Many American houses have basements or crawl spaces, which are handy for extra storage, giving access points to natural gas and water plumbing, and making it easier to carry out future pipe/cable runs. These would all be clear benefits to a tiny house too, especially having an extra storage space - so can these useful additions to houses be added to tiny houses too?

THOWs (Tiny Houses on Wheels) naturally cannot have basements, although they can potentially have crawl space access under the trailer. A tiny house on a fixed foundation can have either, however, since they are constructed in a similar way to standard houses.

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Basements And Crawl Spaces: Why And How

If you have never heard of basements or crawl spaces, then it is worth us having a quick recap:

Basements

A basement is a big open space, usually with concrete walls, which sits below the main house line. They are formed by digging foundations deeper than would usually be needed, and then extra concrete is poured to form the basement level walls and floor. Steel or timber is then added above this to support the main floor (which would traditionally house the living room and kitchen/dining room):

A two-in-one picture (one from Joergelman of pixabay, the other from Wikipedia) showing both the outside access and inside view of a basement, in this case being used as a gym.

Basements are especially common in parts of America with lots of clay soil (making it easier to dig down the required depth to form a basement), and also where the frost line is fairly deep - meaning that a deep foundation dig is needed anyway.

They are usually accessed via a staircase outside of the building, but sometimes there is a staircase or floor loft hatch/trap door inside the house.

In terms of why basements exist: they are pretty useful to store the various household items you have accumulated over the years, plus they can make a fun living space (for adults or children) - but also a gym! From a maintenance perspective, basements can be a useful place to store your boiler, heaters and natural gas/water plumbing access points. Equally putting noisy household appliances like washing machines down there can be better than keeping them in your kitchen.

In short, basements are a very useful, practical space so that your main house can be freerer of clutter and noisy (or large) appliances. They would therefore be very useful in a tiny house which are on a fixed foundation. However a tiny house sitting on a trailer (a THOW) naturally does not have a fixed foundation, and hence could not have a basement. The closest thing to this would be an RV/tiny house park which offers extra storage as part of the land you rent. Whilst this is rare, it can be useful to have.

Crawl Spaces

A dingy crawl space with lots of cob webs, concrete for rodent control/prevention and some utility runs, from Wikipedia.

An alternative to digging a huge hole and filling the floor and walls with concrete is a crawl space which, as the name would suggest, usually just offers space to crawl in - i.e. they can have a height as little as 1’ (30cm). They are built by raising the building off the ground, either by having a ‘below ground’ course of walls (and then steels/timber are put on top for the main floor) or by using concrete or screw piles.

This is much cheaper than building a basement, and costs a similar amount to a standard concrete slab foundation (which offers no basement or crawl space). Whilst you have to be careful what items (if any) you store in your crawl space (so they do not get damp), being able to access any main pipework and cabling supplies is a big benefit. So if you live in the ‘right’ area for a crawl space, it can definitely be worth having one.

You may have noticed we say the ‘right’ area. This is because crawl spaces can be rife for damp/mould issues, and whilst vapor barriers can be used to mitigate this, very damp/wet climates are still not great for crawl spaces. In other words, crawl spaces are better in drier climates which only have limited amount of rain and storms.

Whilst some people prefer basements because they are more versatile than crawl spaces, the fact that crawl spaces are much cheaper to build whilst still giving access to utilities (for repairs and also future building work) and storage is a big benefit in our books. That is as long as you take steps to reduce or eliminate excess moisture which could cause damp, of course.

How THOWs Can Have Crawl Spaces

A crawl space is just where the main house is raised off the ground enough for someone to be able to crawl underneath it. A tiny house on a trailer naturally offers this, by nature of the fact that it is on a raised-trailer base which usually gives sufficient space to crawl under.

We say usually because THOWs which are too high cannot be transported on the roads without a special permit (i.e. extra costs and paperwork) - something many tiny house owners try and avoid. Since height is key, many tiny house specific trailers can be quite low-lying: sometimes not quite high enough to easily crawl under them to repair/inspect/amend utilities.

As a general rule, if the main metal frame sits in the middle of the wheels then it probably will not be sufficient for an effective crawl space, for example this trailer by Tiny Home Builders:

Tiny Home Builder's trailer where the frame is fairly low tothe ground, from Tiny HomeBuilder's website.

This is because even if it looks like you might be able to squeeze under there (which I probably would not be able to based on the above, but some people would!), remember that the ground-to-trailer height will drop a few inches when the weight of the actual tiny house is put onto the trailer.

However something like Tumbleweed’s tiny house trailer should be okay because the main frame sits above the wheel - giving an extra 6” (15cm) or so to crawl under:

Tumbleweed's tiny house trailer with frame on top of big wheels and mountain terrain in the background, from Tumbleweed's website.

As always we recommend that you measure up any trailer you are considering buying, and ask how much it should drop by with the weight of your tiny house (which can be as much as 8,000 lbs/3,600 kg).

Also whilst it might seem obvious, be conscious that storing items under your THOW’s ‘crawl space’ will open you up to theft of these items more than with a standard crawl space (where the access point can be more secured). Only store items under your THOW if you fully trust your neighbors/surroundings, and/or can afford to lose those items!

Nonetheless, having access to the underneath of your tiny house is a big benefit - so it is worth considering your trailer height before purchasing one.

Tiny House (With Foundation): Basements

As mentioned earlier, a basement provides many benefits to a homeowner - including lots of extra storage space, which is more valuable in a tiny house than a standard-size house. There are two main ways to achieve a basement in a tiny house: firstly if you have a sloped building site, then you can always make this work in your favor and have the ground floor towards the top of the slope, and a basement at the bottom:

A two-in-one picture: the left hand picture shows the front entrance to the main house, whilst the right picture shows the basement entrance, thanks to Montana Mobile Cabins.

This is a fairly common way of getting a basement without paying a premium, especially considering that you do not have to pay a fortune on potentially levelling out the site (or looking at alternative foundations for the underside over the slope).

The second way is the more traditional way: digging a deeper hole than usual, then doing the concrete pour so that the walls and floor form a basement:

A photo showing three workmen in an approx. 10' deep hole with concrete floor and steel rebar in the walls (getting ready for the wall construction/pour).

Once the walls are also poured, you then have the basis for a basement. Steel or timber can then be laid over this to provide a stable base for the first (i.e. ground) floor. This is the most expensive foundation approach, but you can probably imagine just how valuable this extra space might be. If you need to dig down (for example) 6’ (1.8 metres) anyway to get below the frost line, why not dig down a little more and form a basement?

You can then store (pump-powered) water tanks and a heating/HVAC unit in this basement, along with having various storage shelves/units, and this will free up a lot of space in your actual tiny house.

Outside view of a crawl space, provided by a gap in the below-floor-level bricks, from OldHouseCrazy.

Tiny House (With Foundation): Crawl Spaces

If you do not have claustrophobia, then a crawl space under your tiny house might be perfect! You can use this to store various weatherproof items (or items in a weatherproof box) which would otherwise take up space in your tiny house, along with giving you access to utilities for maintenance and future building work.

A crawl space involves having your actual tiny house sit off the ground, with the foundation partially exposed so that there is literally only room to crawl around underneath the house. As mentioned earlier, this is a much cheaper option than having a basement and it still brings some of the benefits of a basement.

To be honest, you get some extra storage (but not as much as a basement), and some access to utilities (but not as much as a basement: you cannot store large heater/water units down there, for example) - for some of the cost savings. So a crawl space is arguably a compromise of a basement: you get less benefits, at a lower cost. We still think that crawl spaces are valuable in dry climates, but be sure to weigh up whether a basement (or simply a standard foundation) is more suitable to your needs - and budget.

Crawl spaces are less popular than basements in some parts of America, with just 6.9% of homes having crawl spaces in the Northeast, rising to around 19.4% homes in South. This compares to over 80% of homes having a basement in the Northeast (although just 15-20% of homes in the South have a basement, similar to the number with crawl spaces) - according to research from Northern Kentucky University.

Disadvantages To Basements And Crawl Spaces

Whilst this article has set out various advantages to basements and crawl spaces, there are drawbacks as well. The flaws of a basement are:

  • Significantly higher cost than a crawl space or standard foundation. Whilst the extra space is useful, you will need to consider whether this is really worth the extra five figures that you will almost certainly end up paying for a basement.
  • Precision is important when building a basement: it needs to be well-constructed and occupy the same footprint as your house, to prevent heat escaping and to keep out rodents and critters.
  • Since the basement is below-ground, it will be exposed to more damp and cold than the rest of your house. At the same time, 40% of the air you breathe in your tiny house will come from your basement. In other words, a cold and damp basement (especially one with mold/mildew) will mean breathing this in inside your actual tiny house.
  • You need to carefully plan how to access your tiny house’s basement. A floor trap in your tiny house is convenient, but will take up valuable space that you ideally cannot put furniture over. An outdoor access is therefore better, but this will cost more to construct - and give potential thieves an access point to your basement where you cannot see them.
  • Soil which absorbs lots of water (i.e. when it rains) will expand, putting pressure on your basement walls. This can cause cracks, which can eventually lead to water ingress from the soil. Hence such cracks need to be monitored and filled in when spotted: an extra maintenance headache.
  • Basements seem to be a breeding ground for small insects and spiders (in many cases), which can be a pain to deal with.

Whilst the disadvantages of having a crawl space in your tiny house is:

  • Cost. Whilst they can sometimes be on-par with a standard foundation, they usually work out a bit more expensive. After all, the more materials and complexity that are needed, the greater the overall time and cost.
  • Damp and mould. A properly constructed crawl space can really benefit a property… however some common mistakes or oversights in crawl spaces can lead to damp air constantly circulating against your foundations and timber floor: potentially causing serious problems as time goes on, along with damaging any items that you store in your crawl space.
  • Rodents and critters are usually attracted to crawl spaces as they will prefer this ‘indoor’ space away from the rain. This means dealing with their waste, along with the risk that they chew through utilities which are in the crawl space.
  • Your main ‘ground’ floor will not be on top of a secure concrete slab: it will instead be a ‘suspended’ floor sitting on-top of timber/steel. If your crawl space does have any damp issues, this can cause the floor to fail, especially if it is timber and not steel.
  • Whilst you can insulate your crawl space, a well insulated concrete subfloor will still provide a better level of insulation than the crawl space.