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How to Build a Grow Room

DIY High

Building a grow room from scratch is not an easy feat. Although many of our regular readers are seasoned veterans, there are many aspiring growers out there who might be hesitant to take the first step. Here at HTG, we love to share our knowledge and insights. Although the road of home growing might seem daunting at first, we will try to help you in building your very own grow room (or grow box), with a detailed, step-by-step guide. Reading this tutorial, might help you realize that it might be easier than you originally thought.

Planning, Calculating, and Preparing

Plan Ahead

 “Before you start building a grow room, you must be able to imagine it” -Ancient Marijuana Grower Saying This fragment of wisdom might not be exactly ancient (in fact, I came up with it just now), but it summarizes my point in an excellent way. You should have at least some idea about your expectations before you start building. Specifically, you should know how many plants you want to grow (the more you want, the bigger the space you need), how much money you want to spend (building a grow room from scratch can be costly) and finally, how much effort you want to put in it! Assuming that you will build it yourself, it can take quite a lot of manual labor as well. Consider all these factors carefully before you start.     In this here guide, we will be preparing a grow room assuming that you don’t have a clue about building. At this point you don’t want to go for anything more than an average room. Depending on your needs, you can adjust accordingly. You don’t have to be an expert in anything. The only things you’ll need (besides time and money) is patience and perseverance.

Choose a Location

After you’ve decided how big your grow room should be, you should decide where it should be. This choice is (as everything else) entirely up to you: you can convert an unused garage, your attic or a basement to a grow room. Even a big enough closet can do the trick! However, there are some components that the place you have selected definitely needs. These are
  • An electrical outlet;
  • A water supply that is not very far (unless you have no problem carrying full buckets every time you want to water your plants);
  • A carpet-less floor. Rooms with wooden or tile floors work best;
  • Your grow room needs to be in a somewhat secluded space. Many noisy components will be included and you don’t want them disrupting your (or most importantly, your neighbor’s) sleep;
  • A place to put an exhaust fan and a vent, to ensure proper ventilation.
  A suitable location for your grow room is important for many reasons, most of which are pretty self-explanatory. First of all, you need absolute privacy for your operation. As long as the legality of marijuana is still murky and indefinite, you might want to keep it from prying eyes. Also, you want the location to be absolutely under your control, so you can control the environment (like a little god of sorts). Nothing goes in or out without you knowing.     If you are one of those lucky people that have a cellar or a basement, you’ve hit the jackpot. Temperatures are milder underground, so you can ensure your plants will be cool in the summer and reasonably warm in the winter. If you have absolutely no other option, then you might consider the solution of a “room within a room”, or preferably, a grow box or a grow tent. Click here to find great offers on both!


It makes great sense to measure everything before you start building your grow room. It will save you time, space and money. A little bit of proactive thought can go a very long way in the growing process. Scale the room on paper and decide where the lights, vents/exhausts, miscellaneous electrical supplies and the plants themselves are going to be placed. Also, do not forget to note the entrance and delineate the water supply routes (assuming you will not be carrying the water to your plants yourself). Simple stuff, that will help you set up a functional and practical grow room. It is important to note that your plant(s) will almost double in size when they go from the vegetative to the flowering stage. This is something you should consider when you are measuring your room size-wise. The roof of your grow room will be where your lights and filters are going to be fitted, so be sure you have enough room for all these –plus, your head! In any case, since this is your first grow, we suggest that you go small and then experiment accordingly.


By cleaning we do not only mean sweeping, mopping and vacuuming. Before you do that, you must remove all unnecessary riffraff from the space you are planning to turn into your grow room. It is especially important to rid the room of any carpeting or fabrics, as they tend to hold dust, mold, and unwanted pests. After you have removed all of the extraneous objects, it is time to clean your room. Or, to be precise, disinfect it and thoroughly inspect it. You should give the designated area a proper cleaning out even before you start building. Keeping it clean must become your number one priority. An unclean grow room puts the plants under a lot of stress and massively increases the risk of fungal infection, mold, and diseases, that can quickly ruin whole crops. We can’t stress this enough: you shouldn’t let mold or dust accumulate anywhere in the room.   Also, it is vital that you keep your beloved pets as far away from your plants are possible. You do not want your plants destroyed because of your cat's curiosity or your dog’s clumsiness Besides, pets are more than simple troublemakers: they carry bugs and bacteria that can be transmitted to your plants and ruin your harvest. Before and after you begin a new growing cycle in your grow room, it's a good idea to disinfect. Clean the whole location with some sort of disinfectant, just to make sure you won't be dealing with any latent parasites or bacteria in future crops.   Finally, plants create waste themselves. Dying leaves and excess foliage can create problems to your crop. Do not neglect them, as they can cause potentially fatal problems with fungi and mold.

Decide on the Growing Medium


Unless you have no prior experience with marijuana growing (or horticulture in general), you are probably aware that there are plenty of marijuana growing media. Soil is the traditional method and it is what is best suited for newbies. You can pick it up from practically everywhere and it is cheap as dirt (mainly because it essentially is dirt). However, you should bear in mind that soil buckets coming in and out of your house might seem sketchy, especially if you live in a crowded area. You can also use compost as a great nutrient supply for your soil setup.


Soil-less media like coco-coir, rock wool, expanded clay etc., are generally lighter and give the plant more breathing space, however, they hold no nutrients, like soil. Instead, you must supply your plants with liquid nutrients and manually add them to your pot (don’t overdo it – it is very easy to burn your plants). Soil-less mediums are more expensive, but they tend to make your life easier as they do not need so much maintenance.   Growing hydroponically definitely takes some getting used to. There are several different combinations you can experiment with. Many growers claim that hydroponic grows are more potent, faster and higher yielding. Pros:
  • Faster and bigger yields;
  • Healthier for the plants;
  • No need for transplanting your seedlings after vegetation;
  • Better quality buds.
  • Easier to overfeed and burn;
  • More expensive in all aspects;
  • More difficult to set up.
We recommend soil for new growers because it is simpler, cheaper and less sophisticated. Besides, nothing’s stopping you from experimenting further once you learn the ropes around marijuana growing.

Containers and Pots

Although they are often an overlooked part of the growing process, containers for your plants are still important. It could prove useful to spend a little time choosing the right containers for your plants. After all, they will be the house of your plants for their whole life. Generally, anything that allows for water drainage in the bottom, can become a great container. If you can, be generous with the space you are leaving your plants. Bigger roots equal larger plants and more plentiful harvests. Try to pick up the biggest your grow space allows for. The most usual size are the 5-gallon buckets, although 15 and 25-gallon models are not uncommon. In any case, it is best if you can find buckets with easy handling. There is quite a lot of moving around, so an extra investment might save your back some day!

Building the Grow Room

So, the first step is complete! You have decided where you want to build your first grow room, you have the blueprints and you know all the details. Everything is ready for the hard part: the actual building of the grow room. Now that the very basics are all covered, it is time to get our hands dirty. And by "our" we mean, of course, yours.

Light-proofing the Room

The first step you should take is to ensure that your growing room is completely and utterly light-proof. In past articles, we have stated the importance of light in the course of marijuana life cycles. When you are growing marijuana indoors, you are essentially simulating the actual sunlight that the plant is supposed to take at the respective season.   Confused? Allow me to explain: when your plants' life starts, it expects that the sunlight period is much more than the darkness period. As the seasons progress, sunlight decreases and the plant realizes that the time for flowering comes. This is why pre-flowering marijuana plants need 12 hours of undisturbed darkness and 12 hours of light: less light is effectively telling your plant that winter is coming. It is crucial that no natural light is allowed in your grow room. Therefore, it is important that you check your space for light leaks. If you find one, cover it up with a special light-proof tape. Natural light can mess up your plants really badly and reduce yields or lead to the development of male plants (that can devastate your whole crop, by pollinating the females).   You must frequently check your crop and make sure to eliminate any males that may grow here and there. Generally, you can easily do that at the later stages of the vegetative stage. Also, be sure not to forget to cover any tiny blimps that the electronic devices you use. Even this negligible amount of light can confuse your plants as they have a natural tendency to stretch out to light. Indoor varieties are even more prone to these fluctuations, as they are far more sensitive (there is no moonlight in controlled environments).  

Mylar and reflective material

After you make sure that no external light enters your room, it is equally important to remember that your plants like an equal distribution of light. Proper reflection of light is extremely important and can improve your plants' performance. Light is the most important component of your crop's life. It is, therefore, necessary to get as much of it directly to your plants. When excess light is reflected back at your plants, they get the chance to use more light that would otherwise get "lost". Also, covering your grow room walls with reflective material ensures that no plant stays in the dark. Covering your walls with reflective material can offer many advantages. If you do it correctly, the amount of usable light is multiplied by at least 30%, leading to healthier plants. How to properly cover your walls with reflective material
  • The material must stay flat. Wrinkles and creases disrupt the reflection of light;
  • Try to soften the edges and try to avoid sharp angles as they tend to hold light;
  • Keep your reflective material absolutely clean;
  • Try to spread your reflective material on something smooth, if your wall is somewhat rough, try to use Velcro on it first and then proceed.
  Now the easy solution is definitely a grow box or a grow tent. They come as pre-built setups and they are already insulated and coated with reflective material. However, if you are determined to go all the way, here are some of the most popular reflective materials on the market.
  • Foylon

It is made of spun polyester fabric and reinforced with foil laminate. Although it is costlier than mylar, it makes up for its cost, by being more durable and easily maintained in the long run. It reflects nearly 95% of light and about 90% of heat energy. So, before you go further, make sure that your ventilation system works perfectly!
  • Mylar

Arguably, the most popular choice among growers. It comes mainly in two sizes (1mm and 2mm in thickness). Although it is potentially more reflective than foylon, it is also, harder to clean. Its reflection levels are about 92-97% for light and 85% for heat. If you go for mylar, try to use the 2mm version, as it is more difficult to wrinkle.
  • Matte white paint

Cheap, effective and readily available! Flat white paint can be a really good option if you plan to turn a whole area into a permanent indoor setup. It is also a great option for warmer rooms as it absorbs a lot of heat while reflecting almost 80% of the light energy.
  • Panda plastic

A great short-term solution that can also be easily cleaned. It is called “panda” plastic because of its color pattern (white on one side, black on the other). The premise is that the white side is used to reflect light and the black one to trap it during your dark cycles. However, you have to keep it at reasonable distance from your grow lights because it can melt if it gets too hot. Its reflectivity is about 80%. Opt for the 6mm version for best results.  
  • Orca Grow Films

Orca grow films are pretty similar to panda plastic in terms of design, hence the name (orcas are famously the second most popular black and white animal). However, Orca Grow films are more expensive, thicker, easier to clean and mold resistant. All these features make it shine –literally- among its lesser counterpart. It uses a complex crystalline reflective system that distributes light evenly at about 90-95% reflectivity.

Air-Proofing - NO IMAGE

    Although it is easy to get used to it, your plants' smell can actually become unbearable by visitors and neighbors. Especially in the flowering periods, your plants will begin to produce a strong aroma that can not only become bothersome but can lead directly to your grow room. If stealth is one of your priorities, then you should invest in a good odor control system. A good idea would be to fit your exhaust fan with a special carbon filter or use a deodorizer in your grow room. For best results, do both.  


An air humidifier might be a wise investment for your grow room. They are very common and cheap. Also, they come with in-built hygrometers that can measure the humidity levels of the environment. Being able to control the humidity of your grow room by pressing a single button can save you a lot of time. Humidity is one of the factors that determine how fast your plant metabolizes nutrients. Too low humidity levels can block the proper nutrient intake. On the other hand, too high levels can lead to mold and pest problems. Your plants need different humidity levels according to their growth phase and if you manage to do it properly, you will be rewarded with better yields. Manipulating the humidity levels in larger grow rooms might be a challenge, but this is a more complex problem. At this point we are getting in over our heads: the goal of this article is to give a few pointers on building your first grow room, which should be average in size (at most).


Proper ventilation is absolutely essential for a successful grow room. It automatically takes care of problems like overheating and air circulation so you never have to worry about them anymore. To ensure proper airflow within your grow room, you need some oscillating fans and some overhead exhaust ducts to guide the warm air outside (remember to mount a carbon filter first)! Keep that in mind when you design your grow room and be generous with the ceiling space, as you will also need to fit the lights in as well.   By keeping air circulation at an appropriate level, your crop will get all the CO2 it needs to grow healthily. Your plants love stability and will thrive in a properly ventilated room. Before you start growing, consider how many plants you want to grow and how much air they will need. Place the exhaust fan at the top of the room so it can suck away as much air as possible. Make sure that your input fans are smaller than the exhaust vent. Many growers find that pointing your oscillating input fans towards the grow lights helps with temperature issues. Using horizontal airflow fans can help even further with temperature and humidity levels. A good rule of thumb for measuring your ventilation needs is to keep in mind that 450CFM (Cubic Feet per Minute) of ventilation is good for a 1000W HID lighting setup and about 3/4ths of the air intake. For the first couple of lights a grow room fan will suffice, but if you plan on larger crops, you might want to take things more seriously.  


Your grow room temperature should –ideally- hover around 72-80ºF (20-25ºC) at all times. Any fluctuations should always be within that scale, always depending on the growth stage. Too high temperatures can kill the plants and too low temperatures can cause diseases. If you do not have a central heating system, you probably need a ground A/C unit, the size of which should be relative to the size of your room. Essentially, you are trying to balance the temperature by taking factors as lighting, insulation, and circulation into account. Getting to the sweet spot is pretty much trial and error but you will get there nonetheless. Make sure to pay attention to the temperature levels (it goes without saying that a thermometer is one of the absolutely essential gadgets of the aspiring grower). Always remember that lights cause most of the heat and proper placement are necessary. You will need about 3750BTUs of air conditioning power per 1000W of lighting in a properly insulated grow room. This rating is taking into account other sources of heat too, like CO2 generators or ballast heat. If you can afford it, go for a powerful, quality A/C unit that is capable of operating at a much higher setting than the one you are after. In such cases, it is better to be safe than sorry. Besides, there is a huge selection of A/C units that you can choose from and some market research could pay off.  

Lighting Setups

  How many lights you need depends on the size of your grow room. The golden ratio in such cases is 600W for every 5sq.ft. Lighting, ventilation, and temperature are very closely connected. When thinking about one of them, you shouldn't forget to take the other two into account. Lights produce heat. The more heat, the bigger the fans you need to use. However, there are many types of lights, each with its own pros and cons. 99% of the time, you will be presented with these options Pros: Efficient (HPS), Simple to Use Cons: Can get very hot, energy consuming, need to use replacements often   Pros: Built-in cooling, plug 'n' play, full Light Spectrum Cons: Slightly smaller yields, need to re-adjust every now and then   Pros: Cheap, Ubiquitous, Good Light Spectrum Cons: Not great for flowering, Not Strong Enough All of these light sources emit some heat (although LED lighting technology has made leaps of progress), so do not overdo it, especially in your first grow. There is an abundance of affordable setups out there and it is rather easy for a beginner to lose track of the options. However, if you follow the “600W per 5sq.ft.” rule, you shouldn’t have any problems. Another issue that is worth noting, is that lamps (especially HPS and MH) need a replacement every year while LED lights are generally longer lasting. Frequent lamp replacement increases the financial and the environmental cost of your setup so you might need to weigh in your options carefully. If you need to read more about lighting, take a look here.   From a practical standpoint, it is better to have as few plants as possible under a single light. Of course there is no point in congesting the canopy, as the light does will not be able to penetrate to all the plants. Being generous with the space you give your plants will aid their development and final yield. If you decide to go for older generation lights, go for the models that feature hoods and ballasts that can switch from HPS to MH bulbs and vice versa. Different bulb types may be necessary at each point of your plants’ life, so you might want to avoid installing a whole new lighting setup every now and then. At the very start of this article, we stated that building a grow room requires a significant time and money investment. Do not try to cut corners by purchasing a lesser quality lighting system, as it may backfire and prove costlier in the long run.  

Necessary Appliances and Gadgets

  Growing marijuana indoors demands a lot of attention to detail and careful calculations. Thankfully, nowadays we are presented with a wealth of possible choices to help us automate the most menial tasks that are involved in the process. So, be sure to add all of these electronics to your shopping list. They can (and will) save you from a world of trouble.

Shopping List

  • Cooling thermostat;

  • Lighting control relay and timer;

  • High temperature shut down;

  • Reliable max/min temp and relative humidity monitor;

  • Humidity controller;

  • Night/day temperature control;

  • Carbon dioxide monitor & control;

  • Extension Cords (always useful).

These little gadgets might seem insignificant at first but will become your best friends when it comes to the actual growing part. The cost might seem daunting at first, but –hey- nobody said it is going to be easy or cheap! These little gadgets might seem insignificant at first but will become your best friends when it comes to the actual growing part. The cost might seem daunting at first, but –hey- nobody said it is going to be easy or cheap!

Putting it Together Step by Step

  Building a grow room is a rather complicated and unpredictable endeavor. Although this guide provides you with an in-depth analysis of what you’ll need, there are countless variables and factors that can not be calculated. In any case, in the above section, we have laid the foundation for this moment: the actual building part!   To make it easier for you, we have broken down the process into 11 easy steps so you know what you are up to from start to finish. Ready?  
  • Step 1 – Select the space which will eventually become your grow room. It might be anywhere, between a cellar, a spare room, a basement or even your closet. Technically, you can even turn an old PC tower into a mini-garden.
  • Step 2 – Take some time to plan the layout of your grow room before you start going about like Bob the Builder. A good design can help you realize potentially problematic issues before you even start building, saving you time and money. Set realistic goals about the yield you want to produce and how you are going to achieve that. Use the guide above to create a shopping list that is close to what you need.
  • Step 3 – Clear everything out of the space. Remove chairs, carpets, clothes, curtains fridges or murder weapons from the room. You do not want ANY obstruction before, during and after the building of your grow space. Organize a yard sale if you must, but get rid of all the stuff. It goes without saying that the space has to be thoroughly cleaned and disinfected before you start building.
  • Step 4 – Lightproof your room. Make sure that absolutely no light can get in, even in the middle of a hot August afternoon. If there are any windows in the space, block them from the inside (so the insulation won’t wear off) with curtains or blinds and seal them off. You don’t need light and prying eyes to mess around with your indoor crop!
  • Step 5 – Insulate the room (walls, floors, ceiling) with a reflective material suited to your needs (read the guide first). Try to avoid sharp angles when covering edges of the walls. Instead, aim for smooth curves that reflect light better. In doing so, you will achieve the maximum light reflection, which means more food for your plants. More food=bigger plants=higher yields!
  • Step 6 – Set up both a ventilation and an exhaust fan. This will improve air circulation and help with temperature and humidity regulation. To see how powerful these need to be, refer to the appropriate section of this guide. There you will also find more information about odor control and stealth as well as use both creates good air circulation throughout your grow room.
  Installing a circulation fan: Proper air circulation in your grow room should be a top priority. When it comes to circulation, oscillating fans can come in handy. They are cheap, they are everywhere and they are very easy to move (which will be needed in different parts of the growing process). On average, you will need at least a     Installing a vent fan: This part can be a little tricky and takes a little bit of planning. Generally, installing a vent takes quite a bit of handiwork. Your best option is to locate a place where air naturally escapes. Try to use larger ducts to facilitate airflow (4-,6-,8-,10-,12-inch = 10,20,30cm). Don’t forget to mount a carbon deodorizer on your setup! You don’t want anyone smelling you out!  
  • Step 7 – If you can have water supply within your grow room, you’re golden. If that’s not possible, at least make sure that there is some kind of faucet nearby. Marijuana plants require quite a lot of hydration and carrying buckets full of it each time you want to water them can actually be exhausting.
  • Step 8 – Hang the lights and fit the ballasts. Follow the manufacturers manual and try to attach the lights to the ceiling of the grow room. To make your life easier, in the long run, try to make the connection adjustable. Your plants will require the lights to be at different positions depending on their life stage, so this detail can actually save you a lot of time.
  • Step 9 – Remember the shopping list at the end of the previous section? Find a place for all of these electronics and keep them where you can see them. This way, you will be able to detect any abnormalities on time and act accordingly. Don’t forget to cover any tiny blimps with duct tape; the slightest disruption in the dark cycle of the plants can potentially ruin your crop.
  • Step 10 – Set up your containers. We highly recommend new growers to go with the soil medium. It is easier and far less of a hassle than hydroponics. After one or two successful crops, you can try your hand at something more complicated. However, if you have set your mind to it, always follow the instructions when trying to grow hydroponically. At this stage, I am not going to even mention aeroponics! If you are a beginner, this is not for you yet. However, you can read about aeroponic growing here.
  • Step 11Germinate your seeds (or prepare your clones) and carefully plant them in your growing medium. Your plants will be ready for harvest within the next three of four months!

Final checklist

  • Clean your reflective material often. Photosynthesis is what feeds your plants and you want to give them as much light as possible;
  • If you use CO2 supplement inside your grow room, be sure to insulate it well and watch out for leakage;
  • Clean your grow room often. Dust, rotten leaves, and even minor stains can be potentially harmful to your plants;
  • Like a pilot mid-flight, consult your instruments often. Growing involves quite a lot of detective work and you want to keep all the variables in check;
  • Chances are, you will be using lots of electronics. Do not ignore safety regulation and ensure that they do not draw more power than your network can handle. Try to use longer cables instead of connecting many shorter ones. Power failures are not that uncommon;
  • If you don’t feel very confident about this, start small or invest in a grow box/tent first. By studying their architecture, you’ll get an idea on how to eventually build a larger grow room;
  • Make sure that light reaches all of your plants evenly;
  • Do not get frustrated if things don’t work out at your first grow. It is perfectly normal and the effects are most likely reversible!

Before you plant your seeds

  Last but not least, don’t forget to make a test run! Turn everything on and make sure that all parts are working correctly. Turn on all of the lights and fans to make sure that they all work together. Fill a pan with water and let it sit where your plants would be, to test transpiration. Let everything run for a couple of hours. Check your instruments for any abnormalities on the humidity. After you do that, let the lights run on their own for half an hour and check whether the room is getting hotter and more humid without ventilation.   After that, you are ready to introduce your seedlings/clones into the room. Try to spread them evenly under the canopy and do not put young seedlings too close to HID lamps. 600W lamps should be at least 24” (60cm) above them.   With following this basic tutorial, you can now build your very first grow room. Granted, it will not be the fanciest rig you imagined, but it will allow you to grow your very own plants. After all, practice makes perfect and nowhere is this truer than in marijuana growing.   Happy Growing!