Downpipe rules

MouldyOldDough

Should the downpipe from the main house guttering - release the water via a spout on to the roof of my new extension or should it be carried across the roof to the extension guttering ?

As I see it - it should do the latter - not only to reduce the chance of leaks - but also to stop the spout from blocking up with leaves/moss and other roof debris / very difficult to clear...

Are there any rules on-line that I can quote to the builders ?

pramsay13

If they are your builders just get them to do what you want. 

MouldyOldDough

pramsay13 said:

If they are your builders just get them to do what you want. 

Are there any rules though - because I don't want to get the builders backs up !
Frankly - I am surprised that they didn't realise the possible problems already

Keep_pedalling

MouldyOldDough said:

pramsay13 said:

If they are your builders just get them to do what you want. 

Are there any rules though - because I don't want to get the builders backs up !
Frankly - I am surprised that they didn't realise the possible problems already

I think you are overestimating the potential issues, we have had exactly this set up for the last 12 years and no leaks or blockages have occurred. 

FreeBear

MouldyOldDough said:

Should the downpipe from the main house guttering - release the water via a spout on to the roof of my new extension or should it be carried across the roof to the extension guttering ?

Discharging on to a roof is quite common - You can get wide shoes specifically for the job, or fit a spreader device so that the water flow is not concentrated in one small spot.

To run a length of downpipe across the roof may not look pretty, and you also have problems with fixing it down so that it doesn't move in high winds.

Section62

MouldyOldDough said:

Should the downpipe from the main house guttering - release the water via a spout on to the roof of my new extension or should it be carried across the roof to the extension guttering ?

As I see it - it should do the latter - not only to reduce the chance of leaks - but also to stop the spout from blocking up with leaves/moss and other roof debris / very difficult to clear...

Are there any rules on-line that I can quote to the builders ?

Essentially the 'rules' are the building regs, and these are sufficiently generalised that I don't think you would be able to argue the case with the builders.

As pramsay13 says though, you are the client, so tell them how you want it done, but be willing to accept an additional charge for the work unless it was already specified in the contract they should do this.

Primarily it comes down to good practice.  I personally don't see much harm in a small roof area being drained onto a larger roof area (say a dormer roof onto the main roof) provided care is taken with the detailing.  I'd be less accepting of a larger roof area being drained onto a smaller one.

The issue isn't really one of blockages (so long as the downpipe is correctly terminated), rather the risk of the larger flow causing problems such as splashback onto the walls, leaking through gaps between tiles, or the flow down the tiles overshoots the gutter at the bottom and ends up on the ground.  All of which can be avoided through careful detailing... but then a builder taking the shortcut of draining the main roof onto the extension roof may not be that bothered about getting the details right.

grumbler

IMHO, discharging on a roof is a lazy way of doing this, but there are no rules. Personally, I'd do my best to avoid this.
My friend living in a very expensive house designed by an architect has a problem with water from a big roof discharged to a small roof (part of design, not an 'extension' really). As a result huge stream from the downpipe just flows over the gatter of the lower roof.

stuart45

If you take the downpipe directly into the gutter, the water often overflows at that point, unless a deep flow gutter is used. Having it discharge on the roof via a spreader is better in this case. The best way is obviously every downpipe going to ground, but it's not always possible
Have you got any photos?

MouldyOldDough

stuart45 said:

If you take the downpipe directly into the gutter, the water often overflows at that point, unless a deep flow gutter is used. Having it discharge on the roof via a spreader is better in this case. The best way is obviously every downpipe going to ground, but it's not always possible
Have you got any photos?

No photos - without taking one

MouldyOldDough

Section62 said:

MouldyOldDough said:

Should the downpipe from the main house guttering - release the water via a spout on to the roof of my new extension or should it be carried across the roof to the extension guttering ?

As I see it - it should do the latter - not only to reduce the chance of leaks - but also to stop the spout from blocking up with leaves/moss and other roof debris / very difficult to clear...

Are there any rules on-line that I can quote to the builders ?

Essentially the 'rules' are the building regs, and these are sufficiently generalised that I don't think you would be able to argue the case with the builders.

As pramsay13 says though, you are the client, so tell them how you want it done, but be willing to accept an additional charge for the work unless it was already specified in the contract they should do this.

Primarily it comes down to good practice.  I personally don't see much harm in a small roof area being drained onto a larger roof area (say a dormer roof onto the main roof) provided care is taken with the detailing.  I'd be less accepting of a larger roof area being drained onto a smaller one.

The issue isn't really one of blockages (so long as the downpipe is correctly terminated), rather the risk of the larger flow causing problems such as splashback onto the walls, leaking through gaps between tiles, or the flow down the tiles overshoots the gutter at the bottom and ends up on the ground.  All of which can be avoided through careful detailing... but then a builder taking the shortcut of draining the main roof onto the extension roof may not be that bothered about getting the details right.

This is a large roof (main house) draining on to a small one

The problem is moss on the main roof - blocks downpipes anyway as they are now - we get the gutters cleaned out annually

TELLIT01

MouldyOldDough said:

This is a large roof (main house) draining on to a small one

The problem is moss on the main roof - blocks downpipes anyway as they are now - we get the gutters cleaned out annually

Having the downpipe extending to the extension gutter wouldn't have any effect on the amount of moss coming off the roof and potentially blocking the downpipe.  I think it would potentially make the problem worse as, in my experience, the moss gets ejected from the end of the downpipe and onto the flat roof.  From there is gets washed across the flat roof and into the gutter of the extension from where it is easily removed if necessary.  An almost flat drainpipe across the roof could easily clog with the moss and other crud, making it more likely that the gutter on the main roof would overflow.  We've been in our current house 35 years and have only every had the downpipe block at the gutter union once.