I was planning on having ceiling drywall hung, attend to airsealing on the attic side and then insulating the attic (blown in cellulose). Then hiring a blower door test & noting problems during the test. Fix problems after the test. Then insulate walls (cellulose) and finally wall drywall.

I did a little investigating for hiring a blower door test from the local HVAC company and was surprised that the guy recommended doing the test AFTER the house was all finished (drywalled) - as that is what is 'normally done'. In listening to him describe his background and process it seemed to me that:
- the BDT is done as part of code compliance, not really for performance-fixing during construction
- they don't typically do a BDT with smoke pencils and use a thermal image instead (but I won't have heat before drywall as we're using mini split HP systems)

The cost wasn't all that much, but I think he and I were not on the same wavelength for what we wanted to do during the test and I don't want to waste my money. I could rig up a DIY pressure test, but it would take some time... Also, I'm getting some strange looks from the drywall supplier when I asked about TWO deliveries, one for the ceiling, and later for the walls. My understanding is that ceiling drywall (and mud??) and attic insulation is a must before doing any pressure testing.

I've been sweating over the air sealing for some weeks and months now as dear hubby worked PT on the electrical and plumbing rough-ins. I've really gotten into the air sealing thing and was was thinking, "Yeah, do the BDT and really put the fine point on all your work. Make sure you got it right." But in reflecting on the issues (listed above) with hiring out the BDT or DIY test and the gyrations for the drywall (and mud?) ... I'm also saying, "Enough already. You've air sealed with more detail and effort than anyone in the county. Call it quits and move on. No testing."

So as if the two voices in my head weren't enough,  ;-)  I'm asking for any input you might want to add.

Thanks All!

I wish we had done one before the drywall, while it wouldn't have been done for rating it would have caught some small things that I can't fix without major remodeling. Granted they are small and we still have a great BD test, but the small leaks we have now are the only place we notice when it is really windy out, like a nice 30 mph wind out of the north with our house having an open face to a field to the north. But for rating it has to be when it is all done. To me its like building a boat and not checking it as you go, then throw it in the water and rate how much water leaks in. Why not find that before hand and get it as close as you can to start with.

I like Brock's analogy to building a boat, and then throwing it in the water to see how much it leaks!

I like the idea of a blower door test when something can be done about the leaks. The trick seems to be sealing off the attic space (assuming a vented attic) with sheetrock while the walls are still open. I stole the idea for a blower window test from the excellent site http://www.nlcpr.com/Pressuretesting.php and purchased similar hardware, except with a higher capacity fan. However, this was for testing after construction was complete. Havng your own fan allows you to do the sealing at your own pace, but then you've got a leftover fan to store somewhere.

Even doing the BDT after it's too late to do anything can be useful, in the case of a superinsulated and very tight house. For that scenario, knowing the heat load with a good number in the model for air leakage may mean the difference between two different size heating systems, particularly for heat pumps. I know it did for my situation, where the final BDT numbers confirmed the choice of a two-ton GSHP. I had thought I might just be into a three-ton unit if the tightness wasn't what I had hoped to achieve.

Run your heat loss model for different reasonable values of air leakage, to see if the BDT result might influence selection of heating system. If not, then maybe the BDT after the fact isn't useful.

No brainer alert! You are not trying to pass code. You are trying to make your house have the lowest possible utility bills and utmost comfort for the next 50 years. You should not strive for the lowest quality home that can pass code that is what crummy contractors do. This is unacceptable behavior for the tester or any contractor that lives by this motto. Quality product requires the testing period.
You are in the dark if you do not do the test. It is easy to find and fix problems before insulating and dry walling. It is often not possible to fix sealing issues after drywall economically. ACH 50 below 1 is easy if you are meticulous and careful. If you do not do the test, it is likely you will not make it there. You are determining the level of your utility payments for the next 50 years. Do the tests, find the issues, fix the issues, do the tests, find the issues, fix the issues until it passes. I always find something that gets fixed. Some employee or subcontractor always misses something. All my homes end up in the ACH 50 .3 to .5 because I care and double and triple check all sealing. Do the testing and fixing or you will have a subpar home.

Brian, 30 years of net-zero house experience.

Attic insulation isn't necessary, in fact it's better without it so you can attend to any attic misses. We will take one drywall delivery and make the rockers stack sheets against interior walls only so we can get at exterior walls.

As long as the fan can keep up you can test without the ceiling taped because it's a known leak, you obviously want to find the unknown leaks. Its not as much about the CFM at this point as it is about finding infiltration.

I've decided to attempt the DIY path with a fan only - no measuring equipment - to keep it simpler & to just get it done. As per GreenTree's info, I'll not bring in the mudders for the ceiling. I have 1600 sq ft 1st floor with full basement, 600 sq ft 2nd floor and 8' ceilings throughout. I will likely not be able to seal off basement for the test (and haven't attend to airsealing down there yet) - so I guess one BIG fan is in order ... or maybe two or three smaller ones.

I think getting a highered-out BDT after drywall is up and mudded would be good for HVAC reasons to compare with the assumptions used in my heat load calc and I would be willing to pay the fee for that reason.

Pardon my ignorance here GreenTree - but a few follow up questions if you have time. Does this sound like a reasonable sequence?
- deliver ceiling drywall
- hanger sub puts up ceiling drywall, no mud
- DIY pressure test for unknown leaks anywhere in the envelope and fix them, repeat until satisfied
- insulation sub blows attic and damp blows walls (no one in my area does dense pack & I couldn't find adequate rental equip)
- insulatinon inspection (required)
- hanger sub back to do that walls
- mudder subs come in after that ... and I'm on the home stretch to CO!!!!!

I am leaning toward paying the extra $ for the two drywall deliveries (ceiling and then later, walls) although I can see a Pro builder would not do it this way. I think it might make working on site easier - there is no way I can move those sheets alone if I need to access an area behind them. I'll see what the extra $ is, and then make a final decision.

But otherwise - does the sequence above sound correct? This is a change from what I had been thinking, like splitting the insulation task ... which I now see was silly so I just want to double check my 'dance of the subcontrators' here before I turn on the music.

Thanks so much for the help everyone. Really useful stuff here!

Posted By Brock on 27 Feb 2012 02:59 PM
I wish we had done one before the drywall, ... it would have caught some small things that I can't fix without major remodeling. Granted they are small ... but the small leaks we have now are the only place we notice when it is really windy out

Brock, we get stiff winds from the N and NW also. It sweeps across huge open farm fields and our planned wind break is yrs away from being useful. I put the garage on the NW corner of the house, so that should help, but still, when it's windy.... it really is.

Just out of curiosity, I was wondering what were some of the small leaks in your situation?

Thanks for sharing your experiences.

You're right, they're wrong. I've also found that it's necessary to say to some of these guys that THAT is the way you want it done, regardless of what they've done in the past. They'll learn eventually but who wants to wait for that to happen?

You need to have the ceiling drywall taped, otherwise you'll be pulling air from the attic.

Stand your ground. You won't regret it.

Here's the payoff - just talked to the owners of the house I recently finished in NH- their electric bill for the house - 1500 SF ranch with 1400 SF heated walk out lower level - $167 for Dec 15-Jan15. Includes plug loads, lights, hot water and heat.

The leak that annoys me the most and is well within spec is from the bathroom exhaust fan. The kids bathroom is the in the northwest corner of the house. I had initially thought the air leak was the exhaust itself, but even completely blocking off the exterior and interior the wall behind the shower still gets really cold, the exhaust is just above the shower, so I think air is leaking in around that. If I don't block off that exhaust (I know, I know) when it's windy the bathroom is freezing in winter and its not the HVAC. This is the only place on the winward side of the house for air to leak in, so it does. I don't have a good solution yet other than taping off the exhaust in fall and venting the bathroom with a fan, the HRV keeps the humidity in the home in check. Fortunately the bathroom has two entrances at each end being a jack and Jill from the kids rooms so it's easy to vent out with a fan.

Babybldr,
Your sequence looks fine. I have the luxury of owning a blower door so I know when I reach a certain pressure,(I test for leaks at 30 Pa) and using that info plus a CFM50 reading I know where I'm at and where I need to be.

I would strongly recommend you rent, borrow, steal a blower door or get instrument capability to measure pressure. You are at the stage of a build that you cannot ever get back to, you really only have one chance to get to a buildings bones so now's the time. I rent myself by the hour to other contractors to run my door so they can air seal, perhaps you can find someone to do the same thing. By the time you buy a fan big enough to pull the kind of air a blower door does you could have paid someone to come in with a calibrated door.

Despite what others may tell you, you can check for air leakage with the ceiling only hung, not taped unless you have a huge footprint. We have done it many times and gotten the house up to a useful pressure. If the ceiling hang is a bit sloppy you may have to plug a few of the bigger gaps or wider seams to get the house up to a pressure that will exaggerate the leaks your looking for. Try to do your test with a decent temp. difference, the more the better. Before I had a thermal camera we used a wizard stick smoke device, it's like a kids toy that looks like a hippie smoke pipe but it's cheap and works ok.

I think the best tool is your hand, what you'll want to do is start the blower door or fan and create a controlled leak with a cracked (tiny bit) window or door and train your hand to what it feels like then you have a point of reference when you go probing around your house.

Hopefully this helps you somewhat.

Hi! I don't want to hi-jack the thread, but since I have similar question, I'll start here.

I've been reading about this blower door test, and not sure if anyone around my area does it, or if they only do it after the house is finished. Have not even begun to ask around.
I would like to do it for the purpose of sealing the envelope before drywall is all complete and walls are covered up.
Would this be the way to accomplish that?

1) All electrical, plumbing, etc. etc. is done. (Anything I don't want to miss for sure?)
2) Hang and tape the ceiling drywall - I have a drywaller willing to do that only, and come back for walls later.
3) Spray 1" of closed cell foam in the 2x6 walls, spray 2" closed cell foam on attic side of drywall.
4) Do blower door test for whole house, and seal leaks during the test. (DIY or hire?) The basement walls are ICF, the rim joist already has 2-3" of closed cell spray foam all around. Exterior walls have 1" R-board (no taped seams) insulation on exterior side of sheething with taped tyvek over it, and all exterior doors and windows are in, caulked, and insulated.

Am I missing something?

Thanks for any input!

BG

Boontucky-girl,

Blower door rental should be available for the same cost as the testing. That way you have it for a few days to check, fix and recheck. They are not difficult to run. If your contractors are not used to being checked you will be surprized how many little leaks you will find.

Most foam installers will not guaranty seal with less than 2 inches of foam. I normally spray caulk all seals 2 by to sheeting. I have known of cases where the foam pulled back from the studs and when the wood drys and shrintks you will get a small gap. The caulk eliminates that future issue cheaply. Also all your cut outs for electrical, plumbing and vents will need to be sealed.

Brian

Thanks Zehboss.

What do you mean by contractors not being used to being checked? You mean since nobody checks, there will be more leaks vs. a contractor that has experienced a leak check with a test? What is spray caulk? The wood drying and shrinking, is that in new construction, or do you mean that happens in all houses because of seasonal changes?
I assumed that any cut outs will have to be sealed.

I was wondering if I should have the walls sprayed before running rough ins? Or having wiring does not get much in the way of the foam getting to the sheathing? I thought since wiring and plumbing have to run middle of the stud, it would be better?

Any thoughts? Thanks.

A recent survey of new homes found air exchanges of 3 to 7 on new construction that were not checked and guaranteed to be 1 or less ACH50 exchanges. Spray caulk is an elastomeric caulk bought in 5 gallon containers and sprayed with a paint sprayer. http://www.greenbuildingadvisor.com/blogs/dept/musings/air-sealing-sprayable-caulk or http://www.buildinggreen.com/live/index.cfm/2011/4/13/Sprayon-latex-sealants-A-new-tool-for-air-barriers you can also use sprayable chinking compounds for log cabins.

Wood always shrinks after construction. It then will absorb and expel water causing addition dimensional changes during its life. 20 years later there will be a gap between the stud and the sheeting of 1/64 to1/8th of an inch no matter what you do. Caulking those locations is the only way to maintain the seal.

Rough ins should be completed first. You should minimize the number that are in exterior walls.

Brian

You may want to consider having the walls sprayed first since you are just doing a flash coat, then do rough-ins. Depending on what's going in the walls they can create problems getting foam where you need it, it might be fine for a regular stud cavity but those tight tricky cavities are more effective when the foam installer has complete access without having to jump over wires and pipe. You'll get a better foam job doing it first. You probably dont have much going through the exterior wall, just some outlets and light wires and you can easily touch-up those penetrations.

Thanks for the replies.

Zehboss, about how much does it cost to do that spray caulking? Will it really assure that the air seal will be good for years? The wall setup that we want will be a lot more expensive than the normals fiberglass batt install around here, and it's be hard to come up with a ton more money extra.

I do think it may be better to spray before rough ins, so we'll see what the contractor thinks about that. I think for the most part it will be outlets in the walls, but will not be going to the outside, except for outdoor lights and outlets. I don't think there's any plumbing planned to go through the walls, and only the kitchen sink venting is against exterior wall.

Again, thanks for the comments and input.

BG

Boontucky-girl

The claim is that it will last for at least 50 years. It is a relatively easy and inexpensive thing to do if the cavities are still open. If you have a good paint sprayer you can do it yourself. You can also rent one for a weekend. It will only take a day to do the whole home with one person. You will need the right nozzle for the sprayer. The caulk cost will very but should be at most a few hundred. Count the number of 4x8 sheets on the outside of the house and divide by 32 for complete sealing. That will give you the number of 5 gallon pales you will need.

Sprayer fits into the bucket. Spray to a 1/4 inch minimum fill in the corners. Where eye and breathing protection during spraying. I assume all of this is on the training video on their site.

Run water through the system until it comes out clear for cleaning. I pump several extra gallons just to be sure. Also dismantle valve assembly to make sure it is cleaned out. Oil the seals, reassemble and fill with mineral oil. Not sure what a contractor will charge but at least you know what it involves. I just do this for clients because I build to performance. This is something a home owner can easily do.

Have fun.

Brian

Hi O.P. here,

We got our ceiling drywall installed and we rigged up a crude pressure test device of our own using industrial fans we already had and left over building materials (OSB, wiring, gaskets). No instrumentation, fans only. We did a quick power up test and were able to pressurize the house as a cracked window let out a strong stream of gushing air. It was a quick test at the end of a very long hard weekend of work and I didn't have the wizard stick on site yet to really test it all out. It's a crude setup but was cheap and quick. I have more air sealing to do and then next week end when my husband is back on site we'll run the 'blower door' and test for air leaks with the smoke stick. 

I was thinking we would want a positive pressure test (that is how we set up the fans) so that we could see the 'smoke' from the wizard stick get sucked out the crack - sorta' point you right to the location of the leak. But I see that commercial blow doors seem to be doing a negative pressure inside the house. We can easily flip the fans over to do a negative pressure test. One thing with the positive pressure is that in the room across from the fan it will be harder to see smoke trails due to the fan blowing in. But other than that, I'm just not sure what the advantages would be for negative pressue. This doesn't really apply in my case, but in a commercial BDT on an existing home, I'm really surprised they would use negative pressure as it would seem (to me) that it could suck dust, insulation bits, mold, etc into the building through the leaks one is trying to detect.

After I get done air sealing (and testing and sealing) and have insulation done, I plan to hire a guy I found to do a real BDT so I can use the data to make better informed decisions about house ventilation and heat/cooling loads. He didn't want to do the test until I had the ceiling drywall taped.

I have some other follow up questions on sealing the ceiling drywall but I'll put them in a separate post just to keep things organized.
Thanks for all your help and feel free to chime in on the follow-up post.  ;-)