Sawn Timber 50 × 100 mm (2 × 4)

What it is

Kitovu sells sawn timber of 50 × 100 mm section, the size builders in Tanzania call 2 by 4 (mbao 2x4), at TZS 19,000 a piece from its stock in Zanzibar. It is the general-purpose size of a building site: joists and studs behind formwork panels, bracing for props, rafters and purlins in a roof frame, wall plates and frames for ceilings.

Length, wood and treatment

The price is per piece, and the length of a piece is not in Kitovu’s records yet; nor are the species and whether the timber is treated. Ask for all three on WhatsApp before comparing prices, because a piece price means little without its length. On the island, Zanzibaba Timber lists its 2 × 4 pine in 12 ft and 18 ft pieces, so both lengths are common. One metre of 50 × 100 mm timber holds 0.005 m³ of wood (our calculation), so an 18 ft (5.49 m) piece holds about 0.027 m³.

Treatment matters on Zanzibar, where termites attack untreated softwood in roofs and in timber that touches the ground. If the drawing or the roofer asks for treated timber, say so when you order. Hardwoods that resist termites by nature, such as mninga, are described on the mninga wood page; they cost more and are used for doors, frames and joinery rather than for formwork.

For lighter battens, Kitovu also has Sawn Timber 50 × 50 mm (2 × 2).

How it is used

In formwork. Under a slab deck, 50 × 100 mm pieces stand on edge as joists, with the plywood sheets laid across them and the joints between sheets falling over a joist. On walls they stand upright as studs behind the panels. Their spacing comes from the formwork design: the thinner the sheet, the closer the timbers. Kitovu sells the panels as well — Shuttering Plywood 18 mm for decks and 12 mm for vertical faces.

In a roof. In a pitched roof under mabati or tiles, the same section serves as rafters and purlins. Their size and spacing follow the roof span and the sheet maker’s purlin spacing, so take them from the drawing or from the roofer.

Counting pieces

Pieces for a run of joists or studs follow from the width covered and the spacing, plus one at the end (our calculations):

Counting pieces

Width covered	Spacing	Pieces in one row
4 m	400 mm	11
4 m	600 mm	8
6 m	400 mm	16

Each row needs pieces long enough to span the other direction, which is where the piece length matters again.

On site

Keep the stack flat on bearers off the ground, under cover, with gaps between layers for air. Timber that is used for formwork is cleaned of concrete after stripping and stacked the same way for the next pour.