Pitched or flat, tile or slate, roofs have a very important role to play in our wet and windy climate!
Pitched vs flat roofs
Most Irish homes have pitched (raised and angled) roofs covered in tiles or slate but new build and extension projects are increasingly turning to the flat roof alternative.
A flat roof is generally defined as having a pitch not greater than 10deg to the horizontal. A truly flat roof would not allow rainwater to drain away, so most flat roofs have a fall on them so that rainwater naturally flows to collection points.
Built-up RBM (Reinforced Bitumen Membranes) are the most common material for residential flat roofs. Thanks to RBM, leaky roofs that were once expensive and troublesome to maintain are now a thing of the past; today, flat roofs are low-maintenance and can enjoy a trouble-free life expectancy of up to 35-40 years.
Tiles are man or machine made and commonly formed out of concrete or clay, and depending on the situation or construction, can be expected to last in excess of forty years. Great for curves and intricate details, clay tiles come in a range of colours and shapes, with special tiles for valleys, ridges and gullies. Period builds or renovations can take advantage of impressive detailing such as dramatic ridge tiles/finials, while tile shapes, such as fish tail and bull nose, are used to create interesting patterns.
Concrete tiles have become hugely popular, being competitively priced and offering a vast range. Many models interlock, offering improved waterproofing, secure fixing and shallower roof pitches. The disadvantage of these tiles is that they don’t always weather in the same way as clay and can have a shorter life expectancy.
Natural slate is hard-wearing so can last for over 100 years, but is more expensive and a greater number are needed to allow for overlap. While reclaimed slates can work out cheaper, ensure these have not been sourced form a vernacular building that, in architectural terms, should have retained them (there have been concerns in ROI over homeowners stripping slates off their roofs as a means to generate income).
Slate provides a smart and yet traditional roofing material, usually grey, but also available in colours, from purple to green. Composite versions are often interlocking, reducing the need for overlapping.
Asphalt shingles, commonly used in ROI, have a relatively inexpensive upfront cost and are fairly simple to install. They present a long-lasting roofing material, and provide excellent protection against strong winds and heavy rain.
Cedar shingles are an aesthetically pleasing, light weight and naturally sustainable alternative. They’re suitable for roof pitches as low as 14deg, easy to handle and cut to shape but are more labour intensive to fit as they require a greater overlap and more fixings. They should also be fireproofed which in turn means that the run off from rain is not suitable for use and if there are overhanging trees the resulting moss build up can reduce their life expectancy, which is otherwise 40+ years for treated shingles (can be extended if regularly cleaned and retreated).
Other roof coverings
Metal is also a roofing option that has been around for centuries. Nowadays there are many more metals available, including aluminium and zinc, which can be laid on relatively shallow pitches, usually on boards or rigid insulation. The fixing and seams vary according to the metal and fixing system used. The fixing methods vary according to the manufacturer and metal used.
Thatch gives a wonderful organic shape which is perfect for curves, and insulates well. It’s a traditional and sustainable material that should be encouraged, and fire concerns – which have prevented it appearing on many new builds – can be quite easy to overcome. It requires a steep pitch and has a deep overhang, rarely requiring a gutter.
Green roof covering
In urban environments, green roofs help attract birds and butterflies and provide cleaner air, offsetting our carbon footprint and thus reducing global warming. They can also help to lower the need for air conditioning in the summer, and offer a degree of additional insulation in the winter. The lives of flat roof waterproofing membranes are extended and sound insulation is improved. Not only that, water surface run-off can be reduced thereby helping to minimise flash floods following intense periods of rainfall.
The most common types of green roofs include extensive, intensive and biodiverse. Extensive consist mainly of succulent plants that are highly adapted to our Irish climate and need little or no maintenance.
Intensive usually refers to the grasses often used for recreational amenities, whilst biodiverse feature small pockets of different microclimates, such as a small pond on a large roof, logs and stones for other habitats. Installing a green roof system is completely different to traditional roofing due to the increased loading, which requires a specialist installer that can specify any required strengthening of the original supporting construction.
A common feature of Irish homes, dormers are generally a part of the original construction or a later addition. They create usable space in the sense that they add headroom and provide an opening for the addition of windows. The most popular type of dormer conversion is a simple flat roof dormer that offers the largest amount of additional internal space and light. When constructing these, particular attention should be paid to correctly specifying the details for insulation, wind and weather proofing and ensuring that these are followed on site.
If you are looking to extend the main roof of your house to accommodate an extension, it’s important that it looks like it is an original part of the house, instead of an afterthought. No matter how well the rest of the design blends and materials match with the house, unless you get the roof right, your addition will look like it’s been stuck on. ν
Kevin Taylor & Astrid Madsen