Zinc cappings of NedZink NTZ® are successfully applied as a covering for roof edges of flat roofs which are covered with bituminous, plastic or rubber material, whether or not with gravel or terrace tiles as a load.
These roofing materials can cause problems on the roof edge. This is the result of a number of factors:
- effect of sunlight (heat and UV-rays)
- differences in expansion between trim, substructure and covering
- bulging of bitumen due to a low softening point
- loosing of the glued edge of the roof trim
- mechanical damage of the roof edge
These harmful effects can be avoided by fully covering the edge of the roof with a zinc-titanium capping. If NedZink NTZ® is used and applied with the necessary craftsmanship, the expected
service life is 50 years or longer.
Construction for a new building
The zinc capping is designed according to the example figs. 1,2,3 or 4.
A number of important construction details:
- the drip side can be formed with a bead or so-called “flat drip” of at least 35 mm high, see figs. 1 and 2 respectively.
- the upper surface of the zinc capping must slope down in the direction of the roof or must be provided with a rain ridge see figs. 2 and 3.
- the zinc capping is attached by means of zinc clips of a width of at least 80/100 mm that are fastened to the edge of the roof by a least 2 screws or zinc nails. The distance between the clips amounts to a maximum of 1 metre.
A clip distance of 500 mm is advised for zinc cappings with a developed width of 450/500 mm and more. A zinc capping should be regarded in that case as roof bay.
- if an underplank (unplanned/not grooved) is used, then the clip can also be attached with a nail at the side of the plank. This reduces the risk of the zinc capping being dislodged.
- if zinc cappings are used that have been set at 3 metres length, then folded clips are used on the side of the roof between the soldered joints, see figs. 2 and 5.
The material for the clips must be at least 0.80 mm thick, preferably 1.0 mm
- the use of stainless steel or galvanised steel clips is recommended for the zinc cappings with a long sloping part of > 100/150 mm. The same goes for zinc cappings with a developed width as from 450/500 mm, by which the zinc capping can be regarded more as a roof bay. The number of clips must be adapted to this.
- above 20 m height increase the number of clips.
- in order to prevent damage to the roof covering the zinc capping is given a folded edge on the roof side and must end at approximately 20 mm from the rim.
- the zinc cappings must be soldered to one another up to a maximum of 12 metres length with an overlap of at least 15 mm. The soldered joint must have flowed through at least 10 mm. After every 12 metres an expansion sleeve must be fitted at one’s option, see fig. 6
If a rubber expansion is used then fit an expansion device every 9 metres.
Place the zinc cappings 3 cm on top of one another. Solder the zinc edges of the rubber expansion at the two zinc cappings. Cover the rubber with a piece of zinc, which is only soldered at one side.
- the profile of the zinc capping must be made in such way that it fits “falling spaciously”, i.e. with at least 5 mm space on all sides, over the base.
- the underlying roof covering must be glued over the entire width of the roof edge.
- in the case of roofs with gravel load, the sloping side of the zinc must be covered for a few centimetres by the gravel, see fig.1.
Installation for a new building.
For lengths of 1 metre:
Choose, if possible, the installation direction from left to right, to start at a mitre corner, and the zinc capping is slipped over the first clip approximately 300 mm from the corner. At each joint the clip is slid halfway under the already laid zinc capping and secured. The the nex zinc capping is slid over the preceding one with an overlap of 15 mm. The installation is simpler when the folded section of drip side and roof side of each zinc capping are cut splayed.
Continue in this way until the entire roof edge has been covered, after which the joints (excluding the expansion joints) can be soldered. For soldering see NedZink advice Soldering.
For lengths of 3 metres:
The first clip is attached beforehand for each length and at the same time the two following clips are respectively 1 and 2 metres from the first, see fig. 5. The clips must have excess length at the roof side in order to be able to be bent over later. For the rest, the same procedure as above, with the advantage that only one-third of the number of joints need to be soldered.
Construction in the case of renovation.
There are in principle 2 methods for this:
- To repair the existing roof edge in such way that the same starting condition is achieved as would be for a new building. To this end, any existing roof trim must be removed and the roof covering over the roof edge repaired up to approximately 20 cm on the roof surface. The one can work in accordance with the construction and installation for a new building.
- If a still undamaged and well attached aluminium roof trim is on hand then this roof trim can be used as clip for the outer side of a zinc-titanium capping. The “flat drip” construction can only be used in this case where the folded-section of the drip hooks behind the edge of the roof trim. The other side of the zinc capping is attached with normal clips of zinc-titanium, stainless steel or galvanized steel, see fig. 4. If this method is chosen it is advisable to first make a small test piece of the zinc capping and to check the fitting at various places on the roof edge before starting with the production of the zinc cappings.
Installation with existing roof trim.
- repair of the weathered and/or cracked roof covering of the top of the sloping upstand up to approximately 20 cm of the roof surface.
- check whether the aluminium roof trim is still well secured to the edge of the roof, repair if necessary.
- saw off a piece of 1 cm of the roof trim at least every 4 metres, so that the roof trim can freely expand.
- when installing lengths of 1 metres: attach a clip at each soldered joint in accordance with fig. 4.
- when installing lengths of 3 metres: attach a clip at each soldered joint and at approximately 1 meter distance from one another 2 clips in-between in accordance with fig. 5.
The clips must allow for a sliding movement of thezinc capping.
- for long zinc cappings an expansion sleeve must be fitted every 12 meters, see fig. 6, or if rubber expansion is used every 9 metres.
The use of the aluminium roof trim as a continuous clip for the zinc capping can be recommended without any danger of the zinc becoming corroded as in the range of stress of metals aluminium has a lower potential than zinc. The zinc capping can continue at the place of the glued outlet grating, possibly with an opening to enable a free thermal movement.
A mitre corner, installed with the required space of 5 mm can be regarded for the working of the zinc capping as an expansion sleeve. Alternatively an expansion device can be fitted approximately 1 metre from the corner on both sides. The free expansion of the zinc capping must always be guaranteed.
Wall capping (parapets weathering).
The principle of the zinc capping for the flat roof edges can be unreservedly applied to a wall capping.
It is advisable to provide the top of the wall with wooden parts on which the zinc capping is attached.