Mr Punter Posted January 24 Share Posted January 24 I agree the floor insulation is a simple upgrade. With the pitched section of roof you could have, say, 120mm between rafters and 40mm under. For the flat section, mineral wool. Stick with the 150mm cavity wall and poly beads. Wall ties, lintels etc are easy to get hold of and no redrawing required. I am doing this currently, with a parge coat and insulated battened service cavity. 1 Link to comment Share on other sites More sharing options...
Gaf Posted January 24 Author Share Posted January 24 1 hour ago, Mr Punter said: Stick with the 150mm cavity wall and poly beads. Just called a few insulation companies in other counties (who offer all IWI, CFI, EWI so no necessarily clear vested interest in any approach - though I don't know their margins) and consistently across the board they're all saying every new house they do is 150mm with IWI. Really just seems to be an Irish thing... 1 hour ago, Mr Punter said: I am doing this currently, with a parge coat and insulated battened service cavity. Hadn't heard of the parge coat. Interesting stuff - have you come across anything about allowing a certain amount of breathability/permeability for moister using that? Link to comment Share on other sites More sharing options...
Mr Punter Posted January 24 Share Posted January 24 30 minutes ago, Gaf said: Hadn't heard of the parge coat. Interesting stuff - have you come across anything about allowing a certain amount of breathability/permeability for moister using that? I think it is more to do with reducing air flow through the blockwork. I have just trowelled on a coat about 2-3mm thick. It is thicker where the joints are. It covers all the holes and reduces air permeability. I am using sloppy 1:1:4 cement:hydrated lime:sand. I am crap at plastering so it has given me the chance to practice on bits that won't be seen. 1 Link to comment Share on other sites More sharing options...
Iceverge Posted January 24 Share Posted January 24 Here's a spec from a high volume builder of one off houses in my area. They would have a good reputation for quality and are typically very competitive prices. They do design and build only now so have it down to a fine art with spec vs cost. 1 Link to comment Share on other sites More sharing options...
Iceverge Posted January 24 Share Posted January 24 That's from a 2020 brochure so may have changed for the new regs. Link to comment Share on other sites More sharing options...
Gaf Posted January 24 Author Share Posted January 24 @Iceverge Just doing some ground work before calling SEs and with 200mm cavity this easily gets to the Part L requirements alright regardless of brand name (Kingspan, Korefill, Enerystore). If going with wet plaster on the inside of the external walls, how does that work with services (wiring, sockets, etc.)? All of our internal walls are solid block (ground and first floor) with plasterboard and skim finish to allow for services (was required according to architect who did the construction drawings). If you don't have internal plasterboard, or the wood behind the plasterboard to affix things to (curtains, wall mounted TV), you'll always have to make sure you don't drill into the blocks more than 100mm for fixings right? Side question, maybe I should start a new thread for this one (maybe not though considering the amount of posts I've found on this topic), if we end up having to go with non-insulated internal plasterboard, does this increase the chances of mould behind the plasterboard? We will have MVHR system and UFH. Link to comment Share on other sites More sharing options...
marshian Posted January 24 Share Posted January 24 On 20/01/2024 at 11:42, joe90 said: Well remembered @Iceverge, simply put, insulation works both ways, why a thermos can keep drinks cool as well as hot🤷♂️ I put ice cream and hot coffee in a thermos once - it didn't work out as was claimed.............. 1 Link to comment Share on other sites More sharing options...
joe90 Posted January 24 Share Posted January 24 (edited) 29 minutes ago, Gaf said: If going with wet plaster on the inside of the external walls, how does that work with services (wiring, sockets, etc.)? All of our internal walls are solid block (ground and first floor) with plasterboard and skim finish to allow for services (was required according to architect who did the construction drawings). I just made sure the cables coming into the back boxes were siliconed to make them airtight but my walls were sand/cement rendered then wet plaster So I don’t think it would have been a problem anyway (I don’t like dot and dab or aircrete blocks). Edited January 24 by joe90 Link to comment Share on other sites More sharing options...
joe90 Posted January 24 Share Posted January 24 29 minutes ago, Gaf said: If you don't have internal plasterboard, or the wood behind the plasterboard to affix things to (curtains, wall mounted TV), you'll always have to make sure you don't drill into the blocks more than 100mm for fixings right? I can’t see any fixing needing to be more than 75mm and a rawlplug with a tight screw would effectively seal itself IMO. Link to comment Share on other sites More sharing options...
Gaf Posted January 24 Author Share Posted January 24 47 minutes ago, joe90 said: I just made sure the cables coming into the back boxes were siliconed to make them airtight but my walls were sand/cement rendered then wet plaster So I don’t think it would have been a problem anyway (I don’t like dot and dab or aircrete blocks). Sorry for a likely very silly question. So with wet plastering, is it that a sand/cememt render goes directly onto the inner blocks then this render is skim finished (wet plaster)? If this is how it's done, is the wiring then essentially rendered 'over' for want of a better description? And the sockets / light switches sit 'into' the render/plaster? Do you have to use thin socket backboxes (25mm)? Link to comment Share on other sites More sharing options...
joe90 Posted January 24 Share Posted January 24 6 minutes ago, Gaf said: Sorry for a likely very silly question. So with wet plastering, is it that a sand/cememt render goes directly onto the inner blocks then this render is skim finished (wet plaster)? If this is how it's done, is the wiring then essentially rendered 'over' for want of a better description? And the sockets / light switches sit 'into' the render/plaster? Do you have to use thin socket backboxes (25mm)? Yes, capping covered cables and back boxes are cut into the inner blocks (I don’t like shallow back boxes as it makes cabling within them more difficult). Link to comment Share on other sites More sharing options...
Gaf Posted January 24 Author Share Posted January 24 3 minutes ago, joe90 said: Yes, capping covered cables and back boxes are cut into the inner blocks (I don’t like shallow back boxes as it makes cabling within them more difficult). Is it done like this? Link to comment Share on other sites More sharing options...
joe90 Posted January 24 Share Posted January 24 Similar, those are conduits rather than capping and no need to hack out that much block. 1 Link to comment Share on other sites More sharing options...
Iceverge Posted January 24 Share Posted January 24 2 hours ago, Gaf said: Is it done like this? Yup, the walls are "chased" conduit is shoved in and wires are slid in. Plastered over the top. Normally just a layer of sand and cement render and then a skim coat of finer gypsum plaster for a nice smooth finish. The internal walls are no different. Link to comment Share on other sites More sharing options...
Gaf Posted February 10 Author Share Posted February 10 Just coming back to this as we've to make a call. With a bit of time away from this, I'm wondering is a better option to go with something like a Rockwool RockFall approach (apologies if I'm essentially doing the Kingspan thing of not just calling it mineral wool batts). To achieve the BR of 0.16 u-value, and based on the construction drawings already stating 60mm over rafters, I'd need 60mm HardRock Multi-Fix (DD) plus 200mm Flexi. From what I'm reading, the Rockwool Flexi might mitigate the builder's concerns that the rigid PIR (Kingspan K7) will leave air gaps no matter how good at installing he is. Link to comment Share on other sites More sharing options...
Iceverge Posted February 10 Share Posted February 10 Your builder is saying the right things. I'd follow their advice. Pressing the Rockwool button isn't a cheap approach mind you. You could put a rigid PIR board over the rafters if you wanted to save some cost. Slates, Slate battens Counter battens Breathers membrane 100mm PIR over the rafters. 11mm OSB taped for airtighess. 100mm mineral wool between rafters. U value about 0.14-0.15. Link to comment Share on other sites More sharing options...
Gaf Posted February 10 Author Share Posted February 10 27 minutes ago, Iceverge said: Your builder is saying the right things. I'd follow their advice. Pressing the Rockwool button isn't a cheap approach mind you. You could put a rigid PIR board over the rafters if you wanted to save some cost. Slates, Slate battens Counter battens Breathers membrane 100mm PIR over the rafters. 11mm OSB taped for airtighess. 100mm mineral wool between rafters. U value about 0.14-0.15. Yeah we've really gotten the sense the builder knows his stuff. Reassuring to say the least. Is the Rockwool more expensive than the Kingspan K7 insulation? Link to comment Share on other sites More sharing options...
Iceverge Posted February 10 Share Posted February 10 18 minutes ago, Gaf said: Yeah we've really gotten the sense the builder knows his stuff. Reassuring to say the least. Is the Rockwool more expensive than the Kingspan K7 insulation? Don't know. However k7 is Phonelic insulation not PIR. PIR is only marginally thicker for the same U value bit much much cheaper. Link to comment Share on other sites More sharing options...
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