Page 56 - Build 165

Medium-density housing
Fire spread from lower roofs
It’s important with higher-density housing in urban areas to ensure re doesn’t spread from a lower roof to an adjacent, taller wall. BRANZ re researchers are delving into the validity of the current 9 to 5 rule.
THE NEW ZEALAND protection from re Acceptable Solutions have had a require- ment to prevent re spread to a building from an adjacent lower roof since their introduction in 1992.
9 to 5 rule to prevent re spread
The requirement has been that either the:
● adjacentroofmustbe re-ratedanywhere within a distance of 5 m of a taller wall, or
● 9 m of the wall above the adjacent roof has to be re-rated with no unprotected
openings (see Figure 1).
This combination of re-rating requirements has come to be known as the 9 to 5 rule. The required amount of re resistance and sprinkler concessions have varied as the Acceptable Solutions have evolved.
The 9 to 5 rule comes into e ect if:
● firecells behind the wall contain other
property
● there are sleeping spaces or exitways
behind the wall and the wall is in the same building as the adjacent lower roof or in an adjacent building on the same title.
BY KEVIN FRANK, BRANZ FIRE ENGINEER
Two local res spread this way
Two New Zealand examples where this type of re spread occurred were the 1978 Bryce Street Market re in Hamilton and the 2005 Bracken Court re in Dunedin.
In the Bryce Street Market re, the re originated in a ea market. In the Bracken Court re, the re originated in a converted
Table 1
NFPA 80A minimum separation distances
warehouse with commercial and sleeping occupancies.
Both res caused substantial damage to next door taller commercial buildings on several levels above the lower adjacent roof. The re spread into the adjacent taller build- ings through windows.
Table 2
NFPA 80A maximum flame heights
NO. OF STOREYS LIKELY TO CONTRIBUTE TO FLAMING THROUGH ROOF
HORIZONTAL SEPARATION DISTANCE OR HEIGHT OF PROTECTION ABOVE EXPOSURE
m ft
NO. OF STOREYS BURNING
FLAME HEIGHT ABOVE ROOF (IN STOREYS)
1
1.4
2
1.8
3
2.2
4
2.6
5
2.9
6
3.1
1
7.5
25
2
10
33
3
12.5
41
4
15
49
54 — April/May 2018 — Build 165
FEATURE SECTION