I am trying to understand the logic behind the units for building component types in RTLCA. I’ve tried rewatching all the tutorial videos but they do not touch this subject.
I just created a new floor from scratch of 134m2. The floor should include concrete and a reinforcing mesh. I manually added to new materials:
134m2 concrete
134m2 Reinforcing steel
I then found materials from the library that match what I needed.
For the concrete, the material in the library is declared in m3. Does that mean that I have to enter m3/m2 (meaning the thickness of the slab), or am I asked to enter the m3? Entering the thickness would definitely make most sense.
The same is the case for the reinforcing mesh. I’m I being prompted to enter kg og kg/m2. If the answer is kg, what influence does the m2 I’ve already made have on the results?
The construction engineers usually just declares kg/m2 to us, so that would be the most logic unit in this case.
In this specific case I would recomend to build your own construction with a declared unit of m2 with the exact concrete and how many m3 per m2 and amount of steel in kg.
Otherwise you have to manually enter the correct amount of m3 or kg in the whole project.
I understand that the EPD decides the unit, but I still don’t get what to input in the example above as there are two units in one material - respectively m2 and m3.
In LCAbyg, the structure is quite clear. You declare the unit for the construction and then the unit of the materials is defined by both the unit of the construction and the unit of the EPD.
In the example below, the unit of the construction is m2. The unit of the EPD for concrete is m3 and for the reinforcing mesh it is kg, so the units for the construction becomes:
Concrete: m3/m2 (which corresponds to the thickness of the material)
Reinforcing mesh: kg/m2
The hieraki is quite clear in LCAbyg, while having two units for one material in RTLCA still confusses me. But it might just be a matter of me still having a “LCAbyg-mindset”, so to say
Could you maybe answer, what I should enter in the to examples from the first message in this tread, if I want a 120mm concrete slab with 3,6 kg/m2 reinforcing mesh?
For homogenous material layers, I would do exactly what you’re doing in LCAByg… You’ve set the construction unit in RTLCA to m2… Material unit should correlate to this unit, hence if the EPD is in m3 you need to use that unit for material quantity, just like you do in LCAByg by using m3/m2…
For inhomogenous material layers, like the one you have set up with concrete and reinforcement mesh you have to create a construction with a inhomogenous layer… here you can specify construction unit as in LCAByg and then every material unit corresponding to that construction unit. i.e m3/m2 or kg/m2… as illustrated below… hopefully…
So if I understand correctly, I should enter 0,12 in the marked field below if I want to have a 134 m2 with a thickness of 0,12m, right?
From looking at the material, I would have thought that I would have to calculate the volume manually (134 m2 * 0,12m = 16,08 m3) to get the propper thickness.
Of cause you are right though, that it would make more sense in this case to treat an inhomogeneous layer with both steal and concrete in this case. I actually didn’t think of that, but the question above is still relevant.
No! - not 0,12m… In this case where you have manually created a construction and not imported from Revit, RTLCA does not know the mass of the concrete slab, you have only supplied info on how large it is in m2… You’ll have to manually enter the mass here (i.e. 16.03 m3)… either that or create a construction, like the one I suggested above that tells RTLCA how much m3 pr. m2 you have. With that construction created you are then able to apply it on your concrete slab object as it contains square meter data.
Okay, I can now see the difference between imported and manually created constructions. The imported constructions already have area and volume reported through Revit, whereas this isn’t the case for the manually created constructions.
That being said, it would still be very useful to have the thickness informed for materials that area “cubic” like gypsum, insulation, etc. Thickness is a normal parameter in Revit, so that should be possible, right? That way, I know that an insulation batt of 308,12m2 (see the example below) and 7,09m3 is actually 43mm thick. This is very important information when QC’ing the imported data.
So in my minds eye, there should be an extra column between Preferred and Unit, that says Area, Length, Count, Volume and (as a new feature) Thickness.
Of cause, you won’t be able to report a thickness for non-rectangular objects like steel beams etc., like it isn’t possible to add the length of this insulation batt in this example.
Inhomogeneous layers
The other option you mention is to use constructions instead of materials from the library, as the sublayers have the unit m3/m2 or kg/m2. That’s more intuitive in my head.
However, when creating a custom construction, you are asked to specify the thickness of the layer. So if I have a project with a timber frame, like the one a have modelled below, in different thickness - lets say a thickness of 70mm, 100mm and 250mm respectively - then I wouldn’t be able to use this material, which is modelled with a thickness of 1000mm. I would need to model three timber frames as separate custom materials with the correct thicknesses, right?
