Radon (Leaving Cert Construction Studies): Revision Notes
Radon
What is radon?
Radon is a dangerous radioactive gas that poses serious health risks in buildings. Understanding radon and how to protect against it is essential for safe construction.
Radon originates from a natural radioactive decay process. Uranium, found naturally in rocks and soil, breaks down over time to produce radium. As radium continues to decay, it releases radon gas. This makes radon a naturally occurring radioactive gas that has several concerning properties - it cannot be seen, smelled, or tasted, making detection extremely difficult without specialist equipment.
Since radon is completely tasteless, odourless, and colourless, it's impossible to detect through human senses alone. This invisibility is what makes radon particularly dangerous in enclosed spaces.
The Radiological Protection Institute of Ireland (RPII) provides radon detection services using specialised radon testers. These devices are essential because radon is impossible to detect through human senses alone.
Health risks and geographic distribution
When radon escapes from the earth's surface into the atmosphere, it becomes diluted and poses little danger. However, when radon accumulates in enclosed spaces like houses, it creates serious health hazards. Medical research has established strong links between radon exposure and increased lung cancer risk.
When radon accumulates in enclosed spaces like houses, it creates serious health hazards. Medical research has established strong links between radon exposure and increased lung cancer risk.
Radon levels vary significantly across Ireland. The RPII maintains up-to-date records and monitors radon concentrations in existing buildings throughout the country. Their mapping shows that certain areas have much higher radon concentrations than others, with some regions showing particularly elevated levels that require immediate attention.
How radon enters buildings
Radon gas enters buildings through several common pathways. The most typical entry points include:
- Cracks in walls and floors where the structure meets the ground
- Gaps in floors, particularly around service pipes that protrude through floor slabs
- Junctions between floors and walls where construction joints may not be perfectly sealed
These entry points allow radon to seep up from the ground and accumulate inside the building, where it can reach dangerous concentration levels.
Understanding these entry points is crucial for both prevention in new buildings and remediation in existing structures. Every potential pathway must be considered during construction or retrofit work.
Radon protection systems for new buildings
The Irish construction industry uses two main approaches to protect new buildings from radon accumulation. Both systems aim to prevent radon from entering the building or to safely remove it before it can build up to dangerous levels.
Passive system
The passive protection system creates a complete barrier to prevent radon entry. This method involves sealing the entire ground floor area with an airtight polythene sheet, typically 4μm gauge thickness. A specialist installer must fit this barrier to ensure it remains completely airtight.
Passive System Operation:
Step 1: Install airtight polythene sheet (4μm gauge) across entire ground floor area Step 2: Ensure specialist installation for complete airtight seal Step 3: Barrier physically prevents radon gas from entering building Step 4: System relies entirely on perfect seal integrity
The effectiveness of the passive system depends entirely on creating a perfect seal. Because the polythene sheet prevents radon gas from entering the building, any gaps or damage to the barrier would compromise the entire system's protection.
Active system
The active protection system combines barrier methods with mechanical extraction. This system requires more complex installation but provides more reliable long-term protection.
The active system works by installing a sump during the early construction stages. The sump is essentially a void or container set deep within the hardcore foundations. This void operates at lower pressure than its surroundings, which draws radon gases into the sump rather than allowing them to enter the building.
Active System Operation:
Step 1: Install sump (void/container) deep in hardcore foundations Step 2: Sump operates at lower pressure than surroundings Step 3: Pressure difference draws radon gases into sump Step 4: Ventilation pipes direct gases safely outside building Step 5: Electric fan can increase ventilation effectiveness Step 6: Airtight polythene barrier provides additional protection
Once gases collect in the sump, ventilation pipes or cavities connected to the sump direct them safely outside the building. The system can include an electric fan to increase ventilation effectiveness, ensuring continuous gas removal.
The active system also incorporates the airtight polythene sheet barrier used in passive systems, providing dual protection through both mechanical extraction and physical barriers.
National reference level
Irish building regulations establish a National Reference Level of 200 becquerels per cubic metre (200Bq/m³) as the guideline for acceptable radon levels. When radon concentrations exceed this level, immediate remedial action is required.
The National Reference Level of 200Bq/m³ is a critical threshold. When radon concentrations exceed this level, immediate remedial action is required using active system protection.
For levels above the reference point, installing an active system becomes the recommended solution. The active system is preferred for remedial work because it combines mechanical ventilation with barrier protection, providing more comprehensive and reliable radon control.
Protecting existing buildings
Retrofitting radon protection into existing buildings presents greater challenges than installing protection during initial construction. However, effective solutions exist for buildings that show elevated radon levels.
Sealing approach
The first step in protecting existing buildings involves sealing all potential entry points. Construction teams must identify and seal every crack, gap, and junction where radon might enter. Construction-grade silicone sealant proves most effective for this work because it adheres well to most building surfaces, applies easily, and allows for structural movement without breaking the seal.
Construction-grade silicone sealant is the preferred material because it maintains flexibility while providing an airtight seal, accommodating natural building movement without compromising protection.
Sump installation
Installing a sump system in existing buildings requires more complex work than in new construction. The sump must be positioned as close to the building as possible to maximise its effectiveness. This large, empty space draws radon gas away from the building structure.
The installation process involves breaking through the existing floor structure to create access to the ground below. From there, contractors can install the ventilation system that will safely remove collected radon gas, similar to the systems used in new construction.
Service pipe sealing
Where service pipes or cables pass through radon barriers, special sealing systems prevent gas leakage around these penetrations. The "top hat" seal system provides an effective solution for this challenge.
This system uses double-sided sealing tape placed around the service pipe. An adjustable clip, called the top hat, fits around the pipe circumference and tightens to create a gas-tight seal between the barrier membrane and the pipe surface.
Key Points to Remember:
- Radon is a dangerous, invisible gas that comes from natural uranium decay in rocks and soil
- Two protection systems exist: passive systems use airtight barriers, while active systems combine barriers with mechanical extraction
- The National Reference Level is 200Bq/m³ - levels above this require immediate remedial action using active systems
- Existing buildings need comprehensive sealing of all cracks, gaps, and junctions, plus properly installed sump systems
- Ground floors must meet multiple requirements including radon protection, damp resistance, thermal performance, and structural durability