physical and economic limit (over) insulation? Calculation

[Christophe]

It's all in the title, is there a method to determine the optimum insulation? That is to say the thickness of insulation from which we speak of over insulation and insulating wastes money and planetary resources (gray cost never amortizable)

It is often said that in terms of insulation the more the better, but from a moment, the return on investment can exceed the life of the product (especially with mineral wools).

[chatelot16]

it would be simple if we wanted to insulate a building without window or ventilation: each time we double the insulation thickness, we divide by 2 the consumption of heating

we can see that the doubling of the insulation costs more and more, and that the division by 2 of the heating yields less and less

the balance between insulation thickness and heating savings depends directly on the price of the insulation and the price of the heating

those who heat with an electric toaster may find it useful to use a lot more glass wool, than those who heat with wood by cutting it themselves

whoever installs his own glass wool by choosing the cheapest one will find it profitable to put a lot of it ... while the one who pays a craftsman at a high price will only find economically profitable only a lower thickness

then what is more complicated is that there is not only the insulation of the walls, there are the windows, the ventilation, the people who open the doors to enter: beyond a certain thickness l wall insulation is no longer useful

for strong insulation the simple calculation with thermal resistance is no longer precise enough: especially for double or triple glazed windows: thermal resistance is given which are only rough equivalence: for a true calculation it is necessary to distinguish radiation, conduction, convection ...

[chatelot16]

practical note: the price of the insulation that has been installed can no longer increase ... while it is foreseeable that the price of all energy will increase

therefore the optimum thickness of insulation can only increase ... so for those who have the means to do it, it is better to put too much than not enough

[Christophe]

wall insulation beyond a certain thickness is no longer useful

It is this figure that I would like to determine for a single wall knowing the cost per kWh and the "insulating R" ...

[chatelot16]

the cost of kWh and insulation is not enough ... the climate must also be taken into account

the amortization of the price of the insulation is the same whether the heating operates a few days a year, or all year round

so with the same price it is profitable to put much thicker in a cold country

I will still do a simple calculation for the case of a large hangar without window

I see coming that the expensive so-called ecological insulation wood wool type will be catastrophic: their high price will only make profitable a small thickness, and will push to continue to waste energy

[moinsdewatt]

you ask yourself strange questions. Put the thickness used in the RT2012 constructions now mandatory in the new one and you will be fine.

[Obamot]

The normative aspect poses a problem, because it is not necessarily suitable in all cases!

And here the solution is to go as far as possible, from what I understand.

I'm going to drop the "psychological" side that dictates our choices (although Chatelot did well to recall certain points, but there are a whole lot of them, indeed.) As the "conviction" that a method would be better than another (or not), even confusion in definitions, etc.

I think we've already exploded the limit. And we have always tried to go further and further with it (in a more or less logical order but not exhaustive in history):
- the type of construction material chosen;
- the possible heating method through the ages;
- orientation of constructions (living rooms to the south ...);
- the geographic location, both local and regional;
- ventilation;
- the invention of window glass (16th century ...);
- the idea of ​​warming up rather than dressing?
- the issue of health (prevention);
- the introduction of insulators with the arrival of the concept of comfort and especially the increase in fuels;
- technical considerations about the type of insulation, their specific specifications, their aging over time, their weight, etc;
- the introduction of heat exchangers;
- the concept of passive house;
- energy-producing houses (more than they consume)
etc ... (notwithstanding everything that has already been said and of which I repeat certain points ...)

Each time, the new parameters to be taken into account are added to each other, which makes it very difficult to find a universal formula, it is all on a case-by-case basis ...

And at this stage, we come back to psychological notions, which vary from one person to another, such as, for example, setting the ambient temperature to be reached in the home? So what will be "OK" for some will hardly be acceptable for others! It is also a criterion.

The b_a ba would be to set the right priorities and to ensure the care of the installation of the insulation ... For example, the fact of choosing rubberized joints with hollow profile rather than exclusively honeycomb or to make the list all the "airways" entering the house (I said all) etc ... The type of insulation adapted to the case-by-case and how it will be installed and in what order etc. Because apart from the doubling as stipulated by Chatelot, there is also the implementation. The devil is in the detail, and the result can vary greatly - from one implementation to another - although it shouldn't ...

This is the principle of the eye and the straw or the beam that we have in it: do not quibble over details when there are monstrous errors, as big as ... a house and that we did not see! (Cold bridges, old ventilation duct not condemned or technical duct with full wind in places, defective non-return valve or whatever ...)

The ultimate limit being the calculation (see the measurement) of the dew point and the dew point itself => and which fluctuates with the weather, related to the price of fuel and the depreciation of the work (including it- even variables such as current and future labor costs) ...

That must be why we have so much trouble calculating all this that there are so many variables, experience also plays its role, that must be why there are " pros "to do it, right? Bidouille, if he comes around, knows a lot about the issue, that's his job.

[Christophe]

the cost of kWh and insulation is not enough ... the climate must also be taken into account

Yes, but no because I was talking about the cost of the kWh spent ... therefore itself linked to the climate. Am I wrong?

lessdewatt yes it will be fine but nothing says that it is the optimum econologically speaking (especially if we isolate with perishable chemical !! like rock wool or glass) ...

And standard does not mean optimal either: in 2020 everything must be ... passive and positive! Cf https://www.econologie.com/forums/tout-habit ... 11600.html

[chatelot16]

glass wool is eternal when mounted in good condition ... for example under a well sealed corrugated iron roof ... but not under a tiled roof that lets water through when there is time rain and wind

you can be sheep and follow the mandatory standards! he is so sure that what is compulsory is always good ... he is so sure that the state is never wrong

it still deserves to think about it to seek the true technical optimum

It won't surprise me that the standard is too much for those who pay a high price for craftsmen ... and that those who make themselves by paying only for materials find it profitable to make much thicker

and after having made the calculations it will be even more obvious that the artisans are too taxed: a country managed efficiently should tax more energy, and completely tax all the craftsmen that we need to save money ... completely tax manufacturing and trade in materials, to promote the economy, which would shift the break-even point, and immediately put a lot of people to work!

[chatelot16]

And at this stage, we come back to psychological notions, which vary from one person to another, such as, for example, setting the ambient temperature to be reached in the home? So what will be "OK" for some will hardly be acceptable for others! It is also a criterion.

that's another way of seeing things ... at home it's not insulated at all, but in good contact with the ground ... I heat very little and content myself with 10 ° C ... we can't advise this for everyone

I rather use my skills in insulation to insulate furnaces, a methanizer at 40 ° C, freezers ...