Hi, I'm looking at erecting a small pergola, only around 2.4m square, really only to provide some shade to a small garden patch, but don't want it to look too heavy & bulky. I already have four 100 x 100 mm treated pine posts which I'll use, but want to keep the beams and rafters as light as possible. Can anyone suggest appropriate dimensions for the wood? I've seen that treated pine at 280mm x 42mm for beams and 185mm x 42mm for rafters is recommended, but I'm hoping I can safely get away with something less heavy given the relatively small size. Any suggestions would be greatly appreciated. Many thanks.
Let me mention our resident D.I.Y. expert @MitchellMc who will be more than happy to help with your question.
While you plan out your build, you may also find these projects and discussions helpful:
Feel free to post any questions along the way, and we'd love to see progress photos as you tackle this project.
Many thanks for your question, @Smithrj.
I note you will use this pergola for shade. Are you planning on adding roofing to assist with shading your plants? If so, this could determine what size timber you'll need.
You might like to read through @ProjectPete's discussion on his poolside timber cabana build. You'll see that he has used timbers closer to Woodhouse 138 x 42mm x 5.4m F7 FJ H3 DAR LOSP Structural Primed Radiata Pine rather than the larger beams in the guide. I believe 138 x 42mm would likely be the minimum size suitable to span 2.4m unsupported and could be used for both the beams and rafters. The next available size down from that would be Treated Pine Outdoor Timber Framing 90 x 45mm, and over a 2.4m span, it could potentially sag.
Please let me know if you have any questions.
Hi Mitchell, many thanks for the information. There won't be a solid roof - I was just thinking of placing battens across the top running east-west and spaced appropriately to provide a bit of dappled shade from the northern sun. The 138 x 42mm option sounds good, and I agree that 90 x 45 will probably droop a bit, so won't use that size. One final question - would it be necessary to rest the rafters atop the beams, or would joist hangers be sufficient given the rafters smaller size? I was planning on fixing them at 600mm intervals, so there will only be about five of them. Thanks again.