How many times do I see the following condition; a popped hatch.
Yes it’s popped open or lifted when a door or window is opened somewhere and it’s a windy day or the wind is hitting that side of the house. The sudden increase in air pressure will lift the hatch (it’s not heavy).
It can even be pulled up as sudden gust of wind create a low pressure zone over the roof. This partial vacuum will pull higher pressure air form the house, lifting the hatch cover with it.
Most times it will just fall back down to the same place but sometimes it will catch due to misalignment and will stay open or partially open.
In a closet this may never be noticed till the next service call or inspection requires attic access.
The heated (or cooled) air that can be lost through this is just phenomenal. Just visualize the plug being pulled on a sink full of water. That’s a house loosing hot air through the hatch. The air is not as dense as water but the same principles of fluid dynamics are at play. So it won’t be as fast but it will be continuous as the ‘tap’ is always on (heating or AC system).
For this reason I recommend hold down hardware unless you have the magnetic strip type. (Hook and eye screws, barrel bolts, etc.). The hardware also keeps the hatch tight against the weatherstripping to make it airtight.
Original blog post on ActiveRain: Link to Blog Post