Breathability in a conventional building; is it even worth it?

[Adaman]

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!

 

Edited May 3 by Adaman

[SteamyTea]

Welcome 

 

You are asking the impossible really.

To get anywhere close to comparing to a typical modern build where you have a vapour control layer (VLC) on the warm side, then more vapour open as you move towards the cold side, you will need to know the mu-value (µ = MN.s.gram^-1) of every component you intend to build with.

You will also need to properly analysis your local climate as I suspect it is on the cusp of a Northern Europe climate and a Mediterranean one.  Different climate zones have different building codes to cope with the local climates i.e. UK uses the VLC on the inside (warm side) and then controls ventilation rates, the Southern USA has the VLC on the outside and controls the ventilation via air conditioning.

 

Try and find out what your local building standards are as the first research, choosing materials is a long way down the list.

Edited May 3 by SteamyTea

[Adaman]

16 minutes ago, SteamyTea said:

Try and find out what your local building standards are as the first research, choosing materials is a long way down the list.

 

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.

Edited May 3 by Adaman

[SteamyTea]

7 minutes ago, Adaman said:

We are zone C (in spanish terms) on the cusp as you say

Thank Exeter University, where I studied climates and how they change.

Edited May 3 by SteamyTea

[SimonD]

1 hour ago, Adaman said:

breathability

 

The problem is that this is really a meaningless term. There is vapour permeability - e.g. EPS - and there is hygroscopicity and capillarity - e.g wood fibre and hemp, as is clay. Like @SteamyTea suggests it's best to look to local traditional approachesto see how it has been implemented according to the local climate and materials. For example, gypsum has been used for millenia in Italy for its moisture buffering properties.

 

I went for fully vapour, hygroscopic and capillary in my build and feedback about the internal comfort of the house has been extremely positive. After alot of study, the next most challenging part of this is selecting internal finishes.

 

As a sidenote, from an environmental perspective, EPS is extremely good because it's mostly air - I saw a study a few years back where it was better than the natural materials on a life cycle basis. Quite surprising.

 

 

[saveasteading]

3 hours ago, Adaman said:

We are zone C (in Spanish terms)

That Northern coast is very exposed and very wet. It is green with added cows. 

Also exposed to the Atlantic for wind.

No siestas or heading out around midnight around there, 

Up in the NW is Galicia where Madrid natives head  in summer for the cooler weather.

Head slightly inland and uphill and it's like the alps.

 

So logically there will be lots of insulation and vapour barrier construction...No.

Being nerdy that way I look on sites, in diy stores and online . Insulation is a new fad, and there isn't much choice.

 

These blocks as shown above are regarded as insulating blocks, but obviously have multiple  cold bridges, then just get rendered on both sides.

 

I have seen some new houses being built with 50mm eps on the outside, so it is going to catch on eventually.

 

Breathability , if that means that wet walls will dry out is hit and miss. Away from the north, the walls dry out in the heat. 

In the north They seem to rely on shedding the water. 

 

All of what I've said is based on very limited observation, and there may well be large scale construction in the cities  with a more modern philosophy.

 

 

[Adaman]

@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. 

[saveasteading]

1 hour ago, Adaman said:

What do you mean by shedding the water

 I mean overhanging eaves and road drainage, or gutters and drainpipes or even both.

 

Rendering is an art form that hides the grotty masonry, but it tends to be porous.

[SteamyTea]

20 minutes ago, saveasteading said:

but it tends to be porous

Porous or vapour open?

Then there is absorbent as well.

 

I wish I had more time and resources to study this area as the science is fairly easy, just getting the material data is hard.

[saveasteading]

4 hours ago, SteamyTea said:

Porous or vapour open?

Then there is absorbent as well.

Yes.

 

If you throw water on it, some goes in. Then it stops raining and it comes out again.

If it kept raining it would go right through.

[SteamyTea]

5 hours ago, saveasteading said:

Then it stops raining and it comes out again

The phase it comes out is important.

If it comes out quickly in the liquid or vapour state then it is not that much of a problem, in the solid state it can cause damage to the structure.

[SteamyTea]

This page on the Build Desk website explains it all quite well.

 

https://builddesk.co.uk/wp-content/uploads/2013/01/vapourResistances.pdf

[Iceverge]

On 03/05/2024 at 20:30, SimonD said:

The problem is that this is really a meaningless term

 

Hurray!!! Someone agrees with me!!!!

 

There's no black and white here, just shades of grey. There is no breathable or non breathable. Just degrees of vapour permeability. 

 

You could really dig into the weeds with the units but it's largely a futile exercise without understanding the BIG principal. 

 

The amount of "DRYING" needs to exceed the amount of "WETTING" for the materials used. 

 

EG if you have a mass concrete and EPS you can afford much higher moisture. EG the "WETTING" side of the equation can be huge with factors like:

 

1. Terrible airtighess carrying vapour laden internal air into the structure below the dew point. 

2. Driving rain on an unrendered external skin. 

3. Very high internal humidity. 

4. Incomplete insulation installation causing internal cold spots 

 

 

On the other hand if you have a timber framed wall you will have a structure that can accept lower average moisture levels without damage. This leads to designs with more consideration than concrete walls. Really concentrating on the DRYING side of the equation. Things like. 

 

1. Well ventilated external rain screens

2. External membranes lapped to drain rainwater safely away. 

3. Tightly sealed airtighess layers. 

4. Vapour control layers placed inside the dew point of the wall so they don't provide a location for condensation. 

 

HOWEVER. 

 

Much of this depends on workmanship.

 

Take the poor but very common solution of internal insulation on a solid wall. PIR boards are mechanically fixed to the inside face followed by plasterboard. It is theoretically safe as all calculations consider the PIR boards as a vapour barrier and perfect airtight layer..

 

In reality poor airtighess allows drafts to blow behind the boards  and electrical penetrations and vapour to condensate in the gap. The brick wall is now colder than before too so less of the moisture accumulated from inside and wind driven rain from outside will evaporate. Freeze thaw action may come into effect and the wall will degrade over time.

 

There is too much WETTING and not enough DRYING.

 

This is a delicate balance and a sunny South facing wall may survive while a shaded North facing one may not. You may be able to rectify it to your satisfaction by adding MVHR or external silicone brick cream or sealant to the skirting boards. Think added "DRYING" It's impossible to accurately calculate as workmanship is so variable. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Iceverge]

Similarly some theoretically "unsafe" buildups can be practically very sound. 

 

Take the example of a twinwall timber structure with no internal vapour layer but an extremely diligently tapped external OSB airtight layer. Then add dense pack cellulose with it's superb airtighess qualities.

 

In theory you will get condensation on the inside of the cold OSB layer but practically this doesn't happen as the brilliant airtighess never allows moist internal air to get near the cold surface to condensate in the first place. Assuming the owner added MVHR and a good rain screen the DRYING well exceeds the WETTING so the wall will last forever. 

 

 

 

Edited May 5 by Iceverge

[Iceverge]

Design professionalls cannot specify this buildup however as they can't guarantee the workmanship. They will only specify extremely safe or moisture tolerant structural buildups. Like concrete walls, EWI and oil based insulants. 

 

However if I could over see the quality myself I would have no problem with it.

 

 

 

[SimonD]

On 05/05/2024 at 09:34, Iceverge said:

Hurray!!! Someone agrees with me!!!!

 

There's a few of us hiding out but need more voices! 😊 

 

[SteamyTea]

11 minutes ago, SimonD said:

There's a few of us hiding out but need more voices

Thermal mass!

[SimonD]

46 minutes ago, SteamyTea said:

Thermal mass!

 

Oh yes, and Kw

[SimonD]

On 04/05/2024 at 17:56, Adaman said:

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. 

 

You really need to look at the wall buildup as a whole system, rather than the specific components you are listing here. This is because you will not find a lime render that is suitable for EPS insulation. You will find heavily modified versions that contain some lime but will have lots of other ingredients such as polymers so that is can be applied as a light weight thin coat render, has flexibility and can deal with the thermal shocks of such a system. Traditional lime renders are typically too thick and heavy for eps and also wood fibre ewi. As you're on the continent, you need to look at ETICs systems. These systems are often developed by manufacturers to provide vapour permeability. Europe has an ETICs test standard although countries like Finland and Norway have introduced country and region specific guidance due to premature ETICs failures due to freeze/thaw cycles and wind-driven rain respectively - so essential to check locally.

 

Likewise internally according to what you mention, you don't necessarily need permeability, you just need an internal makeup that has moisture buffering capability that is then balanced with sufficient ventilation - or you go the simple route and don't worry about it but make up the difference with MVHR that can effectively deal with the moisture oscillations and additional moisture load that comes from a non buffering fabric.

 

It's not about liking the term breathability - it is simply that as a term for the things you're describing it ends up confusing everyone. For example, a vapour control layer may be vapour permeable or not, but if using a textile based one like Intello plus, it will not be able to buffer moisture. However, if you use osb as a vcl then is will buffer moisture too as it is both hygroscopic and capillary while providing airtightness too.

 

Probably the cheapest way to achieve good levels of moisture buffering is with something like clay paint on top of gypsum plaster, behind which you can install your airtightness layer, clay bricks and then eps ewi with render. Now, I've obviously just picked this out and haven't run it through anything like Ubakus, but hopefully you get the drift and subject to the usual things like checking for risk of freeze thaw/driving rain where you might just need and alternative such as a void, render carrier board and render outside an ewi layer for example.

[Adaman]

@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:

 

 

[Adaman]

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]

11 hours ago, Adaman said:

You are right that their EPS does not start with a lime layer, however if you choose cork, rockwool or woodfibre it does.

 

The only woodfibre ewi system with 'Lime' that has BBA and European (ETA) approvals is made by Lime Green. If you look at the product, theirs is given as a lime render but you'll find in the technical documentation it is lime based or quoted: "Lime based mineral render - Warmshell consists of insulation panels made of compressed wood fibre, covered with an engineered “Weather Protect” render made from Natural Hydraulic Lime and selected kiln-dried sands, plus a range of additional specified components that together ensure that the system is fit for purpose.."

 

Lime render has to be modified for these kinds of substrates. Your normal 'lime' render is a total of about 20-25mm and would simply be too heavy and provide questionable adherance to the substrate.

 

AFAIK rockwool is not suitable as a substrate for lime render and the only company selling a tested cork system is Cecil, which uses Ecocork insulating render which is then covered with Reabilita Cal AC or the version that just has a cork facade. I think that the only ETA approved systems by Cecil use mineral wool or eps and Cecil Fibraflex as the render.

 

The exception to this is using Ceciltek Isovit Lime as the base coat which is mesh reinforced and then using Reabilita Cal AC as the render top coat - this is what a few suppliers specify as a buildup but I'm not aware there are any system approvals.

 

But this is all Natural Hydraulic Lime rather than the traditional Non-Hydraulic Lime.

 

Be careful in this game as there are suppliers selling untested and unproven systems so make sure you check before parting with your money.

Edited May 8 by SimonD

[Adaman]

@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