G2D3 relates to open fireplaces where timber or other solid material is burned and there is generally no in-built enclosing structure or apparatus across the front to contain sparks, etc.

The construction of a fireplace must comply with the structural requirements in Section B of the NCC. The G2D3 requirements relate to additional measures for fire safety.

G2D3(a) states that the fireplace must have a hearth made of stone, concrete or other similar non-combustible material. The non-combustible material must be similar in nature to stone and concrete. The concessions for non-combustible material in Section C of the NCC, particularly C2D10 (such as plasterboard and similar lightweight materials), must not be construed as complying with these specific provisions.

With the increased danger due to the open-fire area, G2D3(a) contains requirements to ensure the area in front of the opening is protected. The hearth is intended not only to protect adjoining building elements from sparks, but also to reduce the danger of logs rolling out. See Figure G2D3.

G2D3(b) deals with the construction of a fireplace (additional to the requirements of Section B). These relate to the fire box and the need to ensure that the walls adjacent to the fire can withstand the heat. Concrete blockwork is not allowed to form the fire box because it performs poorly under repeated heating and cooling cycles.

G2D3(c) contains the requirements for chimneys.

G2D3(c)(i) aims to make sure the masonry of a chimney is capable of withstanding heat. The construction requirements are less than those for the firebox, because the most intense area of the fire is below the actual level of the chimney.

G2D3(c)(ii) contains a requirement to line the chimney with a rendering mix to make sure it draws properly. A smoother surface:

• allows a freer air-flow up the chimney, and therefore removes smoke more effectively; and
• helps to minimise soot build-up, therefore minimising the risk of chimney fires.

G2D3(d) contains a requirement to ensure that damp-proof courses and flashings are installed.

Figure G2D3: Fireplace clearance from combustible materials