#5 The flat roof – what you need to know…

#5 The flat roof – what you need to know…


Once a month we give you useful tips about building a summerhouse in our series: “What makes a quality summerhouse?”. Our architects and wood professionals explain the most important details when you want a summerhouse to last as long as possible. From material choice to final assembly, we’ll be covering everything. So by following our posts you can become an expert on wooden summerhouses too!

Which roof type should you choose for your summerhouse? This question isn’t as easy to answer as you might think. Of course the appearance is an important decision criterion, but there are additional aspects that you should consider when choosing a suitable roof. What weather conditions will your summerhouse be exposed to? What are the advantages and disadvantages of the roof types? And what about the construction of the roof? Which roofing is possible? Even before the start of construction, in the planning phase, you should consider these issues extensively.

The right roof is fundamental. For a long-lived summerhouse, it’s important to make an informed decision. With this blog series we would like to help you and introduce you to the different roof types in detail.

Our last blog post dealt with the first roof type, the apex roof. In addition to general information on the roof load or tips on different roofing, we covered the specific characteristics of the apex roof. The apex roof is a very popular roof shape, as is the flat roof. Flat roofs are characterised by their clear straight shape and are very popular today. They no longer have the reputation of not being watertight. Technically perfect, flat roofs create a very modern look. Want more information? Read this article:

The flat roof and its bad reputation

Due to frequent design flaws and the choice of inferior materials, flat roofs once had a very poor reputation. In the 1960s and 1970s, flat roofs experienced a boom. Everyone saw the advantages of flat roofs. Since flat roofs don’t slope much, the space in the summerhouse can be fully utilised and even the roof itself offers an additional usable area due to its shape. But although flat roofs were very popular, the technology wasn’t yet fully developed. This caused a lot of problems. These problems are well-known today. With the right planning, construction and choice of materials, flat roofs have been undergoing a comeback for some time now.

Lugarde Flat Roof Summerhouse










What exactly is a flat roof?

Flat roofs are roofs with a low roof pitch. Compared to other roof types, flat roofs are very minimalistic. They appear extremely modern and offer many design possibilities. It’s important that a flat roof is never completely flat. The rainwater can’t remain on the roof and must be able to drain. How does it work? As mentioned above, flat roofs have a low roof pitch angle – or more precisely, the purlins of a roof will be placed so that water can drain off in a given direction. This occurs when the individual roof battens (rafters and wooden battens) are attached to the roof purlins. The roof purlins are connected and an inclined drainage path is created for the rainwater. The following graphic shows the individual parts of a flat roof, to help you understand better. Please note: The black arrow indicates the direction in which the water can drain later.

With this construction, you can be sure that the rainwater will run in a certain direction. There are no puddles on the roof and the water can’t flow off all sides. If that were the case, the water flowing down could splash against the lower boards of the summerhouse walls. This mustn’t be allowed to happen, as it could cause considerable damage to the wood over the years. Just to be on the safe side, it’s useful to install wind boards which, in any case, should be higher than the roof purlins, rafters and wooden battens. This creates a kind of “pool” and allows you to control the water drain even better. The wind boards keep the water on the roof so it doesn’t flow off all sides. The tilt of the roof ensures that the rainwater flows off in a certain direction.

If you now attach a downpipe, all the water can simply be drained into a water butt or into the grass. This protects the walls of your summerhouse from rainwater. The wood stays dry and doesn’t rot.

Roof covering for a flat roof

The right roof covering is particularly important for a flat roof. A flat roof needs a sturdy seal to protect the roof from rainwater. If a puddle forms on the roof despite the gradient, the seal must be able to withstand it. So you should make sure you use only high quality materials. There are a range of different ways to cover the flat roof of your summerhouse. Examples include seals with plastic or even liquid seals. Particularly popular is a roof covering with geomembranes made of EPDM. EPDM is a foil-shaped building material made of rubber, which is of very high quality and very durable.

According to the SKZ test, the lifespan is around 50 years. A roof cover with EPDM foil is easy to clean and particularly resistant to UV radiation. The foil is extremely solid and can withstand almost any weather conditions. If it is glued to the roof with silicone, you can be sure that your roof cover is completely waterproof. This is a building material unaffected by being in constant contact with water.

That’s why it’s perfect for flat roofs. It’s important that the EPDM foil closes properly at the edge of the roof. For this purpose, a wide aluminium roof trim, which completely encloses the EPDM foil, is recommended. On the following pictures you can see exactly what this looks like.

Lugarde Flat Roof EPDM Roof Covering  Lugarde Flat Roof EPDM Roof Covering Corner

Please make sure that the EPDM foil is always pulled over the wind boards. The aluminium roof trim includes the foil and the wind boards at the highest point. Only then you can guarantee a watertight closure. A flat roof should be constructed in such a way that rainwater gathers and then flows off in one direction. If you don’t pull the EPDM foil over the wind boards, this “pool” could leak and water could enter. If applied correctly, a roof covering with EPDM is especially waterproof.

Even roof vegetation is possible, if you have considered this from the beginning in the planning stage and the roof is designed for it. Top tip: Lugarde offers you a complete EPDM package. Each summerhouse with a flat roof includes a wide aluminium roof trim, EPDM foil, glue, silicone sealant and a rainwater drain. You find the idea of a flat roof interesting, but aren’t sure if it’s right for you? In future blog posts we will discuss the features of other roof types. Learn more valuable information about pent, pyramid and asymmetrical roofs.

Other blog articles from this series

#1 Why the choice of the right wood is essential
#2 Construction systems – What you should consider!
#3 The choice of the right window and doors
#4 The apex roof – what you need to know…  

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