Second only to wood as a natural traditional roofing material slate is a fine grained sedimentary rock that has topped castles and large buildings for centuries in europe.
Traditional slate roof pitch.
The total weight of slates on a roof can be calculated as follows.
Generally the steeper the roof the better with regard to service life of slate.
But since there is still a wide variety of slate roofing systems there are occasions when the minimum pitch can go down to as low as 15 0 depending on the uniqueness of the roof.
A couple of likely slate suppliers are consulted and they confirm that they are happy to supply 600x300mm slates for a minimum roof pitch of 20 degrees assuming a minimum lap of 125mm.
However our technical team always believed that it would be possible to specify natural slates with confidence at lower than 20 if the circumstances were right.
It is agreed that the roof pitch should be a minimum of 20 degrees preferably a bit more.
The minimum recommended pitch of a natural slate roof is a function of the exposure level of the site location.
With regards to the pitch the building standard code bs 5534 recommends a minimum pitch of 200 for slate roofs.
If the plan is to place a slate roof on a building which has never had one structurally assess the size and condition of the rafters to confirm that the existing structure can support the weight.
Greek says one must keep rafter length in range of 1 9 to 1 7 th of span but as per roman style the standard dimensions are kept about 1 3 to 2 9 th of span with an angle of 23 to 24 degree.
You consider some alternative solutions.
Example slate type del carmen slate size mm mm 400 250 weight of slates kg 1000 1235 exposure moderate roof pitch 40 roof area m 2 150 length of roof slope m 9 5 the headlap can be found from table 1 by reference to slate size roof pitch and exposure 65 mm.
Traditionally natural slate roofs were not recommended below 20 pitch.
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It is uncommon to find a roof below 15 but for those very low pitch applications there are interlocking clay pantiles available suitable for use down to 12 5.
Slates roofs are very heavy and can weigh ten pounds per square foot for slate when the weight of the slate underlayment and flashings are included.
Usually average roof pitch is determined using the same roof length method.
Commonly it is 3 4 th of span as per gothic rafter must be equal to span.
Minimum roof pitch for shingles.
Imported from wales to colonial america for fire proof roofs in boston philadelphia and new york it was still slow to catch on for houses.
Anything above a 8 12 is preferred and slopes in the 12 12 to 18 12 range are probably ideal.
