Roof Restoration and Maintenance

This section has tips about roof restoration and maintenance work.

Slates

A slate roof should last 80 years; failure is usually caused by corrosion of the nails rather than of the slate itself. Thus, reroofing in recycled slates is a good option; cheaper than new slates and giving a far more attractive result than modern concrete tiles. However, slate can delaminate, becoming absorbent. Slates like this must be replaced.

When restoring a slate roof the options are:

new Welsh slates	These are very expensive, but the best option. They can last for more than 100 years. They come in a range of grey colours, and with plum and blue tints.
recycled Welsh slates	These tiles are a good compromise between cost and longevity
Other slates	A good alternative to Welsh slate is Canadian slate. Spanish slate is too soft and has an unpredictable grain. Chinese slate does not have a British Standard kitemark. Furthermore it sometimes goes rusty due to iron oxide, and is brittle and therefore hard to fit without cracking.
new Spanish slates	These give an authentic look but because of irregular grain, they can split early in their life. They are likely to last 40 or 50 years, being softer than Welsh slate. They are blue/black in colour.
composite	This is a modern material; a cheap solution but it does not weather, is very smooth, and does not have a long life. It looks very shabby in 10 years.
concrete tiles	Although they are available in grey, they are not authentic-looking, and because they are heavier than slates, the roof timbers typically need to be strengthened. When in an interlocking design, they look very different from other slates and tiles.

If you are having a new roof, insist on Tyvek underlay as this does not require unsightly plastic vents on roof.

In rare cases, a roof may have Westmoreland green slates.These are irregular in size and usually laid in diminishing courses with the smallest at the ridge and the largest at the eaves.

Slates may be nailed at the top or, more usually, in the centre.

When repairing an old slate roof, ensure that you match the size, texture, colour and detailing of the existing roof.

When seeking a roofing contractor, get references and visit their previous work. Slate should be sorted into three grades of thickness, with the thickest laid at bottom of the slope, the thinnest at the top. Battens need to be set out horizontally and vertically with stringline before slating. Copper nails should be used for fixing. Check the lines of slates: good slating when viewed from the ground should have straight, perpendicular courses from the base to the top. There should be no 'kickers', tiles which are lifted up to leave a gap underneath. There should be no thick slates laid in amongst thin slates.

There are several elements of a slate roof:

• eaves
• verge
• ridges and hips
• valleys

Eaves

There should be a double course of slates at the eaves using a short under-eaves slate, supported by a tiling fillet (or fascia board), above which is laid the first full course of slates. The overhang should be approximately 50mm to ensure that water discharges into the centre of the gutter.

Verge

The verge (the edge of a roof at a gable end), should normally comprise an undercloak course of slate, which is bedded on mortar and nailed if possible. The upper slate should be well bedded in mortar and finished flush with the undercloak slate course. It is good practice to carry the battens over the edge of the undercloak slate to give additional support. The unsupported overhang of a verge should not normally be less than 40mm and not more than 50mm.

Ridges and Hips

Ridges and hips may be protected with a half or third round terracotta or clay ridge tiles or with dark grey/black angle tiles or, as is usual on lower pitched roofs, a lead roll ridge or hip. Hips may also be formed from mitred slates, interleaved with lead soakers. In exposed situations, the mitred hip slates can be fixed with brass screws and washers.

Valleys

Valleys may be formed by a lead gutter lining – gutter width minimum 100mm; by mitred valley slates interleaved with lead soakers fixed by nailing to battens at the top edge. More rarely there may also be swept valleys or laced valleys using specially sized and cut slates.

Other Details

Sloping edge abutments and junctions or roofs with parapets or chimney stacks or changes in roof pitch (as for example in mansard or gambrel roofs) should always be detailed with lead flashings and not cement fillets.

Clay Tiles

Arts and Crafts-style houses are roofed with, usually, flat red clay tiles.

Thatch

Repairing thatch is not really a job for the amateur. It is important to understand the different materials used. Your roof is likely to be of one of three types:

• water reed or Norfolk reed
• combed wheat reed or Devon reed
• long straw

A water reed roof can last 50-75 years but should be checked every 10-15 years. The other two types are both straw but combed wheat has had the leaves and remaining grain removed; it can last 40 years as opposed to 20-30 for long straw.

If your home is listed, you must contact the local Conservation Officer before having work done.

The most essential maintenance with a thatched roof is actually to the electrical circuits in the loft; these must be checked regularly and frequently for rodent damage and the resulting fire risk. Ideally such cables should be in metal conduits.