A ? about roof flashing

**silentC** · 20th February 2007, 08:56 AM

I think the boys were on about different flashings myself and got all heated up about different things, both were right in their own respect.

Nah, they're both talking about the same thing: flashing a new single storey roof to an existing two storey wall - abutment flashing as Peter puts it. That was the original question - how to do it. The rest of the stuff just came into the debate as a way of illustrating that bricks leak!

**Bleedin Thumb** · 20th February 2007, 10:33 AM

This tread is leaving me with the same feeling as I get post coitus interruptus....slightly unsatified.

We still haven't resolved the issue -

IE What is the correct way to retro fit flashing to a brick wall abutment.

1. Chase cut or
2. Stepped brick removal?

**silentC** · 20th February 2007, 10:52 AM

I reckon that both are compromises in an imperfect situation. They both mess with the integrity of the existing wall. Whether one or the other is the accepted practice probably doesn't mean much from that point of view. A lot of "accepted practices" look dodgy upon closer inspection...

**ausdesign** · 20th February 2007, 12:01 PM

The BCA 2006 prohibits the use of lead flashings for any roof collecting potable water.
Maybe that narrows the debate. Then again . . . .

And just to clarify the debate - this is where the flashing is preventing water getting inside not for example where a carport or the like butts against an external wall.
For the latter I would be detailing a sloped, cut in [30mm] flashing with a 'soaker' tray for a tiled roof & an over flashing on a metal roof.
I really do have an aversion to the look of a stepped flashing [in case no ones noticed]

**journeyman Mick** · 20th February 2007, 10:11 PM

Peter,
if you spec a saw cut flashing how can you guarantee that water wont soak the brickwork above the cut and be drawn down behind the cut via gravity thus wetting the interior wall below the roof? And if there's a power point in this wall and someone with a dodgy heart gets killed will you be partly liable? It's not very likely but it's not entirely impossible.

Mick

**ausdesign** · 21st February 2007, 06:12 AM

'morning Mick.
A couple of points. Any moisture that penetrates the outer skin will run down the inner face of the brick. If any moisture gets across to the inner skin it will be a result of bad workmanship such as mortar breaching the cavity. Any moisture getting to a power point on the internal skin will be from bad workmanship not from a flashing break down.
Compare it to a situation where the wall is a normal exposed to the weather external wall - same electrical hazards.
With the flashing,whether its chased in or cut in, the same installation principles apply - the recess should be part filled with a sealing medium such as sikaflex. The 'overflashing' should have an upward fold back and be pushed into the sealant, not fitted into the slot and then sealed.
There should be at least a 75mm upstand on the apron flashing & a 50mm cover by the overflashing.
I would hazard a guess that a sloped flashing would perform better than a stepped flashing - less joins etc but I don't have anything to back that up.
With a large area of face brickwork, such as with a second storey, above the abutment I would normally run a cavity flashing with weep holes same as you would at g/l with a slab but then again I'm not building now just drawing lines on paper !

**journeyman Mick** · 21st February 2007, 03:39 PM

Peter,
the situation to which I'm refering has a previous outside wall becoming an interior wall. Ie: 2 story house, single story addition is tacked onto the outside brickwork. Water which runs down the inside of the exterior brickwork is now running down an inside of an interior wall when it gets down to the lower floor. Of course an ELCB should protect the occupants but it's not a good situation.

Mick

**ozwinner** · 21st February 2007, 04:26 PM

Originally Posted by journeyman Mick

Peter,
the situation to which I'm refering has a previous outside wall becoming an interior wall. Ie: 2 story house, single story addition is tacked onto the outside brickwork. Water which runs down the inside of the exterior brickwork is now running down an inside of an interior wall when it gets down to the lower floor. Of course an ELCB should protect the occupants but it's not a good situation.

Mick

In a situation like that Mick there should be a cavity tray/flashing inserted, it can be stepped inside the cavity.

______
______........______
______ ........................______

Like so, you just have to have a bit of overlap on each flashing. ( I had to insert the dots as they kept closing up when saved)

It takes a fair bit of effort to archive, but would be well worth it.

Al

**journeyman Mick** · 22nd February 2007, 12:56 AM

Al,
so where does the tray drain to? I'm assuming the high point is in the middle of the wall just under the flashing on the outside and then each succesive piece steps down. How do you insert it?

Mick

**ozwinner** · 22nd February 2007, 02:14 PM

Originally Posted by journeyman Mick

Al,
so where does the tray drain to? I'm assuming the high point is in the middle of the wall just under the flashing on the outside and then each succesive piece steps down. How do you insert it?

Mick

I theory it drains out of the weep holes.

To insert it you would have to take bricks out and replace them.

Al

**journeyman Mick** · 22nd February 2007, 04:01 PM

Al,
the weep holes are now on an inside wall, not good! Must be another way around it.

Mick

**ozwinner** · 22nd February 2007, 04:03 PM

Originally Posted by journeyman Mick

Al,
the weep holes are now on an inside wall, not good! Must be another way around it.

Mick

Ahhr, I assumed you butted a gable roof against the brickwork, hence the stepped flashing.

Then the weep holes would be above the roof.

Al

**journeyman Mick** · 22nd February 2007, 04:18 PM

Al,
still trying to understand this.
Even if it's a gable roof with a stepped flashing that's been inserted in a saw cut in the mortar or brickwork I can't see how you can stop any water that's hitting the wall above this point from soaking into the bricks and travelling down the wall, causing moisture problems on the interior section of the wall below this point.

The only way around this that I can see is what John (Pawnhead) has advocated and that's to retrofit a flashing by removing bricks. Now I know that bricks nowadays are higher fired than they used to be and don't absorb as much water but I wouldn't want to lay my license on the line by doing it any other way. Truth be known, I probably wouldn't want to take the job on anyway

. But I've yet to see anyone coming up with a retrofit flashing for a brickwall that will guarantee a dry wall below it besides removing bricks like John suggests. Well that, or overflash the entire wall from the soffit down to the saw cut flashing which might be just a tad ugly.

Mick

**ozwinner** · 22nd February 2007, 04:39 PM

Originally Posted by journeyman Mick

The only way around this that I can see is what John (Pawnhead) has advocated and that's to retrofit a flashing by removing bricks.
Mick

Thats what Im saying Mick.
Take out bricks, insert flashing into the cavity, thats why its called cavity flashing.

Replace bricks..

Al

**ozwinner** · 22nd February 2007, 04:43 PM

Originally Posted by journeyman Mick

Now I know that bricks nowadays are higher fired than they used to be and don't absorb as much water

Mick

Yeah right, some bricks are fired almost to a glaze, but the still absorb heaps of water, some absorb so much that they almost float when they are wet.

We had some last winter and they got so wet that they wouldnt dry out for us to lay them, even after covering them for a week to stop the rain getting to them they were still bloody awful to lay.

Al

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