To choose an appropriate shed roofing system there are three important factors to consider:
The primary purpose of a shed roof is to protect you and your possession from the weather. To make a roof waterproof, the roof pitch/slope will influence the materials you choose. Roofs can be classified into three broad groups according to roof slope:
Flat roofs: Pitch = 0 to 10 degrees
Roofs with a pitch below 10 degrees are known as 'flat roofs'. For a shed with this type of roof bitumen mineral felt on plywood decking or sheet metal will be the main options. Flat roofs have experienced problems over the years with leakage and durability. The main reason being is that water is not 'encouraged' to drain off the roof. In answer to the question do flat roofs leak? There is a saying in the building industry that there are only two types of flat roof. 'Those that leak.....and those that are going to leak.'
Whatever you do, don't use a 'dead flat' roof (pitch = 0 degrees). Make the roof slope at least six degrees to ensure some positive drainage. Also if the roof is insulated include a ventilated air gap between the insulation and roof deck.
Low pitch roofs: Pitch = 10 to 20 degrees
Tiles or shingles may be used for roofs with these slopes with caution. Extra care must be taken with waterproof underlay and following the manufacturer's recommendations.
Pitched roofs: Pitch = 20 degrees +
Concrete interlocking tiles are really the only tile suitable at a 20-degree pitch. They are rarely used on small timber structures due to their heavy weight, large size and unattractive appearance.
Clay tiles in contrast, particularly handmade ones make for a roof with a lot of character. However, clay tiles need a minimum pitch of about 35 degrees.
Whatever product you end up using get the manufacturers' datasheets. These should state the least roof pitch at which it will remain waterproof. Some Local Authorities recommend you add an extra 5 degrees onto the manufacturer's minimum pitch to ensure water tightness.
To clarify the reason for all this talk about least roof pitches. There is a popular misconception that water only flows downhill! This is not true. At roof level, gusts of wind blow films of water upwards...defying gravity! The film of water then gets blown uphill between the overlapping tiles and into the roof structure beneath. This is why, for any particular roofing system, there is a minimum pitch for which water tightness can be assured.
Also, remember that clay tiles, as well as being waterproof, also act as a hard outer layer protecting the underlay below. The underlay is waterproof and acts as a backup system. Without the clay tiles protecting it from UV degradation, water, abrasion etc the underlay would only have a three-month life.
Tip: When deciding the pitch of your shed roof, make it the same as your house. This has two advantages;
I have compiled a list of common roofing materials below, to give you an idea of relative roofing material costs.
The reason most sheds have a roof covering of bitumen mineral felt is that it has the lowest initial cost. In my opinion, if you are going to the trouble of building your own shed, it is worth investing in a more durable roof covering. Sheds have a small roof area so any increase in cost will be small.
The key factor to consider is the cost per year. Mineral felt is the cheapest material in initial cost but the most expensive on a per year basis. And that doesn't even include the labour for re-roofing the shed every 5-7 years.
Also, the benefit in the appearance of using a more characterful material will give you much more satisfaction over the years. As well as fewer weekends spent repairing the shed roof.
The prices shown are material costs (in GBP). Cost does not include the labour cost of installation. Building material costs vary widely within a country (never mind throughout the world).
Read this table as it is intended - a guide to your further research.
Click on the link below to go the description of the shed roofing type that interests you. Or just browse down the list to find out about the comprehensive list of roofing materials that you could use.
The standard garden shed will come with a roof covered in cheap mineral roofing felt. This system does the job of keeping the water out but is fragile and relatively short-lived. A bit of unseen damage to the shed roofing will allow water in, and cause damage to the structure of the shed.
Standard shed felt has is formed of bitumen impregnated fibres and lasts about 5 years. An improved version of the shed felt with a base of polyester fibres impregnated with bitumen is more durable and lasts for approx 15 years.
The heavier duty felt costs about £5/m2 against £3/m2 for the cheap felt. The cheap felt is often supplied as standard on pre-made sheds to keep the 'sticker' price down. The longer lasting felt is then available as a very sensible upgrade.
Standard shed felt.
Polyester base shed felt.
Using felt tiles is the next step up in quality. Roofing shingles are laid starting at the bottom of the roof. The shingles overlapping each other by about 150 mm, at the ridge a capping piece is used. This roof finish is a vast improvement on using a roll of Mineral felt and is much more durable. This article explains how to roof a shed with bitumen tiles.
EPDM Rubber is a sheet membrane that comes on a roll. It has been used on commercial and factory building roofs for over 40 years. It is now being promoted more extensively for sheds. It is especially suited to flat roofs though, can be used on roofs of any pitch. Find out more on EPDM rubber roofs
EPDM is especially suited to green roofs.
Green roofs are beautiful. They utilise a waterproof membrane on the roof deck with a build-up of growing medium on top as outlined in this article. Modern green roofs use a relatively thin layer of growing medium that particular suits hardy succulent plants.
This article outlines a way that you can grow your own green roof plants from cuttings.
Corrugated bitumen impregnated fibre makes for a durable roofing system. Most likely suited to slightly larger sheds. It is durable and quite cheap. Find out more about Onduline.
Cedar roofing shingles can make a roof look special. The basic installation process is to fix them to battens with a layer of underlay beneath.
Corrugated metal is widely used on larger commercial sheds and buildings. It can look complex and hard to work with for the DIY builder however this need not be the case. It can be an economical and very durable option if you take some time to investigate how the various metal roofing systems work, what tools to use and the best places to buy the materials and fixings. Find out more about Metal Shed Roofing.
Clay tiles are available in a huge range of colours, sizes and shapes. Typically the best choice is to match the style of your house or other buildings in the area. Clay tiles give the building a sense of place and permanence. A note of caution on using clay tiles for shed roofing, they are heavy! The supporting roof and walls must be made strong enough to support them.
Fibreglass is not commonly used as a shed roofing material. I only mention it as I came across this example on a fisherman's hut on a Dorset beach. It looks to me that the reason it was used was for extreme durability. The fibreglass shell would resist the winter storms and sand blasting around the beach as well as be extremely secure. Not sure it is a thing of beauty but it should last well.
I summarised the costs and lifespan of each material into the table below. At the moment it looks like EPDM rubber is the 'stand out' performer in whole life cost. The others vary slightly, but remember to include the labour element into the systems with the shorter lifespans.
Before making your final decision check the quoted cost and lifespan for the system that you select.
The above table just includes for material costs. This means that there is no allowance for your time, or you paying someone, to replace the shed roofing material when it reaches the end of its life. This makes options such as the EPDM roof even more attractive as it is likely that you will need to replace the shed before the roofing material becomes worn out!
Also remember that the visual appearance of the shed is an important factor. Your shed will be a major part of your garden for years to come and it should be pleasing to the eye.
A shed with an ugly roof will detract from your visual enjoyment of the structure. A shed roof can be an item of beauty. If you carefully select your roof materials. You can make a waterproof, economic roof that is also beautiful.
Beauty is definitely in the eye of the beholder. But it has been my observation that the most appealing sheds often use roofing shingles. Wooden shingles or clay tiles are really 'where it is at' in respect of craftsman-style roofs. A modern and increasingly popular alternative is the green or living roof. Green roofs utilise low-maintenance plants, which grow in a substrate on top of the waterproof membrane.
Plain roofs of mineral roofing felt are really for utility sheds which are hidden away. You are much better than that ☺.
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