Insulation under gas condensing boiler in the attic

Hello everyone,

we are building a turnkey project and the condensing boiler was installed by the construction company or its subcontractor in the attic above the upper floor.

We have removed the attic insulation and will carry it out as a personal contribution. The construction company's structural requirement is that the attic should have 20 cm thick insulation (WLG 035) throughout the entire area. The construction company told us that their subcontractor will install the heating system and apply the corresponding insulation underneath it. We can then insulate the attic afterwards.

Now we have seen that there are only 10 or 11 cm of insulation (styrofoam) under the heating system. Is it sufficient if we apply 20 cm of insulation around the system, or is the system already incorrectly installed on the 10/11 cm insulation? Shouldn't there also be a wooden board or similar in that area?

Is the floor insulated or the sloping roof? For the roof it doesn’t matter, then the insulation is just a decoupling. Hope it’s not regular Styrofoam but a suitable / approved one

According to the construction performance description, the floor is to be insulated with 20 cm and the roof with 15 cm insulation. A continuous 20 cm insulation on the floor is no longer possible now if the tank stands on 10 cm and not 20. Before we discuss this with the site manager, we would of course like to know whether it is absolutely necessary and how a 20 cm or even now only 10 cm insulation will affect things later. He will of course say that it does not matter. And whether it is relevant for the building acceptance. Because we can no longer raise the tank ourselves to apply additional insulation. It is fixed.

What properties/designation must the Styrofoam have ?

You should demand what you ordered. The memory can very well be increased further; if it should be done, let the subcontractor do it.

As long as the height is correct, I would also expect the agreed 20 cm. The question that arises for me is rather whether the remaining insulation of the roof is sufficient to declare the attic as part of the insulated envelope, because to my knowledge the heat generator must be installed within this envelope.

Edit: Incidentally, I only see a hot water tank in the picture and no gas boiler.