Short answer
Stop the leak, protect yourself, assess the size and extent of mold, contain the area, remove and discard moldy porous materials, clean and HEPA-vacuum remaining surfaces, dry the structure to target moisture levels, then rebuild. If the visible mold is larger than about 10 square feet, the water was contaminated (e.g., sewage), or mold is in HVAC systems, call a professional remediator.
What’s happening and why it matters
Long-term leaks keep materials damp, allowing mold to colonize drywall, insulation, carpet, subfloors, and framing. Simply killing mold isn’t enough—spores and fragments remain allergenic. The goal is to fix the moisture source, physically remove mold-laden porous materials, clean remaining surfaces, and dry the structure to safe moisture levels before closing walls.
Safety first
- Wear PPE: N95 (minimum) or a half-face respirator with P100 filters, nitrile/latex gloves, goggles, and disposable coveralls.
- Turn off HVAC to the affected room and cover nearby supply/return vents to prevent spreading spores.
- If your home was built before 1980 (asbestos risk) or painted before 1978 (lead), have materials tested before demolition.
- Keep children, elderly, and immunocompromised individuals away from the work area.
Tools and materials
- Moisture meter (pin-type and/or pinless) and optional thermal camera/infrared thermometer
- 6-mil plastic sheeting, painter’s tape, zip poles or furring strips for containment
- HEPA vacuum (true HEPA) and, ideally, a HEPA air scrubber; high-capacity dehumidifier and air movers
- Utility knife, oscillating multi-tool or reciprocating saw, pry bar
- Contractor trash bags (3-mil), duct tape
- Pump sprayer, mild detergent, scrub brushes, microfiber cloths
- Optional: EPA-registered mold cleaner or 3–7% hydrogen peroxide for nonporous surfaces
- Replacement materials: drywall (consider mold-resistant type), insulation, screws, joint compound, primer/paint
Step-by-step guidance
1) Stop the water and stabilize
- Shut off the leaking supply, fix the pipe/roof/window issue, and confirm no active moisture.
- Document with photos for insurance before you open anything.
2) Assess the extent
- Measure the visible mold area. If it’s larger than ~10 sq ft, or spread across multiple rooms, call a pro.
- Use a moisture meter to compare suspected wet areas to known dry areas. Probe drywall, baseboards, sill plates, subfloor.
- Look for hidden mold: stained baseboards, warped floors, musty smell. Carefully remove baseboards or cut small inspection holes to view inside cavities. A borescope helps.
3) Set up containment and negative pressure
- Isolate the room with 6-mil plastic and tape. Create a zippered doorway or overlapping flap.
- Cover HVAC vents. Place a HEPA air scrubber in the space; if possible, duct it outside to maintain negative pressure. If you don’t have a scrubber, keep the area sealed and minimize disturbance.
4) Remove unsalvageable porous materials
- Drywall, insulation, carpet, and pad that stayed wet for more than 24–48 hours are usually discard items.
- Cut drywall 12–24 inches beyond visible damage (or to the next stud) using a utility knife/oscillating tool. Avoid deep cuts; watch for electrical/plumbing.
- Double-bag debris in contractor bags and remove directly outside (don’t carry uncovered through the house).
5) Clean remaining surfaces
- HEPA vacuum framing, subfloor, joists, and nearby surfaces to capture spores and dust.
- Damp-wipe nonporous and semi-porous materials (framing, subfloor, sheathing) with detergent solution. Scrub visible growth. Avoid soaking wood.
- Optional disinfectant: On nonporous surfaces, 3–7% hydrogen peroxide can help after detergent cleaning. Avoid straight bleach on porous materials; it doesn’t penetrate well and can damage fibers.
- For stubborn growth on framing, lightly sand or wire-brush, then HEPA vacuum again.
6) Dry the structure thoroughly
- Set up dehumidifiers and air movers for 2–5 days. Create cross-flow across damp areas without blowing directly on moldy debris.
- Track progress with a moisture meter daily.
Drying/closure targets:
- Wood framing: ≤ 15% moisture content (≤ 12% ideal)
- Subfloor/plywood: ≤ 12–15% MC
- Interior RH: 30–50% for ≥ 48 hours before closing walls
7) Verify and rebuild
- No visible dust or staining, no musty odor, and moisture readings at or below targets.
- Prime and paint remaining stained-but-clean wood with a stain-blocking primer if needed (not as a substitute for cleaning).
- Replace insulation and hang new drywall (mold-resistant or paperless in bathrooms and basements), then tape, mud, sand, and paint.
- Replace or thoroughly clean and dry trim and flooring.
Tips for best results
- Work small to large: remove the worst materials first to reduce spore load.
- Keep the area under slight negative pressure during demo and cleaning.
- Upgrade your HVAC filter to MERV-13 during and for two weeks after the project; replace it afterward.
- Consider treating cleaned framing with a borate-based wood preservative where future dampness is possible.
Common mistakes to avoid
- Painting or priming over mold without removal and drying.
- Using bleach on drywall or wood and calling it done.
- Failing to fix the moisture source before remediation.
- Closing walls while wood is still above ~15% MC.
- Running the home’s HVAC in the containment zone and spreading spores.
- Skipping PPE or containment.
When to call a professional
- Visible mold area > 10 sq ft, or multiple rooms/levels.
- Water from sewage or floodwater.
- Mold inside HVAC systems or extensive duct contamination.
- Recurring mold despite prior efforts (hidden leaks or vapor drive issues).
- Pre-1978 homes where demolition may disturb lead paint, or pre-1980 materials that could contain asbestos.
- Occupants with significant respiratory issues or immunosuppression.
Rough costs and time
- PPE: $40–$120; plastic/tape/bags: $30–$80.
- HEPA vacuum or air scrubber rental: $50–$75/day each.
- Dehumidifier rental: $40–$60/day; air movers: $20–$30/day each.
- Typical DIY timeline: 1 day for setup/demo, 2–5 days drying/cleaning, 1–3 days rebuild (not including paint cure).
Addressing mold thoroughly means controlling moisture, removing contaminated materials, and drying to target levels. Do those well, and you’ll prevent most future issues.