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Estimating Construction Materials ... Rebar (Footing, Columns, Beams, Slab, etc) ...

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  • Estimating Construction Materials ... Rebar (Footing, Columns, Beams, Slab, etc) ...


    if your not an architect or an engineer like me, the most important thing you need to know is how to read and understand your house plan to determine the rebars required for all the parts of the house that will require it - footing, columns, beams, slab, and walls, etc. you can google it as there are a lot of info out there about this topic. for me, it's better you spend sometime (over 2 bottles of beer :-)) with the architect that prepared the house plan and teach you how to understand and get the rebar info you need - make sure you take lots of notes of your discussion so as not to forget it :-) he he he ...
    as far as i know, there is no standard for house plans, although some common info are there, plans made by one architect may be different from others.

    normal rebar sizes (e.g. diameter) for a house construction are not that many ... 10mm, 12mm, 16mm, 20mm ... 9mm deformed rebar for walls instead of 10mm ... standard rebar lenght is normally 12m or 6m each ... last quarter of 2014, the prices i got for the rebars (12m lenght) are:
    9mm deformed rebar - P110
    10mm - P138
    12mm - P205
    16mm - P385
    20mm - P590

    basically, rebar estimation is just counting the rebars (also getting their length) based on sizes that will be use in the construction to get the total length and then determining the optimal cutting list to minimize wastage ... for me, the cutting list is more important as workers will just normally cut a rebar to the desired length without any consideration to the waste (e.g. retaso) that it will produce ...

    from my research and if i remember it right, for joining 2 rebars together, the standard for the join area for the rebars is 40x the diameter size of the rebar ... e.g. for a 10mm rebar, that would be an additional 400mm (16") for a rebar you want to join with another rebar of the same size. this is the reason why the cutting list is more important - as much as possible you want to minimize joining 2 rebars together as it will result in more rebars and i think less strenght also. at the same time, you also need to accept the fact that in some cases it's unavoidable to have joined area due to the design of your house and the standard lenght of rebars ...

    below is the process i did for estimating the rebars for the structure (most rebars are for the structure) of our house construction. you will have to revise your computation at least 3 times from my experience - your initial computation based on your research, after your discussion with your architect, after your discussion with your foreman ... after doing a little research on reading a house plan and before talking to your architect, my advice, do one rebar estimate for each type of area (e.g. footing, column, beam, slab) so that you can see if your initial understanding jives with what is normally done in the construction industry :-) ...

    1. review the house plan and start to identify each part of the house structure (normally labeled in the plan) and it's dimension. the way i did this was i entered each part (e.g. footing, columns, beams, slab, wall,etc) of the house as a row in an excel file and it's dimension (LxWxH ; 1 column in excel for each measurement) in mm. take note of the following:
    - for footings (lowest part to which a column is place), it's like a small slab but the rebars are bend at both ends ...
    - for columns (vertical part, normally from the footing to the roof), it's just a group of bars (e.g. 4, 6, 8 bars) using 1 or 2 diameter sizes (e.g. just 16mm or combination of 16mm and 20mm) ... the bars are held in place by a number of 10mm rebars (bent to form a square or rectangular shape) called stirups ...
    - for beams (horizontal part connecting 2 columns), it's also a group of bars (e.g. 4, 6, 8 bars) using 1 or 2 diameter sizes (e.g. just 16mm or combination of 16mm and 20mm) ... the bars are held in place by a number of 10mm rebars (bent to form a square or rectangular shape) called stirups ...
    - for slabs, the rebars are arrange simply like a mesh of horizontal and vertical bars ...
    - for walls, they are like slabs with fewer bars and vertical when arrange ...
    - all the bars are held using tie-wires (e.g. normal kawad, no need to include in your rebar estimate) when it is assembled to hold it in place before concrete is poured ...
    for my case, our house is a 2-storey concrete house with a lenght of 10m and a width of 9m, so in general, a 12m lenght rebar is ideal for all of the structure to avoid joining in the middle.

    2. for each item, based on the house plan, determine the rebars required in terms of its ... diameter size of the rebar (e.g. 9mm, 10mm, 12mm, 16mm, 20mm, etc) ... the lenght of each rebar ... the number of rebars for each item ... 1 column again in excel for each of the information :-) ...

    3. determine the rebars that needs to be bended and that will require additional length. how much additional lenght for this rebars, you need to get the info from the architect/engineers or from your foreman.

    Click image for larger version

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    example: footing rebar computation ...

    from my house plan, the footing schedule for a single column is shown above. it mentions the rebars required is 9 pcs of 16mm across and 9 pcs of 16mm crosswise for a total of 18 pcs ... the length of each rebar should be about 1500mm (1.5m) based on the area of the footing. the rebar needs to be bend at both ends, but the plan does not specify how long is it. what the plan says is that the depth of the footing should be 400mm (0.4m) and should be 1500mm (1.5m) below the ground. therefore, the bend of the rebar should not be > 400mm (0.4m). first, you assume it's 100mm for your initial estimate and then confirm this with the architect or the foreman ... so 1500 + 100 + 100 = 1700 size of 1 rebar x 19 rebars = total number of rebars for 1 footing. the house has 10 footings, so the total rebars (16mm size) for the footing = 323000mm or 323m of 16mm rebars ...

    12m = 12000mm ... divide by 1700mm = 7.06 ... 1700 * 7 = 11900mm with a 100mm (4") waste for each standard 12m rebar with a 16mm diameter ... rather than waste the 100mm (4") for each 12m rebar, might as well include it (dagdag tibay din) in some of the rebars you will make :-) he he he ... your cutting list for a single 12m rebar for this footing requirement should be 5 pcs of 1700mm lenght, then cut in 2 the remaining lenght to come-up with 2 pcs of 1750mm each. for footing requirement, its not a problem if some of the bars has a longer bent area because the depth of the footing is 400mm (16") which is quite a lot ... so, 323m / 7 per 12m rebar = 46.14 pieces of 12m rebars ... 46 * 7 = 322 pcs of rebars, you need 323, so your missing 1 pc = 1700mm ... you need to take note of this and see if you can get this from the other areas requiring a 16mm rebar :-) ...

    for slabs, as i mentioned earlier, it's the same as what you do for footing rebar computation. the only difference is that the length of each rebar is longer and you use the 10mm diameter

    doing the above exercise for all the other areas (e.g. columns, beams, slabs, and walls) you will, at the end, get the total requirement of rebars for each size - 9mm, 10mm, 12mm, 16mm, 20mm, etc for the whole project.

    4. once you have prepared your estimates, spend some time with your foreman to discuss your estimates of the critical materials (rebar, cement, sand, gravel, CHB, coco lumber, etc) - it should not be a debate as to whose right or wrong, it should be looked at as more of a discussion :-) he he he of your estimate and how it jives with his/her experience.
    your foreman must be able to provide some comments to your estimate. kung wala, palitan muna at hindi pa siya well experienced to have the confidence to know what he/she is doing :-) ha ha ha. if there are any disagreement to your estimate, make sure you understand the "why?" and take notes of it for you to review (is it logical?) later before you finally order the materials.

    you can also do this exercise with your architect (before talking to your foreman) after you finish your estimate and before you get a foreman for your project. this is what i did during the planning stage of our house construction. after the house plan has been finalized, i prepared my estimate and discuss this with my archi and engr friends in SG. and then made some revisions to my estimates after all the discussion. then after finding a good foreman here in south cotobato, i spent 2 days (work has not yet started) with him to discuss in detail my estimate for the critical materials and the labor required. made some revisions again to my estimate and then started to order the materials needed for the first 2 weeks of the construction :-) ...

    the estimate you have prepared will be very important especially when you plan to get a contractor to do the job for you. by comparing your estimate (e.g. just the big ticket materials) against the bill of materials of the contractor, you will already be able to see a lot of things ... if the difference is big and it's on the low side of your estimate, then the house will be built under specs of what is specified in the plan ... if the difference is big and on the high side of your estimate, then either the contractor will be wasting a lot of materials (or he does not know how to estimate) or is jacking up the quantities of the materials to increase the cost for one reason or another ... in the end, it is the owner's responsibility to verify that the contractor's price is fair and the only way to do this objectively is for you to have a sound estimate of your project for comparison ... cheers

    Boo!



  • #2
    Hi Boo-Semi-Retired ! this is a wonderful write up. thanks! I'm aware that there are a lot of variables involved in cost estimates, but for this particular topic. since you've already provided us with a rather good way to compute CHB Wall costs in other posts... using the prices mentioned above, do you have rough figures per square meter for a simple second floor slab? (has more rebars than ground floor slab). thanks!!

    Comment


    • Boo-Semi-Retired
      Boo-Semi-Retired commented
      Editing a comment
      let me check my worksheet and notes again and i'll share the info based on my house construction ... cheers

      Boo!

  • #3
    mig21, below is my computation based on our house construction before ...

    assuming that a 1 sqm 2/F slab will have this area ... 1000mm (lenght) x 1000mm (width) x 150mm (depth) ... this will consume 0.1500 cubic meters of concrete with a ratio of 1:2:4 (cement, sand, gravel) ...

    in summary ... 0.1500 cubic meters of concrete with a ratio of 1:2:4 will require ...

    0.0214 of cement cost is P185.37 0.7566 bag of cement * P245 ...
    0.0429 of sand cost is P10.30 P1200 / 5 = 240 per cubic meter * 0.0429 = P10.30
    0.0857 of gravel cost is P47.99 P2800 / 5 = 560 per cubic meter * 0.0857 = P47.99
    ----------
    0.1500 total cost is P243.66 for concrete

    for the 10mm rebars, based on our house plan, the spacing in between rebars should be 125mm (approx 5") both for across and crosswise of the slab ... so, 1000 / 125 = 8 rebars for across and 8 rebars for crosswise for a total of 16 rebars of 10mm diameter with 1m lenght ... cost based on prices will be ... 16 x 1m = 16m / 6 = 2.66 * P138 = P368 pesos for the rebars ...

    total cost of 1 sqm 2/F slab is P611.66 ... 243.66 (concrete) + 368 (10mm rebar) = 611.66 ...

    NOTES:
    1. the cost does not include midspan rebars (12mm rebar as part of a large slab) as this will be dependent on the design and the total area of a slab ...
    2. below are the prices (4th quater 2014) i got for our house construction here in tampakan, south cotobato ...
    sand - 1200 per 5 cubic meter
    gravel 3/4" - 2800 per 5 cubic meter
    10mm standard rebar 6m lenght - 138 each
    cement - 245 per bag (brand is Mayon - different price per brand, APO is 265 per bag)

    hope this info helps ... cheers

    Boo!

    Comment


    • #4
      Fantastic! At the very least, we have numbers to base for a rough estimate per area of slab, and CHB walls (factor in a % for columns, footings and beams.) thank you very much sir Boo-Semi-Retired

      Comment


      • Boo-Semi-Retired
        Boo-Semi-Retired commented
        Editing a comment
        no problem, glad to be able to share some info to the group :-) ... the goal is really to give owners who are planning on building their house a simple way to do the math of the project and be able to analyze the options available to them like ... do it on their own with a foreman/workers or hire a contractor to do the job for them ... cheers

        Boo!
        Last edited by Boo-Semi-Retired; 10-28-2015, 04:30 AM.

    • #5
      Very nice and well explained post, Boo-Semi-Retired. Thank you for taking the time to educate us!!! The net is a gift from God! hehe

      Comment


      • Boo-Semi-Retired
        Boo-Semi-Retired commented
        Editing a comment
        Erick, thanks for the comment, that was really my goal - share what i learned in constructing our house so that others will have the knowledge of how to estimate the critical materials needed. and from that information be able to objectively decide if you want to do it yourself or hire a qualified contractor to do the job :-).

        you are 100% right, internet is really a booster to learning new knowledge as you have the whole world as your network of friends ... cheers

        Boo!

    • #6
      Help guys... pls estimate how many CHB, cement and round bars needed in 24x30x25 2-story house.

      Comment


      • #7
        You need to hire an engineer/ estimator. Provide him a set of plans.

        This is what we can give you.
        13 pcs CHB/ square meter of wall.

        Comment


        • #8
          puleng, you can do this yourself by reviewing your house plan. if your not familiar with reading a house plan, you can ask your archi or engineer friends in helping you understand how to read a house plan. its really quite simple :-).

          once you know how to read a plan, just follow the old threads in estimating the critical materials for constructing a house. you can just make an excel file for all the computation. there is another old thread about CHB estimation which i have posted before, you can review this.

          if you don't want to do this by yourself. as what bryant77 mentioned, the best way is to hire a professional for this. if you have a house plan that has been prepared by an archi or an engineer, then look at your docs if they have included a BOM (bill of materials) together with the house plans. BOM can be prepared together with the house plan if you specifically ask for it before they make your house plan.

          hope this info helps ... cheers

          Boo!

          Comment


          • #9
            hi guys!i have a couple of questions here:

            1.) what is the right way to pour concrete on column?to pour one time the exact length or bit by bit?

            2.)what is a good spacing for vertical and horizontal bars on CHB wall?we'll only be making a bungalow cottage of 3.5m x 3.5m.

            thank you,
            idp

            Comment


            • Boo-Semi-Retired
              Boo-Semi-Retired commented
              Editing a comment
              @rosy's reply on both items are correct. it has to be poured one time and the spacing of the rebars for CHB ... if your budget is manageable, go for the 10mm rebars and not the deformed rebars that they call for the CHB rebars ... cheers

              Boo!

          • #10
            1. It is still best to pour concrete one time on a column.

            2. Lets say two post of 10 ft length (3 m) in between, for vertical support bars, spacing is every meter. and for the
            horizontal bars on the CHB, always on top of the third laid CHB, then tied to the vertical corrugated steel bars, but
            make sure both ends of the horizontal steel bar are bent at 45 degrees with length of 0.30 m, or 1 foot then
            pasok sa loob ng poste and mga dulo na makaka sama sa buhos ng concrete cement.




            Hope this helps.
            AHP Alpha-TIG 200X welder
            HITRONIC 300 Amp DC Inverter IGBT Welder
            YAMATO 300 Amp AC Stick Welder
            YAMATO 200Amp DC Inverter IGBT Welder
            DeWALT Chopsaw
            HOBART and ESAB Welding Helmets
            Assorted Angle Grinders, Clamps and Vises
            STIHL MS 044 chainsaw

            -----------------------------------------------
            Dreaming and wanting is good and healthy but working hard for it is better !

            Comment


            • #11
              Thank you so much Sir Rosy and Sir Boo-Semi-Retired.it really is a big help.

              Comment


              • #12
                sir Rosy,

                kung yung column ay isang buhosan,does it mean na uunahin muna yung CHB wall to file para ung horizontal bar ay maipasok or masama sa pagbuhos ng column?

                Comment


                • #13
                  My answer is a big YES.

                  Pouring of the concrete mix for the column will be the one to seal and strengthen the two ends of the wall and say up to
                  the beam (biga), that is if there will be beams to be installed on certain required heights of the CHB walls.
                  AHP Alpha-TIG 200X welder
                  HITRONIC 300 Amp DC Inverter IGBT Welder
                  YAMATO 300 Amp AC Stick Welder
                  YAMATO 200Amp DC Inverter IGBT Welder
                  DeWALT Chopsaw
                  HOBART and ESAB Welding Helmets
                  Assorted Angle Grinders, Clamps and Vises
                  STIHL MS 044 chainsaw

                  -----------------------------------------------
                  Dreaming and wanting is good and healthy but working hard for it is better !

                  Comment


                  • #14
                    in our case for our house construction, they first made the structure (e.g. foundation, columns, beams, slabs) with the 10mm rebar protruding at the columns and beams for the CHB support. the CHB was filed after the structure was completed ... cheers

                    Boo!

                    Comment

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