How can I work out how many slates I need for an extension roof?
Question:I am looking to buy on ebay, quite a few available, but how many slates 20" x 10" per square metre?
Answers:
Work on approx 21 per m2, it does depend slightly what guage they are being fixed at.
When buying slate avoid if you can Chinese as there are too many bad ones, really I would advise seeing the slate before buying, there is a vast variation in quality out there.
Speak to your local reclaim yard or Roofing merchant (not Building Merchant) they will show you different types.
Remember Welsh are without doubt best but you will pay.
9x3.75=33.75
x21 = 708.75
x10% waste = 71
71 + 709 = 780
If in UK we don't Head Nail
Slates per sq. m can be found by dividing the total area by the exposed area of the slate. To do this you will need to follow the calculation set out below.
1.Find the gauge (that is the distance between centres of the slate battens:
For centre nailing (CN) Gauge =508 –100/2 = 204mm
For centre nailing exposed portion of the slate = 204 X 254mm
Number of slates per sq. m = 1 sq. m / 204 x 254mm = 19.3
For head nailing (HN) Gauge = 508-100 –25/2 =192mm
For head nailing exposed portion of the slate =192 x 254mm
Number of slates per sq. m. =1 sq. m./192 x 254 mm = 20.5
I would allow 2.5% for waste, if you are not practice at cutting slate you may well need 10% waste.
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