Subscribe or Renew Membership Subscribe Renew

Creating a better insuation & HVAC plan for my new construction urban row home.

matthicks024's picture

Hi, My wife and I are building a new row house on an existing foundation of an old row house in Pittsburgh.  We hired an architect and subsequently a very reputable builder to renovate the row house.  The structure has only one shared wall (we own and adjacent city lot and plan to have a courtyard so the home won't have a shared wall on both sides like most row houses.  As such, we only have one wall to run ductwork and plumbing up and very little wall space to insulate.  The HVAC sub has advised that we will need two furnaces and condensers with the 2nd set being on the third floor due to the lack of wall space (we have no interior walls that run up all three floors and we plan to have 6 zones in the house (lots of duct work). We told the HVAC guy we could reduce the number of zones by 1-2 easily to make ductowork fit better.

I started thinking about the $4k plus cost of the unnecessary hvac equipment and started to wonder if there was a way to better insulate my structure such that i can use two walls for ductwork thereby allowing for only one furnace and condenser.  The saved mech costs could help pay for the additional rough carpentry and insulation, giving me a much more efficient home for little extra cost. 

Here is the catch - the interior of the home is about 16'10" wide and 72' deep.  So losing interior space on the two short walls - no big deal.  Losing it on the long wall - tough to swallow.  Further complicating things the area where we are building does not have the best expertise for green building, so we will run into expertise issues with complex solutions even if they are affordable.  Adding to that - while I am extremely happy with my builder and architect, neither of them are extremely knowledgeable in green solutions.  As such, I need to find a solution that not only improves the envelope of my home and gives me a second wall to run ductwork, but I need a solution that has "low risk" implementation such that the framers doing my house are not scared off by "complex" solutions or bid overly conservative bc it's a new thing for them. 

I plan to hire a local energy consultant to help size our HVAC once we determine a more appropriate wall solution, but I currently need to determine what that best wall solution is.  As I said, my builder is good, but not green, so they haven't proposed a solution that provides the best ROI while being more green, and they are reluctant to price out 4-5 solutions because of the time involved without charging me extra, which I understand.  I haven't spoken with my architect yet, but I also flip houses on the side, and so i figured I would determine the solution that is easiest to implement. 

The way I see it, I have a few options, and the short exterior walls are the easy solution:

1. Short exterior walls - The easiest solution appears to be to lay 1-2" of interior rigid insulation inside my 2x6 walls which will eliminate the thermal break associated with my framing.  I am in zone 5 in the US and need 2" of exterior insulation to avoid moisture accumulation so using exterior sheathing would require verticle strapping, and the row house will be built up to the property line on the sidewalk, so i'm not sure what an additional 2" of external sheathing would do to the look of the home.  I also don't know if I would need my builder to install a drainage plane.  For those reasons it seems like interior rigid insulation with dense pack cellulose makes the most sense.  If I am wrong, please let me know.  That would give me R25-30 on my two short walls with no thermal break. 


2. Long Exterior Wall - Long wall is harder because I don't want to lose much interior space and I need to be able to run ductwork up this side as previously mentioned.  The way I see it, I have four options -

a) double studded 2x4s with no spacing (or 1") between walls.  I only lose 2-3" of interior space and have no thermal breaks.  I can run 4" ductwork up the interior wall and still have 3.5-4.5" of dense pack cellulose behind it providing R-14-18 insulation, and almost R30 insulation where there is no ductwork or frame material.  This seems like the easiest solution to implement, but i lose 2-3" of interior space across 72' and 3 floors. 

b) same as above but I've read that there is a way for the outer 2x4 wall to extend out over the foundation, and not be a load bearing wall.  This would allow more spacing between walls for more insulation, but I don't know the details around doing something like this.  If it's an easy implementation, perhaps this is the way to go. 


c) 2" (or more) of exterior foam sheathing with verticle strapping and a drainage plane.  This is easier as this long run side of the home isn't adjacent to the public sidewalk.  The builder already pitched a 1.5" closed cell + 4 inches of bat insulation package for the whole home, so they should be familiar with implementing an appropriate dry-inward wall associated with exterior vapor barrier insulation solutions. 

d) build a larson truss - This really accomplishes the same thing as B i think right?  I just don't know which is more difficult to implement. 

The fourth long wall will remain a 2x6 wall with dense pack cellulose and a fair bid of ductwork.  The wall isn't shared with the neighbor and there is a slight gap (1/2" or so) between my home and the neighbors, but I am stuck with a 2x6 for this wall. 

Also, the foundation is a +150 year old stone foundation that is quite moist and only about 6' high.  We have no plans to insulate this basement so far... not sure if there is a "good" solution to an old pittsburgh basement like this.  


So, am I missing some other easy/more cost efficient implementation for this long run wall?  Any help would be appreciated.  

I would consider whether (post #214835, reply #1 of 7)

I would consider whether there isn't some way to get an interior chase for some of the mechanicals.  Doesn't have to be the full width of a wall, and a minor amount of "jogging" between floors would be acceptable.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

open concept (post #214835, reply #2 of 7)

The house is a total open concept, so the load supporting beams will run the short width of the house.  The only walls on the first floor are in the very back of the house behidn the kitchen which creatse a space for a pantry/mudroom/half bath near the entry from the garage.  

Above that wall is a totally open living room and above that the master bedroom.  There is no way to run duct work the long length of the home because of the load bearing floor beams running east to west.  We are trying to have no lowered ceilings or wall kcikouts for duct work.  

there is one area that could have an interior run next to a closet on the first floor and running up through closets on the 2nd and third floors, but we are going for a lot of zones in the home given the 3 floors and long width of the home, so one space for interior chases doesn't get me that far.  

I uploaded the floorplan section CDs for reference 

I think you want too much. (post #214835, reply #4 of 7)

I think you want too much.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

You would be better off at (post #214835, reply #3 of 7)

You would be better off at the sight.  They have a lot of people there that are very knowledgeable in this particular prepared to get the suggestion that you use wall mounted heat pumps which carry the advantge of no duct work.

Radiant (floor) heating and (post #214835, reply #5 of 7)

Radiant (floor) heating and cooling will provide all the heat and cooling you need without any ducts at all, and as many zones as you want.    It is a simple system, but requires some attention to detail. It should be designed and installed by someone who is experienced in hydronic systems.   It will probably not be your builder / HVAC sub, since they only mentioned multiple furnaces/condensors.

Add a heat recovery ventilation system, with its duct work run through the floor/ceiling  to provide the required air exhange. 

Because radiant cooling systems do not condense water vapour out of the air, a dehumidifier may be required as part of the ventilation system.

A mini split heat pump system can also be used to provide cooling instead of the radiant system, as well as most of the heat required for the radiant  system.  A very small boiler, or using the domestic water heater,   can provide supplement heat as required.

No ducts running through the walls required.  Seal the house up tight and insulate with the most cost effecitive way for your area.

Of course, as you hint, you (post #214835, reply #6 of 7)

Of course, as you hint, you will have problems with such systems due to the non-movement of air.  At least some ductwork is needed to have an air exchange system to draw in fresh air, and a dehumidifier would be needed in most non-desert climates.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Not a hint, and I don't see (post #214835, reply #7 of 7)

Not a hint, and I don't see it as a problem.  

A ventilation system is required for any moderately well sealed house.  The duct work for such systems is very much smaller than that required for furnaces. and can be readly burried in interior partitions and foors / ceilings without affected the thermal envelope.   Supplimentary dehumidification  may only be required during the most muggy days in the summer if the whole house is cooled, or for the basement if the owner chooses to leave windows open for  natural ventilation.