Wednesday, October 20, 2010

Existing Home Energy Analysis

We are currently designing a remodel on the west side of San Juan Island. The owner is very interested in sustainability and balancing the energy efficiency of the finished product with the desire to keep as much as possible of the existing house (and of course keep the cost as low as possible). The fact that the clients purchased a home to remodel instead of tearing it down or building new is the first step in having the most sustainable home possible. To make sure they are happy with this decision, we must complete an accurate energy analysis to ensure that they are comfortable in the home and with their energy bills, while keeping the budget intact.

The existing house has 2x4 walls, which means that the space in the wall cavities does not allow for the thickness of insulation needed for the prescriptive requirements of the Washington State Energy Code (WSEC). If a building does not meet prescriptive requirements, performance requirements must be met, which in the case of the WSEC requires component analysis for existing buildings, using their Component Performance Worksheet. This entails evaluating the existing components: the types of windows and doors, existing insulation, area of existing glazing vs. wall area. It is time consuming, but a great tool for evaluating an existing building. 

The Component Performance Worksheet is available here.  

The use of this system is great for greening existing homes. There are so many new green products and so many different choices, it can be overwhelming. You may think, oh my gosh, to make my house energy efficient, I have to take out all of the insulation, get all new windows, get a new HVAC system, etc. But you may not have to do it all to get your home up to the current standards of the energy code. 

 A high efficiency heat pump (here connected to radiant floor heat with an insulated slab) can go a long way in improving your total UA

This worksheet automatically tallies your UA (sum of the U-factor times the area) versus the Target UA based on the area and volume of the house and the climate zone. (The definition of u-factor is here. It's really technical and boring, but basically the lower the number, the better. For example, in Seattle our windows have to have a u-factor of below 0.35, while in Georgia they just need to be below 0.75). So, you can play with things until you get the number you need. For this house, it may mean that not ALL of the walls need to be upgraded to 2x6 if I choose the most efficient HVAC system and house that HVAC system within the building thermal envelope. Of course, we want to do all we can to make it as efficient as possible, but most of the time that's just not feasible, especially considering the unknown costs and potential surprises inherent in a remodel. 

Still mystified by how to green your existing home? Feel free to contact us with any questions.

1 comment:

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