Adaman

What width / thickness did you go for on those hempcrete walls?

Hi Jonny, you've probably already done the job, but I'd suggest burnt sand mastic to seal timber winders into a lime rendered masonry. It's hygroscopic and maleable throughout its life time to adapt to the expansion and contraction at differing rates of the materials around it. https://cornishlime.co.uk/products/associated-products/cornerstone-burnt-sand-mastic/ or https://www.lime.org.uk/burnt-sand-mastic.html

@SimonD Right again on all counts The "breathable" alright then, water impermeable / vapour permeable ETICS systems I'm looking at all start with a Secil TEK, Isovit E-cork preparation layer, insulation, followed by another E-cork layer, mesh, then Reabilita Cal AC top coat. If I'm reading you right these'll be ok. Thanks to your post and a bit of reading up - I now know what the NHL 5,... letters I've been seeing stand for! Always good to learn summit new. I'll have a look into Lime Green and warmshell, sounds cosy. Cheers

My main concerns about vapor control layers are that they are not perfect, mistakes can be made, even if you follow code. I think this video explains the matter very well, it reaches the same conclusion as you, @SimonD

@SimonD I really like your insight to look at the wall as a whole system. Food for thought. I know its not just about the parts, although when we come to describe it we otften fall into the trap of talking about something in terms of parts as its hard to but a whole into words. Interested to note that a lime render won't be suitable as a base for ETIC. Looking at the build budget, ETIC will probably be let for phase two once we've recovered financially from the initial build. So the wall will need sealing from the outside. Typically that's a cement render and plastic paint (VCL) - if we choose EPS that'll be a more solid option. The supplier I have sells whole system, multi layer ETIC solutions. You are right that their EPS does not start with a lime layer, however if you choose cork, rockwool or woodfibre it does. @saveasteading Rendering is not a new artform, the romans did it, even the mayans. Funny how tastes change over time, from leaving the outer stone wall exposed, to rendering the whole thing (even to the point of painting stone outlines to make a render look like a stone wall) to back again to wanting to uncover the original stone. In my case the wall will be these thermo-clay bricks with many air gaps. Not very aesthetic, although they require little mortar and generally line up nice, still best to cover them up with outer and inner layers. I'd rather not live in a house like this:

@saveasteading Sounds like you know the area. It's very unlike most of Spain. I was living in Andalucía for 20 years, looking forward to the next 20 I'd rather be up here, climate wise. What do you mean by shedding the water? The studies I've seen support the idea that a lime render will help the wall to dry out easier than if the whole wall was just exposed brick. The capiliaries in the lime help are shaped in a way that funnels to water out. Can't help but feel that EPS would limit that function. But on the other hand a good vapour barrier on the outside should stop much of the ambiental humidity from entering the wall. Code on a new build will require 8-10 cm of eps or similarly resistant material, on at least 25% of the external wall. Inside the house airflow, good heating, and if necessary an installed desiccant dehumidifier should be able to handle the moisture produced by daily life and if I keep the walls breathable on the inside (sorry to those that don't like the term) also be able to mitigate that. These clay bricks are quite hygroscopic so my instinct is to favour permeability.

Thanks @SteamyTea The architect who did the project is open to discussion, although he is open to new ideas. Which Is why I want to test the water in the forum. The code that I have read talks more about % of surface covered, thickness of insulation, e.g. 6cm of insulation with a material offering 0,036 W/mK. Haven't seen anything about the VLC, yet. I will look into it. We are zone C (in spanish terms) on the cusp as you say. Thanks again.

Hi all, I did a lot of research into breathability because I wanted to do a barn conversion. In the end we found a lovely plot with great views and an existing project, already authorised. The climate in northern Spain can be harsh in the winter, cold winds from the Atlantic, rain, humidity, in the summer it can be damp too but can also reach high 30s (ºc). The plan state that the building will be made with hollow clay bricks - Termoarcilla - in spanish, photo attached, sorry don't know what they are called in English. The question I have is if it even worth it, going down the breathability route? The building already has a ventilated concrete slab, building code will require a damp proof course. There should be no danger of rising damp. Planning to include continuos exhaust fan in the bathroom and HRV in the house. Inside I still feel that hemp bricks or woodfibre boards are going to be much more cosy than plasterboard. Outside I'd like include ETICS options are EPS, woodfibre, rockwool. EPS would be the cheapest. Only concern on EPS is the fire risk and that I don't really like plastic derivatives, other that that the benefits are cost and longevity. Would any of you guys even consider going breathable on a conventional building? If so why? If not, what would your preffered option be? Thanks in advance and looking forward to your comments!