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30BUILDERS' DIGEST| OCTOBER-NOVEMBER-DECEMBER 2010IN THE FIELDWater can find its way into basements indifferent forms and by a number of mecha-nisms. Understanding these mechanisms andknowing how to water-manage foundationsand basements is important. When dealingwith the physical properties of nature weseem to need an occasional reminder that theforces in play are always bigger than we are.Sorting out water issues in basements is nota pleasant way to relearn that lesson. Thelaws of nature apply equally to existing base-ments and to new basements that are in theplanning stages or under construction. Flooding from the outside can occur fromsurface storm water that is directed into abasement, or from a quickly rising groundwater table. Flooding from a plumbing leakcan have the same effect if not quickly dis-covered. These events are fairly infrequent,but they can cause a lot of damage in a shorttime. Careful site selection for new buildingsand proper site grading for new and existinghomes will help to protect against floodingthat comes from the outside. Appliance over-flow trays and strategically located floordrains can reduce the impact of floodingfrom an appliance or plumbing failure. Capillary action is not an occasionaloccurrence. Porous materials that are in con-tact with water will draw the water into andthrough the material, like a sponge. Thismechanism works really well in concrete,and basement footings, slabs, and walls arealmost always sitting in water or wet soil.Unless there is an effective capillary breakbuilt into new basements, water will bedrawn to the interior (conditioned) side ofthe foundation assembly. Excavating aroundthe exterior of existing foundation walls toinstall waterproofing and drainage systemscan reduce the moisture load against thefoundation walls and also provide a greatopportunity to add exterior insulation.Unlike new construction, existing homeswere not built with capillary breaks under-neath the footings, slabs, and walls, andretrofitting them to be completely effectivemay be costly and difficult if not impossible.This means that the amount of moisture get-ting to the inside of the basement will have tobe evaluated to determine if it can be keptdry enough for use as living space. Newerbasements that have been built without effec-tive capillary breaks may also have highmoisture levels. Air transported water vapor enters base-ments through cracks at slab edges andseams and through openings in the slab likethose for plumbing traps. When there is highoutdoor humidity, warm, moist air can moveinto basement spaces when windows ordoors are opened and condense on coolfoundation surfaces. Gaps, cracks, and open-ings in the slab should be sealed with flexibleand durable materials, and doors and win-dows should be kept closed when outdoorhumidity levels are high. Once the openingsare eliminated, dehumidification equipmentwill have less work to do. Diffusion of water vapor through solidmaterials is another mechanism that isalways hard at work to move moisture intoWhere does Water inBasements come from?Quiz it.Q: Are there maintenancerequirements for exhaust-onlyventilation?Absolutely! There is a common misconceptionthat exhaust-only ventilation is much better sinceit has no maintenance requirements. It is truethat the maintenance might be less than withbalanced or supply-only systems since there is nointake hood to clog up or filters to clean.However, exhaust-only fans can have a numberof maintenance issues that can cause them toreduce air flow or fail entirely. Exhaust-only venti-lation is a system: a fan, ductwork, backdraftdamper, and exhaust hood. There are a numberof things that need maintenance and occasionalinspection to make sure the system is performingthe function for which it was intended. 1. The Fan - In most applications, the fan bladeswill need to be cleaned yearly. Dirty fan bladescan quickly compromise the flow. It is also impor-tant, especially with the quiet fans, to make surethe fan motor has not slowed down or stoppedcompletely. On occasion, you should recheck theflow with a flow box or even a garbage bag test(see page ??).2. The Duct - The duct should be installed to bedurable over a long period. However, it is quitepossible for someone to step on it, move it, orotherwise damage it while crawling through anattic or making other changes in the home.3. The Damper - Most systems have a backdraftdamper. This damper may be at the fan, at thehood, or - in some cases - a separate item. Thedamper can become dirty and the springs canfail. It is not uncommon for it to be stuck in theclosed position due to ice or dirt.4. The Hood - The hood should also be checkedyearly to be certain it has not become covered,damaged, or clogged.There is no such thing as a "no-maintenancehome" and the same holds true for an exhaust-only ventilation system.Pat Huelman, University of MinnesotaJanuary/February/March's Question:Are the 3 to 5 day activated charcoal radontest kits accurate?>>CONTINUEDTOPAGE58