Spray Foam and Building-Envelope Glossary

An air barrier limits uncontrolled airflow through the building enclosure. Its continuity at seams, transitions, and penetrations matters as much as the material used.

Air sealing closes leaks at joints, penetrations, and transitions to reduce uncontrolled airflow. It should form a continuous air-control path rather than a collection of isolated foam spots.

The authority having jurisdiction, often shortened to AHJ, is the local organization or official responsible for interpreting and enforcing applicable code and permit requirements. Product literature does not replace its decision.

Backer rod is a compressible material placed in a joint to provide backing and help control sealant geometry where the selected system calls for it. Rod type, size, and compatibility must fit the detail.

A blower door test uses a fan and pressure measurements to evaluate building air leakage under defined conditions. Qualified diagnostic work can help locate connected leakage paths.

One board foot is a volume of 12 inches by 12 inches by 1 inch. Board feet estimate material volume, not thermal performance or guaranteed field coverage.

Bulk water is liquid water from rain, plumbing leaks, or groundwater. Insulation is not a substitute for drainage, flashing, leak repair, or capillary control.

A capillary break interrupts the movement of liquid water through connected pores in materials. Foundation details may use one between damp masonry and moisture-sensitive construction.

Cellulose insulation is commonly made from processed paper fibers with additives and supplied for specified loose-fill, dense-pack, or other installation methods. Coverage and density requirements depend on the exact system.

For foam-plastic surface-burning claims, Class A refers to a classification under the stated test and configuration. It does not establish an hourly fire-resistance rating or permission to leave foam exposed.

Closed-cell foam is a denser, more rigid foam category with mostly closed cells. Thermal resistance, vapor permeance, approved uses, and required thickness remain exact-product questions.

Condensation occurs when water vapor becomes liquid water, including at surfaces cooled below the dew point of nearby air. Surface temperature, humidity, and air paths affect where it occurs.

Continuous insulation extends across framing rather than being confined to individual cavities. Joints, attachments, openings, and connections still require a designed detail.

Cure is the process by which applied foam develops its intended physical properties. Time, temperature, moisture, mixing, and thickness can affect it, so the exact product instructions govern.

Dense-pack insulation places an appropriate fibrous material in a confined cavity at the system’s specified density. It differs from loose fill resting on an open attic floor.

Dew point is the temperature at which cooling air reaches saturation for its current water-vapor content. A surface below that temperature can collect condensation from nearby air.

A drainage plane is the connected water-control surface or system behind cladding that directs water out of the assembly. Seams, flashing connections, and drainage exits must work together.

Drying potential is an assembly’s ability to release incidental moisture toward the interior, exterior, or both. Low-permeance layers on multiple sides can reduce that ability.

An evaluation report documents how an exact product was evaluated against stated code provisions and conditions of use. Verify the formulation, thickness, substrate, covering, and report status rather than relying on a logo alone.

Expanded polystyrene, or EPS, is rigid cellular insulation produced from expanded polystyrene beads. Available types have different physical properties, so the actual board specification governs its use.

Extruded polystyrene, or XPS, is a rigid cellular insulation family produced by extrusion. Compare the specific board’s thermal and physical properties and permitted exposure conditions.

Fiberglass insulation uses fine glass fibers and is supplied in several formats, including batts and blown material. Thermal performance depends on the specified product, thickness or density, and installation.

Fireblocking limits concealed draft openings in locations prescribed by code. “Fire block” foam is not automatically a rated firestop or permission to use the product in every assembly.

A firestop is a tested system of components installed around a penetration or joint in a rated wall or floor assembly. Product color or generic “fire rated” language does not establish a listed system.

Flanking transmission is sound reaching another space through paths other than the direct route through the partition under consideration. Connected construction and shared spaces can limit the isolation achieved in a building.

Flashing directs water at vulnerable enclosure locations such as windows and roof-wall intersections. Its connection to neighboring water-control layers determines whether that water can drain outward.

Foam sealants are intended for defined gap and joint applications. Their permitted opening size, substrates, expansion behavior, and protective requirements come from the exact product instructions.

An ignition barrier is a code-defined protective layer used in certain limited-access spaces and conditions. It is not interchangeable with a thermal barrier for occupied areas.

Installation instructions describe preparation, installation requirements, limitations, and other conditions for a particular product or system. A brief technical-data table may not contain those directions.

An insulation inspection checks specified properties and details such as coverage, fit, thickness, and alignment while they can be assessed. Its conclusions are limited to the inspector’s scope and methods.

Isocyanates are reactive chemicals used to make polyurethane products, including spray foam. Application can create inhalation, skin, and eye exposure, so product-specific controls are required.

A lift is a layer or pass of foam applied to a specified thickness. Maximum thickness and required time between lifts are exact-product limits that affect heat, cure, and quality.

Loose-fill insulation is installed as loose fibers or particles in an application permitted by the system. For attic work, coverage records may distinguish initial installed depth from the settled condition.

Mineral wool is a family of fibrous insulation made from mineral feedstocks such as rock or slag. Cavity batts and exterior boards have different intended uses, attachment needs, and documented properties.

Off-ratio foam results when a two-component system does not deliver its components in the intended proportion. Unexpected softness, persistent tackiness or oiliness, unusual brittleness, discoloration, or persistent odor need qualified evaluation; appearance cannot establish mix ratio.

One-component foam is supplied ready to dispense and typically cures using moisture in the air or substrate. Gap sealants and products approved for open-surface spraying can share this chemistry but are not interchangeable.

Open-cell foam is a lower-density, softer foam category with interconnected cells. Its thermal, air-control, vapor, and water behavior must be confirmed for the exact product and assembly.

Personal protective equipment, or PPE, can include respiratory, eye, face, skin, and body protection selected for the exact task. It supplements isolation and ventilation; it does not make an uncontrolled work zone safe.

Polyisocyanurate, often called polyiso, is a rigid foam insulation family commonly supplied with facings. The foam core, facing, thickness, and reported test conditions all affect the documented performance.

A punch list identifies a location, the observed issue, the responsible party, and the status of an agreed correction. It organizes completion work but is not a technical diagnosis.

R-value measures resistance to heat flow under stated test conditions. It changes with thickness and does not by itself describe whole-assembly performance, air leakage, moisture durability, or code compliance.

Re-entry means returning to a work area under specified conditions and may refer to trained, protected workers. It is not automatically the same as unprotected occupant re-occupancy.

Re-occupancy is the point when residents, children, pets, or other unprotected occupants may use the space again under stated conditions. It can require a different threshold from worker re-entry.

Relative humidity is water-vapor pressure expressed as a percentage of saturation vapor pressure at the same temperature. It can rise as air cools without adding moisture. It does not measure moisture held in wood or other materials.

A rim joist closes the ends of floor framing around the building perimeter. The neighboring sill, subfloor, and service openings create several air and moisture connections that need assessment.

A rough opening is the opening in the wall framing that receives a window or door. The joint between that framing and the installed unit needs coordination with fastening, air sealing, and exterior drainage.

A Safety Data Sheet, or SDS, describes product hazards, handling, protective measures, and emergency information. Use the sheet for the exact product and formulation, not a generic document from the same brand.

Sound absorption concerns the sound energy absorbed by materials or surfaces rather than reflected within a space. An absorption test does not measure transmission through a complete wall.

Laboratory Sound Transmission Class, or STC, is derived from ASTM E90 airborne transmission measurements using the ASTM E413 rating procedure. It describes the tested construction, not an insulation sample by itself.

Spray polyurethane foam, or SPF, is a broad family of polyurethane products created or applied as a spray. Small sealants, portable kits, and professional systems differ in chemistry, scale, controls, and approved use.

The substrate is the surface or material receiving the foam, such as wood, masonry, metal, or an existing membrane. Cleanliness, dryness, temperature, compatibility, and condition affect adhesion and cure.

Substrate acceptance records whether the receiving surface meets the applicable condition, moisture, cleanliness, temperature, and compatibility requirements. The responsible professional should connect observations to actual locations.

A Technical Data Sheet, or TDS, reports product properties and often summarizes application limits. It must be read with the label, installation instructions, safety information, and any applicable evaluation report.

A thermal barrier separates foam plastic from an interior space under specified code or fire-test conditions. Temperature limits and barrier integrity matter; the accepted protective assembly must fit the foam, location, and applicable code.

Thermal bridging occurs where framing, fasteners, or other conductive paths bypass or weaken the insulation layer. It is one reason cavity R-value is not the same as whole-wall or whole-roof performance.

Thermal imaging uses an infrared camera to observe surface-temperature patterns. An anomaly may need further investigation, and interpretation depends on the inspection conditions.

Two-component foam mixes two reactive components during application. Ratio, component temperature, flow, nozzle condition, ventilation, and worker protection all affect safety and result quality.

Vapor permeance measures how readily water vapor passes through a material or assembly under stated conditions. For spray foam it can change with exact formulation and installed thickness.

A vapor retarder limits water-vapor diffusion according to its measured permeance. It is not the same function as an air barrier, and its appropriate class and location depend on the assembly and climate.

A water-resistive barrier forms part of the wall’s rain-control system and connects with flashings and drainage details. A product can perform this role only within its documented installation and assembly conditions.

Weatherstripping seals the operating joint where a sash or door closes against its frame. It serves a different location from the fixed joint between the installed frame and the wall.

Yield is the amount of foam a package produces, often stated in board feet under specified conditions. Advertised theoretical yield can exceed usable field yield after temperature, technique, starts and stops, and waste are considered.