Expert: Bruce E. Johnson - 1/21/2010

Question
Hi,

I'd like to build a small (~800 sq ft) L-shaped, slab-on-grade structure to use as a vacation cabin currently, but would like to enlarge it later into a home of ~2400 sq ft. I was considering to build only the 800sq ft section of the full floor plan now, and finish the main floor as well as adding a partial second floor later. (The 800 sq ft part has a roofline separate from the rest of the design).

Instinct tells me it would be a bad idea to pour only part of the slab now, and pour the rest later-- is that true?

Even if i were able to pour the whole slab now, would i still run into problems with differential heating of slab in winter, separation of wall joints etc when i joined new walls on later, or other problems?  (The exterior walls would be ICF, on both the old and new sections.)  The slab may or may not incorporate PEX tubing for radiant heat system.

Thanks for any advice--

Answer
Hi sRon, Unless you plan on building the whole building within a six month period..I would only build the 800 sqft section first..however I would plan for future expansion.  The main concerns for future expansion are plumbing, electrical and air conditioning..The structural part is important also but the utility infrastructure is the highest priority..Try to locate your waste lateral in a place where you can access it for later construction.  The same with water and air conditioning and electrical..locate and size the feeder lines and pipes for future use..Same with your radiant heat..make sure it is expandable and choose a system that will meet your future needs..I hope this information helps, please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com