The purpose of ventilating the attic is to cool the roof deck and reduce humidity in the summer and to prevent condensation in the attic in winter. Proper ventilation also keeps the attic cooler and reduces energy cooling costs in the summer. High temperatures can degrade the roof covering and deck, leading to premature failure. Moisture deposited as condensation in the winter moths and humid conditions in the summer months contribute to mold in the attic area and rot in the decking and other structural members. Sufficient ventilation is therefore vital in a well designed and constructed house as a preventative measure to ensure longevity of the structure and a healthful living environment in the home.
Modern warranty standards established by most roofing manufacturers now recommend a minimal ventilation intake of 9 square inches or more of net free area (NFA) per lineal foot of roof line. Ventilation outlets are recommended at an equal level. These are the minimum standards that must be met for most manufacturers’ warrantees for the roof covering to be in force.
Many existing homes with passive ventilation use a soffit intake and roof ridge outlet configuration. The existing soffit vents are normally punched vinyl or aluminum with a of a little over 6 NFA per per inch per foot of soffit overhang. As most existing soffits have 1 foot or less overhang, this represents a deficit of around 30% of currently recommended input NFA. This translates to most existing homes having inadequate input NFA when they have their roofs replaced, voiding their warranties for future damage related to inadequate ventilation.
To address this, commercial edge venting products or replacement vented soffits meeting the standard that provide the required NFA are available. These products represent a significant, but necessary, increase in replacement roofing costs. Homeowners sometimes do not increase ventilation to avoid cost or are not advised of the requirement because their roof replacement contractors are unaware of the current standards and do not advise the home owner accordingly.
New homes may not be constructed to current industry requirements. Sometimes this is due to a difference in building codes and the roofing manufacturer’s recommendations. Homeowners should be advised that as a result, their new home’s roof warranty may be compromised. Design changes should be considered in the planning stages for a new home’s roof to ensure that sufficient ventilation is included to satisfy warranty requirements, which may be in excess of the requirement in the local building code.
During a normal home inspection the existence of attic ventilation is verified, and the system is described as built. Suspected damage related to insufficient ventilation is pointed out, the expected repercussions explained, and a recommendation given for evaluation and repair by a qualified roof ventilation contractor. Homeowners should have the ventilation corrected at the time of any structural repair to avoid recurrence of damage.
Because of the myriad ways ventilation requirements have been included in the building codes, insufficient ventilation without apparent damage to the structure is seldom listed as a defect. The normal approach is to recommend further evaluation and correction of the ventilation deficiency to ensure longevity of the roof and attic structure and avoidance of mold production in the attic space. Ventilation correction, in the absence of current structural damage or the presence of mold, often falls to the new buyer as an improvement rather than a correction of the defect.
Homeowners are cautioned that insufficient ventilation has a direct causal relationship to structural damage and existence of mold. The limited visual, non-destructive inspection of the attic space may not reveal hidden or latent defects that can later be attributed to ventilation issues. The inspector may also have limited access to all areas of the attic because of lack of access or unsafe conditions, defects may exist.
Homeowners should be aware of current ventilation requirements, and where possible, seek to improve their home’s ventilation systems to protect the structure, avoid mold proliferation, and protect their roof replacement warranties. Use of trained, industry certified contractors is highly recommended to perform this work.
Stephen & John Bittner
© Bittner Property Inspections, LLC