Failed Your Blower Door Test? The 10 Leak Points to Check First in New Orleans Homes

A high blower door result feels like a report card. It is closer to a map. The fan has told you that a certain volume of air moves through your envelope under pressure; it has not told you where, and the where is the only part you can act on.

Local construction narrows the search considerably. The housing stock here has a small number of recurring air paths built into how the houses were put together, and most of them are nowhere near a window. Here is the list, in the order that usually returns the most improvement per dollar, with the reasoning behind the order.

First, check whether you actually failed

Before you spend anything, confirm which standard you were measured against.

As adopted in this state, the maximum air leakage rate for any building or dwelling unit under any compliance path shall not exceed 7.0 air changes per hour, or 0.28 cubic feet per minute per square foot of dwelling unit enclosure area.

Read the “or” carefully, because it is doing real work. Those are two ways of expressing the same limit, and a dwelling assessed on the cfm per square foot basis can satisfy the code without anyone quoting an ACH50 figure at all. 7.0 ACH50 is not a universal ceiling every building has to clear. It is the limit as expressed in air changes per hour.

The base 2021 IECC that most national articles quote sets 5.0 ACH50 for climate zones 1 and 2, and Louisiana did not adopt that figure. A house that “fails” against 5.0 may pass here.

There is a further alternative for smaller and attached homes. An air leakage rate not exceeding 0.30 cubic feet per minute per square foot of enclosure area is permitted for attached single and multiple family dwelling units and for buildings 1,500 square feet or smaller. ACH50 divides by internal volume, which is unkind to compact houses, so a shotgun single can post a poor ACH50 while its actual air sealing is fine. Ask your rater which basis your house was assessed on, and ask for the cfm per square foot figure as well as the ACH50. A house that looks like a failure on one measure may not be one on the other. The ACH50 guide works through both.

If you genuinely are over the line, keep reading.

The ceiling plane and the floor plane do the work

There is a reason the list below is weighted the way it is. Air generally enters a house low and leaves it high, because warm air is buoyant and rising air has to be replaced from somewhere. The Department of Energy puts it plainly: air tends to enter through leaks in the floor and leave through leaks in the ceiling.

In a New Orleans house with an open crawl space underneath and a hot attic above, that puts the top and bottom surfaces of your envelope ahead of the sides, which is not where most instincts point.

One local caveat belongs here. That buoyancy description assumes the inside of the house is the warmer side, which in Louisiana is a winter condition. Run the air conditioning in August and the pressure pattern reverses, and drivers such as duct leakage and exhaust fans start to matter more than buoyancy does. Either way the ceiling and floor planes are the surfaces worth attacking first. The seasonal detail is in our guide to the stack effect in New Orleans homes.

The ten leak points, in order

1. The attic hatch or pull-down stairs

A framed hole in the ceiling plane, usually with a thin panel over it, sitting at the highest point of the house where the pressure difference is greatest. It is also the cheapest thing on this list to fix properly, which is why it goes first.

2. Dropped soffits and boxed-in ceilings

The bulkhead above kitchen cabinets, the boxed ceiling in a bathroom, the framed-down section hiding a duct run. These are open to the attic more often than not, and what looks like a finished ceiling from below is frequently an open-topped box from above.

3. Chases for plumbing stacks, flues and wiring

A vertical shaft running from the crawl space to the attic through the middle of the house. It connects the two leakiest surfaces you have with a clear path, and because it is hidden in the wall you will never find it from inside the room.

4. Recessed lighting and ceiling penetrations

Every can light, bath fan, ceiling fan box and sprinkler head is a hole in the air barrier at the top of the house. Older recessed fixtures that are not rated for insulation contact are the worst of them, because they are designed to vent heat upward.

5. The rim or band joist

On a raised pier and beam house the band joist is a continuous perimeter gap at the floor line, frequently uninsulated and rarely sealed. It is one of the highest-value targets in this housing stock because it runs around the entire footprint.

6. Penetrations through the subfloor

Supply and drain lines, gas lines, wiring and HVAC boots all pass through the floor deck. In a house on open piers the crawl space air is outdoor air, so every one of those holes is a direct connection to outside. USDA Forest Products Laboratory and LSU AgCenter monitoring of twelve Louisiana homes found that air temperature in open crawl spaces tracked outdoor temperature closely and crawl space water vapour pressure was essentially the same as outdoors.

7. Balloon-framed wall cavities

In older local homes the wall cavity can run uninterrupted from the crawl space to the attic with no fire blocking, which makes the wall itself behave like a chimney. Insulating the attic floor over an open balloon-framed wall does very little, because the air path goes around the insulation.

8. Attic knee walls

In storey and a half houses, a knee wall is a vertical surface facing straight into an unconditioned attic. They are commonly insulated with batts and no air barrier on the attic side, which leaves the insulation sitting in moving air and performing far below its label.

9. The chimney or flue enclosure

The framed shaft around a flue is required to have clearance to combustibles, so it is a deliberate gap at the top of the house. It has to be sealed with the right material rather than expanding foam, and that detail matters.

10. The duct system

Ducts are not technically part of the envelope, but in a house with the air handler and ductwork in an unconditioned attic they behave like it. Leaky boots, disconnected branches and an unsealed plenum will all show up while the fan is running. Louisiana also has a local rule here worth knowing: in climate zone 2A, supply and return ductwork must not be buried in insulation.

Where windows and doors actually sit

Somewhere below all ten. The Department of Energy frames it this way: leaks around windows and doors are the most obvious ones, and there are often many smaller and less detectable gaps elsewhere. Weatherstripping a door is visible, satisfying and worth doing. It is rarely the highest-value thing to do first, and a technician who starts there has not looked hard enough.

The order of operations that works

1. Test with the fan running and find the leaks. A number without a leak inventory tells you that you have a problem without telling you where it is.
2. Seal the large bypasses first. Chases, dropped soffits, the attic hatch and the band joist move far more air than a window gap.
3. Establish one continuous air barrier. An air barrier with a hole in it performs like the hole. This is where spray foam often does two jobs at once, forming the air barrier and the thermal layer in one application.
4. Then insulate. Fibrous insulation slows heat but does not stop air, which is why attic insulation laid over a leaky ceiling underperforms.
5. Retest. The second number is the only evidence the work landed.

One thing to settle before you tighten the house

Louisiana wrote a trigger into the code. Where a blower door test is performed and the air infiltration rate comes in under 3 air changes per hour, the dwelling must be provided with whole-house mechanical ventilation in accordance with Section M1507.3.

Spray foam is entirely capable of taking a house past that line. If tightening is the plan, the ventilation design belongs in the same conversation rather than in a phone call three months later. Combustion appliances need the same forethought, because a tighter house changes how a water heater or furnace draws air. Our guide to Louisiana’s blower door code requirements covers the rule and who it applies to.

Ask for the diagnostic, not just the number

A compliance test ends when the number is recorded. A diagnostic test keeps the fan running while the house is walked under pressure, so the air paths announce themselves. Those are different purchases, and the second one is the one that produces the list above for your specific house.

So when you book, say which you want. Ask whether the fan stays running, whether you get photographs, and whether the report names locations rather than just a figure. The order above is a sensible place to start looking because it reflects how this housing stock is built. What the fan finds in your house may reorder it, which is the entire point of testing rather than guessing.

If you want the leak inventory before committing to any work, that is what blower door testing and a full energy audit are for. If the fix is likely to involve foam, the choice between types is set out in open cell versus closed cell insulation.

Frequently asked questions

Find out where your house is leaking

Star Spray Foam is based in New Orleans at the address below. Ask whether your address is inside the working area when you call. If your number came back high and you want a leak inventory rather than another opinion, get in touch and ask what a diagnostic visit on your house would involve.

Star Spray Foam
5826 Louis XIV St, New Orleans, LA 70124
504-229-6500

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