What To Avoid When Choosing Your New Garden Timber Building Supplier

TANALISED E pressure treated timber is impregnated with Тanalith® E, waterborne product based on copper triazole technology. Copper is derived from recycled sources and triazoles are organic biodegradable biocides, commonly used to protect many of the food crops we eat. TANALISED E pressure treated timber is usually specified for both in and out of ground contact applications where there is a medium to high risk of decay or insect attack.

•  An established and proven alternative to traditional chromated/copper/arsenate (CCA) treated timber.
•  Effective long-term protection against fungal and insect attack.
•  Proven performance, widely used and accepted worldwide.
•  Appealing natural green colour with excellent colour durability, blending perfectly with nature.
•  Impregnated using vacuum pressure technology.
•  Conforms to new European Standards and individual countries' national requirements.
•  Ideal for general construction, fencing, garden and leisure timber applications.

Avoid the use of shiplap cladding which exceeds the nominal width of 125mm (finished size after machining to 123mm) , shiplap cladding wider than 125mm has a higher tendency to ‘cup’ and split. Many timber building manufacturers use 150mm cladding as it is quicker to manufacture the building. The thickness of the shiplap cladding is less important as long as it is a minimum of 12mm. We use Tanalised T&G shiplap with a nominal size of 125mm x 16mm with a finished actual size on average of 120mm x 14mm with a 13mm tongue and a 14mm grove on our Hobbyshop & Proshop range timber buildings, this size of tonge and groove allows for the natural swelling and shrinking of the cladding.

All treated shiplap cladding will shrink as the material dries, if the building is facing direct sunlight the shiplap with shrink to a greater degree. Shiplap with a rebate or tongue depth of less than 13mm will have a tendency to separate if the building is in direct sun. Most timber building companies use a rebate or tongue depth of circa ≤10mm to increase the amount of area a board covers and so will use less boards to make the building. With this reduced rebate or tongue depth, if the boards shrink excessively, the boards may (and very often do) shrink beyond the rebate or tongue and groove and such create a gap on the external cladding. We only use shiplap with a 14mm tongue and groove  milled especially for our Hobbyshop & Proshop timber buildings.

As timber is a natural product, it is susceptible to shrinking, bowing, splitting and knots becoming loose. To successfully manage these common issues, it is important to manufacture a timber building using quality materials and 'best practice' construction methods. All our timber buildings use Tanalised timber framework and quality Redwood saw falling grade cladding.

Failure to apply 'best practice' when manufacturing a timber building will very quickly show areas where the new building begins to 'fail'.

Dimensional Timber shrinkage

In addition to being hygroscopic (gaining or losing moisture from the surrounding air), wood is also anisotropic. What this means is that wood has different properties depending on the direction or orientation of the grain—it’s not the same in all directions—and one of the areas where this property is most clearly seen is in dimensional shrinkage.

As opposed to a simple sponge or other isotropic material, wood (anisotropic) does not shrink in a perfectly uniform manner, and understanding this will help to avoid some pitfalls in preventing many shrinkage-related defects which may not crop up until months (or even years) after the wood product is finished.

A basic measurement of shrinkage—expressed as a percentage—is the amount that the wood shrinks when going from its green to kiln dried state. In other words, since wood in its green state is at its largest dimension, and kiln dried represents its driest (and therefore smallest) volume, green to kiln dried is a measurement of the maximum possible percentage of shrinkage; this is referred to as the wood’s volumetric shrinkage.

Volumetric shrinkage tells how much a wood species will shrink, but it doesn’t indicate the direction of the shrinkage. The two primary planes or surfaces of wood where shrinkage takes place are across the radial plane, and across the tangential plane, corresponding to radial shrinkage, and tangential shrinkage; these two values, when combined, should roughly add up to the volumetric shrinkage.

The amount a piece of wood will shrink lengthwise, called longitudinal shrinkage, is so small—typically about 0.1% to 0.2%—that it is usually inconsequential to the volumetric shrinkage.

Radial shrinkage in solid wood can vary from less than 2% for some of the most stable wood species, upwards to around 8% for the least stable species; most woods fall in the range of about 3% to 5% radial shrinkage. Tangential shrinkage can vary from about 3% up to around 12%; most woods fall in the range of about 6% to 10% tangential shrinkage. (Accordingly, volumetric shrinkage is typically within the range of 9% to 15% for most wood species.)

Avoid the use of undersized roofing timbers installed at spacings which allow the roof to ‘sag’. Choose a building which has roof timbers of a minimum 45mm x 45mm giving a cross sectional area of a minimum 2025mm² (the cross-sectional area is simply the 2 measurements multiplied together) and maximum spacings apart of 300mm. We use  full to size 45mm x 45mm Tanalised timbers for our Hobbyshop roof purlins at max. 400mm centres, and  a minimum size of 38mm x 63mm Tanalised timbers for our Proshop roof purlins at max. 300mm centres.

Avoid the use of budget grade roofing felt, choose a roofing felt which is Polyester based with a mineral felt coating (with a minimum weight of 2kg per metre/20kg per 10m role). Polyester based roofing felt has a high resistance to tearing, roofing felt tears are the most common form of roof failure on all timber buildings. You can test this yourself by asking to see a sample of the roofing felt used, put a crease in the sample by bending the felt over onto itself and if you can easily tear it along the crease or even just tear it from the edge of the felt the roofing felt should be avoided. We use Polyester based green mineral coated roofing felt at 2kg/m on  our  Hobbyshop timber buildings and a higher quality Ultrapol SBS Polyester Mineral Shed Roofing Felt at 2.5kg/m on our Proshop timber builidngs.

Avoid  buying a timber building where the door has not been manufactured to provide the best method of keeping the rain out of your new building, the door should have its cladding extended down over the floor to provide as good as possible rain seal (or a door cill provided), the same should be apparent at the top of the door to the door frame. Door stops should also be installed to avoid water penetration from the door shuts. Timber building doors are always problematic with water penetration so best efforts by the manufacturer should always be important in the door design. You will never stop heavy driven rain penetrating an 'opening out' timber garden building door but best efforts in construction seriously do help. 

Avoid buying a timber building where the windows are not adequately made weather proof with the use of a full frame window with window cill. The windows on both our Hobbyshop and Proshop buildings have a full frame with window cill and external window head cover fillets with 3mm glass.

• Please make sure your proposed new timber building can be installed in your garden without needing planning permission or building regulation compliance, ask your proposed  supplier to explain what you can and cannot have if you are in any doubt. If you install a garden building which fails permitted development guidelines or fails to be compliant with building regulations you will have to remove your new garden building.
• Our timber buildings are built to be compliant with the permitted development rights which allow you to install a timber building in your garden as long as the building size and location installed fit in with what is allowed.
• We will always offer you guidance before you purchase.
• Please click on the Permitted Development button above to find out more.