Rooflight Design and Ventilation

 

This page refers to rooflights which, as a secondary consideration, may be required to provide ventilation, perhaps to meet the requirements of Building Regulations Part F. Where ventilation is a primary consideration for energy efficient environmental management or smoke control during fires.

Rooflights introduce light to the interior of a building and can be used to provide ventilation, extraction of stale and the introduction of fresh air. Xtralite provide a range of differing systems with varying performance levels, see table below.

 

Mechanical Rooflight Ventilation


There are occasions when a more positive form of ventilation, with a known, and quantifiable air exchange performance may be required, under such circumstances a power fan can be fitted to the rooflight unit. There are two ways of achieving this:

  • With a power fan unit built into the polycarbonate glazing skins. This option allows either a 150 mm or 225 mm power fan unit to be specified.
  • With a smaller fan mounted into the side wall of the kerb. In such an arrangement the kerb will necessarily be higher, to provide the required 150 mm clear upstand height to the base of the fan unit.
  • The choice of which fan option to use, is entirely at the discretion of the specifier. Such a decision could be based upon performance.

A requirement for an air movement above 230 m³/h will, by inspection of the table below, dictate a power fan set into the dome. Alternatively, if noise is a consideration, the 225 mm power fan provides the quietest performance.

 

Rooflight Rotary Ventilation Performance Chart

Rooflight Side Length

Max Number of Vents / Side

Total Area Per Rooflight (2 Sides Vented) cm²
450
1
70
500
1
70
600
1
70
750
1
70
800
1
70
900
1
70
1000
2
140
1100
2
140
1200
2
140
1250
2
140
1350
2
140
1500
3
210
1800
3
210
200
4
280
2400
4
280
Total area for each rotary vent = 35 cm². Should a greater degree of ventilation be required, vents can be added to the other 2 sides. Obviously, this will double the quoted ventilation areas/rooflight, and will affect the price. Please specify number of vents required.

 

Rooflight Ventilation Performance Chart

Rooflight Size (mm)

Permanent (cm²)

Hit and Miss (cm²)

Controlled Louvre (cm²)

Hinged (m²)
600 x 600
80
46
240
0.36
750 x 750
80
46
240
0.45
900 x 900
160
92
480
0.54
900 x 600
160
92
480
0.45
1050 x 1050
160
92
480
0.63
1200 x 1200
160
92
480
0.72
1350 x 1350
160
92
480
0.81
1500 x 1500
160
92
480
0.90
1800 x 1800
240
138
720
1.08
1200 x 600
160
92
480
0.54
1200 x 900
160
92
480
0.63
1350 x 900
160
92
480
0.68
1500 x 900
160
92
480
0.72
1500 x 1200
160
92
480
0.81
1800 x 900
320
184
960
0.81
1800 x 1200
320
184
960
0.90
2000 x 1000
320
184
960
0.90
2400 x 1200
320
184
960
1.08

 

Rooflight Mechanical Ventilation Performance Chart

Fan Options

Air Displacement Litres/sec

Volume m3/h

Sound db(A)
150 mm power fan in dome
105
380
49.6
225 mm power fan in dome
194
700
43.6
150 mm side-mounted in kerb
69
248
40.0