ᐅ Exposed Roof Structure – Where Should the Vapor Retarder Be Installed?

It’s me again…..

A brief recap: we are building a KFW 55 house through individual contracts with a construction supervisor.

We have exclusively chosen local suppliers, some of which have been in business for three generations. I mention this because it’s reasonable to expect they know what they’re doing and have solid experience.

We have an exposed timber roof frame insulated with wood fiber insulation boards from Gutex. The roof is installed but not yet covered with the final roofing material.

Yesterday, the building inspector came and asked us about the roof structure. We explained it to him, and he suggested we check with the Central Association of German Carpenters to determine the required performance class (I assume it’s class 3 since the standard roof pitch would have been 28 degrees, and ours is 19 degrees), and of course, the roof is part of the living space.

We looked into how a roof like this should be constructed and read that a vapor retarder and a nail sealing tape must be used.

Here is our build-up:

On top of our spruce multilayer panels, we installed an Alujet Professional JKE underlay membrane, then the 20 mm (0.8 inch) wood fiber boards, followed by a hardwood multiplex plywood board, and then, overlapped, another layer of Alujet Professional JKE, and finally the counter battens.

We are annoyed that we didn’t receive any nail sealing tape, but maybe this is acceptable due to the use of the Multiplex plywood. What I’m more concerned about is: where exactly is the vapor retarder? The Alujet Professional JKE doesn’t seem to have that function.

We have now sent an email asking the carpenter for clarification, but I’m afraid, as often happens, we’ll just be reassured without real answers…..

Unfortunately, the roof construction is specified exactly like this in the contract…..but as a layperson, you wouldn’t know that it might be wrong…..