Musings of an Energy Nerd

All About Indoor Air Quality

Posted on March 11, 2016 by Martin Holladay, GBA Advisor

Many owners of green homes are concerned about indoor air quality. GBAGreenBuildingAdvisor.com often receives questions from homeowners who worry that some building materials emit dangerous chemicals. For example:

  • Will the glue in my plywood or OSB subfloor emit dangerous fumes?
  • Will borateBoron-containing chemical that provides fire resistance to materials such as cellulose insulation and provides decay and termite resistance to wood products. Borate is derived from the mineral borax and is benign, compared with most other wood treatments.-treated cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection. off-gas enough to affect the health of my children?
  • What type of clothes dryer is best from the perspective of indoor air quality?

Tales From Armenia

Posted on March 4, 2016 by Martin Holladay, GBA Advisor

In this week’s blog, I’m going to take a break from building science. Instead of providing advice to green builders, I’m simply going to reminisce about my time as a construction volunteer in Armenia.

Combining Exterior Rigid Foam With Fluffy Insulation

Posted on February 26, 2016 by Martin Holladay, GBA Advisor

It’s becoming increasingly common for builders to install one or more layers of rigid foam on the exterior side of wall sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. and roof sheathing. Typically, these walls and roofs also include some type of air-permeable insulation (fiberglass, cellulose, or mineral wool) between the studs or rafters.

How to Design a Wall

Posted on February 19, 2016 by Martin Holladay, GBA Advisor

Builders love to talk about walls. Almost all of us are willing to argue about the best way to build a high-R wall, and we love to debate whether certain wall details are environmentally friendly enough to be considered “green.”

Although these conversations can be fun, our obsession with wall details is often misplaced. Details that inflame our passions are often irrelevant. In most cases, we should just choose a relatively airtight easy-to-build wall with good flashing details — one with an R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. in the range of R-20 to R-40 — and be done with it.

Insulating Walls in an Old House With No Sheathing

Posted on February 12, 2016 by Martin Holladay, GBA Advisor

When the owners of an old wood-framed building say that they’re doing a “gut rehab job,” that usually means that they’re demolishing the lath-and-plaster walls to expose the studs — the first step of renovation work that usually includes new wiring, new plumbing, and new insulation.

Choosing Rigid Foam

Posted on February 5, 2016 by Martin Holladay, GBA Advisor

Maybe you’ve decided that your floor, wall, or roof assembly needs one or more layers of rigid foam. Which type of foam should you choose: polyisocyanurate, expanded polystyrene (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.), or extruded polystyrene (XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.)?

The answer depends on several factors, including your R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. target, your local climate, whether the insulation will be in contact with soil, and your level of environmental concern.

Smart Vapor Retarders for Walls and Roofs

Posted on January 29, 2016 by Martin Holladay, GBA Advisor

During the winter, when indoor air is usually warm and humid, most wall sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. is cold. Under these conditions, we really don’t want water vapor to move from the interior of our homes toward the exterior. That’s why builders in the 1980s installed polyethylene on the interior side of walls.

Passive Air Inlets Usually Don’t Work

Posted on January 22, 2016 by Martin Holladay, GBA Advisor

If your house has an exhaust-only ventilationMechanical ventilation system in which one or more fans are used to exhaust air from a house and make-up air is supplied passively. Exhaust-only ventilation creates slight depressurization of the home; its impact on vented gas appliances should be considered. system, does it need passive air inlets — that is, holes in the wall to let in outdoor air? In most cases, the answer is no. Unless your house is very, very tight — close to the PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. standard of 0.6 ach50 — your building’s envelope is almost certainly leaky enough to allow for the smooth operation of a bathroom exhaust fan rated at 50 cfm or 100 cfm.

Preventing Water Entry Into a Home

Posted on January 15, 2016 by Martin Holladay, GBA Advisor

If it is designed well, the thermal envelope of your home should control the flow of heat, air, and moisture. Unfortunately, the floors, walls, and ceilings of older buildings are often leaky: they leak heat, they leak air, and they leak moisture.

If you are building a new house, you have the opportunity to control the flow of heat, air, and moisture through your home’s building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials.. The result will be a durable, comfortable building that doesn’t cost much to heat and cool.

Air-to-Water Heat Pumps

Posted on January 8, 2016 by Martin Holladay, GBA Advisor

Most air conditioners and heat pumps sold in the U.S. — including most split-system air conditioners and ductless minisplits — are air-to-air heat pumps. During the winter, these appliances extract heat from the outdoor air and deliver warm air to a house through ducts or small fan-coil units. During the summer, these appliances deliver cool air to a house and dump unwanted heat into the outdoor air.

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