I'm an architect, and I'll tell you that the building industry is so entrenched in imperial measurements I haven't used my metric scale in five years. Every single product is based on imperial dimensions, meaning design, coordination, and calculation require the same.
Some examples: joist spacing tables display span lengths for 16" and 24" on center spacings. These tables are everywhere and they've been around unchanged forever. All the plywood sub-flooring is in 48" x 96" sheets. Works great for either joist spacing and in either horizontal or vertical orientation. If you buy a house in the US, standard is an 8' ceiling, "up scale" is 9', exclusive is 10'. (Who would know the status of a 2600mm ceiling?!) Studs are already available and pre-cut to accomplish these heights. Drywall is sold in these lengths. Concrete and soil are measured in cubic yards, roofing by square, carpeting by yard, ceiling tiles in 24" squares, etc. The International Building Code (what most of us use) gives dimensions in Imperial dimensions, including sprinkler head spacing, floor loading requirements, floor-to-floor, allowable areas, etc. Think about it, every plumbing, gas, and sanitary drain system connecting your building to infrastructure is calculated in imperial from engineering tables more than fifty years old. Tape measures are all imperial as is surveying equipment. The entire commercial real estate market is in imperial, changing to metric would crush every agent and developer trying to calculate pro-forma for all real estate in the country. Lumber mills and woodworking equipment that has been around for years and that produce moldings, doors, boards, handrails, furniture, etc., are all imperial. Existing surveys, architectural drawings, engineering calculations, and every other kind of specification, calibration, documentation, regulation, etc. in the building industry is imperial, doing a simple renovation or addition (actually >50% of the building industry) would require the overhead of converting all existing information prior to proceeding.
I've worked on several metric buildings. It takes about two days to get into the swing of it. From an architect's view, scaling and plotting drawings is much simpler than imperial. Not having to deal with foot-inches is easier, too. (Although everybody seems to disagree about whether to use m, cm, or mm. We have native metric users that can't even agree on that.) But it doesn't take long before somebody starts discussing "hard" vs. "soft" metric and wondering if buying 900 mm doors will cost 50% more than 36" doors, if a wheelchair can still fit through it, and where they might come from in the local market if they can even be found. About a day later the whole endeavor goes down the tube when one party in the process gets nervous. We usually switch to "soft" metric for a few weeks (designing in imperial but also stating metric on the drawings) and then abandon the entire metric effort in favor of imperial. The only way a project will stay in true hard metric is if it is being built overseas.
We're going to have to go metric one system at a time. First was soda bottles. Then automobiles. Science is there, and a lot of SI units are becoming comfortable on food packaging. The building industry is going to have to do the same, I predict in places where highly manufactured components interface with imperial ones in a relatively unimportant way. (Think windows cut into a wall.) Commercially, roof membranes are specified in mm and many other components are manufactured in hard metric dimensions with proximal imperial values (like thicknesses of drywall and plywood). But things like bricks, lumber, and plumbing pipe may take a while.