Gutters and Unseasonable Rainfall

[Flyfisher]

The recent spell of intermittent downpours has led me to conclude that my guttering is not entirely adequate. Most of the time it's fine but a really heavy downpour, such as we've had a lot of recently, causes overflows in a few places. When it happens, it's quite disconcerting to see how much water ends up cascading down the walls and, in some areas, windows.

I'm pretty sure that an occasional overflow does little harm but given the recent weather it's happening a few times per week and I'm wondering of the effect on the walls. Hopefully, the effect is no worse than the ground (less, probably), which seems to dry out quickly enough in this warm weather.

However, it does make me wonder about the method I used to calculate water run-off from our various sections of roof.

Am I the only one mad enough to wander around looking up at gutters during in a downpour?

 

[middi]

Very few gutters cope with abnormal rain downfall, this is especially true on older buildings with the average 4 inch dia. half round gutters.

Gutters need to be tightly lipped under tiles in order to catch ALL the water coming off the tiles, this, however, will allow for very little fall especially on a long gutter run which becomes prone to " overfill" during heavy downpour. If the fall is increased to allow faster discharge of water the gutter needs to be well away from the tiles lip at the " lowest" point, problem is that during heavy downpours the rain " shooting" off the tiles will miss the gutter towards the lower point.
Larger gutters can be fitted as these will cope better, better still, increase the number of downpipes used to discharge the gutters.

Decisions, decisions, the choise is all yours

Middi

 

[Flyfisher]

A good description of the challenge!

Watching the most affected run of guttering today, there is no problem with the guttering catching all the water running off the tiles, so I suppose that's a good thing. But you're absolutely right that this means there is insufficient fall to cope with a heavy downpour so the guttering fills up and then overflows.

I don't think larger guttering will completely solve the problem, it will just take a bit longer before it fills up and overflows.

I think the right solution is to fit another downpipe. I know this will work because one side of the roof in question has a single downpipe and the guttering overflows. The other side of the same roof has three downpipes - because of roof dormers - and the gutters don't overflow.

So, really, the answer is staring me in the face.

And I thought I'd finished with digging new drains.

 

[AMc]

I'd guess that the larger diameter or deeper gutters have much more capacity than one might initially assume.
During our heating installation my engineer noted that the "plumber" they'd employed had used 22mm instead of 28mm pipe for a connecting run. I thought - "that won't make much difference" until I did the calculations on (EDITED Pi r squared) and realised how much flow capacity was gained by the small change in diameter.
When we reroofed the back we replaced the plastic guttering with "deep flow" which doesn't look substantially different but has a much greater capacity. Of course none of that would help if you have reached the capacity of the downpipe.

 

[Flyfisher]

The big variable is, of course, the actual rainfall. When I calculated the guttering details, it was close to the limit based on average rainfall and, clearly, we're having above average rainfall at the moment and it's the intensity of the downpours that is the problem.

I've no doubt that deeper/wider gutters would help the problem by holding more water before they overflowed, but they would still overflow at some point.

If I'm going to bother to rework anything I reckon that an additional downpipe would be the best investment - it should actually solve the problem, no matter how much rain we have, and it'll probably be cheaper than replacing the existing guttering - though it'll be more work because of all the digging to connect to the surface water drainage.

I'd been enjoying a good run of ticking things off my 'to do' list so I'm not best pleased about adding new ones!

 

[88v8]

Digging.... depending on the logistics of the surroundings, you could just let some of the water run out of the downpipe shoe onto the ground, or into a pond? So long as it doesn't end up pooled alongside the house, it doesn't have to go into a drain... after all, I bet King Enery the 8fh didn't have drains.
Perhaps a yard of clay gulley to get it on its way.

As I write, it's suddenly tipping down... well at least we don't have to worrry about gutters - there aren't any!

Ivor

 

[MdB]

(Pi R cubed)

You of course mean Pi R squared for cross sectional area though there will be an increase also due to lower drag effects in the larger pipe I would guess.

 

[AMc]

(Pi R cubed)

You of course mean Pi R squared for cross sectional area though there will be an increase also due to lower drag effects in the larger pipe I would guess.

That's what I meant, but not what I typed (sigh)

 

[Flyfisher]

Digging.... depending on the logistics of the surroundings, you could just let some of the water run out of the downpipe shoe onto the ground, or into a pond? So long as it doesn't end up pooled alongside the house, it doesn't have to go into a drain... after all, I bet King Enery the 8fh didn't have drains.
Perhaps a yard of clay gulley to get it on its way.

The side of the roof with dormers and thus multiple downpipes does discharge onto land sloping away from the house and into a pond. The surface water drains on this side are blocked but I've installed a simple length of flexible pipe to dump the water about 10 feet away from the house from where it drains away nicely. It's only a temporary solution until I sort the drainage out properly (well, I say temporary but it's been working this way for about 5 years now ), but it's actually very effective.

Unfortunately, the ground on the other side of the roof slopes slightly towards the house, so a similar solution would not work. But it's not a big problem because I've already installed a new surface water drain on that side of the house (which carries the water to a pond), so the infrastructure is already there - I just need to do some digging and connect a new downpipe into it.

Of course, with hindsight . . . . . :roll: Oh well, we live and learn.

 

[CliffordPope]

One obvious difficulty is that in light rain the gutter needs to be vertically under the slate edge, but as the rate of flow off the roof increases the increased velocity causes overshoot.
Even if the sheet of water flowing off the roof does hit the gutter, it is still liable to spill over. It is impossible to place it an optimum distance everywhere because of the need for a fall from end to end.
Gutter profile may be important. The kind that has a curved profile looks elegant, but it sometimes seems to me it is conventionally fixed back to front. Having the deeper section at the front would be better for catching water hitting it at an angle.

Also firing sheets of water into the trough considerably impedes flow along the gutter. Have you ever played with a pressure hose and observed how you can dam up water by waving a jet across the advancing front? What it needs is a V-shaped section of optimally angled deflector plates, integrally part of a continuous pipe with a slot in the top fixed immediately underneath, like a funnel in a flask in section.

Water might flow faster down a down-pipe if it were rifled on the inside?

 

[Flyfisher]

Not sure about the rifling idea. Wouldn't it result in water travelling a longer path down the pipe, thus spending more time in the pipe, thus actually reducing the overall flow? Just thinking out loud really.

The point about lots of run-off impeding the flow along the gutter is an interesting idea.

Frankly, I think our gutter in question is just too long and, because of this, has insufficient fall. If I increased the fall then one end of the gutter would be too far below the tiles and would not collect the water in the first place.

Another downpipe would allow me to improve the fall as well as increasing the basic drainage capacity.

 

[MatthewC]

I identified that the original(?) 4.25" ogee guttering was definitely the wrong stuff for my house. This may have even been the cause of some of the longstanding damp problems as it was screwed through the flat face to the fascia; of course the screws allowed water through and became loose and so it all leaked; then the holes rotted and the guttering was falling off the rotten fascia. As it all had to be replaced anyway I decided to fit 5" half round which I think I calculated doubled the useable capacity . You can just see in the photo where my 5" cast iron on the left meets my neighbour's 4.5" plastic.

This house has no downpipe at the front and so rainwater in the middle at the front has to travel 50 feet through three right angles round to the sides of the house to the first downpipe.

Am I the only one mad enough to wander around looking up at gutters during in a downpour?

No - you are not alone; everyone responsible for an old building should do it sometimes, as I have recently. For a large building the SPAB advice is to take a pair of binoculars but I have yet to find out how to hold a golfing umbrella and use binoculars at the same time without getting wet! :shock:

 

[Feltwell]

I identified that the original(?) 4.25" ogee guttering was definitely the wrong stuff for my house. This may have even been the cause of some of the longstanding damp problems as it was screwed through the flat face to the fascia; of course the screws allowed water through and became loose and so it all leaked; then the holes rotted and the guttering was falling off the rotten fascia.

That's how they fitted it back in those days. Mine was fixed that way. The new Ogee I bought had the area around the fixing holes protruding slightly, to hold the gutter a little away from the fascia - but even better, I managed to find some brackets to fit instead.

http://www.classicalrainwater.co.uk/product.htm?scID=1&category=OG Gutters & Connections&groupID=116

Am I the only one mad enough to wander around looking up at gutters during in a downpour?

Nope - I do that every time. Skin is reasnobly waterproof, after all. :wink:

 

[MatthewC]

Am I the only one mad enough to wander around looking up at gutters during in a downpour?

Nope - I do that every time. Skin is reasnobly waterproof, after all. :wink:

You weren't wearing ANY clothes?

 

[Feltwell]

It's one way to stop the Jehovah's Witnesses calling round you know :wink:

 

[LadyArowana]

It's one way to stop the Jehovah's Witnesses calling round you know :wink:

Maybe so, but won't the scientologists be there trying to convince you that this lack of clothing represents a subconscious desire to emulate some other state of being? Then Mrs Feltwell will want to divorce you and take all the little Feltwells away to stop them being indoctrinated. Far far better to pop on some shorts and tell the various zealots you already have your own religion.

 

[Feltwell]

Mrs Feltwell will want to divorce you and take all the little Feltwells away

This plan just gets better and better.......... :wink:

(I don't mean it really! I was away on business for 4 nights this week, when I got back I had my normally not at all cuddly youngest offspring clinging onto me for hours. Very cute.)

 

[LadyArowana]

when I got back I had my normally not at all cuddly youngest offspring clinging onto me for hours. Very cute.)

Ah yes, the Velcro sweaters, always a winner.