3.0 Substrate & Installation Overview

Information to help the design and specification of the sub-structure immediately below a Gerard pressed steel roof; rafters, battens, underlays and fixings are covered in detail.

This section and it’s numbered points (3.1; 3.2; etc.) correspond to the equivalent parts of the Gerard Roofs Specification Manual.

3.1 Preparation of structure

3.1.1 Rafters and valley boards

Rafters and valley boards are to be correctly installed by the builder before roofing can start.

Refer to Gerard Roofs Technical Note - Builder Check List.

Where an exact number of complete panel courses is not possible, the top row of panels should be trimmed to fit and then bent up underneath the ridge flashing. 

3.2 Battens

Select batten size to suit rafter or truss spacing. Battens are to be treated to H1.2 and graded on site.

Truss spacing (mm)Batten size (mm)Situation
900 40 x 50 Standard
1200 50 x 50 Occasional
1500 50 x 65 on edge Unusual
1800 50 x 75 on edge Unusual
Table 02 Batten Spacing
3.2.1 Batten setout

Stratos, Classic, Heritage, Milano, Aspen, and Alpine profiles

A row of battens fixed directly behind the fascia with the second batten 330mm up the truss. Subsequent battens are spaced at 370mm (or as specified for profile and coating finish). The final top row of tiles is 365mm or less, depending on whether the top row needs cutting due to rafter length.

Eaves panels at gutter fascia

Panels should extend into the gutter by 40mm. This may vary slightly depending on the rafter length and roof pitch.

Roof ProfileBatten spacing
Textured Smooth
Stratos 370mm 371mm
Aspen 369mm
Alpine 368mm
Heritage 369mm 370mm
Milano 368mm
Classic 369mm 370mm
Table 03 Batten Set-out

*Centre batten 185 mm, second batten from eave not installed
^Centre batten 160 mm, second batten from eave not installed

3.2.2 Tile batten/rafter fastening

Gerard Roofs require that all 40 x 50 mm battens fastened to rafters at 900 mm centres are to be fastened with 2 x 90 mm gun nails in all wind zones up to and including the very high wind zone.

In extra high wind zones a screw fastener must be used for all batten rafter junctions.

This meets or exceeds the requirements of NZS3604:2011

Wind zone900 rafter
50x40 mm
1200 rafter
50x50 mm
Low 32m/s S S
Medium 37m/s S S
High 44m/s S T
Very high 50m/s S T
Extra high 55m/s T T
SED +55m/s Contact GR Contact GR
Table 04 Fasteners for Panel Battens - Wind Zones – NZS3604.

S = 2 x 90 mm x 3.15 mm nails (0.8kN)

T = 80 mm x 10g screw (2.4kN)

*In SED Specific design situations refer to Gerard Roofs Technical Notes on installation in SED wind areas.

3.3 Roofing underlay

Must comply with standard NZS 2295 – Pliable and Permeable Building Underlays. Roofing underlay is installed under the battens but over the bottom batten.

Roofing underlay shall be installed horizontally with a minimum overlap of 75 mm.

All vertical laps to be taken past rafters and lap by a minimum of 150 mm.

The roofing underlay is self-supporting up to 1200 mm and does not need mesh.

3.4 Valleys

Valley trays should be made from 0.55 mm AZ150 coated steel. Typically the steel will be pre-painted. Install valleys in a weatherproof workmanlike manner. Do not fix through valleys. Where more than one valley length is used in one run, have an overlap of at least 150mm. Tag valleys at the top edge of the valley join to eliminate valley creep.

3.5 Solar brackets

Gerard Roofs have proprietary solar brackets which can be installed at the time of roofing or later. These brackets do not require holes to be cut into the surface of the panels offering complete weather security.

Refer to Gerard Roofs for more information.

3.6 Tile installation

Care must be taken when handling, cutting, bending and installing to avoid damage to the surface. In particular, the paint finish must be kept clean.

Use rubber soled work shoes during installation and protective/synthetic padding on bending equipment.

Where work is still to be carried out on upper storey dormer windows or walls, panels can be left off to avoid damage or fall out from paint or plaster coatings. Alternatively, a plank embedded into 3 sand bags along its length can be used on top of the panel, with the sand bags placed over the support batten near the nose of the panel.

Where work is progressing above installed panels, dust sheets must be used held down with sand bags.

Heritage, Classic and Milano

Heritage, Classic and Milano can be installed to a minimum of 12° and may be laid left to right or right to left. All laps to be the same way on each plane.


Stratos can be installed to a minimum of 15° and may be laid left to right or right to left. The laps must be laid facing away from prevailing winds or line of vision. All laps should be the same way on each plane. Courses must be staggered in a random pattern to avoid patterning as you progress up a hip, or gable.


Alpine can be installed to a minimum of 15°, these profiles may only be laid in a single direction, as follows:

  • Alpine - left to right only

Courses of all three should be laid in a random pattern, with staggered start points.


At eaves, the front rows of panels are fixed to the battens alongside the fascia by driving nails through the top face into the eave batten. These nails are positioned at points of low water run off. Eaves nails for satin finish have a synthetic washer installed under the nail head, eaves nails on textured finishes are sealed with the touch up kit basecoat and chip.

Nailing panels

Successive rows of panels are fixed by driving 50mm nails through the centre of the panel nose into the face of the battens. These nails are spaced as shown/described in the product "fact sheets" located on the page of each Gerard profile.

Only Gerard Roofs approved nails should be used in the installation of panels and accessories.


Panels are cut at the valley angle at appropriate points and bent down into the valley, but not touching the valley tray. At the ridge, panels are cut and bent up under ridge accessories.

Ridge, Hip, Gable and Wall flashings

Only factory produced flashings and trim as supplied by Gerard Roofs must be installed. Panels are turned up by a minimum of 40 mm and covered by Gerard Roofs accessories to the prescribed coverage. Special flashings can be formed and coated to order.

Wall roof lower junctions

Gerard roofs have proprietary PVC stop end flashings that direct roof/wall run off water into the rain water gutter system.

Membrane areas

If flat membrane areas such as Butynol overlap onto product surfaces, these can be painted with the touch up kit or base coated and granite textured.

Weather sealing

Proprietary or custom made rubber or metal flashings require neutral-cure silicone or MS sealants acceptable to Gerard Roofs to be used for weather-sealing services penetrating the roof. Sealant shall be applied between the flashing and panel surface and mechanical fasteners (rivets, Tek screws) installed to permanently fix the flashing in place.