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TOPIC: 23. STAIRS
INTRODUCTION: This topic teaches students the technical terms of a stair, how to calculate the number of steps in a stair, the procedure of marking, cutting and assembling a stair, fixing stairs in a stairway and other types of stairs.
OBJECTIVES:
23.1. Students should be able to name all
23.2. parts of a stair with their technical terms.
23.3. Students should be able to calculate the number and sizes of steps.
23.4., 23.5., 23.6. Students should be able to calculate the width of the stringers, and to mark them out correctly.
23.7. Students should know how stringers and steps are joined and assembled correctly.
23.8. Students must be able to fix stairs properly.
23.9. Students should be able to explain why external must be different from internal stairs and the procedure for making external stairs.
METHOD: Stairs are quite difficult to make and you cannot teach it clearly without actually making the real tiling.
It is advised to wait with this topic until there Is an opportunity to demonstrate it by making a real stair.
Otherwise only the terms for the parts of a stair and the way to find the number and size of steps can be taught in the classroom.
NOTE: At the end of this lesson prepare a worksheet for students to complete as homework.
In general, stairways are usually a special section of the carpentry trade. Simple stairs are prepared on the job by a carpenter and these include verandah steps, external and internal stairs of minor importance.
The simplest form of stair is that consisting of only one flight, but this must be designed in the correct proportions for easy travel.
a) Stringer: - The inclined sides of the stair carrying the steps.
b) Riser: - The vertical timber which closes the space between two steps.
c) Rise: - It is the vertical distance between the top of the one tread and the top of the tread immediately above it. Usually 175 mm.
d) Tread: - The board forming the top-surface upon which the foot is placed.
e) Go or Going: - The horizontal distance between the face of one riser and the face of the next. Usually 250 mm.
f) Nosing: - The rounded edge of the tread projecting over the riser. Usually 20 mm.
g) Landing: - The floor at the beginning or the end of a stair flight and the intermediate floor between two flights.
h) Well or Well-hole: - The space in the centre of a staircase between the outer stringers of the flight.
i) Flight: - A complete set of stairs reaching from floor to floor or from floor to a landing.
j) Newel: - An upright post at each end of a flight of stairs to carry the handrails and sometimes also the stringers.
k) Handrail: - The support for the hands at the sides of the stair.
Figure
TIMBER SIZES:
Stringers: 200 mm - 300 mm deep, 40 mm - 50 mm thick.
Risers:
19 mm thick minimum.
Treads: 35 mm - 50 mm thick depending on tread
length.
Nevel: 100 mm x 100 mm
Handrail: 100 mm x 75
mm
You are advised to make the calculation for the stairs on the building site or with a proper drawing in a scale of 1 : 10 or 1 : 20 in order to make sure the stairs will fit correctly.
The HEIGHT of the riser is calculated by dividing the floor to floor height into a suitable number of risers each being approximately 175 mm.
The GOING is calculated by dividing the total going into a suitable number of treads each going being approximately 250 mm.
Figure
Total Going = 3250 : 13 treads = 250 mm
tread
Total Rise = 2450 : 14 risers = 175 mm riser
When more space for the going is available, the go can be made up to 300 mm.
When drawn in all risers and treads with the 20 mm nosing in the plan, draw a line along the nosing and along the back-corners of the steps.
Then measure the width between the nosing-line and the back-line and add on both sides towards the top-edge and the bottom-edge of the stringer 40 mm.
This measurement is the correct width of the stringer.
Figure
a) Gauging the "nosing line": - The nosing line is gauged 40 mm below the stringer-top with a combination square.
Figure
b) Gauging the "setting out line":
- On a steel square, you mark the depth of the going on the blade and the height of the rise on the tongue.
Figure
- The steel square is placed with the rise and the going position on the nosing line. Then measure the depth of the nosing in a right angle from the nosing line and mark it.
Figure
- Also the setting out line is gauged with a combination square along the stringer.
Figure
c) Marking out the "face-lines" of tread and riser: - A fence is now attached to the steel square. The riser height and the tread depth-marks on the square must be placed on the setting out line. The fence enables tread and riser lines to be repeated accurately. The face-lines of tread and riser are marked out by sliding the square along the stringer.
Figure
d) Marking out the thickness of tread and riser:
- This is done with templates made of plywood with the exact thickness and width of riser and tread.
- The tread-template is held below the face-line of the tread with the corner meeting the nosing line.
Figure
- The riser-template is held inside the face line of the riser meeting the bottom line of the tread.
Figure
Stringers must be designed properly in order to give the stair a strong connection to the top and bottom floor.
a) Top-end of stringers:
- The last riser must be measured separately, because of the flooring boards covering it. Having marked the last riser, extend the back line to the top and the bottom of the stringer. The bottom of the stringer is cut out on that line up to the floor level. The corner where the line meets the top of the stringer is marked out horizontally. Mark it with a length of 100 mm and plumb it down vertically. Then cut out the nose so it can rest on the floor.
Figure
- The completed top-end of the stringer.
Figure
b) Bottom-end of stringer: - Make a plumb cut 40 mm in front of the nosing and square off the heel of the stringer to rest on floor.
Figure
For interior stairs, treads and risers are usually joined to the stringers by housing joints which are chiselled 12 mm into the stringer. This job has to be done with accuracy in order to achieve a good result and prevent the steps from creaking.
On the bottom of the tread you have to glue and nail timber battens in the size of 50 mm x 20 mm to support the riser. When assembling, join the riser to the tread by nailing the riser to the support timber.
Figure
Where stringers are not restrained by walls, the stringers must be bolted together with long iron bars, 10 mm in diameter and a thread cut on both ends. These iron bars must be placed at least two to three times in a stair.
Drill 10 mm holes in the stringers directly underneath a tread. When assembled, all treads and risers with the stringers, place the bars into the holes, put washer and tighten the stringers together with two spanners.
Overlength of bars can be cut and covered with a piece of timber to improve appearance.
Figure
a) Top-end: - On the plumb-cut, you screw a flat iron (40 mm x 5 mm) which is bent at a right angle to fit on the underside of the top-floor joist.
The thickness of the flat iron is sunk into the stringer and joist.
First, the angle iron is screwed to the stringer then, when the stair is placed into the correct position, screw the iron to the joist.
Figure
b) Bottom-end:
- On foundations where you have joists, make sure you have a joist where the stringer is sitting. Also here you use a flat iron bent at a right angle, which is screwed directly under the last tread on the inside of the stringer. Make sure the iron, which you screw later to the floor, is in line with the joist.
Figure
- On concrete slabs, a flat iron is fitted into the fresh concrete to hold the stringer. Put it in such a way that the iron can be screwed on to the inside or sometimes, to the outside of the stringer.
Figure
Stairs which are exposed to rain and sun are usually open.
That means that they have no riser, so that the rainwater can run off easily.
Treads are also fixed differently on outside stairs.
An angle-iron is bolted to the riser where the tread rests. Often treads are made in two pieces to avoid water standing on the timber.
Figure
Leave 3 mm - 5 mm space between tread and stringer to prevent the timber from rotting when water enters between the timbers.
Look in chapter 4.3.
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