Green Roofs Myths Debunked: Too Expensive

As the Green Roof industry grows, we are finding more instances where people reject the idea of a green roof on their building due to a lack of information (or misinformation). So here at Sow Green, we are setting out to combat some misconceptions about green roofs with a series of articles debunking the most common myths.

Myth #2: Green Roofs are Too Expensive

Although green roofs do cost anywhere from $10-25 per square foot, they are not more expensive than traditional roofs overall, and there are several reasons why.

Green roofs last longer than traditional roofs. In fact, they often last two times as long, if not more. This is because the layers of soil, root barriers, and vegetation protect the waterproofing membrane of a roof from UV, hail, wind, and other damage. Therefore, you don’t have to replace or retrofit your roof as soon (which can save you a lot of money in the long run).

You also save money on heating and cooling costs. Black roofs often get hot in the summer by absorbing the sun’s rays, which often makes buildings hot too. Thanks to a nifty natural process called evapotranspiration, the vegetation on a green roof can make the ambient temperature above the roof at least 6 degrees cooler. It also insulates the roof, keeping cool air from your A/C or heater inside. This is especially true in winter since warm air rises, many buildings often lose heat through their roofs. But with a green roof, you don’t have to use as much energy to climate control the building, so you save money. How much money varies depending on the type of green roof and the insulation of the rest of the building. And finally, with an increasing amount of volatile weather and many cities experiencing extreme flooding, stormwater management costs are at an all-time high. This is because urban development in major cities is created more surfaces laden with concrete and steel instead of soil and trees. But green roofs reduce the amount of stormwater a building has to treat because the soil and vegetation soak it all up (and in many cases can reduce pollution runoff). So not only are you reducing the impact your building has on the natural environment, but you’re saving money in the long term on stormwater fees. Many cities even have programs that give a reduced rate to buildings with vegetative roofs or permeable surfaces like brick parking lots.

Although it is important to do a cost-benefit analysis before embarking on any large scale project, many green roofs offer long-term advantages. Like with many other sustainable projects, green roofs are a little more expensive upfront but can give you big savings in the long run, and therefore should be treated as a sound investment instead of a financial burden.

Green Roofs Myths Debunked: Leaks

As the Green Roof industry grows, we are finding more instances where people reject the idea of a green roof on their building due to a lack of information (or misinformation). So here at Sow Green, we are setting out to combat some misconceptions about green roofs with a series of articles debunking the most common myths.

Myth #1: Green Roofs Leak, and Often

Because many green roofs require irrigation and drainage, one of the most common misconceptions is that they can leak, and when they do they leak a lot. Although there are cases where vegetative roofs have leaked, especially shortly after installation, whether or not a roof will leak has nothing to do with it being a green roof. In other words, traditional roofs are just as susceptible to leaking, and there is no evidence that green roofs have more of these issues. In fact, more evidence supports just the opposite.

Because the additional layers of vegetation and soil cover the waterproofing membrane of a green roof, it is protected from UV light and therefore receives less UV damage over time. Those additional layers also protect the membrane from hail, wind, and storm damage. This is why green roofs often last up to, if not more than, twice the lifespan of a traditional roof. Also, many green roofs have an additional protective barrier that keeps roots from digging too deep.

One of the reasons why some green roofs do leak is that the membrane was damaged during construction or that the seal between the membrane and the drains are not adequate. Green roofs DO require irrigation and drainage, so it’s important to make sure that during installation, the membrane is installed correctly. Many cities with green roof legislation like Denver, require leakage tests to prove the membrane is waterproof.

When performing maintenance, it is also crucial to make sure that any digging or tilling of soil does not damage the waterproofing membrane. Often when getting a green roof installed, the first few years of maintenance (what we in the industry call the establishment period) is included in the budget and done by a professional contractor or landscaping team that is familiar with the system and won’t damage it.

So there you are! Leaking is not a problem specific to green roofs. As with any project, correct installation and maintenance are key in keeping any issues at bay. That’s one myth debunked, stay tuned for our next article in this series!

The Latest Green Roof Trends in North America

Last week, Sow Green attended CitiesAlive in New York City, hosted by Green Roofs for Healthy Cities. CitiesAlive is the largest Green Roof conference in North America, and we walked away with a plethora of information and soaked up the latest in vegetative roof installation. From that, we gleaned some of the latest trends and the future of the green roof industry. We thought we’d share some of our favorite insights from CitiesAlive here:

Be bold and innovative

We heard from world-class designers across North America, some of which created incredibly innovative green spaces. Their experience allowed them to incorporate nature and aesthetics while still reducing environmental impact.

Fernando Ortiz Monasterio of Mexico City decided he needed to help transform the concrete jungles of the Mexican capital to a lush landscape. So he wrote a petition to citizens in Mexico City, asking how they would feel about covering Mexico City highways in green walls, as well as suggestions on how they should fund it. The response was overwhelming, with over 80,000 signatures! Countless meeting with government officials and city representative later, they were able to fund over 1,000 highway pillars with ad space above the green walls, with felt made from recycled plastic bottles. Talk about greening a city and building community!


We also heard a great talk from Ken Yeang, who initiated and inspired nature-based architecture into modern buildings. Yeang uses a process called bioclimatic design, which uses design to build structures that will naturally heat, cool and light themselves. He creates interactive and functional projects and eco-cities by incorporating natural features, the interaction of people, buildings and the local habitat. Ken has been named one of the Top 50 people who can save the planet.

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Education and client expectation

Managing client expectations is always important, but it can be especially stressful in the case of sustainability projects. The sustainable way is often the natural way, and nature takes time. For clients who expect fast and cheap, this can be a struggle. For example, there are only certain times of the year one can plant vegetation on a green roof. There is a lot of preparation needed in order to select and grow the right plants, and the local climate and habitat often play a part. Green roofs also need to be able to hold more weight and need the correct waterproofing membranes. This is especially necessary for clients who are in need of a retrofit to understand. Green roofs also need irrigation (at least for the first few years) and regular maintenance. This needs to be planned for early and included in the budget. Communicating the process, budget, savings, and work involved in installing a green roof is critical not only for your clients' peace of mind but also to help the industry grow with a solid reputation.

Education is also going to be increasingly important in our industry. There are still a lot of myths (which we will debunk in our next few blog posts) associated with green roofs. It is imperative that everyone in the industry is working to educate the public and their clients about the realities of green roofs.

More cities are requiring green roof laws

We attended a great talk from Rafael Espinal, the City Council member of New York City that proposed a green roof rule for new buildings, and he is not alone. Many cities across North America are creating green roof requirements or mandates. As the conditions caused by climate change become increasingly challenging, cities are in need of solutions that reduce the heat island and increase the number of natural habitats. We talked with Brandon Rietheimer, a young Denverite who started and ran Denver’s Green Roof Initiative, pushing for a local green roof mandate via public election. The initiative won, despite opposition from development (Fun fact: He is 31 years old, and this was his first campaign, but he managed to get 4,000 signatures all on his own!). Experts Andy Creath and Jennifer Bousselot also gave a presentation on their contributions to Denver's Green Roof Law. A group from Portland also attended, discussing their new Green Roof requirement, which took over 8 years to enact! Seeing so many people working together to make their cities a little greener has inspired us, and it makes government support and encouragement one of our favorite trends from this year!

The large crowds and excitement surrounding the CitiesAlive conference got us really fired up for the future! We met a lot of inspiring people and got to witness firsthand how the industry is growing (pun intended). We can't wait to see where things will go from here!

Green Roof Failures and How to Prevent Them

We talk a lot about how great green roofs are. They have amazing benefits to both property owners and the local community. When done correctly, they can offer cost savings and add a great amenity to a residential or commercial building. But what happens when they don't work? They don't happen very often, but green roof failures do exist and they can be costly to a maintenance budget. In this article, we discuss the most common green roof failures and how to prevent them.


A flat roof isn't always truly flat. There are typically a lot of highs and lows in traditional concrete slabbed roofs. And since you'll need irrigation to help plants develop well, good drainage is key in order to prevent a very common issue with vegetative roofs: puddles of water and wetness that perpetuate throughout the year. Before installing planting medium and the plants themselves, proper testing to see where the water goes is crucial to properly place your drains. And in addition to good placement, you also need to ensure you have enough drainage. Many people assume that since the soil and plants will absorb a lot of water that not much drainage is needed, but you probably want to be conservative in your estimate. Too much standing water can lower your plant's survival rate and attract pests. The best way to prevent ponding is to create a 1:60 slope on flat roofs.  

Soil and Plant Selection

Correct plant and soil selection are crucial for your green roof to survive. Sedums (similar to succulents) are often selected because they can survive in a variety of climates and require a growing medium that is dry and has low amounts of organic matter. But depending on the needs of your specific project, you may require shrubs or flowers to make the roof more ornamental. If this is the case, make sure you work closely with your contractor to make sure they are knowledgeable of what does best in your local climate. That means using native plants and native soil (although soil left over from the construction site may not necessarily be the best choice). If the architect or contractors are not familiar with soil and plant selection for the local region, hire a horticulturist. In Denver, many successful green roofs already exist, so we have the luxury of having a lot of examples to work from.

A Different Microclimate

A roof that sits several stories above floor level has a different microclimate than your backyard garden. Temperature and wind vary at that height, and if your green roof sits atop a skyscraper even the barometric pressure can fluctuate. You also get higher UV levels the taller you go. So plants are often exposed to very different elements and they need to be taken into account.


Assuming you have proper drainage, erosion can be another issue especially at the edges or corners of the roof. Making sure that vegetation is sectioned and contained by edges of pebbles or gravel paving will allow good drainage of water without taking soil and plants with it. Often these "pathways" double as access for the maintenance staff, so they may already be included in the design.

Green roofs are becoming more popular every year, so the amount of knowledge surrounding their success is growing. But even contractors with good intentions can struggle with good green roof design and installation. Looking for contractors with experience will help prevent failures up front. The moral? When in doubt, hire an expert.

The 2018 Heat Wave: How can we keep our cities cool?

Every year it seems like this summer was hotter than the last. But the summer of 2018 marked record-breaking high temperatures across the globe, creating a season of emergencies. The heat wave that broke out across North America, Europe, and Asia this year surprised meteorologists and climate scientists alike.

On July 6th, a Los Angeles neighborhood reached a record-breaking 117°F. Peak energy-demand set a new record for July in the city and over 34,000 energy customers experienced outages for up to 24 hours. By the end of June temperatures in Denver had already reached 105°F (1).

The dry and arid conditions across the western United States resulted in wildfires that burned hundreds of thousands of acres of land and almost as many homes. The Mendocino Complex Fire burned over 320,000 acres and had 3,500 firefighters around the clock battling the blaze. It is the largest wildfire in California on record (2). Dry thunderstorms had the Rockies ablaze and even forced Yosemite National Park to close during its top tourist season. Not only do wildfires cause destruction to property and habitat, but the smoke can travel all the way to the east coast, reducing air quality.

Europe and Asia also saw record high temperatures this year. Japan reached a record temperature of 106 °F.  In many parts of Japan, air conditioning is uncommon in schools and homes, and over 70 deaths were reported as heat-related (3). Japan also has one of the highest population of elderly people, with over 33% of citizens being over the age of 65. Senior citizens are far more likely to die of heat-related illness. Climatologists agree that climate change is not going to make things better. But how can we make out cities more comfortable (and livable)?

One of the ways cities are combating high temperatures is by increasing the amount of urban vegetation. That means planting more trees, installing more green walls and vegetative roofs. This summer in Dallas, TX where temperatures soared above 105°F, volunteers and residents in the low-income neighborhood of Oak Cliff planted over 1,000 trees in hopes of combating future heat waves. Seattle, Portland, New York City, and Denver are all working towards encouraging or mandating vegetative roofs on new development (5).

Many cities are also increasing the number of cool roofs (roofs coated with a white reflective surface) to combat the Urban Heat Island caused by so many dark impermeable surfaces. New York City has painted over 5 million square feet of rooftop space with a reflective coating. Some cities (like Los Angeles) are even painting the roads white, which has shown to decrease the ambient temperature by 10-12°F (4). Tokyo is painting many of its road surfaces in preparation for the 2020 Summer Olympic games (5).

Here in Denver, we love the outdoors. We love our parks, our trails, and enjoying a Broncos game in the sun. Massive heat waves like these are a danger to public health and prevent people from enjoying our public spaces. Let's do what we can to help make our city a better (and cooler) place to live.







Sow Green's Summer Denver Green Roof Tour

With summer nearly over we decided to take advantage of the beautiful, sunny Denver weather with our own private green roof tour! We wanted to see what Denver's green roof game had to offer so we made sure to visit a great variety. From a simply functional installation to intensive landscaped terraces, the Mile High City has a lot of cool spaces for those where a mile just isn't enough. Check out some of our favorites:

   Lindsey-Flanigan Courthouse

Lindsey-Flanigan Courthouse

The Lindsey-Flanigan Courthouse boasts 2 green roofs, one an accessible terrace on the 5th story, and a second one on the top of the first story extension that is not accessible but viewable from the courthouse. Both green roofs cover an area of 8,000 square feet. Although most would not enjoy a visit to the courthouse, we loved the downtown Denver skyline view and colorful sedum combination carpeting these rooftop terraces.

   Barclay Towers

Barclay Towers

A residential building nestled among downtown Denver's skyscrapers, this beautifully landscaped rooftop terrace is a quiet reprieve from the hustle and bustle of the city. Only accessible to tenants, it includes a small vegetable garden, pavilion, gazebos, and a grilling area. A great example of how green roofs can be a great amenity in urban areas, where space can be hard to find.

   MSU Student Success Building

MSU Student Success Building

This lush landscape of sedums can be enjoyed by a small terrace on the 3rd floor of the building. A perfect spot to chat on the phone without disturbing fellow students, we think this is another great addition to a college campus. To our surprise, we also found fresh peppers growing on the terrace!

   Community College of Denver Confluence Building

Community College of Denver Confluence Building

This green roof is a great example of maximizing rooftop space for function and added amenity. Although most of the roof is blue grama grass (a native Colorado grass perfect for green roofs) and skylights, it also has just enough seating to allow plenty of busy students to sit back and enjoy a view of the Rockies.

   Denver Botanical Gardens: Mordecai Children's Garden

Denver Botanical Gardens: Mordecai Children's Garden

We've featured the Denver Botanic Gardens before, but during our trip, we had to indulge the child in our hearts. It can be easy to miss, but the Mordecai Children's Garden is an oasis of native plants, environmental education, and fantastical playgrounds. We spent a lot longer here than anywhere else on our tour, since there was so much to explore. Find this gem atop the parking a garage and bring the kiddos on a green roof adventure!

Do you have a green roof (or access to one) that you want us to feature? Or do you want to join our Denver Green Roof tour? Contact us today!

Greening Your Building: Maintenance Part 2

In part 2 of our maintenance article, we are going to focus on the best practices for keeping green roof vegetation healthy. As we mentioned in part 1 of this article, having a regular maintenance schedule and a to-do list will give you a great head start. Many green roofs fail during the establishment period due to lack of surveillance and upkeep. But what exactly do you need to do to make sure your green roof thrives? Weed control, fertilization (if needed), and quickly identifying pest problems or disease.

Weed Control

Weed seeds can be transferred to your green roof via many methods: birds, wind, growing medium, tracked in by human feet, and more. Even a with a well-covered green roof, weeds can still germinate and overgrow the beneficial plants that are trying to establish themselves. Luckily there are a few ways to keep them under control. The first, most effective method is manual weed control. This is especially true for small roofs or roofs with a lot of ornamentation. Just make sure the maintenance team can identify weeds from budding plants.

The second method is mulching. As long as the mulching material is weed free and it is applied with sufficient depth, mulch can prevent weed germination as well as smoother existing weeds. The last and least popular method is chemical control or using an herbicide. They tend to be species-specific, and many chemicals in these products have been known to degrade waterproofing membranes or drainage systems. It is also possible that the chemicals can leach out and pollute local waterways. Because of these factors, this method is controversial and seen as a last-ditch effort to remove seriously overgrown weed problems.


Over the course of the establishment period, the nutrient-rich part of your growing medium will start to biodegrade. The rate of decomposition and nutrient loss varies by climate and the species of vegetation. Typically the decision to use fertilizer is made during the design phase in order to provide specific nutrients to the plants that will be used. Many plants, such as sedums, are not as sensitive to nutrient availability, and may not need any fertilization. If fertilizers are not being used, continually check for signs of nutrient stress in the plants, especially in the first 2-3 years after the installation of the roof.

Identifying Pest and Disease

Weeds and lack of nutrients are relatively easy problems to identify and fix, and once resolved many plants will regain their strength quickly. But pest problems and disease can spread very quickly if not identified, and if the issues are not resolved soon after the entire roof system can be compromised. Many green roofs are less prone to these problems since they are a much more controlled environment, but they are not completely immune to them. Although we can't go over every possible scenario, we can help you look for tell-tale signs of a problem. Evidence of pests on your green roof can include: the pest itself, shed skins, droppings or frass (insect debris), webbing, honeydew, sooty mold, pitch, gummosis, galls (abnormal outgrowths of plant tissues), or slime trails.  Evidence of disease can include mushrooms or fungal growths, galls, powdery substances (white, orange or black), leaf spots, water-soaked areas, cankers, and discolored stem or root tissue. If you see any of these on or around plants in your green roof, document it and have a professional take a look.

After the establishment period of 2-3 years, the amount of maintenance and observation will be reduced considerably. Once plants have been kept healthy they are much less likely to be affected. Keep these tips in mind and you are sure to have a lush and beautiful green roof!

Greening Your Building: Maintenance Part 1

There are very few green building projects that are "set it and forget it." Once the installation is complete, the building owner will be required to monitor all aspects of the project throughout its lifespan. For a green roof, upkeep is especially important to maintain plant life. During the Pre-Design phase, designers and owners should have a mutual understanding of any limitations that the owner has in regards to maintenance. There is no such thing as a maintenance-free green roof (or any roof for that matter).

The Establishment Period

Green roofs have what is called an establishment period, which is the time it takes to cultivate vegetation to a point where the roof is properly covered. The establishment period is normally over when plants cover about 80% of the area they were designed to inhabit. It normally lasts around three years on average, depending on plant selection and climate. During this time, maintenance will be more time consuming and costly, since plants typically require more water, fertilizer, and protection from weeds during the first stages of their life. This time is critical for the long-term success of a green roof. If you've installed a modular system, you'll have a greater chance of success, since they are designed to protect plants and retain water best. In many cases, maintenance during the establishment period can be done by the contractor that installed the system and therefore included in the budget for the project.


Successful green roof maintenance plans require extensive documentation. Your contractor should visit regularly to either ensure that proper maintenance is taking place or to do the maintenance themselves. When they do visit, they should document the following: the date, maintenance performed, testing performed, fertilizers or pesticides applied, weather conditions, and photographs of the roof's condition. In addition to regular documentation, your maintenance plan should have a to-do list. If you've opted to provide maintenance yourself, this checklist can often be provided to you by the designer or the contractor that installed the roof. Keep all the documentation well organized and easy to access. If vegetation is wilting or you aren't seeing the benefits promised by your contractor, you can use the documentation to help you request that something is done.

Performance Testing

Depending on your goals established in the Pre-Design phase, you may wish to perform tests that measure your success. For example, you may wish to test the soil quality or absorption rate of the plants. If anything, you can test and document the energy you will save, or the air quality surrounding the roof. Testing will give you the data you need to make improvements or justify more projects in the future.

In addition to testing performance, you may need to test for other things that might plaque your project or cause costly damage. Although green roofs last twice as long as traditional ones, you may still fall victim to irrigation leaks, moisture infiltration, membrane damage, or drainage issues. Identifying and repairing these quickly can save you money and ensure warranties are kept. One of the biggest reasons for a green roof failing is lack of surveillance and inadequate record keeping.

It is critical to understand the expectations of maintaining a green roof, or any green building project. even renewable energy technology needs regular maintenance and testing to make sure you're getting the biggest bang for your buck. Even though it may seem like the hard work is over, it takes just a little more to make sure you reach your sustainability goals.

Greening Your Building: Installation Part 2

Every project will have a set of standards and personnel to ensure those standards are met. Not only are their legal obligations that the project parameters will complete, but contractors also have means of being held accountable for the quality of their work. In the second part of our installation best practices, we are going to cover quality assurance, quality control, safety and compliance, and substantial acceptance.

Quality Assurance and Quality Control

Before you begin installation you probably will already have a Quality Assurance Plan set in place. Although often confused, quality assurance and quality control are two very different things. Quality assurance is essentially a predetermined set of steps laid out to ensure the work is done to the best of its ability. Quality control is actually carrying out those steps and implementing the plan properly.

Most of the work for quality assurance takes place in the pre-design phase, where managers can research all requirements for the building. Not only is this important for a successful project, but for code compliance and safety as well. Often contractors will have a Quality Assurance Manager and a Quality Control Officer that will handle everything from planning to implementation, but sometimes third-party teams are used on large or complex projects.

Quality control protocols may vary for each trade or sub-contractor that is involved. This is why it is considered a best practice to have a construction quality assurance plan in place. Quality control officers and inspectors tend to visit and test on a set schedule, but often it is the superintendent that is responsible for ensuring that the work is done properly. One way of managing quality control is by offering training and refresher courses. The ultimate goal is to reduce the amount of work that has to be redone in order to keep your timeline efficient and stay on budget.

Safety and Compliance

Through the installation phase, the owner and contractor will need to comply with a Safety Officer to make sure that all OSHA regulations are being met. Your contractors will appoint this person, and you may be required to follow instructions. Many tasks such as crane operations, working on a roof or sloped surface, and operating specialized equipment requires certified individuals who have been trained on proper use and safety procedures. If you are onsite during the installation or construction, make sure you wear safety gear and report any regulations you feel are not being met.

Substantial Acceptance

Substantial acceptance is when the owner agrees that the project is complete enough to meet its intended use. This is when you address any issues and confirm that everything was done within the timelines agreed upon. A good contractor will provide a punch list that you can go through in order to double check that everything is up to snuff. What qualifies as substantial acceptance varies by project, and is outlined in the contract under a substantial completion clause. Your contractor will prepare necessary paperwork to close out the project.

Once the project has been completed and inspected for quality, you will now move forward to the post-installation phase.

Greening Your Building: Installation Part 1

Once you have planned out your space and schedule, it is time to finally start the installation of your green building project. At this point, it will feel like you have already accomplished a lot without anyone picking up a shovel. But it isn't over yet, now it's time to make sure installation goes smoothly and unnecessary crises can be averted. In this article, we will go over the importance of testing and best practices for installing a green roof system.


Thorough testing of all materials, technology, and components in the early stages of installation will be critical to avoiding mishaps or do-overs. For example, testing out your solar panels power output on the ground before installing them on the roof will help you foresee any issues or possible manufacturer defects. If you are installing a green roof, testing for leaks in the waterproofing membrane or drainage system before installing the growing medium can also help you detect early problems. You will also need to make sure any products or materials are tested and warrantied in your specific climate and microclimate.

Testing also helps you determine if the issues are product related or installation related. Once you are done with initial testing and have installed the components you need, continual testing should be done in order to determine if the products are working according to the manufacturer's' standards over a longer period of time. For example, is the renewable energy technology you have installed performing at its best? Is the plant growing medium on your green roof absorbing and retaining enough water?

Best Practices for Installing Green Roofs

First and foremost, you will want to review the design of the green roof system carefully and ensure proper transportation of the materials to the construction site. Hiring green roof specialists will help ensure that the materials are well taken care of during the installation process. Make sure you have a quality assurance program set in place before you begin. We will be touching on best practices for quality assurance in our next article.

One of the most important elements of a green roof system is probably the waterproofing membrane. Carefully inspect the membrane and continually check for damage throughout construction. Testing for leaks on a regular basis will be essential, especially if the membrane is left exposed during installation. Ensure other trades do not puncture holes above or below the membrane.

In addition to waterproofing, irrigation is essential to the success and longevity of green roof systems. You will need to carefully coordinate with other utilities and subcontractors while implementing your irrigation system. More often than not, irrigation will need to be installed by a certified applicator in order to keep the warranty valid. Double check to make sure the design and layout of the irrigation will make future maintenance easy and accessible. And as with the waterproofing membrane, check for damage and defects often.

Of course, we cannot forget about what makes the green roof a green roof: plants. Although you can't really "test" plants, you can keep tabs on your sources and continually check the quality of the vegetation. Inspect the plants at the nursery before transportation and then after they arrive on site. Reject any plants that are dying or have disease, and remove any weeds. If the plants arrive before the irrigation system has been installed, arrange the plants as they will be planted and use supplemental watering to keep them healthy until installers are ready. This is a good opportunity to check with your design team to make sure the arrangement of the plants is appropriate for long-term health.

Although you can't plan for everything, and something may undoubtedly go wrong, proper testing can reduce your stress and make sure that your project components are working properly, the project is easy to maintain long-term, and that it lasts as long as possible before needing any upgrades or retrofits.