The Importance of Roof Ventilation

Trapped heat and moisture can raise energy costs, cause ice dams, and damage roof system components as well as structural and personal items located inside the attic where temperatures can easily reach 150 F (65 C). Condensation that forms inside attics can be caused by the use of washing machines, dish washers, bath tubs, showers, and tumble driers unless these items are properly ventilated through the roof. In some cases the condensation can be bad enough to be mistaken for a roof leak.

Here are some problems associated with an improperly ventilated attic space. Sumps between rafters (deck deflection) can happen because after awhile (sometimes several years, sometimes only a couple years), a plywood roof deck can warp or deteriorate and become spongy and dangerous to walk on. This occurs because one side of plywood decking needs be able to "breathe" by being exposed to circulating air. The adhesives used in the plywood can deteriorate or Dry Rot can occur because of condensation.

Water vapor will condense first on anything metal inside the attic; this will eventually cause the metal to rust. Heads can rust off nails, metal plumbing straps or straps holding HVAC ducting can rust in two causing the ducting to crash down on top of the ceiling joists or through a suspended ceiling. This problem is more common in humid climates.

In colder climates generally where the average January temperature is 32 F (0 C) or colder high inside humidity (40% or greater) combined with low outside temperatures can cause frost to form on the bottom of the roof deck. See Dry Rot in the glossary.

Insulation can trap moisture which will reduce the R-value of the insulation and create a nice environment for the propagation of certain molds, spores, and fungi which will also cause problems. See Dry Rot in the glossary.

There is also the problem of mildew which is both damaging and can cause health problems. The roof system itself will deteriorate prematurely.

Cooling units will need to be serviced or replaced prematurely because of excessive use. Ice Dams - ice dams are the result of melting snow continually refreezing at the roof perimeter and then backing up under the shingles and causing leaks. Proper ventilation used in conjunction with heavy insulation and an air barrier can create a Cold Roof Assembly which will help eliminate ice dams.

There are many types of attic vents available today. There are static vents, power vents, ridge vents, turbine vents, soffit / cornice vents, gable vents, starter vents, and cupola vents. These all come in a wide variety of sizes, styles and shapes. Some will ventilate better than others depending on the roof configuration, attic size, climate, etc.

To properly ventilate an attic, two types of vents are needed. Intake vents, which are located at the downslope edge of the roof (a.k.a. eaves) and allow fresh air into the attic; and exhaust vents, which are located near or on the ridge line of the roof and allow air to leave the attic. The use of an exhaust vent in conjunction with an intake vent uses the natural forces of wind pressure and thermal effect, collectively known as the Stack Effect, to ventilate the attic space. HINT: Make sure your attic insulation doesn't block the intake vents. If necessary, use baffles to keep the insulation back from it.

instantroofingservices.co.uk

Home Mold Test Kits