How to Build a Grow Room: Ultimate Guide

When I started growing cannabis over five years ago, I didn’t know much about how to build a grow room, and I was nervous that I’d do it all wrong. After some trial and error, patience, and a lot of research, I learned everything I know today.

Marijuana is a temperamental plant, as it needs special conditions to produce a good crop. I will walk you through how to build a grow room step by step so you can develop healthy yields. 

Finding A Space

Planning your grow room involves more than a place where you’re going to put your plants. You need to consider several factors

Consider building your grow room near a water source. Such as a sink, so you won’t be carrying bucket after bucket of water to water your plants. 

An outlet and power strip nearby will is needed for installing the lights, fans, and possibly, a heater or humidifier. 

build a grow room space-selecting

Size Of The Space

Many successful grow rooms have started in a small space like a closet. In fact I recently reviewed the best small grow tents and there’s a few strong mini tents candidates.

As long as you have space to work around the plants, the exact size doesn’t matter. For most hobby or novice growers, anything bigger than a 2x2x4 space should be adequate.

You want enough space for not only your plants in the grow room, but also the equipment needed to create the right environment for proper growth.

Flooring

Your flooring material needs to be easily cleaned and sanitized, and it needs to be sturdy and resistant to humidity.

Bare concrete is a poor choice due to how porous it is and how it can soak up moisture and other chemicals. And then leach these things back into the air, creating a poor environment for your plants.

Covering your concrete floor with epoxy, paint, or other fluid coating can help solve it. Or you can lay down mylar or vinyl flooring, which will do the same thing as a good epoxy does.

Humidity

grow-room-humidity-control

Marijuana plants need the right climate for proper development, including moisture.

If the space where you build your grow room is too humid, the plants can develop different kind fungi on the leaves and buds.

Too low humidity will cause the plants to soak up more water at its roots, as well as excess salts.

Cannabis plants need the right level of humidity. Otherwise, your crop will not grow as big or yield as much product as it would otherwise.

There are things you can do about it, so if you think you’re grow space it’s too humid or too dry, check out Climate Control section down below.

Temperature

Not only do cannabis plants need the right humidity but they also need the right temperature.

If your grow room is in a closet or cupboard in your house, regulating your temperature shouldn’t be an issue.

If your grow room is in the basement or garage, and you live in a colder climate, then you night need to invest in grow tent heaters or cooling. You also need to be cautios if temperature usually fluctuates during the day.

Ventilation

grow-room-ventilation-discretion

Without proper airflow, CO2 is depleted, and humidity fluctuates too much, both of which can harm your plants.

Later you’re going to create a way for air to flow inside your grow room. Moving stale air out of the room with inline duct fans, to create a continuous airflow for your cannabis plants to thrive.

Unless your space is very well ventilated you’ll have to install an exhaust and, maybe intake fans too.

Which leads us to talk about discretion and safety.

Discretion and Safety

Be sure to place your grow room in an area where no one can get to it without your knowledge. And make sure is not accessible to pets or animals. Especially when plants are young, if something messes with them enough it can bring plenty of growth problems.

Another thing to figure out is where is the smell going? Can a noisy neighbor be a problem it smells in your surroundings? There are things you can do about cannabis odors (as do the best grow cabinets for discreet home use), and it’s something to keep in mind.

Light leakage might be seen by neighbors as well. Grow room lights are on for long periods of time. And since HID can be extra bright, and LED give often purple light, it might catch unwanted attention.

Please be careful of hot lamps and other electrical devices not coming into contact with water or any material that could react to heat. And never coil up the reflector cables, they can heat up and be a real hazard. 

Cleaning The Space

Before you start building your grow room, be sure to clear the space of everything that could contribute to contamination

Remove carpets or rugs, as they have the potential to leave bacteria, parasites, and other pathogens that can destroy your crop yield. 

So make sure to remove all other items to create a blank slate, then disinfect and clean the room before going forward.

Most Common Grow Spaces

Placing Your Grow Room in Your Basement

A basement it’s an ideal grow space, as it is usually cool in the summer and warm in the winter. Since it is underground, there’s higher humidity, but you can control that with a dehumidifier.

It’s also easier to mask the sounds and smells of growing cannabis from the outside world since it’s inside your house. Be sure to seal all windows for sound and smell concealment.

Build A Grow Room In A Garage

Building a grow room in a garage can be tricky due to the weather can spike temperatures changes in the space.

You can control temperature and humidity using heaters, humidifiers/dehumidifiers and ventilation ducts. If planing how to build a grow room in a garage, plan for these issues beforehand. 

Nosy neighbors may also be able to hear the constant fans and smell the glorious smells of cannabis. There’s less of a chance to have privacy to build a grow room  depending of how your garage is set up.

If you think your garage is the ideal space for a DIY grow room, a specially built grow box or a grow tent might be your best bet. So you will be better able to control the environment in a small enclosed space.

Buying A Grow Tent

Vivosun-grow-tent-4x4

Grow tents are ready-made for growing cannabis. Tents come complete with the perfect environmental equipment. As well as the mylar sheeting necessary to reflect the light to the plants.

They are an excellent & affordable option when you need to figure out your grow room.

Check my Vivosun grow tent review, it’s one of my favorite deals right now.

Wall Cabinet Or Closet

While a basement is ideal, there are other options for you. A spare closet or pantry cabinet might give you enough space to grow cannabis. You need a cabinet space of at least two feet high by two feet wide to provide room for growth.

You also need to vent your closet or cabinet to circulate air and cut down on the smell.

If you cabinet or closet is in your living space, humidity should remain constant (and easier to regulate).

Building a cabinet or closet is a viable alternative. But you need to take extra steps to provide the best growing conditions.

DIY Grow Room

To build a grow room step by step you need to consider the space needed for the number of plants, the airflow, the lighting, and the noise from the fans or humidifiers.

Your grow room needs to be completely lightproof and airtight, as well as away from prying eyes and noses. I have laid out everything you need to consider for you to end up with a grow room suited for your needs.

Now, you can build the grow room from scratch, or you can use a cabinet or other structure. I have addressed both options so you can ignore those sections that don’t apply to you.

diy-grow-room

Things You’re Going To Need To Build A Grow Room

Aside from the physical space to build your grow room, you will need.

  • A tape measure to get the exact size specifications, 
  • Wood or something to build a grow tent or cabinet,
  • Reflective material or paint,
  • Ventilation equipment,
  • Grow lights,
  • Tools, such as screwdrivers, a power drill, and scissors. 

1. Diagram Beforehand

Creating a model of the grow room in paper will let you see what fits on different dimensions. Making it easy to make changes and test multiple distributions.

Take your first measurements width, height and depth of your space and put it down on paper.

The more extra things you’ve got (i.e. rotating fan, dehumidifier, heating equipment) the less space for your plants as you need them to keep distance from most of these.

Height is also important, depending on the type of seeds you’re growing. For example, cannabis sativa can grow up to 6′ indoors, and sometimes even more. This is why there are specialized tents, like the Gorilla grow tent, that have a max height of 10′.

Once you have your first rough diagram, lets figure out how many plants you can fit in your space. Calculating the square footage and cubic feet of the grow room: 

Square feet: width x depth
(i.e. 4ft x 2ft = 8 square ft)

Depending where you are building your grow room there are many configurations you can have.

The simplest is a 2’ x 4’ room that can grow 3 to 6 plants. If you want to go into details here’s a great plant distribution guide.

2. Building The Frame

There are plenty of ways to build a frame, and the one you choose will greatly change depending on the materials you’re going to use. 

My grandfather was a very proud man and a carpenter who created everything he needed from scratch. My dad grew living the DIY life so I’ve always relied on wood for this kind of works.

I encourage you to find your own guide for your preferred materials. Here’s a really good one I’ve found for making a wooden frame.

The size is different but the concepts are the same.

As I’ve had my own DIY grow room in the past, what I would suggest to you is to fix the frame to a wall. This way there’ll be less chance of fiddling if the structure is not 100% sturdy.

Some fiddling in the structure while moving it around is okay, we are not carpenters after all (or maybe you are?). It does have to be strong as to stand on it’s own, and to support the weight of lights and fans.

3. Closing And Light Proofing The Grow Room

Now you are going to cover the frame. You can do this in two ways, you could just cover the frame with reflective material, or you could add walls and then treat the inside for light reflection.

To maximize light usage most grow rooms make use of some some kind of reflective material, or reflective white paint. As having the light reflected from all sides will noticeably improve your yield on side and lower branches.

  • Mylar is a highly reflective and one of the best materials light proofing. Unlike aluminum foil, it lays flat without wrinkles if handled carefully. Mylar comes in different models, the ones you want are called Aluminized or Metalized Mylar, as it’s the most effective for reflecing.
  • Flat White Paint is perfect if you want to lower your budget or if you have a big area to cover. Flat white paint can reflect up to 85% of the light. You can even add fungicide to it and it’ll help keeping away annoying mold.
    If you want the pro version search for flat white Latex paint.
  • Black And White Nylon, I don’t have the statistics for this but if you’re low on budget, my old grow room was covered in nylon sheets. First the was a white nylon layer to reflect the light, and a black nylon layer to keep the light inside. It worked really good but probably not as effective as previous choices.

Light control is essential to the growth and outcome of your crop. If your plants receive too little light too soon, they will begin flowering before maturation in anticipation of the winter season.

A light leak will let ambient light in, which can disturb the dark hoursphotochrome imbalances cause damage to your plants and your potential harvest.

And leaking light to the outside can bring unwanted attention or plain annoying.

Inspect all connections to your grow room for light leaks and cover with thick tape (or lightproof tape) any pinholes or cracks to shut the light out.

4. Airflow In Your Grow Room

The simplest way to move air within your grow room is to install portable fans, intake fans, and exhaust fans.

I have a very in-depth guide about grow tent ventilation. Covering everything from various venting and exhaust systems for different accessories, to how to calculate CFM for exhaust fans.

Here’s three of the most common exhaust systems that you’ll find.

The basics are pretty simple. You install the intake at the bottom of the room, and the exhaust fan at the opposite side of the room near the top. Then you can add a CO2 filter and other accessories.

You can also hang an oscillating fan or place it on the floor to make sure the air distributes well and your plants can thrive.

5. Climate Control: Temperature And Humidity

Did you know you’re creating your own micro-climate?

Depending how air tight your grow room is, or which materials you used, your grow room will maintain it’s temperature and humidity better or worse.

The ideal relative humidity for a grow rooms is around 50%, depending if the plant is growing or flowering, you can check all about it here.

If you find that your grow room is too humid, you will need to invest in a good dehumidifier. Of course, if your room is too dry, a humidifier will help. 

Temperature also must be tightly controlled, as cannabis grow best between 70ºF – 80ºF (21ºC – 27ºC). 

Depending on where you’re building your grow room, you may need air conditioning in the surrounding space for the summer, or heating in winter.

For cool nights, having a small heater or placing a heating blanket under your pots can work great.

Always on a timer to not over do.

6. Cleaning Your Grow Room

As you’re done building your grow room, and before you place any pots in the room, get some kind of collection tray.

A tray will help collect soil, dead leaves, and water, and keep your floor clean. 

Once it’s done, all you needed before planting the next crop is to sweep out the trays and clean them. You want to discourage any bacteria and mold from growing on the floor.  

The Right Kind Of Grow Light

Fluorescent Lights

flourescent-lights-grow-roowGrowers love fluorescent lights due to their price and lighting properties. Like LEDs, they also do not use a lot of electricity and stay cooler longer. They use a full spectrum of light, which is suitable for healthy plants. 

The lights come in various shapes and sizes, and what you get will determine how well the plants grow. 

  • CFL light bulbs, are spiral bulbs and can fit in small places. The advantage of these is that they’re cheap and you can place them close to the plants without burning them.
  • T5 grow lights, are great for indoor gardens, as they are flat and wide, and you can also have them close to the plants.

High-Intensity Discharge Lights (HID)

hid-lights-cannabis-indoor-roomHID are high intensity lights that give really good results. This lights need to be attached to a reflector as to reflect the light down onto the leaves. 

I wrote a guide on the best HID grow lights if you’re interested.

They also burn hot, you need to keep them distanced from your plants as they may burn. And depending on your climate you may need to vent away the heat with an exhaust so to not overheat them. 

While these lights do cost quite a bit more to use because of energy consumption, they do help at producing a more abundant crop. 

LED Lights

best-led-grow-lights-2020LED lights are growing in popularity among cannabis growers, due to how cool they operate and how simple they are to set up.

Plug them into the electrical outlet and place them over the plants. Unlike other lights that emit heat, LED bulbs can be closer to the leaves without burning them.

They are also budget-friendly as they do not use a lot of electricity and will keep your operating expenses low.  

What Grow Light To Choose

If your grow room is in a closet or cabinet, you want to choose a light that can be closer and that runs cooler like CFL or LED without extra ventilation.

But, if you have a larger space HID lights are good as they are very growth efficient. HID lights are also better suited to a garage grow room, especially in colder climates. 

I have a very extensive guide on choosing a grow light that might interest you.

The size of your DIY grow room, your initial budget, long term costs, and the surrounding climate will determine what type of light will be most suitable for you. 

Final Thoughts

You don’t need to be an expert DIYer to build a grow room, nor do you need to be a seasoned gardener to develop a healthy and productive cannabis crop. 

If your grow space doesn’t allow for a custom build, you can always check my grow tent reviews as it’ll make things much easier for you.

But in the end all you need is creativity and careful planning sense to build grow room for your cannabis needs.

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Santiago Pardo
Santiago Pardo
I live to help out cannabis growers have a greater experience with their crop, and not lose their mind over the many aspects of growing marijuana.

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