Well that makes sense! However the OSB first layer of sheathing has already been nailed down. So after the roof is constructed, I will bring the second and final layers (5/8 drywall) through the large access door over the kitchenette.That's why the HVAC goes in BEFORE the ceiling is done... Nobody walks on that ceiling, ever, so it has no additional live load: only dead load.
Good idea. Thanks. That should solve it.If he thinks that the HVAC guy needs a surface to stand on for installation and maintenance, then you could put some plywood sheets up there, on top of the drywall, in the area around where the plenums will be, but the area where the AHU, dampers, intake vent and exhaust vent will be does not have any middle-leaf ceiling below it:
Got it. I will relay this to him and see what he says. but at this point it is mute since the way oversized joists are in.As I implied above, floor joists must carry live loads, ceiling joists do not.
It is the latter. I hired you to design the HVAC only. I did share your sketch-up design with the draftswoman and GC, but those details were not included in the approved plans. Plus you didn't give dimensions for joists and you had inside-out walls which was not in my plan and some other details that you were going to clean up but never did due to saving time and just being busy and it wasn't what I was paying you for. I totally appreciated having those details and if I were to do it again, I would have paid you to design the whole studio with every detail spelled out. The other thing is the GC is not doing the HVAC. I have hired a HVAC company to do that. That company has all your sketch-up jpgs and they will follow your plan EXACTLY, which I am going to emphasize LOUDLY! Of course everything needs to be timed correctly. That said, the GC did screw up the timing. Instead of doing 24"OC and then constructing the roof, and then bringing in the HVAC, he did 16"OC, then put the first layer of OSB on top of the joists, and now the roof. Because it is winter and it's raining, they wanted to get the roof up but for some reason did the OSB first I believe so they could stand on it while constructing the roof?He's also not reading the plans correctly! either that or the plans he has are not taken from the ones I did for you
As stated above he wasn't referencing your plan. The draftsperson/designer also did not indicate the size or span of the joists on the approved plans. The 2x8 roof rafters were on the approved plan and in my email communications with her she mentioned sistered 2x8s for areas where we were hanging HVAC only. All I know is the former builder came to me saying 2x8s weren't going to cover the span. I'm not clear why or where he got the idea that the plan called for 2x8 joists. Agreed sistered 2x10s would be more than adequate., on the design I did originally, those are 2x10 joists, not 2x8! I'm not sure where he got the idea they are 2x8. Both the middle-leaf joists and also the inner-leaf sistered joists are all 2x10. There's no 2x8s in there. The rafters and rim joists are 2x8, yes, but the joists are all 2x10.
This may explain it. Early in the planning process the question to go 16"OC or 24"OC was raised. The GC said he didn't like 24"OC for structural reasons. That early comment stuck with the designer and I think she assumed everything would be 16"OC. On the plans 16"OC is indicated for the walls but again nothing specified for the ceilings.In fact, those distances COULD be spanned using 2x8s at 16"OC (barely), but I opted for 2x10 24"OC for several reasons (including an extra safety margin and also improved isolation at low frequencies)
The only harm here is a possible slight reduction in isolation for very low frequencies, due to going 16" OC instead of 24" OC. If you are concerned about that, then you could add more mass to the deck on that middle-leaf, by increasing the thickness of the plywood deck to 3/4", and/or switching to OSB, instead of plywood.
Well the first layer is 3/4 OSB, not plywood, and it is already installed. Green glue will be put between layers and it has been purchased and will be delivered on Monday. The second and final layer calls for 5/8 drywall. Is that enough to compensate for the isolation loss? What if I exchanged the 5/8 drywall with 5/8 MDF? Would that be better? 5/8 MDF is only $3 more per sheet than 5/8 drywall. It would also solve the standing on issue when putting in the HVAC. What do you think?Another option would be to use Green Glue between the two layers:
Another question is what order regarding the HVAC installation makes the most sense? After the roof is constructed, should we bring in the HVAC and then add the green glue and second layer of mass (drywall or mdf) to the second leaf or reverse that order and put the second layer on and then the HVAC?
I have another decision to make. The former builder's plan was to use the 2x12s for the inner ceiling joists. I KNOW WAY OVERKILL! AND IT LOWERS MY CEILING BY 2.5 INCHES! He brought up the 2x8 span concerns as the reason, same as the middle leaf and I stupidly signed off on it. So he purchased enough to cover the inner leaf and they can't be returned. So I can either use them or I can insist on the sistered 2x10s, but in that case I would have to pay for the 2x12s. [note: they will be at 24"OC]. The ceiling will be inside out. What do you recommend? The GC said he is fine either way but he has no use for the 2x12s if I don't use them.
Of course. Stuart thank you so much again for guiding me through this. Your help has been indispensable.Don't forget to take your camera, and take plenty of photos to document everything that is happening! And post a few of the best ones here...