Why You Should not Over Insulate Your Home

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I have been studying insulation lately, and how homeowners could improve their energy efficiency, but then I remembered moisture control.

Insulation is a big topic in my home inspections. Basic insulation practices can help a homeowner save money, and I honestly think that is the bigger motivator than being green or thinking about green insulation, because you want to help the environment. Adding insulation to your attic is such an easy way to improve energy efficiency. Placing a radiant barrier in an older home may not always be as simple, but this job is not beyond most homeowner’s abilities.
    I was on a forum where a Realtor was asking what could he do to prepare a home for a home inspection? The other Realtors chimed in saying caulking. More properly we should say sealing the home. This project ties in with insulating your home. If cold air cannot flow into the home, the insulation does not need to deal with this lack of heat. I tell clients to seal joints to prevent moisture from entering the walls. The amount of water that can flow through a small crack is incredible. I hardly mention the fact that this has a benefit towards energy efficiency, but sealing a home does play an important factor in energy efficiency. I inspected a new home construction where the builder had taken eco-friendly, green steps. Most builders are incorporating green building techniques, yet home buyers are not always asking about these steps. In this three story home, I ran the downstairs heater. The home was so efficient that the second story was well heated with only the downstairs unit running. By the third story though, I began to feel the chill.
    Why should we be worried about insulation or sealing if they do so well at reducing energy usage and costs? There is a flip side to insulating and sealing, trapping moisture in the home. Moisture in the home does more than damage your clothes, or cause mold. Moisture can weaken and damage the structure of your home. Moisture control needs to be on our mind when considering how to make our home more energy efficient. Simple moisture control steps are vents in the bathrooms and kitchen. Bathroom vents are mainly considered to be for odors, but these vents are meant for moisture control. Another moisture control device is the kitchen vent. Step back to look at your pans when cooking. You may not have added water, yet you will find steam rising. The kitchen vent is not always present in homes. We forget that the basic form of moisture control is opening a window. This technique was how moisture was vented, but we seem to have forgotten about it. Kitchen vents have to go to he exterior to rid the home of moisture. Many homes have recirculating vents. The cooking steam is drawn through a filter, which removes oil and some moisture, but then the vent allows the remainder of the moisture go back into the room. The moisture on the filter will go back into the room as well.
    One popular device for moisture control is an HRV (heat recovery ventilator). These units vent stale, moist air out of the building while taking in fresh air. During cold weather, the HRV captures the heat from the interior air to heat the incoming fresh air. During hot weather, the device takes heat back to the exterior.
    Insulating and sealing are good do it yourself projects, but before sealing and insulating is complete, consider how you will control the moisture which is now trapped inside the house.

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6 Responses to “Why You Should not Over Insulate Your Home”

Kent Keith Says:
February 3rd, 2010 at 8:14 pm
Another reason to seal around the attic door is that I see many installed near air returns which can cause a negative pressure and pull air from the attic.
Another product to consider is an attic tent. I have a picture of one on my website at:
http://www.fortworthinspector.com/save_energy.html
Kent

frankschulteladbeck Says:
February 4th, 2010 at 4:24 am
Thanks for the reminder Kent. I did forget to mention that fact.

TOM Says:
September 22nd, 2010 at 7:28 am
I have recently done a service call on a home and the house had new blown in insulation and vapor barrier in the entire roof and attic, now the home is sweating around all recessed light fixtures and dripping on the floor. I am going to run a Manual J on the home, should Contractors be notified that when changing the heat load factor the Central Air and Heat loads are changing the Central Air and Heat system. These systems may have to be down sized? Tom.

frankschulteladbeck Says:
September 22nd, 2010 at 10:34 am
Tom, it does sound like the system may have to be downsized, and it would be nice for contractors to properly inform their clients of the implications of one job on different systems, so other contractors can be called out to prevent the issue you describe. I would love to see homeowners obtain a manual “How to Operate Your Home”, so that they would understand the correlation between weatherization, insulation, ventilation, the HVAC system, and comfort in the home. If we create a tight envelope with more insulation, then the next thing on our list should be to check our ventilation and the HVAC system, right away. Then it would be nice for the homeowner to understand that they should have fans for air movement.

HotinTN Says:
September 30th, 2011 at 11:04 am
We have heavily insulated our TN home and while that works great in the winter, in the summer it is difficult to get the humidity and temp right at the same time. Basically, we have done such a good job insulating that the A/C is now oversized and does not run often enough to remove sufficient humidity. It requires a dehumidifier to keep the humidity between 60% and 75%, which is high.

And on the notes that say to insulate the attic, as heat rises, I would offer that hot air rises, but heat radiates, so every wall/ceiling/floor should be as insulated as is reasonable.

frankschulteladbeck Says:
September 30th, 2011 at 4:37 pm
Yes, I did mean that the heat in the air is rising up. The transmission of heat in a building does occur by conduction, convection, and radiation, which does mean various surfaces have to be a concern. I do suggest that we need to insulate the walls and under the home as my post of 9/28/11 on pier and beam homes describes. With the heated air rising, we do become more concerned with heat escaping through the attic or roof, so that is why we insulate that area to a greater degree. We also insulate the attic to a greater degree, because we are concerned with thermal bridging (in this case heat radiating through framing to the conditioned space below). In the end, we do need to balance insulation with ventilation, and also properly sizing equipment.