Von Löwen Designs

Infiltration & Exfiltration.

Air leaks, or drafts, can be responsible for 25 percent of the heat loss in a newer house, more in older homes. Moreover, when air moves through the house because of leaks it is often laden with moisture that can end up in wall cavities and condense, increasing the likelihood of mold and structural deterioration. In the course of remodeling air traffic control is the key. We have grown used to sealing the obvious problem areas with foam under bottom plates, expanding foam around window and door framing, and insulation stuffed into smaller wall cavities. It is the invisible and often convoluted paths of air leakage that need our attention. Because air leaks are so detrimental to the energy performance of a house, it is always a good idea to conduct a blower door test after the house has been sealed. A fan housed in a special door frame temporarily replaces the front door and pulls air from the house, ‘depressurizing’ the structure so that air leaks can be detected with a smoke stick. Air leaks become visible so they can be corrected. The test should not cost more than a few hundred dollars and is a simple way of verifying that the air sealing has been successful.

Controlling infiltration and exfiltration requires an air barrier between conditioned and unconditioned spaces. Imagine a balloon with hundreds of tiny pin pricks in it. You can imagine that it won t be inflated for very long. When remodeling adding an air barrier is the way we keep the conditioned air in the house and stop heating or cooling the outdoors.

There are many different materials assembled into the envelope of a house, and where these materials intersect should be the focus of air sealing. A stud doesn’t allow much air to pass through it, but when there are studs nailed together, they form gaps that allow air to get through, When you install a window, you are creating a gap in the sheathing that can allow more air to escape. Pipes, wires, and ducts, as they intersect the structural members, also are places where air can leak. The integrity of the air barrier is one key to efficient heating and cooling.

Establishing and maintaining an effective air barrier is the responsibility of many members of the building team. From the start the architect must understand where the air barrier will be. Framers should frame to meet that requirement, and the insulating contractor should be thorough. The superintendent or lead carpenter must be able to see the potential for air movement before the fact. In other words, everyone needs to be on the same page.

Airflow & The Stack Effect.

Wind speed and direction create pressure differentials on different sides of the building. The side facing the wind encounters higher pressure while the opposite side has a lower pressure. These differences cause air to move in the building. If there are cracks or penetrations on the windward side, air will be pushed into the building through the insulation, and into the living space. That’s often around doors and windows. Or the air may follow wiring and create drafts in unexpected places. Because of the lower pressure on the leeward side of the house, air will be pulled out of the building and enhance the flow. This will always vary by season and microclimate conditions.

Basic convection pressures explain the stack effect. (Please see my post The Holistic House – Part I for more on convection). Cold air is heavier than warm air. It falls after coming into contact with cold window glass or poorly insulated walls, pushing warm air higher in the building. That, in turn pushes air out of the house. Warm air (under pressure) will find any way it can to escape into the attic or out through band joists – the higher the temperature difference, the greater the force. This causes infiltration from lower sections of the building. The remedy is to inspect the attic and seal all air bypasses well before insulation is installed. Also, pay special attention when remodeling to how insulation is installed, and seal around wires, ducts, and pipes that penetrate the barrier between living spaces and the attic.

Any house with an atmospherically vented combustion appliance with a pilot light (furnace, water heater, fireplace) will have flues for combustion gases. They often run from the basement through the house and exit at roof. Even when the furnace isn’t running, the pilot flame is burning and causing a draft up the flue. This draft also carries conditioned home air with it so there is constant loss of conditioned air. All flues work this way, which explains why fireplace flues should always be closed when the fireplace is not being used.

Another way to defeat this energy robbing phenomenon, when say doing a kitchen remodel, is to buy pilot-less appliances equipped with electronic ignition and to install to direct-vent or sealed combustion equipment wherever possible. This type of appliance is typically vented through a sidewall of the house, not a chimney. It uses a double walled pipe that introduces fresh air for combustion while safely venting combustion gases.

As we tighten up the house and seal all potential air leaks, we also have to provide a way to introduce fresh air and expel stale air with mechanical ventilation. Many builders wonder about the logic of tightening up the house so religiously only to install ventilation equipment that seems to undo all that effort. The reason is that it’s much less expensive to control the flow of fresh air in a sealed house with mechanical ventilation than it is to depend on random air migration through the building envelope in a leaky house.

Mechanical ventilation also helps us define the right pressurization of a house. Conventional homes with forced-air systems create negative pressure inside the house because of leaky return ducts. They suck air from the house and draw in air from the outside. Add a dryer vent, a kitchen exhaust hood, and a bathroom fan and the negative pressure can back-draft unburned gases from flues for the furnace or water heater. This can introduce carbon monoxide in the house, a potentially fatal problem.

For even more information about indoor air quality don’t miss my posts Indoor Air Quality – Part I and Indoor Air Quality – Part II.

A good mechanical ventilation system will create a slightly positive pressure in the house that resists infiltration and prevents back-drafting. At a minimum, the house should be pressure neutral.

Heat recovery ventilation, brings in fresh air while exhausting indoor air. Heat recovery ventilators (HRVs) usually have two fans – one pulling in fresh air and the other exhausting stale house air. Air streams pass each other through an air-to-air heat exchanger that moderates incoming air by extracting heat from the conditioned air and conveying it to the incoming air stream – just the opposite as when you’re running an your air-conditioning system.

Heat recovery ventilators are an effective way of taking the sting out of ventilation systems that expel conditioned air that has, after all, been heated or cooled at our expense. You can read more about mechanical and heat recovery ventilation as well as the benefits of installing an air-to-air heat exchanger on my post Greening Your HVAC – Part II.

Water, Gravity & Diffusion.

If we think back to high school physics, we’ll remember that water can be a solid, a liquid or a gas. In all of its forms – ice, rain, and vapor – water can be a challenge to control in a building. Ice dams forming on roof edges allow water to back up under shingles, get around the felt paper, and find its way into the house. In the form of rain, water can penetrate siding; migrate into wall cavities, and cause mold and rot. As vapor, it can enter wall cavities through switch plates and outlets or through any cracks in drywall to find its way into wall cavities. Prevention of moisture in all phases of the remodeling project is our insurance of a very long lasting and durable home.

Water always flows downhill. Plumbers know it, but many of the trades have forgotten that fact. We should always put felt paper on the roof from the eaves to the ridge with the upper course overlapping the lower course – just like the scales of a fish. This is also critical for walls where either housewrap or tarpaper is used. Housewrap with holes or tears in it cannot work as designed, and no seam should face uphill. This may be painfully obvious, but it seems as though some builders do not follow this rule.

Water, like heat, always flows from areas of higher concentration to areas of lower concentration. That means if we have saturated soil on one side of a foundation wall, and warm dry conditions inside the house, water will try to find a way through the concrete to the dryer side. This is why foundations should always be treated to block moisture and why perimeter footing drains and porous backfill around a foundation are important.

Fluid Dynamics & Capillary Action.

Capillary action is the ability of water to flow through a material, from wet to dry. Just like heat, moisture moves through materials based on their properties. Some are better at wicking moisture and some are more resistant. We need to know which building components will be in contact with water and protect them with appropriate materials to resist the migration of moisture.

Water vapor goes where air moves it. Think of it as a hitchhiker on molecules of air. If air can get into a wall cavity, so can moisture. It wouldn’t be such a problem if the people inside the house would stop their bad habits that create a lot of moisture. But it seems we are committed to taking showers, watering plants, boiling veggies, and worst of all, breathing. So if we cannot change our behavior we need to do our best to prevent that moisture from getting into walls and ceilings from the inside.

The most effective way to reduce interior moisture is to collect it at its source and get it out of the house. Installing good quality bathroom fans and range hoods at the same time as remodeling your home is one obvious step. Another is making sure that dryer vents are correctly installed and never terminate in a basement or attic.

Noise Pollution.

Increasingly, Americans are becoming aware of noise pollution. Whether it is produced by a neighbor throwing a party, a stereo in an adjacent room or a nearby freeway, noise can he an unpleasant intrusion. We may aspire to gain peace of mind at home, but that’s hard to do when we’re bombarded by loud and unexpected noises. It makes us irritable, distracted anxious, and hostile, sometimes without consciously making the connection to noise. Good design and proper selection and installation of building materials can reduce the intrusions whether they originate in the house or from outside.

An acoustics expert might tell you that controlling noise at the source is usually the best solution. That may work with your kid’s stereo but many environmental sources of noise like highways, trains, airplanes, nearby construction equipment are beyond our control.

When noise from the outside is a distraction, windows are often to blame. Exterior walls will typically block at least 45 to 50 decibels of sound, but even a very high quality window might not be able to block 40 decibels.

Dual-pane windows with increased air space between the sheets of glass improve acoustic isolation. ‘Superglass’ windows, in which glass is combined with a very thin layer, or layers, of plastic are even more effective. Noise however, migrates through the weakest structural element, and that could be a door or ventilation duct as well as a window. The acoustic isolation provided by a door is only as good as the effectiveness of the door seal so remember if air can get around or under the door, so can sound.

To learn more about windows please be sure to check out my previous posts Window Replacement and The NFRC Window Label.

Walls vary in their ability to reduce noise. A typical single-partition gypsum board/stud wall wiII have a sound transmission class (STC) in the mid-30s depending on such variables as the width of the stud and the amount and type of insulation in the wall cavity. Ideally, during remodeling one would want to match this wall with a similar STC rating for the glass opening. Thinner laminated glass will equal a considerably thicker piece of plate glass.

Typical wall construction of 2×4s on 16 inch centers with fiberglass insulation is not very effective in reducing sound. Structural insulated panels (SIPs) or framed walls with exterior rigid foam are more effective. Cellulose and foam insulation do a better job of reducing noise than conventional fiberglass batts (although there are fiberglass batts specifically designed for sound mitigation). The ideal combination for houses close to noise sources would take advantage of SIPs, sided with cementitious boards, along with Superglass windows. This combination results in a very quite house and coincidentally, is a recipe for a very energy efficient remodeled home.

Another option for homes close to environmental noise is the staggered stud approach, which has the added advantage of reducing thermal bridging. A further option is to add flexible C-channel to inside walls perpendicular to the studs. These are placed on 16 inch centers as backing for drywall. The C-channel absorbs some of the sound and isolates the drywall from the vibrations of the wall assembly.

Something as simple as increasing the distance from the source of noise or putting other materials between the sound source and the house when you remodel can be an effective way to reduce unwanted noise. That can be a factor in deciding where to locate a house on the site, assuming the size of the lot provides some wiggle room.

Noise barriers are also a possibility. They can be earth berms, solid walls, or neighboring buildings. Vegetation provides little if any reduction in noise. To be effective, barriers must block the line of sight between the noise source and the house. A density of 4 lb. per sq. ft. is enough, providing there are no openings in the wall. Barrier walls, however, won’t reduce noise by more than about 10 decibels.

As cities and neighborhoods become ever more crowded and traffic increases, noise becomes more difficult to control. While specialized construction techniques and materials can be used to control noise transmission inside the house, we can’t do much about urban sprawl and commuter traffic. If you can’t reduce sound to a satisfactory level by any other means, you may have to combat noise with some of your own – maybe an outdoor water feature, for example, that masks an unwanted noise or sound with a more pleasant one.

What building science tells us is that good design requires good thinking about the house in a holistic way – as an entire and complete system. By considering the thermal properties of a house from this perspective, codes become irrelevant. Obviously not in regards to passing a needed inspection, but irrelevant in terms of defining what good construction really is.

We can control how a house will perform. Determining the pathways for all forms of water is a cheap insurance policy against mold, mildew, and rot. Deciding where the air barrier will be makes it easier for the trades to do their part in keeping the house tight. Managing air pressure inside the house will keep it healthy for children as well as the rest of us. Paying attention to sound resources and designing and remodeling accordingly will keep homeowners, occupants, and clients happy and comfortable for as long as they live in the house.

To read even more about maximizing your HVAC and a holistic house whole system approach, be sure to check out Greening Your HVAC – Part I and Greening Your HVAC – Part II.

They say a picture is worth 1,000 words, so before you leave be sure to visit Von Löwen Designs to view an assortment of refreshing examples in kitchen and bath design concepts, refined palette and interior finishes, and sustainable yet chic, green remodeling ideas that may encourage and inspire your next remodel or home improvement project.

It’s much easier to turn a remodel green for a house when you understand how heat and cold move from one object to another, and how air and moisture move inside our home. Green remodeling practices and design, in addition to the selection of appropriate materials, revolve around a few basic principles.

• Thinking of the house as a holistic system of interrelated parts.

• Energy loses some of its potential each time it is converted from one form to another, which helps explain why passive solar heat is much more efficient than electric heat.

• Form follows function when it comes to design, meaning that construction should be tailored to the environment in which the house is built.

• Air leaks in the building envelope represent a significant loss of energy and open the door to moisture damage inside wall and ceiling cavities.

• Controlling the movement of heat, air, and moisture involves every part of the home and everyone on the construction and design team.

Nothing is more central to the notion of the home as a holistic system than heat flow, or to get a bit more technical about it, the First and Second Laws of Thermodynamics (thermo = heat, dynamics = movement). Once we see how these principles are applied to remodeling, construction, and design, we’ll never look at a house the same way.

Energy cannot be created or destroyed, only changed. That’s the first law of thermodynamics. All the energy we have is in one of many forms: electrical, chemical, mechanical, solar. The second law says that every time you convert energy from one form to another it’s degraded in the process.

Some forms of energy are more concentrated than others are. Electrical energy, for instance can do all kinds of miraculous things, like make computers work or turn heavy motors. Woodstoves. on the other hand, convert a lot of energy potential from the wood into heat, but you can’t run a laptop with it. So there is a hierarchy of energy forms that we can convert to accomplish the work we want to do.

What the second law tells us is that each time we change the form of energy (chemical to heat – heat to mechanical) it becomes less useful. This is called entropy. Efficiency is converting energy from one form to another with as little waste as possible In the end, we can measure the ‘net energy’ of any given process – the percent of the original energy potential versus the actual work we have accomplished.

Does this have anything to do with remodeling houses? Actually, it does. Our challenge as designers and builders is to make the building as efficient as possible in all energy conversions – that is, to keep energy in its most useful form and not let it escape or degrade more than necessary. In other words, to create the least entropy. The closer the building is to the source – the bottom of the energy food chain – the better.

A classical example of high entropy versus low entropy lies in the contrast between a house that is electrically heated and one that is designed to be passive solar. Electricity makes a long journey before it arrives at the baseboard heater.

Suppose the electricity we use comes from coal. Coal itself is a very concentrated form of chemical energy that was created over millions of years in a process of photosynthesis that converted atmospheric carbon dioxide into a hydrocarbon fossil fuel. Enormous amounts of energy are required to run the extraction equipment, trucks, and processing equipment. Then coal is transported to a power plant that burns the coal to boil water that creates steam. The steam spins a turbine that creates the electricity. The electricity then passes through a transformer to create 240,000 volts for high transmission lines. As it runs through the lines there are line losses until it reaches its destination. It then passes through another transformer where it is stepped down to 240 volts that we can use in our homes.

Passive solar, on the other hand uses radiant heat directly from the sun to heat a home. Here the energy makes only one simple conversion from light to heat. The sunlight passes through south facing windows, strikes a solid object, and turns into heat that is re-radiated to human bodies. There is only one energy conversion.

The efficiency of the process is determined by the transparency of the glass. At a minimum we get 50 percent of the potential heat and with well designed glass, we can get up to 75 percent. And, it’s all free! That’s eating low on the energy food chain.

In green remodeling, having an appreciation for entropy helps us select the best form of energy for the task at hand, using the most efficient appliances or designs that make energy conversions with the least amount of degradation (to heat) and retaining heat where we need it and in the form we want it. This is where the building shell comes in.

Heat Transfer and Thermal Transmission.

Energy moves in three ways – conduction, convection, and radiation – and energy movement is always a combination of all three. While we refer to insulation in terms of its conductive resistance to heat movement, convection and radiation are also taking place on a more subtle level. All of these are important in a house for different reasons and the principals help explain why some design techniques and materials work better than others.

Conduction.

Heat moves through solid substances by this process. It is typically measured with an R-value (the higher the number, the greater resistance to heat flow). Anything that conducts electricity typically has a low R-value. Metals of all kinds fall into this category. Wood, not a good conductor, has a higher R-value than metal. The insulation we use in our houses works because it traps air, giving it a much higher R-value.

So when insulating a house from hot and cold, we look for materials that allow the least amount of conduction or take steps to shield conductive materials so they do not become energy transmitters. Light steel framing for example, can move tremendous amounts of energy through the exterior walls of a house because it is such an efficient conductor. That’s why a steel framed house should be sheathed with rigid foam insulation. Cellulose, foam, cotton, mineral wool, and other types of insulation conduct very little.

Convection.

Convection is the movement of liquids and gases because of differences in density. Convection explains why warm air ends up in the upper floors of a house while the basement stays cold, or why a chimney draws smoke up and out of the house.

Our houses are filled with convective currents, some of which we feel and some of which go undetected. Convection is more subtle than conduction, but when it is not controlled, it can result in a drafty, uncomfortable house. Worse, convection can carry moisture exactly where we do not want it – into wall cavities and attics where it condenses into water and encourages mold and deterioration.

When we become more aware of how convection works, we can take steps in designing and remodeling houses to reduce its impact on comfort and health.

Radiation.

Radiation is the movement of energy from a hot object to a cooler one via waves. Think of the sun on a hot summer day. The air temperature is the same in the sunshine as it is in the shade, but we feel more comfortable when we get out of the sun and out of reach of all that radiant energy. A fireplace can keep us warm even as a great deal of hot air escapes up the chimney.

Radiant energy heats objects rather than air. That s why people are often happier with radiant floor heat than they are with a forced air furnace. Their bodies feel the heat directly rather than feeling the warm air.

Controlling Heat Flow.

We design, build, and remodel houses so we can stay comfortable and to keep the weather at bay. Over time, we’ve gotten better and better at disconnecting our houses from the climate that surrounds them. Houses today can look the same whether you’re in Alaska or Florida, and that doesn’t make a lot of sense. More logistically, houses in those vastly different climates would be designed to respond to the environment around them and thus have very different appearances.

Insulation is a key part of designing for climate. How much insulation we can get between outside and inside is partially determined by the structure of the building. Wood frame buildings were once framed with 2×4s on 16 inch centers, an approach so common that architects and designers referred to this detail simply as ‘typical.’ So this is the place to start with remodeling.

I won’t be getting into framing right now, but the important thing here is to try to avoid ‘TYP’ on construction drawings – it means that too little is being done to fit the house to its environment. A house should be designed to meet the requirements of the local environment. This means that insulation levels, or the overall R-value of the house, should be higher than the minimums required by the local energy code. In a good green home, the R-values of insulated floors, walls, and ceilings are often 50 percent higher than what the building code requires.

They say a picture is worth 1,000 words, so before you leave be sure to visit Von Löwen Designs to view an assortment of refreshing examples in kitchen and bath design concepts, refined palette and interior finishes, and sustainable yet chic, green remodeling ideas that may encourage and inspire your next remodel or home improvement project.