Using extended coverage sprinklers instead of standard spray sprinklers offers a great opportunity for contractors to save money, however the rules for laying out extended coverage sprinklers are very different to those for standard coverage.  This article looks at the rules for avoiding sprinkler obstruction and why some projects may be unsuitable for extended coverage sprinklers.

The ideal case for extended coverage sprinklers is a large open plan area with a suspended ceiling which is flat and level with no protrusions.  If a ceiling has surface mounted lights, it might not be a suitable candidate for extended coverage sprinklers.  Arranging standard spray  sprinklers around 80mm deep light fittings, is not difficult.  NFPA 13 requires standard spray sprinklers to be at least 450mm away from the lights to avoid obstruction to spray.  This is not difficult to achieve because it’s less than the width of one standard ceiling tile, however  If you are using extended coverage sprinklers, it’s more difficult.  The required clearance from lights increases from 0.45m to 1.2m which is the width of 2 full tiles.  The lighting layout can significantly restrict where you can locate extended coverage sprinklers.  Of course if the lights are all fully recessed, they aren’t going to cause any obstruction at all.

Ceilings often have exit signs and wayfinding signs which can disrupt the sprinkler layout.  Even a small 240mm exit sign will need to be coordinated with the sprinklers.  A standard spray sprinkler will need a clearance of 900mm from the exit sign (which is not that difficult to accommodate, it’s only one and a half standard ceiling tiles).  It’s quite different if you are using extended coverage sprinklers, the required separation inconveniently increases to 2m (6’6”).  The designer will have to locate sprinklers carefully to accommodate every single ceiling mounted sign.  You also need to pay attention to minimum spacing between sprinklers.  Extended coverage sprinklers have a minimum of 2.4m (8’) of separation compared to 1.8m (6’) for standard spray.

These examples show that any protrusions below the ceiling could cause issues when using extended coverage sprinklers.  As well as time and money to install pipe work, the owner won’t like the look of the sprinklers if they aren’t in nice ordered grids.

What about buildings with no suspended ceiling?  This may or may not be a suitable building for extended coverage sprinklers.  Both types of sprinklers need to be installed close to the underside of the roof – usually within 305mm (1’).  If the underside of the roof is also crowded with ducts and lights and solid beams, it’s going to be challenging to do any type of sprinkler layout – extended coverage sprinklers should probably be avoided as the rules for sprinkler spacing will make things too difficult.  If the building has open trusses instead of solid beams and the lights and ducts are suspended some distance below the underside of the roof, then this could be an ideal building for extended coverage sprinklers.

For buildings with no suspended ceiling, you also need to be mindful of the ceilings slope.  Extended coverage sprinklers are limited to a slope of not more than 1 in 6 (or 9.5 degrees to the horizontal).