Insulating materials: organic vs synthetic

[Garald]

I recently bought my first place - the greater part of a smallish house from around 1930, near Paris. The place has an energy rating of F, so, obviously, I have to do major work on improving its insulation. (I will also replace the gas heater by a heat-pump.) I will be insulating from the inside. Space is at a premium - each m^2 is very expensive (even in a relatively affordable suburb of Paris), and of course I have only so much space to work with.

 

The architect I am working with is proposing the following materials.

 

A. BioFib Trio (https://www.biofib.com/biofib-trio/?gclid=CjwKCAjwwo-WBhAMEiwAV4dybUHVwwtXg1vwFmjzTDYwYp9q0VjYMxsFENAhgB-WO4JO0wfiTSPiUhoCLLMQAvD_BwE)

- eco-responsible bio-thingie (hemp-linen-cotton)

- pretty good insulation (145mm gives R=3.80, 160mm gives thermal resistance R=4.20; here R=3.8 is the minimum necessary to get subsidies, not that I would get much). Here 160mm would give nearly 200mm=20cm total once one adds an anti-fire plaster panel and so forth.

 

B. Slimisol Siniat (https://www.siniat.fr/fr-fr/actualites-et-evenements/83808/slimisol-techno-isolant-ultra-mince/)

• Aluminum + polyethylene (vacuum-packed)
• 40mm (= 60 mm total) gives R=6.3
•  

C. Isover Isovip (https://www.isover.fr/sites/isover.fr/files/assets/documents/dp_isovip.pdf)

• From the technical specification sheet: very fine silica powder, pressed and vacuum-packed in polyester
• 56mm (= 86mm total) gives R=6.5

 

The question is really whether to use

1. mainly A, with B and C to treat thermal bridges and places where there isn't much space,
2. mainly B or C, with A to treat just one humid wall.

 

What to choose? Obviously, it is better to save space, and that should more than compensate for any reasonable additional cost - so that would point towards 2. But what other factors should I be considering? (Are there any known long-term health hazards suspected in B or C? What about durability?)

 

[nod]

 Natural is probably better if budget isn’t a consideration 

[Thorfun]

the problem you have is space. natural materials will require much thicker insulation layer to get the same level of insulation as non-natural products. so if you need the best insulation possible for the least possible thickness then natural insulation is not an option.

 

the other 2 products are vacuum packed so will be very expensive. also, if a panel gets so much as a little pin prick the insulation loses it's vacuum seal and all it's insulating properties. Personally, using that on a wall would scare the cr*p out of me as I can guarantee that no matter how careful you are you will damage some of the panels during installation. or, more likely, a trade will come after it's installed and drill a hole through the wall!

 

for best insulation you should be looking at phenolic boards which has a thermal conductivity of 0.018 W/mK which means that you can have it half the thickness of the natural stuff you linked above and still get better insulation levels.

 

it's not cheap though!

[PeterW]

7 hours ago, Garald said:

The architect I am working with is proposing the following materials

so your architect has substituted your space for green credentials - this happens ..! What was the brief to him ..?

 

Also seeing you are in France, are there any specific building codes you need to follow ..?

[SteamyTea]

What are you doing about moisture/vapour control.

While Paris is not that far South of London, the climate is quite different.  Higher summer humidity and temperature, colder and dryer winters.

Spring time, just pollen.

[Garald]

The green-credentialed material has good moisture-regulating properties.

 

I suspect that the difference in cost between options is dwarfed by the cost of the difference in space used (think 6k eur/m^2).

[Garald]

The architect also mentioned this one before - how does it compare? https://www.actis-isolation.com/produits/hybris/

[JohnMo]

7 hours ago, Garald said:

The architect also mentioned this one before - how does it compare? https://www.actis-isolation.com/produits/hybris/

Generally taken on here as snake oil.  You need an unvented air gap either side to get quoted performance, by this point you are taking up as much space as mineral wool, which cheaper.

[Thorfun]

so, if you need to get an R value of 3.8m²K/W then with the phenolic insulation you can achieve that with 70mm of insulation. so that's half the thickness of your natural product. even using standard PIR you only need 84mm to get the same R-value. 

 

if you're that worried about space then phenolic is your best bet. I wouldn't be using VIPS personally. they are extremely expensive and although you only would need around 25mm of insulation to get the same R-value I think the risk of puncturing the vacuum and the cost to save 45mm of space just doesn't seem worth it.

 

how much space are you willing/able to lose in the property for insulation?

 

ps. I'm all for natural insulation and I agonised for ages over the decision to use natural hemp or glass/mineral wool and, in the end, the mineral wool won due to costs, better lambda values and narrower walls. over the life of the building I'm sure the energy and carbon I will save will more than cover the initial carbon to create the mineral/glass wool**.

 

**please note I have used no scientific evidence or research to determine this conclusion!

Edited July 6, 2022 by Thorfun
narrower walls as well

[Garald]

On the street side, we could lose 20cm, but would rather lose less; it would detract from the main space - the architect would actually be unhappier than I would be.

 

On the courtyard side, I don't think we even have 20cm to work with - it's smaller rooms, and things could get a bit tight. 

 

So, overall, I'd be happy losing only 15cm, and if it were possible to lose only 10-12cm (counting sound insulation and so forth) I would be elated. This makes sense economically as well - in a place where 1 m^2 of surface is 6k, in a place with a ceiling that is 2.7m high, gaining 10cm is justified even if the material you use costs 222 eur/m^2 than the next best material! Hopefully we are not nearly in that range. 

[Garald]

I guess I could use phenolic boards and still drill holes in walls like a normal person?

[Thorfun]

200mm is loads. are you looking to get the minimum your regulations allow or do you want to go in excess of that?

 

1 minute ago, Garald said:

I guess I could use phenolic boards and still drill holes in walls like a normal person?

yes! can't drill holes through VIPS. 

 

If money is no object then you could look at using spacetherm aerogel. it has a lambda value of 0.015W/mK so is better than phenolic so can get a better R-value for the same thickness.

[Iceverge]

Once you have any kind of continuous insulation layer around your house, airtightness and ventilation losses start to dominate the comfort and heat loss equation. Windows too contribute hugely. 

 

Going from a U value of 0.25 to 0.15 W/M2K with the extra insulation won't make a damnedest difference if you are stuck at 5 ACH. 

 

I would pick a method that allowed for the best continuous airtightness layer, then make sure you have top class windows (great for city noise too) , maybe get those insulating roller shutters common in France. 

 

 

 

. 

 

 

[Garald]

>200mm is loads. are you looking to get the minimum your regulations allow or do you want to go in excess of that?

 

The minimum to get subsidies (not that they amount to a lot...) is R=3.8. For that, if we used BIOFIB TRIO, we would need 145mm, which, once we add a fire-proof panel and possibly some additional soundproofing, would bring us to 18cm.  (160mm instead of 145mm would give us R=4.2.)

 

 

>I would pick a method that allowed for the best continuous airtightness layer, then make sure you have top class windows (great for city noise too) , maybe get those insulating roller >shutters common in France. 

 

I take phenolic boards would allow for a continuous airtight layer? I am in fact replacing the street-side windows for the best windows we can get (my piano room/library is street-side); I am keeping the current double-glazing on the courtyard side - it may not be the best it is, but it actually does provide very good thermal insulation - we tested it. We are getting this kind of shutters:

 

 

 

>Going from a U value of 0.25 to 0.15 W/M2K with the extra insulation won't make a damnedest difference if you are stuck at 5 ACH. 

 

I know I will have to pay special attention to thermal bridges (is that what you mean?). What is best for that?

[SteamyTea]

15 minutes ago, Garald said:

I know I will have to pay special attention to thermal bridges (is that what you mean?). What is best for that?

No, thermal bridges are places where you have a larger than normal surface area.  So corners and internal walls where they meet external walls.

Basically any uninsulated areas that protrude.

 

Airtightness is purely the ventilation.  You need to control ventilation, not let just random holes and joints govern the infiltration.

Airtightness also improves sound insulation.

 

Have you started to think about sound transmission.  You my find that mineral wool is better than rigid board.  There are also 'resilience' bars that decouple ceilings and plasterboard walls.

[Garald]

Well, the architect is an expert on ventilation and sound-proofing, so I'll leave those two to her. (She knows sound insulation is particularly important to me.) She'll install something like double-flux ventilation but not quite - I can look up the details.

[Iceverge]

46 minutes ago, Garald said:

The minimum to get subsidies (not that they amount to a lot...) is R=3.8. For that, if we used BIOFIB TRIO, we would need 145mm, which, once we add a fire-proof panel and possibly some additional soundproofing, would bring us to 18cm.  (160mm instead of 145mm would give us R=4.2.)

 

I had a look at the website for this product. I think your architect is on the right track here. The system requires a battened wall and hemp/linen batts, ultimately followed internally by a breathable lime or clay render over a board of some kind. 

 

The headline R value is only part of the equation. High density insulants (typically made from plants) lend to much higher decrement delays and thermal buffering than lightweight plastic based boards. This translates to more comfortable temperatures in summer and lower cooling bills. They are vapour open (breathable) which protect the existing structure by allowing the existing old wall to dry to the inside and reduce the lightly hood of high humidity trapped in the wall leading to decay.

 

Vapour permeability is often confused with airtightness, They're essentially independent. Continuous lime plaster can be airtight while being vapour open.  Likewise old fashioned "drylining" with poorly a detailed polythene sheet full of holes can be almost completely non breathable (trapping moisture in the wall) while while also contributing very little to airtightness. 

 

 

I know I will have to pay special attention to thermal bridges (is that what you mean?). What is best for that?

 

Thermal bridging is typically non continuous insulation. For instance a a steel beam penetrating through a an insulated wall from inside to outside allowing an easy path to escape. Then there are geometric thermal bridges too like @SteamyTea refers to. This is where the insulation value will differ at a corner or a wall junction because the amount of surface for heat to travel through differs internally to externally. I wouldn't worry about this)

 

 

 

Airtightness is measured in air changes per hour (ACH) where a testing fan sucks air out of the house to simulate a wind of about 50kph. Draft proofing is another word. 

 

 

Have a proper energy model done ( or even use the one on here) to get a feel of the relative benefit of upgrades. For our own build it was in this order, 

 

1. Airtightness.

2. MVHR

3. Triple glazing over double.

4. adding extra insulation beyond building regs minimum.

 

 

[Iceverge]

14 minutes ago, Garald said:

Well, the architect is an expert on ventilation and sound-proofing, so I'll leave those two to her. (She knows sound insulation is particularly important to me.) She'll install something like double-flux ventilation but not quite - I can look up the details.

 googling double flux = MVHR.

 

Ask her what Airtightness strategy she plans on. 

 

If she has a good plan I think you've got a very good architect. 

[Garald]

Right, she's doing MVHR, from what I understood.

We'll get the best library/music-room windows we can - triple glazing if necessary.

 

Is the bottom line that we should consider BIOFIB trio for the wall that has humidity issues, and possibly at some places where we have space to spare (is there such a thing?), but phenolic boards or spacetherm aerogel otherwise?

[Iceverge]

14 minutes ago, Garald said:

the bottom line that we should consider BIOFIB trio for the wall that has humidity issues, and possibly at some places where we have space to spare (is there such a thing?), but phenolic boards or spacetherm aerogel otherwise

 

Biofib trio every where for me. Chasing lower U values alone misses much of the bigger picture about house durability, heat protection and real world vs theoretical performance.

 

Fire hazard, summer heat protection, construction waste, off gassing, thermal looping and high cost are all negatives with phenolic and to a lesser/greater extent with aerogel. 

 

 

 

 

 

[Garald]

Right, but that commits me to >=18cm of insulation everywhere.

 

Is the fire hazard actually greater for phenolic than for Biofib trio? The fire resistance of Biofib trio is mediocre, like that of any organic material I know - we will need to add fireproofing (which adds to the thickness; that's why it is 18cm and not 14.5cm).

[TonyT]

Are the architects on a fixed price or a percentage of the build?

[Garald]

Fixed price (her decision, so she wouldn't be penalized when trying to save me money).

[Garald]

The Solomonic solution may be to use:

 

- Biofib trio (145mm, meaning about 18cm total) on the southern, streetside wall, at least for the double library/music room (summer comfort and sound insulation both essential; we can dissimulate a loss of 18cm by creating architectural features (windowsills) and using shallow bookcases); ditto for the library sidewall that has humidity issues;

- phenolic panels for the other walls;

- aerogel for those odd corners (including those in the library) where we have only 5cm or so to work with.

 

Does this sound like a plan, or is it nonsensical, or inferior to using phenolic everywhere?

[Garald]

12 hours ago, Iceverge said:

 googling double flux = MVHR.

 

Ask her what Airtightness strategy she plans on. 

 

If she has a good plan I think you've got a very good architect. 

 

I will ask her, but, believe me, I trust her on ventilation. She has lots of ideas that I have barely been following: "ventilation par insufflation" (no idea what the technical term for that is in English) as an alternative to "ventilation mécanique contrôlée"; leaving open the possibility of an adiabatic cooling system; placing ducts under photovoltaic panels to heat air taken in; using the cold air from the quarries which lie somewhere under the building (as in the case in the entire southern third of Paris and immediate environs)...   I am not sure I can keep up, though I am sure that I would learn a great deal by doing so.