2-story floor and ductwork framing questions

jeff2013November 3, 2013

I had posted questions and received a lot of comments mainly about floor plans, roofs, elevations. There were also some discussions regarding staircase and driveway. As I am about to meet with our architect to finalize the house design, additional issues coming to my mind include land grading (the lot is in a flood zone, issue to be addressed later) and floor framing.

1. 34" floor spacing excessive?

The current plan has 9ft ceiling height for both floors and 2ft 10in spacing between main ceiling and 2nd floor. The 2'10" seems excessive to me as the previous designer has 18" floor spacing. The architect explained that he would use 2x12 standard joists and need the additional 22" clearance to run ducts without cutting through the joists.

I am still not sure if this is the right way. That means we need to frame the 22" void dropped ceiling for the rest of the house (except the great room and the dinning where vaulted high ceiling is possible).

I don't know anything about framing. I just see that ducts take much smaller area than rest of the house. To me the common sense is not to do the 22" dropped ceiling (for nothing but a leveled ceiling height). Ideally, the duct shall be inside the floor spacing. If not, maybe the duct is partially inside the floor and partially sticking out (say 1ft soffit) to define the great room.

2. Duct inside unconditioned attic?

I had posted the question over the Heating & AC forum and everyone suggested ducting for 2nd floor inside conditioned space. When I raised the issue with the architect, he said he is doable but will cost more as AC in the attic is the standard practice and we are going to pay more whenever a non-standard method is used as the builder/subcontractor will spend more time/materials for it. He went further to say that it would take forever (say 30yrs) to recoup the extra upfront cost with the reduced utility bill.

My current house has the ducts in the attic. We are building in a hot climate and this looks really bad to me in terms of energy efficiency.

Maybe I missed something from the architect to justify the arrangement. I just don't know what is the right way and how to pursue it.

Any suggestions on these two issues? Thanks! JF

Edited with a picture showing floor plan and support beams (orange) and HVAC closets (red).

This post was edited by jeff2013 on Wed, Nov 6, 13 at 16:54

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Sorry, not an answer to your specific questions, but, have you considered mini-splits and PV panels?

    Bookmark   November 3, 2013 at 11:44AM
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Look into open web framing.

And by all means do NOT leave the flood plain building issue to the last. You could have done all of this work for nothing. You might not even be allowed to build the plan as designed. Or your home insurance costs could be 15K a year if built as designed. Or, you might have to build it elevated as pier and beam with the garage lower. That is NOT a minor thing. It affects EVERYTHING.

    Bookmark   November 3, 2013 at 12:13PM
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First of all the finish grading elevations and the house floor elevations are key for getting approvals and getting insurance in designated flood zones. You should immediately check with your home insurance company and your local jurisdiction for details if you have not already done so.

Second, having 34" of clear space between first floor ceiling and underside of second floor structure (?), or even to the top of the plywood sheathing on the second floor (?) (throughout the house?), if I understand you correctly, sounds like someone has not done their homework and not figured out where and how supply and return ducting will be designed.

I agree with you that it is neither reasonable nor acceptable for a custom home design. Properly done, the house designer will have a workable plan for location of all mechanical equipment and distribution systems. Insist on it.

Good luck with your project.

    Bookmark   November 3, 2013 at 4:35PM
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Our architect did a plan for the HVAC ducts (mostly to satisfy the permit) and suggested we get a proper HVAC plan done afterwards. We asked the HVAC contractor to improve upon the basic architect plan (which he described as not sufficient). This contractor then planned out an unacceptable plan that would have had large drop down valances around the perimeter of most main level rooms (and our ceilings are only 8 feet). It would have looked like a basement ceiling and we have a basement where these ducts could have run. He had already begun his install of these ducts before making his plan clear to us. It was a nightmare!!

Luckily we went back to the design board and found a HVAC designer who makes his living doing custom HVAC designs on CAD (he no longer does duct work or installs). He put together a design that met all of our needs, and led to virtually no drop downs. We did elect to do high velocity A/C as these ducts are much smaller (might be an option for you too). We did not need ducts for heating because our heat will come from in-floor. Long story short--- find a reputable HVAC designer and do not rely on either your architect nor an HVAC contractor to do this design. Our HVAC designer works out of Toronto area, but there must be the equivalent designer in your area.

Best of luck.


    Bookmark   November 3, 2013 at 5:24PM
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Maybe your architect is used to doing commercial where dropped ceilings are very typical. You might suggest to him that he actually go out to some houses under construction and see how other people in the area are doing them.

It seems like you might be in a subdivision with existing neighbors so perhaps the floodplain is no big deal (already understood what is required)

Efficiency wise it is always better to keep the HVAC system within the conditioned space (although in Texas it is pretty common that they are not.) The extra heat also causes more wear on the unit.

High velocity AC:

With this type of system I would see no reason that the unit could not be on the 1st level and all ductwork is run in the second floor with a standard minimum floor thickness.

It would cost a small fortune to add in the extra 22 inches.

Here is a link that might be useful: High velocity AC

    Bookmark   November 5, 2013 at 8:52AM
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putting ductwork inside the conditioned space has a
decent payback. 20-30% energy savings in my
hot humid climate.

but it takes detailed work in framing, building furdowns
& determing where & how to locate ductwork.
a lot depends upon the layout of the house.

problems come in framing stages, duct install,
& sheetrock. someone has to be on hand
to oversee the correct procedures.

it isn't common in my area, but we do it sometimes...
with more time spent on the job overseeing variousa

shortened way to do it is to install ducts in attic,
still mastic sealing all ducts & foam insulate the roofline.
this lessens heat gain into attic keeping ductwork
in semi conditioned space.

sometimes you have to weigh time & effort to
oversee vs extra cost of foam install.
then oversee foam install for correct inches to
R-value requirements, correct sealing of
eaves of roof to attic floor etc.
picking the right foam company is critical to
a good install.

I test these unvented foam attic installs with
blower door & make sure attic is air tight,
insulation depth is continous & R-value requirement
are met.

have you conistered foam for the roofline?
what location are you in?

best of luck.

    Bookmark   November 5, 2013 at 10:37AM
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Be careful, the floor to floor height appears to be just 2" short of requiring an intermediate landing. You might want one anyway; it's a long way to fall.

Homes here are usually served by ducts in a conditioned attic and the basement with no ductwork in the second floor framing. Even if it is necessary to use the floor space, I can think of no reason for 22" of clearance since ducts can cross using the joist space.

    Bookmark   November 5, 2013 at 12:31PM
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Jeff2013 -

Why cant the they work the duct-work in between joists in in walls ?? you should be able to run a main trunk in your basement and spider through the walls and joists where needed and avoid sofits for the most part . Then you would have a 10' plus ceiling - or save a ton a money and go with a 9'

22' dropped ceiling is crazy - what kind of vent is he thinking ? I have never heard of this

    Bookmark   November 5, 2013 at 3:03PM
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My ductwork and heat pump are in attic. Like energy rater said above I have foam and my attic never gets hot and I am in the deep south. On efficiency its going to depend on what you are insulating with.

    Bookmark   November 5, 2013 at 4:59PM
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Annie Deighnaugh

We did ductwork in conditioned space, but our ac is our geothermal system so it's in the basement...not only very energy efficient, but no outside air compressor.

    Bookmark   November 5, 2013 at 5:47PM
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my ducts are in fur downs inside the conditioned
space. I designed it this way after looking
at other homes & planning it out.

the problem I find in my inspections
is that duct openings in open web trusses
aren't always lined up as they should be.
then a/c co puts two 8" ducts in one opening,
compressing both ducts so that the air flow
is compromized and rooms are never comfortable.
once trusses are on site, they should be
placed properly, because there isn't an
easy way to fix it once it is done.

I see huge issues with ductwork in new
construction. it passes code because it isn't
unsafe...but just looking at it you know it
will never perform.
low pay man on the job runs ducts...little
consideration other than get it done

pay attention to what is going on & discuss it
with carpenters & hvac company.

best of luck.

    Bookmark   November 5, 2013 at 6:58PM
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Thanks everyone for your input. Very helpful comments! I will get to them later.

After I met with the architect, I had updated the initial message with floor plan showing wood beams and HVAC closet locations. The walls are framed with 2x6 wood studs. Stick built with standard floor joists and regular roof rafters instead of trusses to save money. Brick walls and metal roofs.

Not sure if the added info help justify the architect's approach. Otherwise, I would do more research, get builders involved, hopefully we will identify some acceptable floor framing and ductwork layout.

Thanks! JF

    Bookmark   November 6, 2013 at 5:42PM
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Nope, -The cost of trusses is not nearly as much as adding two feet in height.

Just the brickwork alone will probably add a couple of thousand, but then they will have to go in and frame a whole other ceiling which if it is made from 2x4 to save room will have to be hung from the second floor.

It is a very, very bad idea. I can hardly believe that the architect is even suggesting it.

    Bookmark   November 7, 2013 at 8:21AM
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I would worry more about your flood level. I read an article about how flood insurance is going to change in the next 7 years. If you are not above the flood level they are predicting insurance rates at $20,000 a year.

    Bookmark   November 7, 2013 at 11:55PM
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Yes I do agree that the new flood insurance rates are a very important consideration. Even a $2000 increase would remove a substantial amount of retirement savings.

    Bookmark   November 8, 2013 at 8:57AM
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Going to agree with everyone else, the 22" for ducting seems CRAZY! We run both Heating and Cooling systems here, and everything stays within the conditioned space.

I understand your struggles though. When I brought my plan to local HVAC companies, I was quoted $12k for the system and EXTENSIVE bulkheads throughout the house. It was CRAZY. Thankfully my father works at a college that trains HVAC specialists, and when he brought my plans to the instructors there, they created an AWESOME system, with ZERO bulkheads, utilized all the interior space (just a small double wall in the middle of the house for the main trunk to come up) and the final system was just $3000 including the furnace and all ductwork when we installed it.

Tested all the loads, temperatures and velocity of the air through the system in all outlet vents last night and the guys at the college ran the performance numbers this morning. Just need to turn down one damper and I have PERFECT heat and circulation in the entire house.

Sometimes I just think it's an easy way for these guys to make $$ and get a bigger job by suggesting these crazy (but way easier) systems. It certainly would have been easier to assemble and design with a giant void in the house or bulkheads everywhere, but I'm not paying them 4x the price to make life easy on them.

    Bookmark   November 14, 2013 at 12:21PM
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You should post a section through your house. I'm not even sure if you have an attic or a basement.

This is an HVAC design issue instead of a framing issue. What kind of HVAC system are you using? Who will design it?

    Bookmark   November 14, 2013 at 2:34PM
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I wondered what is up with your design. Any progress to share?


    Bookmark   November 17, 2013 at 11:47AM
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