With a cold frame, it is possible to start garden cultivation earlier, before the end of last frost. It is also possible to extend the autumn crops by sheltering the plants from the cold. Cold frames are sold in specialized shops, but can be built at home. These shelters can be built using the usual DIY tools and by following a few guidelines.

Building a cold frame only takes a few hours. About a day’s work is necessary to put the greenhouse together. For the procedure to be successful, the DIY enthusiast must define the shelter’s layout, and have the right tools for the job.

The materials making up the cold frame

It is essential to choose the location of the cold frame adequately. It should be facing south, and placed near a wall or hedge in order to reduce the impact of weather conditions. The most commonly used material for building a greenhouse is wood, but it is possible to build a cold frame with metal, such as aluminium, bricks or stones. These are recommended for building a shelter in a cold region. The timber used must be a softwood such as Douglas fir or larch. The glazing can be glass, strong enough and of relatively light weight, or plastic, which is more convenient to install, but of which the insulating properties are greatly reduced. To get a good glazing, choose a “cathedral” type glass, which is translucent and diffuses solar radiation better.

Building a cold frame

For a cold frame with a hotbed, the heating substance must be previously installed in its location. The device is to be placed above a 23-inch deep hole, filled with a 15-inch layer of horse manure, and an 8-inch mixture of compost. This project will keep the temperature stable around 77 degrees for a month inside the cold frame. The usual tools, such as a circular or handsaw, will be used for the operation.

The cold frame consists of two trapezoids with rectangular angles with an adequate slope to allow drainage of rainwater. Building a greenhouse begins by assembling the front and rear side panels and corner posts. The side panels are assembled by biscuits, or glued together. The corner posts are positioned to increase the slope of the side panels. They can be glued and screwed to the side panels, of which the position will have been previously checked. The front and back panels can be mounted by strips. The builder must make another cut at the top of the front panel, to adapt it to the angle of the slope. The elements must be glued and screwed, once everything is positioned correctly. Glazing installation requires the preparation of the two glass frames’ 4 crosspieces and 4 poles.

Building the tenons will require a router, hand saw or wood chisel. The mortises can be carved with a router. A rabbet should be installed inside the frame to receive the glazing. The glass, held together by spikes placed every 8 to 12 inches, will be positioned and secured with a sealant. After drying, the glass frames are installed on the frame with hinges. Installing butt straps between the two glass parts, and stops in order to keep the window frames open, will make the cold frame operational.

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Published in Basics by Alexander on 06 Jul 2011