Roof construction with insulation for a self-built garden shed

Hello,

Summary: How is the air at the ridge vented out of the inner layer with double ventilation? Are there ventilation valves or is there simply a gap left in the profiled wood?

More info: First, I know that a garden shed with insulation and such a complicated double ventilation is probably overkill for some people. But that doesn’t matter, because I have both the materials and the desire and time to do it that way. However, I also want to do it properly and not grow mold. I’m not a professional, just an interested layperson.

So far, my roof looks like almost every wooden garden shed: rafters with nailed-on profiled wood and roofing felt as a finish. The walls are timber frame walls with a wind protection “foil,” then battens for ventilation and wooden cladding as a finish.

Next, I want to put a metal roof with a wooden substructure on the roof. However, I also want to insulate between the rafters and in the stud from the inside. To prevent rot, I would continue the ventilation of the wooden cladding of the wall up to under the roof between the planned insulation and the profiled wood. But the air has to get out of the house at the top. So there has to be an opening in the profiled wood. How is that done? Or should I do it completely differently and, for example, insulate directly under the metal roof?

I made a plan with Ubakus and Photoshop showing how I imagine the roof, in case my text is not clear (as mentioned, I am a layperson).

Thank you for your help!

Robin

Hi Robin,

You simply lead the exhaust air of the inner ventilation layer at the ridge via an open, continuous air gap between the profile wood and the ridge board. You don’t necessarily need a classic ventilation tile for this, but the gap should ensure that no moisture can penetrate. A ridge ventilation tape or a perforated ridge sheet is a common solution to simultaneously create a cleanly defined air outlet and protection against insects. Just leaving a slit is enough, as long as it remains permanently open and protected.

If you make the insulation vapor-permeable towards the air layer, that is basically correct already. Important point: How do you plan the supply air at the bottom for both ventilation layers? This is often underestimated.
Good luck!

I intended to continue the ventilation of the wooden cladding of the wall up to under the roof.

I had the ridge ventilation tape in mind for the edge of the metal roof under the roof ridge (metal). But of course, I could also stick it additionally on the slit of my profile wood so that nothing gets in there. The slit should be 3 cm, right?

A 3cm wide slit is generally absolutely sufficient to ensure functional air circulation, provided that air can also flow in unhindered at the bottom and there is no "bottleneck" on the way up. The [Firstlüftungsband] is indeed useful in your case. It actually prevents both insects and driving rain from entering the ventilation layer, which can otherwise become critical at a gap width of about 2cm.

Great, thank you very much for the valuable tips! Then I will continue like that.

I drew a plan with Ubakus and Photoshop showing how I imagine the roof, in case my text is not clear (as I said, I am an amateur).

Your problem understanding your own visualization may be related to the fact that you put together a very strange drawing in which the roof structure is depicted rotated by 90°. The timbers in the drawing used as inspiration are actually rafters instead of battens, the trapezoidal sheet is nailed at the verge rather than parallel to the ridge as in your drawing! So probably a classic case of self-deception.