Appeal 35091

N1101.2.3

Table N1104.1(1) requires basement walls enclosing conditioned space to be insulated to a minimum of R-15 for walls greater than 50% below grade, when those walls form part of the building thermal envelope.

Approval is requested to allow an interior basement wall associated with an existing 1890 solid brick foundation to remain uninsulated or partially insulated, in lieu of the prescriptive R-15 insulation requirement, based on performance equivalency and existing energy measures within the building.

Original Text

Instead of exterior insulation, we propose to achieve and exceed the code’s energy efficiency goals by treating the conditioned basement as a complete thermal unit, focusing on air sealing and insulating at more critical and appropriate locations. Our proposed design includes:

Fully Conditioned Space: The basement is and will continue to be a fully conditioned space, integrated into the home's HVAC system with dedicated supply and return air, along with a whole-basement dehumidification system to maintain a relative humidity below 50%.

Rim Joist Insulation: All rim joists at the top of the foundation wall will be meticulously air-sealed and insulated with closed-cell spray foam (or rigid foam board sealed in place). This is the single most significant point of heat loss in a basement, and our approach will address it directly.

Interior Surface Treatment: The interior face of the brick foundation will be cleaned and, if necessary, coated with a high-quality, vapor-permeable silicate paint. This will control brick dust and spalling without trapping moisture within the wall assembly.

Reconsideration text
-Existing solid brick foundation walls (circa 1890), in excellent mortar condition
-Basement is conditioned and supplied by a central, high-efficiency electric heat pump
-No thermostat or independent temperature control located in the basement
-Basement remains part of a single conditioned thermal zone
-Approximately 80% of foundation wall area is below grade
-Attic, main living spaces, and basement ceiling joists are insulated
-Double-pane insulated windows are installed throughout the basement
-Interior basement wall does not form part of the exterior thermal boundary

Original text
Our request is based on established building science principles for historic masonry. Old brick foundations function as a complete system, and altering one part can have severe negative consequences.

A. Moisture Management and Vapor Permeability:
Historic brick and lime mortar are highly porous materials. They are designed to absorb moisture from the surrounding soil and release it to the exterior (or interior) air, allowing the wall to "breathe" and dry out. Applying a non-permeable exterior or interior insulation traps this moisture within the brick. This moisture cannot escape, creating a permanently damp masonry wall.

B. High Risk of Freeze-Thaw Damage (Spalling):
Portland's climate includes numerous freeze-thaw cycles. When moisture trapped inside the brick freezes, it expands, exerting immense pressure on the clay structure. This process, known as spalling, causes the face of the brick to pop off and disintegrate. Over time, this will destroy the structural integrity of the foundation. Insulating on the exterior keeps the brick cold while trapping moisture, creating the perfect conditions for catastrophic spalling.

C. Concealment of Structural Issues:
A bare brick foundation is its own best diagnostic tool. It allows for the immediate visual inspection of cracks, efflorescence (a sign of moisture intrusion), and mortar joint decay. Covering the foundation with an exterior insulation and finish system (EIFS) or other cladding completely conceals the foundation, allowing minor issues to become major structural failures before they are ever detected.

D. The Conditioned Basement as a Superior Energy Solution:
By fully conditioning the basement and thoroughly insulating the rim joists, we are effectively moving the building's thermal boundary. The earth surrounding the basement provides a natural, stable insulating value (approximately R-1 per inch of soil), with ground temperatures remaining relatively constant year-round. The primary source of energy loss is through the rim joists to the cold outside air. The rim joists are covered and insulated via a ceiling existent in the basement.

Reconsideration Text
A. Objective Heat-Loss Comparison
A conservative building envelope analysis was performed comparing existing uninsulated brick walls to the prescriptive R-15 insulated condition.
Existing brick wall effective R-value: R-2.0 (U = 0.50)
Prescriptive insulated wall: R-15 (U = 0.067)
Wall area analyzed: 417 sq ft
Temperature differential (?T): 20°F
Calculated Heat Loss
Uninsulated brick: 4,170 BTU/hr
R-15 insulated wall: 558 BTU/hr
Difference: 3,612 BTU/hr
Annualized under conservative assumptions, this equates to approximately 706 kWh/year, or $99/year in theoretical energy impact.
B. Energy Offset Through Existing Measures
The modest theoretical heat loss associated with the uninsulated wall is offset by existing energy-efficiency measures already installed in the home, including:
High-efficiency electric heat pump (COP ~3.0), significantly exceeding baseline system performance
Fully insulated attic and roof assemblies
Insulated exterior walls on the main living levels
Insulated basement ceiling joists
High-performance double-pane basement windows
These measures reduce total building heat loss by an amount that exceeds the theoretical impact of the interior basement wall insulation in question.

C. HVAC Control and Operational Reality
The basement does not contain a thermostat or independent zoning controls. HVAC operation is governed by the main-level thermostat. As a result:
Basement temperature changes do not increase HVAC runtime
The calculated heat-loss difference does not translate into measurable additional energy use
The calculated values represent an upper-bound theoretical condition rather than actual system behavior
D. Thermal Boundary Clarification
The interior basement wall separates two spaces that are both within the conditioned envelope. It does not separate conditioned space from unconditioned space or the exterior, and therefore does not function as part of the building thermal boundary as defined by code.
E. Moisture and Durability Considerations
The referenced Keeping the Heat In – Chapter 6 document(https://natural-resources.canada.ca/sites/www.nrcan.gc.ca/files/energy/pdf/housing/Chapter6_e.pdf) notes that older brick foundations:
Contain high mortar content
Absorb moisture from surrounding soil
Were not designed for interior vapor-closed insulation assemblies
The document cautions that interior insulation of historic brick foundations may introduce moisture risks and recommends exterior insulation where feasible or expert review prior to interior insulation.
Allowing the interior wall to remain uninsulated or partially insulated reduces the risk of long-term moisture accumulation and masonry degradation, while resulting in only minimal and theoretical energy penalties.

Supporting documentation and calculation is attached.

Conclusion
The proposed alternate approach meets the performance intent of the energy code by quantifying heat loss, demonstrating offset through existing energy measures, and avoiding unnecessary insulation that presents durability risks to a historic foundation.
Approval of this alternate maintains energy efficiency, preserves historic construction, and aligns with the objectives of the Oregon Residential Specialty Code.