Insulating from the outside: wood fibre vs rockwool vs perforated polystyrene

[Garald]

(Quick summary: this is a north-facing masonry wall that has already been insulated from the inside (with a combination of reflective insulation and 45mm of BioFib Trio; both "breathe"). I am considering insulating from the outside as well because

- I am concerned that there may be condensation problems in the long term (Ubakus thinks there will be)

- the reflective insulation underperforms, or so a thermal camera tells me.

Of course I'd need the outside insulation to also be breathable, i.e., permeable to water vapor.)

 

Two options that have been mentioned by possible installers are polystyrene (this seems very standard; must make sure the installation is breathable) and rock wool. Today, an installer (who will come visit in a couple of days) proposed wood fibre.

 

In brief, he said

- in terms of cost: wood fibre > rockwool > polystyrene

- the R per cm of wood fibre is very nearly as good as that of rockwool.

- he doesn't see the point of rockwool, as wood fibre has much greater thermal mass, and that is helpful during the summer. (OTOH, this is a northern wall, so sun exposure is not a big issue.)

- he said wood fibre gives excellent

- He also says rockwool has much greater environmental costs than wood fibre. Is this true? How does the environmental impact of rockwool vs. polystyrene help?

- He waved away my concerns about the use of flammable materials, saying there are no rules from the fire code about that (this is basically a house, not a tall building). I'd still rather not burn. Is the flammability of wood fibre or polystyrene a real issue?

 

 

[Iceverge]

57 minutes ago, Garald said:

am concerned that there may be condensation problems in the long term (Ubakus thinks there will be)

 

Post a snapshot. I'm curious to have a look.

 

58 minutes ago, Garald said:

the reflective insulation underperforms, or so a thermal camera tells me.

 

More detail again, what product did you use. Any thermal pics would be interesting. 

 

58 minutes ago, Garald said:

Of course I'd need the outside insulation to also be breathable, i.e., permeable to water vapor.)

 

It depends.....

 

I believe you are in Paris, near other buildings. I would probably rule out EPS for the fire reasons you mentioned there. 

 

Rockwool and woodfiber would both be fine.  My preference would be rockwool as it's more flexible and can conform to any imperfections better. 

 

[joe90]

3 hours ago, Garald said:

he said wood fibre gives excellent

?

[Garald]

2 hours ago, joe90 said:

?

Ah, I was falling asleep. That it gives excellent sound insulation. So does rockwool, no?

[SteamyTea]

This is a bit of an old copy now, but still valid as a comparison to see which uses the least and most energy and embodied carbon dioxide.

https://greenbuildingencyclopaedia.uk/wp-content/uploads/2014/07/Full-BSRIA-ICE-guide.pdf

 

 

As for the reflective insulation, it does not come as any surprise that it underperforms.

Edited October 19 by SteamyTea

[Garald]

13 minutes ago, SteamyTea said:

This is a bit of an old copy now, but still valid as a comparison to see which uses the least and most energy and embodied carbon dioxide.

https://greenbuildingencyclopaedia.uk/wp-content/uploads/2014/07/Full-BSRIA-ICE-guide.pdf

 

Would wood fibre be "woodwool"?

 

 

The first two volumes are embedded energy by weight and embedded carbon by weight. Hard to compare if one doesn't have typical densities - what would those be, roughly?

 

(I wonder about the difference in embedded energy by weight between loose woodwool and woodwool board.)

 

 

[Garald]

6 hours ago, Iceverge said:

 

Post a snapshot. I'm curious to have a look.

 

 

The exact (?) data on the insulation is here:

(The diagram there is not from Ubakus - it's from the pdf given to me by the fake architect. Long story - a real lawyer is now taking care of that.)

 

I have tried to reproduce this on Ubakus, with the following approximations:

(a) I couldn't find ATI PRO MULTI HPV there, so I've chosen "AirGuard Reflective";

(b) I've keyed in both layers of air as unventilated (since I do not see how the one next to the masonry is supposed to be ventilated) and

(c) I have used '1952 solid brick,  1400 kg/m3' (a medium density within the list) instead of my unknown masonry from the early 30s.

Here is what I get:

 

 

[SteamyTea]

50 minutes ago, Garald said:

Would wood fibre be "woodwool"?

Wood wool board I think.

51 minutes ago, Garald said:

Hard to compare if one doesn't have typical densities - what would those be, roughly

You will have to look at the product specification sheet.

 

12 minutes ago, Garald said:

the fake architect

Was that the one you first used?

[Garald]

 

22 minutes ago, SteamyTea said:

Was that the one you first used?

Right, the "architect" I first used:

- became very upset when I pointed out to her that her plans on how to install a heat pump ran against physical law (I owe you guys a big thanks - you remember that I posted a question here right after getting a sketch from her, as I had serious suspicions),

- started asking for more and more money,

- left in a huff in the middle of work,

- turned out not to be an architect. Possibly a failed architecture student in the 90s, got a cheap master's degree in urban planning on Saturdays in 2005 or so, spent 15 years working as a fake architect (claiming to be an architect, but being careful not to use the word 'architect' in print; it's the sort of thing you realize post facto).

I was keeping mum about the matter just in case she reads this forum (very unlikely; her English is nearly non-existent, but then there is Google Translate) but, as I said, there is now a real lawyer taking care of things. Who knows what will happen.

[Garald]

7 hours ago, Iceverge said:

 

Post a snapshot. I'm curious to have a look.

 

 

Here is a second attempt - again, approximate, but maybe more realistic.

 

 

What I have done here: 

- ATI PRO MULTI HPV is 40mm thick - the reflective insulation is a combination of linen and some sort of wadding ("ouate"):

It's supposed to have an intrinsic R of 1.96, which doesn't sound very believable for 4cm. I've keyed it in as a reflective insulation layer + 4cm worth of a hemp-jute product that Ubakus has on file.

 

- I've included a vapor barrier (which is the plans; I hope it's really there - I saw it on other walls when the insulation was being installed).

 

As you can see from the diagram, Ubakus still predicts some condensation (nothing as dramatic as before).

FT_ati_pro.pdf

[Garald]

7 hours ago, Iceverge said:

 

 

More detail again, what product did you use. Any thermal pics would be interesting. 

 

 

 

ATI PRO HPV (see the photo and the product specification sheet above). It seems to be used mostly for ceilings.

Here are some thermal pictures of the north wall I took last January. (I thought I had posted some in this forum, but they seem to have disappeared.)

 

Bedroom wall and window:

 

 

Same wall, with roller shade pulled down:

 

Under the small staircase going to the attic:

 

 

Top of small staircase (notice the metal frames inside the wall, clearly visible thanks to the thermal camera):

 

Large staircase:

 

WC:

 

Bathroom, I think:

 

Ground floor: cupboard under the stairs. I had a mold problem there later, specially in the corners.

 

 

Ground floor room, corner.

 

 

 

[Iceverge]

What an experience with your designer. I hope it gets resolved. 

 

I assume you didn't tackle the airtighess yourself and didn't blowerdoor test it or fastidiously supervise the workmanship?

 

The reason I ask is that that multi foil layers depend very highly on stationary air to give meaning insulative value. Try playing with Ubakus to see what happens if you put ventilated air in there instead. It'll collapse the U Value. 

 

What you've effectively ended up with is 50mm of Hemp insulation between battens,decoupled from the solid wall, giving I would estimate a U Value of about 1 W/m²K. It's lightly there's some wind washing behind the insulation too. 

 

Could you describe in words the exact build up for clarity please. 

 

EG

300mm solid wall

20mm render 

 

 

 

 

 

 

 

[saveasteading]

I have some experience of fires.

Firstly playing: put an offcut on a hot fire and observe....

polystyrene bursts into flame, melts and spreads.

Pir catches fire and burns, and disappears.

Wood fibre burns slowly and disappears.

Mineral wool does not burn, but reverts to being sand.

 

In the afternath of warehouse fires I've seen eps had spread the fire quickly and everywhere.

Mineral wool resisted the intense heat for a time, then turned to sand on the floor.

[Redbeard]

Re wood-wool and (rigid) wood-fibre, wood-wool would perhaps be better described as 'wood-spaghetti' (think of the Heinz variety - short lengths pressed together - offers a really good 'key' for plaster or render). However its Lambda value is 0.066 - 0.074W/mK, while that for wood-fibre is in the range 0.039 - 0.044W/mK, so wood-wool only just over half as good for a given thickness. Different horses for different courses.

[Garald]

1 hour ago, Iceverge said:

What an experience with your designer. I hope it gets resolved.

 

She has tried different hats in her career ("urban planner/architect", and also some initials that turn out to just mean some sort of assistant), and, if you follow her tax number, you'll find she's registered as a "plastic artist" (of course plastic artists pay less taxes - perhaps she'll be nabbed for that). She hasn't quite tried "designer" yet - don't give her ideas :).

 

1 hour ago, Iceverge said:

I assume you didn't tackle the airtighess yourself and didn't blowerdoor test it or fastidiously supervise the workmanship?

 

I tried to do a blower-door test myself, but failed due to my fan being sort of pathetic. I queried the fake architect (whom I did not know to be fake at the time) about airtightness, but she only gave evasive replies.

 

I'm still trying to find a ventilation company to do an airtightness test (or whom would one usually hire to do that?). The contractor has told me there are deliberate outlets near the windows in the first floor (I have never been able to find them), as I have PIV and such deliberate weaknesses in the airtightness are necessary - I imagine people who do blowerdoor tests are able to find such outlets and block them. My medium-term aim is finding a company willing to design and install a cascade double-flux system, though I am a bit concerned about noise issues. (I am very sensitive to noise.)

 

I was away while most of the work was being done, but requested and got plenty of pictures, and also took some myself:

 

1 hour ago, Iceverge said:

What you've effectively ended up with is 50mm of Hemp insulation between battens,decoupled from the solid wall, giving I would estimate a U Value of about 1 W/m²K. It's lightly there's some wind washing behind the insulation too. 

 

Could you describe in words the exact build up for clarity please. 

 

EG

300mm solid wall

20mm render

 

From the outside to the inside:

 

old render of whatever kind

Solid wall (it would seem to be a bit more than 25cm, so some 24cm without counting the render, say)

bit of air

reflective insulation with linen/wadding backing, 40mm thick

  (allegedly R=1.96 "intrinsic" and 'as good as R=6 because of reflective insulation", but it's probably more like R=1 if you discount the reflective effect;

    it's not nothing, as it can't be 40mm worth of nothing)

bit of air

45mm of BioFib Trio (hemp/cotton/linen), R= 1.18

13mm fireproof plaster

 

 

 

[Garald]

PS. Is the insulation guy right about the upsides of increasing thermal mass and hence thermal phase (by means of wood fibre)? Ubakus tells me that the phase shift is already 13 hours in the current setup (assuming 24cm of solid wall, which seems like a safe assumption - this is construction from the early 1930s; also, notice the pictures above - sideways bricks mean "solid wall", no?). With any kind of outside insulation (rock wool or wood fibre; oddly enough, Ubakus tells me that rock wool gives a greater phase) we'd be looking at a 20-21h phase. Isn't a phase closer to 12h better (day->night)?

 

Also, it's odd that Ubakus gives a greater phase (21h total) for rockwool than for wood fibre (20h total). Doesn't wood fibre have a much greater thermal mass (2.3 J/g K) than rock wool (0.8 J/g K)?

[SteamyTea]

59 minutes ago, Garald said:

Is the insulation guy right about the upsides of increasing thermal mass and hence thermal phase

No he is not right. It is too small a difference to notice.

 

It is thermal inertia, not thermal mass.

The k-value becomes the over riding property, not the mass or heat capacity.

[Iceverge]

As a general rule anyone who says "thermal mass" doesn't know what they are talking about. 

 

 

[Iceverge]

Ok. I'm going to take a leap here and say that there was no proper Airtightness measures taken with the buildup. The comment about the deliberate weakness in the envelope doesn't bode particularly well for the rest of the gig. 

 

Airtighess is vital in ensuring a building remains healthy, comfortable and economical. 

 

The thermal bridging demonstrated by the metal studs isn't particularly good either. 

 

External insulation I think is a good idea. I'm assuming you don't live in an area of much driven rain. Rockwool gets my vote as it's fire resistant, flexible and can conform to wall imperfections, resistance to rot and insect damage and knits together with a joining boards on install. 

 

 

 

 

 

 

 

 

 

[SteamyTea]

What always amazes me is that people seem to think that it needs to be about 12 hours so that daytime and nigh time equal.

How many days a year does that happen in the UK, 2.

 

[Garald]

12 minutes ago, Iceverge said:

As a general rule anyone who says "thermal mass" doesn't know what they are talking about.

 

You can blame me - I am translating my memories of a conversation on the phone two days ago or so.

[Garald]

4 minutes ago, SteamyTea said:

What always amazes me is that people seem to think that it needs to be about 12 hours so that daytime and nigh time equal.

How many days a year does that happen in the UK, 2.

 

 

What should one aim for, then?

[SteamyTea]

2 minutes ago, Garald said:

 

What should one aim for, then?

The best thermal conductivity you can get i.e. the lowest U-Value.

[Iceverge]

Phase shift or decrement delay for some reason ends up far higher on people's list than it should do. 

 

I think a lot of it is because they misappropriate the effects of over glazing and poor ventilation, Airtightness and poor insulation.

[SteamyTea]

Just now, Iceverge said:

I think a lot of it is because they misappropriate the effects of over glazing and poor ventilation, Airtightness and poor insulation.

Yes.

We often hear, on here, that people are improving their airtightness by fitting new glazing.