Fire Resistance Wall Calculator

Under the National Annex to BS EN 1996-1-2, a 100mm single-leaf wall of hollow or cellular (Group 2) aggregate blocks achieves 60 minutes, while 100mm solid (Group 1) dense or lightweight aggregate blocks achieve a full 2 hours (120 minutes) loadbearing. The governing factor is the unit configuration to BS EN 771-3 — solid (Group 1) versus hollow/cellular (Group 2) — and the wall thickness, not the block density alone. A 100mm aircrete (AAC) wall achieves up to 2 hours loadbearing. A ≥10mm gypsum plaster coat (to BS EN 13279-1) on both sides gives a small uplift, but a cement/sand render does not count. Mortar must be fully filled to BS EN 1996.

Yes, a single layer of 15mm fire-resistant plasterboard (such as Gyproc FireLine) on each side of timber or metal studs with mineral wool insulation in the cavity can achieve 60 minutes fire resistance. This is a tested detail from British Gypsum and other manufacturers. Standard (non-fire-rated) 12.5mm plasterboard typically needs two layers each side for 60 minutes. Always follow the manufacturer tested specification including fixing details and joint treatment.

Metal stud walls can achieve high fire resistance ratings depending on the plasterboard specification. Per British Gypsum GypWall Single Frame tested data (BS EN 1364-1): single layer 12.5mm board each side gives 30 minutes; single 15mm FireLine each side with mineral wool gives 60 minutes; two layers of 15mm FireLine each side (92mm stud) give 120 minutes; three layers of 15mm FireLine each side (146mm stud) give 180 minutes — the maximum for a single-frame stud partition. A 240-minute rating needs a specialist twin-frame or ShaftWall system, not simply more FireLine layers. Metal studs perform well because steel does not contribute fuel to the fire, though they lose stiffness at high temperatures.

Yes, mineral wool insulation within the stud cavity significantly improves fire resistance by slowing heat transfer through the wall. For 60-minute timber stud walls, mineral wool in the cavity is typically required as part of the tested specification. Stone wool or glass wool (non-combustible, Class A1) should be used. Combustible insulation such as PIR or EPS in the cavity would compromise the fire resistance and is not part of any tested fire-rated stud wall detail.

Wall fire resistance is tested to BS EN 1364-1 (non-loadbearing) or BS EN 1365-1 (loadbearing) in an accredited furnace test. The wall is exposed to the standard fire curve and assessed for integrity (E — preventing passage of flames and hot gases), insulation (I — temperature rise on unexposed face) and loadbearing capacity (R — structural stability). Manufacturer literature provides tested details. In the absence of test data, tabulated values from BS EN 1996-1-2 (masonry) or BS EN 1992-1-2 (concrete) may be used.