Should I paint before or after odor treatment?

After, always. Paint over untreated residue holds for a few weeks and then the smell works through, and you have paid for a coat you now have to redo. Treat the source, then decorate on top of something clean.

Why does it smell worse now than it did at the viewing?

An empty house smells more honestly. The furniture, rugs and soft furnishings that absorbed and muffled the odor have gone, nobody is airing it daily, and there is no coffee or candle running. You are also smelling it with a fresh nose each time you arrive, which the previous owner had lost entirely.

Can I claim this back from the seller?

That depends on your state's disclosure rules and on what caused the odor, particularly where the cause was water damage or a plumbing failure. It is a question for your agent or a real estate attorney rather than a general guide, and worth asking early rather than after you have started work.

Is it worth treating before I move my furniture in?

Yes, and it is the single best piece of timing available to you. An empty house is faster to treat, nothing of yours can absorb the odor in the meantime, and flooring that needs to come up is already exposed.

How long does professional treatment take?

Most homes are done in 1 to 4 hours, same or next day, with green non toxic methods and no long evacuation period. The thing that extends it is depth, not size, so a small room with urine in the joists takes longer than a large clean house.

You Just Bought a House That Smells: What to Do First

Almost nobody smells a house properly at a viewing. The seller has aired it, there is coffee or a candle going, you are there for twenty minutes and you are looking at the kitchen. Then you get the keys, the furniture and rugs are gone, the house sits closed up for a few days, and the smell is suddenly the only thing you can think about.

This guide is about the order to tackle it in. The single most expensive mistake at this stage is decorating over a smell, because paint and new flooring do not stop odor and both have to come back off if the source underneath was never dealt with.

Part of our complete guide to odor removal and resale value, which covers every cause and what each one needs.

The short answer

Do not paint or lay new flooring yet. Work out what the smell is and where it lives first, because every finish applied over an untreated source has to come off again. Empty rooms and no air freshener make the smell far easier to identify than it was at the viewing. Most previous-owner odors come down to pets, smoke, damp or cooking, and each needs a different fix. Treat the source, then decorate.

Decorating first is the expensive mistake. Treat the source, then paint.
An empty house smells stronger and more honestly than a staged one, which is why you notice it now.
Identify which of the four common causes it is before spending anything.
Anything still producing the smell, like a leak or damp, is a repair and comes first.

Work out which of the four it is

Almost every previous-owner smell is one of four things, and telling them apart costs nothing.

Pet urine. Sharp, ammonia edged, worse in warm weather, strongest at floor level and near skirting boards and doorways.
Smoke. Stale and slightly sweet, evenly spread through the whole house rather than in one room, worst near return air vents and above where someone sat.
Musty or mildew. Earthy, strongest in the basement, a closet or near an exterior wall, and much stronger after rain.
Cooking. Greasy, concentrated in the kitchen and in soft furnishings, often curry, fish or fried food, and it clings to cabinet interiors.

If you cannot place it, get low. Most odors are heavier near the floor, and crawling along a skirting board tells you more than standing in the middle of the room does.

Check whether something is still causing it

This is the step that decides whether you have an odor problem or a repair problem, and getting it the wrong way round wastes real money.

A musty smell that returns after every rain is water getting in. A sewage smell is a plumbing fault, often something as small as a dry trap in a rarely used bathroom. A sweet chemical smell near an appliance needs a professional look before anything else. Odor treatment applied over an active source buys a few weeks and then the problem walks back in.

Fix the cause before the smell

Any contractor who quotes to treat an odor without asking what is producing it is not doing you a favour. If there is a live leak, a failed seal or standing water, that is a repair, and the odor work comes after it.

The order to do things in

Sequence saves more money than any product choice.

Repair anything active. Leaks, failed traps, damp ingress. Nothing else holds until this is done.
Strip out what is holding the smell. Carpet and pad are usually the cheapest thing to remove and the most likely to be saturated. Take them out before you decide anything else.
Treat the source material. Subfloor, drywall, duct work, whatever the smell is actually in. Most homes are finished in 1 to 4 hours.
Clean the HVAC and change the filter. The system has been moving this smell around the house for years and will keep doing it.
Then paint and lay flooring. New finishes go on top of something clean. This is the step everyone wants to do first and it belongs last.

What it is likely to cost, honestly

It depends almost entirely on how deep the odor went, which is why nobody sensible quotes over the phone without asking about the material. A smell confined to soft furnishings and carpet is the cheap end. A smell that has reached subfloor, drywall or the ventilation system is a bigger job.

What is worth knowing is the comparison. Removing an odor at source is a one time cost. Living with it means either replacing finishes repeatedly as each attempt fails, or accepting a permanent discount if you ever come to sell, and the published figures on that are not kind: indoor smoking has been reported to cut resale value by up to 29 percent in a 2013 Pfizer Canada survey of Ontario agents, and by as much as 30 percent according to the Thirdhand Smoke Resource Center.

The good news for a new owner is that this is the easiest moment in the property's life to fix it. The house is empty, the flooring is coming up anyway, and nothing has been decorated yet.