What is "Air Sealing" and do I really need it?

[zc15]

Thanks to the helpful folks over in General Garage Discussion, now I am trying to learn what "Air Sealing" is. My understanding is that it is taking a spray foam type material and spraying all joints, ie. each stud to sheathing connection, around windows and doors, any wall penetrations, etc.

I can understand that doing this would mean less cold penetration in winter and heat penetration in summer, but I can't see this being economical. It would take a lot of natural gas to make up a $1000-2000 initial investment. Break-even period maybe 10+ years?

I'm in SE Michigan, so around here we put the kraft paper towards the inside of the space. We also use cold roofs/attics to prevent the roof sheathing from rotting out.

Would I basically get the benefit of the air seal by taping all insulation joints?

My garage has full length studs between the plates, so the sheathing is about a few inches shorter than the stud bays, which in turn are partially open to the soffit cavity.

Obviously closed cell spray foam everything is best, but for a 24x30 at 2" walls and 4" ceiling that is $5000+.

 

[mike93lx]

Not everything needs to be ROI positive. Air sealing can reduce moisture movement, reducing the chance of mold. It also allows your heating and cooling system to perform better when operating at the extremes and makes your insulation more effective

 

[billconner]

Poly (or a better vapor barrier) on interior side of insulation, sealed well and not punctured, is also air sealing. Some tape, caulk, and foam in a can might help where poly can't seal.

Heat transfers by convection, radiation, and conduction.C onvection is biggest and air sealing seeks to prevent that. Spray foam is an approach, but gaps from building movement will eventually develop, so not perfect.

 

[Jim greengo]

Houses need to be able to breathe.

 

[mike93lx]

Houses need to be able to breathe.

You need fresh air ventiliation, but getting that through leakage is far from the best way to do it

 

[zc15]

Poly (or a better vapor barrier) on interior side of insulation, sealed well and not punctured, is also air sealing. Some tape, caulk, and foam in a can might help where poly can't seal.

Heat transfers by convection, radiation, and conduction.C onvection is biggest and air sealing seeks to prevent that. Spray foam is an approach, but gaps from building movement will eventually develop, so not perfect.

I've got kraft faced insulation for both the walls and ceiling - What are the dynamics between the kraft facing and an additional vapor barrier?

I know you're not supposed to put vapor barriers on both sides of the fiberglass, but I wonder if it is ok to have the poly sheetright over the paper (Paper side towards the interior heated side)

 

[Firstram]

Air sealing is well worth the money and effort! In Michigan a vapor barrier on the inside stops the vapor drive but air leakage in the stud bays will still happen. When you heat the interior you also warm up the wall insulation. Hot air rises and that sets up convection currents within the walls. Thsee currents draw cold air in the bottom and push the warm air out the top, effectively reducing your R value!

Have you ever noticed how dry the house gets during the heating season? That’s a big side effect of air leakage. Cold dry air leaks in and as your furnace warms it the humidity drops even lower. That warm air leaks out through the ceiling drawing more cold dry air in in a never ending cycle!

Build it tight and ventilate it on your terms!

 

[toyotadriver]

Houses need to be able to breathe.

Not as much as they used to leak air in past construction. Controlled ventilation is far better than uncontrolled (non air sealed) ventilation.

 

[captaindiode]

I recommend taking a look at the Green Building Advisor website.

 

[Jim greengo]

You need fresh air ventiliation, but getting that through leakage is far from the best way to do it

Problem is that most people dont know where to draw the line.
There are lots of bad things things that get caught in the air of a super tight house that are not good for people to be breathing.
I'd say chemicals in new carpet are up there towards top of the list.

 

[billconner]

I've got kraft faced insulation for both the walls and ceiling - What are the dynamics between the kraft facing and an additional vapor barrier?

I know you're not supposed to put vapor barriers on both sides of the fiberglass, but I wonder if it is ok to have the poly sheetright over the paper (Paper side towards the interior heated side)

I don't think both on one side is a problem. As far as the kraft paper, it just seems unlikely to seal all around. Also, at least according to Building Sciences Corporation, the asphalt impregnated kraft paper is semi-permeable to vapor. https://www.buildingscience.com/doc...sulations-sheathings-and-vapor-retarders/view
Ceiling is most important. It's the bouyancy of warm air that holds more moisture you don't want escaping. That means getting a good deal across any interior partitions.

You do want to address air quality, but the nasty effects of warm moist are going into the wall and ceiling can be worse.

When installing the batts, keep in mind that gaps as small as 1/8" can cause thermo siphoning, so take care. One of the reasons I like dense packed cellulose - it fills every gap, crack, hole, and crevice.

 

[mike93lx]

Problem is that most people dont know where to draw the line.
There are lots of bad things things that get caught in the air of a super tight house that are not good for people to be breathing.
I'd say chemicals in new carpet are up there towards top of the list.

Someone asking about the cost justification of air sealing doesn't need to worry about having a house that is actually super tight. It takes a lot of time, money and effort to get to that point and it won't pay back in energy savings

 

[WisJim]

Having been involved in energy efficient construction since the 1970s, I feel that air sealing is as important as insulation, or perhaps more important. Without air sealing, your insulation won't usually work as expected.

 

[yeldogt]

Poly (or a better vapor barrier) on interior side of insulation, sealed well and not punctured, is also air sealing. Some tape, caulk, and foam in a can might help where poly can't seal.

Heat transfers by convection, radiation, and conduction.C onvection is biggest and air sealing seeks to prevent that. Spray foam is an approach, but gaps from building movement will eventually develop, so not perfect.

Have to be very carful with polly .... lots of structure damage directly linked to polly and trapped moisture

 

[yeldogt]

Thanks to the helpful folks over in General Garage Discussion, now I am trying to learn what "Air Sealing" is. My understanding is that it is taking a spray foam type material and spraying all joints, ie. each stud to sheathing connection, around windows and doors, any wall penetrations, etc.

I can understand that doing this would mean less cold penetration in winter and heat penetration in summer, but I can't see this being economical. It would take a lot of natural gas to make up a $1000-2000 initial investment. Break-even period maybe 10+ years?

I'm in SE Michigan, so around here we put the kraft paper towards the inside of the space. We also use cold roofs/attics to prevent the roof sheathing from rotting out.

Would I basically get the benefit of the air seal by taping all insulation joints?

My garage has full length studs between the plates, so the sheathing is about a few inches shorter than the stud bays, which in turn are partially open to the soffit cavity.

Obviously closed cell spray foam everything is best, but for a 24x30 at 2" walls and 4" ceiling that is $5000+.

Since batt type fiberglass offers very little air control .... it needs a vapor mitigator. The movement of air is just as important as the R value.

A tight building is both more comfy and energy efficient

 

[danski0224]

Houses need to be able to breathe.

I have yet to be inside of a house where I am asphyxiated within a matter of minutes...

 

[zc15]

Someone asking about the cost justification of air sealing doesn't need to worry about having a house that is actually super tight. It takes a lot of time, money and effort to get to that point and it won't pay back in energy savings

Thanks for the confirmation. In winter it only gets heated to about 50 degrees, and even then I'm sweating while working in there.

The structure is 40 years old and the chain of owners/renters beforehand really cut every corner they could, so realistically attaining super high seal would not be cost effective.

I'll just go ahead without, but I will seal up any penetrations in the drywall.

 

[mike93lx]

Thanks for the confirmation. In winter it only gets heated to about 50 degrees, and even then I'm sweating while working in there.

The structure is 40 years old and the chain of owners/renters beforehand really cut every corner they could, so realistically attaining super high seal would not be cost effective.

I'll just go ahead without, but I will seal up any penetrations in the drywall.

I am not advocating for skipping air sealing.

I am saying that worrying about getting the envelope so tight that ventilation will be an issue is not likely.

I absolutely feel that you should spend some time air sealing

 

[zc15]

I am not advocating for skipping air sealing.

I am saying that worrying about getting the envelope so tight that ventilation will be an issue is not likely.

I absolutely feel that you should spend some time air sealing

Can you help me understand what products I could use to DIY airseal?

First order of business would be blocking off the stud cavities from the soffit venting.

Right now my walls are about 100" tall, so the sheathing is short of the top plate by about 4". I figure I would have to patch that with 1x6 or equivalent first

 

[mike93lx]

Can you help me understand what products I could use to DIY airseal?

First order of business would be blocking off the stud cavities from the soffit venting.

Right now my walls are about 100" tall, so the sheathing is short of the top plate by about 4". I figure I would have to patch that with 1x6 or equivalent first

Spray foam and caulking are the most common.

 

[billconner]

Spray foam and caulking are the most common.

Sometimes add a roll of aluminum flashing material to your tools.

Think I saw here where someone "bent" their vent baffles down to close gap and blow loose fill to walk line. you seem to have 6" of sheathing plus whatever to vent baffle.

 

[dfiler2]

Don't skip the 6 mill poly on the inside, that will pay for itself in a pretty short period of time as it is very cheap. Don't block off your soffits either, do a little research and look up soffit baffles, these will block the bottom and leave you with airflow for your attic.

Durovent 23-1/2 in. x 46 in. Rafter Vent with Built-In Baffle 10/Ctn

 

[mike93lx]

Don't skip the 6 mill poly on the inside, that will pay for itself in a pretty short period of time as it is very cheap.

It's important to highlight that the inside is not always the right place. You want the vapor barrier on the warm side, which happens to be the inside for MI but it would be wrong for a lot of the country

 

[danski0224]

Best thing to do is go to Building Science (dot) com and research their recommendations for your climate zone.

 

[Firebrick43]

Have to be very carful with polly .... lots of structure damage directly linked to polly and trapped moisture

I agree with you in most instances, but I really think you needed to quantify or explain that answer better. There is nothing wrong with a poly barrier in the inside of the wall, even over kraft paper. For a poly barrier to be a detriment someone has normally placed a second barrier on the outside of the wall creating a double barrier. Such as placing xps foam on the outside, or super sealing osb sheathing.

 

[billconner]

I say poly but would prefer Sto-Cote's Tu-Tuf. Stronger and less permeability.

 

[walrus]

Every time I see someone saying all the extra work and costs to make a tight building won't pay off it makes me laugh. Maine fuel oil prices hit 5 bucks a gallon. I'm sure prebuy Propane prices for next year will be thru the roof. Wood and pellet prices will be up. How much is comfort worth?

My one suggestion is caulk every hole in top plate/bottom plate of outside walls. Wires, pipes whatever, it will help stop air movement in wall cavities and help performance of insulation.

 

[acer66]

Every time I see someone saying all the extra work and costs to make a tight building won't pay off it makes me laugh. Maine fuel oil prices hit 5 bucks a gallon. I'm sure prebuy Propane prices for next year will be thru the roof. Wood and pellet prices will be up. How much is comfort worth?

My one suggestion is caulk every hole in top plate/bottom plate of outside walls. Wires, pipes whatever, it will help stop air movement in wall cavities and help performance of insulation.

This and on top of everything mentioned it also keeps insects etc. out.

 

[beemerphile]

Problem is that most people dont know where to draw the line.
There are lots of bad things things that get caught in the air of a super tight house that are not good for people to be breathing.
I'd say chemicals in new carpet are up there towards top of the list.

The fact that ventilation is needed does not mean that ventilation by leakage is needed. A building can be vapor-sealed too well, but it cannot be air sealed too well. Intentional balanced ventilation allows you to select the air source and quantity rather than taking it from spidey holes full of mold and rat urine. Balanced ventilation (exhausting and admitting the same amounts of air) allows you to keep the building pressure from going negative. The absence of a pressure drive will keep air from flowing through the spidey holes and also allows the opportunity for heat and humidity recovery if you choose. Other than cost, air sealing is all win.

Any talk of optimal vapor sealing and insulation needs to be done in the context of location. What is required in Michigan will not even meet code in Georgia. The audience of this forum spans all of the thermal zones.

 

[walrus]

One other thing, if indeed you make your building too tight, open a window

 

[yeldogt]

I agree with you in most instances, but I really think you needed to quantify or explain that answer better. There is nothing wrong with a poly barrier in the inside of the wall, even over kraft paper. For a poly barrier to be a detriment someone has normally placed a second barrier on the outside of the wall creating a double barrier. Such as placing xps foam on the outside, or super sealing osb sheathing.

Poly caused all kinds of problems when people started using it in the 70's .... There are endless reports where contractors ran into moisture problems ... I saw a bit of it in some of my rehabs.

Poly rated as a one (1) on the VB scale -- that is not permeable. If you study the charts they only list AK as possible use area for a #1.

Fiberglass allows air flow. Poly was used as an air sealing device ... it's still sold that way. Most walls with poly will still leaks -- so teh moisture can be introduced into the cavity and not be able to dry. Same with poly against the drywall ..... in colder areas of the country where winter heating is used and the house has lots of people (humidity) ... it's common to find moisture against the polly traped behind the drywall. Especially if the heat is turned down and it's an R13 wall.

 

[billconner]

If you have condensation behind the poly, crappy poly install leaking and poorly installed insulation and air barrier allowing cold air below dewpoint against interior wall. (Another reason for cellulose.) No matter what your approach, bad workmanship will assure problems.

Here, in zone 6, R25. With continuous insulation, a little less.

 

[theoldwizard1]

Obviously closed cell spray foam everything is best, but for a 24x30 at 2" walls and 4" ceiling that is $5000+.

It is hard to determine the cost savings, especially in a garage that has giant doors that probably leak like crazy ! Also are you going to heat/cool it 365 days a year ? Paper backed insulation is probably adequate, but you need at least 8" in the ceiling.

The best is 1"-2" of spray foam on all the joints and then typical fiberglass insulation.

 

[dfiler2]

I really thought we knew everything in the 70's and 80's After doing some more research I agree with "Yeldogt", here is a good video that explains it well. So, I now would say don't put up a poly barrier but spend your time air sealing as much as possible.

 

[Firebrick43]

I really thought we knew everything in the 70's and 80's After doing some more research I agree with "Yeldogt", here is a good video that explains it well. So, I now would say don't put up a poly barrier but spend your time air sealing as much as possible.

So his first diagram, showing moisture trapped in the wall, shows tyvek on the outside. This is ironic as he knows about rain screen, he has videos talking about house wraps that don't breath or breath well enough, yet his early 2012 videos he talks about how great they are????. Tyvek micro pores plug up with dust/dirt over time reducing its moisture release. So again, poly barriers are not bad, unless you also have a vapor barrier on the other side of the wall as well.

EIFS has a bad rap for this as well. Its generally the most water proof house cladding out there, but without installing it over a rainscreen it also doesn't breathe. Any moisture that gets in from around windows and doors cant get in. Same with foam sheathing on the outside of the wall. You really should have a rainscreen with tar paper on any house. Let the wall breath from out side.

 

[yeldogt]

If you have condensation behind the poly, crappy poly install leaking and poorly installed insulation and air barrier allowing cold air below dewpoint against interior wall. (Another reason for cellulose.) No matter what your approach, bad workmanship will assure problems.

Here, in zone 6, R25. With continuous insulation, a little less.

It gets damaged -- there is no way to glue the rock -- so you end up with more holes. All the switches/ outlets ... there will be holes. Does every house rot .. no. But there are reasons why some have issues ...

 

[yeldogt]

So his first diagram, showing moisture trapped in the wall, shows tyvek on the outside. This is ironic as he knows about rain screen, he has videos talking about house wraps that don't breath or breath well enough, yet his early 2012 videos he talks about how great they are????. Tyvek micro pores plug up with dust/dirt over time reducing its moisture release. So again, poly barriers are not bad, unless you also have a vapor barrier on the other side of the wall as well.

EIFS has a bad rap for this as well. Its generally the most water proof house cladding out there, but without installing it over a rainscreen it also doesn't breathe. Any moisture that gets in from around windows and doors cant get in. Same with foam sheathing on the outside of the wall. You really should have a rainscreen with tar paper on any house. Let the wall breath from out side.

It's the race for a tight building w/ fiberglass ... also as vinyl siding grew in popularity water became an huge issue. People think vinyl siding protects against water .... try removing some after a rain storm -- the whole wall is wet behind. It's not like shakes or claps .. Vinyl leaks and w/o good flashing details -- trouble follows. Flashing details are a lost art. Think about all the flanged windows that are installed on top of the Tyvek ... how will that work over time ? Where is the water is going ?

 

[reader2580]

It's the race for a tight building w/ fiberglass ... also as vinyl siding grew in popularity water became an huge issue. People think vinyl siding protects against water .... try removing some after a rain storm -- the whole wall is wet behind. It's not like shakes or claps .. Vinyl leaks and w/o good flashing details -- trouble follows. Flashing details are a lost art Think about all the flanged windows that are installed on top of the Tyvek ... how will that work over time ? Think about it and where the water is going ?

A lot of people think that caulk instead of flashing can keep water out. It is really easy for caulk to crack and no longer keep water out. Proper flashing can keep water out long term.

 

[danski0224]

Don't forget that interior paint is also classified as a vapor barrier. So is wallpaper.

Electrical outlet boxes have lots of holes in them, and conduit will move air (and water vapor).

Then there's the often shoddy interface between the drywall and the electrical box mud ring, more air leaks.

Window and door openings.

Lots of places for uncontrolled air leaks.

 

[beemerphile]

Electrical outlet boxes have lots of holes in them, and conduit will move air (and water vapor).

Then there's the often shoddy interface between the drywall and the electrical box mud ring, more air leaks.

I am eliminating this in the walls of my current build by making the air control layer the exterior sheathing (ZIP +3 with LiquidFlash). Wall outlets are behind the air barrier and will not contribute to leakage. At the top of the walls, the air barrier transfers to the sheetrock ceiling. The house is full span and the ceiling will be finished before the interior walls are placed. The penetrations are minimized and the few that exist will be redundantly air-sealed. Airtight ceiling boxes will be used where the minimized number of ceiling fixtures are needed. Wall-switched lamps replace ceiling fixtures in some areas.

The idea is to have a plan. Draw each barrier on the plans and make sure that you can trace it out without lifting the pen from the paper. Make sure the integrity is maintained at any transfers (such as floor/sill and top plate/ceiling). If you build the house in a conventional manner you will get conventional results. If you are aiming for a higher performance level, you need to take the steps necessary to make it happen - then do a blower door test to confirm it or show where fixes are needed.

I'll still have door and window losses, but even there, better results can be obtained by spec'ing them properly and installing them correctly. I'm using high quality casement windows where egress requirements exist (bedrooms) and picture windows in other places. A casement window generally seals better than a double hung window. It is better for egress as well.