Slate roofing is considered a high-quality, durable, and aesthetically pleasing material which receives considerable focus in both the sale of properties and in the evaluation of building condition.
Like many building topics, opinions run heavier than actual data. The abandonment of good slate roofs which should have been repaired is a financial shame and the destruction of a valued asset.
From the roof space inside - If the inside of the roof is unlined, check for cracks showing daylight as this will indicate areas needing closer inspection. Shine a torch on the timbers and check for water staining. If stains are found on the timber, try to trace the source of the stain. It is useful to inspect the inner roof space after a long period of rain, as the source of a leak is easier to trace. Slate does deteriorate with age so check for hairline cracks by looking for staining on the tiles.
From ground level - Outside, check the whole roof by inspecting at ground level. It is easy to spot a disjointed or slipped slate against the regular lines of slates. If there is a change to the colour of a section, it could be newly exposed and therefore unweathered. Look for a powdery or flaky surface, known as delamination, which shows deteriorating slate, which is no longer doing its job effectively. Look at the ridge on the skyline and check for gaps in the mortar joints. Check for the state of the flashings at abutments and around chimney stacks. Check for fallen pieces of mortar.
If the roof is too high to allow you comfortable access by ladder for a closer inspection, use binoculars to scan the surface as carefully as possible, from all angles - front, back and sides where applicable.
At the roof level - If you are using a ladder, always make sure it is set up correctly and long enough - at least 3 rungs above the gutter. Always work with someone standing near by when you are working at a height. See our Ladder Users Guide for details on how to use a ladder correctly and safely.
Once at the roof level, only access the surface of the roof using a roof ladder. This is a purpose built ladder that has wheels to allow you to push it up the sloping roof without dislodging or damaging the slates. When the wheels reach the top of the roof ridge, by turning the ladder over a hook securely lodges on the ridge.
You can hire roof ladders. Otherwise, there are wheel and hook sections available to buy which fit onto conventional ladders. If you are going to be working on the house, perhaps a scaffold tower would be worth hiring.