I am sometimes surprised by queries that have answers I assumed would be apparent to anyone trained or licensed in the architectural field.
As other posters have observed, in any state that has adopted any one of the last many versions of the standard building codes, a clear unobstructed path of travel is required to the public way - which does not 'stop' at the threshold of the door in the building's exterior wall. That is the minimum legal requirement. (NOTE there are actually a small number of states that have no adopted code, so they are excepted from that comment.)
To achieve the clear path requirement, it seems obvious something has to be done to ensure parked vehicles do not block the exit. Although it could be argued that this is an "Owner maintenance" issue, experience teaches us that is not a supportable argument.
Blockage of the exit door is an event that can be anticipated (is 'predictable'). What that means is that the Architect (who is presumed to have knowledge superior to that of a layperson) is obligated to ensure the building design protects against injury or death that is preventable (because it can be predicted). Because codes do not always clearly address an issue, it is critical to understand the Architect's primary duty to look beyond the code's 'minimum' compliance language (as a general principle).
Architects are charged with more than just meeting code minimums. They have an underlying obligation to design buildings such that they protect the public health and safety. That is a part of the professional Standard of Care. The AIA ethical guidelines (as well as those of every major professional design organization) emphasize that the licensed professional's obligation to protect the public is elevated even above the duty to serve the Client.
Ensuring that occupants (in this example) have a way to get out of the building and 'away from it' in an emergency situation is a fundamental consideration... and therefore part of the Standard of Care. In this example, the building code already makes clear that the pathway has to remain unobstructed, so there is clear guidance. However, there are other situations that arise in which designers intuitively or by experience understand that providing a safe/healthy building requires something greater than the 'minimum' required by codes. That is when you need to go 'above and beyond' code minimums in discharging your professional duties.
The absence of explicit building code language (for any given situation) does not provide the designer with a justification to look the other way... ever. When a client says (as in this particular case) they don't want a railing, bollard, curbed island, etc., that is not an excuse to eliminate prudent protection measures from your design (i.e. to ensure the exit is not blocked).
Saving space and/or money may be the Owner's concern, but the Standard of Care demands the designer stand up and be counted. Do not let your client's perspective cloud your professional judgment. Tell your client that it is your decision that a physical device is required. Do not sign/seal a design that does not, in your opinion, meet with your underlying obligation for protection of building occupants. Nobody can force you to issue a design that fails to meet the Standard of Care.
And to those who think they can blame later consequences on an Owner's decision (demand) to overlook a safety issue... be aware that no document the Owner says it will sign, waiving your concerns, will legally protect you from a negligence claim.
It is you, the Architect - not the Owner - that is responsible for a 'safe' design. It is you, the Architect - not the Owner - that will be held responsible if occupants end up being injured or killed because the exit door was blocked (AND IF your design, which should have anticipated this possibility, was negligent).
Architects want to be held in high esteem. Part of earning praise is standing up for what is 'right'. Be the 'leader' you want others to think you are. When the Standard of Care begs for something that is not explicitly dictated by building code language, you need to firmly (and politely) explain to your client that you are the one in charge (and the one that has responsibility for your safe design). If your client is unwilling to allow you to exercise your professional duties property, let him/her pay you for what you have done to date and shop around for someone else that is willing to bend to his/her will (and assume the risk).
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Howard Littman AIA
Forensic Architect, Expert Witness
Howard I. Littman, AIA
Agoura Hills CA
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