There are various terms and descriptions used to describe timber garden buildings and structures and it's important to understand what these mean in order to make an informed buying decision. 

Tongue & Groove

Tongue and groove (T&G) timber is used in high quality building construction - often for the roof or floor. It is a smooth, planed, interlocking board.

OSB

OSB is the acronym for Oriented Strand Board, also known as waferboard, sterling board, exterior board and smartply.

It is an engineered wood product formed by bonding layers strands or flakes of wood together to form a sturdy board.

It is often used for shed and garden building rooves and floors and is considered an adequate material for the purpose, however not as robust as a tongue and groove finish. 

Pressure Treated Wood

Pressure treated wood has had a liquid preservative forced deep into the timber to protect it against deterioration due to rot or insect attack.

During the treatment process, the finished timber is placed into a large container containing the preservative treatment. The container is sealed and a vacuum applied to force the treatment into the structure of the wood. Excess liquid is drained and recycled.

The deep nature of the preservation within the wood means it is suited to longer term outdoor use where ordinary, untreated wood would deteriorate. It is still recommened that pressure treated wood receives an annual wood treatment to maintain the product and for it to last longer.

Pressure treated wood can sometimes have a green residue on the surface which can be mistaken for mould. It is in fact surplus residue from the treatment and will gradually weather off or if preferred, can be lightly sanded.

Pretreatment of Garden Buildings & Structures

The majority of garden buildings and structures are supplied with a factory base coat or honey glaze. This treatment is only for protection during storage and it is recommended that you treat the building with a high quality preservative during assembly and annually thereafter. 

If stated, some buildings and structures are pressure treated. This means the products are pretreated under pressure to ensure the treatment is forced deep into the wood for a long lasting protection against deterioration by rot and insects. Although pressure treated products do not require an immediate treatment, it is recommended that an annual treatment is applied to keep the product maintained. 

Timber Quality

Wood is a natural material used in a wide range of construction projects and is known for its sturdiness, elasticity, noise reduction qualities and overall aesthetic appeal as a result of its natural characteristics. It will also change over time and may swell, shrink and crack, release resins, display marrow, gnarls and graining, show inconsistent smoothness and ruggedness, release salts and exhibit pinholes and fungi/ mould.

All of these characteristics are expected with wood and can be explained as follows:

• Swelling, shrinkage and cracking is caused by the humidity in the atmosphere altering the volume of the wood.
• Resins escape from the wood usually in the first year following manufacturing. They fall off naturally or may be planed.
• Marrow, gnarls and grains are unique, natural characteristics of the tree.
• Rugged areas are where the natural texture of the wood differs and despite milling, cannot be removed.
• Salts, mould and fungi are caused by the humidity in the atmosphere and are usually a temporary phenomenon.
• Pressure treated wood often shows markings that may appear to be mould, but are in fact a build up of the treatment applied which may be removed by hand or will gradually weather away.
• Pinholes are produced by small xylophagous insects. These insects were killed while processing the stem into the end product.
• Wood, the same as any natural material will never be 'perfect' as the beauty of the material is the variation in colour, texture and finish.