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August 26, 2010

How do you calculate the pitch of a stairs

Oh dear someone was not listening during the school trigonometry lesson.

OK I am not Pythagoras and it is not the job of this stair man (remember David Bowie sang song about me) to teach mathematics, even if I was qualified to do so, which I am not. I do however understand how annoying it is to not grasp the connection between school boy maths and the steepness of your stair. So here goes for an explanation.

I have to assume that you did at least do trigonometry and although you have forgotten it and probably never understood it anyway, you can at least grasp the fact that if you know certain angles and lengths of sides in a right angled triangle you can work out other angles and sides. In actual fact it does not really matter what you understand you can still get the right answer to your staircase pitch if you apply the following and can get hold of a scientific calculator.

So where do we find a right angled triangle in our staircase. Well there are lots of them but the one we are interested in is the triangle that is formed between one step and the next. The height between the top of one staircase step and the next one (known as the rise) is one side of our triangle. The length from front to back of a tread (known as the going) is another side. If you think about it these two sides are at right angles to each other and the the third side of the triangle is an imaginary line that runs from the front edge of one step to the front edge of the next step (known as the hypotenuse of a right angled triangle). If you can work out the angle of this line to the horizontal this will tell you the pitch angle of your staircase.

Now this is where those clever Greeks come into it, they worked out a way to calculate this angle providing you know the lengths of two of the sides of the triangle, which in the case of your stair you do because you already know the rise and the going. If you do not know these two lengths you are wasting your time asking questions about angles,go and have a rest instead. So trying not to get too complicated Trigonometry tells us that the Tangent of this angle equals the length of the opposite side divided by the length of the adjacent side. Therefore the Tangent of the angle equals rise divided by going. Do not worry if none of this makes sense to you, all you have to do is obtain a calculator that has trig functions on it (scientific calculator), use it to divide your rise by your going then press the inverse tangent key and it will convert the answer to a number that will be the degrees of pitch of your stair. Less than 42 degrees and it will comply with the UK & Ireland Building Regulations. Easy pesy.

OK maybe not easy so here is another non calculation solution that requires a school boy protractor or any angle measuring device. On sheet of A4 paper mark the length of the going along one edge then mark the length of the rise along the adjacent edge. So you now have two lines going away from one corner of the paper. Now draw a line diagonally across the paper from the end of going line to the end of the rise line. You now have a right angled triangle and the angle formed between your going line and your diagonal line is the pitch of your stairs. Measure this with your protractor. You get extra points if the protractor still has your school nickname scratched on it

The Stair man waiting in the sky

August 17, 2010

Which goes in first, floor finish or spiral staircase.

It is always nice when someone asks a sensible question like this, it shows that they are thinking ahead, and that can save a lot of heartache on a building project. The answer is either way will work but there are pros and cons both ways that need to be considered. The main thing to remember is that nearly all spiral stairs finish at floor level with a base plate (usually round approx 200mm diameter) that is fixed to the centre pole and floor. This base plate takes the entire load of the spiral staircase so it is important that it is fixed to a solid construction. Any movement and you will end up with a giant pogo stick. This is particularly important with modern enginereed wood flooring that often has a compressible under layer that can cause problems. It also needs to be considered with any under floor insulation or heating system which ideally should be be omitted in a small area where the base plate sits. Non of the above answer the original question but is non the less important.

So floor or stair first?

Install staircase first then floor finish.

Plus points.

  • The floor finish will not be under the spiral stair base plate so compression at least of the floor finish is not a problem.
  • The stair can go in earlier in the building process so be used for access (see also minus points)
  • The floor finish cannot be damaged by the spiral staircase erection process.

Minus Points

  • It is more difficult and in some cases almost impossible to neatly finish the floor finish around the spiral staircases base plate. Engineering click system flooring is particularly difficult to finish neatly and carpet will need to have a cut right to the edge of the carpet in order to get the carpet around the spiral stair.
  • Putting the stair in early in the project runs the risk of damage from big clumsy footed builders in hob nailed boots with mud on them.
  • Unless allowed for in the design the floor finish will alter the step height of the first tread.

Install floor finish then staircase.

Plus points.

  • A lot easier to fit the floor finish with no awkward cuts around the spiral stair base plate
  • The spiral staircase can be installed late to avoid the hob nailed boots problem.

Minus points

  • The hob nailed boots will damage the floor finish unless it is protected.
  • Consideration needs to be given any compression ofthe floor finish.

On balance in most cases I favour floor finish first as I think that the scribing of the floor finish around the base plate can be the biggest headache. This method also allows you to have it both ways if you wish. You can cut a nice neat circular hole in the already layed carpet or floor board and plonk your spiral staircase base plate into it.

The Staircase Doctor