In-situ concrete:

Concrete which is formed or laid on site.

Indirect hot water system:

The system by which domestic hot water is heated by a boiler and stored in a cylinder or tank, often incorporating a secondary means of heating such as an electric immersion heater.

Inspection chamber:

A chamber of brick, concrete or pre-formed plastic construction sunk into the ground, as a means of giving access to underground drains for inspection and/or maintenance.