An Addition Can Benefit the Whole House.
While adding square footage, add green features
An addition can be a good opportunity to cure some of an existing house's energy evils. An addition offers an excellent opportunity to incorporate benefits for the whole house. For instance, if an existing building is sited poorly for solar gain and daylighting, look into the possibility for using windows, skylights, and solar massing in the addition that can add heat to the house. Or, in a hot climate, plan an addition that can shade other parts of the house.
But keep in mind that adding onto a house might not be the greenest course of action. Before you plan to add out with a new foundation and floor space, consider adding up, which uses fewer materials and is less disruptive to a site, or discuss with your clients how remodeling or reconfiguring their existing space could save money and tread more lightly on the environment.
Figure out how an addition will be used before you decide on its size.
A new space shouldn’t be any larger than it has to be. Keeping the new space as small as possible pays dividends in at least two ways: by keeping construction costs low and by reducing operating and maintenance costs. A smaller addition also makes less of an impact on the site and the neighborhood.
Questions to ask before you begin
Will the new space be flexible?
Wiring, window layout and accessibility can be planned with future flexibility in mind. For example, interior partitions can be non-load bearing so they can be moved in the future without affecting the structure. Wiring can be accessible for changes or additions.
Can the new space heat and cool itself?
Keeping conditioned space to a minimum means lower construction and operating costs. By taking advantage of the sun and creating a high-performance building envelope, it may be possible to downsize or even eliminate heating and cooling systems. With an energy-efficient design, installing small heating and cooling equipment may be more economical than extending ducts or hot water heating lines to the new space. An experienced professional engineer or energy consultant may be needed.
How will the new space affect the durability of the house?
An addition may increase the exposure of the existing structure to rain, snow and wind. A low-slope valley that was barely shedding rain and snow in the past may be overloaded by a new addition.
What type of foundation is best?
Choices include a full basement, a crawlspace, a pier foundation or a slab on grade. Full basements require the most materials and site work but they offer a lot of storage or living space. A pier foundation is often the least expensive option. Conditioned crawlspaces are less prone to moisture problems than vented crawlspaces. A slab can be an economical choice and pairs well with passive solar designs and radiant-floor heat. Climate, soil, site conditions and the foundation of the existing structure are other factors that should be weighed when choosing a foundation type.
In general, a new addition should include, where possible, passive solar design strategies, a high-performance building envelope, and advanced framing techniques that minimize waste and allow the most insulation possible in wall cavities. Raised-heel roof trusses that accommodate more insulation at the eaves also are a good bet.
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Disturb as little of the site as possible. Make sure the earth around a new addition is sloped away from the structure to keep water from pooling at the foundation. Use trees and shrubs to provide shade in summer and keep the addition cooler. Use permeable materials on new walkways and driveways to promote drainage and reduce runoff.
Control moisture at footings with a perimeter drain. Control moisture on foundation walls with damp-proofing or waterproofing. Insulate floor slab and foundation walls. Use concrete that contains fly ash. If necessary, install a radon mitigation system. Use bio-based form-release agents or permanent forms when placing concrete.
Use FSC-certified framing lumber, sheathing and siding. Use insulation with no formaldehyde. Specify window glazing according to orientation on the house. Air seal the envelope, and use durable siding.
Image Credits: Dawn Zuber Studio Z Architecture/REGREEN, Steve Kuzma Photography and Studio Z Architecture/REGREEN