Every night we go to bed in fear of a rock crashing through our roof

Ross and Jill Darbyshire spend each evening uncertain whether they'll survive until dawn. From their compact stone home in Denbighshire they remain alert throughout the night to the sound of rocks striking the exterior walls and debris cascading downwards.

Their existence has become fraught with anxiety. "One night I heard a thud and I thought it was another rock," said Ross. "I got up – it was just the cat. It's scary living here wondering if a large boulder is about to come through the roof." 

The retired pair live at Bedw Isaf, a 600-year-old former drovers cottage in Rhewl, near Llantysilio. The two-room dwelling was subsequently home to a sluice keeper managing a dam that supplied water to an old corn mill, which has long been derelict.

Hailing originally from Stoke-on-Trent, the couple relocated to the home 10 years ago and began restoring the off-grid dwelling, removing corrugated roofing from a tool shed to fashion a kitchen. Existence proved challenging in an isolated woodland location where the only route in is a 100-yard footpath, 

Yet until recently the setting remained tranquil and serene. Around 11pm on Wednesday, January 28, fractures emerged in the vertical slate bedrock merely 2ft from the rear of the cottage. Jill, 69, a former community artist, said: "The first thing we knew was when rocks started hitting the back of the house.

"By midnight the rocks were still falling and we saw a tree root leaning against the back wall. We decided to go to bed around 1am but the banging and bumping made us wonder if we'd be better leaving the house.

"We moved downstairs and by 2am it seemed more settled so we went to bed. We're still getting the occasional bump when a rock falls and there are many more cracks in the bedrock."

The 2ft void behind Bedw Isaf is now scattered with slate fragments and stones. Larger boulders, too substantial to drop into the gap, span the opening at roof level, creating an archway.

In some areas boulders have been buried beneath falling earth and turf still containing embedded bushes.

Ross, a former shoemaker and school bus driver, worries the entire hillside is shifting. "You can now see the bands of slate like layers of a cake," he said.

"Rows of slate slabs are sticking out like dragons' teeth. They're breaking off and we've had two or three large chunks slamming into the house. When I heard the first one I thought: 'What the hell?'"

Ross added: "The biggest ones must weigh three to four tonnes each. Dozens of smaller rocks, five or six inches across, have also fallen into the gap at the back of the cottage.

"They're not actually causing any damage to the stone walls – they're 2.5ft thick and have survived 600 years. In fact the cottage is probably the only thing stopping the whole bank slipping into the valley.

"My worry is that, one night, a big rock won't wedge into the gap but will come through the roof on top of us."

On the evening the hillside started shifting a 0.9-magnitude earthquake struck near Nantlle in Gwynedd. Several hours afterwards Llangollen residents reported what appeared to be their own tremor although the British Geological Society recorded no seismic activity.

Nevertheless it sparked speculation for Ross and Gill. "Perhaps there's a fault line running from Gwynedd to Denbighshire?" questioned Canada-born Ross, 75.

"And that's why the hillside began to move. It would be just our luck. The bedrock here has been stable for millions of years and then is set moving by a quake while we're here."

However this winter's prolonged rainfall is a more probable culprit, having caused multiple landslips and sinkholes throughout north Wales.

November saw Wales receive 59% more precipitation than its monthly average. December brought North Wales 11% above its typical rainfall.

January defied expectations, dropping 13% below normal – yet ground conditions remain waterlogged. The couple face an additional challenge stemming from the property's industrial heritage.

Their land features a 12ft high dam from which water plunges 80ft down a ravine "waterfall" to Melin Gymmo, a derelict mill first documented in the 1690s.

Ross and Jill's dam is reportedly Wales' largest of its kind. Its stone walls desperately require restoration, failing which the couple risk having their access path eroded and swept away.

Should this occur they'll face complete isolation. "We've been told the house is unsaleable until the dam is fixed," said Ross. "But it's a beautiful spot and we've had people here from London offering us £300,000. It would be perfect as a holiday let".

"We've got a guy to sort the dam but he's currently on another job and can't get here until that's finished. It'll cost us £100,000 – and now he may have to underpin the bank behind us as well, a more expensive job.

"The dam was our priority. Now all of a sudden the bank is. It's a race against time and the cost is going to break us. We're living on a knife-edge and we don't know which way to turn or who to approach.

"In the meantime we go the bed at night hearing rocks the pinging and bumping against the wall thinking of Aberfan wondering if we'll wake up in the morning."