Answers to Everyday Questions : How can I insulate an old house ?

Insulate and Save Older homes are often more affordable, located in more established neighborhoods, and just look more “solid” than their modern counterparts. Unfortunately, they are usually under-insulated as well. Lower energy costs, lack of building code requirements, and the expense of insulation materials of that era resulted in insulation levels well below what modern homes contain.

Older homes – those built prior to the 1970’s – contain a wide range of insulation products and amounts. Historic homes, constructed prior to the 1940’s, may contain little or no insulation. Sawdust, corn cobs, and shredded newspapers are some examples of early insulation and crack-filling methods used in older homes. One of the surest methods of enhancing the energy-efficiency of an older home is to increase the insulation levels in the ceiling, floors, and walls. But doing so haphazardly can cause some severe problems with moisture condensation – even to the point of jeopardizing the structural stability of the home.

The Threat of Condensation. This serious situation results from moisture condensation in the walls. Old homes with little or no insulation in their walls allow humid, moist air from the interior of the home to pass into the wall space relatively easily. Within the wall cavity, warm moist air from the inside meets cold and dry winter air, resulting in condensation within the wall. In the winter, this moisture typically freezes so it does little harm to the structure or finishes (interior plaster or exterior stucco) of the home. When warm weather arrives, the leaky walls permit enough air circulation to evaporate the moisture from the air cavity – largely eliminating the threat of dry rot.

A homeowner who installs blown-in insulation in the walls of an older home – a popular and inexpensive means of adding insulation – runs a risk of trapping this moisture in the wall. The humid air is still reaching the inside of the wall and condensing. The new insulation absorbs the moisture like a sponge and the lack of air circulation within the cavity prevents it from drying out. The result may be spalling plaster on the inside of the wall or rapid deterioration of stucco on the exterior. A more serious concern, however, is rotting of the wood framing, particularly the wood plate at the bottom of the wall and the ends of the floor joists just below the wall where they bear on the foundation.

The solution to this problem is a feature, required by all building codes, called a vapor barrier. A vapor barrier is nothing more than a plastic or treated paper covering placed on the inside (or warm side) of a wall to prevent the humid interior air from penetrating the cavity space and causing all those unpleasant side-effects mentioned previously. The kraft facing on most insulation products is a vapor barrier. Four or six mil plastic sheeting is also commonly used. Tyvek, a Dupont registered trademark, or other similar air-infiltration barriers are not, however, vapor barriers. They do not prevent the migration of vapor through the walls.

What this means, of course, is that the safest way of insulating your older home is to remove the existing wall finishes on the inside, install new cavity insulation and a vapor barrier, and then new gypsum board. Naturally, this is a much more expensive and troublesome option than blowing insulation into the walls. If you have a circa 1960’s or later home, you probably have a vapor barrier in your wall. If your home was built earlier than that, and you have wood siding or some material other than stucco on the exterior, you can still try blown-in insulation. Just be aware of the potential condensation problems and examine your siding and floor framing annually for soundness.

Other less expensive options for obtaining a vapor barrier include water-resistant paints (or other waterproof coatings) on the face of the plaster or wallboard. Vinyl wall covering will also serve as an effective vapor barrier. Just remember, for any vapor barrier to be effective, it has to be present everywhere.

Consider Exterior Insulation. If you are replacing the siding on your older home, consider installing rigid exterior insulation boards on the face of your framing as part of the job. These products are available in thicknesses of ½”, ¾” and 1″, and can be purchased with foil-facing to further reduce radiative heat gains. Rigid insulation is typically used as in combination with batt insulation in the walls to enhance the insulation values in a home. Beware of one problem associated with adding exterior insulation: You may need to extend or otherwise make adjustments to the window and door trims around your house. In addition, check the trim along the roof lines, such as at gable ends where there may be no overhang, to make sure you can add exterior insulation without resulting in making major roofing and trim alterations. All of this may also create aesthetic problems if you own an historic home or one listed on the National Register of Historic Properties. In those instances, consult with an architect regarding any exterior alterations.

Enhance Attic Ventilation. The same condensation concerns regarding walls apply to the attic as well, although to a lesser extent. Although you should still strive to have a vapor barrier for the entire ceiling are of the house, there is usually enough air circulation in the attic to prevent any severe moisture problems. The key is sufficient ventilation. Make sure you keep gable vents open and cleared of obstructions. Ensure that insulation or paint is not blocking eave or soffit vents. When you re-roof, consider installing continuous ridge vents, an inexpensive form of venting that helps pull air more evenly under the roof deck. If you are redoing the eaves or soffits of your home (the horizontal portion under the overhang), consider either increasing the number of vents or installing continuous soffit venting. This can be accomplished through either lay-in perforated aluminum panels, or through the use of a 2″-3″ wide aluminum strip that is cut into the existing wood soffit. A combination of continuous soffit and ridge venting is the most effective forms of attic ventilation.

Reduce Air Infiltration. Along with increasing insulation levels in your home, deal with one aspect of energy loss that may save you as much as 25% on your energy bills – air infiltration. Sealing leaks around doors and windows, electrical switches and receptacles, and at exterior siding and trim joints can result in significant savings on your utility bill. Caulk extensively on the exterior of your home, using quality silicone sealant that is either of a compatible color or is paint-able. Install new weather-stripping around existing doors and windows. Use foam inserts to block air infiltration around receptacle and switch boxes. These are widely available at home improvement stores and install under the plates. If you do not own an historic home, consider installing storm windows if you have leaky wood or metal existing windows. Storm windows are frequently less costly than new window installation, and provide greater benefits than a single unit. Storm doors are less effective (they’re also open when the door is open), though they do reduce air infiltration. If you buy a storm door, however, buy a good one. A cheaply construction door will become a maintenance headache. If you have a fireplace, keep the damper closed when not in use. If it has no damper, buy a screen to close off the opening when you aren’t using it.

Increase Efficiency. There are some simple things you can do increase the efficiency of your household – and thereby reduce your energy costs.
*Install an insulation blanket on your hot water heater; keep it set to a “medium” level;
*Remove coats of paint from radiators. It impedes radiation;
*Close blinds and drapes at night to help retain heat in the home. Heavy draperies serve as draft obstructions;
*Ceiling fans in larger or taller rooms help to re-circulate warm air;
*Humidifiers make the air feel warmer at lower temperatures;
*A small fan located near radiators can enhance warming;
*Maintain summer shade trees near the house; plant exterior evergreens to block winter winds.
Finally, enjoy your old house for what it is. You may never enjoy the energy-efficiency of modern homes (though you may come close). Still, that isn’t why you purchased it in the first place. Make your home as efficient as possible, but don’t spend a fortune trying to turn it into a model of conservation.