Cold bridge at new patio doors – sill resting on brickwork? Installer says “nothing more can be done”

[saveasteading]

It's been interesting to follow how strongly you are making this argument.

I think you are wrong, and have even started sympathising with the other party.

Reasonable care is judged by what skills they may be expected to have. In this case that would not apply to knowing all the building regs, esp as they apply to an existing property, and whether they are expected to write a long list of exclusions.

But the credit card company may decide on some other logic.

So I've no more to say.

[fandyman]

2 hours ago, saveasteading said:

It's been interesting to follow how strongly you are making this argument.

I think you are wrong, and have even started sympathising with the other party.

Reasonable care is judged by what skills they may be expected to have. In this case that would not apply to knowing all the building regs, esp as they apply to an existing property, and whether they are expected to write a long list of exclusions.

But the credit card company may decide on some other logic.

So I've no more to say.

That’s fair - we’re clearly coming at this from different perspectives.

Where I disagree is that reasonable care is limited only to what a trade chooses to concern itself with. It’s judged on the service actually provided and the outcome it creates, not on whether the installer considers certain aspects “out of scope”. I’m not expecting encyclopaedic knowledge of building regulations or retrofit design - I’m questioning whether an installation outcome that produces persistent condensation and mould under normal conditions is an acceptable result of the service supplied.

You’re right that the credit card provider may apply its own logic - which is precisely why I’m comfortable letting an independent process assess it rather than relying on forum consensus. At that point it becomes an evidence-based decision, not a matter of sympathy either way.

I appreciate the discussion - I think we’ve probably taken it as far as it can usefully go here.

[SBMS]

1 hour ago, fandyman said:

That’s fair - we’re clearly coming at this from different perspectives.

Where I disagree is that reasonable care is limited only to what a trade chooses to concern itself with. It’s judged on the service actually provided and the outcome it creates, not on whether the installer considers certain aspects “out of scope”. I’m not expecting encyclopaedic knowledge of building regulations or retrofit design - I’m questioning whether an installation outcome that produces persistent condensation and mould under normal conditions is an acceptable result of the service supplied.

You’re right that the credit card provider may apply its own logic - which is precisely why I’m comfortable letting an independent process assess it rather than relying on forum consensus. At that point it becomes an evidence-based decision, not a matter of sympathy either way.

I appreciate the discussion - I think we’ve probably taken it as far as it can usefully go here.

To round it off maybe.. I think your position is intellectually coherent, but a section 75 claim is not a forum for debating where industry responsibility ought to sit. It is about whether the installer breached their contractual duty as one would normally understand it.

 

It isn’t about whether the outcome is subjectively unacceptable, it’s about whether the installer failed to exercise reasonable care and skill in the service they actually provided. Notwithstanding the issue with poor sealing (which is unlikely to be the condensation root cause), In practice they’ll look at whether the door was installed correctly and in line with manufacturer guidance, and whether the opening and threshold construction were part of the installer’s scope or pre-existing building fabric.

 

Your industry expert will look at whether a competent door installer should have identified the sub-threshold detail as unacceptable and either refused to install or required a thermally broken support.  You’ve actually heard from a number of very experienced builders on here, a structural engineer or two and an actual industry expert that runs a door installation company. Whilst many have sympathised with you, none have agreed with your assertion and I think it likely that your industry expert will not find in your favour. I think it’s quite likely they’ll conclude the condensation risk arises from the underlying construction rather than a breach by the installer.

 

It is though, a fairly low risk approach for you to take.  Good luck and I am sure we would all be keen to hear back from you on the outcome. 

Edited December 30, 2025 by SBMS

[fandyman]

1 hour ago, SBMS said:

To round it off maybe.. I think your position is intellectually coherent, but a section 75 claim is not a forum for debating where industry responsibility ought to sit. It is about whether the installer breached their contractual duty as one would normally understand it.

 

It isn’t about whether the outcome is subjectively unacceptable, it’s about whether the installer failed to exercise reasonable care and skill in the service they actually provided. Notwithstanding the issue with poor sealing (which is unlikely to be the condensation root cause), In practice they’ll look at whether the door was installed correctly and in line with manufacturer guidance, and whether the opening and threshold construction were part of the installer’s scope or pre-existing building fabric.

 

Your industry expert will look at whether a competent door installer should have identified the sub-threshold detail as unacceptable and either refused to install or required a thermally broken support.  You’ve actually heard from a number of very experienced builders on here, a structural engineer or two and an actual industry expert that runs a door installation company. Whilst many have sympathised with you, none have agreed with your assertion and I think it likely that your industry expert will not find in your favour. I think it’s quite likely they’ll conclude the condensation risk arises from the underlying construction rather than a breach by the installer.

 

It is though, a fairly low risk approach for you to take.  Good luck and I am sure we would all be keen to hear back from you on the outcome. 

I think we’re actually closer in position than it might appear - though perhaps drawing different conclusions from it.

You’re right that Section 75 isn’t a forum for debating where industry responsibility ought to sit. That’s precisely why I’m not relying on what is customary, typical, or widely tolerated in the trade, but instead on independent assessment of whether the actual outcome of the service supplied meets the standard of reasonable care and skill.

Where I part company is the suggestion that persistent condensation and mould are merely “subjectively unacceptable”. These are objectively observable outcomes, not matters of taste, and they are exactly the kinds of issues that reasonable care and skill are meant to prevent - regardless of how common a particular installation detail may be.

You’re also right that an expert will examine whether a competent installer should have identified the sub-threshold detail and either mitigated it or flagged it before installation. That question sits at the heart of the dispute, which is why speculation about how often this is overlooked in practice doesn’t really resolve it.

I appreciate the confidence expressed about how an expert might conclude. I’m comfortable letting evidence rather than expectation decide that point. If the conclusion is that the underlying fabric alone is responsible, I’ll accept it. If not, responsibility will follow accordingly.

Either way, I agree - it will be interesting to see the outcome, and I’m happy to report back once it’s determined.

Edited December 30, 2025 by fandyman

[Spinny]

Can I add in another consideration.

From what you have described the complete window/door consists of multiple individual parts: The two fixed side windows with their own frame (presumably pre glazed with double glazing units), the central doors with their frame, and the cill piece itself which the other parts sit onto as a base.

 

Have you carefully checked the vertical and horizontal alignment of these different parts ? If for example the two side windows were fitted to the outer edges of the opening first, but the inner vertical frame edge ended up not being perfectly vertical, then fitting the door frame vertically against it would become a problem. Quite possibly a fitter might then choose to then fit the door frame perfectly vertical regardless. So there would then be a variable gap between the side frame and the door frame - quite possibly tight at the top, but with an increasing gap near the base. This could then be filled with mastic/sealant and appear normal. However there could be an uninsulated gap or path left between the fixed windows and the door frame at the lower part - thereby causing cold bridging problems.

 

In a similar way there could be misalignment and gaps occurring between the cill and the window and door parts fitted onto the cill - again possibly leading to cold gaps between the cill and frame possibly hidden by sealant.

 

I have to say it is a skilled and potentially time consuming task to assemble frames into an opening with precision such that all the verticals are spot on plumb and all the horizontals are spot on plumb level. Doors especially need to be true so they don't swing open/closed of their own accord etc and meet correctly when closed.

 

Anything other than expensive spirit levels are unreliable and can easily be out. Small alignment errors which many tradies might think 'good enough lets go down the pub' might mean installation gaps at the lower part of the frame and between cill and frames.

 

I might be barking up the wrong tree, but get yourself a long expensive known accurate spirit level (or plumb line) and carefully examine whether all the parts of the installation are properly plumb and tightly joined to one another.

 

(It took a second fitting visit to get our alu bifolds right and they sent their crack fitters that were at it until 7pm getting it all just so. And I imagine UPVC frames may show more bendability than aluminium.)

 

 

[Spinny]

Also that heat camera is showing the coldest strips at the bottom edge of the double glazed units i.e. just above the bottom frame where the glazing starts.

 

Could it be that the double glazed units were not a good tight fit into the frame itself, so that you actually have cold air finding it's way through the windows/doors themselves - underneath the base of the double glazed unit - i/e/ between upvc frame and DG unit.

 

Window companies may be ordering in ready made dg units to fit into their frames. They will NOT want the glass to end up too big, so it would seem quite possible for the dg unit to end up on the small size sometimes and perhaps not to fit tightly ?

Also there are usually seals between the glass and the frame - are these tightly fitting ?

 

I think it is usual to have a little lee way for heel/toe adjustments, but ultimately the entire door assembly should be perfectly air tight on both sides. If you fart outside you should not notice it inside :0). Maybe you could try some sort of smoke test ?

 

(In my youth I once had to travel around with a fire service chap for a few days as part of a business analysis - the height of his entertainment was taking out a phallic shaped smoke machine which hummed and emitted smoke from the tip to test the smokes. For some reason he thought it amusing to test the smokes in the headmistress office when visiting the girls schools ?!@)

 

[Spinny]

Go to ChatGPT and type in...

"Is it possible for cold air to pass through a double glazed door or window by passing around the sealed double glazed unit i.e. between this unit and the frame it is fitted into ?"

 

When Chat GPT answers and then asks you the frame type etc type in,,,

"a upvc frame which has been fitted a few weeks ago and comprises of a french door fitted between 2 outer fixed glazed windows"

 

(And the first 2/3 minutes of this video may be of interest...

https://youtu.be/rc5DutkQ0WM

Edited December 31, 2025 by Spinny

[fandyman]

6 hours ago, Spinny said:

Go to ChatGPT and type in...

"Is it possible for cold air to pass through a double glazed door or window by passing around the sealed double glazed unit i.e. between this unit and the frame it is fitted into ?"

 

When Chat GPT answers and then asks you the frame type etc type in,,,

"a upvc frame which has been fitted a few weeks ago and comprises of a french door fitted between 2 outer fixed glazed windows"

 

(And the first 2/3 minutes of this video may be of interest...

https://youtu.be/rc5DutkQ0WM

Thanks for taking the time to think this through in detail.
Some of the scenarios you describe - frame-to-frame alignment tolerances, bedding of the cill, or concealed gaps masked by sealant - are interesting. However, they all ultimately point back to the same issue: the assembly and detailing of a multi-part door system at the threshold.
If any of those conditions exist, they wouldn’t be characteristics of the existing building fabric but of the way the system has been installed and integrated. Small tolerances, hidden voids or misalignment at the base may be common, but they are precisely the kinds of details that affect internal surface temperatures and condensation risk.
I also note the suggestion that the glazing units themselves may be allowing air passage around the frame. If that were the case, it would raise a much more fundamental issue with the assembly and sealing of the system rather than with the surrounding structure.
Ultimately, the challenge here isn’t identifying ever more hypothetical mechanisms in isolation, but assessing whether the installation, taken as a whole, has resulted in an internal threshold detail that performs acceptably under normal occupied conditions. That’s why I’m seeking an independent assessment rather than relying on conjecture or what might typically be tolerated in practice.
I appreciate the input, but at this stage the question isn’t what might possibly explain it, it’s what is actually happening — and whether the installation outcome reflects reasonable care and skill.

[Spinny]

6 hours ago, fandyman said:

but at this stage the question isn’t what might possibly explain it, it’s what is actually happening — and whether the installation outcome reflects reasonable care and skill.

OK, but I don't see that there is any other method to identify what is actually happening other than identifying a list of possible hypotheses that might explain it, and then seeking to test and check these hypotheses one by one. It is what we call the scientific method.

 

Once there is an objective identification of the actual problem(s) it is possible to ascribe responsibility and whether reasonable care and skill has been used or not.

 

Unfortunately it is still often human nature for people to start by avoiding blame and attributing faults to other factors as your fitters are doing. They might be right or wrong, and what is needed is a logical scientific identification of the problem(s). Even bringing in other 'experts' can sometimes only generate more opinion unless there is some focus on establishing facts and evidence supporting or refuting hypothetical causes.

 

I will say that in my experience it is too common for some trades people to essentially ignore what the customer says on the basis that the customer is assumed to be ignorant, inexperienced, unqualified to comment etc. To try to be fair there are doubtless customers where this is true but in reality it should matter not who makes claims or statements, only whether they can be established as factually true or false. But I have also had 5 different plumbers give me 5 different opinions on a plumbing problem - some of them fairly obvious crap. However sometimes you do need to bring in somebody with letters after their name and direct experience (e.g. surveyor, engineer, architect, QS etc) to tell some tradespeople exactly the same as the customer is saying and to state the bleeding obvious, before they will remotely accept it.

 

I would encourage you to focus on rigourously identifying the problem(s), because even if you gain a section 75 financial settlement you will still need to get the doors replaced - and if you don't understand the current problem(s) you are likely to see them repeated on a new product/install.

 

It has been my experience in life that things are mostly like the saying about making a cooked breakfast - the hen is involved in the endeavour but only the pig is actually committed. Whether it is a health problem, a car problem, or a building problem you can seek help and opinion but in the end it is only you the pig that actually bears the problem and is truly driven and committed to getting a resolution.

 

Ignore the bullshit, the name callers, appeals to claimed 'authority', those that play politics, the insurers, lawyers, dissemblers, chancers and deniers etc. Find the truth, hold people to account - whether a window fitter, the horizon scandal, the blood transfusion scandal, grenfell, or hillsborough.

 

Find the truth, speak the truth, live the truth.

As the man said 'For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled'

 

Happy New Year

[fandyman]

42 minutes ago, Spinny said:

OK, but I don't see that there is any other method to identify what is actually happening other than identifying a list of possible hypotheses that might explain it, and then seeking to test and check these hypotheses one by one. It is what we call the scientific method.

 

Once there is an objective identification of the actual problem(s) it is possible to ascribe responsibility and whether reasonable care and skill has been used or not.

 

Unfortunately it is still often human nature for people to start by avoiding blame and attributing faults to other factors as your fitters are doing. They might be right or wrong, and what is needed is a logical scientific identification of the problem(s). Even bringing in other 'experts' can sometimes only generate more opinion unless there is some focus on establishing facts and evidence supporting or refuting hypothetical causes.

 

I will say that in my experience it is too common for some trades people to essentially ignore what the customer says on the basis that the customer is assumed to be ignorant, inexperienced, unqualified to comment etc. To try to be fair there are doubtless customers where this is true but in reality it should matter not who makes claims or statements, only whether they can be established as factually true or false. But I have also had 5 different plumbers give me 5 different opinions on a plumbing problem - some of them fairly obvious crap. However sometimes you do need to bring in somebody with letters after their name and direct experience (e.g. surveyor, engineer, architect, QS etc) to tell some tradespeople exactly the same as the customer is saying and to state the bleeding obvious, before they will remotely accept it.

 

I would encourage you to focus on rigourously identifying the problem(s), because even if you gain a section 75 financial settlement you will still need to get the doors replaced - and if you don't understand the current problem(s) you are likely to see them repeated on a new product/install.

 

It has been my experience in life that things are mostly like the saying about making a cooked breakfast - the hen is involved in the endeavour but only the pig is actually committed. Whether it is a health problem, a car problem, or a building problem you can seek help and opinion but in the end it is only you the pig that actually bears the problem and is truly driven and committed to getting a resolution.

 

Ignore the bullshit, the name callers, appeals to claimed 'authority', those that play politics, the insurers, lawyers, dissemblers, chancers and deniers etc. Find the truth, hold people to account - whether a window fitter, the horizon scandal, the blood transfusion scandal, grenfell, or hillsborough.

 

Find the truth, speak the truth, live the truth.

As the man said 'For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled'

 

Happy New Year

I don’t actually disagree with any of that.
Identifying causation rigorously is exactly why I’ve moved away from forum debate and toward independent inspection. At this point we’re well past exchanging hypotheses - the issue is persistent, localised, and observable, and the next step is to establish the mechanism formally rather than speculate further.
I also agree that trades too often dismiss customer observations until someone “with letters after their name” repeats the same thing. That’s unfortunate, but it’s precisely why independent assessment exists.
Whatever the outcome - whether responsibility ultimately sits with the installation detail or the underlying fabric - understanding what’s actually happening is essential before any proper remediation or replacement can be considered.
Thanks for taking the time to set that out, and happy new year to you too.

Edited 3 hours ago by fandyman

[Spinny]

Thanks , that's fine.

Take care in finding your independent inspector and be sure to put all the hypotheses people have suggested to him to have him check and comment on each. Hopefully you can find someone that will come with measurement devices for temps, plumbness, fit accuracy, air gaps etc.

 

It will be interesting to hear what he finds.

I think this is a common concern and has got me thinking again about what to put between the packers under my bifolds.

I had to have celcon insulating blocks replaced with concrete blocks because my builder was seemingly unable to actually securely mortar in the celcon blocks, and the window company doubtful about screw fixing into them.