How to Make a Cold Frame
These instructions can easily be adapted to different dimensions according to the size you want in your garden
If you haven’t yet reached the greenhouse stage with your gardening, what better than a cold frame to give you a taste for growing your own vegetables and flowers from seed ? And if you have a greenhouse, how are you going to cope with all those seedlings in it waiting to be hardened off if you don’t have a cold frame? In any case, you will be needing as much space as possible in the greenhouse for your growing plants as spring merges into summer.
Like most good things in life, a well-made frame is not cheap, so you can save money by making it yourself.
steel measuring tape
set square and pencil
hand or electric drill with 4mm (3/16in) and 3mm (1/8in) bits
timber (as cutting list below)
110g (1/41b) 25mm (1 in) plated(general nailing)
110g (1/4 lb) 40mm (1-1/2 in) plated(general nailing)
twelve 40mm (1-1/2 in) No.8 countersunk brass or plated wood(top frame)
twenty-two 30mm (1-1/4 in) No.8 countersunk brass or plated wood screws (joint reinforcing)
eight 50mm (2 in) No.10 roundhead brass or plated wood screws (final assembly)
2 handles (top frame)
2 sheets horticultural glass 610mm (24 in) square
2 sheets horticultural glass 610 x 305mm (24 x 12 in)
1 litre (2 pints) horticultural wood preservative
Timber Cutting List
First of all, check that the space in your garden allows for a frame of our dimensions and, if necessary, adapt the measurements to the area you have before buying the materials. Then estimate the cost from our Materials and Timber cutting lists so that you have an idea of the total outlay. It is as well to check the current prices with your local timber yard or do-it-yourself stockist.
The cold frame illustrated has been specially designed for home construction using simple wood-working joints only. The finished job, however, presents a spacious and rugged structure capable of giving many years of service.
The timber sections specified in the cutting list are standard stock sizes kept by most timber yards, but if you experience any difficulty in obtaining a particular size, then the next available larger size may be used provided that the necessary dimensional adjustments are made to the various parts.
For ease of construction and to make the frame completely portable, it is built as five separate assemblies. The main frame consists of front, back and two sides, each assembled as a panel and then fixed together with wood screws at the corners. The sides, being slightly higher than the front and back, form a recess into which the glazed top frame is dropped. Runners (part `K.’) are fitted to the inner side of the end members (see cold frame construction image below) and these allow the top to slide back for interior ventilation or for working inside the main frame.
The unit shown is designed around standard sized sheets of horticultural glass to avoid the need or expense of specially cut glass sizes. The design may, however, be re-sized to suit individual needs simply by amending the lengths of the panels affected.
Whether building to the sizes shown or to amended sizes, it is as well to work so that one panel is completed before the next is made, and in the order shown. This should help to ensure that any variations in timber sections or sizes are automatically catered for as work proceeds. Waterproof woodis recommended for all permanent joints to ensure a rigid structure.
The instructions given provide a frame measuring 1350 x 915mm (4 ft 5 in x 3 ft), standing 430mm (1 ft 5 in) high at the back, coming down to 330mm (1 ft 1 in) at the front. Before starting work, be sure to read through the following stages of construction.
Stage 1 — glazed top
Cut parts ‘C’ to length and then notch the ends (see drawing) to present a snug fit to parts ‘B’. Use a tenon saw to cut the notches. Cut parts ‘B’ to length, remembering to allow for any variations in sectional timber sizes. Assemble the frame by screwing parts ‘B’ to parts ‘C’, after drilling pilot holes for the screws.
Taking measurements direct from the assembled frame, cut parts ‘A’ and ‘D’ to length andand nail them in position. Parts ‘A’ provide an edge stop for the glass, and parts ‘D’ a ledge upon which the glass rests.
Stage 2 — front and rear panels
Parts `E’ and ‘F’ must be approximately 6mm (1/4 in) longer than the overall length of the completed top frame to allow this to run smoothly between the side members, so before cutting these parts check the length (parts ‘B’) of the top frame. Now reduce the depth of part `E’ by cutting a 15mm (1/2 in) strip from the top edge to provide clearance for the sliding top frame, using a panel saw.
Cut parts ‘I’ and ‘M’ to length. These parts form the vertical jointing battens for the main cladding, parts `E’ and ‘F’, and are fixed centrally and at either end of the front and rear panels. Study the right-hand inset section on the drawing and note that the side pieces must be set back sufficiently to accommodate parts ‘J’ and ‘L’ and of the end panels. Use a piece of the timber from which these parts will be cut to determine this distance. Assemble the front and rear panels byand nailing to the battens ‘I’ and ‘M’, then reinforce each butt joint with a 30mm (1-1/4 in) .
Stage 3 — side panels
It is vital when building the side panels to be sure to make an opposite ‘pair’ and not two identical pieces.
Cut parts `G’ and ‘H’ to length and note that these should be approximately 50mm (2 in) shorter than the overall length of the side pieces (parts ‘C’) of the top frame. Mark an angled line to parts `H’, allowing the full 150mm (6 in) width of the board at the higher back edge and reducing to 30mm (1-1/4 in) for the lower front edge. Cut to the line — remembering to make a pair.
Assemble the side frames byand nailing, then reinforce each joint with a 30mm (1-1/4 in) wood . Note that parts ‘L’ and ‘J’ must overhang the sides `G’ and ‘H’ by approximately 15mm (1/2 in) to provide a fixing point for the capping timbers, parts ‘O’ and ‘N’ (see right hand inset section). Add the top frame runners (parts ‘K’) and then trim the tops of parts ‘L’ and ‘J’ flush to ‘K’. Finally add the capping timbers, parts ‘O’ and ‘N’, by glueing and nailing.
Stage 4 — final assembly
Drill two 4mm (3/16 in) holes to parts ‘I’ and ‘M’ as clearance holes for the 50mm (2 in) main assembly wood screws (see drawing above). Hold the frames firmly together and, using a bradawl through the holes, bore pilot holes in parts ‘J’ and ‘L’ for thethreads. Fix the frames together, but do not apply glue to the joints; in this way the assembly can be easily dismantled for re-siting.
Try the sliding frame and plane it as necessary to achieve a neat sliding fit. Part `P’ (not illustrated) is then fitted as a ‘stop’ under the central part ‘C’ to butt against part ‘M’ when the frame is fully closed.
At this stage the assembly must be dismantled and given a thorough soaking with a horticultural-type wood preservative. When the preservative has dried, the handles should be added (see drawing) and the glazing fitted and secured by panel pins. To do this, lay the glass in position and with the hammer head lying sideways on the glass, gently tap the pins halfway into the timber frame.
Rest the frame on a row of loose-laid bricks, thus providing a neat finish and also helping to preserve the woodwork by keeping it clear of damp earth.