We’re going full speed in the kitchen now. First stop: a finished ceiling. For that, we first need to finish the insulation part with a vapour barrier.

Why you need it

Simple: prevent condensation. All air contains some water vapour. If the warm air from inside your house travels through the insulation, it cools. Cooler air can hold less water vapour, so at a certain point it will start to condense. You don’t want that. It can get you into all kinds of problems, from insulation being less effective to mold formation or worse.

What are the options

There are different kind of vapour barriers available. First of all you have the typical roll of insulation with a sheet of aluminium directly attached to it. Those are good if you have a very regular space between your beams, which we unfortunately didn’t have. Other than that it’s also a lot easier to just separate the insulation installation from the vapour barrier installation. It just works easier.

Next up is the sheet of plastic. It’s probably the cheapest form of vapour barrier you can get. It’ll do the trick, but it’s not really recommended. Any moisture getting in the insulation will not be able to get out of it anymore.

Finally there’s different kinds of membranes. These are engineered so that water vapour can get through one way, from insulation back inside, but not the other way. These are the way to go if, like us, you’re working under a flat roof that’s preventing any moisture from escaping the insulation any other way than back inside the house.

How we did it

As you probably already guessed (especially if you remember the insulation installation, lacking the use of aluminium coated insulation) we’ve opted for the last choice: the barrier membrane. During my research I found two options: Isover Vario KM Duplex and Pro Clima Intello. They’re kind of equal if you compare their specifications, with a slight favour for the Intello. I also found it a bit cheaper than the Vario KM Duplex (on Ebay for those of you wondering), so the choice was easy.

The installation itself is easy: measure what piece you need (keep 5 to 10 cm extra against the walls), cut…

Vapour barrier cutting

… hold it in place (a second pair of hands is more than welcome) and staple it against the beams.

Vapour barrier stapling

Then repeat, with an overlap of around 10cm (or 4 inches).

Vapour barrier progress

With all the membrane in place, the most tedious part is next: taping every seam and hole up, so that it’s one big unpenetrable membrane. Any gap left open is a spot where moist air can get into the insulation, and we don’t want that. So we taped up everything with the Pro Clima tape: every staple, every seam. We tackled it as a team: I did the overlapping seams, Chrisje did the staples (for which I probably wouldn’t have the patience anyway).

Vapour barrier taping

Finally I sealed up the membrane along the walls with Orcon F, a silicone specifically designed to create an airtight joint between any surface and the membrane.

That finishes the vapour barrier installation. Any of you that recently installed one? What did you use and why? Tell us in the comments!