Polystyrene insulation

Things to think about

Can create a hazard

if not properly installed & maintained

Insulation standards requirements - NZS 4246

We install insulation to the requirements of NZS 4246:2016


NZS 4246:2016 has recently been updated and clearly states that contact between electrical cabling (with PVC coating) and polystyrene insulation should be avoided unless:

(a) the electrical cables are installed in a conduit;
(b) polyethylene or polypropylene tape is installed between the cabling and the polystyrene;
(c) special 'non-migratory' PVC sheathed cabling is installed; or
(d) there are clear separations between the wiring and the polystyrene


What we see in existing houses


In many instances, polystyrene has been installed poorly with sheets falling down as they have been overcut with gaps or not fixed correctly.  In this instance we usually recommend replacing the polystyrene with a mechanically fixed glasswool or polyester blanket underfloor.


What we cannot see is whether or not wires are touching the polystyrene.  This is another reason why we might recommend replacing the polystyrene with another product that does not require clearances or sheathing to existing wiring.


When polystyrene has been installed into ceilings, again the issue relating to wiring may exist, and also to recessed lights when present.  NZS does not offer guidance regarding the placement of polystyrene insulation in relation to recessed lights in ceilings.  In that instance a minimum 100mm gap would need to be maintained or removed completely to minimise safety issues.

Polystyrene 'chip' or 'beads':

We do see DIY installs using these products.  We strongly recommend that these are removed and replaced with compliant bulk insulation to ensure thermal performance and above all safety, particularly relating to electrical devices and cabling.