Is your house still a castle with a tenant in the spare room?

The problem is that there are times I’d prefer to close the door on people I actually know, so perhaps the Airbnb concept is not for me.

Neither is house swapping because while the benefits might be a free gaff overlooking Central Park, the downside is some nosey Yank poking through your smalls in your absence.

But beggars can’t be choosers and in any event there are millions who either earn money or enjoy affordable holidays by making the best use of their own house.

Airbnb – the online company that allows you to rent out a bed, a room or an entire house to visitors – started out as a short-term solution to those having difficulties with the rent.

Just seven years later, it is estimated to be worth around $20 billion with over 1,000,000 listings in 34,000 cities and 190 countries– so clearly someone is doing something right.

Brian Chesky and Joe Gebbia were roommates in San Francisco in the middle of the last decade – and they were struggling with the rent for their loft.

At the same time the Industrial Designers Society of America was staging its Industrial Design Conference – and the two boys realised that there were a number of attendees who couldn’t find a hotel room.

So they married supply to demand and made their living room into a bed and breakfast, accommodating three guests on air mattresses and providing home-made breakfast.

How they took it from Air Bed and Breakfast to a €20 billion company is a longer story – but clearly, given their number of listings, at least a million people bought into it.

And in a way we were doing this in Galway long before anyone else even thought of it – remember when families moved away for Race Week and rented out their homes for a price that more than paid for their holiday?

Airbnb doesn’t equate to couch surfing because while some people do just offer a fold-out sofa bed, some of the more luxurious listings would include, for example, a three-bed Manhattan apartment near Times Square at a cost of $575 a night, which generated an estimated $172,500 for its owner last year.

Clearly then not everyone is in it to try and earn a few extra quid to pay the college fees or budget for the heating oil – but a lot of people have just come to realise that they are sitting on an asset that’s not making any money.

Theoretically it is of course, because house values are again on the rise, but the only people monitoring that are your children and Michael Noonan – the kids so they can estimate their inheritance and the Minister for Finance so he can tap you up for the property tax.

Thus for those living in a University city, the rent-a-room scheme makes sense because you can earn up to €12,000 a year tax free.

But do you really want a student in your spare room – or more precisely one who isn’t related to you by virtue of you being one of his or her parents?

Think of the sweaty waft that comes from your own kids’ rooms – and they actually leave them to scatter their detritus downstairs.  In this case, the paying student would be largely confined to their room.

So you can multiply those odours by two or three – and we all know that opening the odd window won’t undo that.

How do you react if they decide to bring home a guest? Given that you’re already in the rental business, presumably you charge – but do you really want to meet strangers on your way to your own loo at four in the morning?

That said, at least you might get to know your guest if it’s a student for the academic year – but some stray who can’t afford a hotel room? Different kettle of fish.

All of the registration and references in the world cannot guarantee that your iPad isn’t off to Mexico on the next part of your guest’s world tour.

And what do you do when voices are raised in some sort of domestic dispute – or that cold silence chills to the bones?

Do you have to act like you’re one of the Waltons or The Brady Bunch every time you have a house guest?

I know of people who were reared in B&Bs – their families owned them, they were not in temporary accommodation – and they are still haunted by the tension that is created when you cannot say what you want to say in front of the paying guests.

One particular friend of mine, who grew up in a holiday town in the south of the country, spent every summer sleeping in a shed at the bottom of the garden because his room was worth more with him out of it than in it.

And that cuts to the crux of the matter – is your house a means of making money or is it a home?

Admittedly not everyone has the luxury of making that call, because some have no option but to harness every cent of potential income to avoid having to hand the house keys back to the bank.

But isn’t there something about stretching out in your own seat in your own room watching your own telly – wearing whatever you like in the privacy of your own home – that money simply cannot compensate for?

Good luck to the boys from Airbnb and fair sailing to the landlords and landladies of students – I think we’ll keep the drawbridge up and the moat in place for a little while longer yet.