If the sagging occurred some time ago and has now stopped, and it is to an acceptable amount, then it shouldn't be a problem in the future.
As a rough rule of thumb, the amount of the sagging should not exceed one three hundredths of the span of the timber.
More often than not, for the sagging to be visible it may be as much as 50mm.
We must be concerned about the amount of sagging because it causes the tiles or slates to distort.
We overcame this problem by applying bracing to stop the trusses from buckling and the more recent roofs have the buckling built in at the start but the sagging on a modern roof may be the result of inadequate bracing.
In this work, the rheological properties and the sagging behavior of different grades of PP have been studied to assess their suitability in thermoforming operations.
The sagging resistance of PP and ABS was studied by measuring the polymer's melt strength using a Gottfert "Rheotens" Melt Strength Tester as described previously .
In thermoforming processes, the sagging of a polymer sheet is an extensional deformation.
The sagging behavior of PP and ABS was studied in an air circulating oven that was set at a temperature of 190[degrees]C.