What is a portal?

A portal is the entrance of a building together with its architectural surround — and also the space you step into immediately behind that opening. The word carries several meanings in construction, and they are easily confused.

1. The ceremonial entrance

The classic portal is the designed entrance opening: jambs, a lintel or arch, often with columns, cornice or pediment. Church portals are the best-known examples — Romanesque recessed portals, Gothic splayed portals with a tympanum in the arch field.

In Dutch usage the word portaal refers above all to the space behind: the small, closable area between outer and inner door. The inner part is called the vestibule.

The draught lobby is the practical version: two doors in series, so there is never a direct connection between outside and inside. That makes a measurable difference to draught complaints and heat loss, particularly at busy entrances to schools, shops and apartment buildings.

2. The landing

In compounds such as the Dutch trapportaal, the word means the landing: the space at the top of or between flights of stairs, onto which the doors of a floor open.

3. The structural portal

In structural engineering, a portal is a rigid frame of two columns and a beam, with moment-resisting connections at the corners. Such a frame can take horizontal load without any bracing in its own plane. The developed structural form is called a portal frame.

Points to watch

1. Swing direction. Doors in a lobby must not foul each other.
2. Depth. Allow at least the door width plus roughly 600 mm of clear space, so one door can close before the other opens. Accessible entrances need considerably more manoeuvring space; the dimensions are in the applicable accessibility standard.
3. Matting. A lobby is the logical place for a matwell. Allow several metres of walking length to catch dirt and water properly.
4. Airtightness and insulation. Keep the airtightness line continuous through the lobby; break it and you create a thermal bridge around the entrance.
5. Escape route. An entrance almost always sits on an escape route. Doors on an escape route must open in the direction of travel and be openable without a key.

Related terms

• Portal frame
• Portico
• Draught lobby
• Vestibule
• Jamb
• Tympanum

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