How accessible does HVAC ductwork need to be (new construction question)?
#1
12-16-14, 09:52 AM
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How accessible does HVAC ductwork need to be (new construction question)?
I am working on a plan for a second story addition to my ranch home. The ductwork is rigid and run in the attic (long trunk line that runs the length of the house). One of the ways I've read that contractors simplify 2nd floor additions is to build a second floor platform over the existing ceiling joists (rather than sistering them):
Ranch To Two Story-how Do They Do The Tearoff/framing? - Building & Construction - DIY Chatroom Home Improvement Forum
This is typically done in order to get around the fact that there's wiring and all kinds of other stuff run over the joists with no slack. It also keeps the first floor relatively weather tight and allows the homeowner to stay in place while work is going on. I'd like to do something like this, but basically encapsulating the existing ductwork. Would that be permitted by code, etc...? It would look like this:
[ATTACH=CONFIG]43333[/ATTACH]
I'll have to run all of these plans by the code official eventually anyway, but I'm trying to get an idea because if this can't work, I have to change the floorplan entirely.
Ranch To Two Story-how Do They Do The Tearoff/framing? - Building & Construction - DIY Chatroom Home Improvement Forum
This is typically done in order to get around the fact that there's wiring and all kinds of other stuff run over the joists with no slack. It also keeps the first floor relatively weather tight and allows the homeowner to stay in place while work is going on. I'd like to do something like this, but basically encapsulating the existing ductwork. Would that be permitted by code, etc...? It would look like this:
[ATTACH=CONFIG]43333[/ATTACH]
I'll have to run all of these plans by the code official eventually anyway, but I'm trying to get an idea because if this can't work, I have to change the floorplan entirely.
#2
12-16-14, 10:08 AM
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Personally I have never seen another deck built above the existing ceiling with a space between for duct work. I'm certain it can be done but it seems like it wastes a lot of space and would be an expensive method of construction. Adding a second floor is major work so re-doing duct work and wiring is just one little step in a big project.
Leaving the existing ducts, wiring and attic insulation does not keep the house weather tight. Once the roof is off you can forget much of the weather tight stuff. Stay in the home when adding a second floor has been done by a relative of mine. Their family was in that line of work and they were highly organized, had material and labor ready and waited for a good weather window and hit it hard. If you are relying on a contractor I would not count on staying in the home while the work is being done but if you do I would prepare for the possibility of water getting into the home.
Leaving the existing ducts, wiring and attic insulation does not keep the house weather tight. Once the roof is off you can forget much of the weather tight stuff. Stay in the home when adding a second floor has been done by a relative of mine. Their family was in that line of work and they were highly organized, had material and labor ready and waited for a good weather window and hit it hard. If you are relying on a contractor I would not count on staying in the home while the work is being done but if you do I would prepare for the possibility of water getting into the home.
#3
12-16-14, 05:34 PM
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I get what you're saying about moving ductwork seeming a relatively minor part of a big job, but the fact of the matter is, there's nowhere to move it to that's practical. However, I think I found a solution to my problem-my local lumberyard can supply 12" deep open web floor trusses for about $4.25 per foot. However, the question remains-can I enclose my ductwork in that manner?
#4
12-17-14, 05:00 AM
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What do you mean by "in that manner"?
Scissor trusses can allow ducts, water and electrical to pass across in many cases. You'll have to pay attention to your trunk line and what direction it runs. The trunk is too big to pass through the openings in a truss that size and depending on the size of your lateral duct lines it may be a squeeze.
You can also get custom, engineered trusses. Depending on how many you need they are not much more expensive but openings can be built into them for what you need.
Scissor trusses can allow ducts, water and electrical to pass across in many cases. You'll have to pay attention to your trunk line and what direction it runs. The trunk is too big to pass through the openings in a truss that size and depending on the size of your lateral duct lines it may be a squeeze.
You can also get custom, engineered trusses. Depending on how many you need they are not much more expensive but openings can be built into them for what you need.
#5
12-17-14, 07:03 AM
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What do you mean by "in that manner"?
Scissor trusses can allow ducts, water and electrical to pass across in many cases. You'll have to pay attention to your trunk line and what direction it runs. The trunk is too big to pass through the openings in a truss that size and depending on the size of your lateral duct lines it may be a squeeze.
You can also get custom, engineered trusses. Depending on how many you need they are not much more expensive but openings can be built into them for what you need.
#6
12-17-14, 07:59 AM
Member
If it is all metal duct then yes it can be inclosed. If it is flex duct it will have to be replaced sometime down the road so no it should not be closed up in a floor.
#7
12-17-14, 08:02 AM
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Yes, trunk lines can and are commonly put in inaccessible locations. Basically everything between your two floors will only be accessible by cutting through the floor or ceiling.
If your HVAC trunk line runs perpendicular to the joists then that is something you need to figure out up front. My house has 20" tall scissor trusses and even at that size the trunk could not run perpendicular through the standard zig-zag section. A custom truss could probably have an open bay area near a load bearing wall for your trunk line.
There can be trade offs with truss sizing spacing. In my house I could have done 24" ctr to ctr with 18" high trusses but I choose to go to the taller 20" trusses to minimize bounce in the floor and 19.2" ctr to ctr spacing to minimize sagging between joists. I'm also a big fan of the premium OSB products for subflooring like Advantech.
If your HVAC trunk line runs perpendicular to the joists then that is something you need to figure out up front. My house has 20" tall scissor trusses and even at that size the trunk could not run perpendicular through the standard zig-zag section. A custom truss could probably have an open bay area near a load bearing wall for your trunk line.
There can be trade offs with truss sizing spacing. In my house I could have done 24" ctr to ctr with 18" high trusses but I choose to go to the taller 20" trusses to minimize bounce in the floor and 19.2" ctr to ctr spacing to minimize sagging between joists. I'm also a big fan of the premium OSB products for subflooring like Advantech.
#8
12-17-14, 08:32 AM
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If your HVAC trunk line runs perpendicular to the joists then that is something you need to figure out up front. My house has 20" tall scissor trusses and even at that size the trunk could not run perpendicular through the standard zig-zag section. A custom truss could probably have an open bay area near a load bearing wall for your trunk line.
#9
12-17-14, 09:34 AM
Group Moderator
If you buy custom trusses the truss company generally does all the engineering and provide signed and stamped drawings for your Building Inspections Dept. It's all very standard stuff for the truss companies so it's not that expensive to go custom especially when you consider the engineering they provide in the cost.
