What is ’27 plus’ graphite?
Like regular white bead, it is expanded polystyrene granules, but with added fire retardant and performance enhancing qualities.
The insulation industry used white polystyrene beads for years. Why the change to graphite (grey bead)?
The main reason is to accommodate the new building regulations that require a U-value of .27 in new walls. With white bead this standard cannot be achieved in a regular cavity, but by using graphite ’27 plus’, the new requirement can be satisfied.
Why can a builder not simply continue to use white bead and build a wider cavity to achieve the .27 U-value?
He can, but when a cavity wider than 110mm is built, changes will be required in the wall ties, foundations, lintels, etc.
How does the cost compare to achieving a .27 U-value by other means, such as insulation boards?
Blowing graphite bead can be as much as 40% cheaper than fitting insulation boards, as there are no storage, wastage or extra bricklayers costs involved.
Are there other benefits?
Many. Some boards fill the cavity completely but the risk is such that the Agrément Board insists on vertical DPCs on all corners. This is a bricklayer’s nightmare and it causes extra trouble and expense. In addition, to avoid water penetration, gaps more than 2mm between the boards must be filled with special foam by the bricklayer. Anyone with building site experience knows that this is asking a bricklayer to work to very specific tolerances he is not familiar with.
Some insulation boards leave a partial cavity, so these points you make do not apply?
Yes, but to leave a cavity of 50mm (recommend minimum), a wider than 100mm cavity may have to be constructed or special insulation block used in the wall if the .27 ‘U’ value is to be achieved. Again, this brings more expense.