ᐅ Insulating a Roof with Thermal Conductivity Class 032 or 035?, 180mm Mineral Wool

Hello,

I have received a quote for insulation using 180mm (7 inches) mineral wool with a thermal conductivity of 0.035 W/(m·K). Now I am wondering if using 180mm (7 inches) with 0.032 W/(m·K) would be more effective and if it would be cost-efficient.

I have already experimented a bit with a U-value calculator and quickly got a U-value of 0.20 and 0.18 with 0.032 W/(m·K).

Would this difference be significant or noticeable?

The roof structure is planned as follows from inside to outside:
12.5mm (0.5 inch) gypsum board (possibly double) – 30mm (1 inch) insulation below rafters (if useful), otherwise just battens for installation level – vapor barrier (airtight layer) – 180mm (7 inches) insulation between rafters – underlay membrane – roof tiles.

What would you suggest? Most of my research only compares different thermal conductivities with regard to material thickness. I haven’t found any cost advantages.

Regards, Jonny

Hello,
I’d say it depends. How big is the price difference?
From a purely economic perspective, it will pay off late or very late. However, I would still go for it. Key point: sustainable building.

Regards

Hello,

Of course, it’s clear that higher quality insulation is better and costs more. It’s also generally accepted that more insulation is preferable.

However, I’m not fully convinced about simply giving the industry more money when the insulation (with the higher thermal conductivity class) doesn’t bring a real advantage.

When I compare this using a U-value calculator, the difference in U-value is at most 0.03. Whether this difference actually makes a noticeable impact is the key point for me.

Thanks, regards Jonny

Hello,

jonny666111 schrieb:
..Now I wonder whether insulation with 180mm (7 inches) thickness and a thermal conductivity of 0.032 W/(m·K) would be more sensible and if it would pay off cost-wise.

The U-value will certainly improve. However, whether this actually leads to better cost-effectiveness cannot be answered definitively in general. It is often forgotten that better insulation reduces transmission heat loss, but the demand for domestic hot water preparation remains unaffected by this.

jonny666111 schrieb:
...What would you suggest? The search often only compares different thermal conductivity classes in relation to the material thickness. I haven’t found any cost advantages. ..

Cost advantages should be clearly defined! Presumably, the overall cost-effectiveness is the issue here? One must consider the investment required for improved insulation, or the financing costs involved, in relation to the actual demand (power, energy) for heating and domestic hot water preparation. There is, among other things, a significant connection with the intended heat generator or energy source. There are quite a few cases where excessive insulation effort does not actually make economic sense!

Best regards.

I have calculated the following options...

032 insulation value without under-rafter insulation → U-value 0.21 → 1178€

035 insulation value without under-rafter insulation → U-value 0.22 → 786€

032 insulation value with 6 cm (2.4 inches) under-rafter insulation (no 30mm (1.2 inches) wool found) → U-value 0.18 → 2060€

035 insulation value with 3 cm (1.2 inches) under-rafter insulation → U-value 0.19 → 1300€

035 insulation value with 5 cm (2 inches) under-rafter insulation → U-value 0.17 → 1400€


Heating with pellets, currently no solar support planned, nor domestic hot water.

The ten percent lower U-value from 035 to 032 corresponds to an increase in cost of 50–60%. (I hope my calculations are correct).

The question: Is the additional expense worth it?
At some point, the investment will pay off—of course. But how can one calculate that?

Regards

jonny666111 schrieb:
...I calculated the following options...
The question: Is the additional expense really worth it?

In this case, I don’t think calculations are even necessary. A U-value of 0.17…0.18 will likely have a positive effect when using pellets.

jonny666111 schrieb:
.... But how can you calculate that?

For a layperson, this might be difficult, because the necessary “tools” are missing.

Best regards