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Are Tiny Homes built from Sheds a Good Idea?

At least every other day, I see an ad for a tiny home or office that companies or individuals built from what used to be backyard “sheds”.  Now, don’t get me wrong, I am all for repurposing buildings and materials, when they are done the right way!  (In fact, I even repurposed a large metal workshop building into a 2 bed/1.5 bath “condo” for my parents.  This one is on a concrete slab and for all intents and purposes, could have been built that way as a home). What are the advantages, and what are the cautions, of making a home from a shed?  (Many great points adapted from Living in a Shed: 9 Things (2023) You Must Know):

The advantages to living in a tiny home are many, for example:

• Up-front cost is cheaper than a house
• Smaller utility bill
• Less square footage to clean
• Less impact on the environment
• Privacy
• Portability
• Customization
• Ability to live in nature or “off-grid” more easily

However, “sheds” are only a subset of tiny homes, specifically, tiny homes that started out as prefab backyard buildings.  Let’s take a look at what could go wrong from making one of these into a habitation.

First of all, when considering whether to build out a shed as a home, you should check into local building codes.  If you live within city limits, there are likely laws about what type of buildings can be built or placed on your property to become “habitations”.  Plopping a shed down and running electricity to it for your teenager to live in could be a big problem whenever it’s noticed by the building inspectors!  Moving it to the middle of a few acres in the country doesn’t normally pose these legal issues, but again, it’s best to check with your local building inspector!   If it’s illegal to live in a shed, it may be legal to live in an ADU-an Accessory Dwelling Unit.  For example, ADU’s in California are required to be at least the size of an efficiency unit (at least 150 sq. ft. livable space plus a bathroom), they must contain a kitchen, a bathroom, they must be built on a permanent foundation, and must be able to turn on/off the ADU utilities without entering the primary unit.  (ADU vs Finished Shed Comparison)

Construction: This is the largest area of caution we see.  Within this topic, we need to highlight: 

• Off-gassing of toxic compounds from interior building materials.  If the building was never meant for habitation (even as a chicken coop!), then it may contain building materials that are rated for “outdoor use only” which may give off dangerous pesticides/weatherization chemicals.
• Inferior flooring and framing techniques:  We’ve seen them: sheds built to hold push lawnmowers and Christmas decorations may not hold up to daily living over a number of years.  Holes or loose joints that develop inevitably allow pests to come in (they want to be cool/warm/fed too!).  
• Inferior foundation: Setting a shed on a few cinder blocks is typically not sufficient for daily living and if the floor begins to sag, all kinds of structural issues (including leaks and mold) can ensue. 
• Poor insulation:  Typically, storage sheds only need to keep the paint from freezing, not keep a person comfortable, so insulation may not be optimal.  This includes roof and floor insulation–yes, if your shed is not mounted to a slab foundation, it needs to be insulated!
• Improper sealing (which can cause moisture infiltration and mold growth): If siding is applied over the frame without an air or vapor barrier, it’s easy for moisture to condense inside the walls if they are heated for a living space, or similarly cooled during a hot summer.  These steps in normal construction are what inspectors look for, for the safety of the homeowner and longevity of the building.
• Addition of water and sewage facilities warrants several considerations:
  • Where is your water source and how will you deal with sewage?  Sewage service is probably the biggest hurdle to overcome, as there are 3 options which may or may not be permitted in your locale: connection to the city’s sewer system, installing a septic tank, or installing a composting toilet. 
  • Plumbing in sinks, toilets, showers and drains also is done by code for a reason–leaks can cause serious mold and hygiene issues.  It’s not a good idea to buy that shed if these appliances are added without proper spacing and materials by someone who knows plumbing code.
• Addition of power to the shed:  Sometimes power service to a shed (50-100 amp service) is not what you would get for a normal home (200 amp service).  Like the plumbing, wiring the shed for power should be done by someone who knows electrical code, so that it’s wired safely!
• Addition of HVAC to the shed: Sticking a “window unit” AC or space heater in the side of the shed may keep you cool or warm if it’s the right size, but without proper ventilation, you could build up CO2 and mold very quickly.  CO2 is the product of insufficient ventilation, and face it, a shed is just a small, closed room unless proper ventilation is planned and built-in!  The mold can result from simply living in that closed room, because along with CO2, every human exudes water vapor through their lungs and skin.  If there are 2 people living there, the air quality will be even worse.

So far, it may sound like a major “NO” to use sheds as homes, but that’s just not true.  If you’re allowed to use one in your locale, you can safely do so by starting from scratch (buying a bare-bones model) or buying one from a builder that knows good home construction.  Then you can make sure that the construction, outfitting and customization will work for years to come without causing health issues.  Let’s face it, home ownership is expensive, but saving on a tiny home just to live uncomfortably from lack of weatherization or get sick from mold is definitely not worth the savings.  Therefore, planning is essential!

Waterproof wall coatings: should you use them in your basement?

As a followup to our article on Getting the Basement Dried Out, and in response to customer questions, I thought we should talk about sealing basement walls.  There are some really good products like GAF Hydrostop, UGL Drylok Extreme, Koster, Xypex and Sani-Tred to name a few.  These kinds of coatings can definitely stop moisture and are relatively cheap compared to the other measures I’m going to recommend here, but the sad truth is that they’re usually only a temporary stopgap measure if proper drainage is not in place.  The building science experts have determined that the basic rules for water management in buildings are:

• Don’t trap water in building materials or assemblies.
• Allow materials and assemblies to dry to at least one side. (energyvanguard.com)  

In the words of expert Joe Lstiburek:  “Waterproof coatings are not bad; they are not, however, a substitute for an adequate drainage system.” (buildingscience.com) The reason is that waterproof coatings act as a vapor barrier, and applying them to the inside of your basement is not a good thing.  

Without proper grading and drainage, your basement is basically a hole in the ground where water IS going to collect.  Construction of a house with a basement doesn’t begin with pouring the basement; it begins with preparing the ground so that it slopes and drains away water, which is the enemy of all the precious building materials in the home.  If your home was not graded/prepared properly during the construction phase, here are the ways that you can get the water flowing in the right direction (down and away from the house!)

• If you have a dirt floor in your basement, cover it with polyethylene to seal the moisture below it.  You don’t want moisture and possibly radon continuously seeping into your basement air space from the dirt).  If you have a bit more in your budget, dig out some of the soil first so you won’t lose ceiling height. Then install a layer of crushed stone, a horizontal layer of rigid insulation (plus some vertical insulation at the perimeter), a layer of polyethylene, and a concrete slab over it all. (greenbuildingadvisor.com)
• Check/install roof gutters:  Gutters are the first line of defense in routing water away from the foundation, because instead of pouring directly down around it, water is directed away from it.  Ideally, the gutters will drain to areas 10 feet away from the house.  If you have gutters, make sure that they and the downspouts are not plugged up with leaf debris!
• Check/adjust grade around your home: if you have an older home, many times the soil around it has built up over the years with mulch, grass clippings, and vegetation so that it doesn’t drain properly.  A good slope to aim for when grading land extending out from a house foundation is about 6 inches for the first 10 feet (that translates to a "slope" of 5 percent). This article tells you how to determine whether your lot already has this slope, or you need to do some work to get that slope.  
• If you can’t grade the area with a rake, shovel and wheelbarrow and you’re going to hire an excavator, then it’s worthwhile to dig down to the footers and install gravel and a perforated drainpipe, so that any water that drains down the wall will drain down and away from the footers.  If you are doing this, THIS IS THE BEST TIME/AREA TO USE A WATERPROOF COATING: on the exterior of the wall! 
• If your home has nice patios, walkways, etc. around it and you don’t want to tear them up, then go for an interior french drain, so that water around and under the slab can be pumped away.  It’s probably a job you’ll want a contractor to handle, but it’s best if you know what to expect and that the contractor outlines his plan, before work starts!  According to Green Building Advisor, a trusted building science site, here is how they would install a french drain: 
  • Cut a trench about 8 inches wide and at least 8 inches deep at the perimeter of your basement slab, near the wall.
  • Put some crushed stone in the trench, and some perforated 4-inch pipe, followed by more crushed stone. The pipe can be installed level or slightly sloped, and should lead to a sump installed in a corner of the basement.
  • Install a sump pump and connect the pump’s discharge pipe to a distant drywell, to daylight far from the house, or (if permitted by your local municipality) to your sewer drain. 
  • Once the French drain is installed, the concrete slab can be patched.  Before patching the concrete, however, you may want to install a tee in the 4-inch pipe, and connect the tee to a solid 4-inch riser pipe that extends through the roof. This riser pipe, along with a properly sized inline exhaust fan installed in the attic, are the essential components of an active radon mitigation system. Such a system depressurizes the air under a basement slab, and provides an important side benefit: it helps keep your basement dry.  (greenbuildingadvisor.com)

If you have done these things and have a condensation problem on the walls, it’s still not time to break out the waterproof paint, because the condensation is likely because of temperature differentials.  Typically condensation will occur on the upper part of basement walls in the winter, when it’s cold outside and warmer and humid inside, or on the lower part of basement walls in the summer, when it’s cooler down below grade but the basement has warmer, humid air.  Check the wall to see if this kind of seasonal condensation is what you’re experiencing.  If so, this calls for permeable insulation that isolates the interior atmosphere from the cold walls, yet allows any moisture coming through the block to pass through.  .  

The best insulating materials for a basement are those that are permeable or semi-permeable such as expanded polystyrene (EPS) or extruded polystyrene (XPS), as these materials are less sensitive to moisture than other insulation types. However, EPS is preferred over XPS in our opinion for the following reasons (airfoam.com):

• Off-gassing: EPS does not contain hydro-chlorofluorocarbons (HCFCs))
• Loss of R-values: in tests XPS has lost up to 44% of its R-values and EPS only 6%
• Water absorption: in tests XPS absorbed up to 18.9% by volume and EPS 4.8%  
• EPS has higher vapor permeance (thus allows more water vapor to pass through) at about 1.2 perm versus roughly 0.3 perm for XPS for R-12 insulation boards.  Normally one would not think this is desirable as vapor is passing through to the basement interior, but this factor affects the foam board’s own potential to stay dry. 

The best place to insulate is on the exterior.  Exterior insulation is advantageous because it protects the wall from the cold soil so that condensation cannot occur on the wall and the wall can dry to both the interior and the exterior. Installation of exterior insulation is best done during construction, however it can be accomplished as a renovation if  great care is taken to prevent damage during back filling around the foundation. If you don’t plan on excavating to the footings of the home, opt for interior insulation.  It should be vapor permeable or semipermeable as well as “air tight” to prevent warm, moist interior air from condensing on the cold concrete or block wall. Some foam insulations such as EPS and XPS can satisfy both conditions if installed properly (including taping at the seams). (buildingscience.com)

The slab floor:  Once again, the best place to insulate the slab is under the slab during construction, however, if you’re renovating, then insulating on top of the slab is fine.  Because most of the year the slab will be colder than the interior air, it’s a surface on which condensation can occur. The best way to accomplish this is adding a layer of rigid foam insulation, 2 layers of plywood for support, and a permeable finish like wood, carpet or cork (see diagram below).