FIXINGS

Primary fixings must securely retain rooflights to structural members, permit thermal movements and effect a weather tight seal at the fixing hole under extremes of weather conditions for the life of the roof. Primary fixings for rooflights to suit fibre cement and sinusoidal metal profiles must be through profile crowns and incorporate a sealing washer with minimum diameter of 28mm.

For rooflights to suit trapezoidal metal profiles, primary fixings must be through the valley of each corrugation, and incorporate a composite sealing washer with a minimum diameter of 29mm. Where valley geometry is restrictive, smaller washers down to a minimum diameter of 20mm can be used. If the profile has a wide valley, additional fixings will be required. Primary fixings must always pass through high density profiled foam filler blocks placed under the rooflight at each purlin position.

The fixing shank must always be at right angles to the rooflight sheet surface and the sealing washer must contact the surface evenly throughout. It is vital that the fixing is tightened only sufficiently to properly compress the sealing washer.

Fit sealing caps to prevent water ingress and resulting corrosion of the fixing. A small bead of clear silicone sealant placed on the shank of the fixing before insertion will assist in sealing the screw shank and the washer in the watercourse. Crown fixings with sealing washers or saddle washers can also be considered for trapezoidal rooflights profiles where the roof is not subject to high wind loads. However, there must be very firm support under the crowns of the corrugations to weather seal the washer, and to prevent damage to the rooflight profile when the fixing is tightened. Over tightening can also force the valley of the corrugation upwards, which can lead to difficulties in sealing the end cap.

A primary fixing must never be closer than 50mm to the end of the rooflight. Secondary fixings in side laps should be at centres not exceeding 300mm on roof pitches below 10^o and not exceeding 450mm maximum centres on roof pitches above 10^o.

The fixing should have a washer with a minimum diameter of 12mm. See diagram SF1 – 4 below.

Where sinusoidal profiles rooflights overlap the main roofing material, in laps between adjacent rooflights and where rooflights underlap the main roofing material, it is necessary to use self sealing fixings with synthetic rubber shank and sealing cap. See diagrams SF5 to 6 below.

RIVETS SHOULD NEVER BE USED WITH MARVEC

WEATHERTIGHTNESS

Correct profile choice and sufficient care in application of the fixings and sealant are essential to achieve a weather tight roof cover. The lower the roofs pitch, the greater must be the attention paid to design and workmanship. Rooflights should be over lapped away from the prevailing wind direction, particularly where the roof pitch is less than 15^o.

Rooflights to suit many metal roof systems can overlap the metal on both sides. End laps should be a minimum of 150mm.

At least one strip of sealant should be applied to all laps, down slope of the fixings on end laps, and on either side of the primary fixings on exposed and low pitched roofs. The sealant should be fitted close to the fixing to obtain compression.

Additional sealant can be applied, see diagrams EL1 to 3 below, where required by roof pitch and degree of exposure.

Ensure the sealant is applied continuously and evenly along the sheet that is on the underside of the lap.