UNITED KINGDOM Annual driving rain index & HEADLAP TABLES TO BS 5534

Durability against the elements is a key factor in determining the materials selection on a construction project.

Providing enhanced protection for the most vulnerable locations is why many architects and specifiers select Welsh Slate as their chosen material.

Generally any area within 30 miles of a west facing coastline is considered to be in a severe exposure area.
However, localised effects on any site must also be taken into consideration. Further reference to BS 8104 is advisable to ascertain localised effects. Map based on BS 5534.

Less than 56.5 l/m2 per spell

	Minimum Rafter Pitch	20	22.5	25	27.5	30	35	40	45 to 75	85+
Slate Size
600x350		115 *	105 *	95 *	85 *	80 *	70 *	60 *	55 *	45 *
600x300		190 *	130 *	95 *	85 *	80 *	70 *	60 *	55 *	45 *

550x300		135 *	105 *	95 *	85 *	80 *	70 *	60 *	55 *	45 *

500x300		115 *	105 *	95 *	85 *	80 *	70 *	60 *	55 *	45 *
500x250			125 *	95 *	85 *	80 *	70 *	60 *	55 *	45 *

455x250			105 *	95 *	85 *	80 *	70 *	60 *	55 *	45 *

400x250					85	80	70	60	55	45
400x200					85	80	70	60	55	45

350x300					85 *	80 *	70 *	60 *	55 *	45 *
350x250					85	80	70	60	55	45
350x200					85	80	70	60	55	45

300x200					85	80	70	60	55	45

270x180					85	80	70	60	55	45

250x150					85	80	70	60	55	45

56.5 l/m2 or greater per spell

	Minimum Rafter Pitch	20	22.5	25	27.5	30	35	40	45 to 75	85+
Slate Size
600x350		150 *	130 *	120 *	110 *	100 *	85 *	80 *	70 *	50 *
600x300			165 *	120 *	110 *	100 *	85 *	80 *	70 *	65 *

550x300		180 *	130 *	120 *	110 *	100 *	85 *	80 *	70 *	50 *

500x300			130 *	120 *	110 *	100 *	85 *	80 *	70 *	50 *
500x250			150 *	125 *	110 *	100 *	85 *	80 *	70 *	70 *

455x250				120 *	110 *	100 *	85 *	80 *	70 *	50 *

400x250						100	85	80	70	50
400x200						100	85	80	80	80

350x300						100 *	85 *	80 *	70 *	50 *
350x250						100	85	80	70	50
350x200						100	85	80	70	50

300x200						100	85	80	70	50

270x180						100	85	80	70	50

250x150						100	85	80	70	50

* Marked items may require longer or improved ring shank nails or increase slate thickness laps etc in areas likely to be exposed to very high winds. Project specific calculations can be carried out.

Welsh Slate is the perfect natural product for harsh conditions

Welsh Slate is exceptionally durable. It is unaffected by normal extremes of temperature and is highly resistant to acids, alkalis and other chemicals. It retains its colour, even in UV light and is impermeable to water. Welsh Slate is non combustable and is compatible with all other building materials.

Water permeability - Impermeable

Sunlight unfading - Unaffected by UV light

Heat - Unaffected by normal heating, freezing and thermal cycling

Chemical resistance - Unaffected by atmospheric pollution, sea air and sea spray

Biological resistance - Unaffected by vegetable growth, rot or insect attack

Compatibility - Compatible with all building materials

Fire resistance - Slate is non combustible and does not support combustion. AA fire rating

Thermal expansion - 8.5 - 11x10-6 mm per 0C

Thermal conductivity - Approx. 2.0 W/mk

Sales Office
Penrhyn Quarry
Bethesda
Bangor
Gwynedd
LL57 4YG

+44 (0) 1248 600656
enquiries@welshslate.com

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