Roof Slates - how many

[Rick Dipper]

I am trying to caculate how many roof slates I will need for my roof, but have no idea how to work it out.

I have overlaps and edges to taken into consideration, so its not a simple roof area / slate size caculation.

Any ideas ?

Thanks Rick

[The Natural Philosopher]

well, how much EXPOSED area of slate is there? take that as the 'size' of the slate, and divide into total roof area, and add 5% for wastage and edges.

Take maths O level?

[Rick Dipper]

Thats the problem, how much of a slate is EXPOSED, from observation, it seems to be somewhat under 50%.

[Jim Alexander]

Ask a slate supplier, for example Greaves.

A

[Richard]

The actual process of estimating roofing slate quantities, is as you have realised, not a straightforward process. As well as the slate sizes, overlaps, verges etc. you should allow different quantities depending on the roof pitch. Major roofing companies as well as specialist slating companies will have ready beckoners that they may make available to you.

The information basic about the roof that you will need is the pitch, length of ridges, verges and eaves, slate size and if hips and valleys are involved. Having used the calculator it is usual to add a wastage allowance of 5% to 15% for breakages etc. Good quality undamaged slates are a valuable commodity and any overs can probably be sold on or back to the supplier.

If your existing roof is a new one it is presumably suitable for slates. Don't forget you will have to estimate for under felt, battens and depending on local requirements, sarking boards. Unfortunately planning consent will also come into the equation in most areas unless your roof is going on a shed or similar that is below the planning size.

A final thought is ventilation of the slated roof space. There are various requirements that have to be met to ensure compliance with building regs and also avoid condensation problems that could arise from fitting a different roof.

Good luck.

Richard

[Rick Dipper]

Thanks, Its a new roof, it has to be done in welsh slate, cause planning say slate, and I want local materials. New welsh slate is too expensive for me. I know all the figures you suggest, its just a question of how do I get from roof size to slates needed. There is an ammount of overlap, and I have no idea what this is, but it looks to be somwhat over 50%

Thanks Rick

[mrcheerful]

my slates are about two thirds overlap, slates are 8 by 16, but nowadays 12 by 24 is more common.

steeper the slope the less the overlap, but always overlap by at least 50 percent

mrcheerful

[John Rumm]

ISTR from one of the grand designs programs (she with the mock edwardian mansion) that they found chineese slate was less than a quater the price of real welsh slate and looksed the same....

I have only done it with tiles rather than slate as such, but they were flat pan tiles about 9x6". There was about a 2/3rds overlap - so every tile that you see counts as three.

A bit like:

/ / // // // // / /

[John Armstrong]

Theres a diagram and some useful info at

which shows how to calculate the gauge. Number of slates = Area / slate width / gauge plus an allowance for waste, hips, valleys, etc.

[richard]

edwardian

chinese so hard it's a bugger to cut without a grinder, spanish is a good compromise, and still 1/4 price new welsh. To my shame that's what i did my re-roof with, even though in midwales.

[Rick Dipper]

I am having a quest, to build my house with local materials, especially for the traditional ones. Modern materials can come from modern far away places. You may remember a thread where I asked about getting the timber from the local forrest - which I am doing against some of the advide here.

My driveway will be welsh slate, its 200 quid for a lorry of chippings, so my roof should match.

Rick

[Dave Liquorice]

Our roofers didn't have much trouble with it, using the normal upright blade and machette to scissor action with.

[OldScrawn]

Screwfix or similar diamond blades in a 4 inch angle grinder are an alternative

[Dave Liquorice]

But a darn sight slower and messier. Three or four blows and you've trimed the length of slate and the debris is small bits not dust.

[mark]

In message , Rick Dipper writes

Depends on the pitch. The local Building regulations probably have a minimum head lap but the width of the slate relative to its length and the head lap varies with the angle of pitch. Just ring a supplier with the pitch, rafter and ridge length.