I’ve made a start on the south facing greenhouse. My greenhouse is kind of inspired by the pit greenhouse design but I couldn’t dig a pit on the allotment so I’ve aiming for a raised bed design and I’m trying to keep in heat and extend the growing season. I built the base sitting along the long south facing wall of the shed. Here’s the finished greenhouse.
Here’s some pictures of the build. First I leveled the ground as there is a slight upwards gradient away from the shed.
Next I built a frame and supported it on concrete blocks. I also back filled the ground to the level of the blocks and frame.
Next I used an old tarp as a water proof membrane between the ground and greenhouse.
Next I insulated the base. I wanted to do the whole base with celotex to help spread the load but couldn’t quite womble enough from skips to do the job plus I didn’t want to put off the build any longer so I used some old duvets wombled off of freecycle. I’m always on the lookout for old duvets to complete my insulated greenhouse build.
Finally I boarded it over with 22m boarding. I gave the boards 2 coats of shed paint to waterproof them enough to last until the polycarbonate glazing is fitted. I had built the base with a slight upward angle to allow for any settlement. This caused a problem I hadn’t thought of, when it rains the water pooled against the shed and flowed into shed under the door. I’ve hopefully got around this by fitting a door bar and sealing along the length of the shed wall. You can also see that I’ve used stones I’ve removed from my allotment ground to make a mini soak away around the outer edge of the greenhouse.
The triangular area at one end of the shed will become an extra storage area. Apart from getting another coat of shed paint the project is again on hold for a week or two as I need to finish a deep bed I’m setting up.
(Update November 2014) I’ve finally been able to continue construction of my south facing greenhouse. I’d been held up by a combination of money (car failed MOT), work commitments and weather. Luckily the tarp I covered the base with kept it dry enough for a couple of months. Next I built the walls. It’s a 8mm OSB twin wall construction with the cavity packed with old roofing insulation wombled off of freecycle. Greenhouse glazing is 10mm twin wall polycarbonate as glass is no longer allowed on the allotment.
Next I worked out the spacing for the greenhouse 10mm polycarbonate glazing frame based on sizes available online, ordered the sheeting and built the frame based on 2m lengths for the roof and 1m lengths for the front section.
Front view of the south facing greenhouse. I used yacht varnish to water proof the glazing frame and the securing batons.
It only took 4 days for the polycarbonate glazing to be delivered so I installed it the following week. I used a rubberized draft proof strip on the polycarbonate sheets to keep out the water. Here’s a view along the roof.
Here’s a view of one of the front panels showing the draft proof strip.
Finally I had to sort something out to stop my shed roof leaking. I didn’t put enough of a lean on it and the water was pooling and soaking through the bitumen paint / OSB construction. First I used self adhesive flashing to bridge between the roof and greenhouse roof and then I used a 1200 gauge damp proof sheet to cover the roof. I used 100mm wide PVC tape to secure the sheet to the flashing and nailed it around the edge of the shed roof. Finally I put some bricks on a few bits of OSB off cuts to help ensure the wind can’t get under it.
The sheet is still on the roof and the PVC tape is holding. It was advertised as being suitable for repairing poly tunnel sheeting. Just the end sections of the south facing greenhouse to go. I also need the damp in the shed roof to dry out a bit before I can start insulating the greenhouse back wall and the shed walls and roof.
(Greenhouse update April 2015) Been a bit slow with completion of my south facing greenhouse but carrying on from above: Next I skinned the inside back wall of the greenhouse with OSB offcuts. I also fitted the end windows. I stapled a layer of value tin foil to the wall first for extra heat retention. Also note theres a ventilation hole above the window to the right, blocked off during winter.
I also filled the gaps in the pallet wall with bags full of shredded cardboard.
Finally I stuck a layer of tin foil on the walls as I varnished to increase heat retention and light reflection during the winter months.
This was back in January, you can also see that I put a layer of large cell bubble wrap in the roof of the greenhouse and added a layer of plastic sheet to further boost the winter heat retention. All ventilation holes are blocked off. The barrels you see were all filled with water during the winter so probably helped bring down the temperature at night. By next winter they should do a good job at keeping up the temperature at night. About this time I also noticed the south facing greenhouse could easily hit temperatures of 20 – 25 degrees C in the winter sun. Next I started building the raised bed.
I gave it a slight lean to the center of the bed so I could fit a drain incase of any overwatering. I lined the bed with 2 layers of 1200 gauge damproofing sheet plus a layer of some thinner sheet I had.
Next I washed some stones left over from deep bedding my plot and put them in the base to aid drainage.
Then a layer of breathable membrane.
Finally I added a layer of compost to the bottom then filled the bed with sieved soil from my plot. I did try to transfer any earth worms I found to the bed. I then added a layer of compost on top and covered it with old carpet to help retain moisture. Although I’m not growing anything in the bed yet I give it a watering twice a week to keep it moist. Hardly any water drains out so far.
I left the bed for a couple of months to settle before trimming and tidying the the liner.
Almost there! Not to much more to do to finish my south facing insulated greenhouse now! Or so I thought… This April has been a very mild and warm month. In the sun the greenhouse was now hitting almost 40 degrees C so I removed and packed up the plastic sheet and bubble wrap ready for next winter. Also unblocked the ventilation holes, in total there are 3, 2 near the ceiling roof and one at floor level to the left of the 5 gallon water container in the photo above. That’s the wall that gives constant shade outside as the sun moves overhead. Cooler air could be felt being drawn in but the ventilation was totally inadequate for the job it had to do. Still learning how a greenhouse works! To get around this I converted one of the roof panels to a window to further aid ventilation.
I fitted it with a self opener but found on its own the end of the window would occilate in the wind so I fitted 2 cabinet resistive stays, adjusted to their weakest resistance, which do a good job of tuning out the occilation and making the window more solid. You can also see the edges of some cheap car window sun reflectors I’ve fitted to further reduce heat build up. Well, that’s the basic build of the south facing greenhouse done. Now onto the important part, learning how to grow seedlings as buying them is cheating as far as I’m concerned.