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Addendum: Re-reading some of the suggestions I may have misunderstood on my first pass. Will give them some further thought - thanks. 

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The builder visited today…

 

He was actually very good about the situation and quickly held his hands up once he’d checked and measured the firring strips himself. Whilst the finished roof does drain, and in his opinion wouldn’t prematurely leak, he acknowledged that its fall was below-spec it was my prerogative to be concerned and to expect a remedy. To this end we came up with a few options; the choice of which is entirely mine and he will pick up the bill:

 

  1. Leave As-Is – He would give me a guarantee in writing that should the roof fail in the next x years (to be agreed) he would repair/replace and make good any consequential damage. To give me greater confidence he could also get the roofer to add another layer of the liquid membrane to the existing. He would also refund the initial £1000 roofer cost.
  2. Remove and Rebuild – Rip up the entire roof deck (membrane and trims, top boards, insulation, bottom boards and firring strips) and replace (likely with bought firring strips this time – he had no idea they were available off-the-shelf hence why he always cut his own, normally without making a mistake with the measurements!)
  3. Overboard and Recoat – Keep the old roof in place (bar the trims), add a new layer of OSB3 on top of suitable firring strips to give the correct fall and put a new waterproof coating on top.

 

I am not comfortable with option 1 as whilst I trust his word regarding the guarantee (we live in a small town, him and his son just down the road from me; there’s nowhere to hide!) my preference here is to avoid a leak in the first place rather than deal with one if/when it happens. I’d also like to draw a line under the situation rather than leave things hanging over me/us.

 

Option 2 was my initial preference as this gets me back to the position I was in before the mistake happened and therefore not be considered a ‘bodge’ in any way. However, his initial thoughts were that it could cause more problems than it solves. We didn’t get into too much detail about it but his concerns were about the destruction required as with all the fixings now hidden there’d likely be a lot of ‘coercion’ of materials and could lead to damaging other components. Might be worth pushing further though, particularly as I'd be more than happy to help with the removal side.

 

Option 3 sounds like a viable option as not only does it give me the opportunity for a new waterproof coating (I am leaning more towards a single-sheet EPDM membrane rather than another liquid coating - ever since it went on my confidence in it has not been the greatest as it is far from conventional and so seemingly not much information about it) but the extra board/membrane layer may also provide an additional noise and solar barrier? I certainly wouldn’t ever expect a leak through two surfaces either, at least not down into the living space! I am wondering about potential downsides though... It would add ~50mm to the roof height at the rear wall abutment which would eat into the 150mm lead flashing and the roof lantern upstand would require extra timber on top to increase its standoff height. Could there be a risk of interstitial condensation with this extra layer or would it be okay given it is on the cold side of the insulation? Should the gaps between the firring strips be filled with anything? (Note the strips will likely be 40mm to zero over a 3m span so not much volume there).

 

As before I would be grateful for your thoughts. The builder is being completely open and supportive of the situation and keen to make sure I am happy with the outcome – I just need to work out what the best outcome should be!

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What does building control want to sign it off? Surely that’s one of the main considerations? 

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Firstly, well done to your builder!  Probably less than 1 in 10 would offer these options.

 

I would go with option 1 but perhaps negotiate on the money.

 

Option 3 seems a bit of a bodge.  They will need to penetrate the existing membrane to fix the firrings and new deck.

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Option 2 and his wife's recipe for lemon ice cream! :)

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2 hours ago, newhome said:

What does building control want to sign it off? Surely that’s one of the main considerations? 

 

Good point. I've been so focused on finding the best practical solution (for me) I have forgotten to consider what BC might be happy with.

 

I did ask the builder what he thought and he reckoned BC would likely not be concerned as their focus is mainly driven by aspects of legislative interest e.g. safety, conservation of energy etc. I didn't feel he was wriggling out of anything, just expressing his opinion. I do know there's nothing in the regs about roof falls and all my informal chat with BC (not my BCO as he's on holiday) reveaaled was that there is a general requirement for good workmanship which in turn tends to require compliance with recognised standards. The thing is, BS6229 'Flat Roofs with Continuously Supported Coverings' seems to actually be a 'Code of Practice' which might mean it's not quite so black and white. Upstand and flashing details might however be.

 

I will pin my BCO down and see what he has to say on the matter, whether that is from a formal regs perspective or informal advice, so thanks for the prompt.

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2 hours ago, Mr Punter said:

Firstly, well done to your builder!  Probably less than 1 in 10 would offer these options.

 

Yes, refreshing isn't it. It might be easier if I had something to push against though then I would insist on it just all being redone and be done with it!

 

Quote

I would go with option 1 but perhaps negotiate on the money.

 

Option 3 seems a bit of a bodge.  They will need to penetrate the existing membrane to fix the firrings and new deck.

 

Option 3 does have a whiff of bodge about it, and is the sort of thing that might be expected to be done when reroofing a previously-failed roof. Not really something one would expect of a two-week old example.

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I think with Option 3 I'd be worried about creating cavities allowing condensation and or insect / vermin ingress.

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Option 2.5 (as I suggested before)? I.e. remove the membrane and ply then start again from there? I too would think creating a cavity would be a bad idea. Thought you could get insulation with the appropriate slope already cut? Seconds and Co used to have lots of it because people had it cut to specific (wrong) sizes.

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On 18/09/2018 at 18:46, Onoff said:

Option 2 and his wife's recipe for lemon ice cream! :)

 

I'm leaning that way (perhaps not the ice cream though, I don't want to be seen to be taking advantage of the situation 😁).

 

A restrip and rebuild does at least put me back in the same situation as if nothing had happened, assuming of course that the builder's concerns about damage don't come true. I'm not quite sure what the issue is, perhaps it was a concern over the time it would take to do it carefully but I'm more than happy to get up there with a magnet and find the fixing screws and then remove the liquid membrane myself in those areas ready for unscrewing. Perhaps that's when I'll discover how good this Desmopol is when I fail to strip any of it off!!

 

Perhaps the BCO might say it is the most sensible option (for me) and everything else is a compromise even if they are content with them from a compliance perspective.

Edited by MJNewton

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@MJNewton

It's very common on large commercial buildings that use single ply membrane roofs (membranes like yours) for the membrane to be laid completely flat for example along very long and wide gutter runs (most large new Tesco stores are done that way) so IMO there's absolutely zero chance of your roof leaking due to a slightly shallower angle of fall than the 1:80 recommendation.

 

It sounds like your builder is one in a million! If it were my roof I'd definitely go with option 1.

 

I'd agree with your builder that Option 2 carries a risk of creating unintended damage elsewhere which might mean that you end up with a worse job than the original.

Option 3 carries a significant risk of creating a problem with interstitial condensation in the zone between the 2 roof skins.

Edited by Ian
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How deep can the liquid membrane be laid?? 

Is there enough depth to get you nearer your target fall.

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It is self-levelling and so I imagine it could be difficult to build up additional layers to create a fall. Besides which, we are upto ~20mm short and so it could cost several thousand to build it up that much... it certainly wouldn't ever leak though! 😉

 

There was a bit of a development today; the builder phoned to say he'd spoken to the manufacturer and they said their product can be used even at zero falls and would provide a written guarantee (materials only) to that effect. I got the impression that he's now thinking that whilst he might not have got the normal fall right he's not actually ended up doing any wrong. He gave me their number and they confirmed the same thing, although they did concede that they don't have a BBA certificate that explicitly says this. The BCO is visiting tomorrow and so I will see what he thinks of that - surely BBA certs are important to demonstrate compliance with the regs and if that says a fall of 1:80 (recommended 1:40; it basically seems to be a copy and paste of BS6229) is assumed then surely it's not valid at anything less?

 

I also raised with the manufacturer that there were some runs and what looks like pinholes/bubbling in some areas... The roofer had previously said they were of no concern but the manufacturer didn't brush these off at all; indeed they have asked for photographs as they said this could be a sign of poor installation... When the weather gives me half a chance I'll be taking some and sending them over.

 

Next step BCO (tomorrow) and, somewhat unusual I imagine, I hope they are going to be strict about what is acceptable here!

Edited by MJNewton

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Bit more of an update...

 

The BCO came out and listened to my concerns about the falls. He wasn't half as hard-lined about it as I thought he was going to be but did say he'd go back and speak with his manager about the situation, and he also said we should wait for the membrane manufacturer's opinion on the quality of the application as it could make the fall situation a moot point...

 

And it looks like it has... The manufacturer phoned me today and said the application of their product in this instance was 'shocking' with numerous issues including pinholing of the surface, the wrong joint tape being used, uneven thickness etc. They are going to put everything in writing on Monday.

 

I told the builder and he told the roofer. Both seem to be fuming and will be visiting site next week with the local supplier/trainer of the product used as the roofer seems adamant he hasn't done anything wrong. Not particularly looking forward to that one as I don't like criticising people's work, particularly in front of others, but I will have to at least point out all the bits that I sent photos of to the manufacturer so that they can all see what they've seen.

 

So, in my view, the fall issue has been overtaken by the membrane installation issue now. If the manufacturer isn't willing to provide a guarantee against failure in this instance then nobody else is in a position to do so either so that's my option 1 (leave as-is) gone. If the report says that water may have already got through then I think the line I'll be taking is that I want the whole roof structure stripping back to the joists (option 2) as if the roof structure was built well enough to keep moisture out then if any water does get in their it's going to stay in there and I'm not at all happy about that. With the roof stripped back we can of course then put the proper firring strips in before building back up.

 

I've been really enjoying the building of the extension so far but this whole roof business has really left a sour taste which is a real shame for all concerned. Hopefully one day I'll look back and laugh about it.

Edited by MJNewton

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Your not criticising the roofers work the manufacturer is. Just have it in black and  white what they reckon is wrong and show it to them all. Either the roofer done it wrong or he done it wrong because he was shown it that way by the local supplier/ trainer. Doesn't really matter either way. If it's not right it's not right. 

As you say the manufacturer won't give you a gaurantee so leaving the roof as it stands isn't an option. Only one left is strip it back and start again. And take lots and lots of pics this time.

Can the manufacturer give you drawings /pics of how it should be done so you can compare these to the work that will be done on the new roof so you can keep a beady eye on it as it is being done. 

Ask the local supplier when he is out is he able to call in and check the progress as well.

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7 hours ago, MJNewton said:

I've been really enjoying the building of the extension so far but this whole roof business has really left a sour taste which is a real shame for all concerned. Hopefully one day I'll look back and laugh about it.

 

I think you should look at it and think that you have correctly operated the "inspect, check,  correct" part of the process.

 

Catching it earlier than you could have done (eg instead of after the lantern was one) is a saving over worst case, even if it is a cost over best case (ie spotting the wrong angle on the firrings before they were installed).

 

It may not be an A+, but nor is it a D-.

 

Ferdinand 

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Thanks both. I must keep reminding myself that any negativity on my part is merely the result of observations of what's in front of me and if its wrong it needs calling out. Whilst it is wrong to expect professionals not to make mistakes (we are all human), it is only reasonable to expect them to be rectified once identified. 

Edited by MJNewton
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