I'm building a simple bench-style couch and need some advice on the strength of pine. Recently, my husband fell through a cheap pine dining chair, which has made me extra cautious. I'd like to use 76x76 mm (about 3x3 inches) pine for the frame. For the slats under the cushions, I'm considering using reclaimed pallet wood that's 18 mm thick (slightly over 11/16 inches). I'm worried whether this will hold up enough to support some of the heavier guys in my family, many of whom are over 6 feet tall and weigh more than 100 kg. Ideally, I want the couch to safely support up to 400 kg across its 1880 mm width. How many supports do I need between the ends? If 18 mm is too flimsy, would using thicker 25 mm or 38 mm planks be better? Sorry for the metric measurements; it's just what's available here. I'm also anxious to avoid any injuries to my loved ones!
3 Answers
I think you're overthinking this a bit! Pine is actually incredibly strong—it's used in building houses, after all. For your design, I’d recommend adding a support in the middle of each section of the couch. That should be more than sufficient to handle the weight of those larger guys in your family. Just make sure your joints are solid and choose pieces without a lot of imperfections, and you should be good to go!
While thickness matters, the joinery and overall design of your couch will play a huge role in how well it holds up. Good construction is key! I’ve built things using pine without issues, but yeah, keep an eye on how you're joining the pieces and avoid any wood with significant defects.
Using 76x76 mm pine for the frame is a solid choice! However, the 18 mm slats might be a bit too thin if you're planning to support heavy adults. If you're concerned, yeah, you should probably add a lot of intermediate supports—maybe every 15 cm or so, but that could make installation messy. Opting for thicker planks, like 25 mm or 38 mm, would give you better peace of mind.