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

[fandyman]

1 hour ago, saveasteading said:

Quite so. I'd advise you listen to the advice here. it may be free and we aren't always right,  but it is by people who have done it/ do it for a living/ know the theory or the reality or both.

 

Draughts are worse than cold bridges and that thermal pic may make it look worse than it is. draughts can be sorted with standard brush strips. so what do you do if you get awarded £30 towards fitting these?

 

Up to you. You will spend many hundreds and they might agree that it isn't a justifiable claim. 

I've sat with an industry expert (selected by my solicitor) because of a cost claim by a client. I think it was about structural design.  After a very expensive hour he said how interesting it had been, and I clearly knew more than him on the matter in question. That might be the case here, with the free advice above being equally expert. Not mine: the others who know this subject backwards.

The “£30 brush strips” framing isn’t really applicable here.

I’m not pursuing this via FENSA for compensation, and I’m not expecting token gestures. The escalation route I’m using is Section 75, which is joint and several liability for the entire contract value where goods or services aren’t provided with reasonable care and skill. That’s a very different legal framework from snagging or goodwill fixes.

This isn’t about chasing draught brushes or minor sealing - it’s about establishing whether a persistent condensation/mould issue arising at a specific junction is an acceptable outcome of the installation, or whether it points to a defect in the way the threshold detail was executed. If an independent assessment concludes it’s acceptable, that’s the end of it. If it doesn’t, the remedies available under Section 75 are materially more than “£30”.

I think it’s important to be accurate about the mechanisms involved, particularly for anyone else reading this thread who may be weighing up similar options.

[Mr Punter]

I have not made a section 75 claim but will be interested to see how you get on.  It does seem to favour the consumer.  Please let us know how it progresses and what you had to do.

[Spinny]

I have aluminium doors and three have cills. The manufacturers technical drawing shows that the cill (as with the frames) incorporates a thermal break betwen the external facing aluminium and the internal facing aluminium.

 

If you google 'do PVC cills have a thermal break' their AI engine says PVC cills do not incorporate a thermal break etc because the UPVC is itself more insulating, and that air pockets are usually also incorporated into the design to reduce thermal bridging. I think you might start by obtaining and examining the technical drawings of the UPVC cill and frame designs, and also to identify what the manufacturers data sheets and specs and installation instructions have to say about the thermal properties the door and cill etc is designed to achieve - and with what installation detail. This then might allow you to identify specific product thermal specifications you would rightly be expecting to achieve, and to compare this with what has actually been achieved by the install. Any discrepancy will then either be due to a defective product, and/or a defective installation and therefore responsibility rest with the manufacturer and/or the installer.

 

You say a conservatory was taken down and this window fitted into the opening in the wall ? Did you give any consideration to ensuring the opening was properly prepared for the door fitting - e.g. by a builder such as the one doing the demolition ? If you ordered the door without having the opening surveyed or prepared to the installer/manufacturer's instructions then I would imagine this might make a claim more questionable ?

 

From the photographs it looks as though there is two layers of sealant and a DPM between the cill and the brickwork. One might expect this to at least provide a little insulation, but if you can feel draughts it seems the underside of the cill is not properly sealed up. So you might try actually getting the gap between the cill and the brickwork properly sealed up externally to stop all entry of cold air from the outside.

 

I can understand you being very disappointed with the thermal performance - did you research and check this out when choosing your doors ?

 

Personally I would expect the window company to be trying to do something more than complete denial.

 

 

[saveasteading]

Interesting

I looked it up and suspect this will be your problem

 

copies of warranties, photographic evidence or independent expert reports, for example.

 

as I expect your bank will immediately ask for this and you will be into costs.

alternatively the other party will throw some tech explanation at the bank, and then they ask you.

 

OTOH if the window people do think they have some liability, or better things to do with their time, you may get an offer to end the matter.

 

[fandyman]

24 minutes ago, Spinny said:

I have aluminium doors and three have cills. The manufacturers technical drawing shows that the cill (as with the frames) incorporates a thermal break betwen the external facing aluminium and the internal facing aluminium.

 

If you google 'do PVC cills have a thermal break' their AI engine says PVC cills do not incorporate a thermal break etc because the UPVC is itself more insulating, and that air pockets are usually also incorporated into the design to reduce thermal bridging. I think you might start by obtaining and examining the technical drawings of the UPVC cill and frame designs, and also to identify what the manufacturers data sheets and specs and installation instructions have to say about the thermal properties the door and cill etc is designed to achieve - and with what installation detail. This then might allow you to identify specific product thermal specifications you would rightly be expecting to achieve, and to compare this with what has actually been achieved by the install. Any discrepancy will then either be due to a defective product, and/or a defective installation and therefore responsibility rest with the manufacturer and/or the installer.

 

You say a conservatory was taken down and this window fitted into the opening in the wall ? Did you give any consideration to ensuring the opening was properly prepared for the door fitting - e.g. by a builder such as the one doing the demolition ? If you ordered the door without having the opening surveyed or prepared to the installer/manufacturer's instructions then I would imagine this might make a claim more questionable ?

 

From the photographs it looks as though there is two layers of sealant and a DPM between the cill and the brickwork. One might expect this to at least provide a little insulation, but if you can feel draughts it seems the underside of the cill is not properly sealed up. So you might try actually getting the gap between the cill and the brickwork properly sealed up externally to stop all entry of cold air from the outside.

 

I can understand you being very disappointed with the thermal performance - did you research and check this out when choosing your doors ?

 

Personally I would expect the window company to be trying to do something more than complete denial.

 

 

Agreed on separating product design vs installation detailing vs the surrounding building fabric. For uPVC I’m not expecting an “aluminium-style thermal break”, but I do agree the right starting point is the manufacturer’s section drawings / data sheets / installation instructions for the frame + cill so the intended thermal performance and assumed installation detail is clear.

On the “opening prep” point: the opening was already in this state when I bought the property and has not recently been altered. The installer measured and supplied the door set to suit the existing opening; I didn’t specify a brick-to-brick detail or instruct them to omit any clearance/thermal mitigation.

From my side, the key symptom remains persistent localised condensation/mould at the internal sill/lower frame junction, correlating with low surface temperatures on thermal imaging. I take your point that there may also be an air leakage component under the cill if the underside isn’t properly sealed - I’m going to check/confirm that separately - but the issue presents primarily as a cold internal surface at that junction rather than general room humidity.

[fandyman]

25 minutes ago, saveasteading said:

Interesting

I looked it up and suspect this will be your problem

 

copies of warranties, photographic evidence or independent expert reports, for example.

 

as I expect your bank will immediately ask for this and you will be into costs.

alternatively the other party will throw some tech explanation at the bank, and then they ask you.

 

OTOH if the window people do think they have some liability, or better things to do with their time, you may get an offer to end the matter.

 

Agreed - I’m under no illusion this is cost- or effort-free. I’m proceeding on the basis that it now comes down to evidence and independent assessment.

 

Just to clarify for anyone reading this later - warranties don’t really affect the process I’m following here.

Under Section 75, the card provider’s assessment isn’t contingent on manufacturer or installer warranties. It’s about whether the goods/services were supplied with reasonable care and skill and whether the outcome is acceptable. Warranties can be part of the background paperwork, but they don’t limit or replace the bank’s liability.

Photographic evidence and (if required) an independent expert report are what actually inform the decision, rather than whether a warranty exists or what it covers.

I just wanted to make that distinction clear so people don’t conflate warranty routes with Section 75, as they operate independently.

Edited 56 minutes ago by fandyman

[craig]

There is a clear point you’re missing here.

 

You employed the supplier to supply the door at the surveyed size, the installers installed said door into the existing opening. UPVC by design is “thermally” broken by the chamber design.

 

This isn’t product related by the sounds of things but the lack of insulation under the threshold is.
 

This needs done.

 

Installing onto the outer brickwork in typical English builds is standard practice, it’s not the most thermally efficient position but they really haven’t done anything wrong here. I appreciate you have an issue needing resolved and didn’t exist before. Insulate under threshold and monitor. Discuss solutions before going down routes that sours the taste for everyone.

[Roundtuit]

My advice is to take on board whatever @craig suggests. Unless your agreement with the installer included improving building fabric to mitigate existing cold-bridging, then you only have some minor snagging issues that you could probably have resolved yourself with some expanding foam and sealant in the time taken to craft your comprehensive and eloquent posts!

[fandyman]

18 minutes ago, craig said:

There is a clear point you’re missing here.

 

You employed the supplier to supply the door at the surveyed size, the installers installed said door into the existing opening. UPVC by design is “thermally” broken by the chamber design.

 

This isn’t product related by the sounds of things but the lack of insulation under the threshold is.
 

This needs done.

 

Installing onto the outer brickwork in typical English builds is standard practice, it’s not the most thermally efficient position but they really haven’t done anything wrong here. I appreciate you have an issue needing resolved and didn’t exist before. Insulate under threshold and monitor. Discuss solutions before going down routes that sours the taste for everyone.

I don’t think I’m missing that point - I agree that uPVC frames are inherently more insulating due to their chambered design, and I’m not alleging a defective product. My concern has always been about the installation outcome, specifically at the threshold detail.

Where I differ is that I’ve already tried to resolve this reasonably and practically with the installer. The installing team have attended multiple times, and the company owner himself has visited. On those visits, the issue was repeatedly dismissed as “normal” on the basis that heat rises, that the bottom of doors is always colder, and that condensation is caused by breathing or clothes drying indoors - which I made clear we do not do. Beyond additional sealant, no attempt was made to investigate or improve the threshold detail.

I’m not disputing that installing onto outer brickwork is common practice in typical UK builds. I am questioning whether, in this specific case, the resulting internal surface temperature at the sill/frame junction - which is cold enough to repeatedly condense and grow mould under normal occupied conditions - is an acceptable outcome of reasonable care and skill.

If insulating under the threshold is the appropriate mitigation, that’s exactly the sort of conclusion I was hoping to reach collaboratively. Unfortunately, that option was explicitly ruled out by the installer, who stated insulation under the sill is not required and that nothing further could be done.

Given that, it seems reasonable to seek independent or regulatory review rather than continue a circular discussion where the issue is acknowledged in practice but dismissed in principle.