Make a Cold Frame - it's easy
If you want to make a cold frame for yourself, it's really rather easy to do. Just get some scrap wood and some fasteners, and a little clear plastic sheeting for the top, and you're on your way.
Oh, and a little help would be great too. Sometimes it takes more than two hands to build a cold frame like this.
Our frugal living plans have us growing our own vegetables, so we need to build a cold frame or two to help us do just that.
We'll also use this cold frame to help make a "greenhouse" inside of our greenhouses such that we can get a jump on the growing season and extend the season as well.
The design we constructed for our seedlings has an angled top mounted on hinges. It lets in a little more light and allows the top to be held open for watering and venting.
Opposing sides of the cold frame have handles so it's easier to lift and relocate by two people.
Here is a photo of the finished product:
Take a look at the following pictures and descriptions to see how to make a cold frame like this. It's relatively straight forward. I'll leave the exact size up to you, but we opted for a roughly 4 foot square cold frame because it requires a single sheet of 4 foot by 8 foot plywood, or two 4 foot by 4 foot sheets of plywood, and the resulting scrap is minimal.
Make a Cold Frame - the Overall Plan
Here is an overview of the overall approach to cutting out the sides, front, back and bottom in order to make a cold frame like the photo above. Look at the cheesy pencil drawing to the lower left to get an idea of where we're headed.
All measurements are in inches. Don't hold me to the measurements, but they're probably very close to what we constructed for our cold frame in 2008. I'm doing this from memory, so proceed with caution and common sense, with an eye toward what you'd like to see as the final product as you consider how to make a cold frame from these plans.
Please note that the angle of the photograph makes the drawing appear to be something other than a rectangle. It's supposed to be a rectangle, so please view it as such.
Feel free to change the dimensions to suit your interests with respect to pitch of the top, wall height and overall size.
The idea is to make a cold frame that is a good size, portable, and makes efficient use of materials. I think these plans will do that, but I can't guarantee anything from here, so don't get mad if you make a cold frame with these plans that looks more like a bath tub or a row boat.
Seriously, you're not trying to build a Swiss watch. You're trying to make a cold frame. Perfection won't get you to your final goal.
When we built ours, we used two sheets of 3/4 inch thick exterior grade plywood. I think it's a good choice because our cold frame has held up real well. It's a bit heavy, but solid as a rock.
You can use 1/2 inch or 5/8 inch thick material, but I happened to have 3/4 inch in 4 foot by 4 foot sheets as scrap wood, so that's what I used to make a cold frame. In fact, we made two.
The measurements above take into account a kerf (width of cutting blade) of at least 1/8 inch. The cut end will be something a bit less than 48 inches. It's unknown because the kerf of the blade you'll use is unknown.
Nevertheless, when you're finished making the frame, measure the insides and trim off on both sides of your remaining piece as necessary to allow it to fit down into the bottom of the frame. The dashed lines on the drawing suggest that some unknown amount will need to be trimmed from both edges of the remaining piece to make it fit well as a bottom.
The finished size of the bottom piece will depend on how you make your joints at the corners. I recommend overlapping butt joints. They will add strength to the framing.
Tools Needed to Make a Cold Frame
These or similar tools are needed to make a cold frame of this type. Substitutions are suggested (in parentheses) where the recommended tool might be uncommon for the average shop.
- tape measure
- bright marking crayon (felt tipped marker)
- straight edge (long straight 1x4 board)
- circular saw (saber saw, jig saw, hand saw)
- chop saw (saber saw, jig saw, hand saw)
- drill press (electric drill, cordless drill, hand drill)
- pneumatic staple gun (hand operated staple gun)
- ratchet wrench and socket set
- small adjustable wrench
- box cutter (scissors)
- straight screwdriver
- philips head screwdriver
- cordless drill (electric drill, hand drill)
- 1/4 inch wood and metal drill bit
- 1/8 inch wood and metal drill bit (optional)
- framing square (optional)
- hammer, of course
- scratch awl
- large flat and cleared work table or shop/garage floor
- 2 C-clamps if you're going to use a saber saw or jig saw
- rubber or rawhide mallet
Materials Needed to Make a Cold Frame
Here is a rough list of materials for the project:
- One 4 foot by 8 foot sheet of 1/2 or 5/8 or 3/4 plywood, or two sheets of 4 foot by 4 foot plywood. You'll have to nail or screw into the edge of the plywood when you make a cold frame like this, so I suggest 3/4 inch. That will give you much more to screw or nail into with reduced risk of splitting the wood.
Note: If you're going to make a cold frame using 4 foot by 4 foot sheets of plywood, you best reduce your measurements by an eight of an inch because if you don't, you won't be able to fit it all on a single sheet of plywood. There are 4 cuts, and if they take up 1/8 inch each, that will leave your last piece 1/2 shorter than what you need to make a cold frame that is uniform.
- Two pieces of corner iron a foot tall, and two pieces of corner iron 6 inches tall. That's roughly a 3 foot piece of corner iron. Get corner iron that is at least one inch wide on each side. Get it with holes so you don't have to drill them.
Note: If your corner iron doesn't have holes, then use a drill press to make four evenly spaced holes on the one foot pieces, two near the ends and two evenly spaced between the end holes. Make your holes a little more than halfway out from the corner so you'll still have plenty of metal before reaching the edge, and you won't be trying to bolt near the edge of the plywood.
Drill three holes on the 6 inch pieces, using the same approach as described above. Having holes drilled in the corner iron will make marking for assembly that much easier.
- Four garage door type handles.
- Three small door hinges (a bit smaller than a standard interior door hinge).
- One spring loaded hook and eye set of at least 3 inches in length.
- One 5 foot by 9 foot sheet of plastic (UV treated 6mil is preferable).
- Scrap cardboard.
- Scrap 1/2 plywood or flake/chip board (not particle board).
- Two 2x4s, 8 feet long.
Note: our finished product from 2008 used 1x4s, not 2x4s. This plan suggests using 2x4s since we learned that the hinges are difficult to attach to 1x4s. With a 2x4, you'll have no problem getting sufficient wood to bite into with the wood screws.
- Thirty-six 1/4th inch hex bolts, each with one nut and two washers, of sufficient length to penetrate the thickness of the garage door handles and plywood (remember, it's your choice on plywood thickness). This assumes that the corner iron and garage door handles are roughly the same thickness.
Don't get overly long hex bolts, just the size to get the job done.
- Sufficient 3/4 inch long wood screws of the correct size to mount the three hinges. This should be either 18 or 24 screws.
- One hundred 1 and 1/4 inch sheet rock (drywall) screws with fine threads. Nails can be used, but I recommend screws because they have great grip, and you aren't banging on the structure while you make it.
Make a Cold Frame - The Steps
Here are the suggested steps of the process to make a cold frame. Some photos of details of our 2008 construction are provided so you can make a cold frame with reference to our finished product. The steps presented below are in the order that you should follow to make a cold frame like we did.
I leave it to you to modify these instructions to suit your preference of assembly. I'll take no responsibility for the outcome of the project, and I won't take any credit either.
Before you make a cold frame like this, please read through the instructions and envision how you would do it. Don't proceed unless and until it makes sense to you.
Here we go.
Make a Cold Frame - measure twice and cut carefully
- Measure your intended cuts on the plywood and draw a line with a straight edge to guide your saw. Double check the measurements to make certain they will create two identical pieces for the sides, and two rectangles, one tall for the back, and one shorter for the front.
The height of the back must match the measurement of the tallest portion of the sides. The height of the front must match the shortest measurement of the sides.
When you set about to make a cold frame or any similar project, it's always better to check measurements several times than to buy yourself another piece of wood because you didn't.
- Using a circular saw, make your cuts right on the lines. If you're using a saber saw or jig saw, you should clamp a straight board an appropriate distance from the line to act as a guide for your saw. Otherwise, you'll have a regretable wiggly looking cut when you're through.
- After you make all the cuts, match up sides to be certain you have two identical sides. They don't have to be perfect, but they should be very close.
- Match up the back and front pieces to be certain they match with the tall and short ends of the sides. They don't have to be perfect, but they should be very close.
- For reference, rough fit the pieces together and use a marker to indicate which side piece is left and right, and which side is inside and outside. Also mark which edge is up. This step probably isn't crucial, but if this is your first time to make a cold frame, marking can be helpful.
Make a Cold Frame - with strong corners
- Stand up a side and the back, and butt them the way that you want. An overlapping butt is recommended. See the even more cheesy diagram below. Remember, you get what you pay for. :-)
In this drawing, the term "angle iron" is synonymous with "corner iron."
Make certain that you overlap the back and front of the cold frame the same way. If the back piece is on the inside, make certain the front piece is also on the inside.
If you have the back on the outside and the front on the inside, you'll have the back narrower than the front.
It's better to check several times than regret not checking enough and having to disassemble and start again.
- Fit a one foot section of the corner iron into the inside corner and roughly center it between the top and bottom edges of the side piece and the back piece.
Mark where holes should be drilled in the wood for bolts. If you are using corner iron that already has a pattern of holes, just mark evenly spaced holes as described in the materials list step "b" above.
Mark both the side piece and the back piece because you're going to need to drill both of them.
Also mark the corner iron as to which portion is supposed to face up. Now, if anyone asks you, you'll "know which end is up."
- Take the side piece and back piece and lay them down for drilling. Drill from the inside to the outside. Use a scratch awl as necessary to dimple the wood so the drill bit doesn't drift about at first.
- After all holes are drilled, insert hex bolts with washers from the outside to the inside on the side piece, then do the same with the back piece. Use a hammer to tap the bolt through the wood if necessary.
If you find that it's a tight fit, get a slightly larger drill bit, or wiggle the bit about in the holes while the drill is running to enlarge them just a tad.
- Fit up the side and end pieces again, and install the corner iron and place washers and nuts on - finger tight.
- If all looks fine, use the socket set, ratchet wrench and adjustable wrench (or pliers) to tighten down the bolts. Use the ratchet to tighten the nuts. Use the adjustable wrench (or pliers) to hold the bolt head.
Tighten snug on the side piece first, then snug the back piece. Don't crush down on the wood just yet, but the connections should be tight enough that the two pieces stand together with no apparent wiggle in the joint when you jostle it around a bit.
- Repeat the same process with the other side piece and back piece.
Note: When drilling the side piece, it can lay down flat on the table. The back piece will need to lay down flat with the attached side piece sticking up in the air.
Be careful not to bend the corner iron when doing this. Alternatively, you can drill the back piece in the upright position.
- Now, repeat the same process with both corner irons associated with the front piece. This will require some drilling with the partially assembled cold frame in the upright position.
- Check for "out of square" and misalignment (warping) of the assembled frame. Do this with a framing square. Loosen and adjust corner irons, or bend them as necessary. Use a hammer or mallet to gently persuade the pieces into better alignment and square.
Make a Cold Frame - with gusset plates
- Turn the assembly over and make a mark on the bottom edge of the back, sides and front about one foot out from each corner. This is roughly where a gusset plate will be installed on the bottom side of each corner.
Gussets will add strength and keep the floorboard from falling through the bottom.
- Cut triangular shaped pieces of the 1/2 inch plywood scrap to fit each corner. Cutting the corners off of a square or rectangular piece of scrap plywood will do the trick just fine.
If not, then use your framing square to mark out suitably sized right triangles.
The photo above left shows a bottom gusset plate that holds in the floor. Note the placement of screws.
What you are creating are isosceles right triangles, triangles that have a 90 degree corner (like you find with a square or a rectangle) and two sides of the same length (in this case 1 foot) that come out from that corner. The third side of the triangle is longer. This is called the hypotenuse, and it is directly opposite the 90 degree angle. The other two angles of the triangle will be 45 degrees.
When you make a cold frame, you don't need to know geometry, but it helps.
- Install the gusset plates with dry wall screws (preferred) or nails. Use the scratch awl and 1/8 inch drill bit to create a pilot hole if desired.
Screws work best when you make a cold frame because on occasion, you'll want to pick up the cold frame with seedlings inside of it. The gusset plates will have to hold the floor in place without giving way. Nails can be pulled out much easier than screws.
Use care when installing these gussets. You must install the nails or screws directly into the middle of the bottom edge of the sides, back and front to avoid splitting the wood. This is why 3/4 inch plywood is recommended.
Install one side of a gusset, then the other, squaring up the frame as you do so. Make certain the frame remains square as you install subsequent gussets on each of the corners.
Make a Cold Frame - tighten the corner irons
- With gussets installed, finish tightening the corner irons using a ratchet wrench and adjustable wrench.
When the plywood starts to crush down a little bit, that's probably tight enough. You don't have to be Tarzan to make a cold frame.
Make a Cold Frame - install the floor
- Measure the inside dimensions of the cold frame, subtract 3/4 inch from each dimension, and write those numbers down in the middle of the large remaining piece of plywood. These will be the measurements for the floor.
Note which measurements are side to side, and which are front to back.
- Mark off the shortest floor measurement on both edges of the shortest length of the remaining piece of plywood. There should be just a little bit to cut off to match that measurement.
- Check to make certain that the longer floor measurement will fit within the longer measurement of the remaining piece of plywood. There should be just a little to cut off there as well.
Transfer the floor measurements onto the remaining piece of plywood and use the straight edge or long 1x4 to mark where your cuts should be to make the size of the remaining piece of plywood conform to the floor measurements that you had written down.
Also, note with a marker on the floor piece where the front, back and sides of the floor should be.
As always, spend more time measuring and checking before you cut. You can always cut something shorter, but making it longer after it's been cut too short, well, that'll take some doing.
- Cut the plywood with the circular saw to achieve the desired floor measurements.
- Install the floor by first making certain that the floor is oriented correctly with the front, back and sides of the frame. Work it down at a angle until it rests on two of the gussets.
Lay the opposite end into the bottom of the frame until it rests on the gussets at the other side of the frame. If the plywood on the back, front or sides is bowed a bit, the fit might be a little snug on the way down.
You may need to try fitting the floor using a different leading edge. The main obstacles to getting it to fit will be the bolts and nuts that protrude inside the cold frame at the corner irons.
If a couple of different ways of fitting it in don't work, you can either:
- notch the plywood to allow the bolt ends to pass
- shave a little more off the edges near the corners of the floor with a saw
- grind or cut off the excess bolt length
- whack the flooring with the mallet
Oh boy, we get to hit something with a hammer! See, we can make a cold frame and have a little fun too.
Make a Cold Frame - install the handles
- With the floor installed, position the garage door style handles on the sides of the cold frame where they feel comfortable for lifting. Mark where holes should be drilled for the hex bolts.
- Drill 1/4 inch holes from the outside in. Use the scratch awl to dimple the wood as necessary.
- Install the hex bolts with washers through the holes in the handles and into the sides of the box. Install the nuts and washers on the inside and tighten them down good. Stop tightening when they start to crush the wood a bit.
In the photo above, you can see that the nuts and washers are crushing the wood a bit. This is the time to stop tightening. The bolts are tight in place, yet the integrity of the wood hasn't been compromised.
Make a Cold Frame - the lid
- Measure the outside width (side to side) of the frame and subtract 3 inches. Use a chop saw to cut two 2x4 pieces to this measurement. These are the hinged portion and front lip of the lid. Mark them as such.
- Measure the outside length (front to back) of the frame and add 2 inches. Use a chop saw to cut two 2x4 pieces to this measurement. These are the side portions of the lid. Mark them as such.
- Cut four isosceles right triangles with sides of 8 inches, and the hypotenuse of...whatever it turns out to be. These will be gusset plates that hold the hinged lid together.
- Arrange the 2x4s on the work table or flat foor surface such that they have overlapped butt joints. In other words, the side pieces should cover the ends of the front lip and hinge pieces.
- Fit one gusset at a time on the corners and either nail or screw the gusset in place. I prefer screws because they allow me to make a cold frame stronger than I ever could with nails. Work one edge of the gusset first, placing three or four fasteners in place, then work the other edge of the gusset.
Before working the second edge of the gusset plate, make certain your 2x4s are butted up correctly and are square. The framing square can help you verify this.
- Work your way around the lid in a similar manner until you install the final gusset that creates the lid.
- Place the lid on the cold frame in the position that you would expect it to be in when operating it. The hinged end should be flush with the back piece and the sides will overhang equally. The front lip should overhang about the same as the sides.
- Use a marker to trace around the inside upper edge of the sides, and mark this edge on the underside of the lid.
- Use a marker to trace around the outside upper edge of the sides, and mark this edge on the underside of the lid.
Make a Cold Frame - install the plastic
This is the pain in the butt part. Plastic film is hard to work with. You need to be careful not to snag it, heavily scuff it, or deeply scratch it, yet it needs to be stretched a bit in order to work well.
When you make a cold frame, you want the top to be clear, and a double layer for insulation, so we're going to wrap the plastic around the 2x4 lid we just built.
- Cut about six strips of cardboard about one inch wide by twenty inches long. They can be shorter - you'll just need more of them. Load up your stapler with 1/2 inch or 3/4 inch staples.
If you're using a pneumatic stapler, test with a scrap piece of wood to make certain it doesn't sink the staples beneath the wood surface - that will cut into the plastic too much.
- Lay out the plastic on a large, flat and clean surface. A table or carpeted garage or shop floor will work well. Orient the plastic so the length is running left to right in front of you.
Orient the framed lid on the left half of the plastic such that the front lip is near the middle and the hinge end is near the left edge of the plastic. The markings from steps 34 and 35 should be facing down on the plastic. The plastic should overlap the hinge end (on your left hand side) by about 6 to 8 inches. The sides of the lid should be centered on the plastic.
- Test fit the plastic by draping the right side over the frame. It should easily go about 4 to 6 inches beyond the hinge end of the lid. This should be sufficient slack.
Return the plastic to is original position on the front lip side of the lid.
- Position yourself at the hinge end of the lid, facing the front lip end of the lid. Make certain the side portions of the frame are still centered on the plastic.
Fold the bottom piece of plastic over the hinge end and position it so the edge is even with the inside edge of the hinge end 2x4. Don't worry about the overhang on the sides for now.
Start at one end (say, to your right) and lay the end of a cardboard strip over the plastic. Staple the cardboard in place (on the gusset plate) a couple of times at the end on your right.
Pull the plastic taut toward the left side, keeping it lined up with where you started on the right side. Place a cardboard strip at the left end and staple it there (on the gusset plate) a couple of times to hold it in place.
You should now have the plastic lined up straight along the inside edge of the hinge end of the lid. Staple every couple inches or so along the plastic (using the cardboard as a staple backing on top of the plastic), staying on a line that generally runs between the point where you first stapled on the right, and where you first stapled on the left.
Use the cardboard as a backing so the staples don't easily pull through the plastic. Tear or cut off excess cardboard, or add more as you go so all your staples have this cardboard backing.
Following along near the edge of the 2x4, you'll be running off the gusset, onto the 2x4 and back onto the other gusset. Don't staple on the 2x4 too close to the edge of the gusset or else you could punch a hole in the plastic.
- Slide the lid toward you and pull the plastic from the front lip side of the lid such that it tightens it up on the underside. Don't be concerned about ridges or bulges just yet.
- Fold the plastic over the front lip end to bring it over to meet up with the hinge end of the lid just stapled in place. Make certain there are no folds of plastic on the front lip end.
You'll need about 4 inches of plastic to overlap the hinge end of the lid. Cut away excess so you're not fighting with it.
What you'll do next is roll/fold over the plastic and a cardboard strip while pulling the plastic film tight before stapling it in place.
Place a piece of cardboard even with the edge of the plastic film, then fold it with the plastic while pulling snug as you make your way to the final fold. Pull on the plastic to get both the top and bottom tightly against the frame, but don't pull too hard.
The idea is to get your final fold to:
- sufficiently tighten the plastic
- lay flat against the wood frame
- be stapled into place near the outside edge of the hinge portion of the lid.
- If the resting place of your cardboard fold isn't near the outside edge of the hinge end 2x4, then make your folds shorter or longer as necessary to get your final results to meet the three criteria noted in the step above.
You can staple your final fold right on top of the first piece of cardboard if you like.
- Once you have the plastic tight and in the right spot, staple it in place. Start at one end and work your way down to the other, pulling on the plastic and rolling/folding the cardboard to get the plastic relatively tight across the frame.
Don't worry about ridges in the plastic. You'll get those out in the next steps.
This is perhaps the most tedious step of how to make a cold frame because the plastic isn't easy to work with. An extra set of hands will help keep portions of the folded up plastic and cardboard in place until you're ready to staple.
Staple from one side to the other if necessary to get the plastic taut across the frame as you go.
- Turn the lid over so the lines you made in steps 34 and 35 are on the side facing up.
- Position yourself on one side of the lid to attach the plastic there.
Use a similar technique as described above to attach the plastic to one side of the frame, but don't place too much tension on the plastic in an effort to get bulges or ridges out of the far side. You'll do that in the next step.
Focus on getting the bulges and ridges out near the corners and up to the middle of the plastic. Do what is reasonable to do, but don't get too concerned. Remember, we're here to make a cold frame, not build a Swiss watch.
Don't staple cardboard and plastic in between the lines that you placed in steps 34 and 35, as this will make a poor seal for the cold frame.
Trim off excess plastic, but leave yourself enough to work with as you staple it in place.
- Position yourself on the other side of the frame to complete the fastening of the plastic.
Using a method similar to the steps above, fasten the plastic in place and try to get the last serious bulges or ridges out of the plastic film.
Fold over or tuck in any excess plastic and staple it in place using a cardboard strip to distribute the holding force of the staple. Cut off excess as necessary so you're not stapling too much plastic at one time.
Don't staple cardboard and plastic in between the lines that you placed in steps 34 and 35, as this will make a poor seal for the cold frame.
Trim off excess plastic, but leave yourself enough to work with as you staple it in place.
Make a Cold Frame - install the lid
- Reposition the lid as in step 33 and use three hinges to connect it to the back of the frame. Two hinges should be installed about 6 inches from each edge. The third hinge should be installed in between the first two, roughly in the middle of the cold frame.
Install the outside hinges first and then the middle hinge. Make certain the hinge mechanism is centered on the interface of the lid and the back piece (horizontally lined up with the space between the lid and the back). Use the wood screws to attach the hinges.
- Test operate the lid. If it opens with difficulty, you may have to adjust the hinge positions.
- Install the spring-loaded hook and eye on the underside of the front lip. Screw the eye into the lid, and position the spring-loaded hook so it attaches on the front of the frame.
That's about all you need to know to make a cold frame. Get your seedlings started and then get them transferred into the cold frame for access to direct sun and on their way to hardening off.
Before you know it, you'll be fully supporting your frugal living plan by having your veggie seedlings ready to transplant.
Done with Make a Cold Frame, take me back to Build Your Own Greenhouse
There certainly is a broad scope of topics here at Frugal Living Freedom. When you think about it, money permeates so very many activities in our lives, therefore, being frugal encompasses a wide range of interests, from being employed to taking a vacation, and just about everything in between. Enjoy the variety, pick up some new ideas, and start making frugality a part of your signature.
I'm a big proponent of being debt-free, and I mean entirely debt-free - no mortgage payment. It's not essential for financial freedom, but you'll love the feeling once you get there. If you didn't have a rent or mortgage payment, how much more could you do for yourself with your current level of income? I suspect plenty.
If you ever hope to see an abundance of wealth, you need to plug the hole in your boat. The wealthy don't necessarily make lots of money, instead, they know how to hang onto what they make, and make it work for them.