Most people think they have a good grasp of how roofs work – the shingles (usually asphalt) keep the water out, and that they do that by being the waterproof layer that stops water from getting in. That’s more myth than fact.
Another myth, is that caulking is an acceptable way to achieve waterproofing.
Another myth, is that if you have ice-and-water shield on your roof, you’re good.
What all these myths have in common is that they misunderstand how a sloped roof system works in reality.
You were happy to have the roof done a few years ago and you were delighted when the roofer told you he saved you money. Except that now your gyproc is showing signs of water damage, and the last roof lasted 15 years without any leaks in that location. What should you do?
The quick answer is:
Diagnose the problem
Identify the probable cause
Assemble your evidence
Notify the party responsible in writing
Give adequate time for the party responsible to respond and correct
If no acceptable solution is reached, escalate
The long form of the answer follows below. (Disclaimer: I am not giving legal advice in this post. The following discussion is only one of the ways such issues can be resolved, and there may be other mechanisms available to you that are not covered in this post).
Condensation plays the same role in “modern” roofing practice as “bad spirits” did in medieval times. If something went wrong, you blamed the bad spirits. Nowadays, if a roofing system is not working, it’s due to “condensation”. So let’s get into it and understand what condensation is, when can it appear in a roof system, and what corrective action you can and should take if condensation is really the cause of an apparent leakage.