How to install your Roofing Sheets

This installation guide provides general advice on how to install a single skin sheeted metal roof. The advice within this installation guide is of a limited nature and should only be used as a guide its not be relied upon as an exact instruction on how a roof should be safely installed which will vary with circumstances. 

We have a skilled team of Customer Service advisors who will be happy to assist you with any installation queries you have, please feel free to call them on 01837 659 901. Cladco Profiles accepts no liability for any loss or injury caused by any reliance placed on this guide. 

Please click here to download our PDF Version of this guide. 

Cutting Sheets On-Site

If your purchased sheets require cutting we recommend metal sheets are cut whilst on the ground and resting face down on padded supports. Metal Sheets should be cut using appropriate tools that produce minimal heat as this can cause damage to a sheet's coating. 

For longer straight cuts we recommend a circular saw with a fine-tooth metal cutting blade that produces a cold cut. For smaller cut-outs, openings and non straight cuts, a jigsaw or a reciprocating saw is recommended.

For other requirements an angle grinder with a small tooth blade or disc is usually suggested however reciprocating nibblers which are widely used in the roofing trade also produce an excellent cut. Swarf should be removed with a brush to prevent eventual rust marking and scratches.

Lay Sheets

To lay your metal sheets in runs start at the eaves and in the corner away from the direction of the prevailing wind. This will help prevent side laps facing into the wind and water ingress. 

If the first sheet is not laid perpendicular to the eaves and ridge, adjustments will need to be made when laying other sheets and a saw tooth effect will be seen. This may be unavoidable if the building you are working on is not square.

Handy Advice: When laying your first few sheets it may be helpful not to fully fix them down, this is so you can be sure the sheets are perfectly aligned. This can help mitigate the impact of false starts! When you are happy with the sheets position secure them down with the remaining fixings and continue.

Sheets should be overlapped by the next sheet in the run by at least one profile or corrugation ['side laps']. Adjacent runs of sheets should overlap each other by at least 250mm ['end laps'].

The first row of sheets should extend over the bottom purlin and eaves, this allows any rainwater to drain into a gutter or beyond the wall.

Side and End Laps

Side Laps 

It's good practice to use mastic lapping tape and stitching screws to ensure a robust weather resistant joint on side laps.

Lapping tape with a section of 9mm x 1.5mm mastic should be run along the crest of the profile that is to be lapped. Lapping tape is widely considered more effective than silicone.

Sheet to sheet stitching screws should then be used at 600mm intervals down the lap to consolidate the bond created by the lapping tape.

End Laps

A minimum sheet over sheet overlap of 250mm should be allowed for where sheets lap, this lap must be supported underneath by a purlin.

As with side laps, it's good practice to use lapping tape to help create a robust weather resistant joint and a strip of tape should be placed across the full width of the lap approximately 25mm from the end of the top end of the overlapped or bottom sheet.

Handy Advice:  - It is extremely difficult to separate sheets once they are joined by lapping tape, make sure your sheet position is perfect before using the laping tape.

Gaps at Eaves and Ridge in order for a roof to be properly weatherproofed, the gaps that occur under the sheeting at the eaves and between the sheeting and the ridge flashing need to be sealed.

Always Work Safely 

Roofing work can be hazardous. Caution should always be exercised and appropriate safety precautions taken including the wearing of suitable protective gloves, clothing, footwear and hard hat. Roofing Sheets can be sharp and easily cut skin.

Where possible, crawling boards should be used to walk on sheeting. If this isn’t possible, walking over or close to the purlin supports keeping your weight evenly distributed is another option when used with caution. Clean soft-soled footwear should be worn to ensure maximum grip and to reduce damage to sheets.

UK law requires employers and self-employed contractors to formally assess the risks associated with each roofing job. Before starting any work you are required to plan and organise the work so that it is carried out in a safe appropriate manner. Further information on this and other applicable legislative requirements can be found by visiting the Health and Safety Executive’s website www.hse.gov.uk

Handling Sheets

Care should be taken when handling sheets to prevent damage and ideally mechanical handling equipment (e.g. a forklift truck) should be used where appropriate. Dragging the sheet’s edge across any other sheet is likely to cause scratching of the sheet, Cladco advise to take care to lift and not drag sheets. Any packaging should be removed before lifting the sheets onto a roof.

When the sheets are on the roof, before fixing them, sheets should be kept secured to the roof, close to the rafter line and, in so far as is possible, spread out so their weight is evenly distributed across the purlins. Any debris arising should be removed and off-cuts of insulation, surplus fasteners and similar not left on the sheeting.

Create a Purlin Framework

Purlins can be used create a supporting framework and to transfer the loads imposed by the metal sheeting onto the primary building structure. Purlins can be fixed to rafters using boltable cleats.

As a rough guide purlins should be at least 50mm wide to ensure sheets can be easily fixed, and, in the case of 0.7mm thickness sheeting, be spaced no further than 1.2m apart. 1m apart in the case of 0.5mm thickness sheeting. Exact requirements

will vary.

All purlin joins or laps should be supported by a rafter.

Once purlins have been fitted and a supporting framework created an inspection should be carried out before any further work is carried out. A full apropriate safety check should be carried out, It should include but not limited to:

  •  the purlin framework is correctly aligned and levelled;
  •  purlins are correctly spaced and within specified tolerances;
  •  there are no protrusions e.g. bolt heads on the face of the framework.

Z Section Purlins 

Cladco produce metal Z section purlins in Z39 structural grade galvanised steel. These are available with a 140mm, 175mm or 200mm depth Z section and in 1.6mm, 1.8mm and 2mm thickness steel.

Z section purlins can be made to any length and can be joined by overlapping (one Z section can be turned around and slotted inside another) or by using short sleeves where two longer sections meet.

To order metal Z purlins please call our sale office on 01837 659 901.

Fix Sheets 

The fixings used to attach sheets to purlins must be durable and able to withstand considerable wind pressures & heavy rainfall. The exact type required will depend on the sheet and purlin type (timber/light steel/heavy steel) however we usually recommend self-drilling TEK type screws with a 5/16th hex head for standard purlin thickness.

Self-drilling TEK screws have a drill point for drilling through the sheet and purlin on a standard purlin thickness. Under the head is a 19mm stainless steel washer with bonded neoprene pad that compresses to create a seal with the roof sheet. The screws can be fitted through the trough or pan sections of a sheet’s profile, or if fixing corrugated sheets, through the crest of the sheet’s profile using a longer screw and a soft BAZ washer. It can be helpful to use a centre punch to indent the sheet at the point you want the screw to go through to keep the screw on course when screwing it in.

Handy Advice:  - Make sure fixings are not excessively tightened as this can burn off the soft neoprene pad under the washer.

Under normal conditions sheets should typically be fixed to supporting purlins at every second trough or third corrugation with fixings in every trough at the bottom / eaves to help protect against wind uplift if the roof is in an exposed position. However please note this will vary dependant on your sheet type and circumstance. If you are unsure please contact our sales team.

Handy Advice: -  A stretched piece of string along the purlin line can make it easier to keep the fixings in line when the sheet is laid on the purlins.

Ridge Caps

Lay ridge caps from the opposite end of the roof to the direction of prevailing winds. Each cap should be overlapped by the next cap in the run by a minimum of 150mm.

We recommend ridge caps are fixed using self-drilling TEK type stitching screws to the high point of each profile they cover and through the appropriate ridge filler if one is being used. This helps ensure a robust weather resistant joint as well

as keeping out birds and vermin.

Handy Advice: - When constructing your purlin support structure you may need to consider additional purlins to support your ridge caps and other flashings.

Protrusions 

Protrusions such as pipes and ducts should be adequately flashed where they pass through the sheeting surface. Where ribs have to be cut away to permit penetration, additional framing should be installed as required to support the sheeting.

Depending on the position of the penetration through the roof, special attention should be given to back flashing the sheeting to the ridge or point of water entry up the roof from the protrusion.

In all cases, all cutting and flashings should be so arranged that adequate provision is made for the drainage of all troughs and corrugations.

Please note:

This installation guide should be used a guide only. This information provides general advice on how to install a single skin sheeted metal roof. The advice within this installation guide is of a limited nature and should only be used as a guide its not be relied upon as an exact instruction on how a roof should be safely installed which will vary with circumstances. 

We have a skilled team of Customer Service advisors who will be happy to assist you with any installation queries you have, please feel free to call them on 01837 659 901. Cladco Profiles accepts no liability for any loss or injury caused by any reliance placed on this guide.