Ideal Thickness Of Roofs

Maintenance & Safety Building Maintenance
#21

WELL FS SB,,,SIR

your question is on spot , and the reason is here,

1=ppl renovate old houses , and when they notice cracks in roofs ,along with a bit wkness so they reinforce the slab with fine crash and cement layers of bet 2-5 inches,

so keeping in mind this background ,i put this question ,to be analysed professionally,

2=For old well designed houses,its easy to manage with common sense,,,,,but,for old houses not designed properly before, like,,no pillars or columns or beams ,

so

whats the solution for them ??

demolition?

or remove the roof completely and do the roofing again?

1 Like
#22

@ Dk,

If the existing slab is cracked all the way to the upside, then it is already failed. I would prefer removal of concrete, take the steel out of the existing slab and reuse it for the new slab.

2-3 inches of slab on top of another weak slab will further overload it. This layer of concrete on top with very light reinforcing bars will only prevent water penetration and will not share load.

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#23

No use of 2-3 inch concrete over existing RCC slab.

Dk Sb, I hope you know that using extra steel than needed can harden the slab and detrimental to the purpose of slab. It reduces it's tensile strength. So only a structural engineer calculate how much steel is exactly needed and with how much spacing.

I don't think any residential building needed 1 inch steel re-bar. Beams are used to support extraordinary span roofs. Concealed beams are also used though it has lesser utility in comparison with " Latak" beam. The term is widely used in our construction industry.

Correct me if I am wrong FS sb. Sorry in advance in that case.

1 Like
#24

Thanks FS sb ,and Thanks B.R Malik sb,

its now clear,

well may I take some, advantage of your experiences ,and ask another question

in areas where earth quake are frequent, if we make columns of steel in rectangular shapes and place them on 4 corners of the building , and later on attach or bind them together by steel bars running rectangular y ,binding the 4 columns on the corner , and repeat it on ist floor as well , so will it have some safety advantage against earth quake?

#25

You mean in built up residential building or to be built building?

#26

No during new construction , right from start

#27

Usually the principle is to have columns linked together at foundation level than at floor level( plinth beam), than at window n door level and last at roof level. Binding together columns and beams mean to multiply the strength.

But the problem is that columns should be on all corners of almost all major rooms.

But if someone want to save cost and going for non-column based building than yes at least it should be done at 4 corners of the building. Its enough for single story building.

But 2 or 3 story ( including basement) needs columns at all corners of rooms or in other words, major load areas to bind building from bottom to top in such a way that it acts as single unit in earthquake.

#28

B.R.Malik

sir, simply excellent views,

you are so informative and open in expressing the views,thanks

do you have any idea of how much extra tons of steel will be required for 50 90 area if we make such (plinth beam )at foundation ,floor ,window ,door ,and roof level,,with column on all corners of rooms,,

AND second whats your experience ? do the architect or structure engineers suggest or practically apply these in practice

1 Like
#29

Thanks a lot :-)

I think this practice is followed by a lot of people in Islamabad. Even good builders do it because any major structural crack can ruin them. Though they are impressive at concealing the cracks. Followed in Islamabad.

Please note that window level and door level is the same. Its called door beam.No extra steel is used for roof level binding. Usually people/contractors avoid door beam and floor level beam because it involves labour expense too.

Now coming to your main question. I once calculated steel for these beams. I remember it was only 10% of the total steel used I.e 2.5 ton for 50x90.. Main quantity of steel is used in roof. These beams steel usage is nothing compared to roof usage. Its benefits are enormous.

The whole concept lies in binding/tying the whole building as one unit.

#30

@ B R Malik

1 inch think steel bar would be very difficult to handle (bent etc on site). Therefore this size is not used in houses normally. Up to #6 (3/4 inch) bars are normally used in houses.

Concealed beams are not effective and I would suggest the use of "LATAK" beams, If it is not possible, an inverted beam can also be used (I don't know if this thread is becoming too technical).

1 Like
#31

By the way, what is technical name of LATAK beam?

1 inch steel is quite Hot nowadays due to Metro bus project :-)

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#32

The provision of columns in brick masonary is being followed as a good practice specially in earthquake prone areas.

The columns are preferable at all important corners of the building to avoid horizontal movement in earthquake. Plinth beams are used instead of door (lintel) beams as they also serve as damp proof coarse. Beams basically are to control unequal (differential) settlement.

#33

Latak beams are the basic form of beams and are named as “Rectangular” and T-beams.

#34

Generally only # 4 bars which is half inch in dia is being used in slabs… # 5 & # 6 bars which are 16 & 19 mm are being used in beams and columns only… 1 inch steel bar in house construction… No way…

#35

Good input Ali Khan Yousafzai sb

what about horizontal steel beams from one corner column to another , and this way horizontally placed rectangular steel beam attached to corners steel column filled with concrete,

I agree with you about the diameter of steel , but 3/4 of inch diameter steel can apply to double or triple story , any how its understandable .

[[JUST for knowledge and ideas]]

1 Like
#36

B.R.Malik sb ,FS sb, and all members Eid Mubarak

1 Like
#37

Khair Mubarak. Eid Mubarak to everyone seeing the post.

#38

Eid mubarik to everyone…

#39

Eid mubarik to every one…

#40

Thickening of Roofs should be known exact.The thickness of roofs is 14 inch .But walls without iron rod would be risky.I think you should take suggestions from residential structural engineer denver for house structure.

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