The Importance of Roof Ventilation


An approximately 35-year-old home required a second floor renovation. The owners wanted to give the second floor a fresh, new look, while also improving insulation because of unusually high heating bills.
During the demolition phase of the interior drywall, we discovered mould on the underside of the roof plywood. We investigated and found out it was caused by several factors.
First, the roof had been redone several times with asphalt shingles under a final layer of metal roofing. This technique appeared to trap in moisture that created a space where condensation was unable to escape.
Second, the ceiling insulation was insufficient and stuffed against the exterior soffit vents, which reduced airflow.
Third, the concrete cinder block chimney was deteriorating and water was seeping through cracks in the mortar, allowing moisture into the attic space.


We placed an additional piece of 2x6 lumber on the edge of the roof trusses to allow for extra insulation where the wall meets the ceiling. We then built insulation baffles out of plywood with 2” air space to allow for proper airflow to the soffit vent. The insulation baffles created a space where insulation could be fitted tightly against the underside of the baffles, while still allowing air to freely pass in the cavity above without any restriction. All layers of old asphalt shingles were removed and new plywood was installed on the roof with a continuous ridge vent across to allow for proper ventilation in the attic space. The cinder block chimney was beyond repair, so we removed it completely. Water was found inside the pockets of the cinder blocks, creating a high humidity environment inside the attic. The removal of the chimney also created a better view and opened up the space to the master deck. With added insulation and proper ventilation in the attic, the owners now enjoy substantially lower heating bills and a comfortable home.