define poorly installed batts.

if there are gaps between batts blown will fill them in.
but if there are voids where the batts don't lie
flat on attic floor/living space ceiling...then
these areas need to be corrected before
installing more insulation.
blowing insulation over batts not in contact
with attic floor doesn't really help at all.

do you have service platforms around the units?
there should be a 3' walkway to and around
units for service.

check & see if batts were installed under unit platforms
and walkways...water heaters too if they are in the attic.

understand that under heating system you'll only
have R-30, which is code here in La. how about in
Tx? at max we put R-38

I don't know what value you plan to insulate to...
what is your goal?

and what is the purpose of the added insulation?

I find it is usually air leakage into the house that
people try to solve by adding insulation.
it never works unless the new insulation both
insulates and air seals. (foam ins) with propane
you'd have to add combustion air if you foamed
the roofline. many insulation companies don't understand
how to do this...nor to hvac companies.

air sealing is easier with batts than with any other
insulation. move the batt...do the air sealing...
put the batt back.
do you have recessed lights? IC or ICAT? the IC lights
are a big leakage to living space.
were ducts mastic sealed?
or just duct/foil tape?
returns in attic mastic sealed?

to find leakage in attics...look for discolored insulation.
as air leaks from attic into living space it pulls air
thru insulation, this leaves dirt trails.

you can find the same dirt trails on insulation
on ductwork.

always, always do air/duct sealing prior to insulation.
and ducts should be suspended with 3" duct straps.
the last thing you want to do is to put insulation around
ducts in a hot humid climate. works ok in dry climates...
but for us...it causes the ducts to condensate.

best of luck.

Thank you for your response! I'll try to answer your question below

define poorly installed batts. We have gaps between bats AND some sections where batts don't lie flat on the attic floor. Builder's insulation subcontractor originally tried taking the 9inch thick batts and slicing them in thirds (like slicing bread) to make three 3 inch batts that he thought I would accepts as the correct insulation! These were laid between joists. When I caught onto the subterfuge, he claimed that he hadn't been aware of the cheating but would make sure the insulation was done over properly. Instead, he allowed them to just drape 9 inch batts perpendicularly across the joists over the top of the 3 inch thick slices. Because it was very difficult for me to get up into the attic (attic ladder hadn't yet been installed), I trusted builder to make sure it was done over correctly. It wasn't and it is a MAJOR mess. To the extent that we are able to reach the batts, we intend to pick them up and reposition them correctly or just take them out. But there are areas behind the heaters that the only way to reach is by crawling over the heaters so we were hoping we could just blow insulation into those areas without first repositioning (or taking out) the batts. Guess not.

do you have service platforms around the units?
there should be a 3' walkway to and around
units for service. The units both lay beside a platform so it is easy enough to get to one side but there is no walkway "around" them.

check & see if batts were installed under unit platforms
and walkways...water heaters too if they are in the attic. there are batts between the joists that the units sit on. Whether the batts extend the entire distance under the units were only put in place at the very edges to make it look like underneath the units was insulated, I honestly don't know. Will have to pull a couple out to check. Thanks for suggestion.

understand that under heating system you'll only
have R-30, which is code here in La. how about in
Tx? at max we put R-38. We're outside of a code restricted area but under our contract the builder was supposed to have built to meet code requirements of the nearest major metro area which, at that time was R-30 in the attic. New recommendations for this area are R-50. I'm not sure what the nearest metro code now requires.

I don't know what value you plan to insulate to...
what is your goal? and what is the purpose of the added insulation? We would like to get as close to R-50 as possible even if some parts of the roof are only insulated to R-30 or lower. Seems like it is good to insulate as much of the attic as possible to R-50 to reduce heat transfer between attic and living areas.

I find it is usually air leakage into the house that
people try to solve by adding insulation.
it never works unless the new insulation both
insulates and air seals. (foam ins) with propane
you'd have to add combustion air if you foamed
the roofline. many insulation companies don't understand
how to do this...nor to hvac companies.
air sealing is easier with batts than with any other
insulation. move the batt...do the air sealing...
put the batt back. Not sure I totally understand you here. Our attic is not sealed. We have ridgeline vents and soffit vents. So far I haven't seen any signs of inadequate ventilation in the attic and I know that we need to leave space for air to circulate between soffit vents and ridge vent. We intend to be sure to leave the baffles in place and not block either end. As for air infiltration into the house, the house is pretty tightly sealed. We fired the builder before the interior walls were insulated or sheetrocked and I personally went around with cans of spray foam filling in every crack where I could see light coming thru the exterior shell. All the gaps around exterior electrical plugs, etc. Then we hired a different insulation sub to install the wall batts and I checked every piece of it before sheetrocking started. So, the house is tight.

do you have recessed lights? IC or ICAT? the IC lights
are a big leakage to living space. We do have recessed lights. They are ICAT. (I've checked).

were ducts mastic sealed?
or just duct/foil tape?
returns in attic mastic sealed? I don't know. What should I look for to find out? And if just duct/foil tape sealed, what is the proper way to fix it and is this a job a homeowner can do or will we need to hire pros? I'm assuming this should probably be done before blowing in additional insulation so one is not having to tromp over and thru the blown in insulation to reach the ducts to work on them.

I absolutely hate it when these messy installs are done.
I have a friend who's batts are installed similar to yours.
what to do but take them out & reposition them??

as one who climbs over heating systems & thru all that mess...its diy for me. BUT you have to be careful where you put your feet, only on joists. unless you have solid sheeted ceilings...
I use 1x12 walkboards 4' or 6' long...any longer & they are too hard to move around.

and of course the mask, razor knife to cut batts & long sleeves & gloves. I can't breathe in masks, & just wear short sleeves,,,but the trick is to not scratch the first time...or you never stop. home to hot shower...then cold.
good lighting is also necessary. & take advil prior to getting into attic!

so to go from a questionable R-30 to R-50 have ins co blow fiber glass. don't make the mistake of cellulose it
gets into the house thru every gap...supply box & bath fan cuts in sheetrock.

glad that your recessed are ICAT.that solves
a lot of issues. but if you drop the trim...you'll see
the cut thru the sheetrock is oversized too...just like
supply & bath fans. I'll attach a pic of how to seal from
inside the house.

good that you took it upon yourself to do the air
sealing during construction.

as for ductwork...when unit is running ...early in
morning ...make your way carefully to unit. feel around
and under plenum connections (both supply & return).
then feel on supply plenum where ducts are taken off
the plenum. if you have flex push the insulation back
(insulation is usually covered by foil jacket) move ins
& jacket back & see if you see signs of condensation.
or openings into the plenum.
if the ducts are mastic sealed you'll see a gray paint mastic making the seal. some companies use hvac caulk.
don't just look at the top..feel around sides of duct & esp on bottom. this is where they usually miss sealing.

duct tapes & foil tapes don't last long in extreme attic
temps. thus the use of mastics. mastic should be thick..
nickel thick is what code says.

I use CCWI-181 paint on mastic...about $15 at hvac supply. the ONLY tape I use is Hardcast brand #1402
mastic tape. reflective plastic face with red writing, gray mastic backing. thick & strong. 3" wide by 100' long about $25 per roll and worth every penny.
this is the only tape I've found that seals metal to metal,
metal to wood, sheetrock paper, foam board, plastic etc.
as always surfaces have to be clean & dry. tape is pressed down to make a good seal. my hvac supply house usually gives me a small credit card sized squeege that works well to seal the mastic tape.

see attached. this is a supply box sealed from inside the house with hardcast 1402. trace lightly around grill,
remove making note of which way the grill was installed.
cut lenghts of hardcast widthwise making width 1.5" wide
place tape on sheetrock...staying within lines where grill will cover it. fold the tape into the supply box & seal it to
the metal flange. it won't stick to insulation in the box. but will seal well to metal & sheetrock. press to seal, then take a small piece to re-inforce corners.
re-install grill.
do same at sheetrock cuts at bath fans, housing of recessed lights to sheetrock covered by trim piece.

this will make the air seal between living & attic space.
these are the leaks I find blower door testing.
the methods of sealing are ones I've come up with
in my years in the business. I test before & once work
is completed. some house I re-test years later.
so these seals last. unlike foams, duct tapes etc.

best of luck.