The Coverage Squeeze: How Patios and Sheds Limit Your Building Plans

[: 00:00

Bill Reid: Did you know that the concrete patios and that old shed in the backyard could limit the amount of square footage you could have in your new home or maybe even your expansion? Perhaps you're thinking about adding an accessory dwelling unit in the backyard while also remodeling or building a new home. All of these things are factored into what's called lot coverage and impervious surfaces. These are more design restrictions that are lurking about.

If you, as a homeowner, get to know these ahead of time, you can empower yourself to make prudent choices during the design process, as opposed to way too late after you've spent thousands of dollars. Let's dive into the studio and talk a little more detail about this in our Understanding Design Limitations and Restrictions series so that you as a homeowner are empowered. We'll see you there.

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[: 00:49

Bill Reid: All right, welcome back everybody to Your Home Building Coach. I'm Bill Reid, and we're continuing our Understanding Design Limitation series. If you've been following along, we've already covered some heavy hitters: floor area ratio, setbacks, and easements in Episode 35. Each one of these puts a squeeze on what you can do with your property. Today we're tackling two more restrictions that work together to limit your options: lot coverage and impervious coverage.

Here's the thing—these can sneak up on you late in the design process when it's expensive to make changes. I've seen homeowners get all the way through design, excited about their new garage or ADU or outdoor living space, only to have the city come back and say, "You've exceeded your lot coverage."

That's a heartbreaking conversation to have after you've invested thousands in architectural plans. So let's make sure that doesn't happen to you. Let's break down exactly what these restrictions mean and how to navigate them.

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[: 01:55

Bill Reid: Let's start with lot coverage because this is the one that catches most homeowners by surprise. Lot coverage is exactly what it sounds like—it's how much of your lot is covered by buildings. But here's where it gets tricky: the definition of "buildings" is broader than you might think.

The way I want you to think about this is to look at an aerial view of your lot with your buildings on top of it. We're talking about the footprint of buildings. Not necessarily that you're building a 3,000 square foot two-story home, but that you're building a structure that is maybe 3,000 square feet with a thousand square feet on top and 2,000 square feet on the bottom. What really matters is you've got 2,000 square feet of footprint sitting on the land.

Your primary residence is the big one that will always consume the most square footage. But let's back up for a minute and talk about what lot coverage really is. Lot coverage is a calculation based on the square footage of your lot relative to the square footage of the buildings on the property. If you have a 10,000 square foot lot and you have 5,000 square feet of buildings on the property—and believe me, it's easier to get to that level than you think by the time you factor everything in—then you have 50% lot coverage of the buildings themselves.

Each city, county, and sometimes even homeowners associations have limits to the amount of lot you can cover with buildings. We'll get into why those rules even exist, but let's go back to what really classifies as lot coverage.

I just spoke about the primary residence, and that could be your main house footprint—maybe 2,000 square feet as I mentioned earlier. You also have to think about attached and detached garages. You may think you have 2,000 square feet of living area on your first floor, but you really have a bigger footprint than that. That could include your attached garage, or it could be a detached garage building footprint that's on the property as well.

Accessory structures are something you really have to pay attention to because these are also calculated into lot coverage. You could have a 2,000 square foot home, a 500 square foot attached garage, and then another shop in the back that's another thousand square feet. Or perhaps you want to have an accessory dwelling unit in the back of the property. That counts towards lot coverage.

Another thing that counts towards lot coverage are covered patios, porches, and pergolas—anything with a solid roof. Think about the things where if it rains, that rainwater cannot enter into the earth because there's a roof structure over it preventing precipitation from returning back to the earth to recharge the groundwater system. This is one of the reasons cities, counties, and HOAs have these rules: they want to capture as much precipitation back into the property rather than having it run off into a storm sewer system.

Also keep in mind that when an architect calculates lot coverage, they're not just considering the boundaries of the outside walls of these structures. Many jurisdictions have you include the overhangs or eaves around the structure. You could have a 2,000 square foot footprint, but it might end up being 2,200 or 2,500 square feet when it comes to calculating lot coverage because of the overhangs on the buildings.

You can see where I'm going here. By the time you factor in your primary residence, your garage structures, your porches, your pergolas, sheds in the back, maybe an accessory dwelling unit on the back of the property—all of these things factor into what is called lot coverage. Cities will only allow maybe upwards of 30 to 60% of your lot to be covered with buildings.

This is really important. I had a client who wanted to add a detached workshop. The house was 2,200 square feet on a 6,000 square foot lot. The lot coverage limit was 50%, so that's 3,000 square feet of building footprint allowed on the property. The existing garage was 400 square feet. A covered patio was 200 square feet, and then there was an old shed nobody thought about—another 100 square feet. That's already 2,900 square feet. The workshop they wanted was 500 square feet. You can see where this is going: they were already at the limit before they even started.

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[: 07:24

Bill Reid: Let's go through the calculation method one more time.

The lot coverage calculation works just like the floor area ratio calculations that we did back in Episode 33. Remember, these are directly related to each other—both are limiting the size of home you can put on the property. It's a percentage of your lot size: your total covered area divided by the lot size equals your lot coverage percentage.

Typical limits in many cities and counties range from 30 to 60 percent, depending on the zone and lot size. Urban lots usually have around a 50 to 60 percent lot coverage allowance. The further outlying you go into suburban and rural properties, you're usually in that 30 to 50 percent range.

Unlike FAR, lot coverage doesn't care about how many floors you have on the property—it's just the footprint. As I mentioned earlier, you could have a 3,000 square foot home, but if it's a two-story home with only 2,000 square feet on the ground, that's what you use for the calculations.

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[: 08:45

Bill Reid: Let's say you have a 6,000 square foot lot with 50% lot coverage. That's 3,000 square feet of structures you're allowed to have on the footprint of the property. Your two-story house might have 2,500 square feet of living space. But if the footprint is only 1,400 square feet, that's what counts for lot coverage. I just want to drive that point home because some people have made that mistake.

The second floor sits on top of the first. It doesn't add to the coverage. This is different from FAR where both floors are counted. So they kind of have you coming and going, right? They have a floor area ratio they want you to follow. On top of that, they have lot area restrictions you have to calculate.

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[: 09:30

Bill Reid: Here's where lot coverage interacts with your FAR: You might have FAR room for more square footage, but lot coverage might prevent you from building it. This is why I say these restrictions compound on each other.

Let me share why this particular restriction can sneak up on you—and sometimes on your design team. In my experience, lot coverage is what I call a "late discovery restriction." Here's why: Designers tend to focus on floor area ratio and setbacks first. Sometimes they forget about existing outbuildings that get overlooked in the calculations. Sometimes they miss easements going right through your property, which I spoke about in previous episodes.

Sometimes future plans get forgotten—things like a future accessory dwelling unit or a large pool and patio area that you're phasing to the next stage of the project. If that isn't factored into a master plan, you might be burning yourself. When you go to put in the pool, landscaping, and hardscaping, the city or county is going to ask for a lot coverage calculation. Because you've built your home to the maximum floor area ratio without factoring in lot coverage, this is where you can really get into trouble.

Also, people tend to forget covered outdoor spaces, which can add up faster than expected. You may have a nice large outdoor kitchen area with a big covered roof, or a pool house or cabana with a roof over it. Sometimes you have an extended deep front porch—those big beautiful wraparound covered porches. Even though that's not factored into your home's square footage, it's factored into the footprint of the building, which can significantly impact your calculations.

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[: 12:19

Bill Reid: So that's lot coverage—the restrictions on buildings and covered structures. But there's another restriction that goes even further, and it's becoming increasingly important. It's called impervious coverage.

This is almost just like lot coverage—in fact, it does affect the lot coverage calculation—but there are going to be two different rules here. Your cities will tell you what your lot coverage is, they'll tell you what your impervious coverage maximum is, and you have to factor both into your calculations when designing your home. Let's move into that segment and talk about impervious coverage.

I want to start with why this even exists, because understanding the "why" helps you work with these restrictions instead of fighting against them. Impervious means water can't pass through the material. So impervious coverage is any surface that prevents rainwater from soaking into the ground. Obviously, buildings and roofs that direct water away from buildings would count in the overall calculation. Also concrete and asphalt driveways, patios, walkways, hardscape, pool decks, all the decking around the pool, and even some compacted gravel surfaces.

Think about it this way: every square foot of concrete is a square foot that says "no" to rainwater. This water has to go somewhere, and historically that means into storm drains and eventually into streams, rivers, and lakes. Cities are now saying we need some of that water to stay on your property and soak into the ground.

So impervious coverage goes beyond just buildings. It includes all that hardscape we take for granted. And there's a good reason cities are getting stricter about this.

Here's the environmental reality driving these regulations. Understanding this will help you see why these rules are getting stricter, not looser:

Stormwater runoff increases flooding risk in communities. Municipal storm drain systems become overwhelmed. Groundwater aquifers need recharging. Runoff also carries pollutants like oils and chemicals to waterways. Climate change means more intense rain events and an even bigger problem.

I've seen some jurisdictions go from having no impervious limits to requiring as little as 15 to 30 percent maximum impervious coverage—and that's in addition to the lot coverage calculation.

I did a little research because I wanted to look at other communities I'm not familiar with. Wake County, North Carolina limits residential lots to 30 percent impervious coverage. Some Massachusetts towns cap it at 15 percent plus 2,500 square feet. This isn't going away—if anything, expect these limits to tighten up. The environmental rationale is solid. The question becomes: how does this affect your project?

Here's the squeeze that catches homeowners: Impervious coverage is almost always more restrictive than lot coverage. Here's why: Lot coverage only counts buildings. Impervious includes buildings plus all the hardscape. You have to factor those together. You could be under lot coverage but over on impervious coverage. That driveway, walkways, and patio all count.

Let's go back to that 6,000 square foot lot. Say the lot coverage allowed is 50%, which would be 3,000 square feet of buildings. But impervious might be 40%—only 2,400 square feet total. Your 1,400 square foot house footprint plus the 400 square foot garage equals 1,800 square feet. Add a 400 square foot driveway, 200 square feet of walkways, and 300 square feet of patio. Now you're at 2,700 square feet—already over the impervious limit, even though you're under lot coverage.

You need to track both numbers. The good news is there are solutions—ways to get the outdoor living space you want while staying within impervious limits.

In summary of this segment: Impervious coverage includes everything that prevents water absorption—your buildings plus all the concrete, asphalt, and hardscape. Cities are tightening rules because of stormwater management and groundwater recharge needs. This restriction compounds with lot coverage because it counts more surfaces, which is why you might be under lot coverage but over impervious limits.

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[: 17:04

Bill Reid: All right, let's stop complaining about the problem and see if we can come up with some solutions.

Here's where I want to give you some hope, because there are solutions. You don't have to give up that patio or make your driveway smaller—or even make your house smaller just so you can have a bigger patio. There are materials and design approaches that can help you stay within limits while still getting the outdoor living space you want.

The construction industry has developed materials specifically designed to let water through. These are called pervious or permeable surfaces, and they can really be game changers.

Pervious concrete and asphalt have tiny voids that let water pass through. If push comes to shove, you can have your civil engineer, architect, or landscape contractor research that with you and propose different concrete and asphalt products for your upcoming project.

Interlocking pavers with gaps for drainage is one idea. There are also interlocking pavers designed to be permeable. You'll have to look closely at those because I don't know if they're as attractive as regular interlocking pavers. There are also some really interesting ones that are interlocking pavers with large voids in the middle—they come in different styles and designs where you can plant grass in between each of the pavers, but you can still drive on them or walk on them as if it was a concrete walkway. This lets moisture permeate through.

You can also use natural stone for your gravel beds and walkways. You can use compacted stone products for landscaping that doesn't count towards impervious surfaces. And of course, wood decking often allows water to permeate through the gaps between deck boards.

Some municipalities give partial credit for permeable pavers. That 400 square foot driveway might only count as 200 square feet towards your impervious limit if you use pervious material. Be careful though—you don't get full credit just because you're using a permeable material. Check with your county or city to make sure that's the case.

There's a downside: cost considerations. Permeable pavers can definitely be more expensive than regular pavers—sometimes up to 50% more for materials. The labor isn't really going to be much different, but if you're designing a permeable paver driveway, the substrate below is different than a conventional paver system.

If you're interested, search for "permeable paver driveway details." You'll find there's a lot more work below the surface that your landscape or excavation contractor has to do to achieve permeability through the stone and into the ground. Otherwise, you're just putting compacted base rock and sand, which doesn't allow as much permeation through the system.

You can also check whether some cities offer rebates. If you use a permeable surface for your patios, the increased material cost might be offset by rebates. Factor all that in too.

Beyond materials, there are design strategies that can help maximize your property within these limits. Understanding this ahead of time could directly influence the size, shape, and locations of buildings on your property.

Build up instead of out. Remember, a second story on a two-story home doesn't count for impervious or lot coverage. Combine your functions—attach your garages to your structure. If you have a two-story home with the garage attached to the main floor and the second story above it, you're maximizing efficiency of how your building footprint impacts the property.

Strategic removal of existing impervious buildings, walkways, or landscape elements is another approach. When factoring that in, you may want to seriously consider removing that big patio so you can help with your calculations on the overall project.

Rain gardens and bioswales as landscape features help with drainage.

Underground stormwater detention is another option. Many cities require underground stormwater retention, which means putting in what's called a dissipation pit. In a location on your property, all the roof drainage, downspouts, and other drainage off hard surfaces are collected into a large pit—sometimes four feet by four feet by six to eight feet deep in the ground—filled with gravel and filter fabric. All drainage comes into that location, goes into the dissipation pit, and eventually works its way back into the groundwater system.

Some cities will allow you to increase your impervious coverage if you commit to putting in a dissipation pit, because you're still collecting all the water into a drainage system that ties into this pit. Ask that question—it might be a way to get around the general standard impervious coverage calculations.

Remember: Pervious materials like permeable pavers can reduce or eliminate impervious area calculations. They cost more, typically 30 to 50 percent more, but some cities offer rebates to offset those costs. Design strategies like building up instead of out, removing existing impervious surfaces, and implementing a dissipation pit management system could help you increase your coverage allowance.

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[: 24:00

Bill Reid: Here's your action plan that we try to do at the end of every episode. This is your homework.

If you're thinking about doing a project—if you're thinking about doing a large landscaping project but someday want to add on to your home—be thinking about your lot coverage calculations so you don't back yourself into a corner. Then two years from now, when you want to expand your home, you can't.

Or it's the flip side: you're planning to expand your home, maximize your floor area ratio, maximize your impervious coverage and lot coverage, but you plan to put in a pool later or large landscaping patios and outdoor kitchens and covered roofs outside. You might be in trouble if you didn't consider that as a master plan.

First, contact your planning department. Ask specifically about lot coverage and impervious coverage limits for your zoning district. I went online to a random city, went into the municipal code—and if you remember some of my previous episodes, I talked specifically about municipal codes—and I searched "lot coverage," "site coverage," and "impervious coverage." Up came the policies within the city's municipal code. You can start reading through that.

Contact your planning department, whether directly face-to-face or begin on the website to learn about these restrictive elements. If you do visit the county or city, get it in writing, or at least have them show you in writing where it is, because verbal answers are just not reliable when you're dealing with a planner across the counter.

Clarify what counts towards your impervious coverage and building coverage. Get clarity on things like: Are extended eaves covered? Are covered patios included? What about decks? How are pervious materials credited?

Take an inventory of what you have on your property now. List every structure and hardscape on your property with the square footage. Calculate your current numbers. Know where you stand before designing anything new.

I want to mention one more thing—I've mentioned it many times in previous episodes: a land surveyor. If you hire a land surveyor to survey your property for boundaries, setbacks, easements, and topographic mapping, surveyors will show the building footprint, all existing hardscape, and can even give you calculations right off their data. Their survey drawing will tell you how much square footage your building footprint is, how much square footage your impervious coverage elements are. It's done for you.

This is something you'll want to seriously consider when beginning to design a project—having a survey with a topographic map done, especially if you're on a hillside property. This is a very good foundational aspect of good design.

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[: 27:00

Bill Reid: In summary: Contact your planning department. Get coverage limits in writing, or have them show you specifically where it is in the municipal code. Understand what counts towards each limit. Inventory your existing coverage and calculate your current numbers. If you really want to get down to the nitty gritty, have a surveyor do all that for you. Pay the two, four, five, six thousand dollars—whatever it is—a minuscule investment compared to what your project will ultimately cost.

Here's what we've covered today:

Lot coverage limits how much of your lot can be covered by buildings. Everything with a roof counts—just think about it that way.

Impervious coverage goes further, including all your hardscape: driveways, patios, and walkways.

These restrictions compound on each other and sneak up late in the design process often.

But pervious materials and smart design strategies can help you maximize your property within these limits.

If you want to dive deeper into lot coverage and impervious coverage, you can grab a copy of the book, "The Awakened Homeowner" on Amazon. Among all the other aspects of planning a project, you can start digging into that. Start building up your knowledge that way if you're getting tired of listening to my voice.

If this episode helped you understand coverage restrictions better, share it with somebody planning a project. Send it to your friends who are looking at adding an ADU in the backyard, or that neighbor dreaming about a pool. This information could save them from expensive surprises.

I'd love to hear from you too. Have you run into coverage issues on your project? Drop me a DM on Instagram or leave a comment on YouTube.

All right everyone, that's what I had for you today. Lot coverage and impervious restrictions, compounding with all the other ones I've covered in previous episodes: floor area ratio, easements, and setbacks.

I'm Bill Reid, your home building coach. Remember: Enlighten, empower, and protect. That's what we do here.

Thanks for listening. Now let's go make it happen.

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