Hello Pros!

I had a very nice chat with a client the other day.

He and his wife have dealt with a "too hot upper story" (in their 1970s split-level) for 20 years.

They have sufficient attic insulation (about 12-14"), a partial air barrier at the attic floor, and ducts in the attic wrapped to R-4 (but not sealed).

They know their options for improving comfort in the summer (i.e. seal the ducts, boost the insulation level of the ducts, install a radiant barrier, achieve better attic ventilation).

Our conversation has led me to question some assumptions I have formed over the past few years.

I am hoping that y'all can weigh in (as objectively as possible) on the following remedies (keeping in mind that improving the level of attic ventilation, at ridge and soffits, is implied):

1. Remove the existing duct wrap insulation. Seal the ducts with mastic, re-wrap the ducts in FSK foil-faced duct wrap, and blow cellulose on top of the ducts.

2. Aeroseal the ducts throughout the house ONLY.

3. Install a high-quality radiant barrier in the attic.

Cost may not be a deal-breaker, but a solution will HAVE to be provided for the expense.

Thanks in advance!

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Hi Patrick,

Give us a big city so we will know what climate zone you are dealing with, summer and or winter heat.  A few years back I worked with a home owner who had over 3' of attic insulation, but his problems hadn't changed.  The bad news for him was he had not addressed any air sealing underneath that ocean of blown in fiberglass. 

If we go back to basics with your client and do at least a rough energy assessment to better understand where the problem is.  Once you have an idea as to how the house is performing, then you look at the mechanicals, heating system and cooling.

What else do you know about the house?Bud


Washington D.C. area.

Blower door: 3,300 CFM50.

2,200 square feet conditioned.

Leakage at all normal culprits (top plates, rim\band joists, doors & access panels).

Decent mechanicals, but not enough distribution capacity for AC unit. 4-ton, 15 SEER.

No real complaints about heating in the winter. 93 AFUE, direct-vent, 2-stage.

Original single-pane, wood windows with storm units.

Hottest rooms are on the 2nd floor, facing South (go figure).

Homeowner has talked with a neighbor who had similar issues. Aeroseal seems to have solved his problems. HO thinks radiative heat gain is ultimately to blame for his discomfort issues.

HO has even considered triple-pane windows.

Again, HO is interested in solutions, and I am confident that y'all can provide valuable input towards solutions.


In addition to what has been mentioned...

What is the roofing, and how old?

A radiant barrier installation under the rafters might make some improvement. I would not bank on additional attic venting. 

Presumably all the glass is clear, no low-e. Might be worth considering replacing some of the storm glass with low-SHGC IGUs, if you can find a sash/glass shop that can retrofit the existing frames. Or, look into the 4th surface low-e coatings like Cardinal i89 for the storms.

With hot weather here, you should do an IR inspection and see where the heat is coming from. 

Asphalt shingles, about 10 years old. Dark color.

Thanks for the advice on low-E coatings.

I will return to do IR inspection when the temps are higher.

Replacing all windows in a house is one expensive upgrade. If they can't commit to the cost you may want to suggest dual reflective window film. It's is a cost effective retrofit that will save the home owner on their energy bill. 

You didn't mention what color the roof shingles are. Going with a light colored roofing material could be the solution for them.

These HOs in my area are very concerned with what the Jones' think, so lighter colored shingles may be a tough sell. Se la vie.

Decent mechanicals, but not enough distribution capacity for AC unit. 4-ton, 15 SEER.

I think you nailed it right there. Airflow is everything and that's where your customer is missing it for comfort. 4 tons is nuts for that far North, it's not like they are getting it delivered anyways. Having 2 small systems 1.5ton/50k furnace would be the solution. Yes it's an expensive solution, but it will fix their comfort problems once and for all in addition to dramatically lowering their utility bills. Even with 2 basic 80% furnaces and 13SEER AC units will lower their overall utility bills.

I have my HVAC expert heading out there soon.

I'll follow up.

Living in Ontario, I also had excessive roof space heat radiation into the 2nd floor living space in the summer.  20 yr old home asphalt shingles well insulated and roof vents to code, but our home is situated below a large hill which in the summer inhibits air passage across the roof line.

Solved by self-installing (2) 14” manual air turbines for under $200

You listed 3300 CFM50 - air seal the ceiling to attic plane, install proper soffit vents ( rafter to rafter to above the insulation and sealed down to the outside of the top plate).and get your insulation and up to Code or better. . 

Do #1, make sure ducts and insulation cover are sealed.

Maybe do #2 but costly and any leakage is inside the envelope.  You should have plenty of AC service out of a 4 ton unit, check balancing and see about more flow to Hot area.

Skip #3, insulation and air sealing give better results for dollars spent and they work year round..  Check out DOE and other sites opinion of radiant barrier used anyplace other than AZ or NM.


Could you have them make a simple two line graph of the outside temperature, noting sun/clouds,  their comfort in the rooms, vs the time of day.  Home much of this is heat soak from the ceiling, or through the walls.  Give them a cheap ($30) point and shoot IR thermometer to take measurements.  (It will also let them confirm what you later implement is working for them, put your logo on it and encourage them to show the results to friends -- help drive new business...  ).

Radiant barriers are marginal,  they take the same amount of work as bringing the insulation in the attic up to 49+  Is the attic insulation fiberglass "filters", cellulose, denim matts, aircrete? 

If the neighbor had leaking ducts and this is the similar house made perhaps by same developer --- seal the ducts -- it sounds like you have the proof sitting next door.  You could look at using Aeroseal -- leave the insulation on the ducts.

IR themometer will let HO become more involved - they may discover that the source of the heat is from the outside wall plates - where there isn't enough insulation.  They may spot air leaks that would be easy to confirm with thermo-camera,  duct and blower door testing.  They might even discover the south wall is the source of the heat gain...  the chart would show when the heat soaks through the wall.  The cheap IR thermometer would let them see is the heat from above, side walls, or is it just the stack effect with all the heat from first floor moving up.  They can visualize the problem in understand the benefits of improvements you suggest.

On my house -- I've added quite a bit of data logging and measurement capturing.  I have been running a multi-year experiment on it and -- the heat gain/loss on those outside ceiling/wall areas can be killers.  Not just air leaks.  The insulation is often the thinnest or non-existent.  The heat can soak in along the ceiling and create a two foot wide radiant heat  source along the south, southwest walls.  That heat takes time to warm up the mass and soak into the house.  You'd see a delay of a hour or more when you compare it to the outside temps.  but once it soaks in -- it takes longer to radiate out...   I see a 10-15 degree hotter along the outside ceiling, in the areas that I have choose to not fix the top plate (as my test areas).  Winter time its 5-10 cooler under those ceiling areas.  And drafty.    And yes - this summer I an going to end the experiment and data collection and fix these areas.

A radiant barrier  generally doesn't fix the top plate related problems...  Lots more insulation at the outside edges makes a difference...

So where is the heat really coming from...  need to discover that first....


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