You can't, because open plan is dirt cheap and lower footprint.
Cheap, yes; inexpensive, not so much. A (software) company I worked for back in the mid-1990s opened up a new office building on their campus. They'd previously had nearly everybody in 1- or 2-person offices with doors that closed, and full-height partitions between desks of shared offices. The new building might as well have been a warehouse; it was 10 floors of absolutely open, unpartitioned space. They moved eight groups from the existing buildings into the top floors of the new one (and everybody in the old buildings had solo offices again) as guinea pigs for the new building and work environment. Now, the top managers in this company were sticklers for measurement and detail; some even (quietly) called it a fetish of theirs.
But that turned out to be a bit of a blessing for the workers, especially those of us whod been moved. The company had several years worth of data on productivity and error rates for each division and department, down to the work team level (4-10 people). They could, and did, compare the data they acquired from the teams in the new building to the data from those same teams in the old buildings, and they found something profoundly disturbing. The top-performing group after the move was 6% as productive and had over 18x the error rate in production as that same group had been when theyd all had solo (or a few duo) offices. No other team had higher productivity or lower error rates. Not one.
Four months after we'd moved into the new building, they called an all-hands meeting for the entire campus. The CEO and CFO got up, explained the problem, explained why they'd fallen into the trap (basically "we screwed up; everybody's doing it and so we thought it was probably a good thing"), and announced a schedule for the groups in the new building to temporarily move down to the bottom two floors while the top half of the building was remodelled with floor-to-ceiling partitions, noise-absorbing and -diffusing fabrics and materials, and so on. In the all-hands, they pointed out that doing the entire building this way was going to make it significantly more expensive than if they'd simply built offices as in the old buildings, but that they expected to make up that difference within less than two years from recovering lost productivity and reducing the preternaturally high error rates.
The CFO also mentioned something he said he'd found in his research. The open-office plan in tech basically originated with defence contractors during WW2. They were being paid on contracts by the staff-hour, and some "misguidedly bright spark" had had the idea to push for a study on how they could maximise billed hours while still (more or less) meeting agreed deadlines, and the study found that the more (skilled or knowledge) workers were sharing a common work area, especially when mixed with support- or admin-type workers, the lower the productivity. Many contractors quickly standardised on this; it was made more plausible by the claim that "hey, we have to put up these working spaces quickly, so no time for fancy details". Since Sili Valley started with semiconductor companies (e.g., Fairchild) staffed with engineers who'd previously worked for such contractors, they (largely unknowingly) carried the warehouse-as-office-space mentality forward because that's all they'd ever really known. Half a century later, you get us crunching the numbers (and, I later found out, several other companies at about the same time with similar experiences).
Open offices are, at best, cancer for productivity and for mental health. They should be abolished, if not explicitly banned under workplace-safety-and-health laws and treaties.