ᐅ New Construction: The Usefulness of Wood Fiber Insulation Boards for Thermal Insulation

Hello everyone,

for our new build, according to the architect’s plans, we have a standard roof assembly with insulation between the rafters:
underlay membrane (0.2 W/mK) - 20cm (8 inches) of mineral wool (0.035 W/mK) - "PTFE foil" (0.23 W/mK) [what is this actually intended for?] - gypsum board (0.25 W/mK).

I requested quotes from two carpentry companies. Both optionally offered a 6cm (2.4 inches) wood fiber insulation board as continuous insulation above the rafters (because both are "convinced by the system"). Apparently, this insulation partly serves as winter insulation, but the main focus is on summer thermal protection.
To keep it brief without lengthy explanations: the material takes 12 hours to fully heat up and release the heat into the room (normal mineral wool lets the heat through completely after 6-7 hours). By the time the heat is released into the room, it is already nighttime, and with normal ventilation through open windows, the heat can be removed, preventing heat buildup.
--> The entire attic (where we all sleep) should not heat up as much in summer.

Of course, the whole system is not cheap (the system is from the company Steico).

Does anyone have experience with wood fiber insulation in a new build and can share their insights?
Especially in the sleeping areas under the roof, noticeably less heat in summer would make a big difference.

Best regards,
André

No prior experience, but carpentry companies usually offer this as a standard service. I also find it understandable that it has some benefits, and protecting against heat is very important to me.
That’s the theory so far; I would also be interested in hearing about practical experiences. However, probably very few people have both systems for comparison.

The issue with experience is also my problem.
At least it sounds logical. But since the insulation costs €6,000 according to the quote, I’m hesitating.
Although I’m already biased. As a child, I slept under the roof, so every degree makes a difference.
Still, I would be grateful for any experience shared.

Hi Crimson,

we have the panels as continuous insulation above the rafters.
The roof is a shed roof, fully facing south, with a 17-degree (17°) pitch.
So, the sun shines strongly on it all day long during summer.
Of course, it still gets relatively warmer than the floors below, but the difference is only about 2-3 degrees Celsius (35.6-37.4°F), and the room temperature never exceeded 25 degrees Celsius (77°F) this summer.
The extra cost (for about 160 m² (1,722 sq ft) of roof area roughly 4,000 gross) was somewhat steep, that’s true, but I would choose it again anytime if the attic is used as living space.

They also have them and can confirm the 25 degrees Celsius (77°F). A 35-degree (63°F) pitch facing south without shade. Unless you keep the windows open. But then the problem is getting the heat out of the house again.

The panels should also hold up very well in case of possible moisture (roof leakage).

I would do it the same way again, although we have no comparison.

So, you are confirming my opinion to bring the panels onto the roof.
It is definitely helpful when your own line of thought is supported by others.

Thank you very much for the quick (and competent) responses.