Roof Condensation

Many roofs in mountain locations experience roof leaks even when there is no snow or rain. It’s a common occurrence here in the Tahoe, Truckee and Incline Village areas. What is it?

Most likely it is condensation and it can occur at the ridge and in the mid-span beams where the blocking is. We have seen this even in roofs that are properly vented.  Some homes experience this only once because of unusual weather circumstances and it never happens again. In other cases it will recur depending on the conditions both inside and outside the home.

I will explain the conditions that cause it and possible solutions. Water vapor is created inside a house when the occupants do normal daily activities like take showers or baths, wash dishes and laundry, cook and breathe. Some people even run humidifiers to counteract the dry mountain air.  This vapor naturally rises until it hits a barrier, where it regroups and starts to drip. To the homeowner is seems like it’s raining inside without any reason.

This can happen from time to time when certain weather conditions exist. It is usually always associated with an extreme cold event and when there is no snow on the roof. The cold air against the roof freezes any condensation or moisture to the underneath side of the plywood, even with venting, because it is so cold in the air space. Once it warms up or occupants get the home hot, the moisture can drip back through into the living space.

Last December we had one of those events and we received several related calls. The houses appeared to have good cross ventilation in the rafters, but the blocking may only have been V-notched and restricted the air flow. One thing that owners could do is add ridge vent to help air flow in the rafters. While this is not a guaranteed solution, it will definitely give the structure better air flow.

Even roofs with good air flow can experience this problem and it is prevalent in the Tahoe, Truckee and Incline Village areas, especially in the early fall and spring when  no snow sits on the roof to act as an insulating blanket from cold air over long periods. Also, many houses here are second homes and therefore unoccupied most the time; suddenly people will show up for their ski vacation, turn on the heat and create moisture–instant rainforest!

Roofs that are stacked truss and beam always seem to be the ones that have this problem. Some of the things we find are lack of venting at the ridge and lack of proper venting at the freeze blocks at the eave line. Other, more costly, problems can be lack of proper insulation baffles between the plywood and insulation, which allows the insulation to touch the plywood, restricting airflow. One other cause may be a lack of notching in the blocking between the rafters. These latter two can only be addressed by roof and plywood removal, so an inspection can be done.

Does this sound like the problem you’ve been having with your roof? We can help determine the cause of condensation issues and formulate a plan for eliminating it. For more information regarding this or any other roof issue, contact Brad at Mills Roofing Inc.






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