Site hazardous materials: asbestos, lead, mold, radon

One-line orientation

Architects should recognize four common hazards in existing buildings: asbestos, lead, mold, and radon. Each hazard requires a different response.

Key points

• Where they appear: hazardous materials are common in older buildings. Lead-based paint is a pre-1978 concern. Asbestos is also common in older buildings, but age alone cannot confirm it; test before disturbing a suspect material.
• Asbestos: found in vinyl tiles and ceiling tiles; requires professional handling.
  • Removal (abatement): professional abatement and sealing off the affected area.
  • Containment / encapsulation: undisturbed asbestos can sometimes be sealed or built over if deemed safe — left in place.
• Lead-based paint: requires testing and certified work. Depending on its condition and the occupancy, it may be removed, covered, or repainted.
• Mold: thrives in damp, unventilated areas — it is a moisture problem. Stop the moisture source, dry the area, then clean hard surfaces or remove damaged porous materials as needed.
• Radon: a naturally occurring radioactive soil gas (uranium decay) that accumulates indoors and raises lung-cancer risk. Test first; mitigate above the action level.
  • Sub-slab depressurization (primary): a fan creates a vacuum beneath the foundation and vents radon outside.
  • Other methods: sealing cracks/openings, crawl-space ventilation, pressurization (fan pushes outside air in to keep indoor pressure higher), and radon-resistant construction (gas-permeable layer + plastic sheeting + vent pipe in new homes).

Confusions / comparison

Hazard	What it is	Where / cause	Typical fix
Asbestos	Friable mineral fiber	Vinyl/ceiling tiles in older buildings	Remove (abate) or encapsulate / build over if undisturbed
Lead	Toxic metal in old paint	Pre-1978 paint	Test + certified removal, covering, or repainting as appropriate
Mold	Biological growth	Damp, unventilated areas (moisture)	Stop moisture; dry, clean, or remove affected material
Radon	Radioactive soil gas	Soil/uranium decay under slab	Sub-slab depressurization above action level

Related

→ Environmental Site Assessment (this module): Phase II tests for these contaminants · Brownfields and remediation (this module): site-scale contamination + cleanup · Systems / Code: indoor air quality, ventilation, and low-VOC material selection.