Musty smell in garage and infiltrating house

[Spinaroo]

Happens at this time every year- a smell emanates in the garage. there is no obvious reason why and we have spent a lot if time, effiort and money eliminating thinga like drain issues/ roof issues- all proving fruitless. could it be stagnant water in unused central heating pipes? How long would this take to clear if I turn heating on? Would a dehumidifier help?

Any suggestions would be really appreciated-it is driving me insane.

pipes are airtight so don't smell.

What is in the garage? Car? Lawnmower? Freezer? Wildlife (dead or alive)? Manhole cover? Animal feed? Is it damp? Is there a smell outside?

Thanks for responding, pigletjohn.

There is no car, there is a lawnmower, an old freezer not in use, no wildlife I can see, no animal feed and no manhole cover. The garage does not appear to be damp and the smell is strongest in the garage and then in our hall (next to the garage) and especially strong in our ensuite bathroom (above the hall but not directly above the garage).

There is a waste pipe from our ensuite which passes through the garage but we have checked this and the smell does not seem to originate there. We also have a boiler in the garage.

The smell always comes at this time of year. Nothing we have ever done has had any effect. It always goes away of its own accord but it is distressing and extremely frustrating that for a period of several weeks I have to live with this cloying smell.

Any advice you have would be great.

Unless you have wildlife nesting under a floor or in the roof, or carnivorous plants which smell of rotting meat, I expect it is damp related. Foxes have a distinctive smell and leave small, usually very dark or black, territorial poo markers. They sometimes make dens under and behind sheds.

At this time of year it might be heavy rain coupled with warm temperatures causing decay, so could be gutters, downpipes, loose render, puddles around house wetting walls. Or it might be garden tap and hose leaking or soaking nearby ground. Water often runs under garage doors, but damp concrete has a distinctive smell.

It could be a plumbing leak, for example if you have pop-up wastes in the bathroom, or a retrofitted bathroom where the soil pipe has no external vent, but a Durgo or similar hidden behind boxing-in, which may give drain smells. Leaks from radiator pipes show up more in the summer, when the pipes are cold so do not dry up any damp patches. If you have a water meter, turn off all taps and observe the meter with a torch to see if the bubble stops moving.

Thanks a lot- this is really helpful.