#solarREDyhouse in the Summerhill neighborhood of Atlanta goes on sale this weekend. Like a previous development project, this house is located on a narrow 25' wide lot. I had to rezone the property to waive zoning restrictions that prohibited building houses narrower than 20' in the neighborhood. There is a lot of thought that goes into these houses which I will share in subsequent posts but let me start with the main theme of the house: #resilience and #sustainability.

A mentor Jeff Stebar once told me that a project has a greater chance of success if it has a story to tell. Some might call it a mission statement. This vision becomes incredibly helpful when tough decisions need to be made regarding where to spend limited resources and money.

I like cool design that makes a statement, but early in the project, I abandoned a more modern and avant-garde aesthetic. The zoning in the neighborhood suggested that they were burned by some bad developers before the 1990s. To protect the community from future bad developers, they adopted prescriptive zoning laws that governed what a house can look like in the neighborhood. Rather than fight these restrictive covenants that protect from poor design but also ironically limits good design, I decided to focus the story on something else.

Something that bothered me about the first house I designed #aMewsHouse was its energy performance. The projected EUI was 32 kBTU/sf/yr which is unchanged from the baseline case for the 2030 Challenge. The theory why the house didn’t compare well is that for long, skinny and tall houses, the ratio of exterior wall to conditioned space is very high compared to typical houses.

For #solarREDyhouse, I wanted to see if we could do better than #aMewsHouse. From a sustainability perspective, both houses’ main impact on energy results from site selection and size. They are spatially efficient, being 25% smaller than dwellings with similar features reducing its lifecycle costs. That is 25% less building material, 25% less home to heat and cool, and 25% less area to accumulate stuff. Regarding site selection the home is on previously developed land within ½ mile of existing street, bus, and bicycle networks. Additional sprawling infrastructure does not need to be constructed or maintained.

Where else could we do better? One frustration I have is that important tools like energy modeling and third-party certifications in theory shouldn’t be that expensive, but for small developments like these, they are expensive for us in labor and cost. The alternative method I chose to implement was simply to make better choices about construction design and materials based off known evidence.

They are often neatly summarized in “rules-of-thumb” based strategies. A book that does this well is Pretty Good House: A Guide to Creating Better Homes by Kolbert, Mottram, Maines and Briley. BRANZ, a New Zealand building science research company, shared 6 rules of thumb for carbon footprint reduction in 2022 in Build magazine. I also loved Christine Williamson’s Building Science Fight Club social media posts.

So, armed with the advice of folks smarter than me, I embarked on seeing if we can make better decisions about this second skinny spec build.

THE PROBLEM:

You know your house is not working as well as it could. You have ideas about how to improve it, but you have no idea how much it may cost. Is it better to just sell the house and buy a new one? Or is it better to stay put in the neighborhood you’ve become attached to and renovate?

It can be a daunting decision, but I’ve found a simple and useful exercise you can do on your own that may help you frame the problem and how much money it may take.

The problem basically is comparing two options: Do I sell and buy new, or do I renovate?

I won’t spend too much time on the sell-and-buy decision. Just search online and find out how much houses are selling in your community and other neighborhoods. Working with a real estate agent may be helpful without any upfront costs.

I will focus more on how to look at the other side of the equation: renovation/addition/build new.

Most folks have ideas about renovating their existing house -- maybe changing the kitchen and add a bathroom -- and then building a new addition to the house. For various reasons, this is difficult to estimate without detailed drawings. Those drawings require cost and time to produce. Without better understanding of cost however, I would be hesitant to pay for design and drawings to find out that I couldn’t afford the project.

Instead, I’d like you to consider the following “bracketing” scenarios which can be easily done on your own.

There are three scenarios:

A. ALL NEW: Demolish your existing house and build a new one.

B. RENOVATION+ADDITION: Renovate part of your existing house and build an addition/extension.

C. MAXIMUM SIZE: Keep your existing house AS-IS with no changes and build an addition.

Below is a recent example I completed with a young family.

SCENARIO:

A young family with two young children is outgrowing their 1960’s 1,200 sf house. They have a tentative budget of $300,000.

A key assumption is the cost per square foot of new construction. In this case, I know a modest 1,700 sf house was recently built for approximately $245/SF.

Another assumption is how much of the budget is spent on construction. I assumed the cost of experts and consultants is approximately $40,000. That leaves $300,000 - $40,000 = $260,000 available for construction.

Option A “All New”

This option usually creates the smallest house because all your money is going into new construction costs.

The project demolishes the existing 1,200 sf house and is able to build a new $260,000 ÷ $245/sf = 1,061 sf house.

This is smaller than the existing house! As an architect, I’m not as worried about this option because a smaller one can work better for the family if designed well.

Another important note is that none of these options consider the cost of temporarily living someplace else while construction is happening.

Option C “Maximum Size”

This option keeps the existing house AS-IS with no changes except where the new house addition attaches to the old house.

This produces the largest house project: 1,200 sf existing + 1,061 sf = 2,261 sf.

It’s rare this option works for a homeowner because the existing house often has serious or annoying problems.

Option B “Renovation + Addition”

That leaves option B which as stated earlier is hard to evaluate, but it will be somewhere between options A and C.

In this example, the family’s next-door neighbor recently renovated their kitchen and added a bathroom within an existing house. The neighbor’s house is like their house. The project cost $120,000. So, a reasonable version for our project is a $120,000 kitchen renovation which leaves $140,000 for a 571 sf addition ($140,000 ÷ $245/sf.)

As mentioned earlier, this option is always the hardest to evaluate, but I feel that once potential clients have done this exercise, they then have one more piece of information to help them decide whether to hire experts.

Additional thoughts

In my experience, it’s rare that option C works for people. There are just too many problems to solve in the old house, so most people quickly look at option B and option A.

Most people are skeptical that option A can work for them, so I like to suggest that they do another exercise on their own. Determine the number of bedrooms and baths they need in a house. Let’s say 3 bedrooms and 2 baths. Then, look online for a house plan that is 3 bedrooms and 2 baths and 1,000 sf. There are good plans and awful plans published online. If you can find one that looks like it will work for you, then option A is a possible one for your project especially if you hire a good architect who can often make that online plan better.

For option B, it’s helpful to find “logical” places where the old house stays the same and the renovation can begin. Usually, the renovation cost does not get more expensive than new construction, BUT there are times when certain renovation designs are more expensive than building new. You really can’t know this until the house project is designed and drawings are created. A perfect example of a hard-to-estimate design is building a 2nd floor on top of an existing 1-story house. Again, you mitigate this risk by hiring an experienced architect or builder that can advise you when design choices are leading to expensive construction.

Finally, one can see how important new construction cost per square foot is in this analysis. In this example, I felt good about $245/sf because I’m building a 1,700-sf house right now at that cost. A valid criticism of this number is that it needs to be higher because a new smaller house (1,000 sf) would likely cost more per square foot. The theory is that kitchens and bathrooms are the most expensive spaces to build. In a small house, kitchens and bathrooms take up a greater share of the house space than a large house. That helps explain why there is sticker shock from folks trying to build ADUs (accessory dwelling units) aka granny cottages in the backyard. I’m hearing numbers at $400/sf for a small 400 sf flat.

Anyway, I hope this document is helpful to those that have found it. The intent was to give you tools to help analyze your project before having to spend money on expertise.

Alex Wu, AIA

June 18, 2024