my valley roof - have they done it wrong?

juan1972 · 28 Jan 2009

Hi

I've had various troubles with my new roof - but I've just checked how the valley is done, and I can only come to the conclusion that it is wrong, but would like more experienced opinions please.

The valley is EPDM (couldn't afford lead), but it is thick Rhepanol.

Personally, I am convinced that I need some sort of support for the tiles (they just lie onto the valley). Could I place some eaves trays under the tiles to stop the front edges of the tiles applying pressure to the EPDM

Also - take a look at the pics:

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The membane comes down the slope of the roof, goes under the last 2 batterns and then up over the valley boards (the valley boards lie on top of the rafters, not flush to them). Surely this creates a gutter in the membrane, meaning that if the tiles fail, the water will run down the membrane and collect in the mebrane gutter, and not run out on to the EPDM gutter? Thereby, pretty much meaning the membrane can't perform it's main task.

Also, I've had a bit of trouble with condensation in the cold snap and I'm pretty much convinced this design means there is way to little ventilation from the 'eaves'.

Can you give your opinions please?

Thanks

Roofer · 29 Jan 2009

Personally, I am convinced that I need some sort of support for the tiles (they just lie onto the valley). Could I place some eaves trays under the tiles to stop the front edges of the tiles applying pressure to the EPDM

You don't need any support for the tiles and it looks as if there is a plastic tray protecting the EPDM anyway

Surely this creates a gutter in the membrane, meaning that if the tiles fail, the water will run down the membrane and collect in the mebrane gutter, and not run out on to the EPDM gutter?

In theory yes, in practise any water will collect and either evaporate, eventually reach a level and overflow onto the gutter or flow to the end and discharge. Having said that I can't see a purpose to the bottom batten (perhaps it was a temporary fix to hold down the underlay from wind lift) and it could be removed and the underlay pulled down to improve the situation. But essentially water shouldn't get to the underlay - if you have a broken tile repair it. Tiles don't just break on their own

Thereby, pretty much meaning the membrane can't perform it's main task.

The principle purpose of underlay is to prevent positive air pressure from underneath combining with negative air pressure from above causing tiles to be sucked/blown from roofs easier. Its secondary benefit is preventing wind blown snow, rain or dust entering the property, an incidental advantage is to prevent water coming in when tiles are broken/missing

Also, I've had a bit of trouble with condensation in the cold snap and I'm pretty much convinced this design means there is way to little ventilation from the 'eaves'.

I would expect the vapour permeable underlay to prevent condensation (unless excessive amounts of water vapour is getting into the loft) but conventional eaves vent cannot be used in this situation; the only way to ventilate is with vent tiles

juan1972 · 29 Jan 2009

You don't need any support for the tiles and it looks as if there is a plastic tray protecting the EPDM anyway

Sorry, I should have mentioned that it isn't a plastic tray - it is a bit of DPC which they put there when I mentioned that 'surely the end of the tiles shouldn't be resting on the EPDM because any movement in the tiles could be abrasive'. They didn't even think of that. There is only DPC on one side of the gutter.

Having said that I can't see a purpose to the bottom batten (perhaps it was a temporary fix to hold down the underlay from wind lift)

I think it is mainly there to hold the EPDM down at the top of the gutter. I'm pretty sure they've done that wrong as well - cos the top edges of the EPDM goes into the roof space, under the membrane. I'm thinking that surely all EPDM should be totally sealed to the substrate?

in practise any water will collect and either evaporate, eventually reach a level and overflow onto the gutter or flow to the end and discharge.

I don't think this is a feature they've designed into the structure.

I've enquired about tile vents and plan on getting some. But I also don't like the idea of the concentrated pressure of the pointy edges of the tiles digging into the EPDM - I saw some eaves ventilation panels in the screwfix catalogue and thought that they may be good to spread out the pressure and to lift the membrane edge off the EPDM, because mousture on the EPDM is basically making the membrane edge stick to it, thus craeting a seal at the eaves.

Also, I think I've heard that the membrane shouldn't be hanging down into the gutter cos it will start to rot / lose it's breathable properties?

Or could I just use eaves trays to take the pressure off?

Thanks for your info - what do you think about these extra details?

Roofer · 29 Jan 2009

what do you think about these extra details?

I think you're being incredibly picky

because any movement in the tiles could be abrasive'

Do you really think significant differential movement is going to occur?

surely all EPDM should be totally sealed to the substrate?

Do you really think that any overlap of EPDM at the edge of the valley boards is going to make any difference?

because mousture on the EPDM is basically making the membrane edge stick to it, thus craeting a seal at the eaves.

And what exactly is wrong?

Also, I think I've heard that the membrane shouldn't be hanging down into the gutter cos it will start to rot / lose it's breathable properties?

This applies at a fascia situation; your underlay is not exposed and won't be 'breathing' where it laps into the gutter anyway

Roofing is not (and is not meant to be) a precise science. I personally think that the photos show that you have got a well installed roof (albeit an expensive one). Sit back, relax and give your roofer a break. If you have got a problem with condensation or even a leak I'm sure it could be easily sorted, whatever the cause it certainly won't be down to the petty items you are picking at here.

juan1972 · 29 Jan 2009

Yes, maybe I am being fussy, that's why I wanted the opinion of people who know a lot more about these things than me. So thanks for explaining these things.

It's just that it took 4 months of chasing my roofer to come and get him to fix the brand new render that cracked along it's length (he never called me back once). And the fact that I spent a LOT of money on it (because I wanted a really good job after the last roofer used code 3 lead for flashings instead of code 4) - means that I want to make sure I'm not going to be shelling out more money endlessly getting things fixed, when I could have armed myself with a bit more technical knowledge. And rather than finding out about things that might be wrong (only when they have caused some damage) I wanted be able to put my mind at rest that these things weren't going to be a problem and get on with all the other things I've got to get sorted on the house.

This forum is full of people giving thorough info, rather than the vague stuff I've had from the people I've got to work on the roof. Take a look at your answers, and notice that they are all based on your extensive knowledge. I don't have that knowledge, that's why I'm trying to learn more.

I hope you don't think I'm being narky or anything. I appreciate your answers.

Cheers

^woody^ · 29 Jan 2009

I'd prefer not to see any tile edge in contact with any valley felt (or lead) as there is a risk of perforation.

IMO, there should be a tilting fillet to lift the tiles off the valley EPDM

By the looks of things, any water running down the membrane is going to be held at the bottom as there is dip and a trap there caused by that bottom lath arrangement. Standing water at this location is not a good thing

My concern would be the longer term performance of this arrangement, as things start to weather and settle

IMO, I would have specified some 6mm ply to let the membrane from the roof lie nicely over the valley EPDM and then a lath and tilting fillet with some drainage slots cut into the back fixed to this .... and/or some eaves vent tray to kick the tiles up and allow drainage from the main roof

Alastairreid · 30 Jan 2009

I'd prefer not to see any tile edge in contact with any valley felt (or lead) as there is a risk of perforation.

ditto, bad practice all round.

IMO, there should be a tilting fillet to lift the tiles off the valley EPDM

and that is what you should look at doing! it will also give you an airflow under your tiles.

By the looks of things, any water running down the membrane is going to be held at the bottom as there is dip and a trap there caused by that bottom lath arrangement. Standing water at this location is not a good thing

i think he has shoved the dpc below this row of tiles to try and conceal this dip. looking at the longer term this is not ideal and should really be sorted properly.

juan1972 · 30 Jan 2009

IMO, I would have specified some 6mm ply to let the membrane from the roof lie nicely over the valley EPDM and then a lath and tilting fillet with some drainage slots cut into the back fixed to this .... and/or some eaves vent tray to kick the tiles up and allow drainage from the main roof

Yes, that's what I though even though there isn't great pressure on the EPDM, over time, lots of small movement will eat away at it.

By the looks of things, any water running down the membrane is going to be held at the bottom as there is dip and a trap there caused by that bottom lath arrangement. Standing water at this location is not a good thing

I think the main reason that this trap has been created is that they didn't lay the valley boards flush to the rafters - it sits on top, so the mebrane has to jump up about 20mm to get over the edge of the valley boards.

I know 'Roofer' was saying I was picky, but bad design fails eventually, and this design just hasn't been thought through - even I can see that as a layman.

I think the only solution, without ripping too much stuff out and redoing, would be as shown in the new picture - but maybe I'm wrong???

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Roofer · 30 Jan 2009

Whilst it is not standard practice (and therefore not a fault in the roofer's work) I agree that some sort of protective layer would certainly do no harm and may have beneficial qualities.

With regard to the valley construction, this once again is standard, the layboards are always installed on top of the rafters; only pitched valleys have the boards inset between the rafters. Your proposal to install a strip of ply has theoretical benefits but what water are you trying to remove? If the roof is done properly then there is no water on the underlay.

Let's all be honest here - this is the way that it is done in 99.9% of cases - it is totally acceptable practice and there is no in-built latent defect!

In this increasingly blame-culture industry together with over-the-top Specifications, Risk Assessments and Method Statements; clients and designers are all trying to over-engineer and over-specify what history has proven to be fit-for-purpose. If it ain't broke don't fix it!

juan1972 · 30 Jan 2009

I didn't know this was standard for valleys - I had been reading about pitched valleys (it's hard to find the info).

In this increasingly blame-culture industry together with over-the-top Specifications, Risk Assessments and Method Statements; clients and designers are all trying to over-engineer and over-specify what history has proven to be fit-for-purpose. If it ain't broke don't fix it!

Yes, in some ways you're right - but there's also a culture of doing things by half measures and it being 'someone else's problem'. It's throughout all industries. I don't do my work like that and people shouldn't have to just expect something that's 'alright' just because someone can't be bothered - and after they justify their high price by claiming they are better than everyone else, and slagging everyone else's work off.

If it was your house, would you do it like that? Honestly?

Alastairreid · 30 Jan 2009

All fair points roofer!
though the customer has had problems in the past with bodged jobs, and is now being overly cautious..........cant blame him really.

freddiemercurystwin · 30 Jan 2009

juan1972 said:
If it was your house, would you do it like that? Honestly?

Advantage juan!

juan1972 · 30 Jan 2009

Cheers alastairreid

Yeah, all I've wanted is someone to do a job properly and I've always trusted them. My electrician drilled through a water pipe, flooding the cellar. The plumber put the bath in the wrong way round and didn't notice until I mentioned it. My previous roofer used code 3 lead instead of code 4 to pocket a bit of beer money.

Wouldn't it be great if I didn't have to spend my free time trying to learn about their jobs, to make sure they are doing them properly?

Lots of them have just got used to their clients not having a clue, meaning they can do whatever they want. It's a basic lack of respect.

I know joiners/plumbers who take a real pride in doing the best job they can - that's the way it should be.

PS - before you ask, those people live in another country so couldn't work on my house.

juan1972 · 30 Jan 2009

Just so everyone knows - I don't want this to turn into a slanging match with 'Roofer' - he has given me some very useful advice on this forum as has everyone else.

Roofer · 30 Jan 2009

If it was your house, would you do it like that? Honestly?

this is the way that it is done in 99.9% of cases - it is totally acceptable practice and there is no in-built latent defect!

Yes - honestly, I would be happy with that if it had been done by someone else and would not ask them to change it. But even more honestly if I had done it myself I would not have a sag in the underlay.

What I'm saying is don't blame your roofer; unless you have asked him to do something specific to your requirements he will do what is accepted practice.

Even going back to your comment that he took 4 months to come back to fix a crack in the render; I assume that he only joined the new render to old - that is standard practice and a crack will sometimes occur at the join, the only sure way to avoid a problem is to render the whole wall - but it is not reasonable to expect him to do that unless you specifically ask him and he prices accordingly. The fact that he came back at all to re-do the work shows that he cares about his standards - an increasingly rare quality.

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my valley roof - have they done it wrong?

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