How to build an indoor grow room step by step

How to build the perfect indoor grow room step by step:

Growing cannabis indoors is hugely fulfilling. Get your indoor grow room right and you can crop continuously: get it wrong and you will have an expensive hobby that never quite fulfills its potential.

So where do most people go wrong when growing quality interior weed? Well obviously there’s a great deal involved in the actual growing and flowering stages, but surprisingly many people fail before they’ve even started their plants.

We get it. Even if you’re an experienced outdoor gardener, building your first indoor grow room can be tricky if you don’t understand the whys as well as the whats of the equipment you need to use. Hopefully our guide  helps (click here to read this). But since writing this guide I’ve recently set up a new grow room and thought some practical tips might help. If you have any pointers we’ve missed, please comment – despite establishing several indoor grows over the years, there’s always something new to learn!

Firstly, why we’re using a grow room instead of a tent. I might be showing my age a bit here but when we first started there weren’t any tents available, so we’ve got used to setting aside a whole area (a cupboard, a room within a room, a small room, a flat ..) and controlling the entire environment. Each year I intend to buy a tent, and there are some great one’s out there – I particularly like the HomeBox range of modular tents that you can add or subtract from depending on your grow size. But I haven’t got around to it yet. One thing I would say is that if you are new to indoor growing, be careful when buying one of the “everything included” kits. Yes, they are great value for money BUT if you can’t afford to pay more maybe you should consider converting a cupboard instead of wasting cash on low-quality equipment that may not get you through the first crop. If you’re tent isn’t fully lightproof, this will effect the quality of your light sensitive plants. If the extractor supplied won’t cope with the heat generated by the light within the tent area you’ll experience problems etc. I’m not saying all kits are bad, just read around and make sure that a bargain is a bargain …

The best grow room set up

OK. So lets assume you’re fed up with paying the GREEN man and have just decided to grow some proper stinking interior weed for yourself. Firstly look around your home and decide where its possible to set up a grow area. You can grow pretty much anywhere: your loft, garage, spare bedroom. You can set up a grow room in your shed or in your basement IF all the factors are right. Here are some things to keep in mind:

1. Availability of services i.e. Electricity and water.

Where are you going to put your outtake air to? You can to take away the smell. And it will STINK .. don’t assume you can skip filtration unless you live in total isolation.

Where is your intake air going to come from? Best to have this from within your home as cold air from outside will shock the plants. If you’re planning to grow in a stand alone shed, one idea is to partition off one section and use this small area as a control room for your intake environmentals, where you place a heater / air conditioning unit.

2. Size of grow room.

Cupboards can be great as long as you remember that you will have equipment inside the grow area as well as your plants. Don’t limit yourself to too small an area if you can help it. Also you will have extraction equipment coming out of the cupboard so you need to build something to hide this.

3. Water supply in the indoor grow room:

We’ve decided to use a spare bathroom. It has the advantages of 2 outside walls, water within the room, space for a workstation etc. Its upstairs so any venting doesn’t come out at ground level, and the roof is well insulated so it won’t lose heat in winter. The floors and 1m high on the walls are tiled so its easy to keep clean and clear up any spillages etc. It was easy enough to remove the toilet and basin and simply block the drainage pipes. Removing the shower cubicle would cause damage to the property that would take work to repair, so we left it in place. The water pipes running to the basin have had a simple garden tap fitted to use as water supply. The room size is 3.5m by 2.5m but loses a square meter on each diagonal by the door and this cubicle.

4. Safe Electricity:

One thing it lacks is proper electricity. There’s only a light switch within the room. But that doesn’t bother us as we’re going to bring in electricity straight from the main fuse box so that it’s on its own circuit. Its great if you know a trustworthy chap for this kind of job. If not .. well its not so difficult really. Make sure the power coming into the house is switched off at the fuse before making any adjustments, wire in decent cabling that can run a large amount of power (we’re using 2.5mm three ply cable) which is sufficient for our needs). We also have a separate fuse box within the room. That way if anything trips, it only effects the room itself and not the whole house. These single switch fuse boxes aren’t expensive and make things a little safer.

You’ll see there’s a network of wires coming from a junction box to the right of the fuse box. Before we started, we thought like an electrician and drew a quick sketch of where things were going to be within the room – lights, pumps, fans, extractors etc. It was then easy to place in a grid of wires going to the Tower of Power plug extensions for each item. For example, the cabling coming straight down from this junction box runs to an extension fitted with a timer that runs all the lights on both sides; the one going upwards runs to the other side of the room and the work station where the portable air-con unit (or heater in winter if necessary) stands. A little planning, cable pins and a grid design keeps all the electrics neat and tidy, off the ground and safe from water splashes etc. Strips of colored tape can be placed at meter lengths to identify the circuits ie red tape for grow lighting, blue tape for extractor etc.

5. Ventilation and air flow.

Good air flow is essential to a good marijuana grow room. To achieve this, you need clean air entering the grow space at room temperature, and used, oxygen rich air vented out. Fans are also needed to simulate light breezes, stir the air and encourage good stem growth.

Originally we decided to vent the extractor out through the bathroom window. To do this we removed the window’s shutters, and inserted fly netting, net curtain and then a piece of ply board with a circle cut just large enough to fit the extraction tubing (ducting)

However I’ve since decided that this doesn’t quite work. For starters, despite the double layer of net and fly screen, the hole in the white board is visible from the outside. Another of the advantages of using a bathroom is that its perfectly viable (in fact its probably a legal requirement) to have air vents. Thus the landlady’s husband has kindly agreed to come and fit air vents on each of the outside walls (!). One vent will do for the 125mm extractor, the other for a portable air conditioning. There will also be an air vent to the hallway outside the room which will be for intake air (this may need to be powered). I did ponder fitting the tubing from the air con / or the extractor down the waste pipe from the toilet. This would mean that the waste pipe would need venting outside the building (there are plug-in units you can buy for this – “observation caps” (which bring a whole wierd world of wondering why anyone wants to observe their shit passing through) as without venting the pressure of air going through could create a vacuum going to the sewage tank, and possible back flow. Given that the potential consequences should this happen are just too disgusting to contemplate and that it was easy enough to get a standard vent fitted, I went for the latter option.

I’ve got a high speed oscillating fan circulating air around the room from the other end to the air-con. Now because room is going to be a little tighter than I’d like, it would be nice to replace this with an high speed oscillating fan standing on a shelf.  When the budget permits … I get enough air movement using the fan I’ve got, its just not very space efficient.

Budget was also a factor in going for the portable air con unit. I could buy a dual part air con for about the same price, but would have to pay a professional the same amount to fit it. And there might be a few questions raised about why the only air con unit in the house was in the second bathroom! Its also more adaptable if I decide to change the grow area from where it is now. So I decided to go for the lesser option of a portable machine. As I’m using the excellent Fero LED lights I don’t see an issue with this: despite running 2k of lights, the heat they produce is minimal and I am only wanting to chill the room by a few degrees. We’ve had a hot weekend, without outdoor temps touching the 40-S; without air con the room stands at 34ºC – with the little unit, at 28ºC. We’ll see how the plants cope over the summer months. Personally before I started growing with Fero LEDs I never thought it possible to grow weed indoors in Spain. This summer I’m setting up a new grow at the start of the season and concentrating my efforts on that instead of an outdoor crop.

Humidity is a factor as air con tends to dry the air somewhat – not good for young cuttings establishing themselves on the trays. I picked up a small humidifier but I’m not convinced how useful it is for this size space. I augment it by hanging wet towels around the shower tray anyway.

6. Have a workstation in your indoor grow room.

Its always useful to have a workstation within the room. Its one reason I like grow rooms, there’s no spillage of “stuff” into other living areas. Shut the door and no one knows its there. At least no one would if I bought a silencer for the extractor! As space is tight, the aircon is shelved up high with a table unit fitting over the tap area. But it gives me space for bits and bobs as I’m using them (as well as somewhere to put my beer can). I store all my chemicals, feeds etc in a plastic lidded container. There are a few shelves around the room from its previous incarnation as a bathroom and if they’re not in the way, they’ve been left in place.

7. Growing medium for your cannabis plants.

I’m going hydroponic again. Best to return to the old and tested! It suits my style of growing anyway and as I intend doing another LED v HID showdown come the autumn, will allow me to record more accurately nutrient and ph variations under the two systems. I’ve bought 2 5-lane hydroponic trays from Hydrogarden, which will each take up 1m squared grow space give or take the size of the plants grown on them. These I have placed on the right of the room. On the left hand side I have 2 Super Stinky autos in 25l pots, grown in coco-perlite. These monsters Super Stinky are a 20 week auto which certainly show that a super auto can give yield. But until they finish flowering we’ll have to see if they are worth the incredibly long 5 month start to finish.

8. Reflective materials: make your grow lights work well

Unfortunately the black and white sheeting I’d ordered wasn’t, when it came, up to scratch. (Always buy from a grow shop, not a garden centre?). So I’ve gone ahead without it and will get some better quality material before the next grow. Having a reflective surface is important as obviously it redirects your lights down to the base of your plants. I’m relying on the shiny bluey-white tiles for now but am aware its not ideal. Camping shops sell emergency blankets which can be used as a quick and easily bought reflective surface for small areas. Just make sure you smooth them down to remove wrinkles as these can create hotspots. But at only 70% reflective capacity they are not nearly as good as proper Mylar which reflects 98% of light back into the room.

9. Light proofing

The window has wooden shutters and we’ve also put curtains taped to the wall to keep light out of the room – and prevent grow lights announcing their presence to the outside world. But there’s also the door to be considered. The best way is to build a partition wall between room-door and grow room so that there’s a double entrance to pass through. Failing that, you can hang an oversized heavy rug / curtain to act as a lightshield to prevent light seeping in around the door rims.

10. Grow Lighting

Right now I’m stacking the room with lights from Fero LED. I have the 900 4G (which is a 600 watt draw LED) over the Super Stinkys, and over the hydroponic trays, 2 Fero Adjustable lights. These lights have been above the cuttings from the monent they started to root. I’ve started them off with one row of 3 UFOs switched on, at a height of 1m20 from the trays. The cuttings are coping great – and I’ll continue to use the same lights over one tray even during flowering. I’ve even placed the 360 4G between the two trays just to see how the room copes with the consequences of additional lighting.

Read on for a summary on setting up a successful grow room >>

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