5 Types of roof for your extension

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    5 Types of Roof for Your Extension

    The type of roof that you choose for your extension is an often overlooked after-thought, but the choice is a very important one that should be being thought about from the very start. The roof is often a significant cost element for your extension, and it is also the number 1 place for problems (leaks!) to occur over time. It also offers one of the best opportunities to add architectural design flare to your extension.

    As is always the case, the reasons for choosing what type of roof best suits your extension will be dependent on your needs, so in this article, Chartered Building Surveyor, Laurence Murrin MRICS, is going to take a look at the 5 best types of roof for your extension.

    Pitched Roof

    The pitched roof is a classic choice that offers the crucial benefits of providing excellent rainwater run-off, ceiling height and loft space, as well as being able to create a visually impressive architectural feature both internally and externally.

    From a design point of view a pitched roof will in almost all cases look better than a flat roof. Externally you, or your architect, will be able to select a roof covering which matches the style of your building and helps add to the aesthetic, be it traditional or artificial slates, or concrete tiles. Internally you can leave exposed joists, or create an angular ceiling line to fit the shape of the roof.

    You can easily integrate roof lights into a pitched roof in order to increase natural lighting within the space, with roof lights providing significantly more light than windows or french doors.

    Consideration needs to be given to ensuring that the materials you specify for your pitched roof are in keeping with the property in order to ensure that planning permission is granted. That being said, planning officers typically favour pitched roofs over flat roofs as they tend to complement the existing building better than flat roofs and often appear less like an extension and more like an original part of the property.

    Due to the added complexity as well as higher price for the materials used in the construction of a pitched roof, it will cost you more than a simple felted flat roof.


    + Aesthetically better

    + Planners like it

    + Increased Ceiling Height

    + Storage / loft space


    – More expensive

    Felted Flat Roof

    A very popular choice because of its affordability and simplicity, the flat roof offers an easy solution to roofing your extension. A felted flat roof is easily insulated and it can work in almost any shaped extension.

    Whilst a felted flat roof is quick, easy, and cheap, you run the risk of leaks and the roof has a reduced lifespan compared with a pitched roof (typically 10 – 15 years compared to 20 – 30 years or more for pitched). Another risk you take is the chance of leaks, as well as plant and moss growth in cool damp areas.

    All flat roofs make it easy to install roof lights which increases the light internally, however have a reduced ceiling height when compared with a pitched roof.

    A felted flat roof is a common and easy choice and would be recommended if you are looking to carry out a simple extension and do not mind re-roofing it in 10 – 15 years.

    Regarding planning, flat roofs are not as popular with planners as pitched roofs but they are still perfectly acceptable in most situations. They are more appropriate for rear extensions as planners may demand a pitched roof is used on a front elevation or an elevation fronting a public highway. It is recommended that you get advice from a local architect of surveyor, or you contact the planning department directly for more advice.


    + Low cost

    + Common on rear extension


    – Life span of 10 -15 years

    – Planners may only accept on rear elevation

    – No loft / increased ceiling height

    – Prone to failure and leaking

    Inverted Flat Roof

    inverted flat roof

    An inverted flat roof has a flat roof construction but has the waterproof layer beneath the insulation with paving stones or another topping material on the top. This increases the life expectancy of the roof by protecting the waterproof layer from the elements and penetrations, and it also means that because the waterproof layer is protected by the covering the roof can be used as a balcony or deck giving you a new external space.

    The benefits of this are obvious, however you will need to ensure that you can get planning permission to use the space as an external space. You’ll need to ensure that you install suitable barrier protection to stop people falling from the roof, and you will need to provide access to the roof. This can often be achieved by converting an existing second floor window into a door.

    You need to bare in mind that planners will be concerned with overlooking issues if you are near other properties and will consult with your neighbours on this matter.

    The cost for an inverted roof is higher than a simple felted flat roof as the construction needs to be sturdy enough to carry the additional loading of the paving stones or other surface finish, and it will need to be even stronger if you plan to use it as an external area.


    + Extra external space

    + Longer life for roof over felted roof

    + Aesthetically better in some circumstances


    – Extra planning considerations: balustrade / overlooking / access

    – No loft / increased ceiling height

    – Can be more expensive

    Glazed Roof

    glazed roof

    The main advantage of using a glazed roof is obvious – natural light. By fitting your extension with a glazed roof you can create a conservatory like space with the privacy of standard masonry walls. In addition it creates an often impressive architectural feature.

    The down sides to using a glazed roof is that it offers reduced thermal efficiency over traditional roof constructions.

    A glazed roof is an excellent choice for living spaces such as kitchens, circulation spaces, or working spaces where large amounts of natural light are required, such as studios. They are not appropriate for bedrooms or bathrooms typically.

    Things to consider when choosing a glazed roof is privacy, cost, as well as the application of the room.

    Building control will need you to demonstrate that the glazed roof provides the required u-value levels for a roof – that is the measure of how quickly heat is lost through it. You can ask you architect of builder for advice regarding this.

    Planning officers are not typically averse to the use of glazed roofs, though it must be sympathetic to the existing building, and you will find it considerably harder if you plan to fit a glazed roof on a listed building or within a conservation area. Glazed roofs are best placed away from public highways and roads to avoid contention during the planning process.


    + Architecturally impressive

    + Great naturally lighting


    – Can be expensive

    – Reduced insulation

    Green Roof

    Green roof

    An increasingly common and greener alternative is the use of a green roof. Much like an inverted roof, a green roof allows for vegetation or grass to grow on the roof which creates a natural habitat for plants and wild life in a man-made environment.

    These are particularly fondly looked up by planners who see them as being environmentally friendly, and visually beneficial to many developed sites, including within cities.

    Green roofs require more maintenance than normal roofs but this can be reduced with careful selection of which vegetation will grow on the roof. They are also most expensive than a standard flat roof.

    Whilst these are still the exception with home extensions, they do offer an alternative option for the roof for your extension and can create a talking point.

    They are typically more expensive than standard roof construction, and the exact amount more is dependent upon the design of the roof. Whilst green roofs can be both pitched and flat, there are limitations on how pitched the roof can be.


    + Architecturally impressive

    + Favoured by planners

    + Environmentally friendly


    – Can be expensive

    – Requires more maintenance

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