Tegral - Slating Tips

In every country, the slope of the roof is one of the surest indications of the climate. We know all about wind-driven rain in Ireland. Here, roofs must run the rain off safely. One of the earliest records of slating in Ireland dates back to 1622. Even then the buildings were covered with steep pitched roofs. Because slates have proven to be so successful over time, they remain to this day a popular trouble-free choice of roof covering.

National Standards

For guidance on design and workmanship in slating, the relevant national standard is ICP 2:2002, the Irish Code of Practice for Slating and Tiling. The Building Regulations state that a weather-resisting cladding (which is slating) has overlapping dry joints. Therefore, slating should be backed by a durable roofing underlay material that can direct rain or snow which enters the cladding (slating) back towards the outside face of the cladding (slating) system at the eaves, valleys and back gutters.

Avoiding Roof Defects

“Spot them early and eliminate them forever”
Leaks do not occur without a reason. A leak usually occurs as a result of several different things going wrong in sequence. There is usually more than a single cause for any given problem. We’ll look at a few common defects that are easy to spot. You’ll see how simple it is. They should be spotted before slates are fixed to the roof and rectified there and then, thus avoiding any future problems. “Spot them early and eliminate them forever.” That way, you should never have unwelcome defects on a roof you design. The effectiveness of a slated roof covering is influenced by several factors, including capillary attraction, site exposure, the length of the roof slope, the roof pitch and the head-lap of the slates. Choosing the correct combination of pitch and head-lap is the key to preventing water from breaching the head-lap and penetrating the nail holes. For a normal sized roof the battens should be fixed at 245mm centres. This results in a slate head-lap cover of 110mm.

Underlays

Always remember that where roofs are concerned the underlay is your second line of defence. It is absolutely vital that it is installed correctly because underlays can lead to disproportionate damage should they ever fail. The underlay must be fully supported at the eaves to prevent ponding and be protected from UV-light degradation. The underlay can be supported at the eaves by using either a Tegral Underlay Support Tray or a combination of a timber fillet with a strip of durable, UV-resistant, rot-proof material dressed into the gutter beneath the underlay. If you are planning to use some of the more modern underlays, you should first check their resistance to UV light. Many of them will require a more robust material, such as a plastics underlay support tray, to be used at the eaves and projecting into the gutter. The choice is yours but eaves ponding and rotting – which causes anything up to 80% of all leaks on slated and tiled roofs – MUST be eliminated.

Eaves

The eaves is the lower edge of the roof and handles the largest volume of water of any part of the roof, so it is important to get it right. Also, as it is the first part of the roof to be slated, it is at the eaves that the standard of workmanship for the rest of the roof is set. Set out the battens correctly. There are two under-eaves courses needed in fibrecement eaves – to hold the copper disc rivet or crampion in place at the tail which prevents wind uplift. These two under-eaves slates are cut on site from one full slate, thus eliminating waste.

Ridge

If leaks sometimes appear at the eaves, they are usually caused somewhere higher up the roof. Sometimes the problem occurs at the ridge. Even though the leak may be at the eaves, the water can gain entry at the ridge and run all the way down the top of the underlay, just as it should, until it results in a problem at the eaves. Look to the visible slate margins, the part of the slate in each course that is exposed to the elements. The margin of the top course must not be longer than all the rest. If the top or short course is omitted then the ridge does not provide enough cover. Remember this: if you can see more of the top row of slates, immediately beneath the ridge, than you can of any other row of slates, then there is a row of slates missing.

Verge

In areas subjected to high winds the most vulnerable part of the roof is the verge or barge area. To counteract the risk of slates being blown off the roof and to provide a neat finish to this part of the roof you should use aluminium verge trims which are available from Tegral.

Valley

It is vital that on long valleys, the depth and width of the valley is sufficient to carry the water run-off from the two roof slopes. Second only to the eaves, the valley is the edge of the roof that receives most water. The true angle of pitch of the valley is always less than that of the adjoining roof slopes. The biggest danger with valley gutters is that they can surcharge and spill onto the underlay – with potentially disastrous implications – if they are incorrectly sized or detailed.

Roof Windows, Pipes and Solar Panels

All roof windows should be installed in strict accordance with the supplier’s instructions. The underlay must be cut and returned up the sides of the roof windows. Pipes from extractor fans or soil vent pipes from bathrooms can be connected to slate vents which are available complete with the required pipe adaptor from Tegral. One of the most common issues concerning solar panels is how to safely pass the pipe work through the roof. By using Tegral’s Utility Slate this procedure is quick, clean and provides a long term weather proof seal.

Before Slating Begins: 5 Easy Checks

Battens fixed to correct gauge
Valley boards set at correct level and appropriately sized
Underlay properly supported at eaves
Underlay overlaps correctly dimensioned and secured
Underlay penetrations (roof windows), including tears or punctures, properly sealed/repaired

Tegral’s site inspection checklist is printed in the Tegral Slating Manual. There is a right time when your builder/engineer should make their inspection – and for both slated and tiled roofs, that time is when the roof has been felted and battened but the slating or tiling has not yet begun. This is the opportune time to verify whether or not all of the basics have been set up correctly.

Tegral fibrecement slates have recently been environmentally profiled by the Building Research Establishment (BRE) in a lengthy process that took the product’s cradle-to-grave environmental impacts into account. Tegral is the only supplier of fibrecement slates on the Irish market to have received an ‘A’ rating for its products, the most environmentally friendly rating possible for roofing materials.

For technical advice contact Tegral’s Technical Support Department.
Tel: 059 8631316, email: support@tegral.com