@HVAC-Novice
Oh man, there's a lot to answer here. Technical side is easy, I'll start with that:
Which of the numbers should we pay attention to? And what % is it incorrect?
In the video at 0:25 when wall and floor are joined quantities should reflect exactly what's happening in the section.
For wall, plaster should go down a tiny bit (just the thickness of waterproofing), but tiles should go down a lot more (thickness of entire floor).
For floor, everything should go down A LOT.
This is just an example but even on a moderately sized building that is a LOT of square meters that are calculated wrong.
And now to the difficult part:
What exactly is the objective to get very exact numbers?
We're back to different things are done differently in different parts of the world, and with that said let me introduce you to the European Union bureaucracy otherwise known as - hell!
Read with following assumptions:
- I have no Idea how things are done in USA
- I'll probably translate some term wrong
- I may even miss some "steps".
Anyway, exact numbers are required when something is financed through EU funds. So a new school building is being built. But the school is not the investor, investor is the county. But they're getting the money from the state. But the state is getting it from the EU. OK, so there are two oversight agencies that scrutinize everything! So material takeoff, or bill of quantities has to be really well done, tight to the cm2. And it's not just quantities, EVERYTHING has to be specified, every spoon of cement accounted for and described in detail, but without mentioning any manufacturer to avoid favoring. Contractors do not "use other means to estimate".
For example this is a plastering item (chatgpt translation):
Plastering of walls and ceilings
Machine plastering of all INTERIOR surfaces of walls, beams, and columns, rough and fine, to a total thickness of 2 cm.
The price includes: preparation of the entire substrate with cement bonding slurry, application of a 15 mm base coat of cement–lime plaster (with guide strips as plaster screeds), leveling with an aluminium straightedge, and a final 5.0 mm finishing coat of fine cement–lime plaster, including surface smoothing.
Plastering also at locations of ceramic wall finishes (rough coat only). The item includes the installation of protective aluminium corner profiles around all openings and free edges of walls and beams. The item also covers prior priming of all reinforced concrete walls.
Openings up to 3.0 m² are not deducted, and the execution of window and door reveals is included in the price.
Or one for HVAC pipes:
Pipes made of cross-linked polyethylene under high pressure (PE-Xa) with an oxygen barrier layer, impermeable to oxygen according to DIN 4726 or equivalent, SDR 7.4, in accordance with DIN 16892, DIN EN ISO 15875, and DVGW worksheet W 544 or equivalent, for maximum operating temperatures of 90°C and maximum operating pressures of 10 bar, for the distribution of hot and cold water installations. Fitting material made of PPSU, for non-threaded fittings in dimensions DN12 to DN32.
The pipe and fitting connection technique is permanently sealing according to DIN 18380 or equivalent, without sealing elements (“O-ring”) using axial sliding sleeves. Permanently leak-proof connection technique with sliding sleeve according to DIN 1988 and DVGW worksheet W 534 with DVGW registration or equivalent. Applicable under plaster and screed without inspection chambers or similar devices according to DIN 18380 (VOB/C) or equivalent.
Pipe thermal expansion coefficient: 0.15 mm/mK; thermal conductivity: 0.35 W/mK; internal surface roughness: 0.007 mm.
Pipes are supplied up to Ø32 in coils and bars, from Ø40 in bars.
The item includes all necessary fittings, sliding sleeves, couplings, reducers, T-pieces, transition pieces, protective pipes, and other materials required to complete the installation and make it fully operational.
Remember those two oversight agencies, they check everything, first our bill of quantities, then during building process contractor and supervising engineer contracted by the client, (not employed by the contractor) have to validate quantities and money spent.
How far does this go, you ask? Let me tell you three real world examples that we had to deal with.
1. Road signs, at one intersection there was many of them so contractor and supervising engineer agreed to place two slightly smaller ones for better visibility. Oversight agency wanted to know why the change, explain it and list how much did the two smaller sign cost, because that needs to be deducted. They explained to them that smaller ones are actually more expensive than the standard ones, contractor agreed to lose a bit there, insignificant amount in grand scheme of things. Didn't help, explain why, list the prices, everything must be validated. In the end they just returned the standard, slightly larger ones, because it was easier and faster then dealing with those guys.
2. You think that's a little crazy, you say. Well let me tell you about a daycare center remodeling, kitchen in bill of quantities was specified as red. At the time of installation chosen model of kitchen wasn't available in red, only green (I'm not making this up), so contractor got the green one and installed it. IT'S THE SAME EXACT KITCHEN MODEL JUST IN DIFFERENT COLOR. Well guess what, oversight threatened to pull the funding for the entire project! And then the county would have to pay several million Euros, which they of course don't have.
3. This one is so comical it's absurd. They showed up at the site with one of those distance measuring wheels, and they measured how many meters of broken road lines were drawn! Can't have contractor draw 672 meters when 679 meters is specified in bill of quantities.
but in many cases good enough is good enough.
So you see my friend, while I agree with you, sometimes good enough is just not good enough. Which is beside the point anyway because a d***mn BIM program should calculate quantities correctly! That is supposed to be one of the basic BIM things!
And this is the simplest possible example. There are cases where I have exterior wall meeting terrace floor which has heated rooms below it. Lot's of different floor/wall layers that have to intersect each other in certain order, layer priorities made it so easy, until I figured it doesn't work! So back to every layer being it's own d***mn floor, use only cut, forget join as a command exist.
sigh
