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The headache of water intrusion

This is how the headache begins
photo by Rick Zimmerman

Yes, this is how water intrusion can begin. What was once a billowed blanket of crisp white snow along a roof ledge is transformed by a sudden blast of late winter or early spring sunshine into a spreading stain, meandering across the stone or siding or brick of an exterior wall. And water, being as relentless and as insidious as it is, will often find its way to a crack or crevice in or between building materials to enter the structure. Damaged wallboard, sodden insulation, stained paint finishes, shorted wiring, interior drips, musty odors, and the generation of mold may not be far behind. Such are the problems of unwanted water intrusion.

So exactly how does your average homeowner or building manager avoid the troublesome and potentially expensive headache of water intrusion?

Well, just about any competent architect or contractor will advise you to insure the integrity of your entire building envelope: the complete circumferential ‘skin’ of your structure that serves as the lone line of defense against the onslaught of unwanted water. That skin, consisting of roof and walls and windows and doors and floors, is what keeps water out and comfort in. So one must pay careful attention to exactly how all the component parts of a structure are designed, selected, configured, assembled, installed, and sealed. Not so easy a task, but one that can be understood rather simply.

Water intrusion will come at a structure generally from three directions: from above, in the form of sudden downpours or blown blizzards; horizontally, in the form of wind-blown rain and gusts of sleet (as well as the occasional flooding, perhaps); and from below, in the form of seepage up through slabs, and penetration of foundations and subgrade walls.

To protect from above, one needs to construct and maintain a well-functioning roof. First, steeply pitched roofs will shunt rain and snowmelt water down and away far more effectively than shallow pitched roofs. Low-angle roofs — those below a slope of 3:12 or so — can be especially troublesome, as they often allow snow, ice and water to tarry too long atop roofs, patiently awaiting their opportunity to find a pathway within. And, believe me, they don’t need much of a pathway; capillary action and forces of wind and pressure can telegraph water droplets deep within a structure’s manifold layers. Virtually all conventionally employed roofing materials are layered, for good reason. Through layering and overlap, one can work to block water’s penetration. Whether one is using slate squares, asphalt shingles, wood shakes, clay tiles or metal panels, it is the successive layering of multiple small units that facilitates the ready shedding of water with minimal migration or wicking. The use of small modular components not only facilitates their adaptation to any conceivable roof shape and size, but also ease the trouble of repair or replacement should damage occur.

Simpler roof forms are also better than complex, for the most vulnerable areas of any roof are its ridges, folds, seams, gutters, edges and eaves. All manufacturers of roofing products therefore readily provide detailed drawings and specifications to guide proper installation and use of their products. Regardless of what physical condition you might encounter in the design of a roof, the odds are quite good that a roofing product manufacturer has already encountered and provided product guidance for just such a condition.

Where roofs encounter walls, chimneys, vent stacks or physical transitions, flashing becomes a prime consideration. Flashing is the use of relatively small dimension sections of flat, thin-gauge sheet metal or synthetic material to effectively ‘bandage’ all exposed edges of roofing materials and their abutments. Again, flashing details and specifications are readily available from manufacturers.
Flashing also plays a key role in the prevention of horizontal water intrusion, for it is employed around doors, windows, skylights, and other such wall openings. Here too the manufacturers of those building components will offer guidance on the proper installation, flashing and caulking of their components into a given wall system. Never underestimate the value of simple caulk; by continuously and properly caulking every conceivable crack, crevice and juncture of materials on the exterior of a structure, one can not only cut heat loss/heat gain, but also prevent annoying chills from drafts.

In recent years, house wrap has become increasingly prevalent in the construction of homes, offices and other structures. Usually a composite fabric of paper and synthetics, house wrap is typically used to entirely ‘gift wrap’ a structure just before final wall finishes of brick, stone, stucco or siding are applied. Serving as an effective barrier against air infiltration as well as the water vapor carried by such air, house wrap can substantially improve the overall thermal and comfort performance of a structure.

Water penetration from below — through slabs, basement floors, foundations, subgrade walls and via flooding — is perhaps the most onerous water intrusion encountered by most homeowners. The first and best line of defense against such water intrusion is to go where the water isn’t. In other words, if at all possible, build your structure only atop a knoll, hill or relative high point, so that drainage water will always tend to race down and away.

If such is not possible, you then need to pursue further options. Ringing the entire perimeter foundation of a structure with drainage tile, at or even slightly below the elevation of any footings or foundations, will allow for the collection and diversion of water before it can even contact the structure. In low-lying or perennially wet areas, an additional ring of drainage tile inside the perimeter of the foundation and below any lowest basement slab, will form a second line of defense, keeping subgrade water pressure from dampening basement floor slabs or pushing up through a sump. A sump — or recessed pit — with a sump pump connected to an emergency generator is always a wise investment in any area subject to intermittent flooding.

Finally, one should always waterproof — NOT dampproof — subgrade construction. A vapor/water barrier should be placed beneath any subgrade slabs or floor construction, and all exterior surfaces of subgrade construction should be waterproofed. Avoid dampproofing products, as they provide no reliable protection against water intrusion. And remember that the best waterproofing products are always applied to the outer surface of the subgrade construction, where they do the most good. Such waterproofing is relatively easy to do during construction, not so easy after construction or as a retrofit. Virtually all waterproofing systems consist of multiple layered products: asphaltic or rubberized coatings, insulation or protection board, coatings, etc. Invest in the best waterproofing system you can afford.

If you take the time and effort to focus on all the sometimes maddening minutiae of protecting against water intrusion, you’ll likely be spared the headache of serious water damage to your structure.

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