I recently completed an uninsulated 24x24 garage. 2x4 framed, monolithic concrete slab, vapor barrier under T1-11 plywood siding. After a cold spell with some snow, the temperature jumped up to 50°. I noticed the underside of the roof sheathing was wet, along with little water droplets on the tip of each exposed nail head. I did some investigating and lifted up some shingles and it looks to be bone dry where it should be. I have no idea why the nails are dripping, both in the attic space and outside under the 24 inch eaves. Please help!
Condensation. Warmer air rises and hits still cold underside of roof. A continuous ridge vent would have been a better choice over just two tiny Turtle vents.
As mentioned…a continuous ridge vent is needed. Also…what is the intake? “Soffit vent”? Your issue is a ventilation problem created by trapped air.
Attached is a pic from the outside of the building at the eaves. The “soffit vents” are open and stretch the length of the building on the north and south sides. There are also 2 gable vents on each end. I understand any condensation on the inside, but the outside of the building is worse than the inside??
A lot of your issue is likely to do with not having a door yet. I bet the problem will significantly decrease after you install one.
That picture is a little old, I have a man door and a garage door installed. All siding and trim is complete. The building has been bought off, final inspection by the county. just needs paint.
Is the attic space insulated?
Also…how new is the structure? Did the decking get wet before dry in? Was roof wet from rain or dew when installed? Any of these conditions can cause severe condensation issues.
The building is brand new, built through the summer and fall. The plywood decking did not get wet, however it rained after the tar paper went on, before the shingles. The paper was dry when the shingles were put on. Roof was completed Sept 23. Attic space is not insulated. no insulation or drywall at all.
Simple matter of reaching the dew point. I have seen it rain in an uninsulated metal building. http://www.dpcalc.org/
Warm air will hold more moisture than cold air. As mentioned above…if no ceiling…the warm air rises carrying the moisture to your decking. That moisture from the underside is trapped by the shingles and felt…it has to come back out somewhere.