Subtrade Sabotage

Surface-mounted exterior fixtures (electrical meter bases, shutters, dryer vents, hose bibs, etc.) should always be fastened to mounting blocks (Figure 6).

Figure 6. Subcontractors can create problems when they fasten exterior fixtures directly through the siding panels, because the fasteners will prevent the siding panels from expanding and contracting freely. Use mounting blocks for all surface-mounted fixtures.

The rationale is simple: Any item that is fastened directly through a siding panel will lock the panel in place, short-circuiting the nailing slots that allow the panel to expand and contract. Most suppliers keep a number of prefabricated mounting blocks in stock. Larger items (meter bases, for example) can be mounted on a 11/2-inch-thick piece of treated lumber. No matter how careful you are when allowing for expansion and contraction, a subcontractor can undo the best-laid plans of a quality siding installation in less than ten minutes. Plumbers, electricians, and the phone company installers should mount all of their devices or equipment on mounting blocks. The general contractor is typically responsible for providing the siding installer with the type and location of required mounting blocks, but in many cases, the evil deeds are done long after the project is completed. It's always a good idea to explain to both the general contractor and the homeowner what can happen if items are fastened directly through the siding. It may not always prevent problems, but at least you'll be able to say "I told you so."

It's essential that vinyl and aluminum products be allowed to expand and contract freely. The photos illustrate what happens if movement is restricted.

A sliding panel that is not pulled up snug in the locking flange may come loose when warm temperatures cause yhe panel to expand (left). A panel installed in hot weather with the nails driven too toghtly will tear when cold weather causes the panel to contract (right). To reduce the chance of problems, follow these guidelines:

• Think of vinyl and aluminum products as being hung, not fastened, in place. To prevent nails from restricting panel movement, installation literature specifies a 1/32-inch clearance between the nail head and the siding panel. I like to tell installation rookies that they should be able to slip the hook end of their tape measure between the nail head and the siding panel. All it takes is one overdriven nail to create problems.

• Adjust the recommended gapping (typically 1/4 inch) to allow for current temperatures. In extremely cold weather, use a slightly larger gap, since cold panels will be on the short side of the expansion and contraction cycle. Conversely, it doesn't hurt to tighten up the gaps in very hot weather.

•Be sure to place all nails in the center of the nailing slot. A nail shank that bottoms out in the nail slot of an expanding or contracting panel will restrict movement.

•Pull each panel up snug against the locking hem of the previous panel, but do not overtighten. Panels that are pulled too tight can tear when they contract, just as loosely fit panels can pop loose as they expand.

•Fascia runs should never turn the corner. Stop all runs at inside and outside corners and slip a small corner insert behind the fascia to mask the subfascia.