Condensation monitoring under a roof

[dumbfif]

Hi all

I am a complete newby concerning sensors and this site. I hope this post is at the appropriate location.
First a short introduction:
I have condensation trouble under the roof of my house, just under the waterproof layer on top of the insulation layer. I plan to add some king of vapor barrier to avoid that the water vapor reaches the waterproof layer, but I am not sure that this will avoid condensation.

Once the vapor barrier has been built, I will not be able to measure condensation any longer, and I don't want to break my ceiling for that. According to you, is it possible to put some humidity/temperature sensors (typically DTH22), so that I am still able to monitor humidity/detect condensation between the vapor barrier and the waterproof layer? I guess this would require not to have a wireless connection (I will not be able to change the batteries easily)?
Does it seem feasible to you?
Thanks.

[RJ_Make]

@dumbfif Not sure what type of roof structure you have, but typically adding more attic ventilation will solve the moisture problems.??

[ferpando]

@dumbfif
What you should do is add the vapor barrier on the warm side of the insulation layer, that way you won't have condensation problems, and no need to check for them either.

[tbowmo]

sound like it's a ventilation problem. You need an air gap of approx 70mm between the waterproof layer, and the insulation. This is in order to keep the Construction well ventilated.

And yes, adding a vapour barrier on the (warm) inside will also help things. But it's nearly impossible to make it 100% efficient. So always have the ventilation in mind.

[dumbfif]

Thanks very much for your feedback. I'll check what I can do regarding ventilation.
Still I will check if I can do minimal monitoring (and easy) of the condensation.

[Sparkman]

@dumbfif A good rugged humidity sensor is not cheap, I would look at a 1-Wire Humidity sensor as you can run cabling from it for quite a way. Here's one example: http://www.datanab.com/sensors/1wire-temperature-humidity-sensor-th_prb_mini_rj12.php.

Another option is something like this: https://www.adafruit.com/products/1293, but since it uses SPI, you would need your electronics relatively close to it.

Cheers Al

[ferpando]

The problem with these probes is that they are very localized and you don't really know where condensation is going to appear.
That's why you should rely on good construction rather than spot cheking for moisture.