SBMS

Sorry just seen the picture. You’ve designed a cold roof that needs ventilation?

I can’t see the other section orientation but the vented cavity shouldn’t be venting into the firrings void. The whole point of a warm roof is it is unventilated. But also, as etc says this wouldn’t be an issue if your cavity insulation carried on all the way up to meet the PIR…

Not necessarily true. Unilin approved a 150mm PIR warm Roof with 100mm of Rockwool. Showed an annual moisture accumulation of 0Kg/m2. I checked this myself on ubakus.de which showed the same. why is there ‘cold damp air’ in middle? Isn’t that warm side of insulation?

Use an MCS umbrella company? You can still get the grant but self install.

@Great_scot_selfbuild @timhowes I too was nervous of my own calculations using the spreadsheet. It came out around 8.8kW. I then sanity checked and used the free and brilliant tool from Heatpunk that calculated 9.1kW. our MCS installer calculated 12.1kW and was nervous about suggesting a 12kW and was suggesting a 16kW (the range i am looking at is only available in 9,12 and 16. He was using the standard MCS spreadsheet which can overestimate and he had some slightly incorrect u values which was my fault. I then worried even more and so decided to get a heat loss done that was independent and mcs compliant for the installer. This cost £300 and it came out at 9.15kW using heat-engineer and he even modelled it in spruce and it came out at 9.36kW. Moral of the story is Jeremy’s calculator is good - but not foolproof and took me a couple tries to get right. Heatpunk is free, very easy to use and almost foolproof. Would Absolutely recommend you give it a try. and finally If you’re worrying or your mcs installer wants an independent one the company i used (it’s just one chap I think) was pretty good And fairly cheap. DM me if you want The name.

Is it done after boarding or post plaster skim?

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 might be misunderstanding so just want to clarify… previously where this junction existed both sides were effectively warm? Ie one side was your internal house and the other side was a conservatory (heated?)

I think from this you’re hoping that because they’ve bedded it on silicone and packers that this is exacerbating the thermal bridging. It’s not. And I think it’s standard installation. What should have happened is your lower course of bricks should have been taken off and replaced with marmox, compacfoam etc. as others have said this isn’t the installer responsibility and they’ve installed as any installer would.

Im not sure I agree with your interpretation of the thermal imaging. That pattern could definitely be consistent with ground-contact brickwork below bridging cold up. Do you think then that this isn’t the culprit and it’s the frame threshold? Ie a manufacturer issue?

The installer is not responsible for the installation outcome in so far as its interaction with your existing building fabric. They are responsible for installing the door correctly - not for correcting or redesigning a thermally poor threshold detail that pre-exists the installation. Their response doesn’t seem great from a customer service perspective and as others have said they are responsible for foaming, sealing etc in so far as it relates to installation of their product. This will improve things for you no doubt. However, Unfortunately I think your camera shows the brickwork thermally bridging UP (not across the threshold which would imply no thermal break in the frame)… it’s a bit like fitting new tyres to your car.. you’d expect the fitter to balance your tyres and get the pressures right. But if your suspensions fundamentally out and the car pulls to the left: whilst it’s not the ‘installation outcome’ you’d like, It’s not the tyre fitters fault what they’re fitting onto isn’t fit for purpose..

Think I might do this. Not sure if dpm/dpc was taped…

You squirting this up behind the board you mean At the bottom? Is this needed if dabbed correctly? No one done airtight paint on the screed wall junction then?

Thanks - will get plasterer to do full perimeter dab etc, but don’t I still need to worry about airtightness at the floor wall junction itself?

I have made a bit of a sequencing error with my airtightness strategy. I had planned to use a liquid membrane at the ground floor slab to wall junction before the insulation was laid and screed was poured. I neglected this and the 175mm insulation and then a latex screed with foam perimeter was poured. I am dot and dabbing so wet plastering cant help me. Can I use a liquid membrane to seal the finished screed to the wall? There’s the annoyance of the foam perimeter strip to get over and the plastic sheet under the screed would need trimming right back as currently that’s been left long lapping onto the block wall by couple hundred mm. Am I good to just try and seal this junction with liquid membrane (soudatight lq prob) as best I can?

Thanks for the comprehensive answer! 🫡

lol Sorry. Had to put my fingers in a bowl of ice after that.

What did you parge with? Are you brick and block? Where did you use soudatight? How come you taped and didn’t just use soudatight? Are you doing AB before or after plasterboard? Have you had a blower test done? sorry for the onslaught of questions!!

It seems Aerobarrier themselves recommend doing after plasterboarding. I guess if the system is designed to find air paths under pressure you want the physical model to be as close to the finished one as possible. Doing dot And dab would create a service cavity that changes the airflow And would potentially create leakage paths which weren’t present pre PB??

Okay fair enough (and you’re right my cracks comment was a bit stupid!)…. But if it does all that does it matter if the plasterboard is in place or not? Still Can’t see the benefit of doing it after boarding rather than before if all first fix is done?

Understand that first fix needs to be done (but this behind the PB typically).. but if we PB first then AB that puts the AT layer at the PB layer. If there are any cracks etc in plasterboard later then that’s a path that AB will miss? But if the AT layer is behind PB then boarding (with full perimeter dabs) can only increase airtightness? Or am I missing something

So AB after dot and dab? Would have thought having AB at the block layer would be best so pre PB?

Indeed! Think I might have a go myself with soudatight and see where I get?? Any other aerobarriers out there? What did you do pre aerobarrier

Not yet but am not sure what it would tell me. I’ve seen case studies that get airtightness from 6 to 1.0 so if I blew 6 today would that mean I should still crack on with aerobarrier? I worry that aerobarrier gets you a great result on the day but does it persist long term? I know they’ve tested longevity of the material itself but presumably this is fairly controlled. Does it cope with movements around junctions well for example 🤔

Am considering aerobarrier… so far we haven’t done any airtightness detailing for - window junctions/across cavity - slab floor to wall junctiob - liquid membrane/parging of internal block work (traditional masonry, 200mm cavity with eco beads) I have implemented a Tony tray and done airtight board in room in roof with taping.. Does aerobarrier negate the above entirely? Or should I do it (was thinking of using soudatight and parging with it as well). do I need to? I know that aerobarrier gets good results for air blower but does that hold up over time? Eg does it deal with the movement at window joints that tape/liquid membrane does? And if I go around with liquid membrane do I then need to shell out £5k on aerobarrier? I wonder if it’s diminishing returns - the difference in heat loss between a 1.0 blower test result and 2.0 For example is about 150W!