How to Build a DIY Cold frame with Polycarbonate

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Cold frames are a great way to raise young plants in a safe and warm growing environment.

These miniature greenhouses are particularly useful for hardening of plants during their transition from inside to outside. There are many different possible cold frame variations to build yourself or to buy on the market.

Generally there are two typical flaws most cold frames have; being too static or lacking in height. Many cold frames have a heavy brick and concrete base, this makes it difficult move them.

Secondly, as many cold frames are not that tall some plants soon outgrow them before the weather warms up.

​Consequently, in this article, I show you how to build a DIY coldframe with Polycarbonate which is both tall and mobile. The DIY cold frame has a 47mm timber frame for extra strength and durability. 
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Shopping list

• 6 Lengths of 2.4 metre long 50mm x 50mm timber
• 4 sheets of 6mm thick Polycarbonate at 1200mm x 600mm
• 2 tubes of 290ml flexible weather proof grab adhesive
• Sealant gun
• 50mm corner brackets
• 12mm wood screws
• 80mm long external grade screws

Tools you will need

• Electric drill
• Drill bits
• Extension lead
• Coarse wood saw
• Builders pencil
• Tape measure
• Set square 

How to build a DIY Cold frame step by step

Step 1: Measure and mark your timber

Your first step is to cut your timber into all the lengths you need. You will need 10 cuts at 500mm and 6 cuts at 1200mm.
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Step 2: Cut your timber

​Cut your timber into the desired lengths, when cutting; keep cuts as neat and as square as possible. This will allow your timber to fix together square and tight. 
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Step 3: Set out your frame

​Set out your timbers to create your three main rectangles, you should have three rectangles and four side braces. 
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Step 4: Drill pilot holes

​Drill pilot holes through your frame where your corners are going to attach. When drilling try to keep your drill as square on as possible. You pilot holes will guide your 80mm screws and prevent them from splitting the timber. 
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Step 5: Screw your corners

​Place your corners on a flat surface so they are positioned tightly and square. Using a power drill screw your corners together with a single 80mm screw.
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Step 6: Attach your brackets

​When you have attached all your corners reinforce them by screwing in your corner brackets. 
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Step 7: Attach your connector braces

​Using a drill fix together your connector braces to form the main body of the cold frame.
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Step 8: Cut your polycarbonate

​Cut your polycarbonate where necessary with a sharp Stanley knife and straight edge. This will really only apply to your 600mm x 600mm ends. 
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Step 9: Apply your adhesive

​Using a sealant gun apply your adhesive to the outer frame; make sure you apply enough to form a good seal.  
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Step 10: Attach your polycarbonate

​Place your polycarbonate sheets onto the frame; apply pressure around the edges to ensure a good grip. If you have sheltered garden with little wind the adhesive may be enough to hold your polycarbonate. 
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Step 11: Fix your polycarbonate

​​More often than not it is best to fix your sheets down with fixings. This can be achieved with timber beading, glazing bars or even screws and washers.
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Thank you for reading my article on how to build a DIY cold frame with polycarbonate.

​If this article helped build your own cold frame you why not share it with your friends.

Below I will include some other articles you may find relevant. 

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