Flat Roof Insulation

smyth79

The flat roof on our extension is a warm roof construction with 150mm of PIR insulation. My understanding is that adding insulation between the joists could potentially cause condensation by moving the dew point inside the vapour barrier.

The drawing provided by our architect shows 100mm of acoustic rockwool between the joists, on top of the airtightness membrane rather than up tight to the roof, presumably to lessen the noise of rain hitting the PVC roof. Does this create the same risk of condensation as have insulation up tight against the underside of the roof?

Ginger83

https://www.boards.ie/discussion/2058349441/flat-roof-insulation

May I ask why the need for rockwool at all? Surely 150mm is well within regulations.

You are turning it into a hybrid roof.

Are you having heat loss problems?

Biker1

150mm PIR is more than adequate and no need for rockwool between joists. Just make sure the vapour control layer in the roof is also your airtight layer and properly connected to the airtight layer on the walls. (easier said than done). If your architect insists on another airtight layer at ceiling level, use a diffusion open type membrane there.

smyth79

https://www.boards.ie/discussion/comment/122078047#Comment_122078047

It is still under construction so no heat loss problems that I know of. I assumed it was for noise reduction when he specified acoustic rockwool. The ceilings aren't slabbed yet and I haven't put any rockwool in

smyth79

https://www.boards.ie/discussion/comment/122078492#Comment_122078492

The top vc layer is already in place with PIR and pvc membrane fitted so I will have to add the airtight layer at ceiling level

Ginger83

https://www.boards.ie/discussion/comment/122078692#Comment_122078692

Just something to keep an eye on - I had a warm roof done by a chancer and we couldn't understand why it was always freezing. It turned out that they had put insulation on the roof but left the three sides of the roof empty.

Have someone check everything.

smyth79

Thanks for the tip. Did you manage to get insulation into the areas where it was missing?

Mellor

https://www.boards.ie/discussion/comment/122078492#Comment_122078492

In a new build, it's obviously important than airtightness layers are continuous. It's less importing in an extension, how much less depends of the airtightness of the existing. There is little point building an super airtight extension, on leaky old house, as an extreme example.

Mellor

My understanding is that adding insulation between the joists could potentially cause condensation by moving the dew point inside the vapour barrier.

Yes and No. It can be below, in which case it must be ventilated. Or as mentioned, or it can be a hybrid which can be complicated to get right.

The drawing provided by our architect shows 100mm of acoustic rockwool between the joists, on top of the airtightness membrane rather than up tight to the roof, presumably to lessen the noise of rain hitting the PVC roof. Does this create the same risk of condensation as have insulation up tight against the underside of the roof?

Can create a risk. You would need to do a condensation risk analysis. It may well be for acoustics, but will still provide thermal resistance.
It's positioned as per a cold roof, but not ventilated. But the upper insulation may be insulating enough to keep it above the dew point.

As an aside, that detail looks like it was drawn in MS paint. The notes don't make a lot of sense either. C14 grade is for solid softwood, not engineered beams. It mentions battens, but none are shown.

Ginger83

https://www.boards.ie/discussion/comment/122079993#Comment_122079993

Ah our chancer left us with an uninhabitable extension. It was built with a grant and our local authority signed off the work without checking it so in the end a second grant was approved and the work was all demolished and rebuilt by another builder

chooseusername

https://www.boards.ie/discussion/comment/122082401#Comment_122082401

I thought that sounded familiar @Ginger83. Glad it all worked out for you.

Demolished and rebuilt, well done.

Ginger83

https://www.boards.ie/discussion/comment/122083040#Comment_122083040

It worked out in the end. I informed our building control authority that the builder had breached multiple building regulations during construction and during repairs but unfortunately they said that I had left them in a position where they were obliged to prosecute me because the onus is on the home owner to comply. I said come ahead sure I'll have the kettle on.

I was told it would be unpalatable to proceed and I was offered a second grant and a hotel stay with the costs paid. It didn't do the first builder any favours locally though

chooseusername

https://www.boards.ie/discussion/comment/122083185#Comment_122083185

"I was told it would be unpalatable to proceed"

Unpalatable, great word in the circumstances.

Ginger83

https://www.boards.ie/discussion/comment/122083335#Comment_122083335

Yeah I told them that I would have no problem whatsoever accepting the prosecution.

The part that was unpalatable was they realised that they would have been prosecuting a terminally ill wheelchair bound person for work that their council had signed off and paid for without checking. It would have been a bit of egg on their face moment

smyth79

https://www.boards.ie/discussion/comment/122080965#Comment_122080965

Thanks for the reply. Think I will stick with just the PIR. It should provide adequate insulation. And it sounds like the risks outweigh the benefits when it comes to the rockwool.

smyth79

Jaysus, that sounds like a nightmare. Glad you got it sorted out in the end

Ginger83

https://www.boards.ie/discussion/comment/122084333#Comment_122084333

Yeah all sorted and very warm now.

I cannot stress enough the importance of having someone independent checking the work because I speak from experience when I say there's absolutely no law when it comes to building. Yes there is supposed to be regulations however nothing can be done if your builder cuts corners unless you have five years to go through courts.

Mellor

https://www.boards.ie/discussion/comment/122084881#Comment_122084881

To say there is no law when it comes to building is simply not true. There is a clear legal mechanism, how do you think multi-million dollar projects get managed if builders could do what they like. I understand why you are saying that based on what happened to you - buts that's really just down to your inexperience as a layperson. I vaguely remember you mentioned it here before.

What building control told you is correct. It is the responsibility of the building owner. Same way that a car is the responsibility of the car owner, not the mechanic. The mechanic/builder is employed by the owner. Going to build control was not the correct way to deal with it. They are not there to supervise construction.
Obviously they recognised that it wasn't your fault so they didn't want to prosecute. They have that discretion, but they can't make up their own laws.

Ginger83

https://www.boards.ie/discussion/comment/122088114#Comment_122088114

Building in this country is an absolute free for all. All you have to do is look at all the houses falling apart in the west and as Irish as it gets the quarry was/is still operating. I even contacted safe electric about a potentially dangerous issue and they told me to go back to the clown who created it. Comical.

You could pay a builder money to start a job in the morning and if he never turns up you have no recourse unless you have the money to go legal and even then it might not be worth it.

I'm genuinely speaking from experience and that's without mentioning that it took two and a half years to get a vat invoice because we were being told we didn't pay vat…. on a council grant job

Mellor

https://www.boards.ie/discussion/comment/122089126#Comment_122089126

I'm aware you are speaking from your experience. But that was a layperson dealing with a cowboy builder, without a professional involved to administer. Cowboys exist, as many self builders will tell you. But it's a bit foolish to think that a professionals dealing with large projects daily screwed over the same.

As I said above, there is a really simply legal framework for administering building contracts. And I'm saying this from my experience, as somebody who deals with the builder on behalf of my clients.

Who supervised the work? Who certified the works. What happened when you claimed off their insurance?

You could pay a builder money to start a job in the morning and if he never turns up you have no recourse unless you have the money to go legal and even then it might not be worth it.

The small claims courts only costs €25. Pretty clear case. But the actual mistake there is paying in advance. That's not a good way to ensure work is carried out to the require standard. In your case, if the work wasn't completed to standard, the builder should have been paid. No IFs or BUTs.

I'm genuinely speaking from experience and that's without mentioning that it took two and a half years to get a vat invoice because we were being told we didn't pay vat…. on a council grant job

Did the council pay directly? Or did you pay (and be reimbursed)? A lot of people will ask to pay cash, builders are happy to take it. But makes it harder to get the paperwork in order after the wink wink cash payment.

Anyway, glad it worked out, and the council footed the bill for their laziness.

Ginger83

https://www.boards.ie/discussion/comment/122089476#Comment_122089476

Do you mind me asking what the simple legal framework is?

We just trusted the wrong company who led us to believe that they look after it all. We were trying to come to terms with a terminal diagnosis at the time. And I'm not talking about a one man band. I'm talking about multiple vans and even a shop although the locals won't support it since our story got out.

The council paid the grant directly to the builder without inspecting the work. We paid the balance and the following winter the problems arose. We gave them an opportunity to fix it and they bodged it. Maybe it is different on a full build where a builder knows he won't get paid but we had four independent reports detailing a 60k mess. My wife was told whoever built this thought I'd be dead and she would be none the wiser.

Mellor

https://www.boards.ie/discussion/comment/122091221#Comment_122091221

The framework is what you have allude to at the end.

Building control are there to regulate development, not supervise the builder for you. But it's easy to do that. Firstly the work should be under a contract that details that the builder gets paid in stages, the defect liability period, the builders insurance. Then you also engage a professional to administer that contract. In a nutshell, the the builder simply doesn't get paid until it's complete and the job certified.
If the builder is found to have been negligent after completion, then they have an opportunity to fix, then you do to their insurance.

If the professional who certifies or supervises the wok is negligent (and it sounds in your case that somebody from the council was) then you also have legal recourse from their insurance. People often try to undertake large projects on the home without professional help, and i'm sure it saves them money. But it also opens the door on all that risk and a dodgy builder.

Ginger83

Thanks for that. Can I ask what can be done if a building control authority refuse to do their job? What then?

Mellor

https://www.boards.ie/discussion/comment/122097335#Comment_122097335

Which building control authority refuse to do their job?
As mentioned above, Building control is not there to be a site supervisor for contractors.

If they after the project, the work is majorly noncompliant, the building owner is liable (eg mechanic and car example). The contract I mentioned above is to ensure if that there to happen, the owner has a clear and easy pathway to pass that liability to the builder and/or professionals who certified the work and caused the liability. That is a really fundamental principle of design and construction contracts.

For large very projects, the it could be required for professionals to have cover for 10s of millions.

Thespoofer

https://www.boards.ie/discussion/comment/122078884#Comment_122078884

When you say 3 sides do you mean on the upstands or in the wall cavity or what? I'd be interested in this. Thanks

Ginger83

https://www.boards.ie/discussion/comment/122102167#Comment_122102167

The so called builder did a parapet wall in single leaf. The inner leaf finished at ceiling height. He did a warm roof build up and got a company to pump beads into the cavity so we ended up with a 9 inch high empty space between the beads and the insulation on top of the roof

We gave them an opportunity to fix it and then found out that instead of insulating the roof correctly they double slabbed all the ceilings with an insulated plasterboard 😁

Mellor

https://www.boards.ie/discussion/comment/122105242#Comment_122105242

Insulation aside (which is obviously awful), that “detail” also causes a major waterproofing issue, with the roof covering presumably lapped into the outer leaf. Yikes

Ginger83

https://www.boards.ie/discussion/comment/122106171#Comment_122106171

It was a disaster. We had a thermal imaging and a building surveyor and a structural engineer check and none had ever seen a single leaf parapet wall with garden wall cappings. The structural engineer also said the roof span was one metre over the maximum allowed.

dannettesherry

Thanks for sharing!

SeanieRetrofitter

https://www.boards.ie/discussion/comment/122088114#Comment_122088114

That is naive at rest. There's tens of thousands of homes with fire safety, pyrite, mica, and god knows what other issues for which the clients/homeowners have zero comeback unless the government put in place a compensation scheme. The builders did what they felt like, and nobody held them to account.

Contractors doing dodgy work can- and do- disappear when too many people start coming after them. It takes very little effort to run a business through a limited liability company.

And on a good day, a trip to the circuit court costs 10k, 100k to the High Court. And will take years. That's your clear legal framework- risking throwing a ton of good money after bad over the course of years and hoping any judgement you get (assuming you win) can be enforced at the end of it.

You seem to think everything is the client's fault for trusting the professionals. What choice do they have?

You're technically correct though. There's lots of laws. Just no enforcement- certainly none available to the the average punter who hired the wrong contractor. Which is wildly different to a a multi-million project where the client can- and should- have their client rep keep tabs on the contract every step of the way. That's just not an affordable option for someone getting a small extension done.

Mellor

https://www.boards.ie/discussion/comment/122106888#Comment_122106888

If you think's that's naive, then you most likely didn't understand it.
And username/post history suggest you're a DIY home renovator? Meaning you're exactly the person my advice was aimed at.

There's tens of thousands of homes with fire safety, pyrite, mica, and god knows what other issues for which the clients/homeowners have zero comeback unless the government put in place a compensation scheme. The builders did what they felt like, and nobody held them to account.

The builders did what they like, ignoring the professionals who were certifying, breeched the building regs, and the contract, etc still got paid and then pissed off? I doubt that. As I said, I don't think you understood what I said, re-read post #22.

Cowboy builders do exist, and do dodgy work. But they don't get away with it under the professional/contractual scenario I described. You are are describing the builds where that was ignored to save money - to be clear there's nothing wrong with cutting out professionals/formality/contracts to save money. But it absolutely increases risk.

Contractors doing dodgy work can- and do- disappear when too many people start coming after them. It takes very little effort to run a business through a limited liability company.

Which is why you don't pay in advance, why liability periods exist, and why it's pretty sensible to ensure their insurance exist.
You don't need to go to the high court to make an insurance claim.

There was a thread the other day were a builder was showing a copy of his friends insurance, claiming he was covered under it. No matter how much cheaper that guy was, it simple isn't worth it.

You seem to think everything is the client's fault for trusting the professionals. What choice do they have?

What professionals are you referring to?
I'm saying using professionals will cost mode, but it protects you via the framework I outlined. People can cut those corners if they like, and it will save money. But you simply can't expect the same outcome.

To put it simply, Domestic building control is an opt-in/opt-out situation. People are free to opt out and lower costs, that comes with more risk. You can't then expect a safety net from the government when they risk turns into issues on site.
(Pica/Pyrite is different/complex issue, so government bailout was justified.)