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Supervision of pitched roofing work

The only way to check 100% that a job has been done properly is to stand next to the person doing the job, and watch their every move, which is not very productive. Firstly it doubles the man cost, and secondly it generates great mistrust between the worker and the supervisor. So how should you check pitched roof coverings successfully?

There needs to be an understanding between the tradesman and the supervisor, that one is not trying to outsmart the other, and they need to work together to achieve the desired result. This starts with the roofer having not only all the materials and tools that are needed, but also the documentation, be it drawings, specification, literature or tables. There will always be corners and situations that are not covered by the documentation, as they were probably drawn, or written, before the walls went up, or before the original roof covering was stripped off and has uncovered poor workmanship from a previous era. Discussion needs to take place so that both sides know what the other wants, can achieve and the reasons for any decisions made.
      Often people who work with their hands are very good at learning by watching others, and are not necessarily good at learning from the written word, or explaining themselves. While some supervisors are great at talking they may be totally cack-handed at doing anything practical with their hands. A roofer that can do everything well and communicate it to others is rare and should make a good supervisor. Once there is trust between the parties, and everybody is clear as to what they have to do, and what is expected, this relationship needs to be maintained. Once a wall of animosity is built between the parties it is hard to break it down and can ruin a good project.
     Next there is the issue of checking work that has been undertaken, and agreeing the next batch of tasks. It is unreasonable to leave checking work until the very end of the project, as often what needs checking is not accessible once the roof covering has been installed. Furthermore if something is wrong, be it the wrong material supplied, or some other mixup, then it is unreasonable that this was not spotted earlier and put right, before other good work has been undertaken. Whilst there may not be a programme, an agreed programme of inspections at the appropriate time to allow sections of scaffolding to be moved, or other requirements met, will mean that the roofer can proceed at a better pace knowing that they are not being held up or starved of vital decision information.
     Some roof coverings are very easy to inspect with a gauging trowel, a hammer and a tape measure, a few tiles can be slipped out and the underlay and battens checked, along with the eaves, side abutment, top edge abutment and anything that is not mortar bedded. But with slates and some interlocking tiles this can be more difficult when they are all fully fixed. With a roof ladder it is possible to access most parts of the roof and undertake random checks. With interlocking and plain tiles it is possible to push tiles up the roof slope if the tiles are neither clipped nor nailed, to indicate those that have not been fixed.
     Those tiles or slates that can not be pushed up may be lifted on the leading edge with the trowel to see if they are clipped, and see how effective the clipping has been undertaken. By placing the tip of the trowel on the head of the nail and pressurising it, while sliding it off the nail head, you can tell how high the nail head is above the surface of the tile or slate. It is possible to test for missing nails, by tweaking the slates both horizontally and vertically and watching how the slates respond. A gauging trowel is also very good for dressing lead flashing back into position after it has been lifted to look at the top tiles or slates below.

Every tile on this roof should have been twice nailed and once clipped. Clearly the verge clips were missing.

 If you are not able to reach a patch of tiles because you are in a cherry picker, or it would not be safe to run a roof ladder over because the roof has hips and valleys, a telescopic pole with a floor scraper blade on the end will allow you remotely to slide it up between flat tiles or slates and tweak them to see if they are clipped or nailed correctly. Also it can identify slates that are broken above the centre nails, or cracked, or weak below the nail holes. Also the blade can be used to lift broken slates off the roof safely.
     A tape measure is very good for measuring both individual head laps, gauges and side laps, as well as calculating the average gauge over 10 slates or tiles. A small inclinometer for checking the rafter pitch is also very useful.
      From inside the roof it is possible to measure the laps in the underlay and to a very limited extent, by looking through the lap in the underlay, you can see any nail or clip fixings, or water leaking onto the battens and underlay.
     The only way to inspect work at a mortar bedded ridge, hip valley or verge requires a look in under the tile from one or two tiles away. And if there is good cause then the mortar bedding needs to be broken open, especially if the mortar in the cross bed joints are cracked. Where there are verge clips on a mortar bedded verge it is essential that each clip is pulled horizontally away from the verge to check that it is nailed to the battens, and is not just looking as if it is fixed correctly. Dry fix ridge and verge systems normally allow screws to be undone and sections removed to allow inspection. But some with adhesive membranes tear apart before they can be reinstated. Either way there is a lot that can be checked with simple tools.

Having your work checked is a very stressful exercise, as it is a personal criticism of your ability. Therefore whenever items are identified that need correction this should be reported and explained as soon as possible, such that the matter can be resolved. Also the roofer should be allowed to put forward their opinion and explanation as there may be good mitigating circumstances which must be taken into consideration before a final decision is made on how to proceed so the right approach is needed. Good supervisors will learn something from every project and improve their knowledge and technique accordingly.


  • The roofer and the supervisor need mutual respect for each otherís skills and knowledge to achieve the best results.
  • Lots of regular inspections are better than one inspection at the end of the project.
  • There is no substitute for getting up close and lifting, pushing and pulling the tiles and slates to see how they respond to a tweak.
Compiled by Chris Thomas, The Tiled Roofing Consultancy, 2 Ridlands Grove, Limpsfield Chart, Oxted, Surrey, RH8 0ST, tel 01883 724774
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