ᐅ Roof insulation combined with a heat pump – disadvantages if the attic is heated?

Hello everyone,

I have already used the search function but couldn’t find the right information.

We are planning to build a single-family house. A friend (roofer) recommended using external roof insulation. We want to operate our single-family house with a ground-source heat pump (brine/water). The construction company now says this doesn’t make much sense because the annual heating costs are so low that, although external roof insulation saves some energy, the payback period is very long. Furthermore, the site manager said that with external roof insulation, the attic space will be heated since the insulation of the top floor ceiling is omitted.

What do you think, does it make sense to use external roof insulation in combination with a heat pump?

Thanks for your help!!!

Otti schrieb:
... A friend (roofer) recommended an external roof insulation to me.

The decisive factor is the usage (system boundary)! If the attic is heated and thus inside the thermal envelope, insulation is required. The minimum insulation thickness then depends on the energy saving regulations. This can be external roof insulation, insulation between the rafters, or below the rafters. Sometimes also combined. For a new build, omitting insulation between the rafters would mean wasted space.
If the attic is not used as living space, the external roof insulation forms the system boundary. This should then be insulated according to the respective requirements.

Otti schrieb:
... Furthermore, the site manager said that by using external roof insulation we would be heating the attic, because with external roof insulation the insulation of the upper floor ceiling is omitted.

I would be surprised if insulation itself can provide heating ;-) Also, the insulation is not omitted but rather designed somewhat more economically ;-)

Otti schrieb:
... What do you think, does it make sense to use external roof insulation in combination with a heat pump?

This specific insulation detail is not directly related to the planned heat generator.
A ground source heat pump is a good choice, provided the entire system is properly sized. Everything must be coordinated; otherwise, you risk building a money pit. Special attention should be paid to the source design. For this, among other things, the required extraction power and energy demand must be known.

Best regards.