How much office space do I need? The HSE’s 11 Cubic Metre Rule
by Crispin Maby
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.
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 normally working in the office. Infuriatingly though, apart from being very specific about the minimum acceptable volume, they’re thereafter exceptionally vague about everything else. They go on to tell us that 11 cubic meters might not be sufficient if much of the room is taken up by furniture, but they don’t tell us how to factor this into the calculation! And what’s more, does furniture mean desks and chairs? I mean, for goodness sake they’re both furniture items as far as I’m concerned but surely we don’t have to allow additional volume for these otherwise we’re all going to end up needing ridiculously large and expensive offices!
So for the purpose of this article I’ve made the assumption that furniture means anything that’s big and that is not a desk, chair or pedestal. So basically that typically leaves cupboards, and I’m going to make the assumption that they (HSE) want us to calculate the volume taken up by all storage cupboards and then deduct this from the overall volume of the office space before then applying the calculation for cubic metres per person.
I want to show you how this rule can impact dramatically on what you can legally fit into an office, rather than what you can physically fit if you choose to ignore the legislation. In my experience, the typical modern office with a suspended grid ceiling 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! Quite shocking really. 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.
This begs the question as to whether this is all reasonable and fair, and have the HSE got it right, or has a civil servant tasked with creating the regulation just plucked a figure out of the air without any sound statistical and scientific fact to base it on? Well you would hope not, but let’s face it, business can be tough for us all and office space is generally considered to be the second largest overhead for a company after salaries, so hopefully the HSE is not forcing us to take on bigger and more expensive offices than we need without sound justification. The gripe I have is that, as mentioned earlier, the information the Health and Safety Executive provide us with about this is very vague and unless there are other documents that I haven’t been able to find that go into much finer detail, then they’re leaving us to make our own interpretations at the risk of getting it wrong. The main issues I’d like answers on are as follows:
- What do they mean by furniture (does that include desks and chairs) and how do we calculate this against volume of air?
- How should we interpret the word normally in the following sentence provided by them?; “The total volume of the room, when empty, divided by the number of people normally working in it should be at least 11 cubic metres”? Does this mean the number of people that are normally working in the room at the same time, or does it mean the number of people who have a desk there and who are usually in the office most of the day? And does ‘normally’ simply mean more than 50% of the time?
- They tell us that workrooms (in this case your office), should have enough free space to allow people easy access to and from workstations, to move within the room with ease and not to restrict their movements whilst performing their work. All well and good and sound advice, but what are they thinking? Is our idea of sufficient the same as theirs?
I question item 2 above, because perhaps, if you can prove that only a certain percentage of the staff with desks are normally actually in the room at the same time because at any one time some are having meetings elsewhere in the building, some are simply not in at all, some are having a break somewhere else and so on, then you could argue that the concentration of desks can be much higher. Perhaps though, this is one for the lawyers to advise on.
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. According to the Google conversion tool, that’s 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.
A final note simply to clarify an issue. The rule does not apply to meeting rooms, lecture rooms and so on.