Sadly, whichever way you look at it, the life of a commercial roof is finite. Yes, there are plenty of variables ranging from the architect’s original vision to craftsmanship and roofing materials, through to the quality of maintenance.  If you get the right combination of these factors right, your commercial roof will last longer.

Here is Stormforce Roofing’s guide to commercial slate or tile roofs, how to spot problems, and ultimately decide whether to repair or re-roof.

Roof deterioration signs

The first signs of deterioration in the roof covering are usually indicated by the presence of broken and delaminated slates/ tiles or daylight showing through to the loft area. Cracks and eventual breakage are caused by the effects of weather and movement within the roof structure, which increase as the fixings decay.

Delamination occurs with slates and clay tiles, which are of a laminated structure. Water, which is absorbed into the slate or tile during the winter, can freeze and expand, causing the layers to separate and flake off.

A commercial or industrial roof, which has an uneven surface, gives a reasonable indication that the roof timbers and battens are sagging. This may be due to decay in the timbers caused by water ingress or settlement within the building structure. The end result is a general disturbance of the roof covering, producing strain on the fixings and breaking of mortar joints.

Slates or tiles, which have slipped, indicate deterioration in the fixings, which may be nails or wooden pegs. If slipping has occurred in several places on the roof, it must be assumed that all the fixings are in an advanced stage of decay.

On closer examination, it may be found that the bedding mortar used at the ridges, verges and hips is cracked and decomposing allowing movement and water penetration to take place. Metal flashings and valleys may also require replacement as erosion and fatigue can produce hairline cracks allowing water to enter, which is mostly caused by incorrect installation.

Mortar fillet flashings are cheap and were common before the 1940’s, but they are generally less effective than metal due to their durability and inability to accommodate minor thermal and structural movement, which causes cracking. They are also susceptible to frost attack, which also results in the cracking of the mortar fillet.

Repair or re-roof?

Any faults already mentioned will leave a roof vulnerable to water penetration and further deterioration. It is necessary to inspect a roof thoroughly before any major refurbishment work in other areas is started and any faults rectified by taking one of the alternatives we talk about in this guide to repairing or re-roofing your commercial roof. These days, making that assessment is aided by drone surveys for which Stormforce is licenced and accredited.

Is patching a good option?

If the faults are confined to small areas and the remainder of the roof structure is sound, replacement of damaged slates or tiles may be the answer.

There could be a problem in obtaining slates or tiles of similar profile and colour due to tile or slate designs becoming obsolete; second-hand slates or tiles would have to be found.

However, it must be remembered that patching will not prevent deterioration in other parts of the roof and frequent inspections and repairs may be required. Patching isn’t attractive, inconvenient and impractical and the cost of small repair work will rise annually.

This sort of treatment should be regarded as an uneconomic long-term solution.


Re-roofing offers many advantages over repairing. Upon the removal of the old coverings, the timber rafters can be closely examined, replacing and packing-up where necessary to bring the roof structure onto an even plane.

Roofing felt is installed providing a barrier against wind, driven snow, dirt from outside.

New battens, slates or tiles are laid, bringing the roof up to present-day standards and performance associated with newly constructed buildings.

Ventilation products are installed to provide adequate ventilation of the roof void in accordance with current Building Regulations.

Surface Coating

There are a number of surface treatments on the market designed to form a protective layer over slates or tiles. The coating compound is applied in a liquid state, which hardens off, sealing gaps and holding the slates or tiles in place.

This type of treatment does not remedy faults in tiling battens and rafters, which may continue to decay due to moist air becoming trapped in the roof space. Natural ventilation through the roof coverings is prevented and alternative methods would be required.

The life of the material is uncertain, and the British Standard B.S.5534 Slating & Tiling does not recommend the use of surface coatings either internally or externally.

Commercial Roof Maintenance

Roof maintenance is an essential part of building upkeep. At Stormforce roofing we are always on hand to advise clients on best practice and ways to ensure a roof lasts as long as possible.

There are many elements that could cause a problem with your roof. Storms, floods, and other disasters can cause extreme damage, and most of the time, will mean necessary repairs.

Other situations can also cause damage to your roof, such as improper construction, or inadequate care. There are, however, preventative measures you can take to ensure minimal damage to your roof and we at Stormforce can offer help and advice.

A roof is one of the most expensive upkeeps on a building, so it is important to get the longest life possible out of this investment.

Ways to maintain a roof

Many companies offer inspection of chimney flashing, roof valleys, pipe vent roof jacks, roof to wall flashing, attic dormer vents, and roof drains. These are all essential to the protection of your home or building, and care should be taken to ensure they are up to standard.

Another option would be for us to inspect the roof covering for slipped, missing, or broken slates/tiles. If neglected, any of these problems can lead to leaks, and the repair cost will be higher than it would have been had they not been inspected. Again, we can utilise technology to conduct a drone survey [LINK] of your roof which is a safe and cost effective way to investigate issues and show you what is going on.

Also offered is inspection of asphalt shingles for curling, fractures, missing shingles, and for general wear and tear.

Also inspected are flat built-up roof systems for blisters, clogged interior drains, and flat, spongy areas of roof deck.

The eaves should also be checked for water stains, and exterior walls should be inspected in case discoloration occurs. While this refers mainly to pebbledashed walls, it is advised other types of wall materials be checked as well.

There are many other areas of inspection that will likely take place with such a maintenance program, and this is definitely worth consideration. The inspections will take place on a regular basis, and are very important to a long roof life.

At Stormforce Roofing, any new roof we build or indeed fix we always provide a detailed plan on how to ensure the roof does not need any further attention

So, do you repair or re-roof?

Like we said at the beginning, there are many factors to consider and we hope you have found this guide to this question for slate or tiled commercial and industrial roofs useful. Given that you have a roof (or a number of roofs) over your organisation, the answer is a commercial one based on freehold or leasehold status, value of your estate, maintenance budgets and how long you plan to stay where you are.

Ultimately, you and your team, hopefully with the guidance of Stormforce Roofing, will make that decision.