Roof Design – Function, Form and Cost
Thursday, 2nd February 2017
Architecture
If we were to simplify buildings down to their very core elements it could be said that they contain only 3 different parts; walls, floors and roofs. Again, I stress this is a very simplified outlook but a lot of the time it’s these three elements that are often overlooked in design schemes as they are deemed ‘too boring’ to think about. I agree to a percentage, 66% to be exact, walls run up and down, floors runs across horizontally, but roof design is certainly an area that should be considered a little more as there is some ‘fun’ to be had.
Function
Again, simply put, the roof is the uppermost element of a building whose main function is to enclose the space and protect the inhabitants from the effects of the weather. However, this can be further expanded, the roof will also serve to direct any water to the guttering and drainage system. It can also serve as a way to light and ventilate the space beneath it when combined with other elements such as windows. Nowadays we have taken this further, roofs can now be used as a feature of sustainability to save/produce energy through photovoltaic panels or even improve overall performance of the roof with a sedum roof design.
Form
No blog post would be able to include an in-depth look at all roof designs so it is best to stick to the three ‘traditional’ roof options, when looking at residential development these will be the most common, practical and most likely to gain planning approval. Anything outside of these options you will be more expensive, risky from a planning point of view and potentially cause a Building Regulations issue as bespoke structural design may be necessary. One point to note, it is commonly thought that different will ‘perform’ differently, but due to the UK Building Regulations all elements must comply with aspects such as structure, energy performance etc.
Flat Roof
Flat roofs have been around for decades in warmer climates where there is less rainfall and freezing is unlikely to occur. However, they are becoming more and more common in the UK with the development of construction methods. They can be advantageous in keeping a low profile whilst providing the necessary height inside, come heavy rainfall they will mitigate issue of excessive drainage as they drain water slower (whilst called flat they are designed to have a fall of between 1:40 and 1:80 depending upon the covering). Flat roofs are prominent in extension work that falls within permitted development.
Pitched Roof
Pitched roofs would represent a much more traditional option, they can come in numerous forms such as a single pitched (lean-to), a double pitch (gable), a triple pitch (hip) and 4-way pitch (pyramid hip). There are even specialist versions of this such a mansard which incorporates pitches of different levels of steepness or a butterfly which is the opposite of a gable. They work well in draining excess water (an issue we deal with in the UK too much). They also add extra height internally which is useful when there are planning restrictions on eave heights and are usually favoured in planning applications when trying to match the existing property.
Combination Roof
As the name would suggest this is a combination of the two above, not uncommon but not usually first choice when designing a roof, sometimes referred to a crown roof. They can be helpful in creating solutions to design issues that would otherwise not be possible with either roof type; such as a lower height at the boundary that pitches up to the desired level before becoming flat. They do however carry an additional level of complexity in designing, detailing and building but equally can become and elegant feature at any property.
Cost
The difference in cost may dictate the design choice. Generally speaking the more material that is used the more expensive the work will be, however this can be mitigated with a less complex design. For the benefit of this post let’s take an example based upon providing a roof to a rear extension measuring 3.00m x 3.00m. In this instance a flat roof will be the cheapest to build, it will use the least material and is the least complex design. A single pitched roof will be more expensive as it will use more material with a more complex design, following from this a double pitch will be more expensive and so on so forth. Finally and unsurprisingly, a combination roof will be the most expensive, but more so due to the complexity of its design.
