Expert: Richard Taylor, AIA - 1/30/2007

Question
Hello,
   I will start out with my question right off the bat so that you can easily follow our situation.
Question: Would it be better to have a basement excavated under our planned addition, size 26'x28' or add a second story over our new addition?
Our Situation: Our present home is a nice but small ranch style home, 1143 sf. built in 1980. We have large back yard and so my wife and I are planning on adding an addition to the back of our existing home. Our plan is to go back 26 ft and all the way across the back of the home, which is 28 FT. wide. We are also planning on having a full 8ft. deep basement excavated under the new addition. On the main we will keep the same height and roof pitch.
   I have researched and found out that the water table in this area is fairly deep, averaging 140 ft. I did take 3 separate soils samples down to a depth of 106 inches where I hit gravel and coble or bigger. On all 3 holes I hit a layer of silt and clay at approx, 72 inches and water. It had been raining so we have a perched water table that is under pressure because the water came up to 60 inches in my 2" diameter hole. We have a engineer working with us and he suggests putting in a sump pump right off the back for cheap insurance, (I agree), and I think we should make sure that there is plenty of gravel with proper drainage up against the outside concrete walls. This could end up being a very nice space, but also very expensive with the cost of rebar and concrete.
   We could forget about the basement all together and go up a second level. Maybe even go over some of the existing roof to make the second story look like part of the existing instead of a box over the back addition. For the cost of a basement, we could get a lot more upper level addition built.
   So this brings us to my BIG question, actually a couple of questions. One, overall, would the home be worth more having a new basement under the new addition or go up and over the new addition and maybe some of the existing? Resale, which is better? If we go up, we will end up having our master bedroom and bath up, if we go with the basement the master will remain on the main level, which for us would be nicer as we get older. We are 49 and 51 of age.
   Thank you and I will be looking forward to your educational opinion.  

Answer
Hi Kevin - thanks for your question!

It seems to me that if you don't have any need for the second level, then it isn't of any value - regardless of whether it's cheaper to build than a basement or not.

You're nearly doubling the size of the house as it is - what would you do with ANOTHER 728 square feet?

I think you probably have enough of a job connecting the roof of this addition to the house; making it two storey would create a very awkward-looking and difficult to build addition.

Resale depends almost entirely upon what the other homes in your neighborhood are like; will this addition make your house better (not just bigger) than average or will it bring it up to par with the rest?

Is the first floor addition well-planned or is it just a great big room? (I'm always worried when I hear about a deep addition all the way across the back of a house!)

Value, comfort, and usability in a house is not strictly a function of size.  A big but poorly-planned addition may actually detract from the value of your house.  I've lost count of the number of big ugly additions we've torn off houses - and replaced with much smaller, more attractive additions and some remodeling of the interior.  

It's possible that if you really need that much more space that you'd be better off moving to a bigger house - unless your house is already the smallest one in the area.

Assuming the existing house has a basement and that you can control water (drain tiles, grading, sump, waterproofing) then I would assume that a basement is much cheaper space to add than a second floor - after all, you're halfway down there anyway with a frost foundation in temperate climates.

Don't overbuild if you don't have to - you'd be better off spending the money on upgrading the finishes throughout the house!

Hope this helps!

Richard Taylor, AIA
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