Puzzled over damp......

[Feltwell]

I'll get back up the ladders next weekend. One thing I did notice was the size of the hole in the running outlet at the end looks suspiciously small - it maybe that I have a 3" downpipe with a 2 1/2" running outlet on the gutter.

Ideally I suppose I should reverse the flow of the gutter and put a downpipe at the other end, as currently the valley shoots water into the gutter against the flow. Lots of work to do that though, I'd need to dig the driveway up to connect the drainage.

Maybe an interim fix is to put some new 6" gutter up to connect to the existing 3" downpipe - it's all on rise-and-fall brackets anyway so I could reverse the flow in the future fairly easily.

Whilst I think you're right and the design is not good, I'm still not convinced it's the root cause as it's not been that wet lately.

It's due to rain tonight, anyone want any guesses as to who will be outside with a torch?? :lol: The neighbours all think I'm barking anyway.

I can also watch out of the dormer window the water flow to see what happens.

 

[Jon Maine]

The outlet holes very often get overlooked, they should be the correct size internally which for you would be a minimum of 3" I am sure. Those bloody swan necks can jam up with debris fairly easily too.

 

[Flyfisher]

Observation while standing in the rain is at the experimental, rather than theoretical, end of the spectrum. Both can be useful, of course, but guttering design calcs have a big variable in them regarding rainfall intensity and duration. Fortunately, there are standard guidelines and quite a few online calculators and worked examples if you feel like checking your own roof/guttering design.

Some info here:
http://www.roofconsult.co.uk/calculations/drainage/notes.htm
http://www.brettmartin.com/building/rainwater/designinfo/index.aspx

 

[Schoolmarm]

And wind speed and direction need to be taken into account.

Although as you rightly say, it has been very dry recently.

 

[Feltwell]

I am puzzled no more!

It is in fact the overflow - after the radiators have been running for a while, it seems the water level in the header tank is getting high enough to just reach the overflow. Cutting the overflow near the header tank and leaving a bucket under it for a few days has revealed this.

As the pipe coming out of the wall is sloping up rather than down, I'm guessing the water is running back down the outside of the pipe rather than dripping away - and has eventually saturated the wall.

The guttering is OK, but the outlet is indeed too small. On close inspection the running outlet and stop end on the gutter have been replaced at some point, which explains why the wall is stained but appears dry - knowing this house I'd reckon that the gutter was allowed to leak for some time before it was replaced. The "new" running outlet (at least 30 years old I'd guess) needs replacing as it has a 2 1/2" outlet, going into a 3" downpipe. Given the roof area that could be a problem.

Thanks everyone for all your help & suggestions!

 

[Penners]

It is in fact the overflow - after the radiators have been running for a while, it seems the water level in the header tank is getting high enough to just reach the overflow. Cutting the overflow near the header tank and leaving a bucket under it for a few days has revealed this.

As the pipe coming out of the wall is sloping up rather than down, I'm guessing the water is running back down the outside of the pipe rather than dripping away - and has eventually saturated the wall.

So full marks to Schoolmarm, Lime and (modesty forbids....)!

If your central heating vent pipe is venting into the header tank, you need to attend to this. Simply improving the overflow pipe to prevent the damp is not the full extent of the problem. If your central heating system is constantly losing water through the overflow, then it will also constantly be requiring replenishment with new water through the ballcock. This could have several deleterious effects.

1. It will tend to aerate the water in the system, causing more air bubbles in radiators and potentially airlocks.

2. Your anti-corrosion admixture will become more and more dilute, and thus less effective.

3. You're wasting money by losing hot water through your overflow.

4. Worst case, if your header tank water becomes hot enough, it could deform and leak.

You may find that turning down the speed of your circulation pump will resolve the problem.

 

[Jon Maine]

That's good news you have found it.

Perhaps the overflow height is just to close to the ballcock height and the expansion of the water just brings it up over the height of the overflow. Maybe you could try to adjust the ballcock to a lower level to see if that helps.

 

[Feltwell]

That's good news you have found it.

Perhaps the overflow height is just to close to the ballcock height and the expansion of the water just brings it up over the height of the overflow. Maybe you could try to adjust the ballcock to a lower level to see if that helps.

I think that's exactly what it is Jon. The inlet valve is seized anyway (it does let water in - but only at drip speed!), so a new one is going in which will be adjusted a little lower.

Penners, I take your point and will certainly be keeping an eye on it to see if any water is returning to the tank. The pump on the system is large - the plumber commented on that when we had the boiler changed (3 days after we bought the house, the old boiler died :roll: ), but it's also a tall house (3 storeys + high ceilings). I may just fix a cup temporarily under the return pipe to see if any water is coming back, and how quickly.

 

[Schoolmarm]

YAAAY!!!!
I love it when you find the cause of annoying damp bits. 8)

 

[Hatster]

Congratulations on identifying the damp - it's been a fascinating story to read through, and I'm pleased it's turned out so well.

 

[Penners]

YAAAY!!!!
I love it when you find the cause of annoying damp bits. 8)

Or, in this case, when you find the cause...!

 

[Schoolmarm]

No, I meant actually find it after the suggestions. 8)

 

[Feltwell]

Of course, now that the leak is fixed all I've got to do is re-plaster the wall.

But what's the point in re-plastering when that window needs replacing soon anyway? The existing 1970's one is rotten. So I'd better sort out a new box sash window.

And of course to do that I'll have to get a new stone cill cut as some muppet ripped the original one out.

Changing the window will mean that the tiling in the kitchen will need to be re-done. And I'll have to move a power socket. And take a kitchen cupboard out, temporarily. Oh, and I'd better finally get some architrave machined to the same profile as used in the rest of the house, to go round that new window - been meaning to do that for ages, there's lots of places round the house where I need some.

And whilst I'm taking the plaster off I may as well move those heating pipes that could be much more neatly routed. If I'm doing that then the radiator in the room they feed may as well get moved whilst it's all drained down, been meaning to do that for ages as well.

Nearly forgot, kitchen will need re-decorating after all that of course. As will the room where the radiator gets moved.

Please tell me that it's not just me that this series of "well whilst I'm doing that I may as well......." always happens to!!

 

[Schoolmarm]

It isn't just you. It stops me from doing any jobs at all.

 

[Penners]

Please tell me that it's not just me that this series of "well whilst I'm doing that I may as well......." always happens to!!

Just you? In your post above you've just summed up the entire process of period property repair and conservation. I think it was Pythagoras who explained it all succinctly in mathematical terms:-

Job A = sum(Job B + Job C + Job D + Job E + Job D) unless Job E = ∞ (which it usually does)

 

[Feltwell]

:lol:

It could explain why I rarely get round to decorating a room.

I hate quick fixes, and am a perfectionist. Therefore, as decorating is nearly always the last job, I never get to it. As a myriad of other jobs, each of which will affect the decoration, come first (or rather never get done first!)

My last house looked beautiful when we moved out. That was because over half of it got decorated (for the first time ) in the month before we put it up for sale!

 

[Schoolmarm]

My last house looked beautiful when we moved out. That was because over half of it got decorated (for the first time ) in the month before we put it up for sale!

Are you my twin?

 

[Jon Maine]

Triplet?

However I made sure I finished this one before we moved in.

 

[Schoolmarm]

:lol: :lol:

 

[Cloudscape]

My last house looked beautiful when we moved out. That was because over half of it got decorated (for the first time ) in the month before we put it up for sale!

Quadruplet?

We also left behind a very new (and fab) shower room and a brand new bathroom - we finished it the day we moved out. I still wonder if the bath was comfortable or not.