It's enough to drive you batty: What to do if Mother Nature becomes an univited house guest

As Nicol and Dewi Gwynne were renovating an old pub, the Cross Foxes in southern Snowdonia, Wales, they ran into an unexpected problem – bats. "It had been empty for seven years and we did it up for two years before opening it a month ago," Nicol Gwynne says. "It came as a complete surprise to us when the planning authority told us we had to have a bat survey as part of the permission. In fact, we were a bit fed up that the architect hadn't picked up on it."

Bat specialists were summoned to do a new survey for the old stone property, and found no fewer than four different species of bat relaxing in the bedrooms of the Grade II-listed premises. The plans had to change and valuable time was lost: "Building was prohibited during the roosting season, April to September, as well as the delay while we applied for our bat licence, so we did lose time," Nicol says.

Eventually, the Gwynnes accommodated the bats with a new design giving them roosting space and "access points", and are now armed with a vital "bat licence", which they have discovered is taken extremely seriously.

As Nicol has latterly discovered, "everyone is on red alert for bat issues in buildings". The 17 native bat species in Britain which are known to be breeding and their roost sites are protected under the Wildlife and Countryside Act of 1981, and the Conservation Regulations of 1994, and more recently, conservation has been augmented by the Protection of Species Act of 1992, and crystallised by further Conservation of Habitats and Species rulings from the European Union. At no point in history has nature's bounty been so protected in the built environment of Britain, and while this seems eminently reasonable, it can create problems for builders with time and budget constraints. "Many people assume that they can buy a property and start work straight away but they often don't realise that the presence of bats can halt or significantly slow down works," says Suzanne Bowman, a property specialist at law firm Adams & Remers. "Bats are protected by law and disturbing them could result in imprisonment and/or a large fine."

The bat issue is most vexing in historic houses – bats love the venerable calm of quiet rafters – and Bowman says that prospective property owners should therefore take steps to be "bat-aware" before starting work. Indeed, they should be nature-aware, as it isn't just bats; other flora and fauna can also obstruct the best-laid plans of builders and renovators. "The animal issue crops up more often than you'd think," says property lawyer David Johnson of Boodle Hatfield, who has come up against all manner of birds, beasts and blooms in his workload, from water voles to adders and even lichens. "I've seen hold-ups happen with crested newts, barn owls, badgers, and even a rare species of plant on site," he says, adding that in one new-build house, provision had to be made for a badger sett, while developments have necessitated the building of badger tunnels.

Bats remain the single biggest issue, and can even be a potential deal-breaker. "I identified a potential building plot for a client, in a wonderful position with views over a lake," says Charles Birtles, a buying agent of CB Property Search in Hampshire. "They wanted to build a substantial house to replace a derelict bungalow. As it happened, the bungalow had been occupied by soprano pipistrelle bats and they rejected the plot, partly because demolition wouldn't have been allowed for a large part of the year."

Developments are being changed because of bats. David Wilson Homes, Southern, which is currently building 10 executive new homes in Camberley, Surrey, found that the building on site that was due for demolition had the potential to house bats. None was found, but a bat loft was nonetheless constructed. "We provided special badger corridors," says Simon Kirk technical director at David Wilson Homes. "We take specialist advice on these issues."

A bore for them, possibly, but this scenario is driven by the laudable aim of conservation. "Bat numbers have declined a lot, and like the swift, they are reliant on buildings," a spokeswoman for the Bat Conservation Trust (BCT) says. "Consequently, construction issues involving bats occur a lot more than we would like." Natural England has a Wildlife Management and Licensing Service, giving advice to householders so as to "enable people and wildlife to live alongside each other", as a spokeswoman puts it. "Most of us feel that the presence of wildlife around our homes and gardens enhances the quality of our lives, but occasionally, this isn't the case," she adds. "Before dealing with wildlife problems, it is important to remember that some species, such as bats, birds and the great crested newt, are protected species, and this places limits on what you can do without obtaining special permission." The root of the problem lies in the fact that the loss of large old trees and woodland has pushed species towards new habitats in the human environment. It's important to emphasise that bats rarely cause a problem, above and beyond causing delays, and the vast majority of householders live happily with them.

Conversely, protesters against developerments have noticed these increased environmental expectations and cite SSSIs – Sites of Special Scientific Interest – as a way to forestall unwanted interventions, such as at Donald Trump's controversial golf course and hotel in Aberdeenshire, north-east Scotland.

This kind of intervention is less likely to be cited on a domestic scale but, nonetheless, any potential animal or plant issue should be nipped in the bud.

"The problem is worst if an animal halts work unexpectedly, and people get understandably irate if there's suddenly an additional delay and cost added because bats have been found," Johnson says. "But it's a criminal offence to disturb roosting bats and certain other animals."

Therefore, it's important for any householders who feel they might face a problem – such as those buying an old house in a rural area – to run a survey before developing their site. The Royal Institution of Chartered Surveyors offers a checklist of the kinds of biodiversity factors that might hold up a build with which the average house surveyor might not be conversant, and animal well-being even extends to the kinds of refurbishment recommended, with high-quality traditional materials such as oak windows and clay roof tiles given the bat-friendly nod.

Whatever, don't ignore the bats in your belfry – or other animals. Charity worker Dominic Murphy, when renovating an old vicarage near Sherborne, Dorset, was faced with a picturesque dovecote on the side of his stone house. "It looked great but there was bird poo everywhere," Murphy says. "We couldn't really live with the pigeons." So after taking advice from the RSPCA, English Heritage and the BCT – Murphy also had bats in the house's attic – he advertised his inherited birds in the local paper before doing some essential lime render work. Murphy is happy that the pigeons have flown but likes having the bats there, and as a spokeswoman for the BCT says, so he should be. "Bats thrive in healthy places. So if you find bats, it shows that your environment is healthy for humans, too."