Do It Yourself Energy Efficiency Projects: Your Home’s Thermal Envelope (Part 1)

Many people struggling through the tough economy are not going to be able to take advantage of the 2009-10 Energy Efficiency Tax Credit simply because they can’t afford new windows and doors, water heaters, or more insulation. However, there are a few things you can do around your home to air seal it to save money during the winter months and during the summer.

Because of the price and use of energy, architects and builders now design a home to be a “thermal envelope”. That is the sum total of the home’s insulation systems including walls, ceilings, foundation, floors, windows, and doors. These work more effectively with good, tight fits that seal out the weather and air. By having a tight seal on your home’s thermal envelope, the less energy you waste or lose by exchanging it too often with the air outside.

So, with this in mind, let’s start at ground level and work our way up to seal your house.

Moisture Barrier

A moisture barrier (usually plastic sheeting) covers the earth beneath a structure to prevent moisture from infiltrating the structure from the ground. All-wooden structures last years longer if they are kept dry and out of contact with the ground. For a house, not only does it help prevent rot but it also helps keep the drier. Because moisture in the air holds heat, even during the most humid months, a moisture barrier will make your Texas home feel drier and cooler.

Most Texas homes are built on either a slab or have crawl spaces under them. Houses with slab foundations typically have concrete poured on top of a plastic moisture barrier. This limits the infiltration of moisture into the thermal envelope of the house. Homes with crawl spaces, meanwhile, feature a moisture barrier in their crawl spaces. Some older homes do not have one and these can be installed by the home owner very easily.

A moisture barrier is plastic sheeting, usually about 6-8 mils thick and is available at any hardware store, typically in sizes ranging from 25 × 25 feet to 100 × 100 feet. It also need not be one single piece of plastic. As long as the sheets overlap each other by about 6 inches or so, it will be effective.

To install, you will need to know the dimensions of your crawl space and buy enough plastic sheeting to cover the ground in that space. Simply cut the plastic sheeting to cover the earth from wall to wall, laying it flat. You can use either black or clear plastic, but I would use clear because black plastic would make your crawl space feel like a cramped version of Batman’s lair.

You should notice the difference within 24 hours. If your house feels too dry, simply fold back some of the plastic sheeting to expose the earth underneath. Continue adjusting until your home feels the most comfortable to you.

As mentioned, moisture barriers limit the infiltration of moisture into the thermal envelope of the house. The house feels drier: It will be easier to cool in the summer and less likely to develop mold or contribute to wood rot in the winter.

Mudsill and Rim Joists

The next place to check out is the mudsill. The mudsill is the board that is bolted flat on to the top of the foundation wall. An example of one is a 2×8 board bolted onto the final course of cement blocks. It provides a bed to attach the flooring joists and banding boards for the first floor of the house. Depending on how well it is installed, it can let in a lot of cold air and moisture.

Places to look for gaps is where the mudsill is fastened to the foundation. A common building practice now is to put down a plastic foam gasket over the foundation before attaching the pressure treated lumber that will be the mudsill. In older homes, either a paper-backed cellulose material was put down or nothing was used. To find gaps, get as close as possible to the mudsill from the inside and look for daylight shining through between the mudsill and the foundation wall and feel for a draft of cool air.

If your foundation is made of cement blocks, look for the vertical joints between the blocks. When these blocks are put into place, the mortar between the blocks often slumps leaving thin mortar or none at all. Over time as the house settles, holes can appear. While these might be small holes that let through tiny amounts of air, if your home has 10 or 20 of them, you’re letting in a lot of weather and insects. Seal every hole you find with silicon caulk or expanding foam.

Another place along the mudsill to look for is where the rim joists attach. The rim joist (sometimes called “banding joist”) is the piece of wood that closes off the end of the flooring joist or is the last floor joist underneath the exterior wall. The bottom edge is not necessarily an air-tight seal. In fact, I lived in one older house where there was a half-inch gap between the rim joist and mudsill. Now, while this seems small, the gap ran for the entire length of the house: 25 feet. It was the equivalent of leaving a 24 inch by 24 inch window open all the time. Some expandable foam quickly sealed this gap and there was a noticeable improvement in comfort and cost right away.

Windows

If you have double-hung wooden sash windows with storm windows that are drafty, there are several ways to make them more energy efficient.

Make sure the glazing on the glass panes of the sash windows is not cracked or crumbling. The glazing helps hold and seal the glass to the wooden window and thus blocks drafts and quiets rattling – especially from traffic. It also lessens the likelihood that the glass will break if a pet or a child presses against it. Glazing is something of a skilled art. That being said, it’s not that hard to do. Re-glazing a window yourself can save you to 0 or more. All you need is glazing putty (), a putty knife (), some glaziers’ points ( for a box of 100) and some time.

First, remove any old, cracked, or crumbling glazing with a putty knife. Glazing putty dries to be very, very hard and will last decades. It can be loosened with a heat gun, but keep the gun moving or the heat will crack the glass.

When the old putty has been removed, remove all the old glaziers’ points. Now, lift out the pane and set it aside. Sand the channel where the pane fits on the wooden sash. Usually, I apply a thin bead of silicone caulk in this channel before replacing the glass. This helps to seat and seal the glass pane. This especially helps when working on multiple small panes (called “lights”) separated by thin or fragile wooden mullions (also called “muntins”). Next, insert new glaziers points. This is done by using the putty knife to press points into the wooden sash along the glass pane to keep it in place. Take your time so that you don’t break the glass.

Glazing putty can be purchased in either a can or a tube with a shaped tip that fits in a caulking gun. However, it does take some practice to get just the right angle and right amount of putty on the glass. When using the tube mix, keep the 45 degree angled tip steadily against the glass and lay a bead of putty the length of bottom of the pane. If you’re using the putty from the can, roll the putty into long snake (or rope) and place it along the edge of the pane and along the wood. Gently press it into position so that it forms a nice 45 degree angle with the putty knife. The putty is shaped this way so that water runs off the glass to the edge of the window sash instead of into the window pane channel where it can rot the wood.

The next thing to look for is if your windows close snugly. Both the top and bottom window have what is called a “meeting rail”. On the upper window, it is the bottom of the window and on the bottom window it is the top. These meeting rails are shaped so that they mesh together when they close. This helps seat and seal the window properly. Check to see if the bottom window runs firmly – but not tightly – along the window jamb as you close the window. If it’s too loose and wiggles back and forth, it probably won’t seat very tightly when it’s closed. You can use a putty knife to pry out the window jambs and then re-position them to improve how tightly the window will close. You might try adding felt or self-adhesive foam weather stripping. Also make sure you clean out any debris from the window to ensure the window will seat and seal snugly.

As metal storm windows age, the harder they seem to close. This usually happens because of dirt and corrosion. Make sure the window tracks are clean and free of dirt and debris so the window runs smoothly.

Outside, check that the storm window frame is held tightly in place against the wooden window frame. Screws that hold this frame in place might be loose and might need to be replaced or moved to a new spot. Most drafts from storms windows come from where the storm window frame meets the wooden window frame. Once you’re certain the storm window frame is secure, lay a bead of caulk into the seam where the metal storm window frame meets the wooden window frame. Typically, there are two slots cut into the bottom apron of the storm window frame. Do not seal these. These are weep holes that allow condensation to escape.

If you have modern, double glazed windows (windows with two panes of glass), one of the things to look out for is fogging between the panes. Double glazed windows are made by attaching a pane of glass with adhesive to either side of a half-inch wide aluminum frame either in a vacuum or a very dry environment. It is then a single unit and is installed into a standardized window frame. Fogging is a sign that the seal on the window unit has failed and water vapor has penetrated into the space between the panes. If the fogging is still present in summer, it’s a good guess that