We recently purchased a small 3 story row house and gutted the entire first floor. On the second floor we renovated a bathroom, sanded and sealed the hardwood floors with polyurethane and painted the walls. On the third floor, we replaced the hardwood floors and painted.

The previous owners had 5 dogs - which is a lot for a home that’s roughly 1700 square feet. Before we started our renovation there was a distinct odor of animal on just the first floor. However, I wasn’t concerned because we were gutting the entire first floor and I never smelled an odor on the upper levels. Anyway after moving in, I started to smell an animal-like ammonia odor in my sons room (which is located on the second level). The smell comes and goes, but is usually the strongest after the door has been shut for a few hours. If the door is left open, there is no evidence of the odor at all. Also when the odor is preset, you can only smell it for about 20 seconds before the nose gets used to it. Which has made it impossible to find exactly where the smell is coming from.

After smelling this on and off for several weeks, I assumed one of the animals soiled the floors and it was never cleaned properly. So I called an environmental service that specializes in odor and air quality to evaluate. Unfortunately, on the day they came there was no smell present! So the service was unable to determine what the smell was. They did air quality tests which all came back within range. They also used a black light to see if any urine stains were present on the hardwood floors and nothing was detected.

Feeling frustrated, I was still convinced the odor was a result of the animals urinating on the floors, so I had my contractor come back and rip out the old hardwood floor and subfloor. So at this point - we’ve completely replaced the hardwood floors, the subfloor and floor insulation in the room . The ceiling in the bedroom was also completely replaced (as part of the initial reno because we put in high hats). So at this point only the 4 walls in the room have not been replaced - however, we did repaint the walls with Zinsser Odor Killing Primer and several fresh coats of paint. I should also mention that we have baseboard heat and the heater was also replaced before we moved in.

I was sure that replacing the floors and subfloor and repainting would eliminate the odor. However, the smell has started to present itself again! It is not as strong as it was previously, but there is still a faint odor present (only when bedroom door is shut for some time). I am completely dumbfounded and do not know what to do. Does anyone have any idea what this odor could be or where it could be coming from? Should I have my contractor take down the walls and replace the wall insulation and sheetrock? I feel like I’m going completely insane - any insight/ would be GREATLY appreciated.