I'm always perplexed by the ambivalence of many future homeowners towards foundations.  A home's foundation, or its substructure, is of course anything below the lowest wood-framed floor.  These can take many general types, ranging from absolutely nothing (not recommended) to 12' tall drive-in basement garages and pools (also not recommended).  Foundations can be solid, built on piers, or on loose gravel; and common materials include concrete, stone, brick, concrete block, wood, steel, and compacted soil.  But like all of us, chances are you have a picture of what a foundation is in your mind that is largely determined by where you've lived.

A house with too little foundation.  A house with too much.

In fact, foundations are one of the last building features almost fully derived from local, vernacular norms.  If you're in Florida, you probably think "concrete slab" when you think of a foundation.  If you're in California, you're probably thinking "thick concrete walls with lots of steel in them."  If you're in eastern Virginia, foundation probably means "concrete block crawl space" to you.  And, if you live within earshot of an ocean, you're thinking wood piers.

Much of this has to do with local environmental conditions.  If a storm could cause the tide to rise to your doorstep, you lift your house off the ground and let the water move under you, hence piers that don't block the water but simply get you away from it.  In much of California, earthquakes wreak havoc on foundations, which need to be extra strong (hence thick concrete walls) without being too brittle (hence the steel reinforcing rods inside those thick walls).  In the northern half of the US, ground freezes cause the earth to move, which can shift your house around if the foundation isn't sunk at least to the point just below where the ground stays warm enough not to freeze (which maxes out at about 56" for most areas, but is only 2-3' in eastern Virginia, hence building a crawl space (a shallow basement) that is only a few feet deep/high).  In Florida, the ground doesn't freeze, so a concrete slab (a pad of concrete 6-12" thick siting right atop the ground) is both inexpensive and sufficient.

Clockwise from top left:  House on piers, thick concrete foundation with reinforcing steel, crawlspace basement, and "slab on grade" foundation.

The underlying assumption above is pretty much the reality - for most homes, the foundation selected is the least expensive option allowable in the particular environment.  Other factors come into play, of course, such as local contractor knowledge, availability of materials (You won't see a granite foundation in California, but there are plenty in New Hampshire.), and to a lesser extent, aesthetics.  However, foundations perform many other functions than simply holding the house up, and within each environment there are still multiple options that are equally good at doing so.



A foundation is the home's aesthetic connection to the ground, and how that plays out architecturally was in fact one of the primary concerns for Frank Lloyd Wright.  A rough cut stone foundation (admittedly, VERY expensive) between a high mountain home and the rocky ground creates the sense that the home is growing out of the ground, that it belongs, that it is fitting in.  Similarly, a Cape Cod beach house on piers 6' above the beach says, I like the view, but I'm not part of the landscape.  There's nothing wrong with either of these approaches, they are simply aesthetic differences, and in the latter case, may be the only option.

House who's foundation connects it to the environment (Fallingwater, Frank Lloyd Wright, left) and to separate itself from it (Villa Savoye, Le Corbusier, right).

Foundations are often also used for storage, in particular in northern climates where the foundation already needs to be 4+ feet deep.  In much of Connecticut, for example, the thinking is, "If you already need to dig a 4' hole, might as well go to 8' and create a full basement, which can be used to hide the boiler, water heater, washer, dryer, and teenage son."  In certain parts of California, it's not uncommon for the foundation/basement to serve as a whole other level for the home, completely finished and often with windows and doors.  Even crawl spaces can be used to store Rubbermade containers of winter clothes and obscolete baby toys.  Often, builders and homeowners opt to have their basement or crawlspace floor covered with a few inches of leveled concrete - sometimes called a "rat slab" for obvious but not necessarily true reasons - to make this storage or additional living space cleaner, less moist, and generally more "finished."



However, a common misconception exists that basement foundations (which are frequently limited to poured concrete walls with a poured concrete floor) are a cheap way to add storage and living space to a home.  I've heard many builders call this "free space," but this is far from true.  Of course, if you only need to go 48" into the gound to get below the above-mentioned "crawl space," then the additional concrete (used to make an 8' wall instead) isn't free.  While it is true that the majority of excavation (digging) costs for foundations are in mobilization (getting the equipment there and ready), the price to the homeowner is still linked to depth.  Further, there are certain things that can cause two of the exact same foundations in the same state (or even neighborhood), built by the same contractor, to be wildly different in cost.  Hidden in the ground can be "ledge" (huge masses of rock under the earth's surface), large boulders, and even archaeological remains (ok, less likely) - all of which are statistically more likely to be found the more you dig and all of which will dramatically increase the foundation cost (by multiples in some cases).  
Even if an 8' basement ends up only double the price of the absolute minimum foundation required in your area, that additional, say $10,000, has only bought a damp, dark concrete space.  Perhaps that's fine, because the space is just for storage, but in that case, the added convenience of being able to stand fully up in your storage space (as oppose to a 4' crawl space) may not be worth $10k (or $15k, after mortgage interest).  In terms of using the foundation for living space, this will require finishes, electrical, (maybe plumbing), and (really ideally) windows.  Your're far from $10k now, and it still feels like a basement.

There's another way in which basements aren't "free space."  Concrete is very nearly the worst building material from an environmental standpoint.  Extraction of silica (used as the binder in concrete) is heavy mining, cooking that silica and everything else into concrete requires enormous amounts of energy, and transporting heavy concrete that constantly needs to be "rolled" to keep from solidifying consumes gallons and gallons of diesel fuel.  Concrete walls are produced by pouring liquid concrete into, usually, wooden "formwork" (basically, a whole other wood-framed wall), where the latter is often thrown out after as little as a single use.  Insulating concrete (when above ground) is more expensive than insulating wood-framed walls, and concrete releases water moisture for up to 10 years after it's poured, creating the risk for mold and mildew, leading to various health problems and potentially decaying the wood in the rest of your home.  And, at the end of the day, you're left with a permanent thing deep in the ground that is extremely difficult to remove and cannot economically be recycled.

Cement Quarry (where concrete materials are extracted, left) and Concrete Production (right).


So, what are the alternatives?  First, we need to dispel the myth that basements are free space.   Instead, let's consider it cheap space - inexpensive but very low quality.  If that's good enough, then perhaps a crawl space (with or without "rat slab") makes the most sense.  But, if you are thinking "extra bedroom," "workspace," "workout room," etc., perhaps keeping these things above ground makes more sense.  Depending on the design, maybe making the house a couple hundred square feet bigger isn't that much more expensive.  That an additional $20,000 for an extra room will feel like a much smarter investment than the extra $10,000 for a taller basement.

What if you don't want to or can't add the $20k cost right now?  Well, unlike the basement, you can always postpone this decision until you really need to do it (or have the extra money).  Wait a few years, then add that room off the back of your house.  You could even build it yourself (ok, I'm a bit biased here, but a small addition is quite easy to do yourself, unlike a foundation).  If you are thinking that you'll "finish out" your 8' basement in a few years, why not save your money, go with the more minimal basement, and put that money (perhaps taking advantage of a favorable refinancing) into an addition where you don't need to comprimise natural light, air quality, and convenience.  (The added amenity and square footage might increase the value of your home immediately - how's that ROI!)



Another option, which is increasingly becoming common throughout the US, is to build the addition as a separate little building on your property - an "Accessory Dwelling Unit" (ADU).  This work is even easier to do yourself, it can be less expensive than first cutting a hole in your existing home, and the design can be whatever you want.  Maybe your office would ideally not be a stucco Spanish style ranch.  Perhaps you want your Yoga studio to be a bit more airy than your New England colonial?  Not going to use it in the winter?  ...skip the heat and insulation.  Using it to practice drumming?  ...leave out the windows?  Unlike an addition, and certainly unlike a basement, you have very few constraints to what you can build as an Accessory Dwelling Unit.  Build it well, of course, but you're in control, so make it yours.  (You may not even need a building permit!)

Clockwise from upper left:  Morrison's Garden Building (Atlanta, GA), "Shoffice" backyard office by Platform 5 Architects (London, UK), Tool House (Boston, MA), "Pod" guest room by ArchiPod

So, what do you put it on?  Well, you have so many options for ADU foundations!  Concrete walls are still allowed, of course, but piers (concrete, wood, or steel) will probably be easier.  Unless your ADU is your billiards room, you could just build it on a slab, even in cold climates.  Heck, nothing says you can't just stick the thing on the ground (many people do, but you should look up how to keep ground moisture and critters from invading).  Or, one option I really like, is putting it on an 8" bed of gravel.  Either way, you'll end up with a beautiful space that isn't going anywhere, will be level enough (the smaller the footprint, the less it can get out of level), and will be a much greater value for the money - and environmental impact - spent.

Steel 'Helical Pile' foundation posts being installed (left) and garden shed on gravel bed (right).

I'll go into detail about each of these alternative foundation options, and others, in an upcoming post.  But, as a sneak peak, they aren't just for Accessory Dwelling Units.  In fact, once you give up the myth that foundations are free living space, you open the door to many alternative foundations types, reducing the impact on your bank account and the environment, while expanding opportunities for architectural expression.

Thanks for reading.

Dennis Michaud

(Co-Founder, Homebuilt)

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