Hi, pls, I need detailed explanations on how to calculate roofing materials based on roof plan starting from the roof carcasses to the roofing sheets/coverings. Pls use a typical roofing plan to explain it in details, the no of struts, purlin, tie beam, wall plate, noggings, rafters, kingpost etc, pls prepare the precise calculations of the roofing sheets using longspan aluminium, i want to know it. Thanks, expecting your reply soonest.
A home is gotten when you look for comfort based on your fantasy, but a shelter is a necessity, and a building becomes a shelter when it can prevent rain,water,sun, strong wind and other climatic elements from affecting the occupants- human,animal,live and dead loads with personal effects.
As far as I am concerned the moment you have your roof placed on a building, other things are important but they are basically needs. You can’t move into a house without a roof , but we have seen people living in a house with no window or makeshifts windows covered with ordinary bags and cardboards.
Wood/ timber are sawn into various sizes amongst are
2” by 2” i.e 50mm by 50mm
2” by 3” i.e 50mm by 75mm
2” by 4” i.e 50mm by 100mm
2” by 6” i.e 50mm by 150mm
3” by 4” i.e 75mm by 100mm
3” by 6” i.e 75mm by 150mm
What determines the quantity of wood needed depends basically on the height of the roof, how complex the roof is? Which may leads to lots of offcuts e.t.c
To determine the roof members you need to have the floor plan, the section and the roof plan.
From the section a-a above you can see the height of the roof of building and the length and breadth of building is already showned in the floor plan, so left to be knowned is the rafter or the fall ‘x’ as shown in diagram above.
Remember the Pythagoras theorem in secondary school days used in calculating the longest part of a right angle triangle.
The numbers of wood to be calculated also depends on spacing for the purpose of this exercise, we are using the format in diagram above as our specifications for our calculatons.
For ceiling noggins of 600mm centers it simply means the wood are nailed 600mm apart, so add the breadth of plan and 600mm as overhangs both sides i.e 7,800mm or 7.8m +1200mm or 1-2m=9meters
Then divide by 0.6m=15pcs of 16.975m of 50 by 50.
For the longitudinal portion, 16.975+1.2m(the overhangs of 0.6m both sides)=18.175m then divide by 0.6=31 pcs of 9m of 2” by 2” ( Note how the length on one side is used to calculate the pieces/numbers of wood required for the length of the other side)
So to know the number of 2 by 2 to buy in the market for the ceiling noggins-
18.175m x 15pcs=273m of 2” by 2”
9m x 31pcs=279m of 2” by 2”
In the market, the wood comes in 3.6m per piece
So 552/3.6=153 pcs of 2” by 2” timber to buy in the market for ceiling noggins.
WALL PLATE is the timber/wood that are placed on top of blocks or roof beams as the case may apply, so for the fastest way to calculate this, is to add the entire walls length and divide by 3.6m to know the numbers of pieces you need. I am using approximately 100m.
So for 100m, divide by 3.6=28pcs of 3” by 4” or 75mm by 100mm to purchase in the market for timber named wall plate.
For FACIAL BOARD, remember the length and breadth of the plan of the building with its overhangs of 0.6m each, so add the perimeter
Divide 54m by 3.6m=15pcs of 1” by 12”
For TIE BEAM, going by the section, it was recommended that we lay the timber named tie beam which is 2” by 6” or 100mm by 150mm at 1.2m centers apart. So what we need to do is to follow the same format used in calculating the ceiling noggins but it is going to span only the breadth of 7.8m only.
So divide 18.175m by 1.2m centers (spacings)
=15pcs of 7.8m =117m, then divide by 3.6m to know the numbers to buy/purchase in market.
117/3.6=32pcs of 2 by 6 of wood termed as tie beam to buy in the market.
STRUTS are a bit complex to calculate, they are the members placed diagonally as shown in diagram to connect the rafter with tie beams. We can use the numbers of tie beams and multiply by 2-
i.e 32 pcs multiply by 2=64 pcs of 3 by 4 or 75mm by 100mm termed as struts to be bought in the market.
For RAFTER, check the height of roof and the breadth of plan to determine the rafter which is the falling portion of the roof (except is already given from the section)
Lets take the height of the roof as 3.5m and the breadth of plan plus overhang is 9m.
With the diagram above applying Pythagoras theorem
X2 (rafter length )=4.52+3.52
Rafters are nailed side by side tie beam and struts. So we use the numbers of pieces of tie beams because they are also spaced at 1.2m center to center and multiply by 5.7m
15 pcs of rafter (same as tie beam) multiply by 5.7 =85.5m
Now divide by 3.6m to know the numbers of 3” by 4” to purchase in market=24 pcs of 3” by 4” required for rafters.
PURLINS are the wood of 2” by 2” or 50mm by 50mm we nail the roofing sheets on.
Purlins are spaced based on designs or type of roofing sheets. But for our calculations, we are using 900mm spacings.
Going by diagram above add 5.7m +5.7m for both sides=11.4m
Divide 11.4m by 0.9m to know the numbers required =13 pcs of purlins of length 18.175m (The purlins has to span the length of the building which is 16.975 plus 1.2m for the overhangs by sides)
So 13 by 18.175m=236m
Now divide by 3.6m to know the numbers requires to purchase in market =236/3.6
=66 pieces of 2” by 2” to purchase in market for the purlin.
KINGPOST is that piece of wood that stands at the middle of two rafters falling at the opposing sides. Is the one that spans vertically from the tie beam/rafter line, so just the same way we calculated for rafter, remember 15 pieces and multiply by the height of the roof 3.5m=52.5m
Then divide by 3.6m to know the numbers to buy in the market.
Therefore 15 pieces of wood of 2″ by 6″ termed kingpost is needed to be bought in the market.
-culled from buildingcontractorsecrets.com