First of all while most manufacturers have been developing new products and systems to achieve ultimate goals of energy efficiency, leading fenestration manufacturer Mumford & Wood Ltd has been at the forefront of this development and has set a benchmark in timber window design and manufacture. Achieving high performance windows that will look good for years to come requires the use of premier grade materials; here engineered timber takes centre stage. It provides strength and stability which will improve security, provide greater thermal performance, comfort and acoustics, and remain looking good for longer.
The timber required for high quality exterior fenestration not only has to be of a prescribed standard but must meet the performance standards laid down by the regulatory authorities in the UK and Europe. These classifications clarify the attributes and grades of timber and its suitability for use in the manufacture of exterior windows and doors.
European softwood is grown right across the continent on a line of latitude equal to London and northwards; the further south the lower the quality, the further north, the better. For example, the quality of softwood grown in Scotland and Wales is only suitable for fencing and garden buildings; in the very far north – north of the arctic circle in Russia, Finland and Sweden, the very dense, slow growing wood is the variety most suited for high quality joinery products.
This timber is taken from the heart of the tree where the real strength lies. In quite a short time – weeks not months – it will start to curve and twist unless treated and kept in perfectly humidified conditions. The heart wood is scanned for defects early in the process, a computerised action, identifying resin pockets and knots which are cut out. The clear parts are then finger jointed and glued in six metre lengths to create top quality, clear grade timber. Where certificated, wood is the most renewable, sustainable material on the planet. Today’s engineering techniques leave all the wood that is not used in the conversion process in the country of origin where it is recycled at source.
Independent tests have proven that an engineered component is 60% stronger than a piece of solid wood in the same section size which ensures stability and overcomes the risk of misshape. These components are purchased direct from European suppliers and specified in grain direction for each and every component size. This significantly improves stability, visual appearance and the performance of the paint finish as paint will not adhere well to over-dry wood.
Mumford & Wood use Siberian larch, a European softwood, in their standard specification. It grows very slowly and typically produces timber that has tight growth rings and is darker in colour than sap wood. The logs are converted into vertical grain scantlings, finger jointed and then laminated into three, four and six part lamellas.
Indeed the closeness of the annual growth rings means very dense material which is almost naturally durable to meet the extremely testing climatic conditions of finished products in use in these regions. Siberian larch, for example, has a density of more than 600 kg/m³ and needs no further treatment to resist fungal or insect decay while European Redwood has a density of 510 kg/m² and being non-durable requires preservative treatment.
Timber for external joinery can also be sourced at a mid-point in this northern region, the area in both Finland and Sweden, north of Stockholm, known as the lower and middle Gulf. This material will find its way into volume commodity products mainly used in low cost multiple housing units or extensions.
Finally, the condition of the timber in terms of moisture content and technical properties such as density and dimensional stability are extremely relevant to the successful application in the finished installed product. Ideally the moisture content of the timber when received into the manufacturing environment should be no less than 12% and not more than 18%. The factory environment is vitally important as the relative humidity should be controlled to ensure the maintenance of the condition of the timber during the whole manufacturing process. Mumford & Wood’s state-of-the-art manufacturing facilities in Essex operate within these standards.