Heating Equipment with 84% ≤ AFUE < 92% Forming Part of Sentence 3.1.1.3.(2) Component | Thermal Values[8] | Compliance Package B1 | Compliance Package B2 | Compliance Package B3 | Compliance Package B4 | Compliance Package B5 | Compliance Package B6…, SB-12 Table 3.1.1.3.COBC SB-12 Table 3.1.1.3.C. (SI) — Zone 2 — Compliance Packages for Electric Space HeatingTable 3.1.1.3.C. (SI) — Zone 2 — Compliance Packages for Electric Space Heating Forming Part of Sentence 3.1.1.3.(3) Component | Thermal Values[8] | Compliance Package C1 | Compliance Package C2 Ceiling with Attic Space | Minimum Nominal RSI[1] | 10.56 + HH | 8.80 Ceiling with Attic Space | Maximum U[2] | 0.095 |…). Table notes let you substitute RSI 2.11 + 1.76 ci for RSI 3.52 ci and the reverse.

Where the insulation goes

  • Height. Foundation walls enclosing heated space are insulated from the underside of the subfloor to not more than 200 mm above the finished basement floor (SB-12 3.1.1.7.(1)OBC SB-12 3.1.1.7. Insulation of Foundation Walls(1) Foundation walls enclosing heated space shall be insulated from the underside of the subfloor to not more than 200 mm above the finished floor level of the basement. (See Appendix A.) (2) The insulation required by Sentence (1) may be provided by a system installed, (a) on the interior of the foundation wall, (b)…). Part 9 itself says insulation is installed over the full height of foundation walls enclosing a basement (9.25.2.3.(4)OBC Div. B 9.25.2.3. Installation of Thermal Insulation(1) Insulation shall be installed so that there is a reasonably uniform insulating value over the entire face of the insulated area. (2) Insulation shall be applied to the full width and length of the space between furring or framing. (3) Except where the insulation provides the principal resistance to air leakage…), so check how your municipality reads the two together.
  • Inside or outside. Insulation can be on the interior, the exterior, or split between them if the performance is equivalent (SB-12 3.1.1.7.(2)OBC SB-12 3.1.1.7. Insulation of Foundation Walls(1) Foundation walls enclosing heated space shall be insulated from the underside of the subfloor to not more than 200 mm above the finished floor level of the basement. (See Appendix A.) (2) The insulation required by Sentence (1) may be provided by a system installed, (a) on the interior of the foundation wall, (b)…).
  • Slabs. Where part of a basement slab is at or within 600 mm of exterior grade, as in a walk-out, perimeter insulation must extend at least 600 mm below the slab. A slab entirely within 600 mm of grade is insulated over its whole surface, and so is any slab containing heating pipes, ducts or cables (SB-12 3.1.1.7.(5) to (7)OBC SB-12 3.1.1.7. Insulation of Foundation Walls(1) Foundation walls enclosing heated space shall be insulated from the underside of the subfloor to not more than 200 mm above the finished floor level of the basement. (See Appendix A.) (2) The insulation required by Sentence (1) may be provided by a system installed, (a) on the interior of the foundation wall, (b)…).
  • Walk-outs and rim joists. A walk-out basement wall containing the door, or one more than half exposed above ground, must meet the above-grade wall value. Rim joist insulation must be at least the above-grade wall value (SB-12 3.1.1.1.(10) and (14)OBC SB-12 3.1.1.1. Energy Efficiency(1) Except as provided in Articles 3.1.1.4. to 3.1.1.11., the building shall conform to (a) Article 3.1.1.2. if the building is located in Zone 1 with less than 5000 heating degree days, or (b) Article 3.1.1.3. if the building is located in Zone 2 with 5000 or more heating degree days. (2) Except as required in…).

Moisture, vapour and fire protection

Insulating a basement wall is also a moisture problem, and Part 9 handles that separately:

  • Moisture protection for finishes. Where a finish or wood framing is placed against a foundation wall, the interior of the wall must be protected against moisture. If that protection is a membrane or coating, it runs from the floor up to the top of the insulation or finish, but not above exterior grade, and no material below 170 ng/(Pa·s·m²) permeance may be put between the insulation and the wall above ground level (9.13.2.5.OBC Div. B 9.13.2.5. Moisture Protection for Interior Finishes(1) The interior surface of foundation walls below ground level shall be protected by means that minimize the ingress of moisture from the foundation wall into interior spaces, where (a) a separate interior finish is applied to a concrete or unit masonry wall that is in contact with the soil, or (b) wood members are…).
  • Vapour barrier. Insulated assemblies need a vapour barrier on the warm side (9.25.4.1.OBC Div. B 9.25.4.1. Required Barrier to Vapour Diffusion(1) Thermally insulated wall, ceiling and floor assemblies shall be constructed with a vapour barrier so as to provide a barrier to diffusion of water vapour from the interior into wall spaces, floor spaces or attic or roof spaces., 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…).
  • Installation. Insulation must give a reasonably uniform value, fill the full width of the cavity, and touch a low air-permeance element on at least one face (9.25.2.3.OBC Div. B 9.25.2.3. Installation of Thermal Insulation(1) Insulation shall be installed so that there is a reasonably uniform insulating value over the entire face of the insulated area. (2) Insulation shall be applied to the full width and length of the space between furring or framing. (3) Except where the insulation provides the principal resistance to air leakage…). Where it may be damaged it needs a covering such as gypsum board, though mineral fibre in an unfinished basement may simply be covered with a vapour barrier membrane.
  • Foam plastics. Foam insulation in a wall must be protected from the room by an interior finish such as gypsum board or another permitted thermal barrier (9.10.17.10.OBC Div. B 9.10.17.10. Protection of Foamed Plastics(1) Except as provided in Sentences (2) and (3), foamed plastics that form part of a wall or ceiling assembly shall be protected from adjacent space in the building, other than adjacent concealed spaces within attic or roof spaces, crawl spaces, wall assemblies and ceiling assemblies (a) by one of the interior…).

Common mistakes

  1. Looking for Section 9.36. In Ontario it is reserved. Use Part 12 and SB-12.
  2. Quoting one R-value for every house. The basement wall value depends on the package, zone and heating equipment.
  3. Polyethylene on the concrete above grade, behind the insulation, contrary to 9.13.2.5.
  4. Forgetting the rim joist, which must match the above-grade wall.
  5. Leaving foam exposed in a finished basement.

How to look it up yourself

In the 2024 Compendium, open Division B, Part 12 and search "Energy Efficiency Design". Then open SB-12 in Volume 2 and search "Insulation of Foundation Walls", "Basement Walls" (the row in each package table) and "Compliance Packages". For moisture and vapour rules, search Part 9 for "Moisture Protection for Interior Finishes" and "Installation of Vapour Barriers".

Heat transfer (Section 9.25) and energy efficiency (Part 12) are on the House exam syllabus. Read the free House exam study guide and take the free practice quiz on that page.

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

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

Sources

Free accountNo card needed

Start practising for your BCIN exam, free

  • A free practice quiz for each exam
  • Every answer cites its 2024 OBC article
  • Full 70 question timed simulations with a paid plan
  • Works on phone, tablet and computer
Create a free account

Frequently asked questions

What R-value is required for basement walls in Ontario?
Under the SB-12 prescriptive compliance packages, the most common basement wall value is RSI 3.52 continuous insulation (R20 ci), which may be swapped for RSI 2.11 + 1.76 ci (R12 + R10 ci). Some packages, mainly in Zone 2 with lower-efficiency furnaces or electric heat, require more, such as RSI 3.52 + 1.76 ci, and one Zone 1 package allows less. The value depends on the package you choose for the whole house (SB-12, Tables 3.1.1.2.A to 3.1.1.3.C).
Where is the energy code for houses in the 2024 Ontario Building Code?
Section 9.36 is reserved in Ontario's Part 9. Energy efficiency is in Part 12 (Article 12.2.1.2.), which points houses to Supplementary Standard SB-12, Energy Efficiency for Housing, or to a design at least 15% better than the 2012 code's levels.
Do basement walls have to be insulated all the way to the floor?
SB-12 requires foundation walls enclosing heated space to be insulated from the underside of the subfloor to not more than 200 mm above the basement floor, so a gap of up to 200 mm at the bottom is allowed (SB-12, Sentence 3.1.1.7.(1)). Division B, Sentence 9.25.2.3.(4) also asks for insulation over the full height of foundation walls, so ask your building department how it applies both.
Does a basement slab need insulation?
Slabs that are heated, or within 600 mm of exterior grade, need insulation in the SB-12 packages (RSI 1.76, about R10). A slab entirely more than 600 mm below grade generally does not, except in certain packages (SB-12, Article 3.1.1.7. and the compliance package tables).
Do I need a vapour barrier on basement walls?
Insulated walls need a vapour barrier on the warm side (Division B, Subsection 9.25.4.). Separately, Article 9.13.2.5. limits low-permeance membranes on the above-grade part of the foundation wall behind the insulation.