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A Good Shed Roofing System Must Satisfy The Following Criteria:

To choose an appropriate shed roofing system. The three most important factors to consider are:

1. Have an appearance that is pleasing to the eye
2. Be waterproof to keep the contents of the shed dry
3. Be economic in its lifetime cost

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. By careful selection, a waterproof, economic roof can be achieved that is beautiful as well.

Beauty is 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, where attractive low maintenance plants are encouraged to grow. Plain roofs of roofing felt are really for utility sheds which are tucked away.

Waterproof

When considering the waterproof aspect of a roof, the pitch of a roof will influence the materials you choose. Roofs can be classified in three broad groups.

• Flat roofs: Pitch = 0 to 10 degrees
Roof 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, for a variety of reasons. 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.’ My advice is don’t use a ‘dead flat’ roof (pitch = 0 degrees), make sure that the minimum pitch of the roof is 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 water proof underlay and following the manufacturers recommendations.

• Pitched roofs: Pitch = 20 degrees +
Concrete interlocking tiles are really the only tile suitable at a 20 degree pitch and they are not often used on small timber structures due to their heavy weight. Clay tiles generally have a minimum pitch of about 35 degrees.

Whatever product you end up using get the manufacturers’ datasheets, which should state a minimum roof pitch at which it will remain waterproof. Some Local Authorities recommend that you add an extra 5 degrees on the manufacturer’s minimum pitch to ensure watertightness.

Just to clarify the reason for all this talk about minimum 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 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 although clay tiles can be considered waterproof, in many ways they act as a hard outer layer, protecting the underlay below. The underlay is also waterproof and acts as a back-up system. The tiles protect the underlay, which would only have a three-month life if left unprotected from UV degradation, water, abrasion, …….meteorites etc.

Tip: When deciding the pitch of your shed roof, make it the same as your house. This has two advantages in that it should blend in and hopefully you know that the pitched roof of your house does not leak.

Costs Of Shed Roofing Materials

I have compiled a list of common roofing materials below, to help you get an idea of relative material costs. The prices shown are material costs only and do not allow for the labour cost of installation. Also remember that the prices are in British pounds, that building material costs do vary widely within a country (never mind throughout the world). Read this table as it is intended - a guide to your further research.

The reason most sheds have a roof covering of bitumen mineral felt is obvious when you consider the costs per square meter of the roofing options below. My opinion is that if you are going to the trouble of building your own shed, and small roof area of a shed, the benefit in appearance of using a more characterful material than plain roofing felt is well worth it.

• Mineral roof felt.

The standard garden shed will come with a cheap roll of mineral felt, this does the job of keeping the water out, however it is fragile and relatively short-lived. A bit of unseen damage to the shed roofing will allow water in, which will damage the fabric of the sheds structure.

Design life: 3-5 years
Minimum pitch: 6 degrees +
Rough cost /m²: £1.50

• Felt Tiles or roofing shingles.

Using felt tiles is the next step up in quality. The roofing shingles are laid starting at the bottom of the roof and overlapping each other by about 150 mm towards the ridge where a ridge capping is used. These roofs are a vast improvement on using a roll of felt and are more durable.

Design life: 15 years
Minimum pitch: 18.5 degrees +
Rough cost /m²: £6.00

• Wooden shingles.

Cedar roofing shingles really can make a roof look special; these are fixed to battens with a layer of underlay beneath.

Design life: 30 years
Minimum pitch: 20-30 degrees
Rough cost /m²: £35.00

• Clay Tiles.

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 is that they are heavy, the supporting roof and walls must be made strong enough to support them.

Design life: 50 Years
Minimum pitch: 35degrees
Rough cost /m²: £40.00

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