I originally built this greenhouse as a 4m long structure, but later decided to add a polycarbonate greenhouse extension and increase the total length to 6m.
Instead of replacing the whole greenhouse, I decided to extend the existing frame by another 2 metres, bringing the total length to 6m.
The good thing about this type of greenhouse is that the frame is modular, so extending it was much easier than building a completely new greenhouse from scratch.
In this post, I’ll show how I added the extra section, connected it to the existing structure and installed the additional polycarbonate sheets.
Why I Decided to Extend the Greenhouse
The original 4m greenhouse worked well, but once we started using it properly, the available space filled up quite quickly.
Adding another 2 metres increased the floor area by 50%, without requiring a completely new greenhouse.
Since the original structure was still in good condition, extending it made much more sense than replacing it.
Preparing the Greenhouse Extension Frame
I started by laying out the additional frame parts on the ground next to the greenhouse. This made it easier to see how the new section would go together and to organise the curved arches, horizontal supports and connecting pieces before assembly.
Since the extension had to match the existing greenhouse exactly, I assembled the new frame section separately first rather than trying to build everything directly onto the old structure.
Assembling the Additional 2m Section
Once the parts were organised, I started assembling the arches and connecting them with the horizontal frame supports.
The basic construction was the same as when I built the original greenhouse, so the main job was making sure each section stayed straight and the spacing between the arches matched the existing structure.
After a few sections were connected, the shape of the 2m extension became much easier to see.
Connecting the Extension to the Existing Greenhouse
Once the polycarbonate greenhouse extension frame was assembled, I moved it into position next to the existing greenhouse.
The most important part at this stage was making sure the arches and horizontal supports lined up properly with the original frame. If the extension is slightly out of alignment here, it becomes much harder to fit the polycarbonate sheets neatly later.
After checking the position, I connected the new section to the existing structure and started adding the remaining supports to make the whole frame more rigid.
Installing the Polycarbonate Sheets
Once the frame was fully connected and stable, I started installing the new polycarbonate sheets over the extended section.
The sheets were large enough to cover the curved roof and both sides in one piece, so positioning them correctly was the main challenge.
Working with large polycarbonate sheets can be awkward, especially outdoors, because even a light wind can move them around. I adjusted the sheet carefully before fixing it permanently to the frame.
The Finished 6m Greenhouse
After the polycarbonate was fixed in place, the extension was complete and the greenhouse had grown from 4m to 6m in length.
The extra 2 metres made a noticeable difference inside. It gave us 50% more floor space and made the greenhouse much more practical without having to replace the original structure.
Was It Worth Extending the Greenhouse?
Yes, absolutely. Extending the greenhouse from 4m to 6m gave us 50% more growing space without having to replace the original structure or build a second greenhouse.
The extension took some time to assemble and align properly, but the modular frame made the job quite straightforward. Once the new polycarbonate sheets were installed, the added section looked and worked like part of the original greenhouse.
Looking back, I would definitely make the same choice again. The extra 2 metres made the greenhouse much more useful, especially once the plants started filling the available space.
If you’re interested in the original build, you can also see how I assembled this polycarbonate greenhouse from the beginning in my original greenhouse build guide.
Overall, the polycarbonate greenhouse extension was a practical way to gain much more growing space without replacing the original structure.