Vapor Barriers

Confusing Terms

Even professionals often confuse the term "vapor barrier" with the term "moisture barrier". Here is the difference:

• Moisture Barrier - Moisture barriers (like Tyvek, for example) are properly installed on the exterior of a frame wall, directly on top of the sheathing, and under the siding. Moisture barriers help prevent water from entering the wall cavity.

• Vapor Barrier - Vapor barriers, typically a polyethylene plastic sheeting, are installed on the inside of a frame wall between the studs and the drywall. Vapor barriers help prevent water vapor from the interior of the house filtering through the wall and condensing on the warm side of the insulation. Wet insulation is a no-no.

Vapor barriers are also installed under basement slabs to prevent water and ground gasses (such as radon) from making their way through the concrete.

The point of having a moisture barrier like Tyvek outside the sheathing and the polyethylene vapor barrier inside the insulation is that in the event of condensation or infiltration of vapor into the wall system, the housewrap allows moisture to escape to the outside. Housewrap will also reduce the infiltration of water and water vapor into the wall system from the exterior, minimizing the potential for water to condense at the vapor barrier.

In order to be effective, both moisture barriers and vapor barriers must be properly installed and sealed at all penetrations and seams.

Should I Install a Vapor Barrier?

If you live in Des Moines, the answer is probably yes. If you have any questions, you should consult a knowledgeable building professional. A vapor barrier will decrease air and moisture infiltration into your rooms and make your home more energy efficient.

If you are working with an existing frame wall or masonry veneer wall, there are additional considerations you should think through before deciding one way or another.

Water condenses on the warm side of a barrier. There is sometimes a concern in regards to installing a vapor barrier with a masonry veneer wall. This concern is related to the situation where, on a sunny day, water that is trapped in the brick may have a tendency to migrate into the wall system. When this water vapor contacts the vapor barrier (and the house is air conditioned - cool), it may have a tendency to condense and potentially collect in the wall system.

If you are concerned about moisture condensing in a frame wall with a masonry veneer, there are three potential solutions.

• Don't install the vapor barrier. This will allow moisture to continue to migrate through the wall system without getting "trapped" at any one point. Downside is that this solution is not as thermally efficient.

• Increase the air space at the brick veneer. Additional air space (say 2" instead of 1") will allow for more air flow up and out of the wall cavity, lessening the potential for water vapor to be stuck in the system. Current masonry standards call for an increased air space anyways. The downside is that if you are building a new foundation, the width may have to be increased for the additional air space.
• Expanded foam insulation. The closed cell expanded foam insulations are also vapor barriers. Water will not migrate into or through the insulation, so you don't have to worry about condensation at the interior wall surface. Downside is that it may be more expensive than standard fiberglass batt or blown-in cellulose insulation.

Other Considerations

A properly installed polyethylene vapor barrier can create a very "tight" building envelope with little air infiltration. While this is great for energy efficiency, it then becomes important consider interior air quality. Particularly in situations where appliances, utilities, and fireplaces may be powered by natural gas, maintaining an adequate fresh air supply is critical to a healthy internal environment.

A tightly sealed home requires mechanical venting and make-up air supply to maintain healthy internal air quality.

For more information and related resource links, visit:

• RenovateDSM article on furring out walls

• The Wikipedia article on Vapor Barriers

Heating and Cooling

In a typical household, heating and cooling make up well over half of the total energy use. Insulation and sealing up the "building envelope" from outside air can drastically reduce energy consumption. Next in line should be selecting energy efficient appliances and heating/cooling units.

Many older homes come equipped with radiator heat and an older gas-fired boiler, but no air conditioning. Chances are, you will be either upgrading or replacing the HVAC system(s) in your renovation.

Efficiency

Great strides have been made in HVAC efficiency. For air conditioners, efficiency is measured by a Seasonal Energy Efficiency Ratio (SEER) number. The higher the number, the more efficient the unit is (and usually the more expensive the unit is). Purchase the highest rated unit you can afford.

HVAC Types

Forced Air Furnaces
When it comes to heating, the newest energy efficient forced air furnaces approach the mid 90% range - this means that over 90% of the energy created by the furnace is captured for heating your home. This also means that the exhaust produced is significantly cooler than a traditional furnace - the high efficiency units capture much of the exhaust heat and return it back to help heat your home. High efficiency furnaces can often be vented directly through the wall rather than up a flue through the roof. The cost of a high-efficiency furnace is approximately equal to the cost of a standard furnace plus relining the flue (often a requirement). Gas is significantly more efficient than electricity, though electric furnaces (non-combustion) do not have any venting requirements at all.

Hot Water Heating Systems
If adding central air conditioning is a priority, you will have to make the decision whether to keep your existing hot water system and repair it as required, or to replace it with central heating. The first step in making this decision is verifying the operating condition of your existing system. Some of the key things to check are: the boiler (is the pilot light operational, does it fire properly, is it properly vented), the pump, the pipes (is the system filled properly, are there any leaks, does the insulation contain asbestos), and of course the radiators themselves (are there any leaks, are the valves in working order, are they adequately sized).

All things considered, hot water heat is generally less expensive and more comfortable than forced-air heat. Many people feel that because radiators are designed to heat your rooms through both convection (air movement) and radiation (direct heat), they heat rooms more “evenly”. Also, the interior air in the house is maintained with more humidity. It is important, however, to learn how to maintain your hot water system properly in order to maximize its benefit. An important HVAC investment will be a “radiator key” available for under $2 at many city neighborhood hardware stores. This “key” fits the small valve at the top of each radiator and allows you to release trapped air when filling the system.

If it is in good or repairable condition, I generally recommend keeping the existing hot water heat for general heating needs and adding a forced air system on top for cooling in the summer. For a relatively small cost, your contractor will place an electric heating element in your forced air system as a backup. Removing existing radiators nearly always necessitates patching floors where the pipes enter and often repairing the wall behind the unit.

Multi-Zone HVAC Systems
If you intend to add central air and heat to a building with radiator heat, you will need to find space for the blower unit inside and the condenser outside. In a single-zone system, the blower unit is usually placed in the basement. Some buildings, due to their size or layout, require additional HVAC units to heat and/or cool effectively. Multi-zone systems such as this allow greater temperature control and allow each unit to operate more efficiently. In a three-story home, one unit will typically be located in the basement to serve the first floor, and one unit will be located in the attic to serve the third and second floors.

Radiant Heating
In-floor radiant heating is typically considered as a supplementary system rather than the primary means of providing heat. It consists of a grid of heating elements (electric) or small-diameter tubing (hot water)HVAC Duct running between joists that runs throughout the area to be heated. Though in-floor radiant heating systems can be installed under any type of flooring, they are typically used in areas like bathrooms to heat a cold tile floor and provide continuous, even heat to the room.

Alternative Temperature Control
Alternatives to standard heating and cooling include passive systems such as double-hung windows, shade plantings, and solar heating. Active systems include ceiling fans (a cost effective means of regulating air temperature) and geothermal heat pumps.

HVAC Rough-In

Your HVAC contractor will perform “load” calculations based on the size and layout of rooms, location and size of windows, and the location of the fan and condenser units. These calculations indicate the required capacity of the system and the size of ducts and vents. You can compare the suggested capacities (measured in “tons”) from several contractors. If there are significant disparities, ask them to explain their reasoning. An improperly sized system will cool and heat inefficiently resulting in higher energy costs and more frequent maintenance.

The HVAC rough-in work usually involves installation of the main trunk lines and ductwork for air distribution throughout the house. You will need to have space within the walls for the supply ductwork and the return air – your architect will plan for this in the design stages. Also included in this stage is the installation of flexible duct for bathroom fans and range hoods. Because the HVAC system is large and relatively inflexible this contractor should start work before the others. A “high velocity” system uses smaller, flexible ducts to distribute air. The high velocity vents are generally less visible than the standard floor and wall vents. These systems are generally more expensive.

Your HVAC contractor should be responsible for acquiring all appropriate permits and securing the inspection after work is complete.

Plumbing Rough-In

Your plumber deals with all the PVC (plastic), copper, flexible, and cast iron pipes in your house. This includes the water supply, drains, vent stack, sewer connection, hot water radiators, and natural gas. As with all your other contractors, make sure that your plumber has experience working in renovations, particularly if you are pursuing historic tax credits.

It is important to coordinate between the plumbers and carpenters - there may be unique situations where walls, chases, and soffits must be framed to create space for waste stacks, plumbing traps, and vents.

The rough-in stage involves installation of all pipes up to the location they protrude from the wall. Later, after the drywall and cabinets have been installed, the plumber returns to install the fixtures and connect them to the water system. The major exception to this rule is the bathtub/shower. The tub/showers must be installed in their final location before the rough plumbing inspection, which involves filling and draining the tub. You will have to purchase the tub and shower fixtures, shower valves, and drains in order for the plumber to complete the rough-in.

Electric Rough - Let There Be Light

Many older homes are outfitted with “knob and tube” wiring where individual wires are supported (and kept from touching each other and the building) by ceramic fittings. This method of wiring is not inherently dangerous unless the fittings or wires are damaged - as is often the case during renovation. Knob and tube wiring also has no provision for the “grounding” wire required for three-prong outlets. Today’s technology consists of an insulated cable that contains three or more wires including at least a “hot” wire, a “neutral” wire, and a ground wire. In BX-type cables (armored cable), required in some situations, the wires are contained within a metal sheathing that provides additional protection. This insulated wire is easy to install and provides a high degree of safety. All new wiring must meet the current electrical code.

Installation

A licensed electrician must install all wiring for outlets, fixtures, switches, and appliances. Anyone may install telephone, cable, and structured data lines. You can save some money on electric by running these wires yourself – phone lines may be “chained” together, but each cable and structured data outlet should have a “home run” to the basement where they can be managed individually or hooked into a home automation system.

The rough-in phase for your electrical system includes running all the wiring and installing all the junction boxes necessary to implement your electrical concept plan. The wires will terminate at the breaker box, but will not be made "live" until the electric finish later on in the process.

It is sometimes useful to walk through the building with the electrician who will be performing the installation. This will give you a chance to make any last-minute corrections or additions.

The electric system is the most flexible of the three major systems. While your electrician must follow applicable codes that dictate where wires may run, it is generally possible to get a fixture or outlet pretty much anywhere you want. It is much easier, however, to place fixtures and outlets in frame walls than it is to place them in masonry walls. If you must have an outlet in a masonry wall, the brick has to be chipped out to allow space for the wiring and the outlet or fixture. Then the wall is repaired to hide the wiring. I generally discourage surface-mounted wiring and fixtures, even when allowed by code, unless there is not other alternative.

Safety

Some spaces require specific types of safety features. All outlets near “wet” areas like the kitchen and bathroom must be Ground Fault Circuit Interrupter (GFCI) outlets. A GFCI protected outlet cuts power instantly in the event that a ground fault (for example if you drop your hair dryer into the bathtub) is detected. Also, all outlets in bedrooms must be protected by an “arc-fault” circuit breaker. This special type of breaker helps prevent fires by detecting sparks that can pass between damaged wires within the wall.

Special Cases

If your home is particularly large or unusually shaped, you may want to consider having the electrician install a “sub-panel,” or secondary breaker box. For example, in a three-story house, a sub-panel may be installed in a second floor hallway to serve the second and third floors. Some labor is saved this way because circuits on the upper floors do not have to return all the way to the main box in the basement. It is easier to add additional circuits in the future if need be. Also, if a breaker is tripped, you don’t have to go all the way to the basement to reset it.

Ceiling fans require a different, tougher, ceiling-mounted box than a typical light fixture. Since you can mount a standard light fixture into a ceiling fan box, consider upgrading the mounting in all living spaces even if you don’t intend to have ceiling fans there from the start. That way if you want to add a fan in the future, it will be as easy as replacing the fixture.

The permanent alarm system, if you are purchasing one, should be installed after the general wiring and phone line have been connected.