Building a Grow Room in an Outdoor Shed

This is my first indoor grow. I've decided to put it into a 7'x7' shed in my yard.

• 4x4 Flood Tray with 5 plants in 5 gal pots with expectations of a 5x5 canopy
• 5x5 ScrOG screen
• 16x CREE CXB 3590 COBs using 800 total watts with 341 heat watts
• 20 Gal reservoir
• 120 CFM fan (interior of shed is 332 cu ft). It will be mounted near the floor with a 4" vent and we will make a 4" chimney on the roof with light blocks on the vent and chimney
• Grows will run from Nov 1 through the end of May in So Cal. High temps range normally from low 60s to low 80s and overnight lows from low 50s to low 60s. There are heat waves and cold snaps with highs as high as 90 and lows as low as high 30s. About half the year the shed will get no sun and half the year it will get several hours
• I will do my usual outdoor grow in an adjacent area starting March 15.

Questions:

1. My biggest worry is temperature. Though we don't have extreme temps for the most part in the months I will be growing, but it does get cold, and uncovered plants can get frost. I can always put a small space heater on low on cold nights. I'm more worried about heat during our infrequent heat spells in these months and also the months where the shed will get direct sun. The biggest question is whether we should insulate the walls and roof. This will keep out any heat from the outside, but it will also trap in heat from the lights and that concerns me So the question is to insulate or not? Just the roof, or the walls as well?
2. Second is the walls. If we insulate the whole thing, this will put a reflective surface everywhere, but otherwise, what should we do? Mylar or white paint? Glossy or flat? Should we paint the exterior of the roof to reflect back the sun?
3. Finally, the screen. For those of you with a variable height screen, how to you move it up and down and fix it into place? I am going to do a rope/pulley system for the lights, but I don't think we will be able to do 2 rope/pulley systems on top of each other.

Thanks. I don't think this a common setup, so any help is appreciated. When we actually build, I will start a thread to detail the details.

I would insulate the walls and the roof. You can buy that reflective bubble insulation and put it inside on the ceiling to reflect heat back from the roof or put a metal roof on: you can get corrugated metal at Home Depot cheap and it's reflective. You definitely want insulation under that though because it does conduct ambient heat right through. I've always used flat, white paint on my walls at the recommendation of two books and I've been happy with it. Reflective surfaces can cause uneven lighting with some spots getting light burn.

Thanks for the tips, sorry for the tardy response, I am out of town.

I think I'm more concerned with dissipating the heat from inside. Most of the time, it will be operating in low 70s or less temps. I can throw up a pop-up shelter to block the sun for the months where the sun is on it.

Maybe insulate the roof but not the walls?

Thanks for the tip on the flat white paint.

100% insulate. There are many options worth looking at to fit your shed style. It is the only way to take control of your environment. You will need AC and dehu to get it exactly where you want it, otherwise you may as well just stick with outdoors.

Roof insulation is more important than the walls and it is worth insulating better/thicker here, although all sides will need insulation if you're going to do any at all to stop your interior atmos trying to find equilibrium with the exterior.

As said above you can insulate with high reflective surface material and that irradiates light back to your plants, but I know I and many others prefer flat white paint (never gloss).

Good luck!

1. I would insulate. It keeps the heat out in hot weather too. An uninsulated shed can become intolerable in the sun.

2. With 800w of Cree CXB3950s you're not running a massive heat load. Similar load to a 600w HPS. Good ventilation will keep your temps in check. If you run your lights on from 9pm to 9am you should have no heat issues.

3. I would use the dimming function of Meanwell HLG drivers. That way if it gets really hot and you're worried you can turn down 50-60% of your lighting power and your heat load dramatically drops. The beauty of CXBs is they are more efficient at lower wattages so dimming them cuts heat while increasing efficiency so although light output falls, it doesn't fall as much as the heat.

4. Pretty much universally hot countries paint their houses white to keep cooler inside. I would do the same

5. Flat white paint has been shown to be the most reflective. The only reason we have shiny silver tents is there was an incident a few years back with white plastic tents gassing off toxic fumes which killed the plants. Everyone flocked away from white tents and it's sort of stuck even though white would be better.

6. Good luck. Post some updates even if it's interior shots only. Everyone loves to see a good build out

Y'all convinced me. Insulate the whole thing. Should I paint the insulation flat white if it has a reflective backing? And I'm also going to throw an 8x8 pop up over it for hot days.

@ruwtz you mention A/C and dehumidifier. I think the dehumidifier is an excellent idea and we have a lot of damp overnights in the winter-spring. Less convinced about the A/C, but it's probably best to have around in emergencies. Can you recommend brands/models on both the dehumidifier and A/C?

@loftygoals all excellent suggestions. Do you think the 16 COBs are enough for a 5x5 canopy?

Thanks all around

sheckylovejoy said:

Y'all convinced me. Insulate the whole thing. Should I paint the insulation flat white if it has a reflective backing? And I'm also going to throw an 8x8 pop up over it for hot days.

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Can't say for sure but I wouldn't imagine flat white taking to a metallic/mylar material too well. Why not use a white insulation instead? White poly foam board is available in large sheets.

Added shade will win you some, sure. I'm fortunate to have ample tree coverage over my purpose built shed. Check out my build thread if you're interested.

sheckylovejoy said:

you mention A/C and dehumidifier. I think the dehumidifier is an excellent idea and we have a lot of damp overnights in the winter-spring. Less convinced about the A/C, but it's probably best to have around in emergencies. Can you recommend brands/models on both the dehumidifier and A/C?

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If you want total control of the environment for healthiest plants and biggest yields - and lets be honest, who doesn't want that - then you will 100% need both dehu and AC, no question about it. These are essential if you are going to manage temps and humidity indoors with lights etc. What else are you going to do when ambient temps spike your flower room to 89F, or you can't get night time temps down either?

sheckylovejoy said:

all excellent suggestions. Do you think the 16 COBs are enough for a 5x5 canopy?

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Use the COB LED calculator right here on RIU to figure out an approach. Punch in what type of COB, amperage, square footage, and you will see if the numbers match up to what you need. Worked for me and I have 8 3590 COBS @1.4a perfectly covering a 24sqft area, veg only.

ruwtz said:

Can't say for sure but I wouldn't imagine flat white taking to a metallic/mylar material too well. Why not use a white insulation instead? White poly foam board is available in large sheets.

Added shade will win you some, sure. I'm fortunate to have ample tree coverage over my purpose built shed. Check out my build thread if you're interested.

Click to expand...

Can you link to your build post? I can't find it. Will white polyfoam do a good enough job? What do you use?

ruwtz said:

If you want total control of the environment for healthiest plants and biggest yields - and lets be honest, who doesn't want that - then you will 100% need both dehu and AC, no question about it. These are essential if you are going to manage temps and humidity indoors with lights etc. What else are you going to do when ambient temps spike your flower room to 89F, or you can't get night time temps down either?

Click to expand...

Can you recommend brands/models. Can I get away with an "1100 sq ft" model of dehumidifier or do I need something bigger? How powerful an A/C will I need for hot days?

ruwtz said:

Use the COB LED calculator right here on RIU to figure out an approach. Punch in what type of COB, amperage, square footage, and you will see if the numbers match up to what you need. Worked for me and I have 8 3590 COBS @1.4a perfectly covering a 24sqft area, veg only.

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I should have been more specific in my question there. I ran the numbers for a 4x4 matrix of COBs over 23.36 sq ft (the inside of the ScrOG screen with be 4'10" square) and got 850 PPFD which is awesome. The reason I have pause is that people seem to recommend around a 12" center-spacing and the 4x4 matrix will have more like a 16" spacing, so I'm worried it's not dense enough

sheckylovejoy said:

I should have been more specific in my question there. I ran the numbers for a 4x4 matrix of COBs over 23.36 sq ft (the inside of the ScrOG screen with be 4'10" square) and got 850 PPFD which is awesome. The reason I have pause is that people seem to recommend around a 12" center-spacing and the 4x4 matrix will have more like a 16" spacing, so I'm worried it's not dense enough

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Just an edit to the last post with corrected math:
Actually 21.78 sq ft (4'8" sq) and 912 PPFD

sheckylovejoy said:

Thanks for the tips, sorry for the tardy response, I am out of town.

I think I'm more concerned with dissipating the heat from inside. Most of the time, it will be operating in low 70s or less temps. I can throw up a pop-up shelter to block the sun for the months where the sun is on it.

Maybe insulate the roof but not the walls?

Thanks for the tip on the flat white paint.

Click to expand...

Hi there, long time shed grower here.
Insulate insulate then insulate again!
I Just put on new roof of 9mm waterproof plywood on Monday.
Old roof was el cheapo chipboard, bowing in middle about 15 years old.
I had any old scraps of thin polystyrene from packaging stuck all over inside and silver bubble wrap insulation but it needed more , much more.
So the New roof and the sides are getting the treatment.
A layer of cloud 9 carpet underlay has been glued to the inside and outside of plywood roof. One layer of felt on top off that.
I will finish inside walls with cloud 9 as well.
Then I'll staple insulation foil wrap on.
Then 50 mm of celotex insulation boards.
That'll keep heat out in summer and keep it heat in in winter.

My last run - about a month ago - was all cob lights in the old poorly insulated shed.
I flowered at night.
The temps were 22 - 23 degrees Celsius, too cold in my opinion for good growth.
I ended up having to recirculate the heat from cobs back into grow area instead of exhausting outside.
This brought the temps up to a respectable 28 degrees Celsius.
I use an 8" box fan with evolution fan speed controller for extraction with passive intakes in floor.
You'll be surprised at how cool those cobs will run compared to HPS.
People said recirculating the air would never work... what about the fresh air?
Well it worked very well.
I Did not see the point of putting in a heater as that would negate any savings in electricity by running the cobs in the first place.
So to sum up if you use plenty of insulation it will keep area cool in summer and warm in winter and much easier to control temps

Thanks @Moflow. Where do you live? Just curious what the outside temps are like where you are.

Also, can anyone recommend a good inexpensive data logger for temp and RH?

Temps at moment are maybe 16/17 oc and the Sun is actually shining for a pleasant change! It's been raining or overcast for last few weeks.
Problem is shed is south facing so the Sun tracks across front of it most of the day.
I'm in UK, quite northerly, so average summer temps here are crap.


Months Normal Warmest Coldest Normal
January 4.1°C 6.8°C 1.5°C 15
February 4.4°C 7.3°C 1.6°C 11
March 5.9°C 9.1°C 2.6°C 14
April 7.7°C 11.6°C 3.9°C 11
May 10.5°C 14.7°C 6.3°C 11
June 13.1°C 17.1°C 9.1°C 11
July 15.2°C 19.0°C 11.4°C 12
August 14.8°C 18.6°C 11.1°C 13
September 12.6°C 16.1°C 9.1°C 12
October 9.8°C 12.8°C 6.8°C 13
November 6.4°C 9.3°C 3.5°C 14
December 4.9°C 7.5°C 2.3°C 14

Moflow said:

I'm in UK, quite northerly, so average summer temps here are crap.

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Quite different than what I have going on, seems like cold is your bigger issue. I'm hoping I can get away with less than you. Right now, I'm looking at a 4" layer of EPS foam board for a total R-value of 16.

I've started a new shed climate control thread here:

https://www.rollitup.org/t/climate-control-in-an-outdoor-shed.917922/

I Can't believe it....the Sun is Still shining here!
The HPS was a light and a heater combined but the COBs are a different animal.
When I get the shed build finished I'm gonna do one plant that I vegged under
" crappystar " leds for a while then I've put it to natural daylight where it's now resigning.
Maybe scrog it. I always grow short bushes.
I've 15 cxb 3590 cobs to play with.

I was planning on mostly dealing with heat dissipation, but now you have me thinking about heating, even when the lights are on. Great to get so many different perspectives.

The plan is 16 COBs in a 4x4 matrix over a 4x4 tray and a 5x5 scrog screen (actually 4'8" square on the inside)

ideally what you want is the ability to control all variables, in all directions, at all times. underestimating any of them robs you of the ability to respond if and when your ambient environment changes, and that happens even in the most temperate places. you do not want to be left chasing once you have plants in there.

After all the problems I had in my first room, I build in extra capacity for air-flow, temperature control, and humidity control. The only thing I never have is extra height, so I have to very disciplined in veg.