Building A Green Roof For Your Home

The Advantages And Disadvantages Of Green Roofs

Advantages: By using green roofs, you will help keep your house cool. Some people view the look of green roofs as more beautiful and natural than man-made roofs. The plants and the moisture contained with the plants and the soil help create humidity in the air and potentially cools the house as well. Besides that, the density of the materials help keep the house cool which also reduces the need for air conditioning. Some people believe this helps offset greenhouse emissions and could help keep cities cooler. Every roof can leak, but because the soil and plants are protecting the rubber membrane from ultraviolet light, there are studies that suggest a green roof can last longer than conventional roofing systems.

Disadvantage: These roofs require a lot of effort to build. They are usually more expensive over the long term due to the extra required maintenance and upkeep. Plants die, rubber membranes can get damaged, and dirt can blow away in high winds. Although plants and their roots can help prevent the wind from blowing away the soil, it requires enough rain to keep the plants alive. Finally, the weight of green roofs can make it impossible or cost prohibitive for many homes. The expense to retrofit your house to support these loads is probably not worth it to most home owners.

How Much Do Green Roofs Cost?

The biggest expense you’ll have to build a green roof is the rubber membrane. Every green roof you build will require a membrane to prevent water from leaking into your house. You can buy a 60 mil EPDM (ethylene propylene diene terpolyme) for about $1.30 a square foot. You can also buy EPM in one other size, 45 mil; because it’s thinner you’ll pay less per square foot. It averages $0.95 a square foot. I plan to build a 20’ x 40’ building. My 60 mil EPDM will cost me about $1,040. If you install all the optional layers mentioned below you will spend about $10 – $25 per square foot.

Besides the money you’re going to spend on the membrane, you’ll need to create layers to support whatever natural roof you plan to use. Some layers are required and others are optional. The truth is, you only need to have the structure of the roof, the membrane to protect it, and soil to grow vegetation, and plants. Everything else is to improve on the system. I’ll put (optional) next to those layers.

Roof Structure (Base): You need to build the structure of the roof. This can be vigas and latillas. 2X6 beams and plywood, or something else that is strong enough to support the weight of the natural roof. The main issue is the surface needs to be smooth enough not to puncher the rubber membrane.

Membrane: You need to install a rubber membrane. I’m discussing the EPDM, but there are other less expensive options. I personally wouldn’t use them. Some people in Alaska actually use cheap blue tarps that you can buy at the box stores. The problem with cheaper options, is the damage that will be caused once they deteriorate and leak. The main reason to use the rubber membrane is to create a waterproof layer to protect your the structure of your roof.

Protection Layer (Optional): You can add a layer above the rubber membrane to protect it.

Insulation Layer: You can add insulation boards to help keep the roof cool. This layer can also work as a protection layer.

Drainage (Optional): The truth is, given enough time, the pitch of the roof and the rubber membrane will drain any standing water. If you want to make this process more efficient, you can add plastic drainage that is specially designed for green (living) roofs.

Root Layer: If you plan to use plant that have deeper root structures, you will need a root layer to keep the roots from growing into the rubber membrane and puncturing it.

Filter Layer (Optional): This will keep the soil from clogging up the drainage layer. The black cloth you can buy from the box stores will be sufficient for this layer.

Soil Layer: You need to add your soil to support the plant life you choose for your roof. Without this you don’t have a green roof.

Plant Layer: You can plant a variety of vegetation. You don’t want to use plants that have thick roots that will damage your membrane layer. Grass and other small native plants in your area are the best choice. Grass is good because the roots are dense and will help hold the soil in place.

The Lifespan of Living Roofs

The lifespan of a living roof is completely dependent on the effort placed into the layers. The more layers you add, the longer your roof will last. Each layer I mentioned above, even the optional layers, all have value. They help perform a function that will increase the lifespan of your living roof. If you put in the time to design a roofing system suitable for your environment, you will likely have a roof that can outlast conventional roofs. Most conventional roofs will last between 10-20 years. You can expect a well designed green roof to last just as long.

Are Sod Roofs, Green Roofs, And Living Roofs All The Same?

In general, yes. Specifically, no. They all refer to a type of roof that has sub-layers with plants on top. Sod roofs are primarily grass (sod) roofs. These were some of the earliest versions of this roofing type. They date back thousands of years. In America, sod roofs were created by cutting sod from thick layers of prairy grass. This was stacked on top of sod homes. Because the sod was so thick, it helped waterproof these simple structures.

When it comes to “Green Roofs”, these often refer to the idea of adding shrubs, flowers, and sometimes even gardens. You’ll see this most often in highrise buildings. The floor/roof is already watertight do to concrete floors/roofs. I’ve even seen trees planted in some green roofs. Probably not a good idea, but I’m not an archetiect.

The final name typically used is a living roof. These are the type most people are probably considering when buildin a home. They have several layers that insulate, protect, and shed off water, then soil and plants to create a living layer that both uses the rain water and creates some thermal mass to keep the home cool.

What Are Some Layers Traditionally Used In Living Roofs?

If you plan to build a living roof, you’ll need to create layers to protect your home and support the plants you plan to use. Some layers are required and others are optional. The truth is, you only need to have the structure of the roof, the membrane to protect it, and soil to grow vegetation, and plants. Everything else is to improve on the system. I’ll put (optional) next to those layers.

Insulation Layer (Optional): Even though this is option, it’s still a good idea to use it. You just add insulation boards that you can buy at the hardware store to help keep the roof cool. It also functions as a protective layer for the rubber membrane.

Commercial Drainage Solustions (Optional): The truth is, given enough time, the pitch of the roof and the rubber membrane will drain any standing water. If you want to make this process more efficient, you can add plastic drainage that is specially designed for green (living) roofs.

Root Layer: If you plan to use plant that have deeper root structures, you will need a root layer to keep the roots from growing into the rubber membrane and puncturing it.

Filter Layer (Optional): This will keep the soil from clogging up the drainage layer. The black cloth you can buy from the box stores will be sufficient for this layer.

Soil Layer: You need to add your soil to support the plant life you choose for your roof. Without this you don’t have a green roof.

Building A Viga and Latilla Roof

Vigas and latillas are a very old roofing method. It involves using logs to create the trusses (viga) and smaller branches that go across the logs (latilla) to create the rest of the structure of the roof. It is very common to see this structure of roofing in adobe buildings. Especially in places such as New Mexico. Because New Mexico has a higher elevation, you can readily find pine trees for the vigas. This method is absolutely beautiful. The natural logs and sticks complement the earthen buildings. It is fairly common to see older buildings using some form of adobe (cob) and plaster to keep the structure waterproof. It is important that these natural style roofs have the plaster maintained and resealed every year. Using cactus juice and pulp, mixed into the plaster, would create a slick skin that naturally repealed water.

Maintaining A Viga and Latilla Roof

I’ve done a lot of research trying to find answers to how the vigas were treated prior to modern chemicals and I can’t find any real coatings there were used. I suspect there wasn’t any. Thankfully we now have polyurethanes, oils, and other materials that can protect vigas. Every 5 years or so, it is a good idea to reapply a new sealer to your Vigas. This in more important for the part of the viga that sticks out of the building. Because it is exposed to extremely dry and hot weather, it is more likely to suffer from dry root than water damage. If the inside of the house remains water tight, it is unlikely the inside wood will need to be treated too often. Maybe once every ten years or so. If you notice discoloration or water damage, then you’ll need to repair the roof and then reseal the vigas and latillas. Linseed oil is a natural material that won’t off gas or create chemical smells in your house.

Final Thoughts

There are a verity of ways to build natural roofs and earthen floors. This article is only covering a few of your options. Over time we will have more articles on various other methods you can use. Using natural materials offers us a chance to use the materials located on our properties. By using material that already comes on the property we purchased, it reduces our need to pay someone else to buy the materials. The more self-sufficient we can be, the more free we are. That’s the goal of this website. To help find solutions and encourage discussions on lifestyles that promote freedom.