Does the blower door test result conflict with contractor recommendations?
My house is all electric except for a propane cooktop. I had a energy audit done last week. Although I don’t have a proposal yet, closed cell insulation at the rim joists (fiberglass batts are there now), venting bathroom exhaust fans to the outside, and adding to the blown insulation in the ceiling (plus installing baffles) will probably be included. The attic area above the bedroom level of the house is not accessible now, so a hatch would need to be cut in a closet ceiling. My reading suggests this is a fairly typical approach. However, the blower door test gave a reading of 1145 CFM, which apparently suggests that the house is very tight. What would be the best approach?
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I'm not sure what the question is, but, how many square feet is the house and what is the average ceiling height? No need to be exact, round numbers are OK.
Sounds like a job for Rem-Rate Man.
Carol,
If your house (including the basement) measures 3,000 s.f. and has 8 ft. ceilings, your air leakage rate is 2.8 ach50. If it measures 2,000 s.f., your air leakage rate is 4.3 ach50.
Neither value would be "very tight."
The house measures about 2290 s.f. without the basement, 3060 s.f. including the basement. The average ceiling height is 7'7". The auditor is the one who said it's "very tight, almost too tight." An audit done 4 years ago by a different auditor gave a blower door reading of 945 cfm and that auditor said the same thing. The current auditor will bring his proposal this week to go over, along with the infrared camera. I'm just trying to figure out what is really needed. Rem-Rate Man? Please explain.
Carol,
Your building volume is 23,195 cubic feet, and your air leakage rate is 3.0 ach50. That's not too tight.
You can put one of your bathroom exhaust fans on a timer if you want, in order to provide some mechanical ventilation for your house. Here is some more information on ventilation system:
Designing a Good Ventilation System.
Very interesting. One of the bathrooms is rarely used. The other is used for speedy showers, so I'm not sure venting that fan to the outside matters. I'm also concerned about heat escaping from the vent. I'd like to figure out if the insulation projects I mentioned will be worthwhile. I'm surprised at the difference of opinion regarding the blower door readings, so now I'm more confused than before.
From the original post, none of the work scope--rim joist foam, bath fan ducts, and attic insulation--really has much to do with air leakage. Foaming the rim joist might reduce leakage a little bit. I agree with Martin that at 3 ACH50 the house is not all that tight.
You could put a bath fan on a timer if there are any signs of excess humidity, and while it takes an experienced eye to find all such signs, you would usually know if there are problems--fog on the insides of the windows, small areas of mildew growing on drywall on exterior walls, etc. It really depends on climate, how many occupants, building construction details, etc.
I would go ahead and add as much insulation as you can, and the auditor should also have talked about air-sealing your attic floor before blowing in more. Having access to any attic is smart and usually code-required, as far as I know. I also don't know why he didn't have his IR cam when he did the blower door test, that seems odd to me. Maybe he ran out of time or other conditions were not right.
Carol,
I think your planned work is fine, and your worries are unnecessary.
As David mentioned, the only thing you might ask the contractor about is whether the insulation contractor will perform any air sealing work in the attic before adding insulation. Air sealing is a good idea -- don't be afraid of making your house more airtight.
Whether a house is "tight" or not isn't really a matter of interpretation. BPI auditors are taught to use .35 ACHn (air changes under natural conditions) as the standard, meaning the house should have .35 air-changes per hour at natural infiltration rates (as opposed to with the blower door running). If the house has less, then the rule is to make up the difference with mechanical ventilation.
You use the blower door number to calculate ACHn. As a REALLY rough rule of thumb, you can take ACH50 and divide by 20. So, your 3 ACH50 would roughly equate with .15 ACHn, which is why the auditors are saying your house is really tight. But as these things go, many houses are tighter, sometimes a lot tighter. Folks here on the GBA forums are used to talking about houses in the 1-2 ACH50 range, sometimes lower, so 3 ACH50 is not seen as all that tight. I am starting to see new construction in the 2 ACH50 range as builders learn the details.
What matters in your house is what is happening right now. If you are the only occupant and you are not causing humidity problems, then there are not humidity problems. If you do not have a natural-draft water heater or furnace or any other CO hazard aside from the cooktop, then I would not be concerned about combustion issues.
This could all change, Maybe you have five adult kids and they all move back home. Maybe you install a gas water heater or boiler. Maybe you sell the house to someone who does things like that, so the occupant load and the combustion zone issues are much greater. Under those circumstances the house could need a lot more ventilation as well as modifications to provide combustion air.
One more thing. Venting the bath fan to the outside does matter. It's not about venting the house, it's about not dumping moisture into the attic. You can end up with a lot of mildew on the bottom of the roof deck if you let the attic get humid. That's one reason for air-sealing the attic floor, to keep house humidity out of there.
If you want to go all-out on the bath fan ducts, you can install an inline damper in the duct, or a high-quality wall cap at the end of the duct. I am a big fan of Seiho wall caps. During a blower door test they do a LOT better than the plastic crap from the hardware store. They cost me about $45. They will help prevent cold air from migrating in, and warm air from leaking out. The backdraft dampers that are built into bath fans are barely functional IMO, even the good Panasonic models.
I don't know how much closed cell insulation the auditor will recommend for the basement, but I wonder if I caulk the gaps and install 2" rigid insulated foam, I might be able to do it myself a little at a time.
This house was built 40 years ago, so maybe the code regarding attic access was different then. I was disappointed, too, that he said he didn't have his IR camera at the time of the audit, but doubt that he ran out of time, since he didn't know I had all electric until he arrived. I imagine this audit took less time than is typical. The indoor temp. was around 68 and the outdoor temp. was around 30.
The original blown cellulose insulation in the attic supposedly was R-50, but when he examined the area open from the garage wall, he said it's only about 6" deep. No way to know if it has always been that way. I've wondered if building up that wall to the roof and adding an access panel in it would be helpful to retain heat and he said he didn't think so. I also wonder about the blown insulation settling in the exterior wall stud spaces, but his comments about removing the siding to add more are problematic. The siding is in 4' x 8' 3/4" plywood panels (texture 1-11). That is not a likely project.
I really appreciate your comments and suggestions.
You're saying the garage is open to the attic? I don't know that it's much of an energy issue, but I would want the garage completely separated from the living space, in terms of air exchange. As unlikely as it might seem, a fuel leak from a parked car could put a lot of fumes in the house, and there are significant fire hazards too. There should be a complete drywall barrier floor to ceiling, and the passage door should be fire-rated and weatherstripped. Any mechanical penetrations need to be treated per fire code.
Insulation settling in walls, or blown incompletely, is an issue. IR is great for inspecting that, so if he is supposed to do an IR inspection I would make he looks carefully at all exterior walls and ceilings. More can be added through drilled holes from inside (preferable to me) or outside. Yes it does some damage that you have to repair. 6" of cellulose in the attic could be augmented to 18".
Going back to the ventilation requirements, I want to make sure that I am not being too casual here. The governing body for this stuff is ASHRAE. They have a number of published standards that apply to residential indoor air quality. Energy auditors need to know them, and how they differ. To be clear, the guys who have calc'd your house are correct in saying it's tight, in one sense of the word. Martin is correct in saying that it's not that tight, in another sense, but let's bear in mind that the ultra-tight homes we discuss here almost always have mechanical ventilation installed that makes that tightness a good, safe thing. I go over this with my customers so they can understand what's at stake and how to spot problems. It is a complex topic. It's a mistake to over-ventilate because you will feel cold and you'll turn up the heat to compensate. I see more problems with over-ventilated homes and high heat bills than I do home with humidity build-up.
Carol, just want to let you know you are right on track, and keep trusting your own judgment. Use what you learn here and then make up your own mind. Your rim joist idea is fine.
I'll try to clarify the garage/house connection, to be sure we're discussing the same thing. The house is a split-level, sometimes called a tri-level. The kitchen/living room level, with a wall adjoining the garage, is entered 4 steps up from the garage floor. The top of that existing wall ends at the top of the kitchen/living room. So, on the garage side, it's open above the wall. That's where the auditor entered and that's where I wondered about building a wall (with an access panel) up to the roof. The auditor said some of the cardboard holding the blown insulation in place has deteriorated and he recommended replacing it with wood.
The bedroom level is 6 steps up from the kitchen/living room level at the other end of the house. Above it is where the attic currently inaccessible. The auditor said he's assuming that the insulation there is similar to the accessible part.
He also said there are no baffles, but there should be. I don't have a problem with that.
If blown insulation is added to the stud spaces (gulp!), what about the damage to the plastic vapor barrier? Whew!
Carol, your auditor is doing a good job for you IMO.
I can't find where you said you live?
Holes in your poly, easy enough to deal with.
Have at it. Time to get err done.... or pass IMO.
I live in Central New York State, near Syracuse. The auditor said interior repairs would be for me to take care of. So, how do you deal with the poly? And what's IMO?
Carol,
Poly was usually installed as a vapor retarder, and in some cases as an air barrier.
If you make a hole in the drywall and poly to insert an insulation hose, the drywall needs to be repaired with a drywall patch. That will repair the air barrier.
The drywall patch needs to be painted. The paint is a perfectly adequate vapor retarder -- especially considering the fact that 98% of the polyethylene remains undisturbed.
I understand that even without doing anything to fix the polyethylene, I'd have my hands full patching the drywall. Here's hoping the infrared scan doesn't indicate settling.
Thank you all for your input. Now I'll wait for the auditor to bring his camera and proposal. Just wanted to have all my ducks in a row. What's IMO?
Probably "in my opinion." But with AJ, you never know.
The auditor is doing a decent job IMNSHO but surprised he didn't mention air-sealing the attic if he's going to blow more. Not really an auditor's gig, but the garage wall situation sounds problematic.
When the auditor calls me to discuss his findings, maybe he'll mention air-sealing the attic(s). If he doesn't, I certainly will. As for the garage wall, maybe he figures the heated areas are all surrounded by insulation and that should be okay. I don't know how to handle this.
The garage issue, if I picture it correctly, is not an energy issue. The heated areas are surrounded by insulation, as you say. It could be a safety issue if fumes or fire in the garage could easily spread to the house by getting into the attic. I may not have a clear idea of what's going on here.