Insulating from the outside: what is a reasonable cost?

[Garald]

As some people here know already, I am thinking of insulating a wall from the outside. It is a northern wall that already insulated from the inside, but somewhat suboptimally, and it has become clear that there's thermal bridging (where the foundations end) and that it matters.

 

Now, I've asked for some quotes, and they are all more than I expected (for 72m^2). Can you eyeball them and tell me whether they are reasonable? They are from three different companies, but were all obtained through the same umbrella organization (Maison Saint Gobain). The lowest quote comes from a business that has a rating of just 4.3/5 on Google. The middle quote offers rock wool rather than PIR (so it's fireproof). The higher quote offers some extra stuff (insulation on the sides of the windows) but I don't know whether it's worth it.

 

 

DE-202406-528.pdf Devis_Harald_Helfgott_0087.pdf Devis_Harald_Helfgott_0087.pdf

[Marvin]

Hi @Garald

 

Perhaps the first thing is to identify, in detail, what the existing walls are made up of, which you are proposing to externally insulate. Also identifying all the windows, doors and so on that penetrate the walls and what they are made of and what there thermal resistance is.

 

I think that window reveals should be insulated to help avoid cold spots on the inside window reveals possibly causing surface moisture and mould growth.

 

Then perhaps identify what items are required, what the benefit will be.  

 

Is your building two stories high? Do their quotes include access towers or scaffold if required?

 

Rockwool is much cheaper than PIR but less thermally resistant. In basic terms one centimetre of PIR is as resistant as two centimetres of Rockwool.

 

As always the devil is in the detail.

 

Good luck

 

Marvin

 

 

 

 

 

[Garald]

4 hours ago, Marvin said:

Hi @Garald

Perhaps the first thing is to identify, in detail, what the existing walls are made up of, which you are proposing to externally insulate.

 

 

 

Hi Marvin,

 

Oh, the exact material of the existing walls is a mystery to me! It's some sort of early 1930s masonry. I can ask the general builder who did renovation work in my place for more details - but what can it be? Surely it must be *some* sort of brick.

 

> Also identifying all the windows, doors and so on that penetrate the walls and what they are made of and what there thermal resistance is.

 

That's much easier. The ground-floor windows were all replaced during this renovation, and the first-floor windows were replaced during the previous renovation - I have the receipts. The door is a metal security door I've insulated with a 3cm-thick cork panel from the inside.

 

> I think that window reveals should be insulated to help avoid cold spots on the inside window reveals possibly causing surface moisture and mold growth.

 

Right. In the bedroom window, I'm tempted to add a second, sliding window with thick security glass for sound insulation (it's a quiet side, but my girlfriend is somehow bothered by the bell from the elementary school out in the back). Then I could just insulate the space between the windows with cork, possibly topped up with acoustic foam.

 

>Is your building two stories high? Do their quotes include access towers or scaffold if required?

 

Yes and yes.

 

>Rockwool is much cheaper than PIR but less thermally resistant. In basic terms one centimetre of PIR is as resistant as two centimetres of Rockwool.

 

The alternative being offered to Rockwool is not PIR, but polystyrene. (PIR or something like that would be used only for the window reveals.) Sorry for being confusing. We are talking about 16cm Rockwool vs 14cm polystyrene to achieve an R of about 4.5. How eco-friendly/durable/etc. is polystyrene? (It looks just like packing material to me.)

 

 

[Garald]

PS. I repeated one of the attachments by mistake. Here is the correct second quote.

Devis_Isolation_de_facade.pdf

[Garald]

Important point: the wall is insulated from the inside with materials permeable to water vapor (though I'd think there's also a barrier). Does this nale polystyrene unadvisable?

[Garald]

OK, here is the composition of the wall:

 

- wall itself: some sort of masonry from the 1930s (not concrete)

- inside insulation:

ISOLIN HPV  (reflective insulation) + 45mm Biofib Trio + hygrovariable vapor barrier (Proclima) + 13mm fireproof plaster