Ben Weston

I've asked the question of the architect again. It was my understanding this approach wouldn't be possible but I could very well be wrong. I most often am.

Just edited my comment above to explain why but yes, it's a tricky one for me to navigate.

I've had that discussion again with my wife this evening. I'd knock it down, she's sentimentally attached to keeping some of the original structure. Unfortunately, our planning was approved in January after 4 months and, with 3 kids in tow and currently living in a static home, neither of us fancy going to the back of the queue again for a new planning application for demolition. The original intention was to keep the original house – this has unfortunately transpired to retain less and less as the process has gone on.

Roger, you've got me confused with saveasteading. You haven't posted any links in response to me and I've taken onboard the advice you've given me. I've read a TON of information. If your advice is "read some useful info", perhaps a forum isn't the right place for you. There's always one.

Sorry, I'm not really sure what this passive-aggressive comment refers to. I'm here specifically to listen to all advice, yours included. However, "proper facts" do need supporting. Everyone considers their opinions to be "proper facts", with all due respect. What haven't I listened to?

As I said, nothing is remaining. The windows, doors, roofs are all being replaced. The architect is designing it with whatever thickness we add on in mind: he's assuming around 100mm.

Thanks! We're not currently living in the house. It's being stripped back to only the outer 3 walls - new roofs, new doors, new windows, new floors, etc. The disruption and challenges of marrying it up with the extension are moot. The extension design isn't really a concern to be honest: we're actually going to build that first, marry it up with the existing house and 'do' the original house last. The plans are already signed-off (which took 4 months) so not too keen on revisiting anything there. In other news, architect came back having done his research and suggested an injected DPC, leaving the cement render on and using an EPS insulation system on the outside. He'd spoken to the National Insulation Association and Weber, who he works with for most of his projects. That said, the suggestion seems all wrong to me. I want to go back and suggest that the whole house (old and new) are covered in the same external insulation system to ensure continuity. I think it should be, in principle: Breathable external render > 100mm - 130mm rockwool or woodfibre > solid brick wall (block wall in new extension) > breathable internal plaster & breathable paints. No injected DPC. Both renders/plaster likely to be hydraulic lime or similar. This seems consistent with most of the advice I've got here and from specialists in older buildings. Any thoughts? Should we be doing something different to the block walls? Am I way off the mark?

Missed this. We're looking at MVHR too.

Yes, having looked into it a bit more, I think 200mm would be overkill. I think there's scope to go more than 100mm especially as there's relatively little cost difference in doing so. Perhaps 130mm or something like that? That, I think, would still allow fairly 'standard' decoration. That's very kind, thank you. To be honest, I've spoken to quite a few RICS/RIBA-certified people now who all give me slightly different advice. I'm sure there's more than one right answer, of course! At this stage, I just want to understand as much as possible myself so that I have confidence in whatever route we eventually choose. Thanks. I think I'm satisfied that EPS will provide enough permeability for what we need so long as we render in lime internally and use a lime, or lime-like, render externally. Still not sure which external render to go for but we can come back to that. The main thing is establishing how much is being added to the walls so our architect can sort the roof on the working plans. Thanks all for your very detailed help as always.

Thanks Adsibob. Injected DPC already ruled out – realised quite quickly this is one of those 'old wives tales' with little substance. Your approach sounds similar to the one I'm arriving at, though I'm currently looking at K Lime as the outer render. I'm interested in the air void you created. Presumably this had to be vented somehow? I'm going to look into EPS and modified lime render on the suggestion of Simon (thanks Simon). The house is surrounded by trees, so not exposed at all, which might make EPS viable. If we can get away with this, we'd have the budget to over-rate it to 200mm-ish and apply it around the whole house (including the new extension with cavity walls) which would result in a really well insulated house. So today's research is whether the following system is viable: K Lime Render > 200mm(ish) EPS > Vapour-Permeable Adhesive > Solid Wall > Traditional Lime Render I realise that, just as important, is how the details are finished and how it terminates in the roof. This needs more research but it seems like the base should be XPS down to the bottom of the land drain and about 6 inches above to the bottom of the rail the EPS sits on.

Thanks yet again, Simon. This is very thorough and you've certainly looked into it in more depth than I have yet. To be honest, I hadn't really considered that their system wouldn't necessarily meet spec if it's registered with LABC. If we leave their system aside for a second, is the principle of lime render > insulation > solid wall > lime plaster correct? It strikes me that there's no 'vapour control' layer though perhaps the insulation itself performs this function? What's stopping driving rain working its way all the way through to the lime plaster? The AT I spoke to was referred and it was a general half hour non-chargeable chat. My own architect hasn't worked with EWI before: he was the one that suggested whacking EWI on top of the cement render which struck me as incorrect, hence the ongoing research. Am I making a mountain out of a molehill here? It seems to be so difficult to get consensus on this but that may say more about the people I've currently spoken to about it. Essentially, I have three solid walls and want to insulate them to the best possible standard/U-values without introducing, and preferably improving, moisture control.

Evening all, I spoke to an architectural technician today who specialises in 'historic' buildings. He advised the Ty-Mawr EWI systems. He advised that the entire wall must be constructed from breathable materials. Fundamentally, he was saying to remove the cement render and, externally to internally: render in lime, woodfibre board, solid wall, lime plaster. Basically, this system: https://www.lime.org.uk/applications/retrofit-insulation-systems-for-old-buildings/external-wall-insulation-system/expanded-cork-insulation-system.html He thought a land drain around the building might be a good idea so long as it didn't dry out the clay the house is sitting on too much and lead to subsidence. The reason for us considering this is that the cottage sits in a 'dip', the internal and external floor levels are the same, and it's been known to flood in the street. This looks like it would get us to around 0.30 W/m2k, which isn't ideal if we wish to go for a heat pump (even though this only applies to 30% of the house - the rest will be new and up to current spec), but there may not be much more we can do about that? Any thoughts on this?

Looks great! Could I ask how the pricing compares to a more traditional PIR + concrete slab floor?

This is really interesting, Roger, and makes sense. Will look into it, thank you. I instinctively prefer natural materials and have always liked lime render. Wasn't aware of limecrete until now.

It can be made of whatever we want! It's being dug up and started again. It'll have wet underfloor heating if that makes a difference but the construction just has to pass Building Control.

Thanks both. All floors are being dug up and relaid with underfloor heating and to current spec, obviously. First floor coming out and going up so that'll be new. We'll already have scaffolding. New roofs, doors and windows so no issues there. Pretty much only these three external walls are staying in the whole renovation (for a number of reasons I don't want to revisit). So the added complexities of EWI don't really apply here. So if we use EWI, use a breathable render straight on to the internal brickwork? Such as lime?

Thanks again for such a detailed response, Simon. All the floors of the house are coming out (and new roof) so these three walls can be dealt with more easily than if we we were working around a finished house we're living in, if that has any bearing. In other words, we could minimise/eliminate any cold bridging but appreciate still less of a problem with EWI. The house is being rendered anyway so the additional rendering costs of EWI are negligible. We are having all new windows and doors so the headache of that is irrelevant too. From what I can tell, the materials for EWI are relatively inexpensive – it's mostly a labour-intensive job? Unless I've missed something, I think EWI could end up being cheaper/the same cost as IWI but more effective and potentially at no more cost. Which doesn't square with everything I've read saying how much more expensive it is than IWI. Can only assume it's because of the other factors I mention which are already factored into the budget for us, or irrelevant.

Thanks nod, good to know. I'll assume from now on that the pebbledash has to be removed in any eventuality, EWI or otherwise. Does anyone know the advisable route doing IWI instead? Simon mentioned a vapour control layer which makes sense. Presumably we'd render in something like K Rend on the outside so the wall could still breathe, introduce a cavity inside by creating a studwork inner skin and fill with woodfibre with insulated plasterboard on the studwork? Presumably this would reverse the current situation and allow the damp to travel out rather than in?

Thanks all. Yeah, I agree Will. I don't see the need to disturb something that's been working fine for 150 years. The whole point of my enquiry about EWI is ensuring we don't introduce damp problems so I'm not keen on potentially doing so with an injected DPC if we don't have to. I'll look into it again. Excuse my ignorance: what constitutes a 'lightweight pebble dash' as opposed to a cement-based one?!

Thank you for such a detailed response, Simon; hugely appreciated. No existing DPC but also, as I say, no signs of rising damp either. The house sits low in the plot (the internal floors are level with the ground outside) but we are installing French drains around the house to mitigate any potential issues there. I agree that the house has sat for 150 years without damp issues so why interfere with it by adding an injected DPC? Main issue is mortgage lending criteria. Although it's not currently mortgaged (it's not mortgageable!), it will be and almost every lender demands proof of a DPC in older properties. Infuriating as the requirements of the lenders can often be contrary to what's best for the property. That's a separate issue for me to square though. I tested removing a small section of the pebbledash and the bricks behind are very soft – it's highly likely that removing the pebbledash would lead to a much more uneven surface. Probably best to save the labour (not a dealbreaker if required) and apply a levelling coat in that case? It sounds like you're confirming my understanding that EWI may well be the best thing for the building as it keeps the original wall 'warm' and protected. Presumably the walls would still dry to the inside of the house meaning we'd still need a moisture-control layer internally? Battens and plasterboard unlikely to be sufficient?

Hi all, We have an 1870s cottage built with 9 inch solid walls. We're adding an extension off the back which will be built to new cavity spec but we need to get the 3 walls of the original house up to standard. There seems to be so much conflicting advice and 'old wives tales' when it comes to managing damp, solid walls and insulation. The current red brick solid walls are pebbledash rendered on the outside. There are no signs of rising or penetrating damp (though we are looking at an injected DPC as part of our renovation works) and, despite there being no damp issues, I believe the cementitious render won't help the breathability? It's been suggested we use EWI for the outer three walls and marry up with the cavity of the newer extension. This would be complemented with foil-backed plasterboard internally. I'm concerned that applying EWI on top of what we currently have might introduce damp issues by locking that water in the solid wall with nowhere to go. The original plan was to chip the pebbledash off, render in lime so it can breathe and insulate internally instead but I'm open to EWI if it's suitable in this situation. Can anyone help advise?

Thanks. As a follow on to the reply above, it's a complete re-roof and new floors job too. All said and done, it's really only the external four walls that will remain and, as above, they're not great. My main concern is budget. If we decide to knock down and rebuild (which I accept is the better route in terms of end result), that's a VAT saving but also brand new foundations, demolition costs of the house, full rather than householder planning, etc. The VAT saving is swallowed by those additional costs and I can't see how it's quicker? I could be completely wrong so very open to opinions. I certainly accept that many/most would opt to just knock it down and build anew. Unfortunately, we're up against both budgetary AND time constraints. Time moreso.

Yes, that is being seriously considered. I can't get the sums to come out cheaper but it's still a serious consideration at this stage, if only for the VAT saving.

Hi all, We've just bought an 1870s cottage (with a horrible 60s extension but that's not relevant here as it's being removed) which we are almost completely gutting and renovating. It was originally built out of Norfolk Reds and has since been pebbledash cementitious rendered. This will be taken off and we plan to render it in lime render, repairing the brickwork where necessary. The cottage doesn't have any particular damp issues but I'm keen to 'double skin' it as part of our renovation. I realise I will lose ~150mm on the external walls but it'll make it more saleable (mortgages, etc) and warmer. In terms of achieving this in the most space efficient way, am I right in thinking we can add a stud wall internally with a 100mm cavity + insulation? Does it need to 'tie in' to the external wall as in modern builds? My other consideration was that the cavity will not be ventilated – is this OK or do we need to provision for this? All the floors are being dug up and re-laid in case there's anything that can be done while doing this? Any and all advice welcome!

As far as I've been told, it was the wish of the owner who died to prevent development on, what is, a beautiful garden and stipulated in the will. All I know is that two previous buyers have tried to renegotiate the terms down and the sales have fallen through because of that. We've no interest in negotiating the terms down. Yes, I suppose I need to think more about the impact of this. As part of the split, I had considered it would need an access route past the main house (there's the space for this) to sort the land-locked issue. As you say, the titles would be split in the event planning was ever granted (not our intention) anyway so I'm not sure splitting the title initially really makes a practical difference but I may be missing some nuance here. I had also considered offering to increase the uplift to 35/40% as a compromise for explicitly removing it from the parcel of land the house itself sits on. We're basically trying to work out where a fair compromise is here. It may be that there isn't one. We could progress with the purchase and the overage, and it's certainly encouraging that others have managed to secure regular mortgages with a restrictive covenant, but our experience having sent the overage attached above to a few lenders via our broker was not positive.