lookseehear

You also need to remember that there are different types of lime mortar. I'm not sure how familiar you are but broadly you have two types Natural Hydraulic Lime (NHL, available in 2, 3.5 and 5 in increasing strength and reducing free lime content) Non-hydraulic lime (also technically 'NHL' by name but no-one refers to it as that) also called air-lime or you might see 'lime putty' This can be in the form of quicklime which needs to be slaked, or as hydrated lime ('bagged lime' at the builders merchants) which has already been partially hydrated I don't actually know how low carbon the different lime mortars are, but my understanding is that they all require burning either pure limestone or some mix of limestone and other stones in a kiln at very high temperatures, and that energy has to come from somewhere, which could be burning coal I guess. I just asked ChatGPT about this and got the below summary. The issue here is that non-hydraulic lime sets very slowly and isn't very strong. It's the best thing for old buildings with solid walls and no DPC, so while there's carbon to be saved, it might not be something you can get sign off from a structural perspective.

It aounsa like you've been having some similar experiences to me! Where did you land with window detailing in the end? Is there anything you can share?

Thanks for this, although it looks like your roof is a cold/hybrid given ventilation above it? I assume that doesn't matter in terms of the VCL, and that it probably needs to be chased in somehow.

My VCL is going in on top of my plywood sub-deck, which butts up to the existing stone-faced external wall of the house. Where does the VCL go at the house side? The stone is uneven, so I don't think I'd get a good bond if I tried to adhere it to the external face of the house.

If you search for a 'Tony tray' you'll see that a lot of people have wrapped the ends of the joists in 600mm+ DPC, which can be taped to OSB and into the parge coat on the walls.

We are putting a frameless glass balustrade around our roof terrace for our extension, but I'm also struggling on speccing what it should fix into. I spoke to Q railing who manufacture the profiles that the glass fits into, and they said that I need to speak to an SE to make sure whatever it fixes into can take a 0.74kN/m load at 1100mm, but wouldn't help beyond that. I spoke to the SE who has been designing the steelwork for our renovation/extension and he didn't want to touch it, saying that I need to go back to the manufacturer. I feel like the simplest answer is a reinforced concrete ringbeam sat on top of the outer blockwork, but I'm at a bit of a loss as to who can tell me whether or not this is compliant, or whether BCO will know that it's overspecified and sign it off. Maybe I need to find a new SE for this bit in particular? Any suggestions?

You're specifying a warm roof, so no ventilated void, therefore the quoted post doesn't apply (unless I've missed something).

The other photo

Builder needs to repair this hole which he still has the stones from (pic below). He wants to use a 'standard' mortar mix and is concerned mainly with it being structurally sound. It's worth noting we'll be taking some stone out below and adjacent to this to create a doorway, and that there'll be a block wall from the new extension butting up against this corner. He knows I would prefer lime where the old walls are concerned but that's more relating to pointing and plaster than the repair work. Any thoughts?

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?