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I have a feeling that it all revolves around the flowtemperature measurement or what the boiler's PCB perceives the actual flowtemp is, even though the boiler does eventually return to "normal" and your measured readings correspond to the displayed reading. If, for whatever reason, the flowtemp is sometimes perceived to be as much as 5C below the targettemp then the burner output will be outputting as much as +7.53kW (21%) more than that required to satisfy the actual targettemp, even a error of 2/3C is a substantial increase in firing of ~ 3.8kW (10.6%).

I think you need a certain number of air changes per hour to keep all fresh. With trickle vents it’s a blow through. But with MVHR one still (as I understand it) get a good flow through if fresh air. It at first appears confusing that we have a really low air change score to make MVHR worth having, but that’s a test if the leakiness of the house, not the number of air changes that a good ventilation system will give.

Excuse my ignorance, but why do you need such a higher number of changes per hour with a non-heat recovery system?

I honestly couldn’t disagree more. But as we’ve not built the house yet my opinion is not based experience, just theory. However I do know from experience that moving air takes a lot less energy than heating it.

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.

I'm intrigued by your sub £2k system Bonner. Are you willing to share some details? Also, I couldn't agree more re trickle vents, and I do want to have full control of my ventilation. I don't want to compromise on health and comfort, ventilation is not optional. The point Jeremy is making, if I understand correctly, is that the heat saved by the MVHR is not substantial, and it would be more efficient to remove the stale air along with its heat, bring fresh air into the house and heat it via an economical heating method, which I believe I have in the biomass boiler.

Thanks for taking time to reply. Does the NHBC inspector check for gaps on the socks or are they more concerned about the corner joints but butt jointed? Are they not usually covered by the felt and battens at this point (my inspector wants to come once roof is about 80% complete with tiles). Also can I buy 50mm socks to fill any gaps? Rather than use another 150mm wide sock? The only thing is the 50mm are blue - current ones are red, so will be noticeable. But both are 1 HR rated? This still wouldn't resolve where they have been cut either side of the ladder rungs and my issue is the builders have already used 25 socks, probably not fitted to expectations in places, and likely now difficult to fit because of how high they have brought the PIR insulation in relation to the rungs on the ladders.

+1 to lapping down. Our breather membrane is not 100% watertight. If I'd lapped up behind it it the dpm could have collected the small amounts of water that sometimes penetrate in high winds (no cladding yet). Trimmed DPM off about 50mm below sole plate. Left the breather membremane long enough to cover this. Used the stainless steel mesh that is at the base of the cladding battens to stop it flapping about.

We fit them under the ladder. As a full sock and cut at the top. NHBC inspector states that socks can’t be bent around a corner. Should be butt jointed. Sock should be a snug fit to either side of the cavity. If the cavity has spread a little over the height of the building we will either fit a wider sock or 2 thinner ones compressed together. The thing is as a bricklayer, we are responsible for fitting them according to management. We are also told how vital they are since the disaster at Grenfell. However we have never had any official training on fitting them nor do we get paid any extra for it.

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’d assume so yes. But from eyeballing it looks like where the masonry the frame would be bolted to would be. Is a void for some reason.

It’s not no, renovated in the past 15 years but it’s originally a 1955 bungalow. So these bays would’ve originally run into the roof / eaves. When it’s been extended upward I wonder what they decided to do with the bays to convert them. I guess we will find out when the soffits and fascia’s are removed but I’m still a bit confused/concerned as to why I’m seeing a void above the bay. is it likely the bay window here won’t have its own flat roof built in? As in when we swap it out for a new window, it’ll be a straight forward swap of the vertical units?

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.

The detail just shows what most do - DPM just ‘finishes’ directly after the soleplate.

Another vote for a layer of EPS. Graphite if you can, it's even more gooder.

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.

Don’t disagree but maybe depends on the roller, as well as the spray pressure and paint dilution etc, etc. I have recoated bottom half of some walls (because I can’t reach the top without scaffold and it doesn’t need doing!), anyway it has blended really well with a medium pile roller.

Have you work out the price by U-Value, rather than thickness. Regarding unfaced sheet. Unfaced are used a lot in the composite plastic industries because it is easier to adhere to. For any sheet insulation there will be a certain amount of compression when the initial pour of concrete is added over the top. There has been some discussion in the past about whether it should be polystyrene first then PIR, or the other way around. I can't remember what the outcome was, but seemed to remembered it was counterintuitive. The insulation manufactures should have that information. There will also be a long-term creep as well. PUs can keep shrinking for years. They also absorb moisture (as do most materials) that can affect the k-Value quite significantly. I think polystyrene is a bit better in this respect (though it does depend on density. It really comes down to what you want from your floor insulation. I am with @JohnMo in this respect. Get the very best performance you can financially justify, you can put it right later.

It's a modern house isn't it looking at the brick bond? I'd guess a mono truss arrangement above window although might be wrong as its hipped

Hi there, I've left it with the builder to fit fire socks at the top of the walls. Firstly it appears as though the socks aren't really a compression fit and more loose than anything. Will this be an issue in the future for damp and/or fire proofing. My understanding is they are intumescent and expand regardless so my concern is probably more about moisture ingress into the cavity. Secondly, they were happy fitting the socks after the gable ladders had been fitted. What they appear to have done is cut them each side of the timber rather than fit them under the timber. Surely this isn't correct and leaves gaps between each that's filled with a flammable material? Thoughts please all

One point - our entire house was spray painted white by danwood's guys. The finish was great but it has a specific texture. I recently had to touch up a scuffed area in the stairway (using their left over paint) but the brush/roller finish just doesn't match and you can see the join.....

My money is on: First floor joists spanning side to side i.e from coving to coving in the second picture A horizontal beam/lintel spanning from one pier up the side of the window to the other pier on the other side of the window. The upper floor front masonry built off that beam/lintel. The bay roof built as a frame and bolted to that facade masonry The solid bit above the window internally is framed out and clad in plasterboard to form the downstand.

I'm pretty sure this was how ours were done - the join then site behind any cladding. Do make sure that you get them 'permanently' fixed. We had one bit that wasn't that well fastened up and in time started to vibrate in high winds (albeit from a very specific direction) but it took a while to work out what the heck was going on.

Reasonable care isn’t limited to what a trade normally chooses to think about - it’s judged on the outcome of the service. If the installation creates a new internal surface that predictably falls below dew point under normal conditions, it’s fair to at least question whether that outcome is acceptable. I didn’t engage a general contractor or an architect, but I also didn’t instruct a detail that would knowingly create condensation and mould. The installer surveyed the opening, specified the product, and executed the threshold detail. Whether that outcome is ultimately deemed acceptable or not is exactly why I’m seeking independent review - not because I expect installers to be “more than a window company”, but because outcomes matter regardless of marketing labels.

Not exactly. There was a conservatory attached, but it wasn’t part of the main thermal envelope and wasn’t heated to house temperatures. More importantly, the junction itself wasn’t exposed internally. Before the doors were installed, there was a continuous screed/floor build-up across that threshold area, so no cold internal sill/frame surface existed and there was no condensation or mould there. The change introduced by the installation is a new internal sill/frame junction directly coupled to ground-connected masonry. That exposed surface is now cold enough to condense under normal conditions