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How to blower door test a new house before insulation and drywall

A client is working to make his tract-built house as air-tight as possible. Windows and doors will be installed this week, mechanicals are in progress and insulation will start near the end of this week. Drywall is hopeful for the week of 3/14. The builder doesn't typically meet his optimistic schedules but that's what it is right now.

Once windows and doors go in, and hopefully before insulation, my client wants to blower door test so he can seal as much as possible. This test is NOT to collect a number, just find the leakage and fix it. There's about 70 lf of eve (vented soffit) - I think that will be the biggest barrier to get good pressure on the house.

We need a quick and dirty way to block the soffits during the test. I'm thinking to roll scrap fiberglass in trash bags to stuff in the soffit. Is that a good idea or is there a better way? Other suggestions?

Thanks in advance!


  • I have tested 2 of these. Both have the entire air barrier in place. So that means you have to have a ceiling. Have them rock the ceiling and mud and tape. If they really want tight on the test and later caulk the joint between the rock and the top plate in each stud cavity. Run your test as depressurized and then turn the fan around and pressurize. They go looking for leaks in the attic. That is where leaks will probably be located. Check your sill plate leakage while depressurized. For your fun, run a multi-point, let the calculated ELA give you some guidance. When you do a second test then you can use the compare two test features of the software. That is some good learning and a neat submission for your report.
  • A couple more details (sorry about that). We know blower door will compete against the open ridge vent (and other roof details). I can't think of an easy way to solve that. We can use more than one blower door. We have Eco-Sealed the house (with some supplemental spray foam here and there) so the envelope itself should be pretty tight. I know from experience that pressure testing reveals significant missed leakage even when we've done a really thorough job sealing.

    We'll do more blower door guided air sealing through the rest of construction I'm just trying to find a way to get one done as early as possible while everything is accessible.

  • David ButlerDavid Butler Posts: 3,889
    Julie, I understand you're just try to create pressure to detect leakage paths you missed, not to quantify. However, I see a couple of issues with trying to do that before the ceilings go in. First, as you already realize, you have to temporarily seal the soffit and ridge vent, and all other roof penetrations. Otherwise it's going to be hard to get enough air movement through the much smaller leakage paths you're trying to find, to actually find them. Two blower doors? Maybe. I don't think stuffing bags full of scrap insulation in the soffits will do much to block the air. I think you'd have to cover them, as well as the ridge, with taped plastic or cardboard.

    Second, the ceiling itself is often where the worst leakage occurs. Seems like you'd wait until the ceiling is in so you can use the test to full advantage. If ceilings are flat, the ceiling drywall must go in before the insulators show up on site. If the ceilings are vaulted, you should be doing an unvented assembly, no?
  • At a certain point does anyone ask the cost of looking for all the air sealing vs the value of the changes found? If you're not paying for it that's one thing, if you are, finish the drywall first
  • Colin GengeColin Genge Posts: 124
    John, I agree that using leakage area measurements makes a lot more sense so air sealers know what size of holes they're looking for. But there is no need to spend time performing a multi-point test just to get leakage area. That would slow down the process. I believe you can measure square inches of leakage at 25 Pa on the DG-700 with one point, if not you can use the WiFi. They might call it EOLA as I recall. You can also measure leakage area measurement on the DM-2 or DM32 also where you want the EqLA, again with a one point test.

    I agree that attic floor bypasses are the biggest leaks making a pre-sheet rock test of little value. Most important is getting the attic floor sealed before the insulation.

    I have always thought we made a gross mistake with CFM 50 for results since we are really looking for holes and that should be how we present our results but that another story.
  • Stan KuhnStan Kuhn Posts: 170
    It's not practical to test, even just with smoke/fog, without a top on the living space. I would look for sealed wall sheathing, joints, top and bottom edges, all penetrations, window & door jambs, sill plates, "mud sill" & rim joist if there's a foundation. Maybe do a blower door when the ceiling (only) is in and properly air sealed, including the scuttle and all penetrations. But if you do great detailing you should get very good results.
  • Mark FurstMark Furst Posts: 203
    Seems like lots of extra work to seal off the roof venting, work that could be put into detailing the shell to make it tighter. If you can frame up a house with the mindset of sealing as you go you can make a shell very tight, with details such as gluing sheathing to framing, making sure joints are backed up and don't line joints up with exterior foam board joints.

    If the framers have built with air tightness in mind then there should only be very small openings left to seal, which are hard to find if you have a conventional attic and can't get the soffits/ridge VERY well sealed up - something that's hard to do with fiberglass - otherwise the air takes the "easy" path and doesn't show those small leaks.

    In my experience the only time doing a pre drywall BD test has been useful has been in a house where everything is going to be inside (i.e. a conditioned attic / hot roof situation).
  • Hey Julie, what about DuctMask register sealing tape? A 200'x8" roll is less than $50 which should be enough to cover your 70' of soffits. It may even get enough grip to cover the ridge vent from the exterior with the negative pressure from the blower door. The points raised here are valid in that the test won't be conclusive, but if you're just chasing air and have no control over the general construction schedule I can see the value of the test that you've proposed.
  • If the insulation will be fiberglass, and the thermal boundary is the walls and ceiling of the home, I am wondering why we would be this concerned about chasing down these minor leakage areas. I believe the most cost effective method, which would also net the best results in aligning the thermal and pressure boundaries, would be to caulk all of your Sheetrock seams. If this is something that must be accomplished, depending on footage, I would imagine running 2 blower doors and spending quite a bit of time sealing those high vent points is in order.
  • Thank you all! To clarify - this is more of a science experiment than anything "cost effective" or to be used as future method. We have thoroughly sealed this home but skipped over some points we THINK are "past the point of diminishing returns" or "I can't see how this would leak here". We (the homeowner and I) are jointly curious to know how correct our thoughts are (he's a super-savvy homeowner, speaks in ACH50). If we think we can spend a few manhours and cheap material to get enough pressure on the house to check some specific areas before the walls are drywalled, we'll do it. I know temp-blocking the ridge vent isn't in the cards. We definitely plan to seal the attic plane after ceiling drywall. We still hold out hope that we'll be able to "sneak in" a BD test after the ceiling is hung but before the walls but the moon and stars aren't likely to align.
  • Update: windows were still missing before drywall was hung...so any way we tried it would have been too much effort for a curiosity-based test.

    Drywall is all hung now (windows all installed) and finishing is in progress. We're headed back to the project today for our first BD test and really excited to see the results.

    We're also going to seal the attic plane while we're there, BD testing before (during) and after.
  • First blower door test: What's not done: trim, permanent doors, plumbing/electrical fixtures, flooring, big garage door. Prior to sealing the attic plane, we made a temporary attic access panel and tested at 4 ACH50. We sealed all can lights (25 of them), duct boots (yes, ducts in the attic), exhaust fans and light boxes. (also a bit of rim joist formerly "on hold" Then we pressurized to feel the tops of walls.

    We found very, very little leakage at the tops of exterior walls. This was exciting - we used Knauf Eco-Seal + (gasket technology) but we scraped it back pretty much (didn't want to piss off the drywallers). Still, these were the tightest tops of exterior walls I've ever seen (felt) with no attic plane sealing.

    Tops of interior walls were good and leaky.

    We retested and were about 2.5 ACH50.

    Last night we sealed the tops of interior walls, fixed up some thermal issues in the attic and tested out at 2 ACH50.

    We'll revisit again once finishes are complete.
  • David ButlerDavid Butler Posts: 3,889
    @Julie, always great to see the results of type of step-wise testing!

    I'd like to share this with a client who just started framing. He's a retired NASA engineer who, like your client, is savvy and motivated. But his site is in a rural area and the best builder he could find had never air sealed a house before. They agreed to tackle it together as a learning experience.

    In situations like this I refer clients to the the Energy Star Thermal Enclosure System (TES) guide, but I think your report will inspire him. Would you mind briefly describing your air sealing work prior to the first test?
  • I'd be happy to share, what is the time frame?
  • David ButlerDavid Butler Posts: 3,889
    Just post a brief overview of the main points (e.g., caulked bottom plates, eco-sealed OSB joints, etc.). Not anything detailed. As for time frame... whenever you're moved to do it. The basement walls are up and floor trusses were installed end of last week.
  • Brad CookBrad Cook Posts: 153
    I strongly encourage abandoning the use of interior access to an attic. It is so much better to install a gable end vent (or two) and use that as the attic access. Interior access hatches are too difficult to really seal tight and maintain that tightness, never mind the extra work and difficulty of properly insulating the hatch.
  • A blower door test is not the test you need to be doing for this application. As said, the numbers don't matter. You're just trying to depressurized or pressurize the house with a blower door.

    You do not need a significant pressure such as 50 Pascal or 25 Pascal for HVAC duct. All you need to do is overcome the stack effect pressures and wind pressures of the building at the time of the test. Utilizing a thermal imaging camera will identify all leaks in the building, you just determine which ones should be there and those that should not be.

    Doing this in the evening after a hot sunny day or after you have the HVAC hooked up with the heat going, pull outdoor air in when there is a sufficient temperature differential for the type of thermal equipment you're using.

    You have to be efficient in doing this as you can't keep the blower door running too fast for too long or you will pull out or blowout all the heated air in the house at short order. However insulation is supposed to retain
  • However insulation is supposed to retain heat transfer so any cold air blowing through insulation (or vice a versa for summer) should be readily apparent. Follow up with a smoke test it suspected anomalies to ensure they are not conductive losses instead of convective losses.
  • Just remember Air Tight Building Envelopes develop toxicity exponentially. Are you installing an indoor air scrubber? Note this is not the same as an Air2Air heat exchanger. Remember an environmentally friendly healthy living and working enclosure is what any building structure is all about
  • Curt KinderCurt Kinder Posts: 248
    We test all our custom builder homes pre drywall. That way we know the properly sized HVAC system we have proposed stands a much better chance of meeting the load with comfort and efficiency.

    Our typical project has either ICF walls and a spray foamed attic, or a spray foamed attic atop stick frame walls. In those cases I ask to test before fiberglass batts go up, obscuring wall leaks. We are working our way through one, a big one, 9400 SF heated, where we ar still over 1000 CFM 50 despite tightening foam.

    Tomorrow we'll smoke it.