Maintaining your building Tanalising All of our timber buildings are tanalised. This means the timber has been impregnated with a wood preservative called Tanalith E. This preservative is fixed into the timber and cannot be removed. However, be rest assured that the preservative is not harmful to people or the environment. We tanalise our buildings because it increases their lifespan by making them resistant to fungus, insects and rot. You might notice that our timber sometimes takes on a slightly green appearance. This is due to the impregnation treatment and this normally wears off with use. Waterproofing It is important to note that tanalising does not make our buildings waterproof. You will need to apply an oil-based sealer yourself to make your building waterproof. We do take measures ourselves to prevent water from entering (e.g. with roofing felt, silicon beading and facias) but this does not make our buildings completely waterproof. So, we highly recommend that you invest in waterproofing treatment, especially if there will be electrical appliances inside your garden building.