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Home Additions: An Architect’s Guide

Updated: Apr 15

What you need to know for a home addition in Wisconsin.

Home additions can be a challenge. There are many things to consider: zoning codes, existing building construction, existing roof lines, loading bearing walls, floor plan flow, and of course, we cannot forget design!

New residential home in process of being constructed

As architects, we start with the big picture and then we focus on the fun things such as what can my addition look like?  

The Big Picture (Zoning Code)

The zoning code is the most important and also the most boring (and sometimes the most frustrating part) of your project.  The zoning code will tell us what your building setbacks are.  Every lot has property lines and depending on your zoning code, there will be minimum setbacks (distances) from the property lines.  These setbacks tell us where your house or addition can be located. 

There are a host of other setbacks too.  They could be an article in of themselves.  We don’t want to make this article a sleep aid, so we’ll keep it light.  However, keep in mind that there are setbacks existing from septic systems, water wells, detached garages, shorelines, side yards, rear yards, front yards, even different street types (thanks, Wisconsin! - this is unique to you!)

In a nutshell, the zoning code will tell us what you can and cannot build on your property. We start this process by performing a Zoning Analysis.  To get started with our Zoning Analysis, we ask you to provide a Plat of Survey.  (Many people receive a survey when they purchase their home.)  Using this survey, we create a new drawing that includes all of the existing information (house location, property lines, etc), then add the building setbacks and use this document to calculate the allowable house size, allowable patio size, and deck sizes.

The Zoning Analysis becomes your roadmap.  It will tell us exactly what cannot and cannot be done on your property.  

Advanced tip: it doesn’t matter what your neighbors’ houses look like. Zoning codes have changed and evolved over the years.  What was built in the 1950s or even 20 years ago may be much different than what can be built today.

If you made it through that last section, glad to have you.  You’re likely in the minority.  Now onto the fun stuff.  

Start with a List of your Needs and Wants

Identify the Problems

What are your pain points?  This house would be perfect if…. (you fill in the blank).  Sometimes, the kitchen is too small, the laundry room is in the basement or a closet!  Other times, we need a first floor primary suite, a home office, or a place for the kids to hang out.  This is the fun part.  What works and what doesn’t?  We ask you to dream big.  While dreaming, identify the things you must have (your needs) and things that you would love to have (your wants).  

Once we have identified your wants and needs, we then discuss your construction budget.  By identifying your construction budget in the beginning, we can then tailor your drawings to fit this budget.  The last thing we want to do is a draw an amazing addition that exceeds your desired budget.  That becomes a waste of your time and money.

Work Scope Alignment

We have your list of wants and needs, we have your budget - now we determine what we can include in our work scope.  What makes us different is our construction background; utilizing our Design-Build experience, we have a good understanding of construction costs which allows us to tailor the work scope to the budget.

As an added measure of alignment we also meet with trusted contractors during the design phase. When we’re about 70% complete with the project, we meet with a general contractor that we frequently collaborate with.  They will take our in-progress drawings and put together a “ballpark” bid.  This bid will be within 10-15% of the final project cost.  The general contractor uses in-progress construction projects to determine what the current costs of materials and labor will be.  The end result, we have a real handle on construction costs during the architectural phase.  

If the preliminary bid comes in high and exceeds our desired budget, we have the opportunity to revise the drawings during the architectural phase.  Ultimately, this saves valuable time and money.

Visualizing the Space

Once you've pinned down your needs, start thinking about design elements. Do you envision a modern, open space, or something a little more traditional? We often ask clients to share their thoughts.  Sometimes, a rough sketch can go a long way in helping you and your architect get on the same page quicker.  While sketches are helpful, photos are even better.  

Many clients have a Pinterest board or photos that you’ve found elsewhere. Save these and share them with your architect.  Photos help us understand your style and the types of spaces that you like.  This allows us to more quickly align to your vision.  From here, we can develop a space that is unique to you.

Budgeting Like a Pro

Cost Breakdown

When budgeting, you'll need to consider material, labor, and unforeseen costs. Given the fluctuations in material prices and labor costs here in Wisconsin, I recommend budgeting an additional 10-15% for contingencies.  Contingencies are very important for older homes.  It’s not uncommon that a contractor will uncover something in the demolition phase that will need to be fixed.  As architects, we’re very good at understanding older homes.  However, we cannot see through walls or always know if a previous homeowner hired an unqualified contractor or decided to work on their own home without a permit.  

Depending on the age of your home, you could find old galvanized water pipes, antiquated electrical wiring, insufficient insulation, etc.  We usually anticipate and incorporate upgrades in drawings, but surprises still occur.

Keep in mind, a contingency figure is just a placeholder.  If it’s not needed, you do not spend it.  However, it’s something to keep in mind if you’re applying for a construction loan.  


Various financing options are available—home equity loans, refinancing, or specialized construction loans. Each has its pros and cons, so you might want to consult with a financial advisor.

Planning for Wisconsin and Illinois’s Climate

Insulation Is Key

In a climate like Wisconsin's, where winter temperatures dip low, proper insulation is not just an option—it's a necessity, required by code.

Within the last 20 years, insulation and energy codes have been written and strictly enforced.  We now follow the IECC (International Energy Conservation Code).  The IECC has a slew of requirements that covers everything from insulation to window ratings to recirculating pumps on water heaters.  It’s incredibly mundane; we know.

The upside, the code provides a great baseline for a well insulated home.  From here, we have strategies to utilize high performance insulation to make your house ultra efficient.  A design to minimize heat loss can have a utility bill that’s less than $50 a month.  The upfront cost is higher but the return on investment can be significant over time.

HVAC Considerations

Depending on the size of your addition, you may need to upgrade your HVAC system. An efficient system will not only keep you comfortable but can also help save on energy bills in the long run.

It’s rare that a home’’s existing HVAC system can support a new addition. We will often upgrade or install a new zoned system for the new addition.  There are also newer products, such as mini-splits that heat and cool new spaces.

The Maze of Permits and Zoning

Navigating Local Laws

I can't stress enough the importance of understanding your local zoning laws. Your addition needs to comply with height, setback, and land-use regulations specific to your county or city in Wisconsin. As we mentioned earlier, understanding the local zoning code is our first step.  As we approach permitting, all the zoning codes have been considered and met.


The permitting department varies greatly by your location.  In suburban and rural Wisconsin, this may be done by the County, your local municipality, the State, or a combination of these jurisdictions!  It can be confusing.  Some smaller towns have building departments, but no zoning departments.  In this case, we file for the zoning approval through the County and then proceed to the local building department.   All of our agreements include a “permit package” and “permit assistance.”  We work with the contractor of your choice to navigate the permit process.  

Part of the permit process is coordination and communication with the building official.  It is common and even standard practice of some building departments to require additional information as part of their review process.  We anticipate that the building official will reach out with questions and budget time to address these questions.

Choosing the Right Team

A Trustworthy Contractor

Selecting a contractor is where my clients often feel the most overwhelmed. That’s why I always recommend going with recommended contractors who are not only experienced but that we also have experience working with. 

Contracting is often specialized.  Some contractors are amazing new home builders however, they may not be qualified or efficient in building a home addition or renovating a home.  Home additions and renovations require a contractor to understand the existing home construction which may be 100 plus years old.  In addition, contractors must be experienced with selective demolition and temporary structural shoring methods.  For example, how do you remove a first floor load bearing wall with a second floor above it?  On the interior side of things, we’ve seen issues with flooring contractors not knowing or willing to create a seamless flooring transition.  


Architect-contractor collaboration is vital for a successful project. I often work closely with contractors to make sure that what we put down on paper translates into your dream space.  

No two home additions are the same.  As we mentioned, existing home conditions vary and our designs vary based on your unique wants and needs.  Consequently, it’s impossible to create drawings that will answer every question a contractor may have during the construction process.

The contractor and architect must possess open lines of communication.  Sometimes the questions are critical, “we opened up a wall and found something completely unexpected, what do we do here?”  Or it could be a small but critical design question. “We installing a new window and have too little or too much space for the interior trim to look right, what should we do?”  A good contractor will call the architect and ask the architect to devise a solution.  

However, some contractors may just do what they think looks best or whatever is easiest.  Alternatively, the contractor may call the homeowner and tell them they need them to provide an opinion right then and there.  As you could imagine, all of these scenarios end up being a problem.  It only takes a bad decision or two, to derail a really nice project.  Who wants a weird trim detail in their living room or in their kitchen?  

The success of a project is in its execution.  

Realistic Timelines

Planning and Permitting

The initial planning phase usually takes around 3-6 months, while permitting can take an additional 3-4 weeks depending on the local building department.

Construction Phase

Based on the complexity, the actual construction typically takes 5-8 months. Weather conditions in Wisconsin can impact this, so it's something to keep in mind.  Good contractors will work year round, however, concrete can only be poured when temperatures are above freezing and will remain above freezing for a couple of days.

Final Thoughts

A home addition is not just another project—it's an extension of your life and a significant investment. While many of our client’s discussions begin with, “ we need some extra space”, the reality remains that there are many elements that must be considered.  Schedule a zoning analysis with us to see how these elements impact you and your home. We understand the nuances of designing and building in Wisconsin and Illinois, and with the right team and planning, you can create a space that’s not only functional but also adds value and enjoyment to your home for years to come.

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