2 story duplex

This topic contains 5 replies, has 1 voice, and was last updated by  Robert Minor 2 months ago.

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  • #5509

    anniesball72
    Participant

    I have a question about how to correctly model a 2 story existing duplex that is being altered.

    From what I have read I need to model it as two separate reports.

    If this is a 2 story, how do I model the lower story unit ceiling/roof and the upper floor / lower floor ceiling.

    Those are really my questions.

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  • #5753

    Robert Minor
    Participant

    Thanks for the information regarding not needing to put in an insulation value for the floor under the upper duplex. Thinking on it it’s a good idea not to put in a specific R- value because the floor between the two units has to be a 1 hour fire type and it also has to have a STC 50 rating as well as an IIC 50 rating (impact sound).  This assembly also usually is required to be a listed assembly and a lot of listed assemblies are very specific as to what they will allow, calling out R-19 might make an assembly unusable for plan check.

    I just ran it with R-0 for the insulation for the floor over the lower unit and it calced the same, thanks again for the good advice.

    Take care,

    Rio

    #5746

    EproUser1500
    Participant

    I don’t believe there are any energy code mandated requirements for the shared floor/ceiling in this scenario. The energy code only mandates requirements for raised floors that separate conditioned and unconditioned space, which is not the case here. This is likely why when you test different insulation values, it makes no difference. There is no requirement for insulation here based on energy code. However, it is likely a good idea to have some for sound mitigation.

    Since there is no requirement, you do not have to input this surface in the lower unit’s energy model. As far as I’m aware, putting this in as an interior surface on the lower floor will actually add additional floor area to the unit, which is incorrect. There is no way to model a ceiling only, it must only be modeled as an interior surface ceiling/floor on the unit above only. Check your lower unit’s model floor area on the CF-1R and see if it is double counting the area because of the way you’ve input the ceiling in the model.

    For your ductless system, make sure to select the system element, distribution tab, and specify the heating distribution and cooling distribution. This is where you specify your system is ductless, not by selecting the system type at the system input. See attached image for reference.

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    #5737

    Robert Minor
    Participant

    I just tried the lower unit with two different insulation options and it models the same so I’m thinking the software has an automatic number it uses when there is a unit with another unit above.

    #5736

    Robert Minor
    Participant

    I have a similar project except both units are new.  For the upper unit the lower assembly is from the interior surface option and is called out as a R-19 floor with no crawlspace with the ‘next to a different dwelling unit clicked’.

    For the lower unit for the ceiling it’s the interior surface option again but this time I used R-30 with no crawlspace because that’s at least how good the insulation has to be with another unit above, thinking of going with R-38 actually and would like to know what is an acceptable amount of insulation to call out when one has a unit above with a roof above that that is insulated?

    We are using ductless mini splits so the lower unit modeled okay with the ductless options clicked on the distribution tab for the HVAC options and a heat pump selected. At first I made the mistake of clicking the FAU/AC and it won’t calc that way as the software is assuming it will be ducted if that’s clicked.

    Hope that helps and if anyone has an answer on how much insulation it’s okay to call out for a floor above a unit that has an insulated roof above that or the correct way to model that please post it up.

    Thanks,

    Rio

    #5725

    EproUser1500
    Participant

    Assuming that the lower story is one of the residences and the upper story is the other residence, I believe the correct thing to do would be to include an interior surface with type floor on the upper story model and mark it as being adjacent to another dwelling unit. In the lower story model, this room would not have a roof or other interior surface representing the ceiling.

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