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.

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!