allthatpebbledash

Just another follow up topic from my previous as even though the nature of the question is same, new facts. Say you were building a new cavity wall using dual leaf brick. New foundations. Width of wall to be constructed not an issue, as long as it’s not like 600 or something. What size cavity would you have if you were intending to full fill with mineral wool batts? Wall would need to achieve 0.18w/ but lower the better. The question is what’s the sweet spot for performance vs cost vs cavity size? I’ve learnt DriTherm 37 is more cost effective to buy per sqm than the 32 slabs. Almost 50% cheaper online in some places. But when I run a calculation it shows I would need almost double the quantity to achieve the required performance. Kind of makes it the same then and not as cost effective as I’d read on here. Or is there something I’ve not factored in? Thanks.

Using a dense block external leaf, and lightweight block internal seems to achieve 0.18 with 32 batts in the cavity I just seen. Are the lightweight blocks terrible as I’ve heard of them cracking and crumbling easily. Using dense blocks both leafs and 32 batts gives 0.19 which is so close. Would it not be possible to do this and say increase u-value of floor or roofs? Or windows? Anything to compensate for such a small nominal. It’ll allow for using the much cheaper and better dense blocks for walling and go with fully filled cavity mineral wool. For now taped PIR at 140mm is being planned.

Ice I’ve had a go at using the calculators on rockwool and knauf websites and I can’t seem to replicate the results. I get 0.19w and no where near the number shown here. I’ve already said to the architect we should go with 140mm Recticel with 10mm residual as well as I couldn’t replicate the numbers using products available. Ooops.

Oh. I have all moisture areas located either side of say a large rectangle. To have them extract through one roof outlet would mean I would need to run a duct across the attic space which isn’t possible due to raked ceilings and through runs. So it’ll have to be 2 roof outlets. I suppose I can still run a MEV this way, but what advantage would that have over a dMEV stacked and vented vertically through roof in same way?

Ah. Yeah so with the “035” wool at 150mm thickness it gives a 0.15w/ wall which is good. But it also shows a heavy set of rain drops suggesting huge condensation risk.

In the cavity.

Tell me about this, if I’m venting through roof are you saying I should be looking at MEV? Like an MVHR system?

Interesting. I’ve seen them used in a few projects in UK, one is an award winner. The block type would be the ones with mineral wool infilled. They give good u-values off the pallet so to speak albeit you need a wall that’s like 400mm thick. No warranty here. I’ve read the opposite. Airtightness is easier as blocks are continuous with thin profile joints and have an ecoparge coat on them. As for expense, I’m thinking this could be counteracted with no need for wall ties, lots of mortar, no insulation boards to cut shimmy fill, and speed or build. Hoping the 3 members tagged can chime in, can see from searches they’ve attempted this method.

Theres no EWI. Anticipating a concrete block cavity wall with cavity fully filled 100-150-100mm. So is it possible to avoid the filling between rafters and just place boards above them?

Yeah so you’re actually right. I asked and got answers. You run cables through a flexible metal ducting behind the cavity walls or any walls for that matter. Then pull through, cut brick, always at joints for easier installation of back boxes.

Would that mean I’d be looking at a between and above solution then, like hybrid roof? Forgive my lack of understanding, I was under impression you could just plonk a ton of board on top of the rafters reducing the need to cut and fill? Aesthetic reasons, the soil stacks are also venting via same method so no visible pipes externally.

Currently exploring this by use of them clay blocks which don’t require EWI either. What would a proposed build up be for single skin concrete blocks wall with EWI, lay flat on belly?

After reading quite a few previously asked questions, would I be allowed to assume the easiest and least faffing way of insulating a roof is to go above rafters all over? New pitched roof, covered in slate. Gable end to end, simple form. Probably hand cut timber rafters. Intergrated PV panels. Loft boarded for storage with hatch. New ceiling joists below. Was considering cold roof with mineral wool above new ceiling joists as cheaper but being advised it’ll open up potential to damp and mould. Told to go warm roof instead. Either between and below, between and above, or all above. The latter seems most simplest to not go wrong. Therefore, if I throw 140-150mm Recticel Eurothane or something above rafters, and as I have 2 ducts either end coming up from wet rooms on floor below for the dMEV units to extract via the roof, could I install an additional 2 units in the loft space on either side to tap into existing ductwork for any possible moisture to be extracted? Need to achieve 0.15W or better.

Hmm I can see the advantages definitely. But that leaves me having to find someone in the North who can do this and to a good standard. What about using Recticel 140mm with 10mm nominal gap as a way of rigid PIR and having a fully filled cavity?

Assemble @AliG @Gary in New York @Torchia Currently contemplating a 350mm wall of 2 x 100mm concrete blocks, some type of insulation in the cavity and render to the outside. But. I’ve just come across these clay blocks which were used in a project that won awards down south. The interesting thing with these is you can do away with the cavity construction as I understand this can be problematic for builders to do right especially when having to fill with insulation at the same time. As I have the scope to build a wider wall, the monolithic single skin wall is most appealing. Plaster the inside. And render the outside, maybe with some EWI for added u-value busting. I want to achieve better than target u-value of 0.18W, but okay to land at this is costs determine. However I want to understand the costs of this method vs concrete block construction, and any other drawbacks if any. Or points of consideration. I can see some of these clay blocks would be able to meet the target value of 0.18W as just block alone. Whereas others would need a thin layer of EWI to meet this. My thinking is the use of a thin layer of EWI would give a total envelope of insulation externally, but that’s adding to costs. Would looking at a block that meets the target value with just a render externally be a better idea? Looking for advice and input to help determine if viable or not over traditional concrete blocks and cavity fill construction.

The advantage of this is being it fits within the wall better than others?

What if they don’t? Like you’ve built the walls, and then the beads don’t go all over. Then you’ve got uninsulated pockets of walls. I don’t like the idea.

What was the cost difference between using PIR and the wool batts? Are there any alternatives to this specific brand? I want to ideally beat the new wall construction u-value of 0.18w. I did some calculations online using that German website I seen linked on here. Keeping a cavity at 150mm, the PIR on paper appears better. But that’s the topic being discussed here, theoretically it does. If construction doesn’t meet proper standards, how much of the supposed r value is lost? PIR achieves 0.15W Mineral wool batts gives 0.18W I can build a wider wall of course and throw in more mineral wool? Then for the lintels use split lintels and avoid the catnic thingies?

Bringing this back up, significantly in the good way? Or stay away from. Currently being advised on a 150mm cavity partially filled with 100mm PIR. Reading on here suggests I should opt for dritherm 32 at 150mm and fully fill. But I have scope to go to a wider cavity too.

Wow that’s shocking. Can you help what wool batts I should be looking at?

Which ones? Which ones? Why this?

Yeah we were considering this as told the above might not be possible. But can’t get around the rustic look of conduits everywhere.

Here’s a link to the project on the architects website. It is a real project in the UK. They’ve done this on a few of their projects. I’ve seen it on few other UK based projects from London architects. Just trying to work out how they’re achieving this. https://www.fletchercranearchitects.com/tree-house-architect-ealing-london

In the image below they’ve managed to install sockets without any of the wires on show. The socket back box I assume has been fitted into the bricks by cutting a hole. But what about the wiring. How can you achieve this look. Have they ran the cables behind the wall as in the cavity? Is this allowed with insulation in the cavity, on what looks like an external wall. Thanks.

What’s the best way to fill a 150mm cavity with insulation? Should I partially fill it and go with 100mm PIR with 50mm gap as is being suggested? Wall build up intention here; Clayworks plaster or paint Plasterboard dot dab 100mm block not specced yet 150mm cavity 100mm block not specced yet Render by Baumit I think Theres scope for a wider cavity to be honest but architect is saying going wider would increase costs as majority of ties and other ancillaries or all geared for 150mm cavity’s. I’m not keen on blown EPS beads. Editing to add, the roof is a pitched roof, gable end to end. Intention is a cold roof, with loft roll above joists then boarded over for loft storage.