making cold frames from old windows

We recently had our windows changed, and the old ones had secondary glazing fitted to the original single-glazed frames. The secondary glazing was aluminium-framed and mounted on the inside of the windows, running in channels, and it seemed criminal to waste it when the Oak Tree needed cold frames.

Finished Cold frame
Cold Frame made from two secondary glazing window panes

By matching up the front to back dimensions I ended up with four usable pairs of panes. The widths of the panes were all different, but this was not a problem. The frames were made of 2×2 inch pressure-treated wood and the cheapest way of doing the siding was using weatherboard, which ends up with quite a pleasant appearance.  About £120 worth of wood means we now have four decent sized cold frames about 50 inches deep and 70 to 90 inches wide.

Big cold frames can be surprisingly expensive – this large cold frame is smaller than our smallest one can costs more than what all four cost put together, showing that going DIY really scores on saving costs, we got £800 worth of cold frames for less than a quarter of the cost!

Timber carcass of the cold frames during assembly
The cold frame being constructed

Window companies usually trash the large fixed window panes in the process of removing them – they take the glass out then make some saw cuts in the frames, collapsing and folding them out of the opening. However, the openable side panels can usually be salvaged intact if you ask the guys nicely. With older wooden frames you even get a nice set of hinges to mount to your timber frame. We were particularly fortunate in that the secondary glazing meant that we could recover the large panels intact, saving the glass firm trade waste and re-using them.

I also discovered the value of local firms here. I sourced the wood from a local sawmill, Nelson Potter Ltd. I have no table saw or other power saw, but taking the dimensions to them James kindly sawed the pieces to the correct lengths, which also made it a lot easier to transport. However, I forgot one piece, so on a Sunday I thought I would get this from B&Q, since Potter’s are a bit far away for just one piece of wood.

I located a piece of 2×2 pressure treated wood, and thought I’d make use of their cutting facility. So I wander up with my piece of wood, and I observe I can have four cuts. After that it is some outrageous price per extra cut, but fair enough. I only need one to be able to get the wood into the car. So I press the button, and after a while the guy comes up. I’m out of luck though. Sharp intake of breath “oh no sir, pressure treated wood. Contaminates our waste sir, we can’t do that”. So I have to buy the wood as is, and take it out in the car park and use my own tenon saw to cut it, across a trolley. They wouldn’t even loan me a saw to do it because of ‘elf ‘n’ safety.  Jobsworths. I knew they wouldn’t lend me a saw (they used to years ago) as I’ve been had by their game before. I’d have to buy the damn thing, which is why I always have one with me if I am buying material too long for the car. To add insult to injury, the one timber cost more than twice as much as it would have done from Nelson Potter’s.

How not to join the corners 🙂

I am no talented carpenter. It did disturb me at the time to be screwing into the end-grain of the 2×2 pieces of wood, and I have since learned how I should have done this had I started over, with the risers on the inside of the horizontal frames so I could have avoided the ends. However, the weatherboard gives the whole thing more structural integrity – these are pretty solid in their final form despite the dodgy carpentry practices. It goes without saying that screws, nails and any other hardware needs to be galvanised or otherwise plated.


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