How much office space do I need? The HSE’s 11 Cubic Metre Rule

by Crispin Maby

I have re-written this article since first publishing it in 2014 because at the time I was critical of the vague definition provided by the HSE in one of their regulations.  But 7 years on I have re-read the same regulation and, although I might be wrong,  I think perhaps the wording has changed slightly.  Nevertheless, it is still its not entirely clear and I will explain why later. 

Also, in the light of Covid 19 I’m wondering whether regulation relating to this matter might become policed more strictly or indeed whether they might actually amend it.  If it is amended, I will endeavor to update my article again.

One aspect of office space planning that often gets overlooked is the personal space allowance as stated by the Health and Safety Executive (HSE).  It accounts not only for the floor area taken up by desks, but also the volume of space required per person.  So we have to consider a 3 dimensional aspect rather than just the 2D floor plan.

This is of particular importance to you, the office occupier, because it may well be the determining factor in establishing how many people you can have legally working from your office.  I’ll cover this later, but the point of this article is to explain that even though you might be able to physically fit a given number of desks (and therefore full time workers) into your office space, you might not be permitted to do so.

In a nutshell, the regulation (Regulation 10 of the Workplace Regulations 1992 to be precise) states that you have to allow a minimum of 11 cubic metres of space per person working in the office. Unfortunately though, even though this is a regulation, and therefore we must assume that it is law rather than a recommendation, the information they provide us with is somewhat vague.  The key areas of confusion as far as I’m concerned are that:

1. There are 2 contradictory statements,  one referring to the ‘the number of people who may work in any particular room at any one time’, and the other ‘the number of people normally working in a room‘ .  So which do they mean?   
2. The second vaguery is the wording in the following statement: ‘The figure of 11 cubic metres per person is a minimum and may be insufficient if, for example, much of the room is taken up by furniture etc‘.  What do they mean by ‘much of the room’, and what sort of furniture are they talking about?  Do they mean cupboards and large solid objects, or are they also including the desks and chairs that we sit on?

Perhaps its just badly written or poorly thought through, both of  which would be unforgivable considering this is a legal obligation for us to adhere to,  so maybe we should give them the benefit of doubt and assume that they realise it is simply too difficult and far reaching to cover every scenario and instead they are giving us guidance to which we need to apply a common sense approach.

For your own office, you will have to make your own judgement on this as I’m simply pointing out what is being said and what different interpretations mean you might, or might not be able to do.

Firstly to item 1 above – ‘the number of people who may work in any particular room at any one time’, and  ‘the number of people normally working in a room‘.    If you take the first statement literally, and you have, for example, 110 cubic m of clear air volume, then it means that you can only have 10 people seated at a desk at any one time. But if you take the second statement to be true, then perhaps you can have far more people working there on occasions, as long as there are normally no more than 10 people. But in this scenario, who decides what is normal and could it simply mean more than 50% of the time?  Also, specifically in relation to the 11 cubic metre rule, nowhere does it state how many desks you can have in relation to the number of people. So, hypothetically, in relation to both statements, you could have (as long as the space permits) a far greater number of desks than you would either a) have people working at any one time or b) normally working in the room. I suppose it could be argued that if the desks are there, it must then be assumed they could all be occupied and therefore encouraging the breaching of the rules.  My personal opinion on this would be that common sense must prevail here. Firstly, volume permitting or not, the 2 dimensional layout of the office has to be such that it allows for safe and practical working and this is covered (albeit extremely briefly) in the regulation.  But as long as it can be done in a sensible manner, then there is no reason why you shouldn’t maximise your layout to include extra desks as long as you take a common sense approach and risk assessment and ensure that your principles are adhered to.  After all, even in a busy office with full desk occupancy of full-time desk workers,  how often is it that everyone is at their desk (or indeed in the same room) at the same time?  People go for meetings internally or externally, people take different lunch and coffee breaks, people start and finish work at different times and so on, so even in these environments its very rare that every desk is occupied simultaneously.    

And on item 2 above,  we need to be sensible about this, and I don’t think anyone can be expected to start calculating how much volume each desk and chair takes up, besides which there is air flowing beneath and around them, so personally I would only be concerned about the impact of large cupboards and other very bulky items.  

Finally, before we move on, I should be clear that the rule applies only to workrooms and not meeting & lecture rooms (assuming they are used as such and not as full time work rooms).

So, onto some examples to help make everything a little clearer.  Given how unclear the regulation is as I outlined above,  I’ve decided to use the worst case scenario for my examples, that being the assumption that each desk must have an average 11 cubic metres rather than each person (therefore the assumption that each desk is occupied all the time).

In my experience,  the typical modern office has a ceiling height between 2.4 metres and 2.7 metres, so let’s go with 2.5m as a good compromise.  Firstly we need to calculate the volume of the room by multiplying the floor area by the ceiling height and then dividing it by 11. The resulting sum will give us the maximum number of people we’re allowed to fit into this space (if we have cupboards we will have to make a deduction for this before the division).   How does this look in practice?  Below I have done 2 CAD drawings (Figures 1 and 2), figure 1 showing an open plan office packed with as many 1200mm by 800mm desks (these are the smallest of the regular sized desks generally used in offices) that will physically fit, and figure 2 with the same office showing how many desks we would have to remove in order to achieve the capacity we are actually allowed.  To save you counting, there are 104 desks in figure 1, and this is reduced to just 58 in figure 2 – a reduction of 44% no less!

Ok, you say, but that’s an unrealistic office layout. We’d never have so many people in one area. We’d have other things like storage cupboards, reception counters, larger desks, meeting areas, breakout areas and probably also additional rooms.  Well I have to tell you that I’ve seen offices just like this (figure 1) and although perhaps an extreme example, the rule applies no matter how large or small the office is; – for example, we might not be looking at the main office, but a smaller room within the building into which you want to get as many desks as possible because your reception, meeting rooms and the like are in different parts of the building.  So the sake of continuity and simply to demonstrate a point, we’ll stick with the original plan for the time being and I’ll start introducing other factors.  Let’s assume that we’re now down to our 58 desks and we’re looking to fill the rest of the space as best we can with other furniture.   In figure 3 I have inserted 36 tall free-standing cupboards (let’s say 2m high) a couple of meeting areas, reception counter and waiting area.  The cupboards now have an impact on the permitted desk volume because I have had to factor in that each one has a volume of 1 cubic metre, and as a result it has reduced our room volume somewhat and in turn we’ve had to take out 2 more desks to compensate.

All very good, but it’s all very open plan and maybe we need some private space with sound and visual privacy, so figure 4 again shows the same office but this time with a large partitioned meeting room and 2 cellular offices.  Because we’ve introduced partition walls, the areas within these new rooms can no longer be considered to be part of the open plan area and the cubic capacity of the new and smaller open plan area reduces dramatically as a result. I have had to remove yet another 20 desks of the remaining 56, giving us now a mere 36 desks (a further reduction of 35%).  I must be honest, I don’t know whether I’m allowed to include the corridor as part of the open plan space (HSE guidance is not specific about these issues) but for the benefit of doubt I have not.  If it is permissible, then we would have been able to add back in a couple of desks.

So there you have it.   If the ceiling was higher, then we could have taken this into account and increased the volume and therefore quantity of desks, but this applies only up to 3m – there above we have to ignore any further height advantage.

How does this relate to typical office capacities?

If you are interested, the plans I have drawn in figures 1 to 4 have an overall footprint of 259 square metres (2,787 square feet).  When companies are looking for a new office, a very general but typical rule of thumb is that on average you allow 100 square feet per person (this takes into account the entire office, including meeting rooms, breakout areas etc). If you follow this rule of thumb, then on average, regardless of the ceiling height, the 11 cubic metre rule becomes far less relevant because in this example, you would actually only be looking to get 27 people/desks into the office and my worst case scenario allowed for 36 desks.  Be careful though, because it is all about the capacity of desks within a specific room or area and what this does show is that it’s unlikely that you would be able to cram any particular room just with desks and no other furniture or spare space.

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