The most important cost-effective construction solution used to lower energy bills is a reduction of air-leakage. The test used to determine air tightness in a home is required in the 2009 International Residential Code, it is called a blower door test. However, there is a second compliance method, the visual inspection, that most builders in Virginia use to show compliance.
Building code specifies that “the building thermal envelope shall be durably sealed to limit infiltration.” Unfortunately the visual inspection provision weakens this requirement to a point that it makes no impact on most homes being constructed. The blower door is the only effective way to determine total air leakage and verify the home is as air tight as required by the building code (the worst possible construction allowed by law).
A blower door test is used to determine total air leakage of a home’s thermal envelope. The powerful fan is installed in an exterior door and the house is depressurized. The result is a measure of the home’s air tightness. This test simulates the air leakage typical in a building that uses forced air heating and cooling as well as those that result from weather conditions. Every home should have a blower door test in order to find the leaks and reduce the money wasted each month on an inefficient thermal envelope.
Permeability is a HUGE topic in our mixed humid climate for anyone involved in the construction industry. The perm rating of a product is the measure of the diffusion of water vapor through a material. This vapor drive through a building material can make or break the durability, efficiency, and indoor air quality of a project.
In our climate, the key is to have a wall and roof assembly that is air tight and vapor permeable. This is an almost impossible task so there are other things that need to be done for the house to be as efficient and durable as possible – but I will not go into that depth with this post.
Vapor permeability (air tight and vapor permeable) is sometimes referred to as the breath-ability of a system or ability to let water vapor pass. This should not be confused with stopping bulk moisture, which is a must for a wall and roof assembly. Bulk water is moisture in liquid form and water vapor is a gas.
So why is vapor permeability so important to the health, efficiency and durability of a building system? Because walls and roofs do get wet. Condensation will occur in some systems. Plumbing leaks do happen on occasion. Most important, we have two seasons here in Virginia and therefore have two different vapor drive directions. So walls and roofs need to be able to dry in both directions. When a wall cannot dry out, it becomes susceptible to moisture damage (rot, mold, insects).
Anything with a perm rating of less than 1 is a semi-vapor barrier. These products should be used sparingly for the thermal envelope in our climate. Anything less than 10 has low permeability and care needs to be taken to dry the assemblies out and not trap vapor inside.
Many products we use traditionally need extra thought due to their permeability:
Open Cell Foam = 15 Perms
Closed Cell Foam = 1 Perms
Concrete = 3.2 Perms
Gypsum wall board = 50 Perms
Plywood Sheathing = 10 Perms
OSB Sheathing = 2 Perms
Oil Paint = 1.6 Perms
15# Felt = 8 Perms
Kraft paper batts = 1 Perms
House wrap = range 5 to 50 Perms
Having an architect that understands building science is a must in our mixed humid climate. A well planned wall and roof assembly will be healthy, durable, and energy-efficient.
Going green when building a sustainable home is the first step in ensuring you are helping your environment and your wallet for years to come. How are your eco-friendly decisions benefiting your home?
It is easy to dismiss making a decision that protects forests in South America if you have no direct attachment to South America. Using FSC certified wood is more expensive on a cash basis without a doubt. So why would you ever care about using this strategy? FSC is a third-party certification that protects rain forests in South America from being clear-cut.
How do we put value on saving these forests? It is difficult, however those forests are filtering air, sequestering carbon, and producing oxygen to breathe. So inherently we know the health of those forests is important, but again, is it worth paying more to build your home to protect forests half a world away?
Precious wood at Mil Madeiras Ltd. FSC, from sustainable logging. Amazon, Brazil
Deciding to build a healthy, energy-efficient, and durable home is not as complicated a decision as deciding which strategies are right for your home and budget. These are complex issues that should be considered with the full impact on the future of our world and the impact on your project. Installing a more expensive HVAC system, for instance, that saves you money through energy efficiency can easily be evaluated on a payback basis. Installing insulation that is air tight and vapor permeable is critical to maintaining your monthly finances and can also be easily evaluated. Using healthy products that do not off-gas dangerous chemicals into the air you breath should be done without a second thought.
Going green is not a political decision. It does not cost more if planned through design using the right strategies for your project. Going green benefits your wallet, the planet, and future generations to come.
We spend a lot of time thinking about the health impacts of the building when designing an energy-efficient home. The ventilation rate needs to be designed and the materials used should be selected with care.
Then construction starts and it is cold outside. The next thing you know there is a portable heater sitting in the future living room. These machines are terrible for air quality for those building your project. Fuel oil off-gassing can have serious health impacts. The chemicals from the burn process can be absorbed by wood and drywall in your project and held until the project is finished.
Here is a solution used on a project we designed to be LEED Certified to keep the burn process outside the building envelope while sending the heat to the inside of the building.
From a report done by Michigan State University: Following tests of 18 types of portable, unvented heaters, Consumer Reports states that: “We calculated the concentration of four gases produced by these heaters — carbon monoxide, carbon dioxide, nitrogen dioxide, and sulphur dioxide — in a 10x12x8-foot room with normal ventilation. The levels of each gas were high enough to be a serious health hazard to high-risk groups, including pregnant women, asthmatics, people with cardiovascular disease, children, and the elderly. The levels we calculated for some pollutants may pose risks for healthy people.”
I get questions on a regular basis about home comfort and efficiency. This question came from someone who read my blog and wanted to get their HVAC system adjusted and wanted to know who to call.
“Our house is quite cold this winter and our energy costs are pretty high – I suspect our heating system is not very efficient, and I am looking to hire someone to come identify and fix any problems. Who should I call?”
The easy answer for your HVAC system is to call Jay Monger at Excel HVAC. He will get your system right.
The path that I would suggest instead:
Get an energy audit from Building Knowledge so that you can develop a comprehensive approach to make your home efficient. His findings will probably be along the following:
You HVAC system is most likely oversized, insulation inefficient in the attic and basement / crawl space, hot water pipes not insulated, and there is a strong need to air seal your home. Since HVAC systems are expensive, I would first air seal your home, then insulate, then adjust the HVAC system.
To air seal a typical home, you could caulk and weather seal all the gaps and cracks in the thermal envelope (electrical outlets, around recessed lights, attic access, doors and windows, and around HVAC boots). The big holes will most likely be the band board (where the floor joists hit the outside walls). These are best sealed with spray foam insulation (open cell not closed cell).
Then, most likely your attic does not have enough insulation and probably not air tight insulation. This is a hard decision to make – to fix the air tight issue you usually need to remove the insulation that is already there. Most people, including myself, don’t like throwing away something you already paid for. So typically, you just accept the air leakage in the attic insulation and add another layer of insulation on top of what you have there. Code minimum is R-38, but I would suggest a minimum of R-50, but like to see R-72 if budget and space allow.
A basement / crawl space is another good place to attack if the space is not finished. We often find insulation in the floor system above. It should be on the walls for better performance. The band board is often not insulated at all, this area should be sprayed foam.
Once you get the house as air tight as possible and have insulation added in appropriate places, then the HVAC system can be adjusted as needed – perhaps just adding a fresh air exchange depending on how tight you get the home. It might also need some dampers added to get the right amount of air into the right rooms.
For insulation – if you want to skip the energy audit – call Ken Wells at Elite Insulation. For a couple thousand dollars, he can get your home WAY more comfortable even before the energy audit. He understands building science and is fair with his pricing.
If you have questions about your home, let us know!
Many new homes are taking advantage of that space above the attached garage for an additional bedroom / bonus room space. It was made possible by the invention of the attic frame truss that is able to span a two car garage and provide a 12′ wide usable room above. However, most bonus rooms have a problem – they are uncomfortable. You can see in this image that a builder has addressed the problem by adding an ugly through wall heating / air conditioner. This will make the room comfortable, but adds to your electric bills, does not address indoor air quality issues, and is usually noisy – not to mention ugly.
This bonus room space is a nice add to the usable space in a home, but has indoor air quality and comfort issues. This is due to the difficulty in getting them air tight as well as difficulty getting supply and return air into the space. A bonus room above the garage needs extra attention from the insulator. In order to get it air tight and efficient, they need to use a LOT of caulk or an open cell spray foam solution. This will also protect against the air infiltration from the garage below. Good planning may also allow for HVAC ducts, supply and return to reach the room through the knee walls. This all needs to be carefully planned and thought through in advance of construction to get it right.
While I prefer this space to only be used for storage in a detached garage, sometimes the lot demands it be attached. If you do take that route, be sure to plan for comfort and indoor air quality solutions that will allow you to sleep knowing you have protected your family.
We live in a mixed humid climate and so often, you hear from the HVAC contractors in the area that there is a need to add humidification. If the house is tight – energy efficient, healthy, and durable, you should not have dry air and certainly should not need more humidity. In fact, living in the home produces humidity. If there is a problem, it will be high humidity. If you have dry air, your home is not energy-efficient.
A dehumidifier is a piece of equipment that reduces the level of humidity in the air. Humid air can contribute to mold and mildew issues in your home. It can also lead to condensation on pipes. As a rule of thumb, relative humidity in homes is preferably 30 to 50 percent.
Following up on the blog question posted yesterday. This is a photo taken between a vented attic and a conditioned space. The dirty line at the bottom of the insulation shows the path of air infiltration from conditioned to unconditioned space. This is a typical problem in buildings that do not have proper air sealing. Fiberglass insulation works well as an insulator but does not stop air movement. The insulation becomes an air filter without an air barrier. Air movement also brings vapor movement. Once the insulation gets wet it loses all effectiveness. There is also a chance that the moisture movement will be enough to support mold growth. If you find that your insulation is acting as an air filter and not insulating – making the space air tight will solve the air quality and energy-efficiency issue.
More information on Air Sealing, click here, here, and here.