Construction Systems
10 Advantages of a House with a Green Roof
Today we will discuss a roofing solution with a long tradition in vernacular architecture that is currently being revived due to its numerous advantages: the green roof; and we will precisely attempt to define why through an analysis of these advantages. Today we analyze the 10 advantages of a house with a green roof.
The green roof or living roof is a system that has been used for centuries, both in cold climates such as Nordic countries, which have a long tradition of green roofs of all types, and in warm climates.
This is because the insulation and thermal inertia characteristics are so beneficial that they provide this type of roof with a high capacity for adaptation, managing to regulate both excess heat and cold, as we will detail later in this article.
In countries such as Iceland, there are traditional turf houses, a type of very steep green roof made with straw that has a surprising durability of up to 20 years and is still used in rural areas, being so effective that heating is not necessary.
We find a similar example closer to home in our country, where the Galician hórreo or the Extremaduran chozo are solutions based on a steeply pitched roof for a small dwelling.
Currently, the use of green roofs is being revived thanks to their thermal advantages, and it is with good reason that the roof is often called the fifth façade of the building. The roof is the part of our home that receives the greatest solar incidence, and for this reason, managing to cushion all this heat through a vegetative layer is one of the best options for regulating the interior temperature of our house while avoiding overheating.
By covering it with a vegetative layer, which includes a thick layer of soil or vegetation, we achieve high thermal inertia, meaning that our roof accumulates the sun’s heat. This heat in turn evaporates thanks to the moisture accumulated by the vegetative layer of soil and plants, preventing it from entering the interior and cushioning temperature changes between night and day.
What Is a Green Roof Like?
First, we must distinguish between two types of green roofs: the flat roof and the pitched roof. As we have seen, tradition is wise and it is no coincidence that vernacular architecture focuses on the use of pitched green roofs.
However, technological advances have allowed us to avoid the problem of water stagnation that occurred with the first option. This is why in the case of flat green roofs, a drainage layer must be provided to channel excess water.
Next, we will detail the different layers that make up a green roof and describe them briefly, before proceeding to enumerate the 10 advantages of a house with a green roof.
Structure
Any roof that can support the load it generates can serve as the structure for a green roof, bearing in mind that this load will be greater than that of a conventional roof due to the thickness of soil and the fact that in case of rain it will absorb water, further increasing its weight.
Thermal Insulation
Thermal insulation allows us to distinguish between two types of roofs based on its position: cold roof or warm roof.
Basically, the difference between the two lies in whether they have an air chamber or not.
And how does this characteristic affect the specific case of green roofs?
In the case of a cold green roof, what we do is provide a thin layer of air between the thermal insulation and the green roof.
In conventional roofs, this air chamber allows necessary ventilation to prevent water condensation and its consequences, such as moisture deterioration of the supports of roof elements.
Furthermore, if we call it cold, it is because it is designed to promote cooling in summer, when the roof receives a lot of radiation throughout the day and could accumulate it to unsuspected temperatures, especially in Mediterranean climates like ours.
On the other hand, the warm roof eliminates the ventilated chamber and replaces it with a vapor barrier, which will solve the problem of water vapor entering the insulating layer and condensing there.
Waterproof Layer
Every roof must include a layer that ensures its waterproofing, although characteristics such as a high pitch can help considerably. In fact, traditionally this aspect was delegated to geometric characteristics such as slope and eaves.
Currently, we have what are called roof membranes, a synthetic textile product that despite its ecological footprint is the most widely used today even in eco-friendly homes, as there are few real alternatives on the market that fulfill the same function.
Root Protection
This is usually the same layer as the previous one, although it can also be added as a separate layer, which in addition to preventing water from entering the interior, protects the roof and its structure from possible damage caused by the roots of the vegetation that inhabits it.
This layer is the consequence of working with living elements whose change over time we must take into account and generate mechanisms to control.
Drainage Layer
As we previously mentioned, a drainage layer will be necessary to prevent water stagnation on flat roofs. This same layer can be used to store the water necessary for plant consumption in an orderly manner and thus prevent the substrate from turning into liquid mud. In the case of pitched roofs, we can replace this layer by adding porous materials to the support layer.
Substrate and Vegetation
The substrate is the layer that supports the vegetation, where the roots take hold, serving as a nutrient and water storage. Thus, it is closely related to the type of vegetation it supports, and the thickness we assign will depend on this.
We will need a minimum volume to be able to support and fix the vegetation, which is why we consider substrate and vegetation practically as a single layer.
Regarding vegetation, it is always advisable to work with local species, and in the case of dry climates or those with variable precipitation throughout the year, we will use plants that require little water.
10 Advantages of a House with a Green Roof
Having briefly reviewed each of the layers of a green roof, let us go into detail in enumerating its advantages, as more and more clients come to our studio requesting this type of solution.
1 Oxygen Production, Carbon Dioxide Consumption
The vegetation on roofs takes, like all plants, CO2 from the air and releases oxygen through the process of photosynthesis.
Along the same lines, we know that plants are capable of filtering dust and dirt particles through the adhesion of their leaves. In turn, they can absorb harmful particles such as gases and aerosols, and even heavy metals.
If we imagine a future in which the roofs of buildings in our cities are protected by vegetation, this would greatly improve the air quality of our urban areas.
Thus, it is not surprising to highlight this as one of the 10 advantages of a house with a green roof, since it has a significant impact on air quality.
2 Temperature and Humidity Regulation
We must consider the plants that inhabit a green roof for what they are: living and intelligent elements capable of naturally regulating what we have always invested so many technical resources in regulating artificially.
Vegetation reduces oscillations in both temperature and humidity through water evaporation, photosynthesis, and the ability to store heat from its own water.
In this way, in summer, the roof manages to cool down by evaporating the water that the vegetation has stored into the atmosphere.
In winter, that is, in cold temperatures and high humidity, the strategy consists of condensing humidity on the plants at night. The morning dew that we all know implies a recovery of heat, through the storage of heat from the water itself, as well as a decrease in humidity, which is retained by the vegetation itself.
All these processes and strategies minimize the energy expenditure we would need to employ to artificially climate our home. It guarantees ideal interior conditions even in very cold climates such as Germany, where temperatures of 0°C have been measured for an exterior temperature of -14°C, making this one of the main advantages of a house with a green roof.
3 Suitable for All Types of Roofs
If there is one thing we have been seeing throughout this article, it is that the green roof has an adaptive capacity that has led it to persist to our times as a successful architectural solution.
Indeed, the numerous advantages of a house with a green roof have allowed this system to be able to reinvent itself and adapt thanks to technological advances, which today allow us to implement a flat or pitched green roof, cold or warm, walkable or not.
4 Improves the Service Life of the Roof’s Waterproof Membrane
As we explained earlier, the waterproof layer of the roof is usually solved with a bituminous membrane, whose limitation is usually degradation over the years. First, we must be aware that such degradation usually occurs in conventional roofs due to inclement weather such as heat, cold, rain, ultraviolet rays, and wind.
It should be noted that the greatest incidence is produced by mechanical damage resulting from strong temperature changes, which expand and contract the membrane throughout the year.
The substrate layer and vegetation added to the green roof protect this membrane from any inclement weather, as well as reduce the temperature oscillations that generate the greatest damage. We simply need to be aware that we must also protect the waterproof layer from root growth so they do not perforate it, by means of an additional anti-root protection membrane.
5 Greater Thermal Insulation
The substrate layer together with the vegetation layer can replace the thermal insulation layer that is essential in conventional roofs. This is the main reason why this roofing solution was traditionally chosen, another of the 10 advantages of a house with a green roof.
Thus, in addition to the temperature regulation capacity we have previously detailed, it should be noted that the air cushion enclosed in the substrate layer has the effect of a thermal insulation layer—the denser and thicker it is, the greater the effect.
Furthermore, part of the heat radiation emitted by the building itself is reflected by the leaves and the other part absorbed, thus reducing the loss of heat radiation from the building. This would be a kind of greenhouse effect produced by the vegetation itself.
Finally, in the case of very dense vegetation, this will prevent wind from reaching the substrate. This avoids heat loss due to the wind effect, called convective heat loss, which accounts for practically half of the total heat loss through a building’s roof.
6 Acoustic Insulation
Similarly, the plants on a green roof are capable of absorbing noise through a process in which they transform sound energy into movement and heat energy, thus absorbing it.
It would be a process similar to that of a carpet that absorbs reverberation in a room, but much more effective.
This process is combined with the vegetation’s capacity for sound reflection and dispersion. Furthermore, the substrate layer achieves an even greater reduction in high-frequency sound, making it ideal in a house with a green roof in contact with heavily trafficked roads.
7 Fire Protection
A green roof offers ideal fire protection for roofs prone to catching fire thanks to its water retention capacity. This is a problem we recurrently encounter in summer in Spain, unextinguishable fires resulting from the dryness of the substrate in forests. In fact, in countries such as Germany, green roofs have been classified as non-combustible.
8 Integration with the Landscape and Ecosystem
I believe we will all agree when we say that the effect produced by a gray bitumen roof or dry river stones is not the same as that of vegetation with its natural beauty, generating an aesthetic effect that has positive psychological consequences on those who observe it.
There are studies that demonstrate that the undulating movements of plants have calming benefits for people.
Regarding biodiversity and the ecosystem, it should be noted that not only does the time of year modify the formal appearance of the green roof, but there are also variations through the transport of seeds by birds and wind.
These manage to be in harmony and generate a series of synergies, such as bee pollination or the nesting of certain bird species.
Finally, regarding the landscape, it should be said that a green house adjusts more easily to the environment, especially if it is rural, much sooner than a house without green spaces. The example of traditional architecture is worth highlighting, where the roof is so steep that it drops to garden level, so the vegetation rises directly from the ground to the roof, generating an astonishing integrative continuity of green.
9 For All Audiences
An advantage of the popularization of a roofing solution is that it becomes democratized. When market supply increases, competitiveness is generated that lowers costs by systematizing and optimizing technical solutions. It is precisely for this reason that today we can affirm that the green roof represents an alternative to the conventional roof for all audiences.
As with so many other examples of bioclimatic architecture that we describe in this blog, the same applies to the green roof. The initial budget we must invest will be slightly higher, but the long-term savings allow us to amortize the investment thanks to improvements in the home’s performance, such as climate savings and maintenance savings.
When it comes to achieving a more adjusted budget, everything starts with planning. At Slow Studio, we recommend that for a green roof to be cost-effective, its geometry must be greatly simplified, as well as generating gentle slopes that will facilitate substrate retention.
10 Minimum Maintenance and No Need for Irrigation
In addition to all the thermal, functional, aesthetic, and ecological advantages of a home with a green roof, there is still one last characteristic to add to our list of the 10 advantages of a house with a green roof.
In a climate with variable precipitation such as the Mediterranean climate, it is possible to implement a green roof that does not require irrigation, what we call a xerophytic garden, by correctly selecting the plants that compose it.
We must bear in mind that the rainfall in our Mediterranean climate is not constant, so we cannot design a garden that depends on a constant water supply. It is true that this type of xerophytic roof may require irrigation at certain points of its implementation, such as initial irrigation, irrigation during seeding, and even seeding after installation.
For everything else, a house with a green roof will not require any other type of maintenance. Except for the removal of shrubs or tall weeds that may grow sporadically and pose a risk to the structure and layers of our house’s roof.