I need to build a fascia - how?

[Bluebirdnick]

Hi all.

3 years ago we built a single storey rear extension with a flat roof. It was a parapet roof, with capping stones, finished in a light thru-colour render. Like this:

It looked great at first, but after a short time some issues became apparent. Firstly the capping stones didn't really protrude far enough from the face of the wall which meant rainwater just ran down the face of the wall rather than dripping away freely. Secondly, the mortar between the capping stones quickly washed out, staining the wall and increasing the problem of water running down the wall. This has led to staining, and in one case a crack in the render:

The company that did the render have been back once to patch up but have said, quite fairly, that until I sort out the issue of water running off the roof and down the wall, they won't come back again.

So I need to do something. The options I have come up with are:

1) A second layer of coping stones, corbelled off the existing ones and protruding a further say 15cm (the stones are 400mm wide).

2) A retrofitted fascia board.

For 2 - not really sure how to do this. The image below shows how I might attach lengths of U-shaped metal that I could get made up. They come in 3m lengths so I would need 4, and they would need to overlap. I envisage fitting them right up underneath the existing capping stones. I am thinking that I could fix two battens to the wall - one to take the top lip and one to take the bottom lip. I would then slot the metal "fascia" over the battens and fix with roofing screws from top and bottom. I'd silicone between the capping stone and the metal, and probably the render too. I would have to find a way to put an end cap on as well.

Does this sound sensible? I am a bit concerned that there is no drip on the U-shape, although I could try to get one added by the company that would do the manufacturing.

And am I missing something obvious? Are there ready-made systems out there that I am overlooking?

Any help would be much appreciated.

 

[Newboy]

Unless I'm missing something obvious ..... why not remove the existing copings and replace with correctly sized ones (with drip grooves).
Surely a lot less work, aesthetically better than your two proposals and almost certainly more effective?

 

[Bluebirdnick]

Thanks. I'll be doing this myself, so thought it would be easier to add a layer of coping stones, in In particular as they rendered up to the bottom of the existing stones and im not sure that I could remove them without damaging the render. It would also be half the cost of doing larger stones. The existing stones have drips on both edges. And i would get a bigger overhang by adding new rather than replacing existing.

Although I actually prefer the idea of the metal (or plastic) fascia- I think it would be more effective as i could have it stick out more and it would protect the top part of the wall which has the cracks.

 

[securespark]

Which company fitted the inadequate capping stones?

 

[Harry Bloomfield]

I'm not convinced your facia would help much at all. I would also be wary of the over hanging coping stones - too much risk of someone grabbing hold and pulling one down on their heads.

Doesn't the location of the stains and the crack, suggest the problem is more at the joints between your coping stones, rather than the depth of overhang of the stones? Might some sort of colour matched outdoor mastic help prevent water passing between those joints?

If not, might some upside down L profile metal or plastic, lip sat on top of the coping stones and sealed to them form a much more effective drip strip?

Like the above, but using those roof tile edges where a roof meets a vertical wall?

Might Flashband work, stuck over the coping stone joints?

 

[^woody^]

You need wider copings with at least a 50mm projection and a suitable drip properly laid and jointed. Nothing elaborate, just that.

 

[Lower]

Option 1 with another layer of coping stones would probably work but will look odd.

Option 2 (your facia) won't give you any kind of drip cill so you'll still have water running down the wall. You'll struggle to stop water getting down the back of it.

I would replace the coping stones with larger ones and do the job properly.

 

[Bluebirdnick]

Thanks all. In answer to the questions:

The builder who built the extension laid the stones. But I'm not going to throw him under the bus here, the stones were specified by the architect and he was uncomfortable with the parapet wall from the off - he was completely up front about never having built one before and advised me many times that a normal flat roof would be easier and cheaper. My other concern is that the crack might actually be caused by a crack in the blockwork rather than the water running down the wall.

The visual problem is largely the mortar washing away, but the overhang really is not big enough. The colour match mastic seems like a sensible no-regrets option though so I may do that and see how much of an impact it has. But the overhang really isn't big enough. Water dripping off the stones hits the cils for the bifolds beneath, so no more than a few cm from the house itself. And clearly the drip is ineffective as water pours down that wall. The overhang needs to be at least 10cm bigger really, I think. I share the concern regarding stones coming off and being dangerous.

As regards drip cill - i could make the metal form into anything I wanted really so could incorporate a drip cill. I think it would be easy, cheap and look good but I am hearing that people disagree and think it would be ineffective. Is that just beause of the basic design I have shown; or because in principle it's just not a very good way to do this? The pic above was just an example of what I had in mind but I could well do it in another design eg:

As regards cost/doing it properly - i should add that this is a temporary measure. We will extend back over the kitchen when we can afford it, which is hopefully in the next 2 years. I just want to do something that prevents the wall from getting too messed up (and prevents the walls getting damp) in the meantime, which is why I want to do this as a DIY job and not one for a builder. I had a quote to replace the stones with ones that are 20cm wider (so offering an additional 10cm overhang) and it was a lot for something that would be largely removed again shortly afterwards, and would set us back quite a few months from doing the rear extension.

 

[securespark]

I would explore going back to the architect. Get them round and show them what is happening.

 

[Lower]

If you have access to press brakes etc and can make whatever profile you want, i would recommend making a steel capping that covers the existing copping stones in their entirety and gives you a suitably large drill sill away from the wall. Why put something beneath it when you could go over the top and make it look like it was always intended to be there.

 

[Bluebirdnick]

If you have access to press brakes etc and can make whatever profile you want, i would recommend making a steel capping that covers the existing copping stones in their entirety and gives you a suitably large drill sill away from the wall. Why put something beneath it when you could go over the top and make it look like it was always intended to be there.

Thanks
Yes, this was the original plan. The issue my wife has is that from the upstairs bedroom window, the existing coping stones look really smart (and whatever I do will be permanent outside the bedroom window as we are not extending off that part of the house). Bolting the fascia to the wall would be invisible from the bedroom window and as I'd put it right up against the underside of the existing stones, the stones wouldn't be visible from the ground so it would look "normal".

But if fixing it over the existing stones is better then I can go back to that.

 

[Harry Bloomfield]

My other concern is that the crack might actually be caused by a crack in the blockwork rather than the water running down the wall.

I agree that the crack is unlikely to be a direct result of the water running down. Is the inner leaf showing any cracks or damage?

Metal covering the coping stones completely would be the more certain fix, guess it would have to be alloy or stainless steel - I hadn't realised you had access to a metal folder.

 

[Bluebirdnick]

I agree that the crack is unlikely to be a direct result of the water running down. Is the inner leaf showing any cracks or damage?

Metal covering the coping stones completely would be the more certain fix, guess it would have to be alloy or stainless steel - I hadn't realised you had access to a metal folder.

No sign on the inner wall which is a relief.

I dont have access to a metal folder myself ( or at least not one large enough) but a company I've used before that sells metal roofing materials can do bespoke shapes at very modest prices, colour matched to the bi-folds. The benefit of going over rather than under the existing stones is presumably elimination of the risk of water getting behind the fascia?

 

[Lower]

Thanks
Yes, this was the original plan. The issue my wife has is that from the upstairs bedroom window, the existing coping stones look really smart (and whatever I do will be permanent outside the bedroom window as we are not extending off that part of the house). Bolting the fascia to the wall would be invisible from the bedroom window and as I'd put it right up against the underside of the existing stones, the stones wouldn't be visible from the ground so it would look "normal".

But if fixing it over the existing stones is better then I can go back to that.

I would design a profile that hooks over the coping stones where it would be visible from bedroom and is fixed into the building wall on the side that you're going to change at a later date. That way you could remove it as and when you change the wall on the non bedroom side.

 

[Harry Bloomfield]

The benefit of going over rather than under the existing stones is presumably elimination of the risk of water getting behind the fascia?

Yes, it would guarantee that.