So I'm renovating an old farmhouse with a metal roof and there is no insulation in the attic. I was up in the attic checking for leaks since we just got some freezing rain and it is currently melting I thought now was the perfect time to check. I found no leaks but I did notice the roof was sweating with noticeable beads of water in many places and many of the 2x4's that act as the frame were damp, although none were rotted (I found that odd as the house is approx. 140 years old and those are the original 2x4's. I could tell that the attic does have vents so I guess it dries out before rotting or mold occurs.. but makes me wonder if I put down some roll-in faced R-30 Owens Corning Insulation and then add a plywood floor over top if everything will be fine.. or not so fine..
I own an 80 year old house -- a home originally built as temporary housing for people working in the airplane industry during the war, and for returning soldiers. Temporary housing that is better structurally than many new homes. In fact, the original design and work was brilliant in its simplicity and precision, and I have found that the problems with my house are the result of work done later on -- additions and fix ups that screwed with the original integrity. One thing I have learned RE old houses is it is often best to leave well enough alone. This does not mean one should not address definite problem, or add certain features, but it does mean one has to think things through and do a great deal of research before acting. As you say, the structure of the roof is the original, so all the folks who had the house before you must have been doing something right. If I were you, I would ask around my community, do some internet searches, and find someone in your area who is an expert on dealing with historical structures of the area. This person will not necessarily be a master craftsman with a PhD in history and another in architecture. It may actually be a skilled handyman or carpenter who is continuing the old family business. He also probably lives in an old farm house, or knows plenty of folks who do. THAT is the guy you want to consult.
Hi, GA. On my second coffee here, so bear with me if a little fuzzy. Trying to envision what you're looking at, first thing I hear is 2x4 roof framing, not say the 2x6 or 2x8 rafters I would expect. A 2x4 structure and metal roof is a light build more suitable for a shed or outbuilding than a home. Wouldn't tolerate much additional weight, like from plywood. Next thing, which I don't hear, is whether there's moisture on the attic's "floor", where you're standing. I'm thinking the moisture you're noting is above you, on the undersurface of the roofing, and on the rafters. Finally, while some condensation on the underside makes sense, it would also seem quite possible that there are a number of small leaks through the roof. My goals would be to first ensure there are no leaks through the roof surface, then to ensure the attic indeed has enough venting, then to both reduce air from the lower living level bleeding through up to the attic space (also good to reduce convective heat loss), then to insulate the attic floor to reduce radiant heat loss from below and warming of the attic air, pretty much in that order. The prize is a leak-free roof over a cold attic space.
You need to make a determination as you if you want your attic to be conditioned or unconditioned. If you want it unconditioned, you need to make sure you have venting up high and soffit vents to allow air in. You would then insulate the floor with batts or blown cellulose or blown fiberglass. If you want the attic to be conditioned space, you would insulate the roof itself. For this I would recommend contacting a spray foam company and get their opinion. Spray foam is great for insulating roofs but it has to be done right.
If there is condensation on the underside of the roofing then you do not have sufficient ventilation of the attic. You can certainly insulate the ceiling but you do need to add soffit and roof vents to get some air circulation into the attic. You should do this regardless of adding insulation to the ceiling.
Is the attic floor completely uninsulated now? You need a single layer of vapor barrier between the living space and the attic space. This is often done with faced insulation rolls. A vapor barrier between the living space ceiling and your new insulation may be enough all by itself to prevent the condensation from forming. If there's existing insulation, you'll have to pull some up to check for a vapor barrier. If there's already a vapor barrier, you can add unfaced insulation. Never put in two vapor barriers with insulation between them.
