lookseehear

Just wanted to send a message to say you seem surprisingly chipper given the absolute sh*t show in evidence here. So many people would just accept this as 'what it is', so kudos to you to get sorting it! I hope you retained a significant chunk of the ££ against the builder.

That sounds interesting but I'm also not that keen on the idea of having to replace something after a few years to keep it watertight. I've come to the conclusion that the easiest option might be to cast a 200x100 ring beam on top of the outer skin as a mini parapet, which means I can fix posts or the balustrade channel (if we go frameless) into the concrete. I would cast drainage channels through the ringbeam at intervals and have single ply membrane run right through these into collector boxes, which avoids having the posts/channel in the drainage pathway. I did a sketch somewhere that I can dig out if you're interested.

I'm trying to reduce cold bridging where there is a change of floor level of 370mm (two steps) in our extension. The builder is constructing a dividing wall with blocks laid flat because it is buttressing a 200+ year old wall of the existing building. I want to put in a layer of thermoblocks into the dividing wall because this will be a break in the insulation under the slab. This is what he wants to do: And this is what I'm proposing, but I'm not sure where to lap the DPM from the two slabs. I'm using a 35mm concrete paver cut down to make up the 65mm marmox to a full 100mm course. Which of these is right in terms of where the DPM should lap? I should probably also say that the drawing is directly underneath an opening between the two rooms hence why I've drawn the floor covering, but either side of the opening the blocks will continue up, hence why I need Marmox and can't continue the PIR from the top slab over onto the blockwork. Any other comments on this plan?

I've just been through this process and decided that instead of going with an aerated block, I'm going with plain and simple dense 7N concrete blockwork for both skins, with a 150mm full fill cavity with Dritherm 37 and an insulated 50mm service cavity on the inside with mineral wool batts, finished with plasterboard and skim. This gets me under 0.18 U value requirement. I plan to parge the internal face of the inner blockwork to make this my airtight layer, meaning that I don't need to worry as much about taping the back of socket boxes etc, and makes running services super simple. I've read (on here and elsewhere) that thermalite blocks are prone to cracking, and I assume that would compromise my airtight layer if the blocks crack as the parge coat is likely to crack as well.

I'm glad you asked (and I should have come and updated this). Don't bother with the Flir - really poor thermal resolution (60x80) and lacking things like set high and low points. I returned mine and bought the Topdon TC001 for about £200 and I'm much happier with it. The app seems better and more fully featured and the image quality is a lot better. It will also track the hottest and coolest items in the frame as well as the centre spot.

We're also trying to work out the solution here - did you get anywhere?

I've gone down the rabbit hole multiple times with lime, and the only thing anyone seems to be able to agree on with pointing is that it should be softer than the bricks or stone. The heritage route would be a non hydraulic lime mortar with some pozzolans (natural additives like brick dust, wood ash which act as a source of carbon to help the mortar go off). This would be best given that your walls are constructed with mud, as its soft and will help to keep the joints dry. It's also very slow to go off and can only be done in the milder months. This YouTube channel has a lot of information on lime https://youtube.com/@michaeljamesdesign?feature=shared if you want to do some research. A mild 6:1:1 sand to cement to hydrated (bag) lime is probably the pragmatic answer if you want to get it done in a hurry.

There's a cut layer of insulation above the layer you can see the top of to account for cavity tray. The wall ties start in the next course up.

You could eat your dinner off that!

This is what I always do. Have a good jump on it myself and know that the kids at 1/4 of that will be no problem.

I've done something similar in the kids playroom and screwed 3x2 to the ceiling joists running perpendicular, then some little stainless brackets with 4 screws on each into the 3x2s. The stainless ones you linked look like they would be absolutely fine as long as the correct size hole is drilled.

'Fluffy stuff' as my builder calls it is going in. Seems pretty easy to work with. And here's the jig for cutting the cavity tray profile. Straight cuts are super straightforward, but on an angle it's a lot trickier to hold the line.

I came up with a solution for this today. I bought a couple of packs of these driveway grids https://www.wickes.co.uk/Wickes-Ground-Grid-Base---100-x-100cm/p/236266? which are 250x250 and come in a pack of 4. They cut really easily with a track saw, so I've cut them into roughly 120mm wide strips. Should do the job nicely.

Firstly - welcome to the forum and sorry to hear all the issues you've been having. Old houses are a bit of an enigma in terms of damp. Some will be fine when you expect them to be damp and some damp where it doesn't make sense. In general it's probably good to start by making sure you've covered the basics. Are all gutters and other RWG in good repair? Any high external ground levels? Ventilation it sounds like you have covered It seems like the work you have had done is all to contain water within already wet walls by tanking and re-rendering with highly waterproof products (I'd be highly suspicious of the lime they said was used in the render - throwing in a bag of lime hydrate into a cement render doesn't make it a lime render). The pointing looks like standard cement pointing to me as wel. Wet, uninsulated walls will generally be cold in winter because wet walls require so much more energy to heat than dry walls and are much worse at insulating than dry walls. This means that even if the moisture within the walls is contained via tanking, you're much more likely to get mould and damp spots in corners because you have cold walls in areas that are hard to ventilate. I highly suspect that the walls being wet all the time is bad for their general structure over time, and can lead to joist ends rotting, but that seems to be the direction the damp proofing industry has gone because it's easy to hack off what's there, stick a load of tanking stuff on the walls and charge a lot for sorting it out. The 'heritage' approach would be to repoint all the walls with a lime putty based mortar, remove the tanking products and plaster with a lime putty (non-hydraulic) based plaster. These are time consuming tasks because they can be seasonal (you can't use lime putty mortar in winter) and take a long time to set in the right conditions (days to weeks). It's also hard to find tradespeople who do this and do it well for a reasonable price, so a lot of people learn to DIY it. How attached are you to the house? It looks like quite a lot of disruptive work to make it right in any case.

Would you expect the batts to stay in with friction alone? In one section there's enough cavity below floor insulation level to have a gap, but too low for there to be any ties to sit the batts on. I'm tempted to buy some little plastic plant pots or something to put in the bottom of the cavity for the batts to sit on. For the other section of wall, the batts need to go pretty much right down to the base of the cavity. Does it make sense to stand them off the bottom 25mm or so, so that they could drain if water did get in, and so they can't wick moisture up from sitting on damp concrete? Again, are there products to use here? I looked on Knauf's website which seems to have no technical advice.

Our builder seems to be very keen on squirty expanding foam (he keeps talking about all the areas he likes to use it). I have heard not great stuff (it can sag, it can be used to fill bigger gaps than it should really be, it can be a lazy way to get something done etc etc). Is there a general concensus or guidance anywhere about where the appropriate uses for it are? I'm guessing between sheets of PIR is probably a good place because it's probably a similar type of material and the gaps should be small if the PIR has been cut properly. Anywhere that it often gets used that it really shouldn't? Also any brands to look for or avoid in particular?

This is so so helpful - thank you!

Just wondered if anyone had any insight here, thanks in advance!

As someone who is just about to trust his builder to install full-fill batts, can anyone provide practical advice? My builder is skeptical about the whole thing. We've got a roll of knauf loft roll knocking about which he's been using to insulate some pipes temporarily until they get moved, and he keeps saying to me that the loft roll and the cavity batts are basically the same thing and showing me a wet piece of loft roll which got wet and now resembles something the cat dragged in. My specific questions are: Do you fill right down to the bottom of the cavity or leave a small gap at the bottom to avoid moisture wicking up? If using cavity trays, should the batts be packed below and above in contact with the trays or a gap left? How well does it need to be protected while block-laying? It's guaranteed that we'll see bad weather while the walls go up. I assume just a layer of DPC to keep an area dry. What about actually installing it in the wet? Anything to note with wall ties or junctions with existing walls? I assume you air on the side of overfilling vs underfilling, ie slightly compress the insulation into place? Reading through this thread, I'm wondering whether EPS beads are more foolproof. What about the fire performance though? U value in a 150mm cavity looks v similar to Knauf Dritherm 32.

Not an expert, but I would be a little wary of IR camera results from window panes themselves. Glass will allow IR radiation through, so it's possible you're measuring the temperature of what is outside when measuring from inside, or what's inside when measured from outside which will distort your view of the windows. As has been said before, if your glazing isn't blown and is generally in a good state of repair, you can find out what the u value is roughly and therefore what is to be gained by replacing them. Thermal cameras are better for identifying cold bridging around the windows, unseen draughts and the overall performance of the frames than the window panes themselves.

I've been looking more into this after taking some plaster and old newtonite off the walls at home. As expected the stone is pretty uneven, but looks pretty dry. This is about 2 feet above the ground. I'm thinking about making up my own base layer of lime plaster as a levelling and airtight coat, rather than a cement based parge coat. I was thinking that a 3:1 mix of sharp sand and lime putty (slaked quicklime) with some synthetic hair added is probably the 'best' thing for the walls. I assume this would suffice from an airtightness perspective and would likely be cheaper than bagged alternatives like Baumit and better than a cement based parge from a drying and wall-health perspective. If I'm only using this to roughly level, hopefully I can get it done in one coat and it won't have to be particularly neat. Over this I'd do the aformentioned wood fibre or mineral wool with ~50mm battens or a 63mm CLS stud wall creating a service cavity, then plasterboard and skim. If the plasterboard turns out to be problematic down the line, it would be possible to swap these out for a wood fibre board with lime skim, but I'd hope not to have to do this obviously! Window reveals would also be lime plastered, then lined either with some PIR or somthing like Bosig Phonotherm (https://www.ecologicalbuildingsystems.com/product/phonotherm) or maybe a wood fibre reveal board. Any thoughts on the above? If the lime putty based plaster is sufficiently airtight I wouldn't bother with an intello membrane, and instead would focus on getting the details of the lime plaster and taping to joists/floors etc right.

Does this mean that Intello type membranes are not worth the cost? Should we be looking at cheaper alternatives instead? I've always had a nagging doubt about gore-tex in outdoor clothing. Wearing it while cycling leaves me similarly sweaty to wearing a standard waterproof.

That at least should offer you some comfort - less of a discussion about how you think it should be done vs how the contractor does, but a simple failure to follow the agreed plans. I hope it doesn't set you back too much time-wise.

This is the hard bit though - when do you actually commit to something? Or do you just reconcile yourself that you'll learn more after you've committed and just have to make the best of what you've already committed to?

Good point! I suspect the hob will be on an island though so we'll likely have an extractor above. I'll have another look at what's available when we come to spec the kitchen fully, but I just want flexibility in terms of pan size and position. I've got a 14" round cast iron crepe pan which I've not been able to use since we've had induction. It worked great on our old electric aga but the electricity bill was eye watering.