Can't find the source of mouldy smell

[Whatsthatbloominsmell]

First time of posting on here but getting desperate!

Moved into house in September. Not a particularly old house (around 14 years old) but since beginning of April there has been, what I can only describe as, a mouldy smell in one of the bedrooms. Can only smell it in this particular bedroom, although occasionally in the hall but usually if the bedroom door has been left open, and not in adjoining bedroom. The master bedroom's ensuite shares a wall with the smelly bedroom but I can't smell it in here - I have open the vent hatch too and there's no smell either. Equally if the shower was leaking we would see a damp patch over the stairwell.

There is no sign of mould anywhere in the bedroom. I have lifted the carpet, cleaned the carpets and soft furnishings, cleared out the room there's no sign of mould on the walls - actual mould, dampness, marks on paint, damp carpet or floorboards anywhere. We put in fitted wardrobe and bookshelf in October so thought it could be lack of airflow but we took 2 panels off the back of the bookshelf and drilled a whole in the back of the wardrobe but no smell or sign of mould.

The room is above the garage but I've checked in there and there's no sign of mould or damp. Also can't see or smell any sign of mould in the attic (although i guess it could be right under the insulation or floorboards)Someone suggested the air vent from the downstairs toilet which is boxed in, but again we drilled a hole in the wall and can't smell anything.

Has anyone got any other suggestions as to what could be causing the smell/ had a similar issue where they couldn't initially source the smell but found it somewhere obscure? It's driving me crazy!

It might be a leak that’s yet to show itself. We had a mouldy smell in one room and couldn’t work it out - and a month later the wall became wet. We’d had rain come in through broken external victorian pointing and it was just making the wall and then the rubble inside the wall wet before soaking through. I’d get/ borrow a damp/ moisture meter and see if any of the walls are showing a high reading.

Also - are they new carpets? As something may have been spilt on it and cleaned up. Or it might be the paint? There was an issue with Valspar paint a few years ago which made the rooms smell horrible?

Do you have a teenaged boy? That’s the smell in my house atm.

Thanks so much for taking the time to reply. They're not new carpets still the ones from when we moved in. We hired one of those carpet cleaners again last weekend but the smell is still there. Tbh when I sniffed the carpets I couldn’t smell it there. We used Dulux paint when we repainted the rooms but will explore this further and get a damp meter. Husband took the back of the wardrobe completely today and nothing there. Think I'll send him up the attic for more in depth prodding around too.

@Fraaahnces I have a son but he's only 3 hoping we are not at the smelly boy stage yet 😆

Maybe it's not mould? Some strong smells come from things like untreated/waxed wood (especially when sun shines on it/near radiator), paint that gets warm, wet shoes ... or probably most horrid, a mouse or similar that has died under the floorboards.

You didn't use old paint, did you? Because that can smell absolutely minging sometimes.

You’ve recently built a new patio and your DH has been missing ever since?

I have a nearly new build, around 6 years old. Last year I noticed a slightly loose tile in the shower, went to repair it and noticed black mould behind it. I stripped all the tiles off and found a huge wall full of black mould, it had affected the plasterboard, the wall board behind and even the wall insulation between the shower and bedroom behind. No smell of mould so goes to show how bad a mould problem can be with no signs. We had no damp patches under the shower because the walls and insulation were absorbing the water.

Is there a loft space above it? Does it get worse if it's warmer if it rains etc?

If the former, maybe more likely to be a dead rodent.

If it's worse after rain is there guttering or a down pipe outside that room?

The source of our mystery smell in one room turned out to be a bird decaying between layers of loft insulation.

Is there a blocked-up fireplace or chimney breast in that room?

Get the floorboards up, builders leave all sorts under there inhibiting airflow from the airbricks, which may be blocked.

Does your son have a plastic mattress protector? My sons room was stinky, and I tracked it down to the bed. I'd removed the breathable cover that sat on top of the plastic mattress part to wash it (kids m and s mattress). In the meantime the plastic part had a blanket and sheet on top, but I'm guessing any sweat from his body was going and sitting on the plastic.

It absolutely stank and I was going crazy trying to root out the smell. As soon as I took the bedding off and washed down the bed, replaced the proper cover it was all fine.

Thanks again everyone. Really hoping I don't have to start tearing walls down to find the smell as that will be so expensive!

@Fraaahnces nope not yet anyway 🤣
@KievLoverTwo nope brand new tins at the time.
@tailinthejam no chimneys at all in the house
@lndnbrdge91 I stripped everything off his bed and washed it all but smell still there. tbh can't smell it off his bed.
@Calmdown14 don't notice a difference with weather but funny you say that about the dead bird as there have been birds flying at the part of the house so I'll investigate further in the loft. How long was your smell there for? I thought if it was a decaying animal the smell would start to go after a while.

Has anyone tried one of these mould investigation companies which use a fog to clear out mould? Email one at the weekend but I'm so wary of companies like these that they are just a scam.

Thanks again for all your suggestions.

Is there a lot of dust somewhere inaccessible? Under the bed, on top of a wardrobe? Sometimes dust can smell pretty stale/mouldy if it builds-up.

Before you go for mould clearing gas, find someone who can use a damp monitor in the room. It's like a meat thermometer prong, they poke it into the wall/floor etc. to see if there is any residual damp.

Have you gone round and smelt the walls ? We started getting a damp smell in the bedroom and it turns out it was from a roof leak. Basically the water was coming down the internal wall but not showing through the paint/wallpaper. As the wall would dry, it would admit a distinctive damp smell.

@Kyokyo did you notice in leaks/damp/smell in your attic from the leak? How did you resolve the issue?

My DDs bedroom once smelt really musty and I just couldn’t find the source of the smell.
Eventually after a lot of sniffing, tracked it down to a bag of damp Orbeez she had been playing with….

A dead mouse under the floorboards would be my suggestion.

Have you thoroughly checked the radiator? A very slow leak might not make the carpets noticeably "feel" damp but is enough to give that horrible damp smell.

So we only notice the leak when it started appearing in the room next to our bedroom (damp wall when it rained, the wall was painted white and it would dry yellow where the leak had come down the wall). We didn’t realise the leak was also coming into the bedroom as there was never any signs of water. It was only the smell we would get in the bedroom.

It was really weird, I would just get a whiff of damp/mould every so often (more in the window was open as there was a breeze). Eventually I realised it was coming from one area of the wall and it would be worse a few days after it rained (so the smell would appear when it started to dry rather then when it was actually wet). Our bedroom was painted light grey but I think it was painted with an oil based paint or something as it never looked wet like the white wall in the other bedroom did.

Unfortunately we can get in the attic but both leaks appeared under roof valleys so we had a roofer come take a look and the valleys were blocked so they just needed cleaning out

Thanks @Kyokyo