6 Ways to Retrofit a Green Roof

Green roofs, sometimes called living roofs, are increasingly popular in both large and small cities. More and more building owners are creating these urban gardens because of their many benefits: The plants help insulate the building, deal with stormwater runoff, filter the rainwater and even extend the life of the roof. They are also good for the environment, add beauty to the building, and in some cases, give occupants a place to sit and relax.

Nearly any roof can become a green roof with the right combination of planters, plants, insulation and drainage. As more building requirements specify eco-friendly building techniques and materials, green roofs are becoming an increasingly popular way to meet these requirements, while also adding benefits to the owner and occupants.

Here are six methods of creating a green roof that can help any building achieve its green goals.

1. Vegetated Roof Top

Green roof large image


While not the most common method of creating a green roof, vegetated rooftops are a viable option for older roofs that would need significant restructuring before they could become a true green roof as they use a much smaller area as a growing surface. Plus, the plants and the depth of the soil are smaller, making the weight of the vegetation is much lighter than with other green roof systems.

In a vegetated rooftop, the area you intend to cover must be treated the way any green roof would - by first insulating, then creating a drainage system, and lastly adding soil and plants.

The reason vegetated rooftops work better for older buildings is that by limiting the size of the plants and scope of the work, you lessen the load on the existing roof so no reinforcement of the roof is necessary. Depending on the age of the roof, you can make the area as big or small as you would like.

2. Modular Roofing

Modular Green Roof


Another method of creating a green roof on older roofs or buildings that can’t currently undergo much reinforcement is to use a modular green roof. In this case, rather than building the plants right into the roof itself, you plant the vegetation in planters that then line the roof. You can plan, customize and layout the planters to create a rooftop garden, to line the perimeter of the roof or even to completely cover large sections.

The planters will still filter rainwater and will help with stormwater management. However, by using planters, the roof itself will not receive as many insulating benefits as a typical green roof.

3. Intensive Green Roofing



While not as common for retrofits, intensive green roofing is still an option, particularly for new buildings or buildings that will need a completely new roof. This method allows for greater use of the roof, more plant options and better drainage.

An intensive green roof is designed to hold roughly 150 pounds of vegetation per square foot. They are cultivated and tended like a garden, so while it can support larger plants and trees, you’ll also want to consider the long-term maintenance of the roof.

When creating an intensive roof, the drainage system needs a great deal of thought and planning. A pitch is laid beneath the vegetation to help direct any excess rainwater to the drains.

Beneath the drainage system, you have several options for waterproofing, insulating and vapor management. Keep in mind that an intensive green roof uses more soil, so it won’t need the same insulation as other types of green roofs. It will, however, need waterproofing.

After ensuring you have proper water management in place, up to 20-inches of soil or growing medium is added to the roof, followed by the plants and trays. This method does take longer to get started and for the plants to grow, but it will produce the most customizable results.

4. Extensive Green Roofing

If the roof can’t handle the weight of an intensive green roof without significant restructuring, an extensive green roof might be a better choice. This roof uses about 6-inches of growing medium and adds about 40 pounds per square foot. Instead of planting deep growing plants right into the roof, you can plant vegetation with more shallow roots or use trays and planters instead.

The same waterproofing and drainage systems are required, but because there is less growing medium, insulation is also necessary. The key is to use a very thin insulation to prevent bulk but to still help get all of the insulation benefits the building needs. In this case, Kingspan’s OPTIM-R insulation is an excellent choice. In 1.6” of thickness, the Optim-R can deliver R-46 performance, helping to keep the roof insulation build-up quite thin.

With less soil to filter the rainwater, extensive green roofs need more moisture management added to them than intensive roofs. Combined with a drainage system, this type of green roofing protects the building and still offers the same benefits.

5. Semi-Intensive Green Roofing

skyscraper green roof


Semi-intensive green roofing is normally used for retrofitting, instead of new roofing. It’s a little deeper than an extensive roof, but not as heavy as a full intensive roof. You have more plant options, as you can use closer to 10-inches of soil, and you still have the option of using trays or planting directly onto the roof. This creates a less heavy growing field, while still allowing for more customization.

With semi-intensive green roofing, you still need to add additional insulation, waterproofing and drainage systems. The difference is the roof is less likely to need serious structural modification to create a rooftop garden atmosphere.

6. Partial Green Roof

The entire roof does not need to be made green to gain many of the benefits of a living roof. In fact, for retrofitting purposes, it’s common to create a green roof on only one section of the roof, while leaving the rest in a more traditional roof style.

When making a partial green roof, the same drainage and insulating concerns exist for the living portion, but new considerations arise for the rest of the roof which needs great insulation and moisture management as well.

This ensures the building is still insulated and gains many of the benefits of a living roof, even though only part of it is technically green.

Get the Benefits of a Green Roof

Whatever type of green roof you opt for, it will have benefits for both your building and the surrounding environment. Just be sure to consider the best products available for those invisible parts of the roof, such as insulation, drainage, moisture management and vapor barriers, all of which are crucial to a green roof’s success.

Let Kingspan help with our extensive options for roofing insulation and moisture management and start reaping the benefits of a green roof today.

Kingspan Insulation North America

Head Office & Sales Office – North America

Kingspan Insulation LLC

2100 Riveredge Parkway, Suite 175

Atlanta, Georgia



Call: +1(800) 241 4402