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How to Install a Flat Roof

Flat Roof Construction Details


If you don’t yet know much about it, flat roof construction might seem confusing and complicated on the surface. And yes, there is a lot to learn and discover, but that doesn’t mean it’s beyond you because the details are pretty easy to get your head around once you take the time to learn. We’re going to help you do that now by talking you through the most important aspects and factors associated with the flat roof construction process.


There are lots of things that go into the construction of new flat roofs. The way things pan out and the approach taken tend to depend on the needs of the specific job. No two jobs are different, but there are some common themes and principles that apply to all flat roof construction. You’ll learn all about this and a lot more below, so read on now and make the most of what you learn.


The Basics of Flat Roof Construction


Timber joists and rolled steel joists are used to secure in place the flat roof during construction. This makes up the fundamentals of the roof that keep everything else in place. The timber joists will generally lie on top of the steel joists, and they’re all spaced apart to evenly cover the area that needs to be covered.


Waterproofing is a very important part of all this because if the wood were to get damp, all kinds of other problems can arise and the flat roof could be rendered virtually useless as a result. There are many different ways to approach waterproofing, but rubber or felt is often used to do the job.


Timber Joists


Choosing the right timber joints for the job is obviously very important because the size and strength of them will impact the finished roof when all the work has been completed. Because this is part of the roof’s fundamentals going forward, it’s vital to get it right and corners can’t be cut.


The support that comes from the rolled steel joists should mean that stability is assured, but it’s still worth finding the best quality timber joists if you’re building your own flat roof. The stronger they are, the stronger the roof will be.


The Building Process


The first thing to know about the building of the flat roof is that flat roofs aren’t and shouldn’t be level. If they were completely flat, this would obviously cause problems because rainwater wouldn’t be able to run off the side of the roof, and instead water would stand on the roof.


The precise angles and dimensions of the roof have be worked out in advance, and the number of layers that’s used for the covering needs to be taken into account too. It needs to be folded over the arris rail where it can be sealed properly so that there’s no gap between the roof and the facia board.


Warm and Cold Flat Roofs


There are two main ways to construct a flat roof; they can be warm or cold. Which you choose will depend on the requirements of the building and how it will be used. Warm roofs are named as such because they have lots of insulation filling all of the available gaps in the property. 


Cold flat roofs on the other hand allow for air to flow naturally between the joists and there is no insulation packed in there. They’re designed so that there is a continuous air flow through the roof itself.


Air Flow for Warm Flat Roofs


There is a slight contradiction that complicated the above definition of cold and warm flat roofs though. It is possible for flat roofs to have air flow too. This is basically about allowing for the best of both worlds, and it’s quickly becoming the most common solution for people.


This all works by allowing insulation that makes the roof warm, but there is also space made for air flow between the joists. This is important because it makes rot less likely in the timber joists. You will need a vapour barrier to prevent problems like condensation though.


Flat Roofs for Building Extensions


Lean to extension structures will usually make use of flat roof designs, and this is one of the most common reasons why people want to find out more about them. It provides a simple, straightforward and safe way to construct roof when a lean to extension is being built.


Water and debris can flow off in the correct direction, preventing any potential problems that might be caused by water. If you need to install the roof yourself, choosing a flat roof solution is the best option because they’re relatively straightforward to install.


Preventing Damage From Moss


The fall or slope of your flat roof is really important and it definitely has to be thought about because if the fall is not steep enough, water can be allowed to stand. That’s why you start to get problems with things like moss. The standing water breeds all kinds of nasty things that you’ll want to avoid.


The weight from the moss as it grows can also put pressure on the joists below, causing even more problems than you could have imagined. It’s a simple case of increasing the fall of the flat roof if you want to prevent these kinds of unnecessary problems.


Professional or DIY?


Rubber EPDM roofs are relatively easy to install, so if you want to take the DIY approach, that’s the kind of material you should be looking to use. However, for most of the process and most types of covering, it’s best to use a professional because they know how to get things done properly and safely for the best long-term outcomes.


The construction of a new flat roof is an intricate process, but when you understand how it all works, it’s not all as complicated as it might initially seem on the surface. Hopefully you now have a better idea of how flat roofs are constructed and what all the little details mean.