As someone with spare bedrooms, this itself is a problem of undersupply. If you can't be sure of being able to trade up when you need to (e.g. after starting a family) because house prices are up 100% in 10 years, then you're going to want to buy a house for all possible future needs, rather than current needs.

Add to that, things that might be desirable for other reasons, like garden space, rooms for use as offices, large kitchens, etc. all tend to scale with bedroom count too.

Also trading up comes with stamp duty, which is a damper on moving house unless you absolutely have to. Not only is your new house bigger and more expensive then anything you've ever bought before with that extra bedroom, plus the large expenses and hassle of moving in general, it's likely another £10k or more in stamp duty unless your new 3-bed is somewhere pretty cheap in the country. You don't get the first time buyer discount either, as you already have a house.

It's basically a tax that punishes labour mobility and not oversizing property.

Of course, you have to pay to heat and maintain that bigger house and pay higher council tax on it, so your saved stamp duty will probably be used after a few years, so in an ultra-rational way, it comes out in the wash, but it certainly doesn't feel like it at the time.

House ownership is higher among boomers, who are not going to have children anyway. Maybe for some people concern for future prices is a good reason, but certainly it is not for everyone. If there’s spare capacity enough for 20% more people and population growth forecast by 2050 is just one third of that, you cannot really talk about undersupply, when there’s enough accommodation to cover even future demand.

This assumes a level of fungibility that's just not there. Apart from the discussions elsewhere in this thread about why spare bedrooms might not be suitable to rent, even for those that are, splitting a family of 4 across 4 spare bedrooms in 4 different properties is suboptimal at best and legally child neglect at worst.

Equally, houses in Cornwall are of little use when the jobs are in London.

The owner is living there and happy with the space or they would move. That is not underutilization. The solution to housing shortage is to build more housing, not to create “bedroom police” who go around and tell you’re not allowed to have your house because they will decide for you how much space you need.

Lol bedroom police. Yes, because that's exactly what we were discussing.

Or, you could, you know, make it more affordable to build smaller homes with fewer bedrooms so people actually have options when they become empty nesters.

That would fall under "build more housing".

Just to conceptualize this, it's like every 5 bedroom house having 1 unused bedroom, perhaps being used as an office. Of course, most houses don't have 5 bedrooms, so in reality this is an extra bedroom for every 2 houses. Again, possibly being well used for another purpose. That doesn't seem like a lot of underutilization to me.

Rooms used for another purpose are not called bedrooms. See yourself: https://www.ons.gov.uk/peoplepopulationandcommunity/housing/...

How does a guest bedroom get counted, out of curiosity?

Guest bedroom is underutilized space unless you are a hotel or full-time Airbnb. How often people are staying there? A few months a year in total, if children spend the whole summer with grandparents and visit on rare holidays?

Is that a problem? It's a guest bedroom for every two houses. Something approaching the vast majority of all economic output goes toward things which are extraneous when measured against the historical median standard of living. But people like nice things. And a guest bedroom is a nice thing that some people like.

That feels... weird. Would you say a car is underutilized if it's not being driven 24 hours a day?

They can be. My house is a four bedroom house. One of those is used as an office.

Nothing in the ONS link says otherwise, they just ask

"How many bedrooms are available for use only by this household?"

Also consider that many 3rd bedrooms in the UK are tiny. Like, "don't fit single bed frames and allow the door to open properly" tiny.

Underutilized would imply that it's literally useless dead space.

I have more rooms in my house than people, they have purposes.

UK census differentiates between rooms and bedrooms, so indeed an unused bedroom is likely a dead space.

My home is listed as having more bedrooms than people.

They are not dead spaces, and they wouldn't somehow become more useful if I knocked a wall or two through to reduce the room count or reclassified them.

Are you purposefully being obtuse? The point is the difference between bedrooms, bedrooms used as offices, etc, and spare bedrooms. You can have more bedrooms than people and fully utilize the rooms not being used as bedrooms; the statistic is 20% of rooms are being underutilized ie spare bedrooms that don’t get used.

I'm not deliberately being obtuse - I simply don't believe that many people have literally empty rooms that they don't use.

I don't know anyone that has an empty room in their house, or one that no-one enters for weeks at a time, etc. Maybe the odd country estate is like that.

To a communist, the concept of having a guest room, office, storage room etc might feel like "underutilization".

If we apply that more generally, then the park outside my house is underutilized because the maximum capacity are not sunbathing in it at all times. I think that's a pretty silly use of language.

I absolutely know people with rooms that are literally unused. They aren’t empty, but it’s not a valuable use of space just because it means you don’t have to get rid of your last three couches and a desk that’s nice but not nice enough to use.

Who decides what "valuable use of space" is? Next we'll be taxing people whose living rooms are too big because they're not "valuable use of space" and could be split into another bedroom.

In life, some people look up, some people look down.

I'll never understand how someone could think that completely normal things like a house, garden, car, etc are somehow "too much". But they do. It's baffling.

I can understand, though not agree, with being angry with someone who owns say, tens of thousands of houses, millions of acres of land, and leaves it all empty.

But the idea that a house is underutilized if it doesn't have as many people as could possibly live in it? All I can say is, Hong Kong exists, Manhattan exists, feel free, I'm not in for that.

Labeling formal logic as „communism“ won’t help (it‘s also kinda funny when people with certain cultural background use this word as synonym for some biblical evil, rather than for what it is). Guest room is not a necessity in most cases, it is convenience for which alternatives do exist and may even be more cost efficient/practical. Since it is not, downsizing your home in retirement to release space for bigger family will be more efficient than building everyone a house with a spare bedroom. It does not have to be expropriation of the property for this to happen, just a policy with good incentives (less maintenance effort, less taxes to pay, better investment opportunities etc).

> Since it is not, downsizing your home in retirement to release space for bigger family will be more efficient than building everyone a house with a spare bedroom.

This is true. The problem tends to be that people become settled in an area, and would prefer to downsize there so they don't need to uproot themselves. This is often very difficult, as there may not be availability in that area for a suitable smaller property.

> I don't know anyone that has an empty room in their house, or one that no-one enters for weeks at a time, etc.

I don't have any statistics to hand but, based on experience, there are a lot of houses in the UK like this. Particularly among middle class couples in their 60s, whose children have left home. In fact, my parents have two spare bedrooms that are only used a handful of times each year.

If you're talking about the study that everyone was talking about last week, that definition of "spare bedroom" includes a family of four with three bedrooms who gives each child their own bedroom when they could just have them sleep in the same room.