Insulation woes; Jetrock 2? (Alternatives?)

[Garald]

This chapter in the insulation saga:

 

Originally, the plan was to

(a) insulate the first floor and my part of the ground floor up to current standards or a bit beyond (estimated U = 0.23, once we count both the insulation and the walls as such),

(b) make no radical changed in the attic, which was insulated some ten years ago - just fill out some gaps and replace some of the existing rock wool.

 

However:

- the staircase going up to the attic is a weakness.

As you can see, the contractor has managed to insulate the short side of the stairwell in the same way that we've insulated the rest of the courtyard-facing wall (reflective material+cellulose based), but the long wall (2.25m) seemed at first impossible to isolate - not enough space. However, we just noticed that there's space behind the wall panel (about 5cm) and that behind that space there is... air.

  The lower part of the long wall adjoins the building next door, which may or may not be regularly heated, but the top part of the wall has nothing on the other side.

 

 

(My house is the red one.)

 

- the isolation in the attic turns out to be poor. On the gable walls, there a few centimetres of goodness knows what (well, my contractor and my architect know, but I either didn't ask or have forgotten). In the "combles perdus" (lost height) on the long sides, there is rock wool for the most part, but it's in poor condition. There are some voids that the contractor had agreed to fill.

 

You can see this sort of thing behind my new bathtub:

 

(You can also see that there is plenty of work left to be done.)

---

Now, the question is what to fix and how.

 

1. The architect would apparently be happy leaving the long side of the staircase uninsulated. Now, that side is 2.25m long (more if you count the landing) and let us say that 2m of it lie above the neighbouring building (it may be a bit less on average, though it's more towards the middle of the gable walls). The brick walls are not particularly thick, and they date from 1930; let's say they have U = 2.2. Then, if we want to keep the stairwell at no less than 18C, and we are designing for an outside temperature of -2C, we are talking about a heat loss of at least

 

2.25*2*2.2*(18-(-2)) = 198W;

 

compared to decent insulation (U=0.35, say), we are talking about a difference of 166W.

 

The architect suggests just putting a small radiator there. Reason? The contractor estimates that the cost of insulating that wall properly (labor costs and so forth included, obvs) would be 2400eur. 

 

Let me do a back-of-the-envelope calculation (please check to see whether I have made an obvious mistake): 

assuming the heating is on half of the year, we are talking about 166*24*(365/2)/1000 = 727kWh,

or that divided by the heat-pump's SCOP (about 3.5, say) if we actually manage to heat the stairwell entirely by means of a radiator.

Let's say the radiators cover 70% of the heat loss, and the rest is electric heating. Then we are talking about 727kWh*(0.7/3.5+0.3) = 727/2 = about 364kWh per year,

which, at 0.174eur/kwH, adds up to 63.3eur per year. In other words, it would take me 38 years to amortize the cost of insulating the staircase (probably less since energy prices won't stay constant, but still) . The architect is right (if the contractor's price can't be negotiated further, and she says she hasn't managed to).

 

2. Now, if we redid the entire insulation on the stairs _and_ the gable walls to the same standard as the rest of the house (U=0.23 for the most part - probably a bit worse on the staircase),

and also redid the insulation on the combles perdus up to a reasonable but not sterling standard (see below from the contractor's suggestion),

 

- the bill would be 5k eur,

- the heat loss avoided would be on the order of 166W + 550W taking into account only the gable side walls (assuming the current insulation on the gable walls is negligible); if we also consider what we would gain from a better insulation of the combles perdus (compared to just filling out some gaps in a perfunctory fashion), we are probably at about 166 + 800W, at least. Thus, on top of the 63eur mentioned above, we would be saving 800*24*(365/2)/(SCOP*1000) = about 1000kwH per year, meaning 174eur per year, or about 240eur/year in total; the costs would then be amortized in about 21 years, which is... not great, but not terrible. Worth considering.

----------

 

On the other hand:

(a) if I ever have money again, it would make sense for me to invest to raise the roof. The contractor thinks the work on the stair side and the gable walls would not be lost; the architect is not sure about the latter. Somewhat bafflingly, the architect tells me that the insulation of the combles perdus would not be lost if I raised the roof, at least not if I had it raised in a parallel way she has suggested - the lower red dashed line in the following:

 

I

 

'll have to press her for ideas on how that would work, as I really don't see how that could be kept. The depth and height would not be the same.

(b) While the contractor is proposing using the same insulation system that we have used on the courtyard-facing wall and the kitchen side wall (reflective + cellulose), he is suggesting something else for the combles perdus (won't someone tell me what the technical term is in English?):

 

https://www.rockwool.com/syssiteassets/rw-f/telechargements/guides-de-pose-et-mise-en-oeuvre/combles-perdus/rockwool_mise_en_oeuvre_jetrock_2_combles_perdus_202001.pdf

 

Reasons in favor: it's apparently cheap, and made for this purpose.

Reasons against:

a) well, we didn't use any rock-wool elsewhere - we have kept the rock-wool in the roof, and were going to leave the rockwool on the c....s p...s , with a mind to replacing them when and if I have the roof raised. If the insulation we'll put here in the c..s p...s can really be conserved if the roof is ever raised, then, does it make sense to go cheap?

b) not very impressive lambda, though perhaps that doesn't matter because of all the depth we've got

(c) one of the reasons we've avoided rock-wool is that it can be an irritant; its long-term effects are not fully known. And yet we are going to have it loose on the sides, separated from bedrooms by just a panel? If there's an opening somewhere, particles will go through.

 

What do you think? What are some alternatives at a similar price-point? There are of course things like cork, but that's expensive.

 

(A quick Internet search gives me: https://conseils-thermiques.org/contenu/ouate-de-cellulose.php . Does this sound like a plausible alternative?)

Edited December 24, 2022 by Garald

[ADLIan]

I don’t think any insulation manufacturer would market a product that was inherently dangerous to health either in its install or use. Mineral wool products are well understood and newer formulations are much more pleasant to handle. In France look at ‘pure one’ from Ursa, better thermals than rock wool and claimed much better handling, softer & less irritant.

[Tom]

27 minutes ago, ADLIan said:

I don’t think any insulation manufacturer would market a product that was inherently dangerous to health either in its install or use.

 

Ummmmmm...... really?

 

[Alan Ambrose]

>>> I don’t think any insulation manufacturer would market a product that was inherently dangerous to health either in its install or use.

 

Ha ha ha, ha ha ha, ha. Grenfell maybe? Asbestos was only completely banned as a building material in ... 1999. The building I'm in right now has 50mm of (very flammable) expanded polystyrene in the walls and it was built in the '90s. The manufacturer is still selling this as a building material.

 

Maybe you were being sarcastic.

 

Alan

[Alan Ambrose]

While cellulose has low embedded energy, I think I would go with Rockwool for its fire and damp behaviour. It'll be boxed in, so the ongoing irritant factor will be negligible.

 

Alan

[Garald]

5 minutes ago, Alan Ambrose said:

While cellulose has low embedded energy, I think I would go with Rockwool for its fire and damp behaviour. It'll be boxed in, so the ongoing irritant factor will be negligible.

 

Alan

 

What are the downsides of cellulose?

 

(Its fire behavior when treated with boron salts (as is standard) seems reasonable - isn't it graded B? As for dampness, the rock-wool insulation put in by the owners from 10 years ago is a very striking demonstration of what can happen to rock wool when it's damp. I'll have to find a good solution for that in either case.)

 

I know rock wool is much less of an issue than fiberglass, which is itself much, much less of an issue than asbestos, but (a touch of) asthma runs in the family, the bedrooms will be partly in the attic, and I'm not positive that things that are boxed in remain 100% boxed in when you have old construction (this is a house from 1930). I'm not anti-rock-wool, but, given that we managed to find a solution without it for the rest of the house, it seems like a bit of a pity to have to recur to it now.

Edited December 24, 2022 by Garald

[ADLIan]

Fire is a totally different issue and not part of the ‘normal’ use of insulation, or most other construction products. Most houses are full of materials that are perfectly safe to use on a day to day basis but set fire to them and is very different scenario. Combustible insulation products are still acceptable in many instances under the Building Regs provided they are encapsulated within the construction - within masonry cavity walls, concrete floors etc. the risk is deemed to be low and they will not contribute to the development stage of a fire. Smoke inhalation from burning furniture and fittings in a house will kill a person a long time before the insulation in a cavity wall is involved. Grenfell was very different with certain manufacturers conspiring to promote the use of combustible insulation in an application where the risks were already well understood, documented and covered by the Approved Document B.

 

Rock and glass wool products, both ‘mineral’ wool, are safe to use; modern glass wool formulations being much more pleasant to handle and install.