CHAPTER
18

Utilities and Envelope Considerations

In This Chapter

• Discovering the best HVAC for THOWs
• Installing plumbing, electrical, and sewer lines
• Connecting to the internet with your THOWs
• Learning about various insulation options
• Installing windows and doors

Discovering the right HVAC system for your tiny home can be daunting. We will guide you through the tangled web of these systems, as well as others.

In this chapter, we cover HVAC systems, plumbing, electrical, sewer lines, venting, roofing, insulation options, siding, and finally window and door installations.

Choosing and Sizing Your HVAC Systems

It’s important to properly size your HVAC systems for your tiny house. One that’s too small will find you wearing nine layers on a cold winter night, while one that’s too large will leave you wanting to wear nothing more than a bathing suit.

To determine the right fit, fill out a web form on an online British Thermal Units (BTU) calculator. You’ll need to collect the following data about your tiny house first:

• Square footage
• Height
• Number of exterior walls
• Number of doors and windows
• Number of occupants
• Insulation R-values

If the form doesn’t ask for this level of detail, find another one because detail is the key to your success.

DEFINITION

The definition of British Thermal Units (BTU) is how much energy it takes to raise the temperature of one pound of water by one degree Fahrenheit. BTUs are the standard unit of measurement when comparing heating and cooling appliances. Once you know how many are required to condition your space, find a unit that can deliver said amount.

The form will tell you how many BTUs are needed to heat and cool your space. Look for units that meet those requirements. If your BTU value falls between two potential models, choose the larger of the two. Assuming your unit can be thermostatically controlled, it can always be set to turn off when the temperature falls out of programmed range.

Grid-Tied Electric HVAC Options

Not all climates require air conditioning to keep inhabitants comfortable (we don’t have AC in hOMe). Some places, on the other hand, never use heaters, but they would become dangerously hot without air conditioning. If you plan on moving your THOWs through various climates, look for a unit that combines both cooling and heating functions. Our recommendation for that scenario is a mini-split system.

Mini-splits are simple, compact, energy-efficient, affordable, ductless, provide both heating and cooling, and mount seamlessly to a wall. They work in conjunction with a small compressor, which installs to the exterior of a house (usually on the trailer tongue on a THOWs).

Mini-splits are reasonably priced and quite energy efficient (compared to other electric units). They look pretty sleek and can be mounted high up on a wall, taking up no floor space. They come with a thermostat and operate reliably, even in extreme climates.

There are also other electric heat sources that work well in a tiny house. One such option is radiant floor mats. They’re typically used in bathrooms in conventionally sized houses, though because tinys are so much smaller, they can work as the primary source of heat here, too. The matts install under the finish flooring, giving off lovely heat to warm the toes while taking up no additional space. Be sure to choose a model that produces enough BTUs to comfortably condition your space. Some are quite small and insufficient for cold winter applications, even in a tiny home.

TINY TIP

Some tiny housers simply use portable oil-filled radiant heaters, electric fireplaces, wall panels, plug-in baseboards, and the like. These options install easily and are inexpensive. Similarly, a lot of options exist for electric air conditioning units as well.

Off-Grid HVAC Options

Those of us living off-grid don’t have the option of electric heating systems. Even the most efficient ones draw too much power and require an enormous and expensive solar system. Instead, we look to wood and propane heaters to warm our spaces.

There are now several small wood-burning stoves appropriately sized for a tiny house. It’s especially important to choose one that’s not too large because you won’t have the option of controlling your temperature with a thermostat.

With a wood-burning stove, you’ll need to budget space for storing kindling and logs. You’ll also need to factor where you’ll place your vent stack if you plan on being mobile. Remember that measurements for road restrictions are taken at the widest and tallest parts on a trailer. You might want to install a vent that can be removed with relative ease as needed.

Wood-burning stoves typically produce a significant amount of heat and are very hot to the touch. As such, they require quite a lot of clearance and space around them. Search for a unit with minimal clearance requirements and low weight.

In terms of propane heaters, we only recommend direct-vent units in which fumes and vapor are carried outside. Though some claim that nonvented heaters are safe for indoor use, we can tell you from personal experience that they smell bad and create a significant amount of indoor condensation, even when windows are left partially open. They’re tempting because the costs are so much lower and the installation is so easy, but we can tell you that after three days of trying a couple different models, we ran to the store to invest in a direct vent unit. Important options to look for are thermostat control, nonelectric ignition (in case of power failure your unit will still work), and proper BTU sizing.

Many units are quite large and put out way more heat than needed. Fortunately, there are a couple wall-mounted and freestanding models being used successfully in tiny houses today.

We chose the Hampton H27 for hOMe. It mimics the appearance of a wood-burning fireplace and produces enough heat to keep us toasty warm even when it goes down to -10°F (-23°C). It does take up quite a lot of space and wasn’t inexpensive, but we like that it comes with a remote thermostat and requires very little safety clearance. We have no complaints about it at all.

Ventilation

It’s essential to provide adequate ventilation in your home because moisture and stale air accumulate very quickly in a small space. The most obvious locations for vents are in the kitchen and bathroom. We’re often asked if it’s important to install them in both and our answer is always yes.

If you only install a kitchen vent, all the moisture (and odor!) produced in the bathroom will be pulled through the house to the kitchen vent. On the other hand, if you only install a bathroom fan, all the steam, grease, and exhaust produced in the kitchen will be dragged through the house before exiting. Thus, it’s best to add both.

Kitchen fans not only mitigate food odors and grease but also exhaust dangerous carbon monoxide if using gas appliances. Tiny houses are more susceptible to the buildup of noxious gases than conventionally sized homes because of the minimal square footage. If you use a gas oven, cooktop, or range you absolutely must install a vented range hood.

We highly recommend you install a moisture sensor switch connected to your bathroom fan. This simple and inexpensive device automatically turns on and off as moisture levels in your home rise and fall. You decide what ambient internal humidity level you want it set to (varies with the season and external temperature) and the switch does the rest. They can work in conjunction with any fan on the market and simply replace the wall switch that activates the unit.

TINY WARNING

Regular bathroom fans often fail to fully remove moisture because homeowners don’t leave them on long enough. In time, this moisture can penetrate walls and cause mold issues. The use of a moisture sensor switch completely mitigates this issue.

Let’s assume you’ve built a tight home with very few air gaps and leaks. When your kitchen and bathroom fans are on and pulling air from the interior, where will the replacement air come from? Without adding what’s called make-up air (the outside air used to replace exhausted air in a structure), your tiny house will be forced to pull air through gaps in the insulation envelope. That’s a terrible idea because you’re literally forcing moisture laden air into the cracks of your home, and that’s exactly what you want to avoid for the long-term health of your home.

Instead, we recommend you install a passive make-up air vent to provide replacement air. Bringing air in through a controlled pathway eliminates the risk of moisture getting trapped inside the wall cavity. Perhaps more importantly, controlled make-up air eliminates the risk of pulling air back through the exhaust vents from places such as your greasy stove vent, the stinky composting toilet vent, or sooty wood-burning stove vent.

You might also want to consider adding an energy recovery ventilator (ERV) or a heat recovery ventilator (HRV) to your tiny house. These provide conditioned, fresh air to your home by means of exchange. Stale interior air is dumped to the outside, while fresh air is brought in through an exchanger. These systems only have a 10-percent temperature loss between the intake and outtake air, saving you energy and money. HRVs and ERVs also help eliminate interior moisture buildup by condensing excess water and draining it to the exterior.

Having a source of fresh air is important, especially if you live in a tightly sealed home. Nobody wants to breathe stale air all day long. Provide yourself with a healthy, fresh alternative by using the techniques we’ve laid out.

Plumbing and Gas

Though not particularly glamorous, rough utility lines are a vital component of any house because they enable water and gas to travel to the right locations. The effort you put in here will keep you safe, warm, and clean once the house is done. Let’s go over various considerations.

• Copper comes in long rolls and can be relatively easy to install. The biggest challenge is the flare fittings at each connecting point. Copper is soft, so be sure it can’t rub onto hard surfaces such as your trailer as this may cause it to break over time. Bed the lines in flexible and soft material (or use minimal expansion foam) wherever they penetrate the house.
• Black Pipe is perhaps the easiest material for a first timer to work with. It’s strong, durable, and offers fittings of nearly every shape, length, and size you could possibly need. Secure the joints with the appropriate pipe thread tape. There are lots of potential options, so make sure you choose the ones specifically rated for propane. Use two pipe wrenches to tighten the fittings and connections, ensuring there are no leaks.
• It’s a good idea to protect black pipe from rubbing at the house penetrations in the same way we outlined for copper lines. In fact, we suggest you take this precaution with any material you choose. Wherever gas lines terminate at an appliance, install a shut-off valve so you can easily disconnect the appliance for service if/when needed.

TINY TIP

When calculating the lengths of runs in black pipe, you have two main options available.

1. Purchase standard length pieces off-the-shelf and use couplers to create the length you need.

2. Have custom lengths cut and then rethreaded at the store.

• Flex Line requires a special permit to purchase and install. You can get a permit with some simple training, so you need to decide if it’s worth the effort. Flex line is great because it installs easily, is flexible (important when you’re towing your THOWs), and comes in long lengths. The fewer connections you have in any system, the fewer potential locations for leaks, so the long uninterrupted runs of flex line are very advantageous.

Once your pipe is installed, perform a leak test. Close all shut-off valves by each appliance and install a pressure gauge with an air cock on it at the initial tank/point of system entry location. Fill the system with more air pressure than you intend on having for the gas. In other words, if you plan on running your gas at 40 psi, test your system at 50 psi. The best way to discover the pressure of your system is to contact your propane supplier and ask them what their tanks are charged to. It’s important to also know the manufacturer specifications for all your appliances to make sure they don’t require higher or lower pressures than what your tank supplies.

Leave the system charged for 24 hours. When you return to the gauge, the pressure should be exactly the same. If it’s less by even a tiny amount, fill a spray bottle with soapy water and check every joint by spraying it. Start at the pressure gauge and work your way back through the entire run, looking for bubbles. Take your time and get it right. Once you connect the gas source to your lines, be sure to check that the connections to the main line (from the tank to the house) are leak free as well.

There is no room for error here, so pay attention. If you’re not completely comfortable working with gas lines, there’s nothing wrong with hiring a pro to tackle this important job.

Sewer Lines

Providing sewer/waste lines is the first step of the plumbing process. You want to install them before you install the supply lines because they’re harder to adjust around existing utilities. Water supply lines, on the other hand, can always be shifted around waste lines if necessary.

There are two main options for waste line materials: ABS and PVC. Whichever material you choose, stick with it throughout the build and don’t mix and match. In addition, use the proper adhesive for that material. Each waste-line type has its own specific glue, and in the case of PVC, a special primer is also required.

There are some important details regarding sewer line installations such as the angle of the fittings as they meet the main lines, what fittings are appropriate when, and more. As such, we highly recommend you find a reliable resource, specific to plumbing installations, that can outline this process for you in more detail than we can provide here. A poorly draining sewer line can cause more issues than just an odor buildup.

DEFINITION

Short for acrylonitrile butadiene styrene, ABS is resistant to abrasion, durable, nontoxic, and slightly easier to install than PVC. While it’s more durable and has a higher impact strength, it’s more likely to deform when exposed to UV rays. It does not contain BPA.

Short for polyvinyl chloride, PVC is resistant to abrasion, but less durable and has a lower impact strength than ABS; nontoxic, and slightly harder to install. It contains BPA (bisphenol A).

It’s crucial to install in-line vents with your waste lines. Without these vents, water in your P-traps will completely drain after each use. This water is necessary to provide the seal from sewer gases entering your living space. These gases and odors will present an issue if you don’t provide vented P-traps whether you’re on a municipal, septic, or black-water tank system.

If you’re wondering what P-traps are, take a look under your kitchen sink. That curved section of pipe below the sink drain is a P-trap. Water remains trapped in that curve, creating the seal needed against sewer gas.

In many locations, air admittance valves (AAVs) are a code-approved, under-cabinet vent solution. These are great for THOWs because they don’t require a penetration through the exterior house walls. Instead, they work by providing a break in the suction that would otherwise drain your traps, the same way an in-line waste vent would but without penetrating the roof.

AAVs must remain accessible, so they can’t be hidden inside walls unless there’s an access panel. In time, AAVs need to be replaced because they’ll stop working when the seal eventually gets too brittle to fully work. This could be every 5 to 10 years depending on usage.

If you prefer not to use AAVs, you can install standard roof stack venting. The issue for a THOWs is that the venting needs to extend above the roofline. If you plan on being mobile, you’ll need to either factor that consideration into your design and lower your roof height or remove the stack each time you relocate. Check your local code requirements, however, as you may be required to provide one roof-penetrating vent line in the home.

Waste lines can be drained into a municipal system, a septic tank, a black water tank, or to the ground if you’re using a gray water system and a separate black water system. Whatever option you choose, be sure to provide a safe and approved shutoff at the end of your main lines where they exit your tiny house. This way you can close off the systems when traveling. The people driving behind you will appreciate the gesture.

If you plan on installing a gray water tank, RV black water tank, or fresh water tank under the trailer, remember to include the weight of the full tank(s) into your weight-distribution calculations. Also, place them in a location that will minimize the risk of damage during transport. An installation toward the rear of a THOWs may be riskier as you change road grade and potentially scrape the bottom of your tiny house.

Air admittance valves (AAVs) are good options for THOWs because they can be installed inside a cabinet, eliminating the need for a conventional vent line through the ceiling and beyond the roof line in most cases.

Water Lines

The next step is installing the water supply lines. We recommend you plumb your entire house with PEX (or cross-linked polyethylene). This flexible material is easy to install, reliable, resistant to breakage during freezing events, and color coded (red for hot, blue for cold).

Drill holes in your framing members to create channels for the water lines. Make the holes just large enough to fit the PEX spacers/anchors but not so wide that the wall’s structural integrity becomes compromised.

Keep the holes as close to the center of each framing member as possible. This minimizes the risks of puncturing lines with nails while attaching wall finish materials. It also leaves room for insulation around both sides of the water line. If you end up placing the hole too close to the edge of the framing member, nail a steel plate over the hole location to protect the water line. These steel plates can be found at any plumbing or electrical supply store and are specific for this purpose.

Use spacers/anchors to protect your water lines from rubbing when the house is in motion. If you can’t find spacers, use spray foam to protect the lines as they pass through the framing.

As far as couplers and fittings go, we recommend a system made by Shark Bite. Although individual fittings are expensive, they’re incredibly simple to use and very reliable. They also don’t require any special or expensive tools during installation. We used them in hOMe and were very pleased with the product.

There are other systems, but some require special training and expensive tools, while others lack durability and quality. Look for something that’s within your budget and skill level.

The Shark Bite system is incredibly simple to use and nearly impossible to mess up during installation.

Install individual shutoffs at each point of use and charge the system to pressures above the usage level. Let it sit for 24 hours as you did for your gas system and check for leaks. Although the risk of explosion is nonexistent, a leak can still cause major damage to your house over time.

Electrical

As was the case with gas line installation, electrical work can literally kill you if you make a significant enough mistake. We don’t mean to incite panic, but we also don’t want you to take this job lightly. Do your research before you even think about starting this process. Make sure you’re being extremely mindful while working. Even the pros sometimes suffer injuries and death when they lose focus for a few seconds.

Never ever attempt to work on powered-up electrical lines. In the early stages of setting up your system, this is easy since there won’t be any electricity in your structure anyway. This caveat applies to the time after everything’s hooked up. Always turn off the power at the breaker before you make any modifications to your electrical system.

With that said, wiring your own tiny house is definitely possible. Many tiny housers with no previous building experience brought light to their home safely and successfully.

When installing the actual electrical lines, make sure to place them in the middle of the framing members in the same way you did with plumbing lines. You don’t want to risk puncturing a line with a nail in the construction process. If you do drill a hole for the line too close to the edge of the framing member, install a steel plate on the stud right over the electrical line location.

When electrical lines are running perpendicular to the framing members, they don’t need to attach to the framing and instead, can simply suspend in place. However, when they run parallel, they must be attached to the frame every four feet with fasteners specifically rated for the job. Those fasteners should also be placed within 6" of a turn and as well as within 6" of electrical boxes.

The type of fastener you use depends on whether you’re working with wood or steel framing and whether all your electrical is running in conduit (such as when you’re working with SIPs). You can choose to surface mount your electrical wiring in conduit. If so, be sure to use proper anchors to hold the lines in place. That said, the most common application is the use of insulated electrical staples on wood framing.

There are several different options when it comes to electrical boxes. The most common are plastic, fiberglass, and metal. Metal boxes need to be grounded because they can conduct electricity. To ground metal boxes, simply attach a pigtail off the ground wire from the line that enters the box to the ground screw provided. Plastic and fiberglass don’t require grounding.

TINY TIP

A pigtail is a small length of wire attached to the main wires inside an electrical box that can be used to make connections to the fixture or to the box itself when grounding metal boxes.

Plastic and fiberglass electrical boxes are much easier to install than metal boxes because, unlike metal, they don’t require grounding.

The most commonly used boxes are the blue plastic ones which come with self-mounted nails for wood stud construction, which make installation easier. They even provide small tabs allowing you to space the box’s face edge exactly one-half inch (standard drywall thickness) beyond the framing member. This feature allows for a flush installation of the electrical box face with your finish wall material.

The most common wire installed in residential construction is known as Romex, a nonmetallic sheathed wire. The two gauges most commonly used are 14g and 12g. Which one to use depends on your specific project so make sure to research your options ahead of time.

There are requirements about which gauge of wire is used where so be sure to investigate what you need. For example, you must use 12g wire on two separate 20-amp circuits for your kitchen plugs. Another example is in bathrooms where a 20-amp circuit, wired with 12g wire, is required.

There are also requirements about what type of plugs to use and where, as well as the number of circuits in rooms such as kitchens and bathrooms. For example, you must install a ground fault circuit interrupter (GFCI) in each bathroom at the exterior of every entry door and in any other potentially wet location. Furthermore, arc fault circuit interrupters (AFCIs) are required in all bedrooms and might, in fact, be required for all outlet circuits not protected with GFCI technology. Check with your local electrical inspector to confirm what you need and where.

There’s a lot to know about electrical wiring and how to install it correctly. Whatever resource you choose, make sure they can be trusted and that you understand each step.

If wiring a house doesn’t seem the least bit appealing, any reputable electrician can help. If you do opt to install your own, please hire an electrician to come for a site inspection before you close up your walls or power it on. An electrical report is actually required for some tiny house insurance policies, so if nothing else, get one for this reason.

TINY WARNING

Remember to always install smoke and carbon monoxide detectors. Many municipalities require them to be hard-wired (not battery operated) into the main panel. You may as well buy the extra piece of mind by installing yours this way, too.

Internet and TV

In today’s modern world, internet access is nearly as much of a necessity as electricity or plumbing. The good news is that connecting to it is becoming easier, even for those of us living in a THOWs.

The simplest way to tap into the web when living tiny is by connecting to a personal hotspot. A hotspot is a WiFi network created by a smart device such as an iPhone. It pulls data from a cellular phone plan, which is then shared with a computer via a protected WiFi signal. A cellphone signal is required for this system to work.

Of course, using free WiFi at a business, library, or other location is an option. It won’t allow you to have internet within your tiny house (unless you park in range of a signal), but perhaps it will help create a new routine in which you don’t have web access in your home 24/7.

Satellite is another option for tiny houses. If you plan on being mobile, look at the RV industry for mobile solutions. It’s very slow and quite expensive when compared to other options, but if you live remotely, it may be your only hope.

No matter what system you use (unless you’re completely remote), we recommend you add a Virtual Private Network (VPN) to your devices. A VPN protects your devices from hackers in public WiFi areas. After enduring a couple cyber-attacks on our computers, we never use our devices (smartphones and computers) without connecting to our VPN first.

DEFINITION

A Virtual Private Network (VPN) is a security measure added to a network that encrypts personal information and data. VPN services are becoming increasingly available for private users and can be purchased in subscription services at reasonable cost.

Insulation Options

There are many options when it comes to insulation for a tiny house, whether mobile or fixed. To find the right one for you, consider your budget, what R-value you’re aiming for, whether you want to use natural materials or not, how thick your walls will be, and how easy you want the installation to be.

DEFINITION

Roughly put, an R-value refers to the insulation potential for a material and how well it resists the tendency of heat loss. The higher an R-value, the better the insulation. Though not a perfect measure, it’s the most standardized option out there and a good starting place when comparing various insulation materials to each other.

Natural Choices

The market for natural insulation has grown in recent years and there are now many materials available. You can choose from sheep’s wool, denim, hemp, cork, cellulose, rock wool, and more. Their major advantage is that they don’t emit chemical fumes.

Natural materials are generally more expensive than other options. Some, such as denim and wool insulation batts, tend to slip down the walls when forced to endure motion while in transit. To minimize this risk, use an insulation adhesive on the sheathing and studs to help secure the insulation in the stud bay.

Standard Choices

The most commonly used insulation in construction is fiberglass batting. It’s available practically anywhere and is one of the less expensive options out there. It also has one of the lowest R-values per inch, and the paper facing is prone to mold issues if there is any water penetration. If you choose fiberglass insulation, look for formaldehyde-free options to reduce the health risks of the material.

Rigid foam is a high efficiency material that can be a great option in a tiny house. It’s a bit tricky to install properly because of its lack of flexibility. Electrical wiring, plumbing, and other obstructions make it challenging to neatly place in each stud-bay. This foam can cause a significant decrease in a wall’s potential R-value if gaps in the insulation envelope are left unaddressed. Use low expansion spray foam in conjunction with the rigid foam to fill any potential gaps. Take your time here as a fully sealed insulation envelope is very important for not only the energy efficiency of your home but also its long-term durability.

TINY TIP

Rigid foam comes in three common types: expanded polystyrene (EPS), extruded polystyrene (XPS), and polyiso (ISO). They come in varying thicknesses and can be found in either 4'×8' sheets or 2'×8' sheets. Costs are moderate when compared to other options.

SIPs panels are another option. The insulation value within them varies with thickness and the foam material used for the core. In a standard assembly comprised of white EPS foam sandwiched by two exterior layers of OSB (oriented strand board sheathing material), you can expect an R-value of 16 on a 4" panel. In a graphite gray EPS/OSB combo, you can expect R-value of 20 for the same thickness. Keep in mind that the higher the R-value, the better the insulation potential of a material.

Spray Foams

There are two types of spray foams out there: closed cell and open cell. In both cases, a two-part mixture made of Isocyanate (Side A) and resin (Side B) combines at the tip of a spray gun and forms an expanding foam. There is conflicting evidence on the safety record of spray foams, so be sure to do your own research and assess the risks before opting for this choice.

Closed-cell spray foam insulation is denser than open-cell foams and offers excellent air- and moisture-barrier properties. Unlike open-cell spray foam, it’s rated for use in external walls. It won’t sag over time and is the best insulation on the market when it comes to minimizing air leakage. Although it can be installed by the DIY builder, it can be difficult to locate the necessary equipment, so you may end up contracting it out in the end.

In open-cell foam, gas pockets intertwine with each other, like a bath sponge. While nonozone depleting, water-based varieties can be eco-friendlier than closed-cell foams, and they’re not recommended for exterior wall applications. Even though several people have used open-cell foam in exterior wall locations, we still recommend that you consult a local installer to ensure it’s a proper use for your project.

The Importance of Roof Venting

Roof venting is sometimes overlooked by novice builders, so we want to stress how essential it is. Roof venting allows for vital air flow in the gap between the ceiling/roof insulation and the underside of the roof sheathing. Without it, your sheathing, rafters, and insulation will succumb to moisture damage in as little as one to two years. The fix for the damage? Tearing off the roofing material and sheathing and replacing any rotten insulation, rafters, and the like. It’s no small task.

TINY TIP

The need for air vents and gaps below roofing sheathing can be eliminated if you use closed-cell foam insulation. It’s the only insulation currently on the market that provides a complete air seal and doesn’t require venting at all.

It’s imperative you leave an unobstructed ventilation gap directly below the roof sheathing and provide screened vents at the bottom and top of the roofline. There are several materials available on the market that make this process very simple. Called insulation baffles, they simply install directly below the roof sheathing. The insulation can then be pressed up against the baffles.

By design, the baffles provide an air gap above the insulation and below the roof sheathing. This gap allows air to move up and across the sheathing’s surface, removing any condensation that might otherwise form as warm, moisture-laden air from the house meets the cold surface of the roof sheathing.

To provide access for air, you’ll need to install screened vents at the bottom of the rafters, where they meet the double top plate and at the ridgeline in a gable roof or top of the rafters in a shed roof. These vents are installed in between the rafters in the blocking that supports each rafter.

Installation Tricks and Know-How

The most insidious risk to any home is water/moisture intrusion. If any of the wet stuff becomes trapped in your walls or roof assembly, your house will develop issues. Depending on how conducive your environment is to mold spore growth, you could be facing a significant issue in as little as one year.

For years, there was a concentrated push to create airtight homes. Unfortunately, some of the adopted practices created more problems than they fixed. For example, the use of plastic vapor barriers in walls and ceilings ended up actually trapping moisture, rather than eliminating it.

What the construction industry learned from this is that the biggest focus needs to be on stopping the free movement of air. Air is laden with moisture, so a gap in an air seal can allow moisture to build and become trapped in the walls when it hits the plastic barrier.

Steps you should take in a tiny house include sealing all windows and doors gaps with low-expansion spray foam insulation, installing a moisture barrier (not a vapor barrier) to seal air from entering the home, taping all housewrap joints with the manufacturer-specified vapor tape, and using foam gaskets on all switches and outlets under the finish plates. These simple techniques will do far more to protect your home than wrapping a plastic barrier around it.

DEFINITION

A vapor barrier is typically sheet plastic that’s installed on the interior face of the wall and ceiling assemblies in an attempt to seal out any moisture penetration. It’s completely impervious to moisture and vapor.

Typically referred to as housewrap, a moisture barrier is placed on the exterior face of wall assemblies and is designed to eliminate the movement of liquid moisture (water) and air movement into the house. Unlike vapor barriers, moisture barriers allow water vapor to escape the home.

Envelope Options

Keep your interior walls dry by installing a good hat (roof) on your tiny house and wrapping it with a waterproof jacket (siding). As previously mentioned, keeping your place dry is the best insurance policy you can invest in.

Roofing Considerations

Your roofing material choice is important. Get it wrong and all those months (and possibly years) of construction could be ruined in just a couple heavy rainfalls. Choose something that’s been tried and approved not only by the building industry, but also by tiny housers.

Factor aesthetics into your decision and choose something that brings out the best in your tiny house. As always, consider weight and how it will perform in sustained high winds. There are many roofing options and most should work well in a THOWs application.

Metal roofs are an excellent choice. They can be installed on low-sloped roofs when others can’t. They do an outstanding job of shedding moisture and perform well in high-wind conditions. Metal roofs are relatively easy to install on a shed or gable and are highly durable with a 50-year expectancy.

We recommend you hire a local company to custom make your roofing package. They’ll provide you with all the hardware, installation tools, and flashing required. Look for companies that offer standing seam metal roofs. These are the best option, in our opinion, because they are designed in such a way that the fasteners on the roof panels are completely hidden and no longer exposed once the installation is complete. The only exposed fasteners are on the flashing details and those come with a rubber gasket.

DEFINITION

Flashing is a thin piece of material in construction which stops the penetration of water into a structure in places such as window seams, roof penetrations, wall joints between the roof and vertical wall, etc.

Composition roofs have improved dramatically both in aesthetics and performance in recent years. You can find some with a whopping 50-year warranty. Composition shingles can tear off a roof at high rates of speed, so look for options rated for high-wind events.

There are other choices ranging from rubber shingles to wood shakes and beyond. Consider your needs, budget, aesthetics, and choose the option that best matches your wishes and wants.

No matter which choice you make, use high-quality roofing felt beneath. Better yet, use an adhesive membrane such as Grace Ice and Water Shield, which seals around fastener penetrations and creates the most waterproof and durable shield for your tiny house’s roof. This material fully seals to the roof deck and eliminates the risk of water damage from ice dams, wind-driven rain, and more.

Gutters and Catchment Systems

In most residential construction, gutters and downspouts are ubiquitous. Their purpose is to direct water away from the structure, providing an extra layer of protection from moisture intrusion. Why do we rarely see them on THOWs then? Because a tiny house is measured from the two widest points and because gutters are included in that dimension. Most people don’t want to lose 5" (on a shed roof) to 10" (on a gable roof with gutters on both sides) from their tiny house interior to accommodate them.

TINY WARNING

Gutters count in the measurement from widest point to widest point. If you get pulled over by a police officer and your gutter(s) puts you over the 8'6" highway limit, they may issue you a ticket. If you want to install gutters, either have a wide-load permit while towing your THOWs, or take the gutters down before transit and re-install them when you reach your next parking spot.

If you do want gutters and don’t plan on moving often, you can remove them during relocation and re-install them once parked. You’ll need to decide if having gutters is worth the hassle. Keep in mind the potential damage that water can do to your home and what a hassle fixing that damage would be.

Siding Choices

Nobody has ever walked up to a house and said, “Wow! The rough plumbing and electrical work looks great!” Instead, they see the finishes. If your siding looks amazing, people will be impressed. If it looks like you dragged some wood out of the forest and nailed it to your house, most people won’t have very nice things to say about it.

Consider weight when making decisions for a THOWs. For this reason, an option such as fiber-cement board isn’t ideal. Instead look for materials such as wood planking, shakes/shingles, light-weight metal siding, or anything else that can weather the storms but not weigh you down.

Different siding materials require different fasteners, so be sure to research which ones are right for your project. Nongalvanized nails may leave rust streaks on your pine siding after a couple rainfalls. As such, galvanized nails are the best option for most siding materials. However, cedar siding doesn’t work well with galvanized nails and may actually eat through the nails over time. That’s why stainless steel is required when working with cedar.

In terms of attaching siding, you can choose to blind nail (hiding nails from view) or face nail (keeping nails visible). Both approaches are acceptable. Face nailing provides better resistance against wind but makes the siding more prone to expansion and contraction as the fastener swells and shrinks with external temperatures. This can cause holes in the siding, leaving the wall behind it susceptible to water intrusion. Blind nailing doesn’t provide the same resistance against wind, but it conceals the fasteners and eliminates the issue of leaks developing at fastener locations over time.

Prime both the back of the siding and all the ends with stain or paint to provide protection for the material and significantly increase longevity. Caulk any butt-joints to seal your building envelope.

Rainscreens allow for trapped moisture behind siding to escape. An easier alternative is a housewrap with built-in crinkles and waves that serve the same function and allow moisture to drain out from behind siding.

Install a rainscreen to add protection to your tiny house. Rainscreens allow moisture to escape rather than become trapped behind siding. A ventilation gap between the sheathing/housewrap and the back of the siding prevents condensation and moisture buildup, adding years of longevity.

Instead of a rainscreen, there are housewraps that provide the same protection through the use of ridges and dimples in the material itself. These ridges provide a drainage channel for any moisture buildup. It’s a lot easier to install than a full-blown rainscreen.

Windows and Doors

There are several window and door material choices to pick from. You really do get what you pay for, so you should invest in the highest quality possible. The more energy efficient your windows and doors are, the more power and money you’ll save over the life of your home.

Many manufacturers use their own specific rough-in measurements. We’ll use vinyl windows as an example. When ordering one that’s listed at 3' wide by 2' tall, you need to frame your rough opening to 3' wide by 2' tall. The window will arrive one-half-inch smaller in each direction to allow for shim space, so you can plumb and level the unit within the rough opening.

A custom wood window, on the other hand, might be a totally different situation. You may need to frame the rough opening at 2'11¾" wide by 2'½" tall so that the window will actually fit. Always choose which window manufacturer and what material you’re going to install before you frame out the rough opening (R.O.).

To be clear, a rough opening call-out is very different than the actual window size.

Make sure to flash your window and door openings correctly. These areas are major sources of water penetration in any house. It’s best to start with a counter-flash pan of some sort. This can be a rigid material but is more commonly created with self-adhesive flashing materials around windows and three lines of caulk below door thresholds.

After the pan is installed, install your window or door into the rough opening. Once set, be sure to use self-adhesive flashing around the unit. As is the case with any waterproofing material installed on a home, you always install from the bottom up so that water is directed away from the structure, not back into it. This is called shingling your flashing.

DEFINITION

Rough opening (R.O.) is the opening into which a window and door are installed.

Rough opening call-out is the dimension noted on the plans of the rough opening, not the actual window size.

Shingling is the act of installing materials from the bottom up so that water drains away from the wall plane.

You might choose to install a metal flashing over the top of the window, door, or trim above them as a final safeguard. Check the manufacturer’s recommendation as many units now come with a similar flashing already installed on the unit and another one may not be necessary.

The Least You Need to Know

• Several electric heaters and air conditioning options exist for tiny houses, but far fewer options are available when only considering propane.
• Plumbing ventilation is more challenging in a THOWs because vents need to extend beyond the roof line. Air admittance valves (AAVs) are a viable venting alternative.
• Most insulation options available for conventional houses are appropriate in tiny house applications; however, some are better than others.
• Venting your roof assembly is vital. Without it, moisture-laden air will become trapped under the roof sheathing, causing significant mold damage over time.