Roof insulation on the inside - quotes - discussion

[Garald]

Currently, the attic (inhabited: home office, bedroom/home office, bathroom) is the worst-insulated part of my place: the ceiling was insulated by the owners before the previous ones, at least 15 years ago if not more, with what looks like fibreglass. It's expensive to heat in winter and it gets rather hot in summer. Putting outside shades on the skylights has helped a great deal with the heat, but the main issue remains. Sound insulation is also an issue.

 

Insulating from the roof from the outside (called "sarking" over here) would be very expensive (ca. 40k apparently). I've asked for quotes for insulating from the inside. It's not an optimal solution (I have only 18cm to play with - I do not want to lower the ceiling any further, since it is low as it is) but it is what is possible for now. Since summer is at least half of the problem, I've asked quotes using materials with high thermal inertia (wood fibre, not rock wool; I may also get a quote for cork).

 

I'm attaching the two quotes I've been able to get so far. The one with the lower surface area (60m^2) has the right measures - folk from that company (ISOVEO) came to measure, whereas the fellow from the other company (SMCI) had visited a while back and went off an estimation.

 

My take:

* Both quotes seem rather high (SMCI, in particular, proposes to charge me an insane amount for painting the attic ceiling and preparing it to be painted).

* The R given by SMCI is mistaken - the figure should be R=5.

* Neither company wanted to raise the tiles a bit to reach a higher R, as has been suggested here - they said it would cost a fortune (presumably in labor costs).

The idea in both cases is the same - watertight membrane, 18cm of woodfibre, air layer, plasterboard. I include an UBAKUS simulation that ISOVEO Sent me.

 

- Should I keep looking, hoping for something significantly lower? What price would you expect in the UK?

- In part because the plasterboard and painting would be such a large part of it, I'm tempted to consider just having exposed cork insulation. My girlfriend, however, would kill me (she might have a point: the attic might look a bit too much like non-inhabitable attic) and not having plasterboard could go against local regulations. Perhaps I should consider decorative cork in place of a paint job, on top of naked plasterboard? Is that a possibility? (Sounds expensive until you see that SMCI wants 6 186,68 € for painting and preparation.)

 

Any ideas? Comments?

 

Also, I've given up on getting to R=6 (the level at which I would get a bit of subsidies), but if you have any notion of how to get there without losing space, be my guest. Perhaps I should consider losing a couple of centimeters in the lower parts, where one can't stand anyhow.

 

SMCI.pdf UBAKUS_SIMULATION_M_HELFGOTT.pdf devis isolation combles ISOVEO.pdf

[SBMS]

Wouldn’t ordinarily recommend PIR but I think the best insulating material to use in this instance would be PIR, is there a reason you haven’t considered this? It’s probably close to

double the thermal resistance to wood fibre, so twice as insulating?

[Garald]

13 minutes ago, SBMS said:

Wouldn’t ordinarily recommend PIR but I think the best insulating material to use in this instance would be PIR, is there a reason you haven’t considered this? It’s probably close to

double the thermal resistance to wood fibre, so twice as insulating?

 

Low thermal inertia (would be a particularly serious problem during the summer). Worse than that of fibreglass, no?

[Garald]

Also, cork has higher thermal inertia than wood fibre, no? (Why am I having a hard time finding a good table?) The ISOVEO folks objected that they wouldn't cut cork boards in such a way that everything would be airtight - but surely I can suggest a combination of cork and wood fibre, or will I sound like a ninny?

[nod]

Why not simply fix insulated plasterboard on the inside 

Re skim Or more likely tape in France 

re paint You can get an extremely high level of insulation with this method 

For less than half what you are being quoted 

Edited April 12 by nod

[Garald]

1 hour ago, nod said:

Why not simply fix insulated plasterboard on the inside 

Re skim Or more likely tape in France 

re paint You can get an extremely high level of insulation with this method 

For less than half what you are being quoted 

 

Not sure I understand - flesh out the details, please?

[Garald]

Let me include a couple of pictures, in part to make clear that this is a fiddly structure that not every builder *wants* to insulate from the inside, and in part so that everybody can see how short I am of headspace as it is.

 

 

 

I *could* consider losing a couple of cm in the lower parts (where one can't stand anyhow) just so as to reach R=6 (the magical level for the however rather paltry subsidies). Not in the middle part, however - places where a 180cm-high person can still stand are worth their price in gold (plus, I am 178cm, and I want to hit my head as little as possible).

 

I can of course remove all the furniture myself. The bookshelves are DIY - I can modify them a bit if the ceiling on the lower part needs to be dropped 3cm, say.

Edited April 12 by Garald

[BotusBuild]

Would something like that Superfoil stuff help. Or insulation stripped out from old airliners? Good recycling credentials 🙂

[Garald]

9 minutes ago, BotusBuild said:

Would something like that Superfoil stuff help. Or insulation stripped out from old airliners? Good recycling credentials 🙂

 

Folks here have dim views on reflectant insulators such as superfoil. I have a combination of BioFib and a reflectant insulator on the northern wall (a muddling-through decision by a fake architect) - it's probably better than nothing, and might actually be a good thing to have if you are insulated up to code. I may insulate that wall on the outside at some point.

 

At any rate, that's all moot because, let me repeat myself: *the main problem is during the summer*, and I don't see how to deal with that in any way other than thermal inertia.

 

Sure, it might be nice to put reflectant facing both ways. We can discuss where to put each reflectant layer. But that would just be the cream on top.

 

The main point is: I don't know of any synthetic stuff that would do the job. If somebody can tell me of any (preferably recycled) high-tech stuff that thermal inertia higher than that of cork or wood fibre, please tell me.

 

In the winter, the question is: isn't it a shame that the attic is the coldest place, whereas it should be warm? (Energy conservancy, (non-)professional pride.)

In the summer, the question is: how can I work here when is it so darn hot? I can't use any of this space as a bedroom, particularly not for anybody young or old, with the possible exception of my great-aunt from the tropics, if I ever convince her to come visit.

 

 

[BotusBuild]

I should have expanded. My thinking was make these "thin" materials a part of the solution to help get the R up to 6. I was not suggesting using these materials alone. I should perhaps have been clearer.

[Garald]

42 minutes ago, BotusBuild said:

I should have expanded. My thinking was make these "thin" materials a part of the solution to help get the R up to 6. I was not suggesting using these materials alone. I should perhaps have been clearer.

 

Right, that could be part of the solution, though neither reflective insulation nor something I would scavenge myself with help with subsidies (not that they amount to much); they may not even be counted towards energy ratings (the reflective insulation I have on the north wall got counted last time, but the examiner told me he was being lenient).

 

I think of a radiant barrier as a possible nice addition once one reaches the R one can realistically reach. This is a side issue, but: I imagine the ideal thing would be to have one layer outside the insulation, shiny part facing in, and one layer on the bottom of the insulation, shiny part facing out?

Edited April 12 by Garald

[Mike]

Based on your constraints, I think that the (insulation) spec is about as good as you'll get. I'm not too shocked by the price either. A few observations:

 

• If you're still planning to install MVHR, you can very probably drop the vapour barrier from the spec; the MVHR unit is very likely to keep the moisture below problematic levels. Having said that, it may be difficult to convince the contractor to omit it, as it is required by the French DTU. And ideally you'd want a WUFI analysis to prove it (and obtaining the data for that could be tricky - I may have some next year).
• However, unless you already have one, I'd add back in an airtight membrane on the outer face of the insulation. That will be fiddly, so will cost more than the vapour barrier would have done (unless you DIY it)
• Think about a double layer of plasterboard, or at least upgrading the plasterboard to a high-density version, as it will be very exposed to knocks in your situation, and the extra layer will help somewhat with sound insulation.

 

FWIW, my mansard spec isn't too dissimilar : Mento used as an airtight barrier + 100mm Biofib Chanvre + 45mm Biofib Trio + 2 layers of Gypso Omnia (aka Gypso Lignum).

 

Edited April 12 by Mike

[Conor]

Smaller, and triple glazed, roof lights would make a bigger difference than new insulation. It looks like you've some 30-50% glass in those rooms. You could make each one half the size and not make the spaces feel too dark. Cost would be more like €5-7k, and youd properly insulate the reveals. You'll never see the money back on those above quotes. More heating / cooling would be cheaper over a lifetime.

 

I'm assuming the roof lights are of the same generation of the remedial roof works, ~15 years old?

Edited April 12 by Conor

[Garald]

29 minutes ago, Conor said:

Smaller, and triple glazed, roof lights would make a bigger difference than new insulation. It looks like you've some 30-50% glass in those rooms. You could make each one half the size and not make the spaces feel too dark. Cost would be more like €5-7k, and youd properly insulate the reveals. You'll never see the money back on those above quotes. More heating / cooling would be cheaper over a lifetime.

 

I'm assuming the roof lights are of the same generation of the remedial roof works, ~15 years old?

 

No, all roof lights (except for one) are new, from 2 years ago - double-glazed, not triple glazed, but with good specs (U = 1ish if I remember correctly). That is, half of the roof lights were already there, but I had the windows remplaced entirely. I also put retractable outside shades on all of them (that made a very big difference - as far as summers are concerned obviously).

 

It's not 30-50% glass, it just looks that way (on purpose ). It's about 21% glass. A very pleasant space in mid-season (I'm sitting there right now). 

Edited April 12 by Garald

[Garald]

2 hours ago, Mike said:

Based on your constraints, I think that the (insulation) spec is about as good as you'll get. I'm not too shocked by the price either. A few observations:

 

• If you're still planning to install MVHR, you can very probably drop the vapour barrier from the spec; the MVHR unit is very likely to keep the moisture below problematic levels. Having said that, it may be difficult to convince the contractor to omit it, as it is required by the French DTU. And ideally you'd want a WUFI analysis to prove it (and obtaining the data for that could be tricky - I may have some next year).

 

I wouldn't rely on it. Two teams of ventilation people came to visit. One of them said that le jeu ne vaut pas la chandelle (i.e., MVHR wouldn't be worth the insulation cost right now - maybe if at some point I raise the roof). The other team was more optimistic (even though they said that, in all honesty, the MVHR systems they work with recover only 30% of heat, whatever the manufacturer says - is this normal? are MVHR systems in France backwards? are French MVHR installers pathologically upright?) and promised to send me a quote... and then they never did, though I've reminded them. Time to give them a ring.

 

2 hours ago, Mike said:

• However, unless you already have one, I'd add back in an airtight membrane on the outer face of the insulation. That will be fiddly, so will cost more than the vapour barrier would have done (unless you DIY it)

 

Ah, funny - I could swear the ISOVEO guys mentioned that verbally. Somehow it hasn't made it to their quote or their model - will ask.

 

2 hours ago, Mike said:

• Think about a double layer of plasterboard, or at least upgrading the plasterboard to a high-density version, as it will be very exposed to knocks in your situation, and the extra layer will help somewhat with sound insulation.

 

Or I could put plasterboard and then a layer of decorative cork (which comes in widths ranging from 3cm to 15cm), which would in effect not just be decorative but also help with everything you say (besides being safer for my head than plasterboard). At the price SMCI wants to charge for painting, I could put gold leaf on the ceiling if I wanted to. I imagine decorative cork can be put directly on unprepared plasterboard without further ado, or not?

 

2 hours ago, Mike said:

 

FWIW, my mansard spec isn't too dissimilar : Mento used as an airtight barrier + 100mm Biofib Chanvre + 45mm Biofib Trio + 2 layers of Gypso Omnia (aka Gypso Lignum).

 

I love Biofib Trio - have it on my southern first-floor wall, which faces a busy street. How do wood fibre and cork compare in terms of noise reduction?

Edited April 12 by Garald

[Mike]

2 minutes ago, Garald said:

the MVHR systems they work with recover only 30% of heat, whatever the manufacturer says - is this normal? are MVHR systems in France backwards?

Yes and no. France was into centralised ventilation decades ago, and it seems that quite a few manufacturers added cheap heat recovery units to their line-up (much like extractor fan manufacturers have in the UK) - and the performance of many probably isn't very spectacular, so may deserve a poor reputation. It's also true that the figures reported by most manufacturers over-state reality, thanks to the ill-conceived tests that that are used.

 

The exception are MVHR units listed in the Passivhaus database, which can be relied on. They've been independently tested to realistic standards, rather than those used by manufacturers: https://database.passivehouse.com/en/components/list/ventilation_small. The 'Efficiency Ratio' (which takes into account electricity used as well as heat recovered) is the key figure for comparison. For example, the near-identical Zehnder ComfoAir 200 & 225 models both have a heat recovery rate of 92%, but the 225 has more efficient fans so has a higher Efficiency Ratio (0.69, rather than 0.67).

 

15 minutes ago, Garald said:

At the price SMCI wants to charge for painting, I could put gold leaf on the ceiling if I wanted to

It would help reflect the heat back :)

 

Note, though, that the larger part of the SMIC cost isn't the actual painting, it's the preparation with 2 coats of 'skim'. Except in France they use something more like filler, which isn't anything like as good as the gypsum skim used in the UK, but is still better than regular jointed plasterboard (though not €3.5K better). Still toying with the idea of importing some gypsum board finish from Italy for mine; so far I've only bought 1 bag to test...

 

23 minutes ago, Garald said:

I imagine decorative cork can be put directly on unprepared plasterboard without further ado, or not?

It could indeed, provided you buy the right grade - there are some really interesting decorative ones around too: https://www.liege24.fr/shop/80-liege-mural-3d/

 

It would be likely to get accumulate some damage from knocks, but it is easily repaired.

 

27 minutes ago, Garald said:

How do wood fibre and cork compare in terms of noise reduction?

Not sure about that - you'd need to compare with the online tool I mentioned in one of your other recent posts. However the density and structure of a material affects the frequencies that are reduced, so in principle having two different materials could be useful in reducing the overall sound spectrum. Not not sure how much difference you'd hear in practice at the likely thicknesses, but it was a secondary factor in choosing to mix Chavre & Trio in my mansard.

 

[Garald]

14 minutes ago, Mike said:

Not sure about that - you'd need to compare with the online tool I mentioned in one of your other recent posts. However the density and structure of a material affects the frequencies that are reduced, so in principle having two different materials could be useful in reducing the overall sound spectrum. Not not sure how much difference you'd hear in practice at the likely thicknesses, but it was a secondary factor in choosing to mix Chavre & Trio in my mansard.

 

 

Is there a good reason to prefer BioFib Trio or Chanvre to Steico wood fibre (036 or 038) or cork? The lambda seems to be always in the same range (around 0.038, though with cork it depends on the source) and the thermal inertia of Steico 038 seems to be about 15% higher than that of BioFib (and the thermal inertia of cork should be much higher, no?).

[Garald]

Hah! The MVHR company I just contacted has sent me an apology and a quote - which is huge! My reaction has to be: le jeux ne vaut pas la chandelle! Separate thread for that.

[Mike]

1 hour ago, Garald said:

Is there a good reason to prefer BioFib Trio or Chanvre to Steico wood fibre (036 or 038) or cork? The lambda seems to be always in the same range

Cork is in a separate category - it's got an exceptionally strong set of characteristics, and for wet conditions it's the only option. However the price is much higher than the others and it's not compressible, so it can't be squished between rafters / other obstructions. I have used some on my current project, but mainly fixed to the faces of the chimneys, hidden behind plasterboard.

 

For hemp / flax / wood fibre, there's not a great deal to choose between them. From memory, wood fibre is fractionally ahead in terms of insulation, but one brand / product nudged ahead for winter insulation, and another for decrement delay in summer. Hemp & flax just top wood fibre for moisture buffering and, as that's my top concern, it was a leading factor in choosing Biofib. The exceptional physical flexibility & compressiblity of the Trio was also a big plus in adapting to uneven surfaces, so using one layer of Chanvre + 1 of Trio seemed optimum.

 

Edited April 12 by Mike

[Garald]

45 minutes ago, Mike said:

Cork is in a separate category - it's got an exceptionally strong set of characteristics, and for wet conditions it's the only option. However the price is much higher than the others and it's not compressible, so it can't be squished between rafters / other obstructions. I have used some on my current project, but mainly fixed to the faces of the chimneys, hidden behind plasterboard.

 

 

Aha. Yes, comprensibility is why Isoveo demurs - but why should it be impossible to mix cork and fibre, using cork down the middle and fibre for edges, nooks and crannies? Does the much higher density of cork mean it would all fall apart somehow?

 

Of course cork is pricey, but given how much I seem to be about to get charged for nonsense, it may make sense to pay a bit more for the insulation material (which right now is only 35% of the total cost).

[Mike]

5 minutes ago, Garald said:

why should it be impossible to mix cork and fibre, using cork down the middle and fibre for edges, nooks and crannies?

Yes, you could do that. Though I'd spend the money on the MVHR instead!

[Garald]

6 minutes ago, Mike said:

Yes, you could do that. Though I'd spend the money on the MVHR instead!

 

Look at the quote I got for MVHR!

[Mike]

1 minute ago, Garald said:

Look at the quote I got for MVHR!

I have - see me comments!

[Garald]

53 minutes ago, Mike said:

I have - see me comments!

Ah thanks - just replied. Wonder why the system didn't notify me...

[Garald]

While we are on the subject - what about blocking sound from the outside? I face a busy street, and my attic is actually noticeably noisier than my first floor (... which is insulated with some 18cm of BioFib Trio and has not just good, new sound-reduction double glazing *and* an additional layer of thick single glazing in its rather large windows). I know cork is better than wood fibre - but could I ask the insulators to, say, drop a layer of mass-loaded vinyl somewhere in the ceiling? Where - above or below the insulation?