Sealing Air Infiltration ??

brjones · Sep 27, 2011

I have spent many hours sealing any duct work that I can access, exterior wall outlets and light switches, canned lights on top floor, sliding doors, etc.

There are still a few places where I am fairly sure I have excessive infiltration. I have not had a blower door test done so I don't know for sure what my leakage rate is.

My idea has always been that the space behind my brick walls gets pressurized and the air then finds it's way in around some window trim, outlets, etc.

I am about to replace all of my cedar siding, soffit and facia with Hardy board cement fiber product. This will be my chance to seal some areas that will be exposed.

I will attach a couple pictures of the area I am most concerned with. Where the cedar overlaps the brick there is a gap which would let the wind pressurize the area behind the brick. I removed some siding and sure enough there is a gap. A while back we had a storm with strong winds, I found dirt on the basement floor in an unfinished area along this wall the next morning. I know it didn't blow past the brick ledge so it about had to come from this gap?

Does anyone except me think this is a problem?

What or how would be the best way to seal this gap before the new siding is installed?

Shophound · Sep 27, 2011

There is supposed to be an air gap between the brick and the sheathing behind it. The sheathing itself should be covered with a water shedding membrane, such as tar paper or house wrap. The air gap is to allow any water that penetrates the brick veneer facade to run down the inside face of the brick and out the weep holes along the bottom of the brick wall.

Best I can tell from your photos it appears you're concerned about where the sheathing behind the brick on the first story meets the sheathing behind the horizontal siding of the second story. Hard to tell from the close-up photo but it looks like the second floor protrudes over the first floor wall top plates a bit. Could have been done so siding could lap over brick, as shown in photo.

It would be helpful if you also posted photos of where you found the dirt blowing into the house through the unfinished wall section in the basement.

brjones · Sep 27, 2011

Yes I know the gap is suppose to be behind the brick and yes the 2nd floor protrudes over the first floor so the lap siding fits over the brick.

The walls are 6" with the type of white insulation that has the netting behind the drywall. The outside is a foam board I think 3/4". I have no idea how well they sealed the foam board.

The fixed window you see below that area has a lot of air that comes in around the trim, not around the window. It comes out of the wall. It has condensed enough to cause a rotten spot. The window/brick is sealed tight.

The area where I found the dirt in the basement is unfinished. There is a seal between the concrete and sil board if that's the right term? The brick ledge outside is sealed tight, it didn't blow under the brick.

That was a very strong wind gust, probably over 100 mph, lost some roof. This is the N side of the house and the wind blows all winter!

I am just trying to use this oportunity to improve the envelope.

brjones · Sep 27, 2011

The little overhang you see on the right side is just for looks. I have taken a soffit vent off so I could look inside. The 2nd floor joist run E/W. It's very hard to tell but I can see insulation in what looks like gaps between the joists. Like there is no rim joist on the end? When the soffit comes off I will be able to see better.

Can you get any idea what the framing might look like from the picture? Enough that you might be able to tell me what to look for?

There is a sliding door under that overhang. Here is the odd part: the air leakage comes up from below the door inside. I am talking about the 2 fixed panels of the sliding door. Not under or around the door. It comes out of the wall below?? The door is sealed really well on the outside. This is another reason I think that gap behind the brick is where the air is getting where it shouldn't. Then is just find a path in?

Will add more pics.

Shophound · Sep 27, 2011

That little overhang has soffit vents. Being that this little overhang does not communicate with an attic, I see no reason why soffit vents should be there. That you said when you removed a soffit vent on the overhang you saw insulation stuffed between joists says a lot. If it's fiberglass insulation it is doing nothing to stop airflow into the space between your first and second floor. There should be a rim joist where you were looking and you should not have been able to see the ends of each floor joist.

When you take the soffit bottom facing off to replace it with Hardi board, see if you can insert blocking between each joist member inside the soffit. Caulk all seams when you do this. You may need to carefully push the insulation a little bit inward to get the blocking to fit. After you do this, recheck the leakage around your sliding glass door. If nothing else I think you'll see an improvement in keeping the room behind that sliding glass door comfortable, provided you can access the entire exposed run of joists and insert blocking and caulking.

Amazing that there's no rim joist there.

Also, that deck. Do the joists actually go into the house, or is there a rim joist bolted to the brick veneer? If the latter, that you say there is no rim joist above the sliding glass door makes me suspicious there may be no rim joist behind the brick veneer that the deck framing is lag bolted into.

brjones · Sep 27, 2011

I also see no need for soffit vents in the little overhang, I plan to use the none vented Hardie soffit panel on that area. That brings up another question, is the vented Hardie soffit panel ok? Does it provide enough free sq in of vent?

Attic ventilation on my house is another topic on it's own.

If you look at the elevation of the 2nd floor joist in the picture and compare to the area behind the overhang it looks like the joist would be higher than I was able to see? Can't see much through vent hole. I'm no frame carpenter but it seems very unlikely or even difficult to not have a rim joist? But I could see bat type insulation and I can't think of a good reason that I could see any insulation? The room behind this is the master bedroom.

All of the interior walls and floors in this house are insulated, for sound I guess?

As far as I can tell the red wood deck rim joist is bolted to the brick veneer but it would explain a few things if I found that the brick is not solid. The deck project is next year.

Shophound · Sep 27, 2011

If there's truly no rim joist (which is hard to imagine) you would be able to see the ends of each floor joist exposed, like this: I I I with insulation stuffed between. If they used engineered floor joists, it might appear even closer to the "I" used here to depict the joist ends.

How old is this house?

There's a formula for determining attic ventilation...you need to know the volume of the air enclosed by the attic in square feet, and then you can determine how much ventilation opening provision to calculate.

But you are right, attic ventilation is another topic by itself, and it has been discussed extensively here on HVAC talk. After all, the "V" in HVAC stands for "ventilation". You may want to do a search on this site on the topic.

Re: the soffit...it's possible that instead of no rim joist enclosing floor joists you're seeing through the removed soffit vent, you're seeing the wall with no sheathing installed, with the thought that the soffit covering it up made the sheathing not necessary. If the "I" used earlier runs vertical and is fairly long, that is what you might be looking at. If you can, remove the soffit vent again and stick your camera up there for a shot.

tipsrfine · Sep 27, 2011

brjones said:
The little overhang you see on the right side is just for looks. I have taken a soffit vent off so I could look inside. The 2nd floor joist run E/W. It's very hard to tell but I can see insulation in what looks like gaps between the joists. Like there is no rim joist on the end? When the soffit comes off I will be able to see better.

Can you get any idea what the framing might look like from the picture? Enough that you might be able to tell me what to look for?

There is a sliding door under that overhang. Here is the odd part: the air leakage comes up from below the door inside. I am talking about the 2 fixed panels of the sliding door. Not under or around the door. It comes out of the wall below?? The door is sealed really well on the outside. This is another reason I think that gap behind the brick is where the air is getting where it shouldn't. Then is just find a path in?

Will add more pics.

Could be the "weep holes". I've seen rain damage from wind driven rain blowing into those weep holes & comming out the other side.

My advice would be to at least have someone come out & do a blower door test in conjuction with infrared imaging. It will take the guess work out of most of what you are trying to achieve. Also, I would try and find a company that does the siding work you plan on having done who has some of their people BPI certified as a Building Analyst & Envelope professional.
Removing & replacing the siding & soffits could be a golden opportunity lost if you have the work done by someone not trained & experienced in Building Science. You don't want to find out what you should have done after you spend all that money.

brjones · Sep 27, 2011

House built in 1990. No engineered joists.

I removed the soffit vent again today. It was several years ago when I looked before. I think I figured it out this time. I can see the bat insulation stuffed in between what I thought were 2nd floor joist but if you look at the picture looking south you can see that the 2nd floor is offset back where this little overhang is. I think what I can see is just the framing where they attached the overhang and little roof. And they stuffed the gap. There should still be a rim joist behind that and maybe a little higher?

So that does not solve my air leak source? Back to the gap behind the brick on the N wall?

1st pic is area in basement where dirt was all over after high wind. This wall is on the E end of the N side and the area where I removed the siding is in the W end of same wall. The area below the W end is finished.

2nd pic shows offset in wall 1-2nd floor

3rd pic is up through the soffit vent

billygoat22 · Sep 27, 2011

see if you can buy a Builders Guide (specific to your climate), by Joseph Lstibureck. I have one for my climate and it shows building details for sealing up a house and addressing the "drainage plane" as well.

it will have your overhang in there and how to handle.

Shophound · Sep 28, 2011

In this photo:

I'm think I see what's going on...you're only seeing part of the floor joists between the first and second story. If you were to reach in and place your hand on one of the joist ends, and then follow it up to the sloping roof deck of the soffit extension, I think you'd find the joist end continues above the decking and at some point terminates at the subfloor for your second story.

Regardless of whether this situation is contributing to your patio door issue or not, this is a problem you can't afford to ignore. You need to understand that fiberglass batt insulation does NOT stop airflow! It only acts as an expensive air filter. Expensive in that air being able to move through this insulation is costing you in terms of heating and cooling comfort and money.

You can either apply wood blocking or cut foam board insulation to fit between each joist, caulking all seams once the blocking of your choice is installed.

I'm confident that if our friend Tipsrfine, an energy auditor by trade, came to your house with an infrared camera on a cold or hot day, a scan of the ceiling of the first floor below the area in the photo above would tell you the same story I'm saying right here. With any wind blowing or a blower door test in progress it would become even more painfully obvious, that you effectively have little insulation here, in spite of the nice, healthy looking batts you see in the photo.

You have a great opportunity while you have the soffit facing removed, prior to the Hardi going up, to work on this problem.

brjones · Sep 28, 2011

Now you have me second guessing what I was thinking earlier today. If you look at the middle picture I posted above and imagine where the foam board would be just behind the brick it still leaves quite a bit of roof sheeting? Tomorrow I am going to look back in the gap where I removed the siding. From there I should be able to see if there is a rim joist behind the little roof. I hope so because it will be near impossible to get enough access to properly seal the places currently stuffed with bats. Even with the soffit removed you can't get to it. It would really require tearing the roof and sheeting off.

I searched the BPI site this evening and sent a couple emails. The nearest ones are in KC.

I can use a FLIR camera anytime I want but the current 70 deg weather won't work very well.

Yes this is my golden opportunity to tighten the envelope and I want it done right. Figuring out what is right is the hard part.

SkyHeating · Sep 28, 2011

I saw that ventilation was mentioned but if you are fully sealing up the house it's time to research ERVs and HRVs and they are just good to have in general.

tipsrfine · Sep 28, 2011

Going to the BPI website will not show you where the nearest certified BPI energy auditor is! This is because of 2 things. 1) There is a difference between being an ACCREDITED company and being a CERTIFIED individual. If you search for only accredited companys you will not find all the certified people and 2) only the people who request that they be listed on the BPI website are listed. The best way to find a BPI energy auditor is by google mapping your address and then hit "search nearby" and enter "BPI energy audit" and then just visit each website listed 'til you find one you like.

Also, look into what kind of energy rebates & credits are available to you, depending on your area & utility providers. I know ATMOS ENERGY (a gas provider) is starting a new rebate program, and it also pays $500.00 to have an energy audit performed before doing any work to your home.

Air leakage can be tricky. Vary rare is it that you can find an opening on the outside and see that it goes straight through to the inside. Most take weird routes, called thermal bypasses. This is why the blower door & IR camera used together is great. It finds them.

Shophound · Sep 28, 2011

Brjones, I'm curious. Does the room with the sliding glass door facing west have a change in ceiling plane at that side of the room? IOW is there something like an interior sofft right over the sliding glass door?

When I get home I'll try to scan in a sketch of how I think that overhang is framed. I find it odd how the first floor juts out underneath it...just eyeballing the brick dimensions it goes out a bit to the west of the upper story west facing facade.

Shophound · Sep 29, 2011

Well, I haven't used Google Sketchup in awhile, so what I'm attaching below is just a quick run-through of how I think the section of house in question is framed. Still not too sure about where the overhang intersects the first floor wall sections and the second floor overlap. Had I drawn it to scale I might have got closer to what you actually have. Maybe I'll try that later.

Looking at drawing again just now. Yep. Definitely need to try again. But maybe including this attempt in this post will spur some conversation. I think you said your house is framed with 2 x 6 lumber. I'll go back through the thread to see.

What I think I'm seeing overall is a lack of a rim joist on the west side between the first floor ceiling and the second level subfloor, leaving the insulation and joist bays exposed to the weather. For fiberglass insulation to work effectively it needs encapsulation on all six sides. Not three, not four. Six.

brjones · Sep 29, 2011

Yes the exterior is all 2x6.

I removed the little triangle plywood on the right side of where I removed the cedar siding. Now I can see for sure that there is a rim joist on the west side. And the bats are just stuffed in the gap formed by the framing of the little roof/overhang. If I have more time tomorrow I will take a picture in the opening.

If you look at the picture looking south where you can see the setback of the 2nd floor, you know where the north rim joist would be just above the brick level. The west rim joist is right where you would expect it directly below the upper west wall if that makes any sense.

If you think this is confusing you should take a journey in the multi levels of attic! With cathedral ceilings and the way the roof comes down to the 1st floor level in places it is a maze! This roof design is what makes attic ventilation difficult at best because very few of the soffit vents communicate with the real attic.

That is another topic all together so I won't go there right now.

pstu · Sep 29, 2011

I am bedazzled by the things you are discussing which are not even in my vocabulary. I have the intuitive hunch you might find something practical in this paper of Lstiburek's, if you have not already read it.

Best of luck -- Pstu

Sealing Air Infiltration ??

brjones

Shophound

brjones

brjones

Shophound

brjones

Shophound

tipsrfine

brjones

billygoat22

Shophound

brjones

SkyHeating

tipsrfine

Shophound

Shophound

brjones

pstu

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