Thanx for your expertise Sparkstation

I had the impression that in the breathable membranes the vapour travels only one way (as it is the case in the trekking clothing for instance). I have no idea about the technology used, but if there is really a chance that I will have water dripping after some time, then I will skip this option.

Maybe the condensation won't be real bad after all, as there is no attic space (only the wooden beams and lining will be visible from inside). So the area with the low temperature during winter will be minimal.

By the way, when you mention second vapour barrier, you mean just the wooden lining, or yet another membrane?

Let me ask you something else: What about allowing some openings so that air form outside can penetrate the area between the insulation and the membrane? I wonder if any such access to the outside open air is enough to remove the accumulated humidity (will there be any adequate air movement?) or if it makes the problem even worse by introducing humidity from the outside. It's rather a question out of curiosity, as the area has quite some interesting pauna ready to use my roof as a nest, should I allow any openings!

Maybe, I could use the good-old iron sheets and allow some openings at the highest point, which will be loosely covered by a membrane to keep rainwater out. What do you think?

Let me add that the general area I'm building the house has to follow some strict building regulations. See in the photo how houses should look like around there. So no much room left for implementing any fancy modern ideas, I'm afraid... Otherwise, EnviroMan proposal seemed good.

Anyway, although I'm not 100% certain of what I will do, I know what one should NOT do:

1) Use metal sheet roof without using insulation and vapor barrier (=Condensation)

2) Use non breathing membrane in a non ventilated roof (=Condensation)

3) Use breathing membrane in a ventilated roof (=no point!)

4) Use breathing membrane right over dense decking like, tongue-groove (=No room for the membrane doing its job)

5) Use no roof at all (=problem when it rains)

Whatever, I lean towards using metal sheet under the lime and over the insulation, as I won't be living there for long periods (it's a holiday house) so condensation might not be that important, I guess. I will surely use some sort of vapor barrier underneath the insulation, but even without it, wood may probably have time to absorb any extra moisture accumulated in that short period of time. (I wonder, can ever vapor become an issue if the house is not inhabited?) The metal sounds a good choice as I won't need to take care of the roof every decade or so. I guess, there will also be some breathing at the joints.

But, I may change my mind again!... Anyway, thanx everybody for your advice.

"...can ever vapor become an issue if the house is not inhabited?..."

Well, it won't be an issue for the inhabitants, at least...

From what I see in the picture, you could have soffit boards with vent screens under the eaves, and that would alleviate much if not all of the problems. Lovely local architecture, by the way!

ups and downs of house flows are best to the eaves in this roof setup. I do not know what that lime tastes like on a down moist sunless cool day.... I bet its quite cool in the summer minus the moisture. If by traditional you do not have sheathing on the roof that locks in by a tongue-groove or lap seam, or planks.Sticky Stuff comes in rolls called "ice and water shield" should be quite nice on a hot greek day to lay down and the go about tradition. My area gets it real bad going "traditional", as that has been outdone since a simple thing called plywood. I would not let roof breathe though such a powerful insulator as lime, slate, or even thick shingles (architectual) like my area uses alot of. you can keep gretaer value of lime and let house breathe with modern hvac/vent eves or even valved attic. for a long long time, it seems infinite to think about and analyze actually...maybe metal on the edges of roof a few feet or even a meter, or depth of eves however the many ways to deal with this, then the ice and water shield over that.. sounds like a very nice house to build. I would help just to say I helped build a lime roof house...(I used to build houses, and many roofer helpings.)

I am not too sure if this would help, but couldnt you just buy a dehumidifier and leave the roof as is? Dont really know if this would help...but a dehumidifier in a humid house would get rid of the humidity, or at least lower it which would stop mould or at least slow it down. If people think this might work, it may be the cheaper method ~ 500-1000$ CAN.

Here (Florida, USA) we have high humidity, and all sorts of critters wanting in the house. Can you have vents in the soffit (underside of eaves) as shown in this pic? It would solve much of your problem...

Leach your roof with thin admixture of :

[80 % Flyash ]

+

[20% OPC Cement]

+

[Sufficient Water to make it slurry]

= Spray / spread on the roof