Why Do Hip Roofs Contain Mold? A Home Inspection I Performed in Averill Park NY: Hip Roofs
A Home Inspection I Performed in Averill Park NY.
I decided to write this blog after performing back-to-back inspections for 3 days in Averill Park NY and discovered mold within the attic of all 4 structures and they had a few things in common. The homes were all located within a 3-mile radius in Averill Park NY and contained hip roofs, all of the attics contained mold and all of the homes I performed home inspections on the attic did not contain adequate ventilation. I came to realize most hip roofs I inspect contain mold, so I put together this blog to go over hip roofs and the pros and cons of hip roofs and the reason mold growth is prevalent in attics that contain a hip roof.
What is a Hip Roof and the Advantages?
A hip roof general design is ideal for protection against severe weather. The design of the roof has an advantage in areas that contain high winds reason being all sides of the roof are angled toward the ground reducing the exposure to upward drafts. Most hip roofs are walkable, do not contain valleys which makes them a little easier and cost efficient to repair or replace.
What Are the Disadvantages of a Hip Roof?
Generally speaking, in upstate New York & Averill Park NY roofs typically start venting from the soffit (outside air enters the soffit) and exhaust through the ridge (the peak of the roof). The ridge vent runs across the peak of the roof and pulls the air through the soffits and exhausts through the peak. The design flaw I see with homes I have inspected is the lack of ridge vent - which is the vent that runs across the peak of the roof that allows air to escape from the attic. See a picture below of a general venting setup.
The Image to the left represents how the ridge vent runs the entire peak of the roof.
The picture to the right represents a home in Averill Park NY that contains a small ridge vent. Additionally, the soffits are smaller than usual, so the intake of air is reduced. The home inspection revealed excessive mold on the sheathing noted in the attic and the further assessing of the ventilation was recommended.
Hip roofs are a challenge when trying to establish proper exhaust for ventilation due to the reduced size of the ridge vent.
The argument between which ventilation is the most economical, effective and reliable varies within the industry.
Some professionals will advise that a power vent or a couple of box vents on top to help pull the air - will correct the ventilation issue as long as the soffit vents are present. Other professionals will advise that mixing ventilation types will not be effective I.E adding a fan/box vent to a roof that contains a ridge vent as the 2 different types of ventilation will work against each other.
Unfortunately, in the 4 homes I inspected in Averill Park NY - 2 of them contained the setup noted in the picture above (ridge vent with power vent fans) and mold was still present. The 3rd and 4th home I inspected in Averill Park contained just a soffit and ridge (small ridge) that wasn't sufficient as mold growth was present.
Overall, there is not one method of correction or theory that applies to all. Generally speaking, an attic should contain a proper balance of lower ventilation along with upper ventilation. Approximately 50% of the attic ventilation should come from the lower portion of the roof. The other 50% of the ventilation should come from the peak and or near the peak. Meaning the area that is open near the ridge and soffit should be similar in overall size. An imbalance of ventilation can lead to the loss of conditioned within the home. If the attic contains too much ventilation near the ridge and not enough ventilation opening near the soffit the attic could pull conditioned air from the habitable space below cause condensation on the sheathing which can lead to energy loss and mold growth.
Although this isn't a hip roof the picture below represents the idea of an attic that contains - well balanced ventilation.
Due to the complexity of attic ventilation in hip roofs, air leakage within the attic, soffit, roof and ridge design it is always recommended to call a qualified contractor to further assess the attic to prevent mold growth. A qualified contractor may be a roofer, mold assessor, architect and or general contractor. If you have a hip roof and have questions regarding mold within your home search the web for reputable home inspection companies.
Looking to read more about ventilation? Check out our other blogs!