We are living in the age of “tight” homes. Homes today do not naturally breathe in the ways that the homes of the 50’s and 70’s did. For energy savings we now ensure that thermal transmission through the walls, floors and roofs our homes are minimal. We typically use plywood and OSB (Oriented Strand Board) sheathing on all of the exterior walls of our homes. These type of products guaranty little air transmission even if we use the most modern and “breathable” house wraps. Windows and doors are installed to keep any air or moisture from passing around the assembly. Our roofs are tight and are floors are typically concrete slabs poured over a 15-mil vapor barrier.
What are potential issues that could arise from our modern methods? Moisture generated within the home has no where to go unless it is planned for. Bath exhaust fans are not there just for odor control. Their prime purpose is moisture removal. Laundry rooms rarely have exhaust fans yet they contribute greatly to the moisture load of your home. Ever walked into a laundry with the dryer running and noticed a little extra humidity?
In the old days, mopping a wood floor with a damp mop was not a bad thing. Today – if some of that water finds it way under or between the boards – a warped floor could easily result. That spilled glass of water really does need to be wiped up quickly! This is not to scare you into never having your floors mopped – rather to make sure the mop is not too damp and the floor is able to dry off quickly.
When you travel and leave your home closed up little or no fresh air will exchange within your home. During the summer, if you are running air conditioning your windows will be closed and the air in the home will not be able to mix with any fresh air. In the winter, when running the heating system with all the doors and windows shut – the same lack of fresh air occurs. The moisture build up in the home can increase leading to potentials for molds and mildew.
What can we do? As builders we need to be aware of the juxtaposition of building systems in the home. We need to be aware of how we live in our homes and what potential problems we may be creating. Making sure that exhaust fans are automatically running (usually controlled by motion detectors) in critical rooms of the house. The ability to use those fans wisely. The fan for the bathroom can stop running ten or fifteen minutes after you leave the shower. The fan in a laundry should run for an hour and a half after you exit. Enable the home to bring in fresh air when it needs it. This can be passively with the use of a fresh air intake port for the home. This will balance the pressure of the home. When the bath fan or dryer is pulling air out of the house the vacuum created pulls in new fresh air from a controlled location. New fresh air ventilation systems are available. The two typical systems are the heat-recovery ventilator (HRV) or an energy-recovery ventilator (ERV).
The link below can provide more depth on the subject http://www.greenbuildingadvisor.com/blogs/dept/musings/hrv-or-erv. These are very effective at creating a positive pressure within the home. The benefits are cleaner, less toxic air and control of in home humidity lessening the possibility of molds and mildew.
In this day and age we are creating the most energy efficient homes ever seen. They are great to live in if you keep in mind the potential issues and deal with them right up front in the design and construction of your home.