ᐅ Order of Installation for the Attic Floor Finish

Hello everyone,

We are currently at the stage of finishing the attic in our new build; the shell including the roof frame and windows is completed.

Relevant details:

• Single-family house with 1.5 stories and collar beam ceiling in the attic
• KfW55 standard (meaning a Blower Door test is required)
• Cross-section of the new building shown below

Basic concept for finishing the attic:

• The collar beam ceiling will be insulated (with friction-fit insulation) and a vapor barrier foil will be applied underneath.
• The vapor barrier should only be penetrated where absolutely necessary.
• Below that, the ceiling will be suspended about 12cm (5 inches) using profiles.
• A few ventilation ducts plus most of the electrical cables will be installed within the suspended ceiling (since there is not enough space on the floor).

Now to the problem:
We initially planned the following sequence:

• Install friction-fit insulation
• (immediately after) apply and seal vapor barrier under the collar beams
• Run ventilation ducts and electrical cables (excluding lighting) from the sub-distribution across the ceiling to the rooms, then continue within walls and floor
• Plaster the walls
• Allow drying time
• Blower Door test
• Install screed
• Allow drying time
• Mount 22mm OSB boards on the attic floor
• Attach ceiling profiles and hangers for the suspended ceiling
• Run electrical cables for lighting in the ceiling
• Install drywall panels
• Install light fixtures

However, the sequence gets stuck at least at step 3.
How can the cables be fixed inside the ceiling if the suspension framework for the ceiling is not yet installed?
We can’t find a workflow where the installation of electrical cables really fits.

Looking forward to constructive suggestions and any other comments:
Good luck

There are wooden beams there. Can't you fasten it to those? If necessary, with a counter batten?

Hangman schrieb:

There are wooden beams, right? Couldn’t you fasten it directly to those? If needed, with a counter batten?

First, thanks for the quick reply.

Regarding fastening straps:
But how exactly? I would have to go through the vapor barrier everywhere to reach the beams!?

Regarding counter battens:
That would reduce the height available for the ventilation pipes and the lighting setup, although it might work with flat battens. However, the counter battens would also have to be fixed through the vapor barrier to the beams, and the whole process would be just to temporarily secure cables. Once the suspension is installed, the battens wouldn’t really be necessary anymore. I’ll keep the idea in mind 😉

Maybe there are other approaches? This issue surely isn’t uncommon...

For fastening straps, there are probably screw-on cable ties or similar products available. If you screw them directly onto the beams and possibly use a washer, you will compress the vapor barrier again, making it airtight. You can also use silicone or soft rubber pieces or similar materials... this will certainly ensure it is more than airtight enough. Counter-battens, of course, only where they are necessary (if at all).