Step 3: The Concrete Form

I decided to build the greenhouse with a concrete footing mostly to discourage our infamous Newfoundland winds from picking it up from my yard and delivering it swiftly to the next town. In September of 2010 when Hurricane Igor hit, that's almost precisely what happened to my neighbor's patio of about 10 by 15 feet. So yeah... concrete footing it is.

The footing itself is 5 1/2 inches tall by 5 1/2 inches deep going all the way around the perimeter of the greenhouse. The outside dimensons are 10 feet 2 inches by 14 feet 2 inches and the inside dimensions are 9 feet 3 inches by 13 feet 9 inches. The framing is 2 by 4 lumber  so when the bottom wall plates are placed on the concrete the is an inch of concrete exposed all the way around both inside and outside.

The form itself is constructed out of 2 by 6 lumber with some 1 by 3 strapping for braces. This should be pretty stright forward to anyone with decent DIY skills. I built the form in the driveway and then moved the whole thing into position later.

Next came the anchor bolts and rebar. I drilled holes in each piece of strapping and inserted the anchor bolt, secured temporarily by the washer and nut. Then came the rebar. I bought the rebar in 8 foot lengths so it worked out that I only had to make one cut to get it all to fit right. That cut I made rather tediously with an angle grinder. I took advantage of the hook shape of the anchor bolt to hold the rebar up off of the ground a little, so that it is suspended inside the concrete rather than underneath it. Everything was tied up nice and tight with tie wire before calling that a day.

Before pouring the concrete I made sure everything was nice and square by checking the measurements of the corners. The distance between each pair of opposite corners should be the same or it's not square...even though it may look like it.

FInally, the last picture shows the PVC sewer pipe for the greenhouse drain. It goes from the inside of the greenhouse, underneath the footing and ends right where the french drain will be running perpendicular to it.
<p>Hi, nice job I can't wait to see it finished. I have a question, The poly carbonate panels you are going to use, did you get them from alibaba.com as the picture shows? I have been looking at that sight for years but am a little nervous buying from the site due to all of the different company's and no pricing, having to contact someone for any little question, the minamum quanty on alot of products and of course shipping isn't cheap ect. How was your experience? </p>
<p>Hi,</p><p>I'm quite interested in your greenhouse project and have a question for which I can't seem to get a clean answer. </p><p>Where do you place the temperature sensor, inside the greenhouse? And how do you protect it from the sun, and moisture / wind?</p><p>i.e. how do you know the temperatures reported are accurate, and not affected by the elements?</p>
<p>Hi! The best place to mount a temperature sensor in a greenhouse is at crop height, away from walls or heat sources. Basically center-of-zone at crop height is usually best. A sensor for greenhouses should be aspirated (have a small fan to blow air over the sensor) and should be solar shielded (think piece of white ABS pipe). We typically suspend them from above, and we use stainless encapsulated sensors to prevent any damage from the high humidity and mist/water found in greenhouses.</p>
this is possibly the greatest piece of greenhouse porn I have seen on instructables. Very professional. I cant wait to see how it turns out.
How do you heat your Green House? I have 15x20ft green house in Colorado and I paid out the wazoo trying to heat it this winter... I think im going to build a rocket heater for next season. Have you ever heard of a company www.dragonheaters.com? MY friend has built many rocket heaters but they never last. Has anyone heard of this company?\
Hi Billy, <br><br>To date, I have not made an attempt at heating this greenhouse. I've had to abandon the project last summer before it was completed and coincidentally I just started work on it again today.<br>I have a few heating strategies planned. The first would be to take several black-painted 55 gallon plastic drums full of water and place them in the greenhouse. Hopefully the water would heat up during the day and have enough thermal mass to keep the greenhouse warm overnight. If this isn't enough I'll build an active solar thermal collector to heat the water in the drums. I'll use an electric heater as backup.<br>I am also going to convert the greenhouse into a &quot;passive solar greenhouse&quot;. Basically, all sides are sheeted and insulated except for the South wall and South slope of the roof. This would reduce night time heat loss and make the water barrels more effective. You can find out more here http://www.passivesolargreenhouse.com/<br><br>Hope this helps.<br><br>Lance
This may be a dumb question but where did you buy your polycarbonate. Cause the web address on those pics only sell it in bulk of 1800 square meters?
Looks like a nice greenhouse but it seems a little overbuilt to me, all those big pieces of wood combined with polycarbonate glazing will cut a lot of light out. In my opinion half boarding the sides with ship lap and polystyrene and then glazing with 4mm safety glass adding clear plastic or bubble depending on heating expenses in winter is the best setup.
I don't think there's such a term as &quot;overbuilt&quot;. It is built with a concrete footing and 2x4 framing in order to have the strength to put up with this area's notoriously strong, constant and damaging winds. The polycarbonate was used for it's impact resistance from flying debris and hailstorms where glass would shatter easily (not to mention glass is several times more expensive, heavy and has a low R-value). <br>The light levels in the greenhouse are fine. I had no problem growing a bountiful crop of tomatoes in it last summer, despite our very short growing season. <br>Thanks for your comments.
Its good that you have had success with the greenhouse. I live in England so i never considered the effects of strong winds or debris. I get a lot of shade so I'm constantly looking at getting as much light transmission as possible. There are other options like wind fences, hedges or toughened glass but if cost is an issue it could be at least partially offset by reducing the thickness of the wood. And while polycarbonate is cheaper initially it does have its disadvantages and only lasts maybe 10 years, the glass in my greenhouse is probably 40+ years old and still going strong.
Good luck getting a wind fence or hedge to work here in Newfoundland. My neighbour's 32 RV flipped over the other day and it was behind a 'wind fence'. Hedges aren't suitable for the salt spray either, they grow so thinly and are not worth the effort you need to give them in our harsh climate. As for toughened glass, I've seen sky lights, car windows, and industrial windows destroyed by blowing debris and hail stones here in NL. Neither of those materials are suitable for our climate, perhaps for yours but definitely not for a rugged place like Newfoundland and Labrador. <br> <br>Thanks for the great Instructable LancePenney. It suits me perfectly! I live on a plateau of cliff overlooking the ocean in central and I need a durable greenhouse. :) While the ocean gives me awesome fertilizer and sand for my soil she sure is rough on my garden..
Hey! It's great to see a fellow Newfie on here. Greetings from Torbay. My greenhouse construction and materials were inspired by Igor when I watched my neighbor's deck detach from the house and roll down the street. I don't think the polycarb has been impacted by any debris yet but it stood up to Leslie no problem. Thanks for your comment!
Those were some pretty wild storms, we never got hit too bad for Igor or Leslie out near Gander Bay but there was a storm in the December after Igor that caused a lot of damage. <br> <br>I actually went to Instructables to look for a greenhouse plan and decided to search &quot;Newfoundland&quot; since I knew I would need one made by someone who knew the climate and you showed up!! I'm right happy!! LOL
i good idea is to add a solar powered exhaust fan more sun the more the fan works
This looks fantastic! Nice work. I have been considering building a <a href="http://www.secondnaturehydroponics.com" rel="nofollow">hydroponics</a> greenhouse now I know how. How long did this take you? Thanks for letting us know about all the ins and outs of this project. You are great!
Nice clean job! One other easy item is to add at least 2 rafter ties. They are horizontal 2x4s attached from one rafter to the opposite side at about halfway up from the top of the top plate to the ridge. They are simple, but important bracing to keep the center of the greenhouse from spreading out, or &quot;caving in&quot;. You can cut and paint them on the ground, or indoors, and then install them and touch up the nails. Even just one tie would do a lot.
As it ran in my mind what you describe are more often called collar ties, I did a search and located <a href="http://www.nachi.org/collar-rafter-ties.htm" rel="nofollow">http://www.nachi.org/collar-rafter-ties.htm</a> . from that page;<br> <br> Collar Ties<br> collar rafter tie<br> Collar ties are designed to tie together the tops of opposing rafters. This helps brace the roof framing against uplift caused by wind. Collar ties must be placed in the upper third of the roof.<br> <br> <ul> <li> <em>Collar ties, contrary to popular belief, do not prevent walls from spreading.</em>&nbsp; </ul> &nbsp;<br> <div> <strong>Rafter Ties</strong></div> <div> &nbsp;</div> Rafter ties are designed to tie together the bottoms of opposing rafters. This helps keep walls from spreading due to the weight of the roof. When the walls spread, the ridge will sag. A sagging ridge is one clue that the home may lack adequate rafter ties. Rafter ties form the bottom chord of a simple triangular roof truss. They should be placed as low as possible in the roof framing.<br> <br> Personally I really never knew what their &quot;official&quot; purpose was. until now. Thanks to your comment now I do, along with a web site I can search for other items.<br> &nbsp;
Thanks. I had a plan to use some steel aircraft cable together with the appropriate rigging and turnbuclkes. That way it wouldn't block out as much sunlight and I can turn the turnbucles whenever I need to draw the two sides of the greenhouse together.
Cable will only hold up to tension (spreading out) and not compression (caving in). At 48degN you need to be concerned with both wind and snow which usually exert a large amount of compression. You really should use a rigid material for the rafter ties. Sunlight getting through is important so metal-especially steel-is a good choice so instead of cable look for u-channel, hollow square, or angle stock (flat pieces are likely to bend). Copper and aluminum are too likely to bend or stretch so try to avoid them if possible especially where snow is an issue. Another option is *rigid* metal conduit meant to safely bury electrical wires-I've known several people who have used them successfully for the ties in various greenhouses in the northern US although the connections can be tricky since conduit doesn't normally have any flat sides.<br> <br> If cables are all that you can find, instead of putting them straight across like the rafters are, put them diagonally from corner to corner in pairs so that they form an X. It's not perfect and will still be susceptible to compression but it shouldn't be quite so bad and the frame is more likely to stay square. Structural cables are really meant to be placed diagonally and are just to keep walls/frames square and plumb. When used in pairs they make a loosely framed wall much more rigid and better than nothing but again, they won't help with the compression such as from wind or snow.<br> <br> Sorry about the long winded reply but I've seen a few too many structures supposedly reinforced by cables that still collapse from snow load or a good windstorm.
The plan was to put the cable on the two long walls that are not the gable end walls (I dont know what you call them). If the cable were to run from top plate to top plate then any compression on the roof would translate to tension on the cable. <br>However, I have two pepole now who seem to know what they're talking about telling me I should use rafter ties. Perhaps I will use ties but I will install the cable first and use the turnbuckles to draw the two walls together and hold them in place while I install the ties. <br>As for the rest of the structure, the corner braces on the walls should be enough to hold everything stiff. It cant be any worse than the 7/16 OSB (or &quot;Cornflake Board&quot;) they use for houses these days. <br>Thank you for all your advice, both you and &quot;Indegreen&quot;
I'm not sure what running the cables along the top plate of the non gable walls would accomplish, unless the top plate is pieced and it's pulling apart with no load. The compression on the roof would create tension in the direction of the top plate of the *gable* walls but the compression would just result in a downward force on the non gable walls-not tension along the top plate. Things change when you take wind into account but the non gable walls still don't experience much tension structurally.<br> <br> Push straight down on an upright pole and you aren't going to do much other than sink it deeper into the ground. Push straight down on the top joint of an A frame without a horizontal cross piece to hold the legs in place (so really an upside down V) and it's going to collapse as the legs spread out.<br> <br> Triangles are only more sturdy than a rectangle if all three sides are attached to each other, remove one of the sides and it fails which is the reason for using rafter ties.<br> <br> The frame of your greenhouse is already looking much more secure than most, especially with the crosspieces in the corners of all the walls. A lot of people buy kits with metal frames that bend a bit too easily (including me) with joints that aren't as secure as they should be and have to spend a lot of time jury rigging repairs or see everything come crashing down.
The cable I was proposing would run from one leg of the upside down V frame to the other leg of the a frame. When you push down on the top joint of the V frame, the cable would prevent the two legs from spreading out and collapsing. It would also prevent the downward force on the V frame from spreading apart the two non-gable end walls. So weather the cable or rafter tie (doesnt matter which one) is attached between the legs of the A frame or attached between opposite non-gable end walls, the dynamics of the entire system are the same and a downward force on the roof does not translate to lateral force. The only difference is that the rafter ties make the structure look like an A and the cable between the top plates make the structure look like a triangle. If you were to use a piece of wood in place of my proposed cable placement, you would essentialy have the bottom cord of a truss which we all know is structurally sound.
If you are trying to extend your season more, consider 5 layer polycarbonate glazing. It has thick layers inside and outside, and 3 thin intermediate layers. Remember that polycarbonate sheet made for greenhouses has a co-extruded UV absorber <em>on one side only</em>.&nbsp; If you put it up backwards, it will be degraded quickly!&nbsp; Usually the UV-protected side is coated with a light blue plastic protective sheeting.&nbsp; After cutting to size, peel the blue sheeting off only around the edges, then install.&nbsp; After everything is done, you can double-check that all the panels are facing correctly (blue film to the outside) before peeling off the film.&nbsp; (Beware when cutting triangle shaped pieces that are not mirror symmetrical, that you cut them properly so the blue faces out!)<br> <br> Do not stack polycarbonate panels on the ground in the sun!&nbsp; The heat can accumulate amongst the panels and melt them!&nbsp; Cover them up or place on the ground one layer only.
Nice work Lance, and a detailed set of photos. <br><br>We are interested in erecting a very similar type of greenhouse, using an arduino controlled automated watering system. I have seen a simple controller setup on this site.<br><br>Will follow your progress, particularly how the carbonate sheeting stands up to punishment. Hale can be a problem where we live (sub tropical Queensland), sometimes biggier than golf balls... <br>I have plenty of toughened glass for the sides, was looking for something more resilient for the roof, so that may be the answer. <br><br>
Thank you so much for this wonderful project! I really wanted to thank you for the great information about permits, rules and regulations!!!! These are often forgot about!! I look forward to following this project, I live almost on a Great Lake, so I am not sure I can built this unless I can some how figure out where to put my waste water without it going into the ground, this would be a big NO NO and huge fines in my location. Thanks again!
I've built a couple of greenhouses and learned from my mistakes; there are a few special considerations in greenhouse design that many inexperienced builders overlook, if you design it like you would a garden shed only with clear glazing, you're going to have problems. The most critical factor to consider is control of condensation, under certain weather conditions, there will be a LOT of condensation formed on the glazing, you need to make sure that all that water has somewhere to go, if for example, it collects on the top or bottom plate of the wall or in the soffits, you'll quickly get mold and mildew problems, wood rotting etc. designing away as many of those flat horizontal surfaces as possible will pay dividends in the long run. Along those same lines, use a good quality, mildew resistant paint. Also, design in as much ventilation as you can, it's almost impossible to have too much and make sure some of it is useable when it's raining.
Lovely work.<br>We do want to see how she turns out.<br>If you could explain a bit more about the polycarbonate sheeting and where you got it and how you install it, that would be good.<br>Thanks.<br>rf
Thank you. I will be sure to provide much detail on the installation of the polycarbonate panels when I am able to. I got the panels from a company called &quot;Harnois&quot; that are based in Quebec I believe. I found a local distributor here in St. John's and they shipped them in from Toronto.
Lance, I'd like to thank you as well for putting this up. I've been thinking of doing something like this for a while and seeing your design has encouraged me to go ahead and get it started. I have a very sloping yard so I will do a lot more foundation work than your project, but renting a cement mixer is the way to go for sure. I look forward to seeing the finished product when you get a chance to finish it.<br> <br> Happy New Year, from Sparkie in Quinton Alabama
Thank you for this comprehensive and clear Instructable!
Hi,<br><br>a real interesting project. Please do not forget to precise the code used with your arduino (networking project).<br><br>For information I found this arduino (supported code) with already more specification that the original arduino (for the same price) :<br>http://www.freetronics.com/products/etherten<br><br>This self sufficient arduino is also a need to reduce cost :<br>http://www.instructables.com/id/Self-Sufficient-Arduino-Board/?ALLSTEPS<br><br>A moisture control is also interesting : <br>http://www.instructables.com/id/Garduino-Gardening-Arduino/step4/Build-Your-Moisture-Sensor/<br><br>To manage a watering controller :<br>http://www.instructables.com/id/A-watering-controller-that-can-be-home-networked/<br><br>And this could also interesting you :<br>http://www.instructables.com/id/Backyard-Automated-Greenhouse/<br>http://www.instructables.com/id/Garduino-Gardening-Arduino/<br><br>Then I will stay tuned to your project because I hope be able to do the same.<br><br>I wish you a Happy New Year.<br><br>Miguipda ;-)<br>
Why are the footings on the surface? <br>Why do they not go into a trench as a foundation is usually built?
Once the area around the greenhouse is landscaped, the footings will be backfilled right to the top with topsoil and that way it will kind of be in a trench.
i was planning on making an instructable similar to this in the next couple months, but now i guess i won't since you provided very good explanations for everything, very good thus far.<br>
Do it anyway. Yuu might have some variations that would be helpful for someone.
Thank you for putting this up. I really like your thorough process on erecting the frame. When I get somewhere where we're not renting a house, I'll be sure to use these methods to make mine. Hope to see your hydroponic system by then too! =D

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