Sustainable Design — Blog

What is net-zero?

The definition is simple. It’s a structure the produces as much energy as it uses. However, there is definitely more than one way to get there.

Why net zero?

Buildings contribute 30% of greenhouse gases towards global warming and it’s not necessary. We CAN do better. Energy efficiency is the simplest and most effective way to combat global warming.

We love the pristine environment of Cape Cod that we live and work in. We want to set an example of what can be done through design to create construction that is in harmony with its surroundings. Cape Cod is ground zero for climate coastal sea rising and we think it’s imperative to act.

Also, it makes financial sense! An initial investment of slightly higher construction costs – 10% or even much less, can result in no energy bills! That means once you’ve completed construction the annual energy usage would be offset by annual energy production. This is powerful stuff!

A3 Architects we have specialized in energy efficiency and high performance thermal envelopes. We design these net-energy zero homes on a variety of budgets and work with many available incentives. There are several basic strategies for getting to net-zero.

HOW TO GET THERE?

1. “THE NOT SO BIG HOUSE” –FLEXIBLE BUT KEEP THE DESIGN SMALL

The most important ‘green’ thing you can do with a new house is to make it smaller! Susana Susanka’s “Not so Big House’ resonates with our design philosophy. We ask clients to not design their Cape house for the Fourth of July when extended family & guests are here but to design their house how they live most of the year with the idea of designing flexibility into the spaces. So this means, you don’t make a dining room that accommodates a table for 20 guests, but think hard about an open living/dining space that is room for 4 to dine most nights but can be expanded for larger dinner parties. This is important!

http://www.notsobighouse.com/

2. USE ENERGY MODELING

No matter the scale of the project, start with an energy model. WE use energy model as early as conceptual design to understand how siting, glazing and wall thickness affect performance. In the early stages of design we can try multiple wall, roof, foundation and window insulation levels. This gives us the confidence early in the process that the design will approach net-zero.

3. SITING IS IMPORTANT!

If possible south facing glazing, and roof make passive solar and future active solar feasible. If there are major views to the north, or other restrictions on this we can design around it. But, there is no substitute for thinking about the suns path as it relates to your home. We naturally crave light, particularly in the long dark months on winter. And orienting living spaces towards the south can make a dramatic difference in comfort level with natural lighting. Furthermore, south facing roof is required for solar panels that are part of the big picture – energy production.

4. INSULATE, INSULATE, INSULATE!

Insulation is one of the least expensive building materials. Doubling the insulation budget is not going to double construction costs. Infact, although it requires some thoughtful detailing, super-insulation can be achieved in many ways. In general terms we aim for R:10 under slabs, R:20 below grade walls, R:40 walls and R:60 roofs. Most of these numbers are twice what’s required by code. This extra insulation can be placed inside or outside the structural wall depending on the situation.

5. WINDOWS CAN MAKE A BIG DIFFERENCE

Once you’ve decided to add that extra insulation you’ll notice that double glazed windows might not make much sense. There are some exciting triple glazed European windows available that have higher R:values than most homes! This can make a big difference at night when standing by a window in the winter. We pay attention to window details like u;value and solar heat gain coefficient to make sure that the windows are working to help heat the home in the winter.

6. DIAGNOSTIC TESTING DURING CONSTRUCTION CAN ‘CATCH’ MISTAKES

We rely on testing during construction. We test airtightness before insulation, after insulation and at the final occupancy. Airtightness is a measure of how ‘leaky’ a house is. We want to build the tightest house practical. This way we know that are minimal leaks in the exterior envelope for air and water movement.

7. VENTILATION IS VERY IMPORTANT!

The first question we often get is “Don’t you want the house to breathe?” Yes, of course we do. However, we want to control that. We don’t want the house to breathe through walls and windows. If you add insulation and don’t consider ventilation there can be problems. We want ventilation – whether from a simple exhaust-only bathroom fan or a more sophisticated intake/exhaust whole-house ventilation system that controls how the house exchanges air. Old houses breathe, but new energy-efficient house do too. They do it in a smarter more efficient way.

8. HEATING WITH ELECTRICITY MAKES SENSE!?

Many Cape residents no longer or never had access to natural gas for heating. We can’t make natural gas on our roofs, but we can make electricity by utilizing solar photovoltaic panels. If we are serious about getting to net-zero, it’s important to heat/cool/heat water with electricity. Fortunately, there are great options for heating these days. We use mini-split heat pumps for heating and cooling as well as heating hot water for most projects. They are two-to-three times more efficient than the electric resistance baseboard heating of the 1970s and 80s. There are options for ducted and ductless units.

9. GETTING TO NET-ENERGY ZERO

A net-energy-zero house is a building that produces as much energy as it uses. This is a very simple definition but it gives quite a bit of leeway for different approaches. Passive house is another energy standard, one of the most rigorous ones in the world. The standard was developed in Germany but is based on building science from the 1960s and 70s passive houses built in North America. The basic principal is to insulate a house enough so the mechanical load is dramatically reduced. In our climate zone, to achieve near net-zero or near-Passive house standards, insulation levels would have to be R:40 walls, R:60 roof, triple-glazed windows, R:20 basement wall and R:10 under slab foundations. While this certainly requires an initial cost for upgraded insulation, and a serious strategy about where and how to accommodate this additional insulation, the upgrade comes with a significantly reduced mechanical load and monthly energy costs. In many cases, the heating could be as simple as one mini split heat pump. The final piece to achieve net-zero is adding renewable energy, typically photovoltaic panels that produce electricity.