Calculation of Flammable / Non-Flammable areas - Block B

Description of parts.

Updated 24th November 2025 [*'d].
Updated 7th February 2026 - corrected summary error on garages [small impact], added note of sensitivity for whole estate calculation.

There are seven elements to the buildings to be considered which are as follows:

1. Roof
2. Water Tanks *
3. Front Wall
4. Rear Wall
5. Southern End Wall
6. Northern End Wall
7. Garages *

The calculation of flammable and non flammable areas of each is described below.

Data from Reports

Taken from FRC External Wall Survey Report, Page 23:

Item 8.1.4: The maximum height of the buildings is estimated to be approximately 10.1m, with a habitable top story level calculated to be approximately 7.4m to the slab level of the uppermost floor.

Thus the floor height is 2.7m [soffit to soffit].

Taken from Wandsworth Council:

Specific Planning Permission for a roof using Mastic Asphalt was granted by Wandsworth Council as follows:
59/14350/B 21-50 GARDEN ROYAL Kersfield Road London SW15 3HE
Details of roofing materials to Blocks "B" and "C" pursuant to planning permission dated 15/12/59.
FINAL DECISION Details - Granted.

Noted that Google AI states:

Mastic Asphalt is not flammable and is considered fire-resistant. Its high mineral content makes it virtually incombustible. Mastic asphalt is often used in applications where fire safety is a critical concern, like flat roofs, due to its ability to resist flame spread and penetration.

Noted also that repairs may have been carried out using Bitumen which is flammable. DHP's estimates included for Bitumen as an alternative.

Water Tanks.

Measurements from Photographs

Taken from an RGTR Photo - for first floor: [picture measurements in cm] window height: 4.3 cm, tiles height: 2.5 tiles, bay width 9.0cm.
Width of concrete frame column is 0.8 cm.

Thus 6.8 cm equates to 2.7 m. Thus the indicated window height is 1.7 m, and the indicated cladding or tile height is 1 m.
And the indicated bay width is 3.6 m, indicated clear [windows] width is 3.3 m, with the frame being 0.3 m wide.

Taken from an RGTR photo - for rear small bay: [picture measurements in cm] small bay 4.5 cm, full bay 7.7 cm
This indicates that the smaller bay is 2.1 m wide, and 1.8 m window width.

Taken from a Google Maps Aerial View, the building measures [picture measurements in cm] 4.1 cm depth and 12.2 cm width. The scale indicating 5m measures 2 cm. The indicated overall building size is 30.5 m wide and 10.3 m deep.

Taken from Google Maps Street View, a window [picture measurements in cm] 2.5 cm high and 2.3 cm wide.
The door is assessed at being 1.8 cm wide by 4.4 cm high.
The scale is 4.5 cm beteeen floors of 2.7 m.
The indicated size of a window is 1.5 m by 1.4 m viz 2.1 sq m.
The indicated size of the door is 1 m by 2.6 m viz 2.6 sq m.

Taken from Google Maps Street View, a window [picture measurements in cm] , the front door bay has cladding to each side of the door measuing 2.5 cm wide by 5.5 cm deep. The scale is 9.5 cm beteeen floors of 2.7 m.
This indicates two panels of 0.6 m by 1.6 m viz 1.9 sq m in total.

Assessment of Areas

Roof

There are 12 roof lights, and 3 water tanks. The indicated size of the roof lights is 0.7 m by 0.7 m viz 0.5 sq m, i.e. 6 sq m in total. The indicated size of the water tanks is 2 cm by 0.6 m viz 5 m by 1.5 m viz 7.5 sq m, i.e. 22.5 sq m in total.

The indicated overall size of the roof is 314 sq m, with non flammable areas of 28.5 sq m leaving 285.5 sq m of possible flammable area - depending upon the resurfacing material used. Bitumen is flammable.

Google Maps Aerial View indicates that three bays 3.6 m wide by 10.3 m deep have been re-roofed. The bays are the most southern ones and the penultimate on to the north. These cover an area of 111 sq m.

* In 2025 a further bay was re-roofed bringing the flammable are to 148 sq m.

Rear Wall

There are 7 full bays, 3 to the south of, and 4 to the north of one smaller bay accommodating the stairwell.

There is no cladding to the rear.

The wall area is calculated as 4 stories by 7 bays of 3.3 m, and 3 bays [excludes ground floor] of 1.8 m 92.4 sq m plus 5.4 sq m totalling 97.8 sq m.

Front Wall

Similar to the rear wall, there are differences which are as follows:

• Ground Floor: 4 front doors assumed at 0.8 m width. These also have higher walls of 1.5m compared to 1 m
  All 7 bays have cladding not tiles or bare prior to 2017. The smaller bay is the front door has cladding below the wiindows.
• First Floor: 4 bays with cladding, and the smaller bay.
• Second Floor: 5 bays with cladding along the protected fire routes, and 7 front doors of which 2 are not in a counted wall.
• Third Floor: All bays are tiled.

The rebate for the second floor access has been ignored.

• Ground floor: All  bays are clad.
  3 bays 3.3 m wide 1 m deep. 4 bays with doors 2.5 m wide by 1.5 m deep. Total for 7 bays cladding 24.9 sq m
  The total including the smaller bay is thus 26.8 sq m.
• First Floor.
  4 bays cladding [3.3 wide by 1m deep], 3 bays tiles [3.3 wide by 1m deep], smaller bay clad - 1.8 m.
  The total area is 24.9 sq m, of which 15.0 sq m is cladding
• Second Floor:
  Cladding: 5 bays with doors 2.5 m wide by 1.5 m deep indicates 18.8 sq m.
  3 tiled bays including the smaller bay
  Total wall area of 27.2 sq m.
• Third Floor: No cladding. 7 bays at 3.3 m plus 1.8 m smaller bay gives

Northern End Wall

Taken from Google Maps Street View: the wall is brick, and four stories tall. There are four windows, and one door.

No cladding. Area assessed at width 10.3 m and height of 10.1 m viz 105 sq m less 4 windows and door indicates 94 sq m.

Southern End Wall

Taken from Google Maps Street View: the wall is brick, and four stories tall. There are three windows,

No cladding. Area assessed at width 10.3 m and height of 10.1 m viz 105 sq m less 3 windows. indicates 98.7 sq m.

Garages [*]

There are effectively 5 blocks, with each garage generally 2.5m wide by 2.5m high and 5m deep. Wall and roof areas are as follows:

• 1-9. Rear Wall: 56m2, End Walls: 25m2, Roof: 113m2.
• 10-20. Rear Wall: 68m2, End Walls: 25m2, Roof: 138m2.
• 21-25. Rear Wall: 31m2, End Walls: 25m2, Roof: 63m2
• 26-30. Rear Wall: 31m2, End Walls: 13m2, Roof: 63m2
• 30-31. Rear Wall: 10m2, Roof: 10m2
• 31-36. Rear Wall: 37m2, End Walls: 13m2, Roof: 76m2

Total all garages: Flammable Roof: 463m2, Walls: 344m2

Total for Block B [12 of 36 30 garages]: Flammable Roof: 154m2 185m2, Walls: 115m2 138m2

Assessment of Percentage Flammability for Block B

 
The percentage clad is thus assessed at about 25%. However, if the roofing repairs have been done using bitumen, then the percentage rises to nearly 40%. [error has no impact to nearest 5%].

CAVEAT: The calculations need to be carried out by an independent Chartered Engineer, Chartered Building Surveyor or Chartered Quantity Surveyor.

Note on calculation sensitivity for whole estate. Block B is the smallest block. Hence the effect of the end walls on the flammable assessment is greatest in reducing the flammable ratio. Thus the assessment for the whole estate is to increase the flammable percentage - but not by much.

Description of risk

Taken from FRC External Wall Survey Report, page 70:

Comment classed as "Negative"

External Wall Type 2 (Sandwich Panels) Ground floor (<2m)

At this height, the likelihood of a fire originating externally (e.g. involving a parked vehicle or waste skip started either accidentally or deliberately) igniting the cladding is highly likely.