House Engineering 101

If you are just starting the new home planning process and have been through it before, you know how complicated it can be.  One of the biggest challenges involves balancing design ideas with house engineering.  Sometimes we set our sights on a particular design idea but it can be difficult to create a solid structure that meets those needs in an affordable way.  Let’s talk a little about how house engineering works and discuss how changes must be carried out properly to avoid structural problems.

Column Supporting Floor Above

Loading and Support

The easiest way to describe the home structure is to say, “every part of the home needs to be supported by something solid below it.”  If we take a look at each individual piece of the home, we can see how the weight of that structure is supported from below.  There are the obvious structural items in a ranch plan with a basement…

• Roofing – supported by roof decking below
• Roof Decking/Plywood – supported by the rafters or trusses below
• Rafters/Roof Trusses – supported by the framed walls, beams and girders below
• Framed Walls – supported by the floor decking below
• Floor Decking – supported by the floor joists or floor trusses below
• Floor Joists/Trusses – supported by the foundation wall/beam below
• Basement Beam – supported by the steel columns and foundation wall below
• Steel columns/Foundation Wall – supported by the footings below
• Footings – supported by the soil below

This is a simplistic way of looking at house engineering, but it shows how all of the home components work together to create a sound structure. 

Changes

It sounds easy to change a structural item in a house or plan.  As a builder, I can’t tell you how many times I’ve heard statements from customers like, “it’s just a column, just move it over there…what’s the big deal.”  When the item is not a structural component in the home (i.e. the list above), it can be moved without much effort.  But when the item in question is part of the structure and is supporting something above, it involves much more analysis to prevent future settlement problems or even worse, collapse. 

So whenever a change involves a structural item, the house engineering needs to be reviewed.  For example, let’s say you want to move a structural column on the first floor of a two story home with a basement.  Here is a list of items that need to be reviewed/changed:

• Column – Identify exact location of the new column and evaluate the loading from above.  If there is a beam resting on the column and the span increases, the beam may need to be replaced with a larger one.  If the column no longer rests under the beam above, a second beam may need to be added to support the end of the original beam.  This will create addition loads under the new beam added.
• Column Support – The column being moved will need support from below.  If it currently rests on the decking of the first floor, this decking and framing below will need to be evaluated.  If the column is supporting any real weight, there is most likely a beam in the floor framing below that supports it.  This beam will need to be moved to pick up the weight of the column above.
• Beam Support – The beam under the column in the first floor framing will need to be supported as well.  If it is moved, the basement steel columns and beam will need to be re-evaluated.
  

Laminated Beam Supporting Floor Above

• Basement Columns – With the changes to the loads above the columns, the house engineering will then focus on the size and capability of the columns to carry the changes in weight. 
• Basement Column Footings – If the columns move or the loading from above the columns changes, the column footings will need to be evaluated to make sure they are the correct size and in the correct location.

Protocol to Avoid Structural Problems

It’s easy to see how a small change to a house’s structural components requires some hefty analysis to make sure everything will be sound when built.  So it’s important to have a qualified house designer, architect, or engineering review any changes that are considered before construction starts.  The contractor or owner builder should also evaluate the change to see what the potential impact will be on the new home budget.  Once the decision is made to make the change, the building department will need to approve it (if the permit has already been issued).