Sheet Metal Roof Flashings

Flashings are the purpose made pieces of bent and formed sheet metal, usually made out of the same coil stock as the roof sheeting itself, that are fixed during the course of the sheeting job.  Sometimes before the sheets are laid (valleys, box gutters), but more often after the main sheets are laid.  They add the final touches to the visual aspect, and  waterproof the roof.

Here's a swift tip.  Don't just price the roof iron and then add a bit extra for the trims.  Price them separately and accurately.  I have done heaps of jobs where the trims cost more than the sheeting.  They also took longer to fix too.

A Colorbond hip flashing.  note the difference between the flat surface type screw and the cladding screw. Also note that were there is a need to fix the flashing to the sheeting under then pop rivets have been used to tidy things up.

Here's a nicely fitted COLORBOND hip trim to a Custom Orb roof.  You can see that the main sheeting uses a different screw and washer combination than the trim.  Also at the bottom edge the roofer has fixed the trim to the loose ends of the roof sheeting, (where here is no batten to fix to) with pop rivets.  These are usually blind rivets, that is ones that are sealed on the ends.

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Flashings are final pieces that trim and weatherproof the roof when the sheeting is all fixed.  Don't treat them casually.  They are vital for the performance and looks of a good roof.

The ones shown below are fairly average for our conditions.

 I have seen roofers or builders cut down on the sizes a fair bit from my suggestions here.  Where I have shown a 200 lap, others use 150. less material equals cheaper, equals more chance of water penetration.  

Depends on roof the  pitch also.  
The turn down into the valleys or pans varies with the cladding used.

Here is a sketch of a typical ridge flashing, to a timber pitched roof.  The hip ones are the same, just a touch flatter on any given roof. MOST important is the turn up right at the top. The Sisalation/sarking is not shown on any of these sketches, but it will be there of course.

Again a timber roof, this time the barge flashing at the edge of a gable roof.  In the sketch I have noted it as a timber fascia, but more correctly the fascia is a horizontal board and the barges are the ones that go up the slope. I always prefer the "L" shaped return at edges like this as it gives a good straight sight edge, and a positive fixing.

Here's the same thing again on a steel verandah or carport.  the 20mm x 20mm step is a bit bigger than necessary, but it is as small as the modern large folding machines can do.  If there was a ceiling underneath, the barge would fit over the battens and the sheeting fit neatly to the deeper rebate.

Here's one of a valley gutter. Usually these are made out of thicker material than the rest of them on the roof. To try to get them as deep as possible, the ones shown are sitting directly on the rafters, or trusses, which are at say 900 centers. so they are usually of stiffer material to take the greater span. Otherwise the place where the valley flashing sits would have to have something to help it span between the rafters, which would in turn reduce the depth of the valley gutter. This could be a timber board, or a metal ribbed roof or wall profile.

Here's a top end of a roof where it abuts a wall.  In this instance a stud wall with external cladding.  The flashing goes up behind the external wall cladding. A similar  detail could apply at a side wall also.  That is fix the trim first to the stud work, then run the external cladding over.

A roof abutting a masonry wall at the side.  Because of the slope of the roof and the need to step the flashing it is done in two sections, otherwise if it is a very flat roof, a tapered trim could be used in one piece. The detail of turning the flashing into a saw cut in the wall is important.  I have seen them fixed straight to the wall with just a silicone seal, but while OK short term, it is asking for trouble. later on.

Now this is a crappy photo! Still it is quicker than drawing it out.  Here is a shot of trim stepping uphill against a masonry wall.  Start from the bottom with each succeeding one overlapping the previous one. You can also see the parapet wall flashing on the top of the wall.

Simple capping trim for a parapet wall.   I like using something like the metal drive pin type fastenings for this sort of fixing.  That is a say 5mm metal plug, that has a metal nail with it, that when the nail is driven in the plug expands. There are many similar ones on the market, out of plastic, and they fix OK, but the plastic perishes after a few years exposure.

Here's a join between two roof surfaces at different angles.  Quite often done like this when the bottom one is added at a later date.

I have done a lot of extension roofs like this, cutting back the existing roof at the eaves and adding the new one under the old with plenty of lap, and inducing a curve to both of them.   As shown I leave the batten spacing as wide as possible, otherwise I have packed up the batten at the middle of the curve.

This is what is commonly called up here a soaker .   A soaker used to be a flashing  on the upside of say a chimney, that went under the roof material.  Here we do it like this, We pay the extra for the material and go over the roof sheeting up the roof all the way to  and under the ridge capping.   This one has to go past the roof penetration (solar tube light, a poor man's skylight) and fixes to the next batten down. Note that on the sides it turns into the valleys of the sheeting. Having a side lap at the hole at least the same as the sheeting itself.

For smaller penetrations through a roof, like this 50mm vent pipe a Dektite fitting is usually used.  The seal is EPDM  I am not sure what the metal strips are, but they are soft and easily shaped to the  sheeting profile.  Again a crappy photo, but if I get a better one I will swap it.

At the top is a ridge capping scribed over a Trimdek type cladding.    To get the cuts right I lay the ridge flashing in position and hold it with a couple of screws.  I make a template out of a bit of scrap trim material and lay the bottom cut out on the sheet ridge and mark the cut out on the flashing with it.  Working along until I have marked them all. I then take the thing off the roof, into the shade and cut it on a couple of saw horses.  I have to be careful lifting it back onto the roof, as the stiffness has gone out of it and it is easy to buckle at this stage. Top gun roofers would laugh at me doing it that way. They cut in position, without templates and invariably get it spot on.  Practice makes perfect. They do the same with the hips, all cut in place, and I do the same with a template.

This shows the turn up of a flashing at an open Dutch Gable, but the same detail would be used at any vertical surface.

Here's a shot of a Kliplok roof, showing the scribing of the top trim to the roof sheeting.  The flashing itself turns up 100 or so vertical.  In this case the architect has left the Dutch gable surface open, for ventilation as the roof is covering an open area.  The same flashing is used just like this, when wall cladding is added.

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