Types and Lifespan

Flat roofs are usually made of felt, asphalt, GRP fibreglass or EPDM rubber. The lifespan of a flat roof will vary depending on the material used. Most have a warranty period of 10-20 years. If they are well maintained, a flat roof can last more than 20 years. Flat roofs made from EPDM rubber are expected to last for up to 50 years. Some are coated in shingle (sometimes called Pea Shingle) or gravel; these coatings add a weight to the surface material and protect the roof from sun damage, so are popular in south-facing properties.  

Regular Maintenance

The following tasks should ideally be carried out three times a year, but at the very least bi-annually in early Spring and early Autumn, and after adverse weather (especially snowfall).

Apart from your time, there is little specialist equipment required. At most you’ll need a long-handled wire broom costing around £20, a rubber cleaning broom costing around £10. You will need access to the roof, either with a  ladder or from a window (if it is safe to do so). It is important not to stand on your flat roof unless it was specifically made to hold this weight; if you are determined to stand on your flat roof to clean it, mosskillers.co.uk advise is best to stand on a timber plank to help spread your weight across the structure and avoid falling through!

Remove dirt and debris

Using a long-handled broom, carefully remove dirt and debris from the flat roof. This can include twigs, branches or fallen leaves. If this is allowed to accumulate, it will add undue pressure to the roof structure and will often trap moisture next to the roof’s coating, leading to splits and leaks.

Remove fallen leaves

Using a leaf blower or long handled broom, clear the roof of any fallen leaves. Again, these can add weight to the roof if left to amass, but they will certainly trap moisture against the roof material which can ultimately lead to leaks.

Cut back overhanging branches and nearby trees

To reduce the damage from leaves, twigs and fallen branches, it is advisable to ensure nearby trees are cut back if possible.

Clear drains and gutters

Keeping these working effectively will reduce the chance that water will build up on and around your flat roofs, leading to pooling and leaks.

Carefully remove moss and lichen

Moss and lichen hold moisture against the roof’s surface, which again adds excess weight and moisture to the roof. Roofs coated with shingle or gravel often grow moss more easily because these coatings provide ample shade and moisture for moss to thrive. This can quickly lead to splitting or blistering, and bigger problems such as sagging joists and leaks.

To remove moss and lichen, firstly use a small brush to clear the area of any shingle, gravel or debris. Then brush the affected area itself, which will hopefully remove much of the moss or lichen. Let the area dry either under the sun or over a day or two in dry weather conditions. Apply a moss killer, there are many different makes including Baticlean, Batiface, Moss Clean Xtreme and Moss Clear; these start at around £9, but if your roof is prone to moss or you have a large flat roof to treat then it may be worth buying a larger volume for upwards of £40 for future use. You will need to wear goggles, a mask and gloves when applying moss killer, and a standard safety kit can set you back around £12. This chemical treatment will kill moss and lichen growth that is too small to brush away, as well as the spores. Finally, replace any displaced shingle or gravel to ensure the roof is weatherproof.

Check for missing shingle or gravel

This will need to be replaced to prevent blistering and maintain the roof’s waterproofing and weatherproofing. A 20kg bag of 10mm roof shingle costs around £65-70.

Check the ceiling for signs of water damage

Maintenance does not stop at the exterior of your flat roof. If water has been able to penetrate the roof structure, you can expect leaks. Check the ceiling for signs of water damage, including: green, brown or black stains, sagging or bulging, new cracks, flaking paint. If any of these signs are spotted, act quickly by contacting a roofing specialist to address the leak and avoid further damage.

Occasional Maintenance

You will need to reseal a felt or asphalt-coated flat roof approximately every five years, but you may want to reseal more regularly if it is south facing.  Resealing keeps your roof weatherproof and can significantly prolong its lifespan, so it is well worth scheduling in this maintenance task. If your roof has gravel or shingle, this will have to be removed prior to resealing.

You can hire a roofing specialist to reseal your roof, but it is not beyond the bounds of DIY. A small tin of roof coat seal costs between £5 - £10, with larger volumes upwards for £35.  The sealant can be applied with a brush or roller, but a brush is often easier.

Common Problems- Felt and Asphalt Flat Roofs:

• Blistering: usually caused by excessive heat. Air and moisture trapped between layers of felt warms and expands, creating blisters in the felt; these blisters can then create a puncture or split. If a blister occurs on a join in the felt, water can easily seep through to the roof structure and cause a leak.
• Splitting: usually caused by excessive pressure on the roof or thawing after severe cold weather. Splitting allows water in through the roof and so leads to leaks. 
  Providing they are addressed in a timely manner (before leaks develops), blisters and splits can be repaired with minimal cost. For asphalt and felt roofs, you’ll need a tin of roofing tar (costing between £18-25), a small trowel and a roll of reinforced mesh (a 1m x 10m roll costs around £35).
• Ponding/pooling: where water pools in specific areas on a flat roof, and does not evaporate easily or drain away. This problem can require an automatic pump or drains to be fitted, and is best repaired by a roofing specialist.

Common problems- GRP and EPDM roofs:

Bubbling: usually the result of poor installation practices, where there was moisture in the roofing structure when the installation took place. In the case of GRP, it may require the entire topcoat to be reapplied and it is best to consult a roofing specialist to determine the cause and course of action.

In the case of EPDM roofs, bubbling could be the result of two issues. Firstly, it could be that not enough time was allowed for bonding adhesive to ‘gas off’ when the rubber was bonded to the roofing deck; the gases are then trapped and expand over time, appearing as ‘bubbles’ towards the edge of the roof (where the adhesive was applied). Roofing specialists often say that these bubbles are innocuous and will disappear over time, or that applying a small weight to the bubbles will speed things along.

Alternatively, it could be that there was moisture in the roof structure at the time of installation or there are large gaps between boards of the roof structure; in either case, air between the boards or moisture in the structure will expand in warm weather, creating ‘bubbles’.It is best to consult the professional who installed the roof, or a separate EPDM roofing specialist, if you have issues with bubbling.

Flat roofs have a bad reputation for failing and a short lifespan. However, with a regular maintenance schedule, some basic equipment and close inspection after adverse weather, you can prolong the lifespan of your flat roof and keep it functional for the foreseeable future.