Roof and tunnel hacking is the unauthorized (generally prohibited and often illegal) exploration of roof and utility tunnel spaces. The term carries a strong collegiate connotation, stemming from its use at MIT, where the practice has a long history (see vadding). It is a form of urban exploration. Some participants use it as a means of carrying out collegiate pranks, by hanging banners from high places or, in one notable example from MIT, placing a life-size model police car on top of a university building. Others are interested in exploring inaccessible and seldom-seen places; that such exploration is unauthorized is often part of the thrill. Roofers, in particular, may be interested in the skyline views from the highest points on a campus.
Thus, vadding and vadders began to refer to people who undertook actions in real life similar to those in the game. Since ADVENT was all about exploring underground tunnels, the MIT sport of roof and tunnel hacking became known as vadding.
Today, the word vadding is rarely used at MIT (usually only by old-timers) and roof and tunnel hacking has returned as the preferred descriptive term. Those who participate in it generally refer to it simply as "hacking".
Most buildings at American universities have flat roofs (pitched roofs are impractical for roof hacking). Entry points, such as trapdoors, exterior ladders, and elevators to penthouses that open onto roofs, are usually tightly secured. Roofers bypass locks (by lock picking or other methods) or use unsecured entry points to gain access to roofs. Once there, explorers may take photographs or enjoy the view; pranksters may hang banners, plant fake police cars, or execute other sorts of mischief.
Some universities have utility tunnels to carry steam (central steam heating being more efficient than installing a boiler in every building) and other utilities. Utility tunnels are usually designed for infrequent access for maintenance and the installation of new utilities, so they tend to be small and often cramped. Sometimes, utilities are routed through much larger pedestrian access tunnels (MIT has a number of such tunnels, reducing the need for large networks of steam tunnels; for this reason, there is only one traditional steam tunnel at MIT, built before many buildings were connected).
Tunnels range from cold, damp, and muddy to unbearably hot (especially during cold weather). Some are large enough to allow a person to walk freely; others are low-ceilinged, forcing explorers to stoop, bend their knees, or even crawl. Even large tunnels may have points where criscrossing pipes force an explorer to crawl under or climb over a pipe — a highly dangerous activity, especially when the pipe contains scalding high-pressure steam (and may not be particularly well-insulated, or may have weakened over the years since installation).
Tunnels also tend to be loud — pipes clank, machinery whirs and hums. The background noise may prevent an explorer from hearing another person in the tunnel — who might be a fellow explorer, a police officer, or an underground dweller (this is more of a risk in urban areas, where underground spaces may be used as labs by drug dealers or as makeshift dwellings by the homeless). Tunnels may be well-lit or pitch-dark — and the same tunnel may have sections of both.
Tunnel access points tend to be in (locked) mechanical rooms where steam pipes and other utilities enter a building, and through manholes. As with roofs, explorers bypass locks (or look for unlocked doors) to enter mechanical rooms and the connected tunnels. Some adventurers may open manholes from above (with crowbars or specialized manhole-opening hooks) — a practice with risk.
Some tunnelers may make maps of their campuses; an internet search will turn up a handful of these.
Regular use of a shaft can wear down insulation and cause other problems. To fix these problems, hackers sometimes take special trips into the shafts to correct any problems with duct tape or other equipment.
Universities generally prohibit roof and tunnel hacking, either by explicit policies or blanket rules against entry into non-public utility spaces. The reasoning behind these policies generally stems from concern for university infrastructure and concern for students. Consequences vary from university to university; those caught may be warned, fined, officially reprimanded, suspended, or expelled. Depending on the circumstances, tunnelers and roofers may be charged with trespassing, breaking and entering, or other criminal charges.
MIT, once a vanguard of roof and tunnel hacking (books have been published on hacks and hacking at MIT), has been cracking down on the activity. In October 2006, three students were caught hacking near a crawl space in the MIT Faculty Club, arrested by the MIT police, and later charged with trespassing, breaking and entering with the intent to commit a felony. The charges raised an outcry among students and alumni who believed that MIT ought to have continued its history of handling hacking-related incidents internally. Charges against those students were eventually dropped. In June 2008, another graduate student was arrested and faced charges of breaking and entering with intent to commit a felony and possession of burglarious instruments after being caught after-hours in a caged room in a research building's basement.
Utility tunnels carry everything from drinking water to power to fiber-optic network cabling. Some roofs have radio broadcast or radio reception equipment and weather-surveillance equipment, damage to which can be costly.
Roofs and tunnels (especially tunnels) also may contain switches, valves, and controls for utility systems that are not meant to be publicly accessible; manipulation of any of these may cause problems ranging from annoyances (an interruption of power to a dormitory room) to disasters (a catastrophic steam depressurization, a campus-wide electrical failure, a burst water main).
Roofs are dangerous; aside from the obvious risk of toppling over the edge (especially at night, in inclement weather, or after drinking) students could be injured by high-voltage cabling or by microwave radiation from broadcast equipment. In addition, laboratory buildings often vent hazardous gasses through smoke stacks on the roof.
Tunnels can be extremely dangerous — superheated steam pipes are not always completely insulated; when they are insulated, it is occasionally with carcinogenic materials like asbestos. Opening or damaging a steam valve or pipe can be potentially deadly. Steam contains significantly more thermal energy than boiling water, and tends to dissipate that energy when it condenses on solid objects such as skin. It is typically provided under high pressure, meaning that comparatively minor pipe damage can fill a tunnel with steam quickly.
Confined spaces contain a range of hazards — from toxic gases like hydrogen sulfide and carbon monoxide, to structures that may flood or entrap an adventurer. An explorer who enters a tunnel via a lock bypass method or via an inadvertently-left-open door may find himself trapped if the door locks behind him — quite possibly in an area with no cell phone reception, and no one within earshot.