Box Gutter.

[skipdiver]

Been asked by a roofer mate if i will form a box gutter between two roofs on an extension he is tiling at the weekend and was wondering if anyone had any links to sites with info about materials,gradients etc.

The extension has been built on a diy basis by the customer and is adjoining a previous extension.Both have hipped roofs joining in the centre on the same wall (outside wall of existing extension) which if you can imagine is an 'M' shape when looked at from the front with a box gutter to be formed in the lowest part of the 'M'.

To add to the (in my opinion) poor design,both roofs are cut into the main house roof,forming two valleys which will also add water flow to the box gutter.

Would have been a far better solution and less problematic in the long run to take off the roof of original extension and form a new one over both but it's done now and my roofer mate has been given a headscratcher which he has asked me to help with.

Despite being a joiner for many years,my experience of box gutters is virtually nil.Seems like a major future problem in the making to me but any info/advice would be appreciated from anyone who has come across a similar problem.

Cheers.

Steve.

 

[jeffinfrance]

i'd make it as big as possible, with as steep a gradient as possible and cover it in zinc.

you can calculate the total flow. 1 sqm of roof will throw off 1 litre of rain per mm of rainfall. check the areas rainfall records for 50 year peaks and make sure your gutter at the downpie can take the total volume.

hope this helps,

jeff

 

[jimi43]

And cut any trees back and give them a broom...they are going to keep an eye on any debris build-up.

Jim

 

[plug]

This is how we do them.
150mm outlet between the roofs, 1 in 80 fall, if using lead first bay is 1700mm long. 55mm step up to next bay and all the other bays are 1800 long. 300mm minimum upstand up the rafters.

 

[Jacob]

Needs to be well supported from below so that any movement or settlement won't stretch the lead, bearing in mind that it will be walked on many times during roof maintenance and leaf clearing etc.
Any internal corners want rounding off with fillets so that the lead is well supported and without sharp bends, or that is where cracks will appear first.

 

[Limey Lurker]

About 10 years ago, I made a box gutter for a bakery which was under notice from the local environmental office because of the water leaks over the ovens. I made a wooden tray which was about 20 metres long, and bought a "Plygene" liner for it. It was the easiest and best possible solution, and has never given any problems, and I strongly recommend that you use it. It's very simple to use and easy to fit. I can't give you any contact details, but they still advertise in the back of "Professional Builder" magazine which is free at Jewsons BM branches. HTH!

 

[skipdiver]

Thanks for the replies so far.

I think it will made from ply and covered in lead and i understand that the base will need to be supported.What i don't know is,do i cut the rafters back and form a proper square box between the rafter ends,or do i simply fix timbers across the existing rafters to form a base for the ply and put ply up the rafters forming a sort of flat bottomed delta shape?

Either way,the lead is going to be very wide?

So hard to try and explain things in words isn't it but appreciate the efforts guys.

 

[plug]

Leave rafters in, fix supports accross rafters and ply up the rafters. As the valley gets wider you will need a mop stick down the middle of the bays so the lead sheets can be joined. eg \_._/

 

[plug]

http://build-rite.co.uk/images/DSC00030.JPG

 

[skipdiver]

Thanks plug and the others that have posted.

It's a lot clearer now and that picture helps a lot.

 

[MickCheese]

I have a box gutter I inherited with my house. It is a complete pain. Never completely water tight. It seems expansion and contraction is the problem.

I have replaced the roof and as hard as I try to seal the gutter in really heavy rainfall there is always a few drips in my workshop.

And the comment about cleaning is good advice. Even though it has no overhanging trees it still gets full of leaves.

Why would anyone design a roof with a box gutter is beyond me, all the previous owner has gained is about 8" in width by building right on the party line.

Mick

 

[dickm]

Not particularly relevant, but my late Mother's house was part of a 17th century rectory which had exactly that type of box gutter over the spare bedroom. Staying there when the girls were young (about 5 and 9) they got remarkably adept at placing buckets in the right places if it started to rain in the night.

I suspect the lead was replaced after a fire in about 1918, so perhaps a 50 odd year lifespan for the lead wasn't too bad. But still not a good idea.

 

[plug]

We build loads of leal valleys in fact I am building another one tomorrow, as long as the lead is installed correctly and the right thickness is used you should have no problems with a lead roof or valley for 50 odd years, it can last well over 100years.

 

[MickCheese]

After saying cleaning it out is good advice I thought I had better have a quick look at mine.

Managed to get out half a muck bucket of leaves, sand from the roofing felt of my workshop roof and a thick layer of moss.

Maybe it wont leak quite so badly next time it rains?

Mick

 

[wobblycogs]

We have a box gutter type at the front of our house (only one pitch drains into it but the front of the house drains to the back through the loft - stupid design). It leaked like a seive when we bought the place. We had assumed lead was the only option but our roofer convinced us to use fibreglass instead. Worked out about half the price in the end and was done in a day. Unlike lead it also doesn't need any steps making the box much easier to install.

 

[reynotted]

Yes you can form a box gutter between those roofs. You can go to Commercialroofingsydney website. You can find instructions and materials for gutter box and roofing things.