Flat roof fail

[D0GMAN]

@sxturbo thanks I get it, as I said, clearly we've been far too trusting and accommodating but have been on their case repeatedly but maybe not forcefully enough. This is not some cowboy builder though, they have been trading under the same company name, his own name in fact, for over 20+ years with seemingly a good reputation and is quite well known in the area and done work on several minor celebs homes. The chance of him folding up shop only to open up with another name strikes me as remote. They might very well do amazing work 99% of the time, maybe its just my bad luck he cocked it up this time, but cocked it up he clearly did and for whatever reason is shirking his responsibility to correct the mistake. Getting the roof fixed properly and not just a temporary botch will require a proper independent inspection/survey as you suggest, which we're looking into. I imagine converting it to a proper warm roof is going to cost several thousands.

Yes it does have a parapet perimeter around the roof. In fact the roofer keeps complaining that the reason for the leaks is because the boss man refused to remove the coping stones as he asked so he could lay the felt underneath them so he had just to felt up to them.

 

[sxturbo]

Ah ha, bingo.

It's a parapet wall, no wonder your having so many issues.

The parapet is built and detailed all wrong and the roof has been installed wrong.

I've been there with this, except my roof was a warm roof.

Parapet walls are expensive to do right and cheap to do wrong.

My fix and was the cheapest fix, I went for a fibreglass roof, and had it all molded as one piece that went up and over the parapet with a drip edge set 40mm set away from the wall, (I had no coping stones, yours would need to be removed)

It would work better as a warm roof which was originally specced.

 

[D0GMAN]

it’s not actually clear what the roof construction is.

it sounds like it may be a “hybrid roof” - where the insulation is in between the rafters but directly below the roof deck.
Are there firrings between the roof joists and the deck? - and does this leave a void between insulation and deck?
if you have downlighters do they penetrate the insulation?

You might want to look at Steve roofer

Funnily enough I watched that video about an hour ago! My understanding is that with a hybrid roof you have some insulation above the main deck which there isn't in this case. What we have above the plasterboard ceiling is no vapour barrier then an air gap of 100-150mm, the insulation layer then another air gap of around 50mm, then the deck and felt. Here's a couple pics (if they show up), can provide more if requested.

20160523_121638

• D0GMAN
• 7 Nov 2021

20160630_170914

• D0GMAN
• 7 Nov 2021

 

[Notch7]

Yes it does have a parapet perimeter around the roof

Parapets need a cavity tray and a proper closure….or they leak.

NHBC details:

https://nhbc-standards.co.uk/6-supe...l-masonry-walls/6-1-17-dpcs-and-cavity-trays/

type J2 dpc support and closure

https://www.roofingsuperstore.co.uk...MI6Z6x6aKH9AIVje3tCh0XkwUdEAQYASABEgIUmvD_BwE

 

[D0GMAN]

The parapet completed roof.

IMG_0062

• D0GMAN
• 7 Nov 2021

 

[Notch7]

What we have above the plasterboard ceiling is no vapour barrier then an air gap of 100-150mm, the insulation layer then another air gap of around 50mm, then the deck and felt. Here's a couple pics (if they show up), can provide more if requested

exactly what I feared - insulation has been done in between the joists flush to the top, then the firrings above.

What is sad is the carpentry is lovely and neat….and about as wrong as is possible.

I used to run a business building high end timber orangeries and have loads of experience doing roofs like yours.

To create a warm roof, we used small joists, then firrings, then 11mm OSB, then insulation, the deck - it’s tricky to work out because the firrings are below the insulation.


For your roof which has a small lantern and biggish span of joists, a cold roof is needed to keep the roof build up to a minimum. However cold roofs need insulation below the joists and make downlighters an issue.



Unfortunately your roof is going to have to be stripped and rebuilt, I see no other option for a permanent fix.

As it is it will continue to suffer interstitial condensation and a leaky wall cavity.

 

[dilly]

Your best option maybe to approach the builder and explain you would like to get an independent surveyor in to check the work and you would like him to agree to a surveyor which you both agree too.
If he agrees make sure you have a paper trail of the agreement.
If you go ahead and instruct a surveyor he could argue that the person you have picked is not independent and you will have wasted money because the court will make you pick one both parties have agreed.

 

[D0GMAN]

The architect drawings do specify cavity trays. Whether or not they were put in correctly I cannot say, likewise with the closure.

It would work better as a warm roof which was originally specced.

No, actually a warm roof wasn't in the original spec. When I alerted the builder to the initial problems he insisted that what they had constructed was a warm roof which I think he actually believed, maybe that's what they usually do but didn't in this case perhaps due to height restrictions, I'm not certain. But the architects document specifies the insulation to be placed between the joists so making it a cold roof.

 

[D0GMAN]

@dilly thanks for the advice, I will do that. Giving him till the close of play tomorrow then will inform him of our intension to seek the legal option.

 

[Notch7]

I can see the roof falls have been created using counter batten firrings.

If all the firrings were removed (including those sitting on the joists), then new firrings setout diagonally to the joists and thinner so they go down to say 10mm around the edge, then 18mm OSG, then a bonded 120mm insulation, it may be possible to keep the roof low enough for the parapet and have a warm roof.

That way you could have a new roof without affecting the internal ceiling.

 

[Notch7]

Remedial work if possible as I suggested will be sort of in the order of £4k - £5k mind you, with Covid stupid prices who knows

 

[D0GMAN]

Thanks very much @Notch7 that's really helpful and giving me a lot to think about. I would prefer the warm roof option after the experience we've had and all I've read. Do you have a ballpark cost?

 

[D0GMAN]

Oh, just notice your reply, thanks, that's roughly what I thought

 

[Notch7]

I would prefer the warm roof option after the experience we've had and all I've read.

height is the problem with a warm roof.

Is another course of bricks on the parapet a possibility (how does your extension height compare to drawings used for planning consent?

A cold roof would mean stripping all the internal ceilings - and I think ventilation around the lantern won’t be that successful, cross flow won’t work too well as there will be dead spots with no cross ventilation.


It’s a real shame as generally the work looks nice and neat - clearly not a cowboy builder, just one without experience of warm / cold roof detailing.

Was it a private building inspector

 

[D0GMAN]

I think height limits has a lot to do with what has gone wrong. I remember some conversation about them struggling to keep it under a certain height and that it might be a couple inches over and joking that the building inspector probably wouldn't check. I can only guess that 9 times out of ten they do a warm roof but were forced to do a cold when height became an issue at some point. Definitely not cowboys, in fact we got on very well with all the construction lads who were hard working and pleasant to deal with and have no other issues than the roof.

One other thing worth mentioning, the roofer who came out the other day also pointed out which I hadn't so far noticed was that the paintwork all along on the outside render at the top of the wall in the area just below the coping stones was becoming powdery. He was a little sheepish pointing it out, probably concerned if he was giving me more ammunition to use against his employer. But clearly another sign that something was very wrong up there.

The building inspectors were directly from the local council, not private.