Roof sheeting fixing

On this roof sheeting fixing page.
Fixings,Screws | Check for Square The First Few Sheets | Sheet Overlaps | Hip Roofs | Capillary Attraction. | Laying Short Sheets | Infill Strips. | Turn Ups and Turn Downs

I can't recall doing a job with short sheets, that do not span the full length of the roof surface.  We measure the roof from the ridge to the fascia, and say allow 30 or 50 shorter at the ridge and add say 80 for the overhang at the fascia.  We order this length and it comes exact, cut with square ends.  The length of roof sheet that can used is only governed by the transport available from the factory.

string line at eaves
Roof sheeting fixing - String line to set sheet overhang at the fascia.
To start off laying the sheets decide the amount of overhang that the iron will have at the fascia.  I use 80mm or so.  Maybe 65 if a small to medium gutter is being used.

Don't be tempted to let it overhang a lot, just because you have extra length on your sheets.  We have a maximum unsupported length of about 200 for standard "Custom Orb " and for the slightly thicker stuff it is only 250.  This means also that your bottom batten has to be in the right place also.

Use a bit of scrap and put a string line the length of the fascia you are working to.  In the photo above the roofers have used a bit of "Speed Brace" material, screwed to the end purlin.

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Fixings, Roof Screws, Wall Screws

Always use the correct fixings. I did a job for a neighbour a few months ago, he had his house almost sold, and right at the last minute the buyer's engineering inspection turned up the fact that the screws on his wall cladding were the wrong thickness. It was a large high set house, and apart from the fact that he had the worry of nearly loosing the sale, he had the extra expense.

In the photo, the thick 14 Gauge screws with timber threads and metal threads, were the replacements for the ones in the middle, that were only 12 Gauge with no seals. In a couple of later additions to the house, the fixers had blindly followed what the previous guys had used. Don't assume that old fixings etc. are still OK for your new job. The building codes are changing all the time. (By the way, I've got the odd few thousand of those old screws if anyone's interested :-)

tek screws for metal wall cladding
Roof sheeting fixing - tek screws for wall cladding
  • When I do a drawing for building approval, on a the page that details the roof cladding, I will include something like this: "Lysaghts Custom Orb sheeting fixed to DTCM M/101/1-4".
  • The DTCM refers to The Northern Territory Deemed To Comply Manual. It is a set of standard drawing many hundreds of pages long covering materials and components permitted for use in building work in the NT.
  • The M/101/1-4 relates to four pages of detailed specifications, put out by the manufacturers for the fixing of this one product, Custom Orb. It covers the max. sheeting spans, the design wind pressures etc. In these pages are given the types and sizes of fixings to be used in various conditions. In hardwood, in softwood, and in steel of various thicknesses.

This month I have had visitors to this website from over 60 different countries, so there is no point in me trying to guess your conditions. All I can say is check your building regulations, if any for the specifics of the fasteners for fixing roof sheeting in your area.

steel metal roof screws into timber and steel
Roof sheeting fixing - A few roof screws
  • Your supplier will have the relevant fixing roof sheeting details for your area. Ask for a photocopy if you have any doubt that the salesperson doesn't know.
  • A sheeting supplier will also carry the correct fixings etc. but most times a specialist outlet that only sell fixings will be cheaper.
  • The cost of the screws is a significant part of the cost of a roof, so it pays to shop around.
  • The coatings on the screws differ. For instance if you are close to the sea you should be spending more money on extra protection. Even on normal screw there are different qualities of screw coatings. The ones in the photos above have what appears to be a heavy gal coating that we use almost exclusively these days.
  • With the Colorbond coloured sheets the fixings are also coloured. If you are a few short towards the end of the job, don't be tempted to paint up your own with touch up paint. It fades differently to the main roofing, and they may just stick out like dogs balls after a couple of years.
  • Make sure you get the recommended seals. EPDM is what we have to use. Not neoprene. Some wall screws come with the seal on, and you can get the same screw without. Check first.
  • When screwing to metal purlins or battens, we use obviously the metal thread screws that pre-drill and fix in one hit. The average screws like the ones pictured above are good for all standard metal purlin thicknesses.
  • If you are fixing to, over say 3mm thickness of steel, you can buy special screws with a longer drill tip, but I don't usually bother. I just pre-drill the hole with a standard drill bit and then use the standard screws. Most times it is not worth buying a box of special screws for a small job.
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Check for Square

Before you start fixing roof sheeting, you should do a couple of checks.
  • Check the roof for square.
  • Check it for parallel. if it has a bit of a variation from the ridge to the eaves the ridge flashing will take care of that, but at least be aware of it.
  • If you are working on a gable roof and the gables seem out of parallel, be aware of it. In most cases you can stretch each of your sheets a little bit to make up a fair discrepancy.
  • If the worst comes to the worst you will have to get a tapered barge flashing made up, but try to avoid that.
  • Do a quick check of the batten set out just in case. If you did them yourself you should be OK but if someone else did it check that the battens that the flashings are fixed to are parallel.
Fix the sarking as required, I usually don't like getting to far in front. I fix enough for say half a days work of sheeting. I definitely don't fix so much that I it uncovered overnight. It can be blown off fairly easily. Back to top.

The First Few Sheets

In the sketch below I show part of a gable roof, and how I set out the first few sheets of roof sheeting to start me off. Quite often if we already have the scaffold on site, I set a plank up at the eaves, with the fascia about waist height. One guy works on that fixing the bottom row of screw, adjusting the sheets etc. I set a string line parallel to the fascia at about 80 away. I line the sheets up to the line, not quite touching.

fixing steel metal roof sheets
Roof sheeting fixing - Starting off, first few sheets, get these right and the rest is easy.

It is important to get the first sheet right, and a very small difference starting off can be a lot after say 20 sheets. To this end I use a few pairs of multi grips to hold a few sheets together temporarily until I have the bottom edges just right.

In a small roof like this with only four battens I would fix each sheet on the joint at position "1" first, then at position "2" then remove the multi grip and fix another one. Doing them all. Then screw all the others off afterwards.

If you try to screw off the full sheet before fixing the next one, you could spread out the sheet more than you should. Say the guy at the top was screwing down a bit more than the guy at the bottom, the sheet could be 10mm wider at the top. There'd be strife in no time.

Of course you may want to do that on purpose. Spread say the last 5 sheets say 5mm each to pull back a 25 mm difference in parallel.

I nearly always use a chalk line for marking the batten positions. I like the blue chalk. Don't ever use the red oxide based chalk, it is hell to shift. Whatever way you do it, chalk line or straightedge and marker, make sure it wipes off easy. Don't use a black pencil.

The old days of punching the sheets with a prick punch are well and truly gone. Don't do it. The roof screw will do it all. Just press the screw firmly down and press the trigger. Hold the gun and the screw square off the roof, not vertical. Don't try to start the screw while the driver is still spinning.

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Sheet Overlaps

Pick the correct end of the roof to start laying the roof sheeting, so that the prevailing weather is blowing over the lap join, not into it.

metal roof sheeting overlaps of sheets
Roof sheeting fixing - Sheet overlaps.
crest fixing steel metal roof sheets
Roof sheeting fixing - Sketch showing the overlap on corrugated sheets and the fixing patterns.

Roof sheeting fixing -   5 screws per sheet is on the top.   For less wind loadings 3 per sheet may be OK.
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Hip Roofs

With a hip roof, lay the longest sheets first to start off and then work your way into the hip roof corners.

laying metal roof sheets on a hip roof
Roof sheeting fixing - laying metal roof sheets on a hip roof

As the sheets abut the hip, they get shorter. The amount they get shorter is the diminish. See my roof angles page to calculate the diminish. When marking out the cut sheets don't forget to allow for the overlap.

In the above sketch I have represented the join on the sheets in red. You will see that if you order extra full length sheets, you will be able to use the offcuts on the opposite corner. If you are meticulous with the calculation, and then still allow a bit extra you may save a few dollars. I say may, cos I've tried it a few times and finished up short. It works, but don't depend on it if you are not certain. I finished up ordering a few shorter sheets for the hips. with plenty of allowance for waste.

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Capillary Attraction.

When two surfaces are close together, due to capillary action, water will tend to creep along the gap. Even going uphill.

metal roof sheets anti capillary features
Roof sheeting fixing - Anti-capillary features

To counteract this the manufacturers have built into the sheets features that stop this.

Look at your profile and make sure you are fixing them the right way. Custom Orb is reversible, so you can't go wrong, but I have seen the odd Trimdek sheet fixed with the capillary notch on the top and not underneath.

Quite often when you get to the finish at a gable end, you may think you will have to cut up the full length of a sheet. Sometimes you can just overlap the last sheet more to save cutting it. (The off cut will be useless anyway). Just make sure you keep the the screw pattern right.

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Laying Short Sheets

I can't remember the last time when I laid short sheets, (we can some awfully long sheets on a semi-trailer).

laying short steel metal roof sheets
Roof sheeting fixing - Laying short roof sheets.

For guys like the motorcycle rider on the previous page, the theory is that you lay them like in the sketch. Just as though the separate sheets were joined together.

On some profiles especially in heavier thicknesses, you have to cut a notch out of one of the sheets at the spot where they all join. Check the manufacturer's details.

I have done heaps of verandah type additions where we added another row of sheets under an existing roof, and with the correct lap and fixings they never leak. So If you have a particular reason to want to fix the whole bottom row first, then I'd say go for it, at least with corrugated profile. In corrugated sheets I can't see it making any difference.

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Infill Strips.

Closed cell foam infill strips are produced to seal various roof sheeting profile. On the right is one for Custom Orb.

closed cell foam infill strips for sheet metal roofing
Roof sheeting fixing - Infill strips
  • They should be moisture resistant, that is not soak up water. (That's the closed cell part).
  • They are used at the eaves and at the top, under the flashing when the roof pitch is very low for waterproofing.
  • Sometimes an architect will specify them for vermin proofing.
  • I believe that fire resistant insulation type strips are available for use in bushfire prone areas to stop sparks entering the roof space.

They can be fixed one piece at a time as the fixing progresses, or by leaving the bottom sheet not screwed (fixed) they can usually be slipped into position afterwards.

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Turn Ups and Turn Downs

The top edge of all roof sheets, the part that goes under the flashing, must be turned up. This is to stop wind driven rain from creeping uphill under the flashing.

metal sheet roofing turn ups under roof flashings
Roof sheeting fixing - Turn ups under flashings.
steel metal roofing pan turn up under flashing
Roof sheeting fixing - Turn ups.

Here you can see a hips in Custom Orb that are turned up after the sheeting is fixed. The valley (the low portion of the profile) is simply given a small kink with a shifting spanner.

For cladding with trays, the manufacturer's sell tools to turn up the ends. Many roofers make their own, or just use wide flat jawed multi grips. You need to get a feel for it, don't be to severe, as it is easy to tear the material. Remember the stuff is less than half a millimeter thick in most cases.

With pan turn ups, like in Trimdek, Kliplok etc. it is possible to turn up the sheets at the ridge after the sheets have been fixed, but mostly the turn up is done before the sheets are fixed.

I once built a verandah roof onto an existing roof. Later the owner rang me up and told me that my roof was leaking.

After a bit of investigation it turned out that the roof sheeting on the original roof was not turned up under the ridge capping. Every time conditions were right over the previous few years, water would get in at the ridge and trickle down the sarking for 5 meters and out at the open eaves, with nobody being any the wiser.

When I put on the new roof and lined the ceiling, it made water stains on the new ceiling. We had to lift the ridge capping and turn up the sheet ends.

It is almost unbelievable that any roofer would fix a roof without turn ups. The roof was only 15 deg. pitch also which made it worse.

Kliplok metal roof sheeting with turn down at eaves
Roof sheeting fixing - Turn downs on Kliplok

Not quite as critical as turn ups are turn downs at the eaves. With profiles like the Klip-Lok pictured it is common to see it fixed with very shallow roof pitches, down to 1 degree. When water is slowly running off a sheet edge with very little fall to it, it is possible for it to run back uphill on the underside, to the fascia or wall edge and cause staining. What causes it to go uphill is our old mate, capillary action. It is made worse of course by wind.

So to stop this happening the pans of the sheets are turned down, as they are in the photo, to make the last bit of the edge steeper which causes the drips to drop off cleanly.

Turn downs are not done with corrugated sheeting, as the profile would split, but with corrugated the pitches are generally steeper anyway, so the turn down is not needed.

Corrugated iron fold up tool
Roof sheeting fixing - Fold up tool

Here are the contact phone numbers for a couple of Aussie guys who have invented a fold up tool for corrugated sheets. As I mentioned early,there are tools for wide pan type profiles, but this is the only one I have seen for corrugated iron.

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Please Note! The information on this site is offered as a guide only!  When we are talking about areas where building regulations or safety regulations could exist,the information here could be wrong for your area.  It could be out of date!  Regulations breed faster than rabbits!
You must check your own local conditions.
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