Valley gutter construction

[Andrew Gabriel]

Any good websites describing how a sloping valley gutter (join between two roof faces) is supposed to be constructed?

[Adrian Brentnall]

I'm guessing you mean a 'gully' - where two roofs join (kind of like a

3-D mitre when viewed from above...?) If it's not one of these that you're looking for then the following details won't be any use

I did this a couple of years ago to make our new utility room - which sits out at 90 degrees fron the main bungalow.

Started off by setting up the roof trusses for the new roof (the 'at

90-degrees' bit).

Extend a line along the new roof trusses to show where the new roof-line intersects the old one.

In our case we had a series of 'mini-trusses' which stepped up the slope of the old roof - set these in position.

Then run one length of planking (think we used about 8" x .75") up the join - supported on timber packing pieces as necessary.

Work out what thickness of timber you need on top of this plank to make it all as deep as your roofing battens - and nail two lengths of it (maybe 1 - 1.5" wide) down the length of the plank (either side), to create a shallow 'trough'.

Then lay a roll of lead down the timber trough (cut the length and overlap if necessary - can be cumbersome to handle) and dress into the trough and flat across the top of the timber battens - tucking the roofing felt up and under the edge of the lead.

Finally - (the boring bit !) - cut the tiles to fit the angle of the gully and pack under the edge along the top of the lead with mortar. Run the bottom end of the lead into the gutter and finish off neatly.

This is what we did - not sure if it's the approved method - but the guy I was working with had many years experience in general building - so I can only hope that he knew what he was doing !

Hope the above is clear - if you need sketches / photos etc then please ask

Adrian Suffolk UK ======return email munged================= take out the papers and the trash to reply

[Andrew Gabriel]

Probably, although my surveyor called it a valley gutter.

Thanks. This is how mine is constructed except it has a plastic (fibreglass I think) rather than lead liner.

So where's the water which runs down the roofing felt towards the valley supposed to go? What it seems to have done is run down the inside of the junction of the roofing felt and mortar seal, eventually causing the felt to tear at that join (helped no doubt by a pile of waste mortar dropped onto the felt and keeping it in tension). OK, there isn't much water there, just the odd drip with the downpour and wind going on at the moment, but I don't see how it's supposed to get out.

[rrh]

I recently had two valleys replaced - not DIY but by a very experienced roofer whose skills I respect. He insisted that although the old valleys were sealed with mortar along the edges, that's not how they were supposed to be done. After some concern at the amount of daylight now showing from beneath, I must confess that they don't leak (at least the one I can get at...). I don't have roofing felt but if I did it would be the same: the water would run off into the valley and away.

[Adrian Brentnall]

Hi Andrew

Same principle, I guess

Is this water that's got in under the tiles ? If so - I'd guess it gets out at the fascia and into the gutter... or maybe I'm misunderstanding the problem.

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[Andrew Gabriel]

Yes.

Yes, in the case of the felt which runs down to the facia boards. But what about the felt which runs down to the valley gutter, and is then sealed in the mortar? Such water has no way out.

[Adrian Brentnall]

I hope I'm understanding this (difficult to explain without a diagram).

If water gets under the tiles, it can run down the felt until it meets the timber that makes the 'upstand' at the sides of the valley. At this point the felt is lapped up and under the lead (or fiberglass) - so the water then runs along the felt and down the _outside_ of the valley - finally emerging at the fascia & into the gutter. ISTR that we relieved the back edge of the tile battens a bit where they met the valley to provide somewhere for the water to go.

Hope this is clear...? - or maybe I've mssed it again ??

Adrian ======return email munged================= take out the papers and the trash to reply

[mark]

In message , Andrew Gabriel writes

There shouldn't be any water getting to the felt at all. The felt is only there for condensation and to prevent draughts. Its good practice to lap the felt over the edge of the valley board (usually 9 x 1) but there's usually several nail holes close to this area where the ends of the battens have been cut; its not intended to be water proof. Many people do not bother but a 1/2" tall triangular tilt can be fixed along the edge of the valley board to help 'kick' the slates up as they go over the valley board (top of the valley board and battens should be flush) mortar is generally to help secure the triangular end of a slate where a nail cant be fixed.

The above applies to slated roofs rather than pantiles.

[The Natural Philosopher]

Mine is just overlapping bits of lead laid about 15" up each side of the valley, with the tiles on top..each bit is about a meter long, laid bottom to top. Expansion or summat is why its not one long strip.

[The Natural Philosopher]

Rain does not run down the roofing felt: Thats what the tiles are for.

[The Natural Philosopher]

Runs down the edge of the valley and out of the soffits?

[Andrew Gabriel]

That's it. In my case the felt has rotted where it meets the upstand timber. I can't help thinking this isn't a very satisfactory design, which is why I was initially thinking mine must be done wrongly.

Ordered scaffolding today. I already had the facia boards to replace and some painting and repointing at the gutter line which I normally do on a ladder, but given the roof needs attention too, decided to go for full scaffolding instead.

[Andrew Gabriel]

Mine was originally one long lead strip. It failed after about

80 years due to cracking across due to expansion and contraction in the sun. It was then replaced with a fibreglass one, which is in two pieces (I presume because it doesn't come in long enough lengths).

[Andrew Gabriel]

Well, I will try and investigate where the water comes from. It was raining hard non-stop yesterday, and I think probably a cupfull in total came down the roofing felt, so it's not a large amount. I peered through the roofing felt overlap in other places, and there was no water running down it, but the concrete tiles were wet on the backs, so I could imagine a small amount getting in that way. I might find something like a cracked tile when I get up on to the roof. There is a bit of moss there, and it could be one or two pieces are forcing water back up behind the tiles (roof is not very steep).

[Andrew Gabriel]

Any recommendations for good roofing felt, preferably better than the black tar-cloth type? As per the Valley gutter thread, this is to be mortared into the sides of a valley gutter. I've noticed (white?) felt relacement used in some new houses.

[mark]

In message , Andrew Gabriel writes

Tyvek or similar. It isn't felt its a breathable membrane. My son in law wears suits made of Tyvek while working with nasties at the microbe level :)

think kingspan make their own called nilvent for roofs in fact :) Bit expensive though 70 quid a roll.

[Andrew Gabriel]

OK, that's probably what I've seen in newbuilds. However, breathable isn't required here as the roofspace is well ventilated. Properties I'm after are waterproof and longevity. Was thinking of using damp proof membrane just around the valley gutter itself.

[mark]

In message , Andrew Gabriel writes

It would certainly be waterproof; being dpm and all :) The trouble is the problem you've already got; the water tends to run down to here and finds its way in through nail holes/tears caused by the ends of battens being nailed down/positioned against the valley board. Dpm would be less likely to suffer than felt though, the 1200 gauge stuff is pretty tough.

[The Natural Philosopher]

My original valley gutters were the 'last straw' that had me demolish the house. Got 'a man' into fix em and things just got worse.

Be prepered to strip back a reasnonable section either side and redo it properly.

Bodging does NOT work for very long, if at all.

[Shane]

Have a look at Protect A1. Easy to work with and performs very well.

local building control guy wouldn't allow Tyvek (which is breathable) without using counter battens to leave an air space between the membrane and the tiles. Protect A1 is a good job in a roof that is already well ventilated.

All the best,