Why Is My Upstairs Bedroom So Hot? Why Is My Basement So Cold?
For some homeowners, it’s the kid’s bedroom that burns up in the summertime. For others, the basement turns into an icebox during the winter months. As an energy auditor, one of the most common complaints we come across is a room or area of the house that gets too hot, too cold, or both. This post will explain what causes these problems and break down some simple, cost-effective solutions available to homeowners.
The ‘stack effect’ describes the natural movement of air into and out of buildings driven by temperature differentials at the top and bottom of the structure. Since heat always rises, warm interior air is constantly forcing itself upwards, which increases both the temperature and the pressure at the top of the house, relative to the bottom. As the pressure at the bottom of the house drops, air is forced inside from the outside to replace the air being forced out of the top of the building. As the temperature difference between the top and bottom of the house increases, so does the stack effect. Tall, skinny houses are particularly susceptible to stack effect because of their configuration.
Poorly Installed or Missing Insulation
Almost everyone knows that insulation is an important piece of home construction, but few people know what insulation actually does. Insulation works by inhibiting the flow of heat across a surface, like the walls of your house. This means insulation is designed to keep heat inside the house when it’s cold outside, and keep heat outside when it’s hot. Having inadequate, or poorly installed insulation allows heat to enter or exit the building at an accelerated rate.
The picture above (to the left) shows an attic area that is missing insulation at the floor. The homeowner had complained that the bedroom below was always hot, and after taking a look in the attic, it was easy to see why.
Even small areas of missing insulation can have a significant negative impact. For example, if 5% of a surface has gaps in insulation coverage, then the effective insulating value drops by as much as 60%. In the above picture (to the right), there is insulation present, but there are also visible gaps in coverage, which was causing serious comfort problems in the room below.
Because your attic sits at the very top of the house (remember, heat always rises), it is the most important area of the house to have insulated. After the attic, the basement, or crawlspace, is the next highest priority for insulation. A typical problem area for basements is at the rim joist (pictured below, outlined in pink), which is a framing piece that wraps around the perimeter of the basement ceiling.
In general, we recommend ensuring adequate insulation in your attic and basement areas before worrying about the insulation in your exterior walls, but all exterior surfaces of your house should be properly insulated if you’re looking for maximum comfort and efficiency.
An overlooked, but extremely important aspect of home efficiency is air leakage. That is the natural flow of air into and out of the home, driven by pressure differences between the inside and outside, and measured by the size and location of the leaks. Note that air leakage and insulation are two separate entities. Most insulation used in residential applications is fibrous (like fiberglass or cellulose), which means that while it is good at slowing the flow of heat, it does not do a good job of slowing the flow of air.
Reducing air leakage throughout the house requires sealing up any holes, cracks and gaps that connect to the exterior, which is usually done with foam sealant or caulk. The attic floor, for example, usually has a myriad of electrical and plumbing penetrations that need to be sealed. Attic access hatches are another major culprit for air leakage.
In the infrared picture below, cold winter air from the attic is leaking into the house (indicated by the purple streaks) because of missing or shoddy weatherstripping at the hatch. The hallway below the hatch was described by the homeowner as being cold in the winter, and the leakage from the hatch was identified as the largest factor.
Large openings at the attic floor (called ‘chaseways’, like the pipe penetration pictured below) should be covered and sealed with foam board or drywall. These ‘chaseways’ promote the ‘stack effect’ in houses, as it creates a natural avenue for heat to escape into the attic, causing cold air to enter through the basement to replace the escaping heat.
As you can probably tell by now, the ‘stack effect’, insulation, and air sealing are all related. With that in mind, the hot bedroom and cold basement described in the beginning often have the same root cause: Insulation deficiencies and excessive air leakage which promote the ‘stack effect’. These three factors taken collectively form the biggest source of energy inefficiency and discomfort in most homes.
However, they are not the only factors to consider. The heating and cooling equipment, windows, and habits of the occupants are also critically important to determining the overall energy profile of the house.
The best way to diagnose and correct your home’s energy problems is to have a professional energy auditor inspect the house. At Advanced Green Home Solutions, our certified staff of energy auditors can help you identify, prioritize, and implement the improvements you need to make your house healthy, efficient and comfortable.