How to waterproof wood siding

Wood-frame walls consist of studs and other structural members covered on the outside with sheathing, sheathing paper, and an exterior coating of wood siding, brick veneer, shingles, stucco, or wallboard. Such walls, when constructed with materials of good quality, should have long life if properly maintained.

Wood siding includes two types: drop or rustic siding and bevel or lap siding. Usually the finish siding is applied over sheathing paper and sheathing on wood studs. However, in mild climates or where economy is desired, the finish siding is sometimes applied directly to the studs without sheathing. Where sheathing is omitted or the type of sheathing used does not add strength to the wall in resisting racking loads, the wall framing should be braced at corners and at door frames with let-in or blocked-in diagonal bracing. This bracing should extend from plate to sill and be strongly nailed at each end and at intervening studs.

If the siding on a house is laid up with tight joints, the trim closely fitted, and window and door heads properly flashed to prevent water from penetrating the siding, the exterior of such a house will need little attention except repainting every 3 to 5 years. However, if water has been allowed to get behind the siding and dampen or rot the wood, the paint film is likely to blister and scale off. If siding is subject to alternate wet and dry conditions as a result of leakage, it is likely to warp, split, or decay. It is important, therefore, that all open cracks ,or defects which admit water into the wall and behind the siding be repaired and made watertight. Defective siding and trim should be replaced by new material applied to seal the joints, and sheet-metal flashings should be installed where required.