Margin of Error: 1/4”
Most Common Mistakes
- Not leaving a space between the wall and the ledger.
- Not screwing ledger into something solid.
- Not using rustproof lag screws.
- Using galvanized washers with aluminum siding
- Not caulking holes before installing.
You probably think you are now ready to attach the ledger to the wall, but not quite yet. There is still one crucial detail you must attend to. The situation is as follows. If the ledger were attached directly against the wall, so that the back surface of the ledger was tight against the wall, rainwater running down the wall would get trapped between the wall and the back surface of the ledger. This would cause rotting. To avoid this you need to leave a small space (1/2”- 3/4”), so that water can continue to run to the ground.
The easiest way to do this is to install washers on the lag screws between the ledger and the wall. These washers should be hot dipped galvanized (HDG), which do not rust. Use aluminum washers if your wall is aluminum siding. Galvanized metal touching aluminum causes corrosion. These washers will leave an adequate gap. Also, if your siding is not flat but has different surface levels (beveled siding, aluminum siding, shingles, etc.), more or fewer washers can be installed on the top screws than on the lower ones, to compensate and cause the ledger to be installed true vertical.
After you have threaded the lag screws into the ledger, installed the proper number of washers on each screw, and squirted caulk into the holes, lift the ledger into place, tap the screws into the wall, and, with a socket or crescent wrench, tighten the screws. Be sure that the screws are biting solidly into the wall, especially the last 2”. You are now ready to install the two edge joists and locate your pier holes.
If you are using pressure-treated lumber or a decay resistant lumber that is not all heart, we recommend that you paint a waterproofing on the cut ends of the ledger and all other exposed boards.
Tip: Use a combination square and mark a perpendicular line across each joist so that you can place all your nails in a straight line.