Your septic or sewer lines arent leaking are they?

That was my first thought, too, but no, our sewer lines look fine. The odor isn't near any of the sewer lines, anyway, and this isn't a sewage smell, it's really an ammonia smell.

The POs had a dog; I wondered too if there might have been "accidents."

I have some Nature's Miracle, but I've never used it. I guess I can give it a try.

What I'm really worried about. I guess, is that it could be something that can't be addressed. It's not pleasant.

Ammonia smells can also come from fertilizer (ammonia is a nitrogenous fertilizer).

I'd try the Nature's Miracle, and or a new product I've used for the same purpose called Get Serious.

I'd also try forcibly ventilating the space with fans to the outside for a couple of days and see if that improves things.

Another thing that occurs to me is reports we've seen up here about farmers are being plagued by crystal-meth makers who need ammonia to make their product and are stealing it from tanks in fields. I have no idea how or in what state they use it in, but perhaps someone was making crystal meth in your basement and ammonia was still spilled there?

Molly~

PS: As I was proofing this another thought occurred to me: We have a couple of drainage pits (not cesspools) that various drains use to be routed to (milking parlor, clean room, etc.) and these drains sometimes smell a bit ammonia-y to me despite not having been in use for nearly two decades. Perhaps you have a long-forgotten grey water system and that is just making it's presence known now?

I'd be gobsmacked if there was meth being manufactured in our basement; the POs are religious upstanding members of the community with two small kids. I'd suspect pet urine first. Although you never know, do you?

I haven't seen any floor drains in our basement (which surprises me, actually) but I'll keep an eye open for them.

I'll give the Nature's Miracle a try. I assume I should just mop the floor with it? Walls too?

We're planning to cover the earthen floors of our "extra" basement spaces with heavy plastic. Perhaps that will help.

Could the urine (if it is urine) have come from the floor ABOVE the basement? You know, the pets soiling the floor above the basement and the urine working its way down through the floorboards and soiling the subfloor?

Maybe cats used the bare earth as a litter box. Cat urine odor can hang around for years and is a bear to get rid of. Cellar dampness seems to aggrevate it.

Any piles of diapers lying around?

You don't suppose there's bodies in them thar crawl spaces, do you?

Seriously, are you sure it isn't moldy? I had a terrible mold problem a couple of years ago and the trigger to discovering it was not unlike the smell that you described. BTW, I would think twice about putting plastic over the dirt. It could trap moisture and help mold and mildew grow and that is almost impossible to get rid of and could affect your health. Seriously, I am just now getting over the mold issue w/ various and sundry off-the-wall techniques, but I can tell I'm feeling better.

The first question I asked the real estate agent was "who's buried in that crawl space?"

We've got a dehumidifier working in the basement now and it's making a huge difference. No more ammonia smell and only a little mustiness. But there is mildew on the walls here and there, so mold isn't out of the question, I guess. I am allergic to two common molds (October and November are horrible months for me) but I don't seem to be having any problems. Yet.

When the movers brought things down to the basement I asked them to put everything in the middle of the floor, because one of my "jobs" in the next week is to get after the walls with bleach.

We are about to purchase (it's been on loan for a week) a UV air filter. I can't believe the difference it's made in the house in terms of smell (much less musty) and I generally just feel better. It's pricey (about $700) and not sure, it might be a pyramid scheme, but it's the first thing that I've come across that really seems like it might work. Good luck..

Here is a link that might be useful: ecoquest air filters

We've had problems with a strong ammonia/fishy smell in our den and spare bedroom since the house was built six years ago.
The odours occur only in autum and spring, and usually during rainy or low-pressure weather.
At first we thought the smells were coming from the air exchange vents in the rooms but we've had our HRV system checked and were told there was nothing wrong.
Both rooms are located at the front of the house, and our municipal sewer connection is in the front yard. But I wouldn't describe this as a sewery smell, although from what I've read about odours, sewer line problems can produce a range of odours.
The smell, although irregular, can be strong enough to induce headaches. We're going out of our minds trying to figure this out, and have a long list of plumbers, HRV technicians, etc., who have tried to figure it out.
Any suggestions would be appreciated.

I have been reading about your problem with the ammonia smell in your crawl space and noticed that someone suggested using a vinager and water solution to mop the floors with. My question is can the solution be used in a spray bottle to spray the crawl space itself or would this cause other problems as mentioned when using the plactic?

I might have your answer. I had the exact same smell in my basement. It turned out, I had a light bulb adapter, so I could plug things into it. I screwed it into the ceiling fixture in my basement, and ran an extention chord to it, so when I hit the light switch, all my cool things would turn on, when I entered the room. I didn't have the adapter screwed in tight. It was just loose enough so that a current was running between it, and the inside of the socket. It fryed it out, little by little, and let out a foul amonia smell, just like you described. I pulled it out, and sure enough, it was charred black. Plus, I was probably running to much power through it to begin with. I would say, double check where every thing is plugged in, and make sure bulbs and adapters are screwed tight and grounded, and don't run too much power to anything. Hope this helps. It cured my amonia thing. -Robert

this smell is most likely a type of mold, I just bought a house built 1906 with a very tight crawl space strong amonia smell and noticed a black mold on some spots under the house some that actually loked like black hair growing like grass , but there is also a openin g in the sewer line but in my experience with sewer gas it rarely smells like mold either way you need to take this seriously because mold can make you seriously ill (has been linked to some cancers) and methane gas produced by the break down of sewage is hazardous, not only that it makes you sick and smells bad but its highly explosive houses have been completely destroyed from explosions caused by methane gas ,I am planning on mounting 2 salvaged furnace blowers under thge house directly to the foundation vents these will pull the air from the vents on the opposite side thru drying and airing out the crawl space, you can go one step beyond and wire these thru a humidistat so that they come on when the humidity/moisture reaches a ceartain level , doing this will eliminate the mold becdause mold can not survive in dry climates BUT MAKE SURE ITS NOT A SEWER LEAK BECAUSE THE SWITCHING ON AND OFF OF THE BLOWERS CREATE A SPARK THAT COULD IGNITER THE METHANE IF ITS UNDER THERE.
by the sewer she lived... by the sewer she died ...they said it was murder but it was......... sewerside

This has absolutely nothing to do with animal urine. It is a chemical reaction that is caused between the basement barrier and the soil. When they react together, it can have an extremely strong smell of ammonia which is always mistaken for cat urine.

It took me forever to figure this out and I was going out of my mind trying to find the source of the smell!

I haven't found one basement professional or contractor who has any knowledge or experience with this. By fluke, I stumbled upon a short little article.

I hope this helps!

Anyone figure out how to fix it?

Obscureboutique is spot-on! Needs a Vapor Barrier (liner) between soil and structure or else ammonia smell. Worse when water is trapped.