Hygrothermal Analysis

Hygrothermal Analysis

Purpose, Scope, Methods

Numerical hygrothermal analysis was conducted to compare the proposed DfD wall assemblies with corresponding traditional baseline assemblies for light wood frame, mass timber, and precast concrete construction. The purpose of the comparison is to test whether the DfD material and assembly changes can maintain comparable cold-climate thermal and moisture performance while supporting reversible construction and greater use of bio–based materials.

The analysis uses Jonathan Ochshorn’s Exterior Wall Psychrometric Analysis Calculator as a first-pass screening tool. A temperature gradient describes how temperature changes from the exterior to the interior as heat passes through layers with different thermal resistance. The dew point is the temperature at which the local water vapour condition would reach saturation; where the local wall temperature falls to or below the local dew point, condensation may occur. Vapour permeance describes how readily water vapour can diffuse through a material: lower values indicate greater resistance to vapour diffusion. Permeance is a material transport property and should not be interpreted as moisture content [1].

All assemblies were assessed under the same winter temperature boundary conditions: 21°C indoor [2] and −23.7°C outdoors [3]. An exterior relative humidity of 80% was held constant as a screening assumption. The DfD assemblies were evaluated at 35% and 50% indoor relative humidity, while the traditional baselines were evaluated at 50%. Health Canada identifies 30-50% as a recommended indoor relative humidity range; accordingly, 50% is used as the upper- end moisture sensitivity case, and 35% as a drier winter sensitivity case [4]. The comparison is therefore tests whether the DfD assemblies remain compatible with the same imposed winter conditions without introducing additional condensation risk.

The analysis is intended for schematic comparison and not final envelope design. Ochshorn notes that the calculator assumes fixed material permeances and steady-state conditions and does not fully represent humidity-dependent properties, air leakage, moisture storage, drying, rain exposure, or changing environmental conditions. Detailed calculator inputs, material-property assumptions, and raw tabulated outputs are therefore provided in Appendix A for transparency [5].

Tables 1-3 establish the reading framework for the analysis: Table 1 defines the reported psychometric terms, Table 2 records the common winter boundary conditions, and Table 3 summarizes the unit conversions and modelling conventions applied to all three assembly comparisons.

Manufacturer data were used where available for wood-fibre insulation and vapour-control products. Calculator preset values were retained for materials such as Tyvek, fiberglass batt, polyethylene, plywood, and gypsum board where those presets were used directly. Where product-specific values were unavailable, representative values were adopted as preliminary screening assumptions and applied consistently across comparable assemblies. The DLT/CLT and precast-concrete permeance assumptions are therefore not certified product properties. Detailed calculations and sources are provided in Appendix A.

The report figures are intentionally separated to improve readability. Each assembly includes

a temperature-gradient comparison between DfD and traditional construction
a DfD dew-point profile showing the 35% and 50% indoor RH cases
a DfD vapour-permeance profile.

The permeance figure is used to show where vapour-diffusion resistance is concentrated through the wall. For assemblies with non-matching layer sequences, DfD and traditional interface labels are shown separately rather than implying that non-equivalent interfaces are directly comparable.

Tables 4, 5, 6 summarize the nominal thermal resistance of the proposed light wood frame, mass-timber, and precast-concrete DfD assemblies, respectively. The totals are used as an early-stage check against the Québec Part 11 screening targets adopted here: R-24.5 (RSI 4.31) for above-grade exterior walls and R-41.0 (RSI 7.22) for roofs/ceilings [6]. On a nominal basis, all three proposed wall and roof assemblies exceed these screening values.

Hygrothermal Analysis Results By Assembly

Light Wood Frame

The DfD wall replaces conventional XPS exterior insulation, fiberglass cavity insulation, and polyethylene vapour control with wood-fibre insulation and a humidity-responsive vapour-control membrane. The principal layer sequence remains sufficiently similar that corresponding DfD and traditional interfaces can be compared directly. Figures 1, 2, 3 present the temperature gradient, dew point, and DfD vapour-permeance results for this comparison.

No condensation was identified in either light wood –frame wall assembly. (Figures 1 and 2). At 50% indoor relative humidity, the temperature within the DfD wall remained above the dew-point temperature at every evaluated interface. The traditional wall retained slightly more heat at the sheathing and insulated stud cavity because a greater proportion of its thermal resistance is provided by exterior XPS insulation. The DfD wall achieves a comparable screened thermal and moisture result under the same 21°C indoor design condition while using wood-fibre insulation and responsive vapour control in place of the conventional XPS/fiberglass/polyethylene strategy. This supports the project’s circularity and lower-impact material objectives without introducing additional condensation risk.

Mass timber

The DfD mass-timber wall uses exterior wood-fibre insulation, a smart vapour-control membrane, a screw-fixed plywood shear layer, and a DLT structural panel. The traditional baseline uses exterior XPS, a polyethylene vapour barrier, a CLT structural panel, and an interior gypsum finish. Because the layer sequences are not identical, the graph uses separate DfD and traditional interface labels. Figures 4, 5, 6 present the temperature gradient, dew point, and DfD vapour-permeance results for this comparison.

No condensation was identified in either mass-timber assembly (Figures 4 and 5). In the DfD wall, most of the temperature rise occurs across the exterior wood-fibre insulation, keeping the smart membrane, plywood, and DLT panel on the warm side of the 50% RH dew-point profile. The traditional XPS layer produces a similar exterior thermal break and also avoids a condensation flag. Although the two systems distribute thermal resistance differently, both remain compatible with the same 21°C indoor design condition. The DfD assembly therefore demonstrates comparable preliminary envelope performance while substituting a bio–based exterior insulation strategy and reversible layering for the conventional XPS-based approach.

Precast Concrete

he DfD precast wall uses exterior wood-fibre insulation and an air/vapour-control layer outside a single structural concrete wythe. The traditional baseline is a double-wythe insulated sandwich panel comprising an exterior precast wythe, continuous XPS insulation, and an interior structural precast wythe. Figures 7, 8, 9 present the temperature gradient, dew point, and DfD vapour-permeance results for this comparison.

The physical traditional wall contains one continuous 150 mm rigid-foam insulation layer. It is represented in the calculator as two identical 75 mm XPS entries only to provide an intermediate plotting point; this split does not change the total thermal or vapour resistance of the homogeneous 150 mm insulation layer. Unlike framed wall assemblies, an insulated precast sandwich panel does not necessarily require separate sheet membranes for air and vapour control. CMHC guidance identifies the interior structural concrete wythe as the air and vapour barrier, with sealed panel joints maintaining continuity, while the exterior wythe and joint system provide precipitation control [7]. CPCI describes the same control-layer logic in a Canadian sandwich-panel case study [8]. This is also consistent with the National Building Code of Canada vapour-control requirement of no more than 60 ng/(Pa·s·m²) for vapour-barrier materials; the preliminary 150 mm interior-precast value used here is 5 ng/(Pa·s·m²), although final code verification would require tested product data and complete detailing [9].

The DfD precast assembly produced no condensation flag at either 35% or 50% indoor RH (Figures 7 and 8). The traditional sandwich-panel run, by contrast, identified a potential condensation condition at the interface between the exterior concrete wythe and the XPS insulation (Figure 7). At this location, the calculator reports approximately −23.21°C and a dew point of −3.87°C, corresponding to 100% RH. The exterior wythe is intentionally located outside the continuous insulation, so its inner face remains close to the exterior design temperature; the cold exterior wythe itself is therefore an expected feature of this conventional configuration. The next sampled point, an artificial midpoint within the XPS layer, approaches saturation at 94.8% RH but is not flagged.

The traditional flag should be interpreted as a conservative screening indication rather than evidence of envelope failure or a prediction of moisture quantity. Ochshorn’s steady-state calculator assumes fixed permeances and does not fully represent moisture storage, drying, air movement, or changing environmental conditions; he specifically cautions that real wall assemblies can accommodate some condensation where wet materials can subsequently dry [10]. No corresponding flag was identified in the DfD precast assembly, where the wood-fibre insulation is located exterior to a single structural concrete wythe.

Comparative Findings

Table 7 consolidates the assembly-by-assembly screening results shown in Figures 1-9 and highlights the principal comparison between the proposed DfD walls and their traditional baselines.
Across all three construction systems, the DfD assemblies remained above the dew-point profile at every evaluated interface at both 35% and 50% indoor relative humidity. The traditional light wood-frame and mass-timber baselines also avoided condensation at 50% RH, while the traditional precast sandwich panel produced one potential condensation point at its cold exterior-wythe/insulation interface. Taken together, the results indicate that the proposed DfD material and assembly interventions can maintain comparable temperature separation between indoor and outdoor environments without introducing additional condensation risk.

The comparison is especially relevant because the DfD assemblies achieve this screened performance while supporting a different material and construction strategy: reversible connections, greater use of wood-fibre insulation, and reduced reliance on conventional petrochemical insulation in the DfD wall concepts. Where a traditional assembly shows a locally warmer temperature profile, that difference should be read as a consequence of its material-specific distribution of thermal resistance—not as evidence that the DfD assembly fails to meet the same design condition.

Methodological Limitations

This analysis is a one-dimensional, steady-state screening exercise. It evaluates a fixed winter snapshot rather than hourly or seasonal conditions and does not model air leakage, wind pressure, rain entry, capillary transport, framing factors, three-dimensional thermal bridges, construction moisture, or time-dependent drying. Material permeance can vary with product, density, moisture content, coatings, orientation, and test method. Where product-specific data were unavailable, representative values were adopted as preliminary screening assumptions and applied consistently across comparable assemblies; in particular, the DLT/CLT and precast-concrete permeance values should not be presented as certified product properties. Rainscreen cladding, strapping, and selected finish layers were omitted where necessary to maintain a consistent comparison of the principal thermal and vapour-control layers. Accordingly, a ‘no condensation’ result should be interpreted as favourable preliminary evidence rather than proof of long-term durability, and the single traditional-precast flag should likewise be treated as an indication for further investigation rather than a definitive failure.

Disclosure

The calculations presented are schematic, nominal comparisons intended to support early-stage assembly design. The moisture analysis is based on theoretical, steady-state numerical calculations using a psychrometric calculator rather than physical experimental testing, laboratory mock-ups, or field monitoring. The analysis should therefore be treated as general information only. Final effective R-values, condensation and mould-growth risk, structural performance, fire resistance, acoustic performance, and code compliance ~~would~~ require detailed manufacturer data, thermal-bridge modelling, transient hygrothermal simulation, and professional review. All assemblies should be developed and verified in consultation with qualified building-envelope engineers to prevent envelope failure and mould growth.

References

Hygrothermal Analysis

Reclaimable materials: Exterior cladding, façade systems, staircases and railings.

This step is focused on processing substructure materials within the Site layer, including reinforced concrete foundations, piles, and slabs-on-grade. These elements are deeply integrated and rarely recoverable as components. Instead, material recovery is achieved through crushing concrete for aggregate and separating embedded steel for recycling.

As the most permanent layer, the Site layer offers limited adaptability, and circular outcomes depend primarily on high-volume recycling strategies rather than component reuse.

Reclaimable materials: Beams and girders, columns and floor slabs.

This stage is focused on extracting materials from the Structure layer, mainly reinforced concrete and structural steel.

Steel elements may be recoverable in some cases where connections permit disassembly, although most are directed to recycling. Concrete is typically cut, removed, and processed into recycled aggregate.

Due to the structural interdependence of this layer, removal must follow strict sequencing to avoid instability, highlighting the challenges of recovering long-lifespan materials in highly integrated systems.

Reclaimable materials:Exterior cladding, façade systems, staircases and railings.

This step is focused on removing façade and enclosure systems within the Exterior layer, including curtain wall panels, cladding units, and roofing assemblies. Panelised systems may be recovered intact if disassembled carefully, while metals such as aluminium and steel are directed toward recycling. As these systems are often integrated with both Services and Structure, their removal requires careful sequencing to maintain stability.

This step establishes clear separation between the building envelope and the primary structural frame.

Reclaimable materials: Floor tiles, wall finishes, ceiling systems and non-load-bearing partitions.

This stage is focused on separating high-volume materials within the Partition layer, such as suspended ceilings, gypsum board, and floor finishes. While reuse potential is generally limited, certain modular or demountable systems may be recovered.

Material separation is critical to prevent contamination and enable recycling pathways, particularly
for metals and gypsum. Removing these enclosing layers exposes the structural frame and service routes, allowing the transition from short- to long-lifespan layers within the deconstruction sequence.

Reclaimable materials: Electrical wiring and panels, plumbing lines and mechanical systems.

This step is focused on removing extensive Services layer networks, including vertical risers, ductwork, piping, and centralised mechanical equipment. Materials such as copper, steel, and aluminium are prioritised for recycling, while larger equipment units may be recoverable for reuse. Given their integration with multiple layers, including Structure and Exterior, services must be removed in a sequenced manner to avoid damaging adjacent materials.

This step reduces system interdependencies and enables the exposure of structural and enclosure layers.

Reclaimable Materials: Doors, hardware, cabinetry, and fixtures.

This stage is focused on extracting Stuff-layer materials at scale, including furniture, fixtures, and modular interior elements.

Standardised components such as doors, ceiling tiles, and demountable partitions are often present in large quantities and can support bulk recovery. As these materials are weakly connected to other shearing layers, they can be removed without compromising overall stability. However, variability across tenant spaces may affect reuse pathways, requiring careful sorting to maintain material quality and value.

Reclaimable Materials: None

This step is focused on isolating hazardous materials distributed across several shearing layers, particularly within Services, Partition, and Exterior systems.

Asbestos-containing fireproofing, PCB sealants, and contaminated insulation are commonly embedded within structural protection layers and façade assemblies. These materials constrain the recovery of adjacent steel, aluminium, and concrete elements. Controlled abatement therefore enables the decoupling of contaminated layers, ensuring that structural and enclosure materials can be recovered without cross-contamination, which is critical given the scale and integration of these systems.

Reclaimable materials: Foundation, slabs-on-grade and footing.

This step involves removing materials associated with the Site layer, including concrete foundations, basement walls, and footings. These materials have minimal reuse potential due to their permanence and integration with the ground. However, bricks or stones may occasionally be recovered, while concrete is typically crushed for use as recycled aggregate. This stage marks the transition from selective deconstruction to material processing, with recovery focused on bulk mineral streams.

Reclaimable materials: Beams and girders, columns and floor slabs.

This stage involves dismantling the Structure layer, typically composed of light timber framing. Materials such as beams, joists, and studs can often be recovered for reuse if connections are mechanically fastened and carefully reversed.

Sequential disassembly preserves material integrity and prevents damage to adjacent elements. As the Structure layer has a longer lifespan and higher load-bearing function, its careful removal is essential to maximise reuse potential while maintaining safety throughout the process.

Reclaimable Materials: Exterior cladding, façade systems, staircases and railings.

This step involves dismantling materials located at the interface of the Exterior and Partition layers, including roof assemblies, brick veneer, balconies, and light timber framing.

Timber elements may be salvaged where connections can be reversed, while brick recovery depends on mortar condition. These components contribute locally to load distribution but are not part of the primary structural system. Their removal separates enclosure systems from the structural core, enabling access to higher-value materials within the Structure layer.

Reclaimable Materials: Floor tiles, wall finishes, ceiling systems and non-load-bearing partitions.

This stage involves removing materials associated with the Partition layer, including plaster, gypsum board, hardwood flooring, and interior finishes.

Selective dismantling allows the recovery of durable materials such as flooring and trim, while gypsum-based products are typically directed to recycling. As the Partition layer mediates between Services and Structure, its removal exposes concealed timber elements and mechanical systems, improving access for
further disassembly and enhancing the visibility of recoverable materials embedded in longer-lifespan layers.

Reclaimable Materials: Electrical wiring and panels, plumbing lines, and mechanical systems

This step involves dismantling materials within the Services layer, including copper wiring, plumbing lines, compact HVAC units, and radiators. These systems are typically interwoven with the Partition layer but remain accessible within walls and floors.

Recovery focuses on high-value metals such as copper and steel, while certain components may be directly reused. Removing services decouples intermediate-lifespan systems from longer-lifespan structural elements, facilitating safer and more effective subsequent material recovery.

Reclaimable Materials: None

This step involves the removal of hazardous materials embedded within the exterior, partition, and services layers. Materials such as asbestos insulation, lead-based finishes, and mold-contaminated assemblies are isolated to prevent the contamination of recoverable materials. In Quebec, building materials from before 1990 are presumed to contain asbestos unless tested otherwise [1]. These hazards often affect interior finishes and service zones, and their removal enables the safe recovery of uncontaminated elements located in the Structure and Partition layers. This step separates contaminated from recoverable layers, allowing subsequent disassembly to proceed under safe and controlled conditions.

References

Gouvernement du Québec, “Preventing Health Problems Associated with Asbestos,” Gouvernement Du Québec, January 12, 2021, https://www.quebec.ca/en/health/advice-and-prevention/health-and-environment/preventing-health-problems-associated-with-asbestos.

Reclaimable Materials: Doors, hardware, cabinetry and fixtures.

This stage involves the removal of materials associated with the Stuff layer, which comprises short-lifespan and loosely attached elements with high reuse potential.

Components such as furniture, appliances, lighting fixtures, doors, cabinetry, and radiators are extracted intact to preserve their functional value. These elements are minimally integrated with other layers, allowing efficient recovery.

Early removal reduces the risk of damage during subsequent operations and prevents contamination of these high-value components by materials from longer-lifespan layers.