Expert: Richard Taylor, AIA - 9/22/2011

Question
QUESTION: Good evening, We are planning a great room addition to our existing 11 year old home.  It will be approximately 900 square feet.  My concern is the ground settling AFTER the addition is complete. How can we avoid this from happening?  Is there special material to prepare the area, or some type of pipes, or ???

ANSWER: Hello Laura - thanks for your question!

What about the addition design or the site gives you concern?  Have you had settling problems before?

Settling has a number of causes, all related to soils conditions.  Soils are classified partly by their ability to support structural loads.  A building design takes this into account; the same building on two different soils for example, might have two completely different foundation designs.

Residential foundation design variations might be as simple as the width of the footings or as complex as a grade beam on pilings (what you probably meant by "pipes"). Some soils can be worked with - but some can't be built on without very expensive mitigation.  You have to know this up front to keep you from making big and expensive mistakes.

Settling of course can be a minor annoyance, or can be catastrophic! Either way there's no excuse for not predicting and preventing it.  And that takes specialized knowledge.

First step is a proper analysis of the soil - for that you need a soils engineer (also called a geotechnical engineer).  You'll find geotechs at any significant engineering firm, or you can contact your county health department - they usually keep lists of soils engineers.

The soils engineer will sample the soils at the site, analyze the soil.  He'll tell your Architect what loads he's designing to, and what foundation type he recommends.  Working with a structural engineer, your Architect will design the proper foundations for your addition.

I know that sounds like a lot of work, but the only option is guesswork, and then you're taking unnecessary risks.  There aren't any shortcuts!

Hope this helps,

Richard Taylor, AIA
www.rtastudio.com
www.rtaplans.com
www.rtastudio.blogspot.com

---------- FOLLOW-UP ----------

QUESTION: Hi Mr. Taylor,  We have a two story house.  We are replacing doors and windows.  On the first floor, in the living room, we currently have a single window.  I'd like to replace it with a large picture window.  
The installer will have to cut a bigger "hole" in the structure of the house.  My concern is, is there a worry about the weight of the rest of the house (the entire upstairs & roof) on this new "hole" for the picture window?  Is there a certain  construction/additional framing that I need to ensure is around the new picture window on the first floor?  
Please help.

Answer
Hello again Laura!

You are right to be concerned about this - if the the new, larger "hole" in the wall is WIDER than the previous opening, then yes, you need to have new structure placed above it.  The structural member you're concerned with is called a "header" and it's job is to carry loads from above and distribute them to either side of the opening.

Depending on the width of the opening, and on the loads above, you may want to have this looked at by an Architect or Structural Engineer.

Good for you for noticing this - it's kind of a big deal!

Hope this helps,

Richard Taylor, AIA
www.facebook.com/rtastudio
www.rtastudio.blogspot.com
www.rtastudio.com