As a remodeling contractor, I’m often faced with plans that detail the finishes in full but which address the structural stuff with few details and a note saying, “Structural members to be sized by the prescriptive method.” That means I have to look in the code book and figure out what works. This isn’t stuff for greenhorns.
Up, down, and sideways
One of the keys to the kind of building I do is understanding that structure is all about direction. Gravity loads go down. That’s intuitive and easy. Most of what’s in the prescriptive structural tables in the code books deal with this, and all you need to do is read the book.
Wind loads are more interesting. Their direction is often up or sideways. This is one area where builders need help from architects and engineers because wind pressure can work in ways that aren’t intuitive. In areas with higher wind loads, that information is clearly addressed in the plans. In my region, not so much. It wasn’t long ago that I toenailed rafters to wall plates and went home. Now, hurricane ties or structural screws through the plates into the rafters are common.
Wind that pushes things sideways is interesting too. It’s why we brace walls with sheathing or diagonal members. It’s also one reason we anchor mudsills to the foundation—earthquakes are the other, but we don’t have many of them in New England.
The point is, the direction of the force determines how you have to handle it.
What else moves up, down, and sideways?
Heat, of course. It doesn’t just rise. I cringe every time I hear someone say, “Heat rises.” That statement keeps people from understanding the whole issue.
Heat doesn’t rise anymore than…
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