Wood selection for framing and cladding: do the math

I’m evaluating different materials for cladding the walls of the van, and for building frames and panels for furniture (bed, kitchen units, etc.)

Commercial outfitters here in the UK use materials I find unappealing, whereas DIY convertors often stick to what they can find in the out-of-town DIY store. I’d like to weigh up – literally – the pros and cons of a few approaches that are in scope for me.

Absolute weights

Weight is a key factor, not least because of the payload limit of the van. But also efficiency, handling and sizing. I consulted a few sources to find out the weight of different wood types. The excellent Collins Complete Woodworker’s Manual gives ‘average dried weight’ for a range of hard and soft woods. (This is just a selection of woods that are available to me, and might be appropriate.)

Soft woods

  • Sitka and Norway spruce — 450 kg/m3
  • Pines (White, Ponderosa, Yellow) — 420 – 480 kg/m3

To verify, I weighed some 44mm square batons I bought from Wickes (the same product is also available at B&Q). It’s usually labelled as ‘whitewood’ or  spruce. It worked out at 423 kg/m3.

Hard woods

  • European beech — 720 kg/m3
  • American white ash — 670 kg/m3
  • American white oak — 770 kg/m3

Plywood

My local timber merchant also stocks lovely BB Grade Birch Plywood, and they gave me the specs for a couple of thicknesses:

  • 12 mm 8×4 sheet — 25.25kg (707 kg/m3)
  • 9 mm 8×4 sheet — 19.50kg (728 kg/m3)
  • 6 mm — extrapolated: 749 kg/m3
  • 18 mm — extrapolated: 665 kg/m3

These are the woods and panel materials that are available to me (discounting the crap I don’t want to touch).

Wall cladding

Many DIYers seem to go for either cheap plywood faced with car felt, or wooden cladding boards, made from spruce or maybe pine.

I like a wooden finish, but those cladding boards are either thin or heavy. Here’s a typical review of some 8mm spruce cladding (just labelled ‘softwood’) from a DIY store:

At least 20% of these poor quality timbers where so warped, bent or sub standard that they could not be used for the project. They are only finish sanded on one side witch means that you cant switch boards around to hide knots and holes where knots where.

Large chunks where often taken out of the tounges or groves making them incredibly hard to fit together. Every single piece is labled with an incredibly sticky label that is impossible to peel off on the face side of the board making for a enfuriating few hours of peeling and scrubbing.

This chimes with my experience too. You could go for thicker boards, but then you’re looking at some serious weight. To clad an 8′ x 4′ area with 14 mm softwood cladding would weigh about 18.8 kg. The same area in 6 mm birch ply (which has a lovely finish) would weigh about 13.4 kg.

There are other factors of course, (how well does the cladding conform to the curves of the van, does it need to bear weight or hold a screw), but the weight and aesthetics certainly point to the thin 6 mm ply as a good option.

Furniture framing

I’ve made lots of furniture out of stud timbers and that 44mm section whitewood. It’s fine, and in certain orientations and thicknesses, adequately strong.

But I’m interested in using something that cuts more cleanly, is stronger and has some flex for the construction of cabinet and bed frames. Ash looks promising here. I need to do some practical experiments – and more research, but the weight difference doesn’t look too bad, especially when you consider you could get away with smaller cross-sections of wood for many applications in the van.