What Causes House Attic Rafters to Pop?

Thermal Noise

• When the roof temperature changes drastically, dimensions of the roof actually change. The sheathing of the roof expands in sunlight and contracts at nightfall both in summer and winter. Movement caused by expansion and contraction distorts the roof slightly and makes the roof framing shift in relation to the stable interior house frame. Where rafters and other framing members meet, small shifts cause popping noises as the parts of the building adjust to the new stresses. Metal fasteners such as rafter framing plates also twist and pop under load. Roofs made of dissimilar materials such as metal roofing and wood framing make the most noise.

Loading Noise

• As a winter storm deposits snow and ice on a roof, the increasing load causes rafters to shift against joists, causing creaking and popping. Where heavy snows are common, structures meet higher standards and support greater weight. Stronger framing moves less under load, creating a quieter roof. In northern regions, roofs support up to 40 pounds per square foot, according to North Dakota State University. Southern construction styles support less weight. A cubic foot of heavy snow might weigh 20 pounds. Six inches of ice weighs more than 30 pounds per square foot. Uneven loading from heavy snow combined with ice dams can cause structural damage as well as pops and groans.

Ducts and Pipes

• Older buildings with galvanized iron plumbing sometimes make much less noise than modern homes with PVC pipes and central heating systems. Metal heating and air conditioning ducts and plastic pipes expand and contract with every change in temperature. Turning on the hot water in an upstairs bathroom heats pipes and causes pops and bangs if the PVC rubs against bare wood. When the furnace or the air conditioner runs, metal ducts in the attic expand or contract, popping as the surfaces rub on rafters and joists. When thermostats turn off, temperatures in the ducts change again, causing another sequence of pops and ticks.

Preventing Noise

• Keeping the roof in good repair reduces stress on the framing by keeping the upper framing dry and stable. Even a quiet asphalt shingle roof makes some noise. In aging roofs, many shingle nails have gradually popped loose, a signal that the roofing might need replacement. Slightly relocating attic ducts where they rub on rafters or joists can reduce thermal noise. Special fittings allow suspension of ducts, creating a quiet gap between the metal and the building's frame. Pipe supports and stud insulators do the same for PVC plumbing, separating the pipe from the wood frame with flexible brackets that expand and contract with the pipe, quietly.