Maintaining a Sound Roof

A sound roof keeps out water – and thus helps prevent problems caused by damp. In this article on roof repairs, we describe how to deal with the most common types of roof damage and look first at slate roofs.

Roof slates deteriorate over a period of time as a result of weathering and movement of the roof structure. If you have slates, check the roof regularly so you can make repairs before the damage lets in water. The first sign of wear may be a hairline crack. or flaking may occur along the edges or round the fixing holes. You should also check for loose slates. Slates vary in size, shape, thickness and colour, so note your requirements carefully before ordering new slates. It is a good idea to take one of your slates to a builders merchant to match it up. You can buy second-hand slates from a builders’ yard or demolition site, but examine them carefully to make sure they are undamaged. If you cannot get a replacement of the exact size, choose a larger one of the same thickness and cut it to size. ROOF LAYOUT Slates are laid from the eaves upwards and each row. known as a course, is overlapped by the one above. The vertical joints of the slates are staggered, so each slate partially covers the two below. The slates are nailed to battens, spaced according to the pitch of the roof.

The slates on the first row. at the eaves, and those on the last row, at the ridge, are shorter than those used on the rest of the roof. At the end of every alternate row a wider slate, called a tile-and-a-half. is used to fill the gap left on a straight edge. If the roof is angled at the edge, slates have to be cut to fit. On the edge of a gable roof there may be a narrow slate, known as a verge or creasing slate. which is laid under the slates at the end of each row: these slates give the roof a slight tilt and prevent rainwater running down the wall. V-shaped slates are used for the ridge of the roof.


Roof slates may be nailed in the centre or at the lop. When replacing slates, use the same nailing position as that of existing slates; to make nail holes, place the old slate over a new one and mark the position of the holes with a nail. Lay the new slate on a piece of wood and make the holes by hammering a nail through or by drilling, using a bit to match the size of the nail to be used.


Remove all the slates from the damaged area and stack the undamaged ones carefully. Remove any unsound battens by sawing through them diagonally where they cross the rafters.

Cut new lengths of the same size softwood as the existing battens – usually 50 x 25mm – at a matching angle to provide a tight fit; fix the new battens with a 50mm nail at each end. If there is any bituminous felt which is damaged, repair it before you fit the battens in place. Cut the torn piece to a neat rectangle, fit a larger rectangle of new felt over it and stick it down with bitumen adhesive. Coat all new timber and the surrounding old structure with a wood preservative before replacing the slates.

FIXING SLATES Start at the eaves with a row of short slates. If you are making the repair in the middle of an existing row, slide the first new slate under the last overlapping slate, placing the holes over the centre of the batten. Secure the exposed part

If you need to cut a slate, score the cutting line on both sides with the point of a trowel. If you are cutting a large slate down to a smaller size, use an old slate as a guide. To mark out a shape – for example, to fit the angled edge of a roof – use the old slate as a guide or make a template. Place the marked slate on a firm, flat surface with the waste section overhanging. Chop halfway along the cutting line with the sharp edge of a trowel, then turn the slate over and work in from the other end so the cuts meet in the middle. Never try to snap the slate along the cutting line.


When removing a single slate, take care not to damage surrounding slates. If the fixing nails have corroded through, you will be able to pull the slate away quite easily. To remove a securely nailed -•- – – <•¦-<-.-;.,.„„. cu^o _j,e <-1Q«,- Q£ the into position under the overlapping ones, lining up the edge with adjacent slates, and bend up the free end of the lead strip to hold the slate in place. RIDGE SLATES These are bedded down in mortar. Remove any loose ridge slates for refitting and take away any damaged ones. If you need access to the top batten for fixing the top row of replacement slates, remove the relevant ridge slates. To remove securely fixed ridge slates, loosen the mortar under the slates with a sharp brick bolster. Hold the bolster parallel to the slate and tap it with a club hammer. Clean away old mortar from the top course of slates in the same way and chip away mortar from any ridge slates which are to be relaid. For relaying ridge slates, mix a mortar of one part cement to three or four parts sand. Lay the fresh mortar along the ridge with a trowel and roughen the surface. Place the ridge slates on the of the slate with a nail driven into the batten. Butt-join the remaining slates in the row and fix each one with two nails, lining up the upper edges.

The second row will completely cover the row of short slates. Fix the slates as for the first row. covering the vertical joins of the slates below. Continue fixing the slates, moving up the roof one course at a time. All vertical joins should be covered and each course should overlap the one below.

Unless you are restating to the ridge of the roof. the nail holes of the last few slates will be covered by the overlapping slates above, so use lead strips to fix these in position, as described earlier. If you are working right up to the ridge, you will have to remove the ridge slates to fix the top row of slates.

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