The primary way that steampunk will be different from today is the transmission of energy and information would be through mechanical and fluidic means rather than electrical as we are used to today.
Architecture would have accommodations to allow for the use of mechanical transmission inside and between buildings. Communications would be via devices like pneumatic tube transport. Because of the size and space requirements for these devices, there will be a need for protected galleries in the houses for driveshafts, pneumatic tubes, drive belts, reduction gears and other assorted mechanisms. There will also be room inside the galleries for maintenance men to enter and perform work. Another consideration is there will probably be storage rooms for tools and spare parts in the larger houses and public spaces.
Tenements and row houses will have much smaller galleries, since there will be fewer services provided for poor people. One might imagine an open attic spanning the entire top of a row house for the drive shaft and belts leading down into the rooms below, much like the machinery hall of a factory.
The other thing that will be evident in a Steampunk world is the ned for elevated pathways for pneumatic tubes, driveshafts and other mechanical parephanalia. Because of the size of the devices, they will resemble miniaturized elevated railways, and may even serve as the roadbeds for real elevated railways (especially in densely populated areas where there would be lots of tubes and drive shafts in close proximity). Of course, since there are limits to how far mechanical or fluidic transmission could go, the system will need lots of repeater stations.
Since large blocky buildings housing boilers, steam engines, Babbage machines, vacuum pumps and other paraphernalia will take a lot of room. The city and especially the wealthier citizens will probably try to disguise the buildings with clever facades. People won't be fooled since there will still be smokestacks, large structures that carry the pipes and driveshafts and a big driveway for the coal delivery service, but will probably appreciate the effort to make the buildings either good looking to unobtrusive.
So architecture will be adjusted to take the needs of mechanical and fluidic systems into account.