Pre-Purchase Home Evaluation

Why a Standard Inspection Is Not Enough

A home inspection is a valuable, cheap and limited product. It answers: is this building safe, are the systems functioning, is there visible structural damage. Those are the right questions for most buyers.

They are not the questions that determine whether a house has good indoor air. An inspector will note an active roof leak; they will not tell you that the wall assembly cannot dry once wet. They will confirm the furnace works; they will not tell you that forced air through an uninsulated crawl space distributes whatever is growing down there. Nothing in the standard scope covers material off-gassing, past water events that were repaired cosmetically, or whether the building can recover from the leak it will eventually have.

This checklist runs alongside an inspection, not instead of one.

How to use it

Work through it on the first or second visit, before an offer. Findings fall into three groups: walk away, negotiate or budget, and note and monitor. Most houses will have several in the middle group — that is normal and is what the budget is for.

1. Water History — The Highest-Weight Section

Past water is the strongest single predictor of future indoor air problems, and it is the thing sellers most often address cosmetically.

• ☐ Ask directly, in writing: has there been any leak, flood, roof failure, plumbing failure or sewer backup? Disclosure requirements vary by state; a written question creates a record either way.
• ☐ Fresh paint on one wall or ceiling only. A repainted section in an otherwise older finish is a repair. Ask what it was.
• ☐ Staining at ceiling perimeters, around chimneys, below bathrooms and under windows. Water travels along framing, so a stain is downstream of the entry point.
• ☐ Replaced flooring in one room, particularly a bathroom, kitchen or laundry.
• ☐ Basement or crawl space: efflorescence (white mineral crust) on foundation walls, rust at the base of appliances or supports, a tide line on stored items, a sump pump — and whether it shows signs of frequent operation.
• ☐ Smell the crawl space and basement directly. The single most informative thirty seconds of the visit. Musty, earthy or sour means active growth, whatever the surfaces look like.
• ☐ Under every sink. Open the cabinets. Look for staining, swollen particleboard bases, and repair fittings.
• ☐ Water heater and washing machine pans, and whether either has a drain.
• ☐ Roof age and remaining life. A roof at end of life is a scheduled water event.

Walk-away signals: repeated flooding history, a below-grade finished space with no drainage plane and a history of water, or a musty smell the seller cannot account for and will not allow investigation of.

2. Assembly Type and Drying Capacity

Every building gets wet eventually. What separates a minor repair from a major remediation is whether the assembly can dry. This is the core idea of the Forgiving Wood Assembly pathway, applied backwards to a house that already exists.

• ☐ Construction era. Pre-1980 construction is often leakier and better at drying. Post-2000 construction is tighter, which is better when detailed correctly and worse when it is not.
• ☐ Insulation type, if determinable. Spray foam in cavities cannot be inspected and does not dry — see our spray foam evaluation. Fibreglass and mineral wool can be opened and dried.
• ☐ Sheathing and cladding. Is there a rainscreen gap behind the siding, or is cladding applied directly to the wall? Look at a window return or a soffit edge.
• ☐ Grade around the foundation. Does soil slope away? Are downspouts extended away from the building, or discharging at the foundation?
• ☐ Finished basement. Framed and drywalled below grade, over a slab, is one of the most common concealed mold conditions in residential housing.
• ☐ Unvented or conditioned attic with foam at the roof deck — difficult to inspect and difficult to dry.
• ☐ Crawl space: vented or encapsulated, vapour barrier present and intact, standing water or damp soil, insulation falling out of the joists (a moisture indicator).

3. Heating, Cooling and Ventilation

• ☐ Heating type. Radiant hydronic and electric resistance do not distribute air. Forced air distributes everything, including whatever is in the ducts and in the space the equipment sits in.
• ☐ Where the equipment lives. Air handler or furnace in a crawl space, attic or attached garage means the system draws from and leaks into that space. See HVAC Equipment Placement.
• ☐ Duct condition and material. Flexible duct in a crawl space, internally lined duct board, or visible dust and debris at registers.
• ☐ Filter slot size. A one-inch slot limits filtration options permanently unless the system is modified.
• ☐ Mechanical ventilation. Is there any — an ERV, HRV or continuous exhaust — or does the building rely on leakage?
• ☐ Bathroom and kitchen exhaust: present, actually vented outside rather than into an attic, and functioning. Test with a tissue.
• ☐ Combustion appliances: sealed-combustion or atmospherically vented. Any unvented gas appliance, including a decorative fireplace, is a combustion source in the living space.
• ☐ Attached garage: connecting door gasketed and self-closing, wall sealed, no ducts or air handler in the garage.

4. Materials, Finishes and Recent Work

Recent renovation is a mixed signal. It may mean updated systems, and it may mean a house full of new material still off-gassing. Both are worth knowing.

• ☐ How recent is the work? Paint, new flooring, new cabinets and new furniture off-gas most in the first weeks and continue for months. See How Long Does Off-Gassing Last?
• ☐ Flooring type. Wall-to-wall carpet, especially older or over a slab, is a reservoir for everything the house has accumulated. Vinyl plank and laminate vary widely by product.
• ☐ Cabinets and built-ins. Particleboard and MDF are formaldehyde sources — see the cabinets question.
• ☐ Smell the closets and the primary bedroom closet in particular. Small, enclosed, poorly ventilated spaces concentrate whatever the house is emitting.
• ☐ Fragrance masking. Plug-in air fresheners, scented candles or a strong "clean" smell during a showing. Ask what is underneath it.
• ☐ Pest treatment history. Termite treatment, ongoing perimeter spraying, past fumigation. Ask; it is rarely disclosed unprompted.
• ☐ Smoking history. Tobacco residue persists in drywall, framing and ductwork and is not resolved by paint.
• ☐ Pets. Relevant if anyone in the household reacts; dander persists in carpet and ductwork.

5. Site and Surroundings

The building can be corrected. Most of this cannot.

• ☐ Immediate neighbours: dryer vents facing the house, wood-burning stoves and outdoor boilers, a business with exhaust, regular lawn treatment.
• ☐ Agriculture within drift distance, and what is grown — the spray schedule follows the crop.
• ☐ Roads, rail and industry. Traffic-related pollution falls off sharply within a few hundred metres of a major road.
• ☐ Wildfire exposure and the region's smoke season. See Wildfire Smoke and Outdoor Air Events.
• ☐ Radon zone and whether the house has ever been tested. Testing is inexpensive and mitigation is well understood.
• ☐ Drainage of the lot itself: does the site sit low relative to its surroundings, and where does surface water go in a heavy rain?
• ☐ Trees and vegetation against the building, holding moisture on cladding and blocking drying.
• ☐ Visit at different times. Early morning for inversions and wood smoke, evening for neighbourhood activity, and after rain for drainage. A single midday showing shows the house at its best by design.

6. The Trial Visit

For anyone who reacts to buildings, the most reliable assessment is time spent in the building. It outperforms every test on this page.

• ☐ Ask for an extended visit — an hour or more, not a fifteen-minute showing. Sellers frequently agree, and a refusal is itself information.
• ☐ Ask that the HVAC run during the visit. Many air quality problems only present when the system distributes them.
• ☐ Ask that no air fresheners, candles or cleaning products be used beforehand. A reasonable request that is sometimes declined, which is also information.
• ☐ Where the transaction allows it — a rental, or a purchase with a cooperative seller — negotiate an overnight or multi-day trial. This is standard practice in some sensitive-housing searches and unheard of in others; ask.
• ☐ Record how you felt, in writing, the same day. Memory of a physical response degrades fast, and across several viewings the notes are what let you compare.

Weighting the Findings

Not every item carries equal weight. Roughly:

Two houses will rarely score the same way, and the middle group is where judgment lives. What this checklist is for is making sure the walk-away findings are identified in week one rather than month six.

If a house passes, the Homeowner Remodel Checklist and the Moisture Control Protocol cover what to do next. If it has an existing mold problem you are considering taking on, price it using Mold in a Home You Already Live In before the offer, not after.

Evidence Basis

Institute of Medicine, Damp Indoor Spaces and Health (2004) and WHO Guidelines for Indoor Air Quality: Dampness and Mould (2009), for the association between building dampness and respiratory outcomes. ASHRAE Standard 62.2 for residential ventilation. EPA Indoor airPLUS construction specifications. EPA radon zone mapping and testing guidance. Building Science Corporation guidance on assembly drying capacity, foundation drainage and crawl space conditions. ASHI and InterNACHI standards of practice, for the documented scope boundaries of a standard home inspection. Published research on the distance decay of traffic-related air pollution.