Shed maintenance is part and parcel of owning sheds, and some simple fixes and quick repairs can help to prevent you from having to purchase an entirely new shed roof. Here we take you through the steps involved in repairing small problems you may encounter with a sagging roof or rotten roof boards.

Read on to find out how to repair a leak in bitumen sheets made of felt, how to mend holes in an EPDM rubber roof deck, and replace steel sheets on a leaking roof. It's important to get the job done properly to prevent a shed roof leaking again and having to repeat the whole process.

Common types of shed roofs include bitumen felt, EPDM rubber, Onduline and Steel roofing sheets. From general wear and tear to a sagging shed roof, damage by rain or objects can lead to cracks over time which in turn can lead to water leaks.

Identify whether or not your garden shed roof leak is causing permanent damage to the whole shed roof or just part of the roof. This will help you decide if you'll need to fully replace the roof or just the affected area.


Bitumen Roof Felt

Bitumen roof felt is a type of material that is affordable and easy to install. You are most likely to find bitumen felt on small to medium-sized garden sheds, creating excellent waterproofing. When installed with a torch-on method instead of nails, the risk of shed roof leaks is reduced even further.

Commonly used on a flat to shallow-pitched roof due to its excellent water run-off properties, bitumen provide low-cost benefits which are outweighed by regular maintenance and repairs that might be required throughout the year, depending on weather conditions.

Why is it Leaking: Common Causes

Felt roofing may need repairing for a number of reasons. These could include tears, nail holes, sagging, which could expose the timber underneath.

Felt is known to weaken in wet, windy weather and due to pooling water, this can affect timber supports underneath.

A build-up of debris can cause the felt to sag and create a concave in the roof for water to pool. This can seep through into the shed. As soon as you see sagging on damaged felt, it is recommended to undergo maintenance and repairs.

How to Repair a Felt Shed Roof


Repair Using Felt:

Step 1 - Remove the existing, damaged fascia boards and felt from the roof and check the condition of the underlying wood panels. Replace or reattach any loose or damaged wood panels.

Step 2 - Using a tape measure, calculate the length and width of your roof to work out how many rolls of new roofing felt you'll need for your shed.

Step 3 - We recommend cutting using a utility knife and laying the roofing felt across the roof. Leave a 50-80mm overhang at either end. Apply bitumen adhesive to joins between sheets and allow for a 100mm overlap. Using large clout nails, hammer the joins together.

Step 4 - Nail the felt across the timber at regular intervals of 100mm and finish with a ridge felt sheet secured along the apex of the roof. Fascia boards can be fixed to the gable ends for a professional finish.



If you need to repair shed roof felt, the costs are minimal. A roll of roof felt, fixings, and bitumen adhesive will be needed, as well as new timber for the roof deck and fascia boards if required. You could be looking at between £50-£200 depending on the thickness and specifications of the materials.

Alternatives to Bitumen Roof Felt

Consider using felt shingles or stone effect shingles for sheds instead of roofing felt sheets to improve the quality of the shed. Be sure to check the timber supports underneath for rot to determine whether or not you'll need new rafters for shingles.

EPDM Rubber


EPDM rubber roofing materials are hard-wearing, rubber-based sheeting that is preferred for a flat roof. Fixing a new shed with EPDM takes specialist knowledge, but if sections need to be replaced, this can be undertaken by DIY enthusiasts. A rubber EPDM roof can become damaged when scratched with a sharp tool and this can lead to a leaky flat roof if left untreated.

Why is it Leaking: Common Causes

The common causes of EPDM leaking are splits in the rubber surface caused by sharp objects, or objects scoring the surface. Another common issue is the deterioration of the adhesive due to UV sunlight and heat in the hot summer months, which can lead to a leak. This can lead to repairs at sections of the rubber and ultimately reduce the life expectancy of the roof.

Rotting wood underneath the rubber can occur if water gets trapped underneath and this can create a sagging shed roof. If this has happened the structure of the roof will need to be replaced.

How to Repair an EPDM Shed Roof

Repair Using EPDM Patch:

Steps 1 - Clean the area first free from debris using warm soapy water and allow it to dry.

Step 2 - Measure and cut a new section of EPDM rubber to sit at least 75mm (3 inches) around the damaged area. Round off the corners to prevent peeling.

Step 3 - Apply a primer to the surface using a brush. Leave until dry to the touch.

Step 4 - Peel back the backing paper to reveal the sticky side of the EPDM patch. Press firmly using a small seam roller, or fingers to press down to the surface.

Step 5 - Apply bonding sealant to the seams and joints to create a watertight seal.


Repairing EPDM is low cost, requiring a few standard tools, such as scissors, a small roller, and a brush. EPDM repair kits, for example, are available from £15 or more, containing primer and cover tape.

Alternatives to EPDM

Felt sheets, or roofing shingles, are a suitable replacement for EPDM per square metre. Ideal for a flat structure, bitumen is a quality shed roof option without producing too much weight over the roof.a

Metal Roofing Sheets

Metal Roofing Sheets are used mostly on pitched roofs, due to minimum pitch angles. The minimum pitch angle will vary depending on the profile of the Sheet. Corrugated Profiled roofs have a minimum pitch of 10 degrees, whereas Box Profile has a minimum pitch angle of 4 degrees and Tile Form Profile has a 12-degree minimum pitch. The steeper the angle will improve the water run-off efficiency of the Sheets.

Why is it Leaking: Common Causes

Galvanised metal roofing sheets are strengthened against rust and corrosion, providing longevity over time. However, when scratches occur on the surface this could expose the untreated surface of the steel sheets, and exposure to moisture and air can then create rust.

Another common cause can be due to the fixings becoming loose and leaks occurring around the fixing point. This can easily be repaired on a shed by replacing the screws or resealing around joins and overlaps.

In uninsulated roofs, condensation can occur on the underside of steel sheeting in certain conditions and can result in water droplets forming and falling onto timber purlins. This could result in timber purlins becoming damp and, over time, could become prone to rot. This will inevitably lead to the roof becoming unstable and could be weakened across the rafters.

How to Repair a Metal Shed Roof

Treating the common causes of metal shed roofs can be undertaken by re-coating the sheets with anti-corrosion outdoor metal paint. Large damaged areas of a metal shed roof may require full panel replacement, depending on the size of the shed roof, it might be worth replacing the sheets fully.

Repair Using metal profile patch:

Step 1 - Clean the damaged area to remove any grime or dirt. Any rust can be removed with an angle grinder or wire brush.

Step 2 - A metal patch can be used to cover damaged sections of the roof to stop your metal shed roof from leaking further. Be sure to secure a patch over the damaged area.

Step 3 - Measure two inches around the patch and apply plenty of sealant to the area.

Step 4 - Secure the patch over the area and fix it with screws, allowing the sealant to dry. The roofing patch can be painted with matching RAL colours to blend it in.


Overall, the cost of repairs for a metal roof can be more than other types, as materials for larger sections could require entire panel replacement.

Repair Using new fixings:

Step 1 - Depending on the source of the leak, check the shed roof fixings and joins between sheets and overlaps. It could be a case that the screws are no longer sealing effectively.

Step 2 - Replacing individual TEK screws that have new rubber, or neoprene, sealing pads could be all that's needed to stop the roof leaks. Ensure bonded washers are not over-tightened, or under-tightened, to prevent the seal from warping.



Costs of fixings can be minimal depending on the type and size of the screws. Always check your roof boards or rafters for rot before you replace nails or screws.

Calculate the cost, number of sheets and fixings you may need using the Cladco Roofing Calculator.

Alternatives to Metal Roofing Sheets

Onduline is a good alternative to Metal Roofing Sheets for a shed roof. Much like steel sheeting, a shed roof with Onduline will not suffer from sagging or rot over time.

Onduline Roofing Sheets


Why is it Leaking: Common Causes

Onduline roofing sheets have a tendency to weaken over time if adequate support is not provided for the sheets, which can lead to possible damage to the interior of the shed, or the structural integrity of the roof.

Onduline is also known to fade in colour over time. Although this doesn't affect the strength of the sheets, you may want to consider this as part of the decision-making process when choosing Onduline.

How to Repair an Onduline Shed Roof

Step 1 - Be sure to have a safe and stable platform set up to access the damaged area. Safety equipment, including gloves, eye protection and suitable clothing, is important to have before repairs are undertaken.

Step 2 - Remove the damaged sheets from the purlins by removing the fixings from the purlins either with a flathead screwdriver, pry bar, or power driver. You may need to unfasten the ridge flashings where the sheet is secured.

Step 3 - Be sure to check the condition of the timber purlins underneath. Replace the new Onduline sheeting panel in the same place as the old sheet, replacing the fixings.

Step 4 - Offcut Onduline is classified as a non-dangerous waste material. We always recommend checking with local regulations when disposing of damaged Onduline sheeting.



The repair costs for replacing Onduline roof sheets will vary depending on sheet lengths and the number of sheets. Expect to pay from £8 per square metre.

Alternatives to Onduline Roofing Sheets

Alternative options to Onduline are Steel Roofing Sheets that can be produced with a similar profile to match the correct size of Onduline Sheets.

Talk to us about replacing your shed roof with steel Roof Sheets by calling 01837 659901.

For more information about Cladco Roofing Sheets or Flashings, see our website, or contact a team member on 01837 659901.