How to do 5m "horizontal" valley

[bazmdiy]

Hi all – Please can someone help with the detail of a “horizontal” roof valley?

I am building a single storey extension made up of 2 pitched roofs. The valley in between is 5m long and horizontal (but can be made to have a slope of say 30-40mm in 5000. The base of the valley is a 5m 250mm oak beam. The valley discharges water onto a pitched eaves.

My original instinct was to have a 5m run of lead but reading about the minimum recommended lengths of lead I’m now having second thoughts.

Does anybody have experience of creating such a valley and is there a danger of condensation under lead?

I attach drawing.

Many thanks

View media item 49602

 

[doitall]

Lead is the best if it's done properly, and also oiled when finished.

You should have a roofing paper under the lead.

Best get a roofer that does lead work.

 

[^woody^]

Lead is the best if it's done properly, and also oiled when finished.

You can't have a flat horizontal lead gutter 5m long. It will have to be stepped

EPDM in one peice may be better

 

[doitall]

Lead is the best if it's done properly, and also oiled when finished.

You can't have a flat horizontal lead gutter 5m long. It will have to be stepped

EPDM in one peice may be better

You could if both ends are floating.

 

[Roofer]

The best way is to use lead with expansion joints

http://www.britishlead.co.uk/t-pren-expansion-joints.htm

 

[doitall]

The best way is to use lead with expansion joints

http://www.britishlead.co.uk/t-pren-expansion-joints.htm[/QUOTE]

I be darned Roofer, didn't know they made such things. Any idea about the longevity of the joint.

 

[Nige F]

A big consideration with the planned gutter - is access to clean out leaves/debris

 

[bazmdiy]

Hi all and thanks for enlightening replies.

Doitall got me thinking. I think there may may an exaggerated fear about the expansion of lead so I looked up the extent of the problem...

It turns out that 1m of lead will expand/contract 0.028mm for every 1°C rise/fall in temp.

If I lay my lead at 15°C and the temperature rises/falls to say 45°C/-15°C then 1m of lead will expand/contract by 0.028 x 30 = 0.84mm. 5m will expand/contract by 4.2mm. If the lead is fixed in the middle (or even unfixed) it allows the ends to expand/contract by 2mm. I think this is manageable.

I would go with lead if anybody can advise about condensation?

Cleaning the valley is not a problem - access via flat roof.

Roofer - I found the t-pren joint would do the job but it would require someone to weld and it would treble the price of the job. I think it would ideal for a very long gutter.

 

[Nige F]

it allows the ends to expand/contract by 2mm. I think this is manageable.

I would go with lead if anybody can advise about condensation?

.

have a look @ www.leadsheet.co.uk/lsa-pocket-guide Substrate underlays and ventilation you might get away with one length if it`s free to move and not nipped anywhere by tilebattens etc. I did a job some 25 years ago with a sheet aprox 7 foot by 3 foot over a lean to kitchen roof extension - One concealed fixing in the middle of the sheet on a 20 degree pitch . NOT to spec as it should have been copper nailed @ the top - but I went there again recently with the builder ( a glass panel in the roof had cracked ) and the lead hadn`t moved at all . I said @ the time , if there was any trouble I would have done more fxings Free of Charge - seeing as I reckon I`ve got 25 years left where I could still do it - I`ll call it a Lifetime guarantee . I went to school with the builder .We both left in 1970 . Why wasn`t it fixed @ the top with copper nails , because the lead laid on a sheet of celotex insulation - so you`d have been hard pressed to get nails long enough . Good enough for a country job by a P*key Plumber

 

[doitall]

You need something like this, although a roofer will probably have an off-cut you could buy.

http://www.sandpipersupplies.co.uk/shop/buy/ALM/Geotec_Lead_Underlay:_25mtr_x_1mtr_Roll/

Condensation isn't usually a problem for this type of work, and I wouldn't worry too much about it.

http://www.buildingconservation.com/articles/leadsheetroofs/lead-sheet-roofs.htm

There's also some good stuff in the lead book Nige posted

 

[Roofer]

When lead is laid in oversized lengths or bays, failure (cracking) occurs because of metal fatique.

If the lead is in a sunny, exposed situation then this failure is much more likely to happen than in a shady, sheltered situation.

But there is no way that you can lay lead in a continuous 5 metre length without early failure.

This table shows maximum recommended bay sizes


http://www.leadsheetassociation.org.uk/maximum-recommended-sizes-of-sections-bays-and-panels

 

[Nige F]

Well I was thinking the OP would use code 8 lead

 

[bazmdiy]

Lots of ideas - thanks very much. I've now got a lot more confidence in this job

Sensibly it would appear that 3 t-pren expansion joints would be the way to go. But I think it will look ugly and be a big expense. I can't have drips unless I expand up the rafters but I'll see how bad that looks. Will also see if I can get a middle joint so half the rainwater goes to the flat roof. Thanks for the Geotile tip and the lead assoc guides.

Nige F - I'm suprised you thought I was thinking of code 8 lead - I thought maybe code 15 (6.35mm thick)

Another reason for having second thoughts about a single lead piece is the weight issue - code 5 at 6m x 600 = 91.5kg

I'll post my solution when I get there...

Many thanks

 

[hardmetalking]

Just finished 4 of the same in Middlesex. We used 0.4mm stainless steel. The whole thing weighs less than 20kg and is guaranteed for over 100 years. To avoid the condensation issue I would bituthene the valley first, always good practise.

£500 cash supply and fix including lifetime guarantee.

 

[^woody^]

If I lay my lead at 15°C and the temperature rises/falls to say 45°C/-15°C then 1m of lead will expand/contract by 0.028 x 30 = 0.84mm. 5m will expand/contract by 4.2mm. If the lead is fixed in the middle (or even unfixed) it allows the ends to expand/contract by 2mm. I think this is manageable.

You would be foolish to think that is how lead will expand.

Your gutter will be subject to differences in exposure and temperature along it's length, and the expansion/contraction will never be linear over the whole section length.

It will develop fatigue cracks every 1-2m if you use a single length