Main features

Zinc is an excellent roofing and cladding material which will give long and almost maintenance-free service if installed properly.  Proper installation means not only the correct fixing of the zinc itself, but also the correct design and installation of the supporting structure.

The building envelope design

The building envelope is built up in a series of different layers on site.  Depending on the design of the roof, it can include, from outside to inside:

  • elZinc® cladding
  • Underlay
  • Substrate
  • Air layer (ventilated roofs and walls only)
  • Insulation
  • Battens or metal rails and wall brackets
  • Vapour control layer / vapour barrier
  • Principal load bearing structure

Layers in a traditional ventilated build up

vented roof with battens 3

  1. elZinc® cladding
  2. Underlay substrate.
  3. Air layer.
  4. Battens/rails.
  5. Breather.
  6. Insulation and structure.
  7. Vapour control layer
  8. Ceiling

Layers in a typical unventilated build up

warm roof 3

  1. elZinc® cladding
  2. Underlay substrate.
  3. Insulation.
  4. Vapour barrier.
  5. Deck.
  6. Structure and void for services.
  7. Ceiling.

Underlays generally

An underlay is installed directly under the zinc.  The underlay should be:

  • Stable between -20ºC and +80ºC
  • Not stick to the zinc
  • Stable for up to 3 months outside in the sun.
  • Conform to EN 13859:1 and 2

Its functions can include:

  • Acting as a separating layer
  • Acting as a slip layer
  • Substrate protection during construction
  • Draining condensate from the underside of the zinc

Peel and stick

Peel and stick self-adhering waterproofing membranes with rubberized asphalt adhesive are commonly used on warm roof applications over metal, plywood, OSB, etc. substrates. The underlayment must self-seal around punctures such as nails, screws and staples and have a non-slip surface. Asphalt membranes are ideal for warm roof underlayment and are water proof, protecting the roof from the weather until the zinc is installed.  This can be especially important in countries with cold winters (such as Canada) where zinc work stops during the winter months, and in general in markets where commonly some time elapses between substrate completion and zinc work commencement.

Structural underlays

Structural underlays are recommended by elZinc® on all roof types as they have proved beneficial to the longevity of zinc roofs.  They also:

  • Reduce friction between the zinc and the membrane
  • Reduce rain drumming noise by up to 8dB.
  • Even out slight unevenness in the substrate

Higher standing seam clips must be used to compensate for the height of the mat.  It is also important that operatives use a piece of plywood or similarly stiff board when kneeling on the zinc to spread the load and prevent the zinc from denting.  The same applies to any other point loads.

Breather membranes

Breather membranes that are used on elZinc® roofs and façades should have a maximum Sd value of 0.04m.  Sd is the symbol for the Equivalent Air Layer Thickness, in m.  The smaller the Equivalent Thickness, the less the resistance to moisture vapour transmission.  See table Sd to MNS/g to Perms.

Clips

Higher standing seam clips must be used to compensate for the height of the mat.  It is also important that operatives use a piece of plywood or similarly stiff board when kneeling on the zinc to spread the load and prevent the zinc from denting.  The same applies to any other point loads.

a.

Substrates and supporting material generally

The substrate provides the structural support for the zinc, and generally the standing seam or flat lock clips are fixed to it.  It should provide a minimum clip pull-out value of 560N.  Surfaces that are single plane in geometry are simple to construct, curved surfaces can require a multi-layer approach of curvable thinner sheathing.  Double curved geometry is best achieved by layers of softwood boarding.

2

Open gap boarding

p 31 a PAQUETES CONSTRUCTIVOS izq

This is formed from solid softwood boards of zinc compatible species fixed to wooden supports and should:

  • Be fixed parallel to eaves, with a 2-3mm gap between boards, using countersunk screws or nails driven to just below the surface.
  • Use rough sawn boards 80 to 140mm wide, conforming to EN12775-2, with a moisture content of 18% or less.
  • Be treated with zinc-compatible wood preservatives.
  • Should have a max. difference of 2mm (+/-1mm) in height, both between boards and over the width of each board.

Board thickness depends on rafter spacing, but is generally around 22-24mm.

Sheathing

p 31 b PAQUETES CONSTRUCTIVOS der

Plywood, OSB or particle board sheathing is fixed using countersunk screws or nails to wooden or metal supports, driven just below the surface.  The boards should fixed as shown in the drawing and:

  • Have a 2-3mm gap between them.
  • Be protected from the rain before the elzinc® trays are installed.
  • Be supported at ≈600mm centres.

Sheathing board thickness is generally around 18 to 24mm, and the boards themselves are 1200 – 1250mm wide by 2400 – 2500mm long.

Plywood should be specified as structural plywood according to EN 636:2003, class 2.  This is suitable for external protected applications.

Orientated strand board (OSB) should be specified as complying with EN 300:2006 OSB/3 load bearing boards for use in humid conditions

Particle boards should be specified as complying to EN 312:2010 class P5: load-bearing boards for use in humid conditions.

Insulating boards

Factory bonded insulation boards made of plywood and rigid insulation are used on warm roof designs.  They avoid cold bridges and are quick to install, and provide a plywood or OSB deck for the elZinc® trays to be fitted to.

Rigid insulation

Rigid insulation is used on warm roofs and obviates the need for a timber substrate.  The elZinc® trays are fixed through it to a deck below using a special clip.  The insulation should be able to:

  • Remain stable at temperatures of up to 100ºC
  • Resist the compressive loads of foot traffic and kneeling operatives such that the elZinc® trays are not deformed.

Sandwich panels

Metal skinned rigid insulation panels can be used as a substrate in warm roof construction.  Their outer skin should be thick enough to ensure minimum clip pull-out values of 560N.  They have good spanning properties making them useful on steel structures, and eliminate cold bridges. The inner skin acts as a vapour barrier, and so the joints between the panels must be effectively sealed.

 

SIPs (Structural insulating panels)

Normally used on warm roofs over laminated wooden structures which take advantage of their spanning capabilities.  The exterior wooden skin should be made of suitable grades of plywood, OSB or particle board and a minimum of 18mm thick.

Consult SIP’s manufactures for advice regarding vapour control.

 

Profiled metal decking

Installed to support traditional façades where its non-combustibility allows it to be used on taller buildings where fire regulations prohibit the use of wooden boards or sheathing.  It is always installed ‘façade side outwards’ to give the zinc cladding the most support, and perpendicular to the longitudinal seams of the cladding.  Its fixing must allow for thermal expansion and contraction.  It should be thick enough to ensure a minimum clip pull-out value of 560N.

Wooden battens and blocks for zincwork

Wooden battens, blocks etc. should be treated with zinc-compatible preservatives, and have a moisture content less than 22% at the moment of zinc installation.

Substrate supporting materials

Metal profiles

Made of either extruded aluminium profiles or galvanised sheet, they are recommended to have a fixing face of 60mm.  When supporting sheathing, they are set at centres of around 600 to 625mm, tying in with commercially available sheathing board widths and lengths.

Wooden lathes

Used more commonly to support soft wood open gap boarding, they should be regularised and appropriately treated with preservatives.

Thermal design

Traditional façades are generally ventilated, with an inlet at the foot of the cladding and an outlet at the head.  This is because the vertical nature of vented façades means the air layer is working at its best and dissipates diffused moisture vapour effectively.  This keeps the building envelope dry in the winter months and helps to cool the building in the summer.

Ventilated façades

The ventilated façade incorporates an air gap behind the substrate which is connected to the outside air via an inlet at the foot and an outlet at the head of the cladding, and also at window sills and lintels.  Perforated zinc is used to provide an insect mesh along these openings.  Structures that are not airtight may need an airtight membrane installed.

p 37 a FACHADAS VENTILADAS DISEÑO

Ventilated façade designs

Open gap boarding

Sheathed vented façade

Underlay

Underlays are optional with open gap boarding, (for weather protection before zinc installation for example).  With other substrates a breather membrane is used as a separation layer.

Substrate

Fixed perpendicular to the direction of the seams with a 2-3mm gap between boards

Substrate options (in decreasing quality).

  • Open gap soft wood boarding
  • EN 636 class 2 plywood
  • EN300 class 3 OSB
  • EN312 class P5 particle board

Supporting battens or rails

Plumbed and even to create a flat plane for the fixing of the substrate.  They are fixed back to the main structure by means of adjustable wall brackets.

Air gap

20mm minimum, some countries require more, usually up to 40mm (eg. residential projects in UK generally require 38mm).

  1. elZinc® traditional cladding (angle standing seam shown)
  2. Seam clip
  3. Breather membrane underlay
  4. Substrate
  5. Wooden battens @ ≈600mm centres
  6. Insulation between battens
  7. Wall bracket
  8. Solid wall

In many countries, façades over a certain height are required to be constructed of non-combustible materials.  In these cases trapezoidal metal decking is commonly used instead of wooden substrates.

Profiled metal decking on blockwork

Underlay

A breather membrane is used as a separation layer.

Metal decking

It is fixed perpendicular to the direction of the seams.  Vertically fixed decking ventilates through its own section.

Air gap

20mm minimum, some countries require more, usually up to 40mm (eg. residential projects in UK require 38mm).

Wall brackets

Helping hand’ type wall brackets are adjustable and allow for thermal movement of the metal profiles.  A range of bracket depths allows for varying insulation thicknesses and structure unevenness.  A thermal break can be inserted between the bracket and the wall if required.

  1. elZinc® traditional cladding (angle standing seam shown)
  2. Seam clip
  3. Breather membrane underlay
  4. Profiled metal decking
  5. Metal profiles
  6. Insulation
  7. Structural liner tray
  8. Adjustable wall bracket
  9. Structure

Structural liner trays

These products have good spanning characteristics and can be micro-perforated for acoustic purposes.

Underlay

A breather membrane is used as a separation layer.

Metal decking

It is fixed perpendicular to the direction of the seams.  Vertically fixed decking ventilates through its own section.

Air gap

20mm minimum, some countries require more, usually up to 40mm.

Wall brackets

Helping hand’ type wall brackets are adjustable and allow for thermal movement of the metal profiles.  A range of bracket depths allows for varying insulation thicknesses and structure unevenness.  A thermal break can be inserted between the bracket and the wall if required.

  1. elZinc® traditional cladding (flat lock panels shown)
  2. Seam clip
  3. Breather membrane underlay
  4. Profiled metal decking
  5. Metal profiles
  6. Insulation
  7. Structural liner tray
  8. Structure

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