Sash window flashing

G'day

I have pulled out a rotted double hung sash window intending to copy it in new materials. My problem is that the sill is so badly decayed on its underside that I can't see how it worked. The previous person to work on it simply tacked lead flashing over the top of the whole sill (which let water in at the sides, of course, doing untold damage).

The house is old and double brick, but there is no cavity between the inner and outer brick walls. A sandstone outer sill has been set in the outer brick wall. The top of this sandstone block is 3–4 mm higher than the top of the inner brick wall, on which the wooden sill will sit

I thought I might add mortar (or some modern compound) to make the inner brick platform flush with the sandstone, then cut a slot in the wooden sill and run flashing from that out and a couple of cm over the edge of the sandstone. Does that sound reasonable? Do you know where I can find drawings/plans of how it used to be done?

Thanks
Dean

Hi, Maybe this will help. The sill board over the inner skin would just be blocked up to the desired height rather than trying to get the levels matching with mortar. The first diagram gives a cross section through such a window.

Good Morning Dean

I suspect your construction technique is much older than that in Fuzzie's photocopy - it was not normal to have a wooden sill protrude over the top of a sandstone sill - a design feature.

My house was built in the 1870's and I did some work on one of my windows last Christmas. The sandstone sill sloped outward to facilitate water run off. In my case the side brickwork was stepped by half a brick to house the wooden window frame, and we used spacers to lift the wooden sill about 5mm above the sandstone sill - to stop water wicking and dry rot. We then draft proofed the in room side of the sill/wall join with mortar.

Perhaps a couple of photos, from insed and outside would help.

Fair Winds

Graeme

As I understand the house is double brick without a cavity between the inner and outer leaf???? If so you may be having major problems with dampness with the transfer of moisture through the outer leaf and into the inner leaf.
In the case of the sill I would have a " Z" metal tray made from Zinc sheet which has a turn up to be located at the back of the new timber sill member and a turn down over the sand stone sill. This tray would need to be turned up at each end behind the new window jambs at each side. The turn up at the back of the sill could be covered with a window board or such.
You should also need look at the jambs as you may need a side flashing at each side running down and joining up with the new sill tray.
If you should consider the zinc material for the sill tray may be to expensive you could use galvanise steel sheet or bitumen coated aluminium (Alcor), aluminiul "Z" extrusion or another alternate would be Stainless steel.
Cheers
Mac

Thanks for the diagrams, Fuzzie. Not exactly my window but lots of useful things there.
Graeme I think raising the sill in that way may be a good idea. The wood will eventually get sodden otherwise, in prolonged wet weather.
Mac raises an issue which freaks us out, water getting through the outer leaf and into the inner leaf. The mortar is also quite soft and porous. The place was plain brick for fifty years then painted for 70. We are stripping the paint off ... possibly moisture will be able to get in. There is some clear product for sealing masonry, which we will have to try. By the way, double brick without a cavity is very noisy compared with the more modern arrangement.

I am getting window sills shaped from tallow-wood. Will produce the rest from treated pine using my own router set-up.

Side flashing sounds like a good idea but I thought it would be unnecessary, provided the bottom flashing went around the bottoms of the front vertical sections of the frame. These sectons butt up against the opening in the outer brick leaf, and there will be a moulding at each side. So, very little water should get in, and if any does it should run straight down. I suppose it would be a good idea to force it to run straight down, with flashing.

Is lead flashing out of fashion, too poisonous or too expensive?

Thanks
Dean

By the sound of it the house must have a historic background, perhaps it may be worth delving into.
The bricks could be hand made, the method of construction with out a cavity seems odd but who knows what went on 120years ago.
There are a number of products on the market for sealing masonry check it out thoroughly particular how they stand up over time when exposed. Perhaps you should consider cement rendering or one of those latest texture finishes on the market from Dunlops to be applied over the brick work with some type of moisture additive added to the mix.
May I suggest you pass on this thread to the renovation forum as one of the member may have the more up to date knowledge in this area.
In the case of the jamb flashing you could cut a groove down the brickwork reveal and fit a weather stop to protrude say about 25mm sealed with a suitable sealant such as one of the polyurathe product put out by Seka , the jamb of the frame would then butt up to the stop and be sealed to stop water penetration at the junction.
Hope this is of help
Cheers Mac

Window should fit from inside and butt up to inside face of outer brickwork. Timber sill should be made wide enough to sit out over inner edge of the sloping masonry sill. Inside bottom edge of timber sill should be rebated approx 25mm x 3mm. Flashing can be attached to rebate, bent out under sill and turned up at ends or the flashing can be fitted to the opening with turn up at each end. The window is then slid into opening, on top of flashing and the back edge of flashing turned up into the rebate. Timber reveals on inside cover the flashing turn up on sill. Outer edge of flashin should protrude to front face of storm moulds. For best results and extended sill life, the under side of sill should be sloped outward but you never see it these days.
Hope this helps.

Quote:

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Originally Posted by dean11

Thanks for the diagrams, Fuzzie. Not exactly my window but lots of useful things there.
Graeme I think raising the sill in that way may be a good idea. The wood will eventually get sodden otherwise, in prolonged wet weather.
Mac raises an issue which freaks us out, water getting through the outer leaf and into the inner leaf. The mortar is also quite soft and porous. The place was plain brick for fifty years then painted for 70. We are stripping the paint off ... possibly moisture will be able to get in. There is some clear product for sealing masonry, which we will have to try. By the way, double brick without a cavity is very noisy compared with the more modern arrangement.

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Good Morning DeanAttachment 232573

First a little history.

Solid brick walls (no cavity) were essentially the norm for a thousand+ years until around 1850 when cavity brick started to be phased in. Periodically a brick is laid sideways so that it links the two stretcher walls together - called a bond. This bonding could be every second brick - English bond, but there were other patterns - eg Flemish bond. Cavity brick construction did not fully displace solid brick until around 1900 - building is a conservative industry, then and now.

In the 1800's bricks were hand made and were a lot softer than modern bricks - often they are called sandstock bricks or convict bricks. Around 1900 there was an improvement in kiln technology, kilns could reach much higher temperatures than their predecessors, and they produced bricks that were both harder and cheaper. My house is built with convict bricks and has been painted. We let the paint deteriorate and then tried to remove it but found that it had seeped so far into the bricks that we could not remove it without damaging the bricks. We are resigned to repainting every ten years. Solarguard seems to work well - use a very hairy roller.

None of our windows have any form of flashing apart from the sandstone sill. The sandstone sill is about ¾ brick wider than the window cut-out, and set into the brick courses. The top of the sill is sloped so water runs off it. Effectively, the sill is the flashing. After 130+ years there is no dampness. See photo.

Agree with Mac that you may get a better response in the Renovate Forum. But photos of your window will help.

Fair Winds

Graeme

Hi All,
Thanks for these replies. Following an earlier discussion about Home Spindle Moulders versus Home Router Tables, I settled for the router option in very fear. Have had much fun devising ways to get my work bench to act as a router table ... and it works.
Sash windows are beginning to look simple, but there is one logistical problem: with tallow-wood sill and all vertical and horizontal members combined, they are very heavy. Hard to try out in position, as one needs to.
Under the house I found large heaps of cast iron window weights.
My current problem is that I would like to use good old-fashioned soft, vegetable matter, circular-section sash cord, but haven't seen it for sale anywhere for decades. Where might I buy some of that in Newcastle on Hunter, NSW?
Thanks,
Dean