Other Building Materials

Overview

Building envelope materials beyond conventional insulation and structural components significantly impact HVAC load calculations and system performance. Glass, ceramics, roofing membranes, gypsum products, and earth materials each exhibit distinct thermal behaviors that influence heat transfer, thermal mass effects, and overall building energy performance.

Accurate thermal property data for these materials enables proper load calculations per ASHRAE Fundamentals and ensures compliance with energy codes including ASHRAE 90.1, IECC, and Title 24.

Glass and Glazing Materials

Window Glass

Glass exhibits high thermal conductivity compared to typical insulation materials, making it a critical component in building envelope thermal performance.

Thermal Properties

Standard float glass:

where:

• k = thermal conductivity
• c = specific heat capacity
• ρ = density
• α = thermal diffusivity

Low-emissivity coatings:

Low-e coatings reduce radiative heat transfer but do not significantly alter the glass substrate thermal conductivity. The coating layer (typically 100-300 nm) affects surface emissivity (ε):

• Uncoated glass: ε = 0.84
• Hard-coat low-e: ε = 0.15-0.20
• Soft-coat low-e: ε = 0.04-0.10

Insulating Glass Units (IGU)

The effective thermal resistance of IGU assemblies depends on:

1. Gas fill thermal conductivity (W/m·K at 10°C):

   • Air: k = 0.0241
   • Argon: k = 0.0163 (32% lower than air)
   • Krypton: k = 0.0088 (63% lower than air)
   • Xenon: k = 0.0051 (79% lower than air)

2. Gap width optimization:

   • Air/argon: optimum 12-16 mm
   • Krypton: optimum 8-10 mm (allows thinner profiles)
   • Below optimum: increased conduction
   • Above optimum: increased convection

3. Edge effects:

   • Aluminum spacers: k = 160 W/m·K (thermal bridge)
   • Stainless steel spacers: k = 17 W/m·K
   • Insulated spacers: k = 0.2-0.3 W/m·K

Solar Heat Gain Considerations

While not purely thermal conduction properties, solar optical characteristics directly affect HVAC cooling loads:

Reference: ASHRAE Handbook—Fundamentals, Chapter 15: Fenestration

Temperature Limits

• Standard annealed glass: continuous service to 100°C
• Tempered glass: continuous service to 250°C
• Thermal shock resistance: 40-50°C for annealed, 200°C for tempered
• Glass stress failure occurs at temperature differentials >20°C across pane

Glass Block

Glass block walls provide daylighting with improved thermal performance versus standard glazing.

Thermal properties:

The glass itself: k = 1.0 W/m·K, but the assembly includes air space and mortar joints.

Specialty Glass

Fire-rated glass:

• Wired glass: k = 1.0 W/m·K (wire has negligible impact on bulk conductivity)
• Ceramic glass: k = 1.1-1.3 W/m·K
• Intumescent interlayer systems: k = 0.9-1.0 W/m·K (base glass)

Security glazing:

• Laminated glass: k = 0.95-1.0 W/m·K (PVB interlayer: k = 0.17 W/m·K)
• Impact-resistant: k = 1.0 W/m·K (multiple glass plies with polymer interlayers)

Ceramic Materials

Clay Brick and Tile

Fired clay products exhibit variable thermal properties based on density and firing temperature.

Solid clay brick:

Hollow clay tile:

Temperature Performance

• Continuous service: up to 800°C for standard brick
• Thermal expansion coefficient: 5-7 × 10⁻⁶ /°C
• High thermal mass provides beneficial thermal lag in diurnal temperature swings
• Time lag for 200mm brick wall: approximately 8-10 hours

Ceramic Tile and Porcelain

Wall and floor tile:

Thin-set mortar adhesive:

• k = 0.7-0.9 W/m·K
• Typical thickness: 3-6 mm
• Contributes minimal thermal resistance

Grout:

• Cementitious grout: k = 0.9-1.1 W/m·K
• Epoxy grout: k = 0.3-0.5 W/m·K

HVAC Design Considerations

1. Thermal mass impact:

   • Ceramic floors provide thermal storage for radiant heating systems
   • High heat capacity moderates temperature swings
   • Porcelain: volumetric heat capacity = 2.11 MJ/m³·K

2. Radiant system response:

   • Higher conductivity improves surface temperature uniformity
   • Thermal diffusivity affects system response time
   • 12mm porcelain over radiant: response time ≈ 1.5-2 hours

3. Condensation risk:

   • Low vapor permeability creates moisture barrier
   • Surface temperature must remain above dew point
   • Critical in humid climates and pool environments

Gypsum Products

Gypsum Wallboard (Drywall)

Standard gypsum board consists of gypsum plaster core between paper facing layers.

Thermal properties:

Foil-backed enhancement:

• Adds reflective air space resistance
• Requires minimum 19mm air space
• Additional R = 0.44 m²·K/W (foil facing 19mm air space)

Moisture Effects

Thermal conductivity increases significantly with moisture content:

Water has k = 0.60 W/m·K, dramatically increasing heat transfer through wetted gypsum.

Fire Performance

Type X gypsum board contains glass fiber reinforcement and other additives:

• 15.9mm (5/8"): 1-hour fire rating
• Gypsum dehydration endothermic reaction absorbs heat
• Releases chemically bound water at 100-150°C, creating steam barrier

Gypsum Plaster

Three-coat system thermal properties:

Total assembly:

• 19mm three-coat plaster: R = 0.086 m²·K/W
• Higher density than drywall provides greater thermal mass
• Volumetric heat capacity: 1.32-1.38 MJ/m³·K

Gypsum Sheathing

Exterior gypsum sheathing used in wall assemblies:

The glass mat facing (not paper) provides weather protection but does not alter thermal properties.

Composite Materials

Fiber-Reinforced Polymer (FRP)

FRP panels used in humid environments (kitchens, pools, healthcare) have distinct thermal properties.

Material properties:

Thickness: typically 1.0-2.5mm over substrate

Temperature limits:

• Polyester matrix: continuous service to 80°C
• Vinyl ester: continuous service to 95°C
• Epoxy: continuous service to 120°C
• Heat deflection temperature: 95-180°C depending on formulation

Fiber-Cement Panels

Fiber-cement cladding and siding materials:

Thermal properties:

Characteristics:

• Non-combustible (reaction-to-fire class A1)
• Stable thermal properties across temperature range -40°C to +80°C
• Low thermal expansion: 6-8 × 10⁻⁶ /°C
• Moisture-stable thermal performance

Phenolic Foam Composites

Rigid phenolic foam boards and faced panels:

Core thermal properties:

Faced panels:

• Aluminum foil facers: add vapor barrier, improve R-value
• Glass tissue facers: improve fire performance
• Composite facers: k = 0.020-0.023 W/m·K (overall assembly)

Temperature performance:

• Continuous service: -180°C to +120°C
• Fire performance: self-extinguishing, low smoke
• Aging: k increases 5-10% over 25 years as cell gas diffuses

Roofing Membranes

Single-Ply Membranes

Flexible roofing membranes exhibit low thermal resistance but affect total roof assembly performance.

EPDM (Ethylene Propylene Diene Monomer):

PVC (Polyvinyl Chloride):

TPO (Thermoplastic Polyolefin):

Thermal Resistance

Individual membrane R-values are negligible:

• 1.5mm EPDM: R = 0.006 m²·K/W
• 1.5mm PVC: R = 0.008 m²·K/W
• 1.5mm TPO: R = 0.008 m²·K/W

Solar Reflectance Impact

Membrane color significantly affects cooling loads via solar reflectance:

SRI = Solar Reflectance Index per ASTM E1980

Cooling load impact:

• White membrane vs. black can reduce roof surface temperature by 30-50°C on summer day
• Peak heat flux reduction: 50-80 W/m² for well-insulated roof
• Greater impact on poorly insulated roofs

Temperature Limits

Service temperature ranges:

• EPDM: -45°C to +150°C (brief exposure)
• PVC: -35°C to +80°C continuous, +105°C brief
• TPO: -40°C to +115°C continuous

Heat welding temperatures:

• PVC: 425-650°C (hot air welding)
• TPO: 540-600°C (hot air welding)
• EPDM: solvent or tape bonded (not heat welded)

Built-Up Roofing (BUR)

Asphalt and tar-based systems with aggregate surfacing.

Typical assembly layers:

Four-ply assembly thermal properties:

• Total thickness: approximately 15-20mm
• Effective k: 0.12-0.16 W/m·K
• R-value: 0.094-0.167 m²·K/W

Aggregate surfacing impact:

• Provides thermal mass and UV protection
• Light-colored gravel increases solar reflectance
• Gravel holds moisture, maintaining cooler roof temperature via evaporation

Modified Bitumen

APP (Atactic Polypropylene):

• k = 0.17-0.20 W/m·K
• Thickness: 3-4mm
• Heat applied installation
• Service temperature: -30°C to +120°C

SBS (Styrene-Butadiene-Styrene):

• k = 0.17-0.19 W/m·K
• Thickness: 3-4mm
• Heat or cold applied
• Service temperature: -45°C to +135°C
• Superior low-temperature flexibility

Asphalt Shingles

Composition shingles widely used in residential steep-slope roofing.

Thermal Properties

Standard three-tab shingles:

Architectural (dimensional) shingles:

• Thickness: 6-8mm at thickest point
• Similar k values
• Slight additional thermal mass

Solar Reflectance Properties

Shingle color dramatically affects attic and cooling loads:

Cool roof shingles:

• Specially formulated pigments increase solar reflectance
• ENERGY STAR rated steep-slope products: SR ≥ 0.25 (initial)
• Can reduce attic temperature by 10-20°C versus standard dark shingles
• Cooling load reduction: 10-20% in cooling-dominated climates

Composition and Structure

Material layers:

1. Mineral granules (ceramic-coated): weather protection, color, solar reflectance
2. Asphalt coating: waterproofing
3. Fiberglass mat: reinforcement (k ≈ 0.04 W/m·K)
4. Asphalt coating: adhesion
5. Back surface treatment: anti-stick coating

Temperature performance:

• Service range: -45°C to +110°C
• Surface temperature on black shingle: can exceed 80°C
• Thermal cycling drives aging and degradation

Earth Materials

Soil Thermal Properties

Soil thermal characteristics vary dramatically with moisture content, density, and mineral composition.

Dry soil (moisture content <5% by mass):

Moist soil (moisture content 15-25% by mass):

Saturated soil (moisture content >30% by mass):

Water content dominates thermal behavior: k(water) = 0.60 W/m·K versus k(air) = 0.025 W/m·K.

HVAC Applications

Earth-coupled systems:

1. Ground-source heat pumps:

   • Require accurate soil k for ground loop sizing
   • In-situ thermal conductivity testing recommended for large systems
   • IGSHPA guidelines specify thermal response testing for systems >50 kW
   • Typical design assumption: k = 1.5-2.5 W/m·K for moist soils

2. Earth-sheltered construction:

   • Soil thermal mass moderates temperature swings
   • Annual temperature amplitude at depth z: A(z) = A₀ × exp(-z/d)
   • Damping depth: d = √(α × P / π) where P = 365 days
   • For typical soil α = 0.05 × 10⁻⁶ m²/s: d ≈ 2.1 m
   • Temperature stable at depth >3-4 m (approximately mean annual air temperature)

3. Underslab insulation design:

   • Soil heat loss path must be considered
   • Higher moisture content increases heat loss
   • Perimeter insulation more critical than center-of-slab

Temperature variation with depth:

Compacted Fill and Base Materials

Crushed stone/gravel base:

• k = 0.8-1.5 W/m·K (dry)
• k = 1.5-2.2 W/m·K (moist)
• High drainage reduces moisture content and k
• Used under slabs and earth-coupled heat exchangers

Controlled low-strength material (CLSM):

• k = 1.0-1.4 W/m·K
• Flowable fill used around underground piping
• Provides uniform thermal contact for buried thermal systems

Rammed Earth and Adobe

Rammed earth walls:

Adobe brick:

• k = 0.50-0.70 W/m·K
• ρ = 1400-1600 kg/m³
• c = 950-1050 J/kg·K
• High thermal mass benefits in climates with large diurnal temperature swings

Thermal performance:

• R-value: 0.20-0.30 m²·K/W per 300mm thickness
• Time lag: 10-12 hours for 300-400mm wall
• Decrement factor: 0.15-0.25 (significant peak load reduction)

Temperature Correction Factors

Thermal conductivity varies with temperature. For most building materials:

k(T) = k₀ × [1 + β(T - T₀)]

where:

• k₀ = reference conductivity at T₀ (typically 20°C)
• β = temperature coefficient (1/K)

Typical β values:

• Glass: β = 0.0001 to 0.0005 /K
• Ceramic materials: β = 0.0002 to 0.0008 /K
• Gypsum: β = 0.0015 to 0.0025 /K
• Polymers: β = 0.002 to 0.005 /K
• Soil (dry): β = 0.001 to 0.002 /K

For temperature range 0-40°C encountered in most building applications, correction is typically <5% and often neglected in load calculations.

ASHRAE and Code References

Primary references:

1. ASHRAE Handbook—Fundamentals, Chapter 26: Heat, Air, and Moisture Control in Building Assemblies—Material Properties

   • Tables 1-3: Thermal properties of building materials
   • Methodology for effective assembly properties

2. ASHRAE Handbook—Fundamentals, Chapter 15: Fenestration

   • Window thermal and optical properties
   • NFRC rating procedures
   • Solar heat gain calculations

3. ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings

   • Minimum thermal performance requirements
   • Fenestration U-factor and SHGC criteria by climate zone

4. ASTM C177: Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus

   • Reference method for thermal conductivity determination

5. ASTM C518: Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus

   • Alternative test method for thermal conductivity

6. NFRC 100: Procedure for Determining Fenestration Product U-factors

   • Standard window thermal performance rating

7. IGSHPA Design and Installation Standards

   • Ground thermal properties for geothermal systems

Design Considerations

Load Calculation Accuracy

1. Use appropriate material properties:

   • Reference ASHRAE Fundamentals tables
   • Account for moisture effects in humid climates
   • Consider aging effects for foam insulations

2. Fenestration dominates envelope performance:

   • Window area and properties critical in load calculations
   • SHGC more important than U-factor in cooling-dominated buildings
   • Properly model shading devices and overhangs

3. Thermal mass impacts peak loads:

   • Materials with high ρ × c reduce peak loads and shift timing
   • Important for thermal storage systems
   • Radiant time series method accounts for mass effects

Assembly Performance

1. Material layers interact:

   • Series thermal resistance: R_total = Σ R_i
   • Parallel heat flow paths reduce effective R-value
   • Air films and cavities contribute significant resistance

2. Air barriers and vapor retarders:

   • Convective loops in air spaces increase effective k
   • Moisture accumulation degrades performance
   • Proper sequencing of materials prevents condensation

3. Thermal bridging:

   • Metal components create parallel high-conductivity paths
   • Steel studs, window frames, balcony connections
   • Isothermal planes method or finite element analysis for complex geometry

System Selection

1. Radiant systems require conductive surfaces:

   • Ceramic tile excellent for radiant floors (k = 1.0-1.5 W/m·K)
   • Carpet poor for radiant (k = 0.05-0.08 W/m·K with pad)
   • Surface material affects system capacity and control response

2. Cool roof selection:

   • Mandatory in some jurisdictions (Title 24, ASHRAE 90.1 Climate Zones 1-3)
   • Greater benefit for buildings with high roof-to-wall ratio
   • Consider aesthetics, especially for steep-slope applications

3. Ground-coupled systems:

   • Require site-specific soil thermal properties
   • Thermal conductivity testing for systems >100 kW
   • Soil moisture content varies seasonally—impacts performance

Moisture Management

1. Hygroscopic materials:

   • Gypsum, wood, earth materials absorb moisture
   • Thermal conductivity increases 50-100% at high humidity
   • Can lead to mold growth and IAQ issues

2. Vapor drive:

   • Materials with low vapor permeability trap moisture
   • Vapor retarder placement depends on climate
   • Avoid double vapor barriers

3. Interstitial condensation:

   • Occurs when vapor pressure exceeds saturation in assembly
   • Dew point analysis required for cold climates
   • Insulation placement affects condensation risk

Summary

Thermal properties of glass, ceramics, composites, membranes, gypsum, and earth materials significantly impact HVAC system design and energy performance. Key considerations include:

• Glass thermal conductivity (k = 1.0 W/m·K) creates fenestration heat loss/gain; low-e coatings and insulating gas fills improve performance
• Ceramic materials provide high thermal mass (ρc = 1.8-2.1 MJ/m³·K), beneficial for load shifting and radiant systems
• Gypsum products offer moderate insulation (k = 0.16-0.17 W/m·K) but performance degrades significantly with moisture
• Roofing membranes provide negligible R-value but color/reflectance dramatically affects cooling loads (ΔT = 30-50°C)
• Soil thermal properties vary by factor of 5-8 with moisture content, critical for ground-coupled systems
• Accurate material data from ASHRAE Fundamentals and testing per ASTM standards ensures proper load calculations and system sizing

Understanding these properties enables HVAC professionals to perform accurate load calculations, optimize system selection, and design energy-efficient building envelopes that meet code requirements and performance objectives.