Airsealing

What is Air Sealing?

Air sealing is used to restrict the passage of conditioned air into unconditioned spaces, and vice versa. It is the systematic finding and sealing of air leakage points throughout your home, from the attic to the basement and/or crawlspace to the walls. Caulks, spray foam, and other materials are used to block any holes or gaps to stop warm internal air from leaking out of your home. This means your heating equipment does not need to work as hard to keep your home at your desired temperature, you are more comforable and it reduces your energy usage and utility bill.

Why Do I Need to Air Seal?

1. The Stack Effect

This is the main reason to air seal your home. A house works a lot like a smoke stack. Hot air rises through the house until it exits in the attic. If you seal off a smoke stack at the top, the bottom, or both, you don't have a smoke stack. In air sealing a house we are trying to stop the stack effect as much as we can.

2. The Winter Coat Principle

An unzipped winter coat doesn't work very well because it allows air to flow around your body, which makes you cold. An insulated house can also perform poorly if uncontrolled air can get in. There is not a consensus, but nearly half of the energy leakage in a house can be caused by air leakage - that costs a lot of money!

Where Do I Need to Air Seal?

The Home Performance Diagnostics will help locate many of the air leaks. The larger leaks are quickly found, but some of the smaller leaks will be harder to find until the larger leaks are sealed. Here is a brief breakdown of the process for the various parts of your home.

1. Attic Air Sealing

Air sealing starts in the attic because warm air rises bring moisture with it into your attic. These can cause a variety of issues, like ice dams, mold, and rotting your roof.

Lights, Fans, Plumbing Stacks, Chimneys, top plates, cabinet soffits, etc. - Any hole in your ceiling is called a thermal bypass, or air leak. Caulks, spray foam, sheet foam, and sheet metal can be used around most of these, including around boxes for light fixtures, bathroom fans, open wall cavities, and plumbing stacks. Other items like chimneys and recessed lights require special methods. There are a large number of items that require a professional to find and correct properly.

2. Basement/Crawlspace Air Sealing

The bottom of your home is next because this where most of the air enters your house. It is NOT done before the attic because this will cause the first floor to become more uncomfortable. That is because the air will still be leaving through the ceiling and replacement air is still needed to make up for the exiting air and that will now come from leaks in the first floor walls.

There is a lot of leakage in the basement, and since it is accessible in most homes. Here are the big areas we focus on. These all make good DIY projects too!

a. Band/Rim Joist

This is the vertical board on top of the masonry foundation that runs like a band around your house. The top of it sits just below the floor of your first floor and is a major leakage point. The bottom of the band joist sits on top of the sill plate, and is another major leakage point. Also, any holes through the band joist like the electrical service, dryer vent, hose spigot, air conditioner line, etc. also need to be sealed. Foam board along with caulk and foam are our usual weapons.

b. Sill Plate/Sill Sealer

The sill plate is the horizontal board that sits directly on top of your foundation. Between the sill plate and foundation is the sill sealer, which ironically rarely seals the sill. It can be either a layer of mortar in older homes, a 1/2” thick black felt-like band in 1960s-1980s homes, or a thin layer of foam. This is best sealed up with foam.

c. Holes in the Floor

Any holes through the basement ceiling, such as electrical and plumbing lines, chimneys, or duct work. Any of these items, particularly plumbing lines and the chimney, can be connected through walls from the basement to the attic, creating a direct passage like a mini smokestack. Since there is no way to know for sure which ones connect and which don't, it's best to seal them all.

3. Wall Air Sealing

Wall are last surfaces of the house to be airsealed because they sit in the middle between the high pressure above at the ceiling and the low pressure below in the basement/crawlspace. This means that there is less pressure difference to the outside, positive or negative. Less pressure difference means less air movement. Although, the taller the building, the stronger the stack effect, and the more this has an effect on the walls (either high or low).

The door and any other connections to the garage are the highest priority, due to IAQ issues with air from the garage. Next the windows and door need to be sealed, the weather stripping replaced if necessary, but around the trim is where most of the leaks usually are located.

Insulation and/or Outlet Sealing – The simplest item on walls is to put foam backers behind the outlet covers and child proof plugs to stop air coming out the outlet holes (admittedly, this is a bandaid fix, but it is simple enough for anyone to do.). The harder part is insulating walls. If you have a newish home, about 1970 or later, your walls are probably insulated. If you have an older home, especially before 1965, your walls are may or may not be empty. Empty walls generally account for 20-40% of air leakage, and is a good area to reduce leakage. By using dense packed cellulose insulation in the walls, you can drastically reduce the air leakage, improve your comfort, and cut the energy bills of your older home.

4. Leaky Ducts

Duct work typically leaks 10-30%, meaning that a lot of the air you are paying to heat or cool is leaking to somewhere it shouldn't be going. If the ducts are in the walls, there isn't much you can do short of ripping walls apart (don't bother unless the duct is fully disconnected, you are doing a duct renovation, or you are doing a major remodel project ). Any ductwork in the basement can be sealed though. Ironically, don't use duct tape, it will fail within a few years. On any seams or cracks, cover them with mastic and mesh tape. Mastic is a glue that can be found in the duct work area at your local building supply store. 'Aeroseal' can be done to seal up inaccessable duct work.

However, we do not recommend sealing the leaky ducts until a HVAC Airflow & Efficiency Test of your heating and cooling system is completed. This is because the leaky ducts may be what is keeping the system running. By tightening the ducts, it can cause the system to work too hard and fail prematurely.

After Airsealing, what is next?

When airsealing is done, you will need to get the house reinspected. This is because airsealing changes how the house functions. Do you remember the "House as a System" and all the interactions? Airsealing can make a water heater backdraft and let carbon monoxide into the house, so do not skip this step. Additionally, this test will prove how effective the airsealing was in stopping the air leakage. This second inspection is referred to as "Testing Out", and can be done by us or the company that does the airsealing (if they offer that service). Then it is on to adding insulation and getting that comfortable home.

Final Thoughts - Air Sealing - Reduces Drafts & Increases Comfort, while decreasing Energy Bills!

Air sealing is the service you have never heard of, but can't live without. It almost sounds like black magic. Like most things about home improvement, once you learn a little bit about it, it is more hard work than mystery! Our Home Performance Diagnostics can help you find where the leaks are that need sealing.

The Top 10 Things to Know About Air Sealing

Your house likely leaks 1.5 to 3 times as much as it should. This means you are paying to heat and cool air that escapes outside to quickly.
A truly drafty home has a lot of air leaks. Airsealing can stop drafts.
Air leakage into the attic is a primary cause of ice dams. Even if you have a lot of insulation, leaking air carries more than enough heat to melt snow on the roof.
Air leakage is measured with a blower door. A blower door is a special fan that fits in one of your doors and pulls a little air out of your house in order to measure how much it leaks and where from.
Air leakage is measured in CFM50, or cubic feet per minute at 50 Pascals. A Pascal is a very small unit of pressure. 50 Pascals is the equivalent of a 25 mph wind blowing at all sides of your house at the same time.
Your house really can't be too tight, but below a certain amount of leakiness mechanical ventilation will need to be added. This isn't an issues with many older houses.
If your house needs mechanical ventilation, there are several methods that can be employed, such as adding bathroom fans, HRVs, and a supply fan. This controlled ventilation will also improve your IAQ.
The maximum leakage rate for a house should be 3 to 5 air changes per hour at 50 Pascals (ACH50) according to most new building codes. This means that your house will naturally change its air once every 3 hours. Very leaky houses may change their air over every 30-60 minutes, working the furnace very hard, decreasing comfort, and greatly increasing your gas bills.
BPI, or the Building Performance Institute, is the most accepted standard maker for existing homes. RESNET focuses on new homes.
Many air sealing tasks are easily undertaken by homeowners. The basement is prime territory for DIYers. Sealing up outlets, light switches, and trim on door and windows is also very simple. Attics are not quite as easy because leaks are harder to find. Insulating walls is best left to the professionals because rental equipment is not powerful enough to do the job.

Interesting Links

Dept of Energy - Retrofit Techniques and Technology: Airsealing -or- Cached copy

Energy Star - Airsealing Info DIY Guide -or- Cached copy