dk,
Can I call you dk? I hope it's not too informal.....
Whatever. Anyhow I saw your other thread and can see you've gotten a bit of advice already. Let me make one clarification. Felt is the waterproofing, shingles are the weatherproofing. They armor the felt. It's important.
I read somewhere that a family of four can put as much as 2 gallons of condensation into the household airspace every day. Years ago homes were extremely porous and moisture usually found a way into or out of a house through all the myriad gaps around windows, doors, attic penetrations and the like. For the last 30 years or so we've been focused on sealing up every dollar wasting crack and adding vapor barriers wherever we could find a spot to cover up. In a lot of cases we've created problems where indoor humidity gets trapped and causes all sorts of unwelcome conditions. You should probably get an indoor air quality assessment when the budget allows.
As for the roof it looks as though you may be in what we call a "Cape Cod" style house, ( commonly single story, tall pitch, gable end roof line, sometimes a dormer or two) which has a converted attic. It's common to insulate the walls/ceiling of the conversion and often there's plastic sheeting or plastic backed insulation acting as a vapor barrier. That's what they told us to do back in the 70's when this whole new methodology emerged. Problem is your house was probably not designed to have it's attic taken up by bedrooms. The ventilation got short-circuited, the original air volume where condensation would normally dissipate went away and now what was not a problem is a big issue.
Assuming the shingles went down as per directions ( I read about the felt issue, BAD dk) and you don't have any dormer roofs, vent collars, or chimney flashing causing water to enter from the roof we have to look inside to find the cause of all that condensation. I still wonder if it's a bathroom ventilator. If your house is like the million or so I've seen with a converted attic, the baths are usually still on the first floor. Unless it's an uncommon design it will be, like the kitchen, in the "back" of the house. Over them is usually attic space/wet wall since the plumbing vents rarely get moved. If you can say the there is no "fart fan" in the bathroom or that it has a proper duct and roof vent then we have to look at more complicated fixes.
If there's no fan or it's installed properly (which is rare) then you need to look at your heating system. Forced air units usually have a humidifier which can be turned up too high delivering too much vapor into the home (happens a lot). Also fairly common is the lack of cold air returns installed in attic conversions. You need to pull air from rooms with supply vents if only to effect adequate circulation but also to get moist/cool air back to the furnace which will de-humidify. Often this condition telegraphs itself with the creation of mildew, not always but often.
If you have a radiant system then it can be that a bleeder is leaking, another common problem but that usually manifests right where the problem radiator sits.
There's also the issue of humidity bleeding up via a chimney or duct chase from the basement and causing the condensation but I doubt it. It really sounds as though you have a source of uncommonly humid air being introduced into your attic spaces.
It just occurred to me that you may have a power attic fan. There's an outside possibility that it's equipped with a humidistat controlled switch. If so, disable it. One problem with power vents is that they move around 300-400 cfm. or more and since most inlet vents can't support that much free airflow they suck air in from every gap in the roof. Sometimes the humidistat triggers during high outside humidity periods (rain) and can actually suck water into the attic. There's also a small chance your roof install is causing some water intrusion but I doubt it.
Now, as far as attic ventilation is concerned what I typically do on houses like I've described is install gable-end vents at the peak and vents at the ends of both front and back crawl spaces. That means three vents per side. Once that's done you can usually insulate and vapor barrier until the cows come home. You've created airflow and if you have any breeze at all, Mr. Bernoulli will handle the rest.
Sorry for the wordy reply, now you see why my kids ask their mom most of the "where do babies come from?" type questions.
But seriously, look for the bathroom vent. The number one cause for the condition you describe in my limited experience. I've had homeowners tell me the same thing (no vent) and sure enough, we look and there it is. I've gotten to the point where I can tell how many females are in a home just by the size of the ice sheet forming on the underside of the deck. Just don't wrap up the living area until you've addressed the venting. That can be a nightmare.
