I have a small 12 ft x 12 ft aluminum sided cabin/shed (built in the early 80’s) that has a ventilation problem. It was built very tight. It is a simple square box with a peaked ridge roof, nothing fancy. The upper attic/loft area is separate from the main floor, you access the attic from a stair built onto the back of the shed. We occasionally use it for weekend getaways. All of the walls were insulated with fiberglas batts and then covered over with wood paneling (the thin stuff popular back then). No drywall. The outside is sheathed in aluminum siding with felt/tar paper beneat that-all on on top of wood ply sheathing.

The problem is that it is so tight that there is no air circulation at all and the main room always has a musty smell that has developed over the years. We close it up for the winter and it gets even worse. It is so bad that you can’t sleep in the cabin because of that mustiness and it even tends to cause irritation in the nostrils after you’ve been in it for any period of time. I suspect a mold problem as evidenced by a line of white powder like mold low to the ground on the wood paneling.

The shed sits on a solid concrete slab.

I want to remedy this situation by adding natural ventilation. Anybody have any ideas? I suppose I could cut a vent into the wall somewhere to allow fresh air in and out but what is there on the market that will look decent? I’d like this vent system to be passive. 

There is no ridge vent. The upper attic area doesn’t have that musty smell at all. The upper attic/loft really has no natural venting either but for some reason the mustiness hasn’t crept up there.

The cabin has one door, with two small windows faling the door and a small window on each side of the cabin except for the rear for a total of 4 windows on the bottom floor. The attic has a small window at it’s gable end over the front door and an access door with a small window at the rear gable end. 

I can’t leave windows open as there have been break-ins occasionally.

Thanks