An Air Sealer's Work is Never Done

Well, we are back at it - working on the house again.

No, we do not have our construction loan yet.

Yes, the house is gradually nearing completion.

Yes, this drives me crazy. But we do have assurances that the construction loan will go through. Our contractor is willing to go ahead and get back on the house despite not having the actual loan yet. Thank you, Randy.

Anyway, so I am trying to get to some additional air sealing details. These photos show the water supply Pex tubing in the kitchen which runs from the mechanical room under the floor to the kitchen. In other words, this tubing bridges the thermal envelope. The plumbers sealed it with the orange foam in a can. You can see that the Pex tubing is not completely sealed to this extreme air sealer's standards. The orange foam doesn't cover the entire side. In addition if the tubing moves as in the 3rd photo, it opens up and fails to maintain the seal with the tubing.

So what does a good Air Sealing Specialist do? The choice is tapes or flexible sealants. For this area I choose tapes to make a good seal with the tubing.

I used Pro Clima Unitape with a flexible hole in the center to run the pipes through. 

Then I reinforced the seal with one of my favorite tapes - Pro Clima's Tescon Vana.  Love this stuff. I also use it on holes in my work jeans. 

For the vent pipe, I went with Siga Wigluv tape. 

One area I have to air seal and I don't really know how is around the electrical boxes.

It's not really needed because the boxes are in a space in front of the insulation layer and do not penetrate the thermal envelope. (Remember the thermal envelope on this house is sealed at 3 levels - taped on the exterior,  taped and caulked on the inside every single stud bay, then the dense pack cellulose was blown into the stud bay covered with a completely air sealed vapor permeable membrane, Intello Plus. I still like the idea of having redundant layers of air sealing layers so I do want to seal around the boxes. Not to mention that the inspector said we have to because that is where the thermal envelope is usually sealed and that is what they expect. But I don't really know how to do this. More internet study.

We are getting ready to tile the mechanical room because we need it so we can have some heat. We've chosen a wood look tile from Home Depot that is only $2.39 sq. ft. John really likes it. 

I'm going to install it over Schluter Ditra membrane to uncouple the tile from the floor to help prevent cracking. I figure in the laundry room I need to do that.

Well, that's sort of where we are now. Lots more going on - 4 inch red oak floors have already been  installed, doors will probably be installed tomorrow, followed by window trim. So we are getting somewhere. I'll try to keep you better informed the last half of this month. 

Cozy Mineral Wool Sweater on the House

John's house has a number of uncommon features that are designed to make the house more efficient and more resilient, better able to withstand weather and time. I'd like to talk about a couple of those details, the mineral wool exterior insulation today and the function of the rainscreen in another post.

Here is our cozy Mineral Wool Sweater before the addition of the rainscreen.

The most time-consuming of these two features is the exterior insulation and all that installation details that entails. So we (I say we, but it is, of course, Carlton and his crew that have done this) covered the entire house with a cozy mineral wool sweater, so to speak. This 2 inch thick sweater of insulation  (total R value of 8) provides an uninterrupted layer over the house that is insect, fire, water resistant and helps maintain the desired interior temperature with much lower energy use. It reduces thermal bridging - the transmission of heat through the parts of the building that are more conductive such as the wood studs and beams. Remember the R-value (defined as resistance to heat flow) for wood is about 1 per inch whereas most insulation ranges from 3 to 6. 

This is a drawing of a thermal scan showing where the heat loss occurs in a normal stud framed house. You can see that more intense heat loss occurs through the windows but a significant amount happens through heat flow across the wood studs. In the average home built with 2' x 4' or 2' x 6' framing, approximately 25% of the exterior is wood which means LOTs of thermal bridging.

Here is an actual thermal image showing the interior of a house where you can clearly see the wood studs and bracing in the wall. The deep purple is probably due to air leaks through the intersection of the studs in the corner. 

From Erik North's Energy Auditing Blog

When I re-sided my house about 3- 4 years ago , I covered the entire house with Polyisocyanurate foam sheets (polyiso for short) to reduce the thermal bridging. I chose polyiso because it has the highest R-value for common insulation materials and was relatively easy to install. Also that was early in my studies on energy efficient design. Disadvantages of polyiso are that it is made from oil, somewhat flammable, insects love to nest in it, and it has "global warming potential" from the blowing agents used in the making of the foam. So at that early stage in my studies, that's what I chose. 

After realizing that there are many other options out there, we chose Roxul Rockboard 80 for John's house. It's much more of a pain to work with because it itches (some people aren't bothered by it, but I try not to touch it without gloves on) and the sheets come as 2' x 4' rather than 4' x 8' for foam sheets. Truthfully, I did not calculate the cost difference because I was set on Roxul and was not going to consider foam. I feel that this is the proper choice for John's house based on fire, insect, and water resistance. 

Later in the construction process, we will do an energy audit so we can see how effective the cozy mineral wool sweater actually is.

Back to Reality - Homebuilding, Work

This week has been a serious back to reality week. I was exhausted after coming back from Oregon last week. I slept like crazy. Going to bed early and everything. I had wonderful days at work, busy, but not overwhelming. I have to take my Pediatric Emergency Medicine recertification boards this week. Pretty scary. I studied some, even in Oregon, but you can't study enough to feel comfortable. I am pretty anxious about that. And then there is the house which is going really well. That's mostly what this post is about.

You may recall the we are using an exterior insulation called Roxul. I looked for Roxul Comfortboard  but was unable to find it easily. I could have gotten it from one of the big box home improvement stores but it would take 6 weeks or so to get it in. I did find Roxul Rockboard online from ATS acoustics, an acoustic supply house. Their lead time was about a week. I posted online at Green Building Advisor (my favorite website) to see if Roxul Rockboard and Roxul Comfortboard were equivalent and Albert Rooks of Small Planet Workshop (where I am getting a lot of my air sealing supplies) said that they were. The compression resistance of both products is 743 psi so the products were very similar. I ordered from ATS despite very high shipping costs, but we were able to get the product in one week.

Carlton and Chris and Myron have been installing this material on top of the very well air-sealed exterior for the past week when I was gone.

Front view of the house with the installed 2 inches of Roxul. Foam was used around the windows so we could make sure that we airsealed well around the windows. The rainscreen  which goes on before the siding has not been applied to this area of the house.

You can see the rainscreen has been applied to the back side of the house. The fixed transom window is above the stairway. I know it looks a little funny, but it is about all that would fit there. We were going to put a window in the bathroom, but decided against it because that can cause all sorts of problems with mold and rot. Since we are trying to build a highly efficient, long-lasting, resilient home, it does not make sense to put a window in the bath/shower area to catch water and cause rot in the wall. So it looks a little strange, but it is on the back of the house. To bring light into the bathroom, we will install a sun tunnel on the roof of the dormer.

Driveway, gable end side of the house. Again, the rainscreen has not yet been installed on this side. You can think of exterior insulation like a sweater for your house. There are essentially no thermal bridges on the outside of the house to conduct heat in or out of the house. So the insulation inside can do a much better job maintaining the desired temperature. The comfort level of the house is going to be amazing, I think.

See what a great job they have done installing Roxul Rockboard 80.

You can see the rainscreen details a little bit better in this photo. There is a small air gap around the windows to allow any moisture in the siding to evaporate which will significantly prolong the lifespan of the siding, the sheathing below the insulation and even paint on the siding.

Well, that's where we are this weekend. Next week Carlton and Myron will work on the soffits and more rainscreen on the gable ends. Then I don't know what is next. I have to figure out penetrations though the wall. Most electrical and plumbing should be through the floor (which brings its own set of problems), but there are still some things that will have to go through the wall. I need to make sure that is planned for now.

Carlton's helper, Chris, was switched to the day shift so he is no longer able to help in the mornings before he goes to work. That is kind of sad, because he has been a very good worker and great help to Carlton. We will miss him.

Sealing the edge of the foam on roof

To add more effective insulation on the roof and to eliminate thermal bridging we have add 2 layers of 1.5 inches of polyisocyanurate foam insulation. The first layer was applied as a continuous layer on top the plywood and the felt. Then the second layer was installed between 2 x 4 nailers with no overlap of seams below. I'll get Carlton to take some pictures tomorrow. 

This photo is from a commercial construction site but it demonstrates that the seams between the polyiso are staggered so you don't have a continuous seam where they line up and leak air, heat, and moisture. (http://continuingeducation.construction.com/article_print.php?L=140&C=442 accessed on 8-25-13) 

I am trying to figure out how to seal these edges of foam on the roof. I meant for the Carlton, Chris, and Myron crew to do that as they went along, but I did not specifically tell them to do that. 

I have posted a question on Green Building Advisor for help with this matter.

Roof Assembly Details - Challenges in Designing an Energy Efficient Home

I have been looking on the internet for days trying to find good photos that explain in more detail how I want to do the foam insulation on the roof. I have found a few photos that are similar to what I want to do, but not exactly. I've included a list of related references and links at the end of this blog post which might be useful if I don't explain things adequately. I have also noted the reference in the photo caption if I have posted a photo from the internet and listed it in the reference section as well.

So now for the actual roof assembly discussion.

I'd like to use a type of foam insulation called polyisocyanurate for a number of reasons. Polyiso (as it is usually called) has the highest R value/inch of the commonly used foams (EPS, XPS). It is more fire resistant than the other 2 and more environmentally benign. That is, the blowing agents used to make polyiso contribute are thought to contribute less to global warming than the blowing agents for EPS or XPS. Polyiso has some disadvantages though. It is less dense than the other 2 foam boards and cannot take much weight on top. It shrinks somewhat. See 2 articles below to Dr. Joe's barn. Dr. Lsturibek wrote about it in his article in Fine Homebuilding. And finally polyiso is still a fossil fuel product which we are trying to avoid for the most part in John's building assembly.

The plan is to place about 3.5 inches of polyisocyanurate insulation on top of the roof sheathing to provide about R-21 insulation in addition to the dense pack cellulose insulation between the rafters which provides R-33 giving a total insulation of R-54. On top of the insulation will go another layer of plywood sheathing to provide a stable base for the metal roof.

One of the challenges of installing foam insulation on the roof is that you are working at height. Another is trying to install the insulation without causing "thermal bridges" where heat is transferred easily. And finally you have to figure out how to attach the metal roof securely through 3.5 inches of foam and 2 layers of plywood sheathing which usually entails using some long ass screws.

One of the best articles I found that shows one way to install polyiso on the roof is on a house in California called the "CLAM" Blue House, the first passive house in California. First they airsealed the roof sheathing. Second they installed 2 x 4 sleepers (installed on the narrow edge of the 2 x 4) to the roof sheathing nailed from the UNDERSIDE of the roof sheathing between the rafters to prevent thermal bridging. The function of the sleepers is to provide an attachment for the plywood layer onto which the metal roof is attached. There is still some minimal thermal bridging by using the 2 x 4 sleepers but not much. Remember the R-value of solid wood is about 1/inch. It has little resistance to heat flow.

See the air sealed roof sheathing. The gentleman is spraying the sheathing with a boric acid solution to inhibit mold and prevent insect infestations. This photo is from the CLAM Blue House blog.

Photo of the installation of the 2 x 4 sleepers on the CLAM Blue House roof.  Remember these sleepers were installed from the underside between the rafters to decrease the thermal bridging through the rafters.

Photo of the installation of 3.5" of polyiso between the sleepers on the CLAM Blue House

This photo shows the sheathing over the polyiso and sleepers on the CLAM Blue House

You can see in the photos of the CLAM Blue House that they made the roof overhangs by extending the sleepers over the edge of the roof. This prevents the thermal bridging problem of using the rafters themselves for overhangs. 

Overhangs established by using the sleepers on the roof sheathing on the CLAM Blue House

Advantage of using this method of insulating the roof - relatively easy design with polyiso. Disadvantage is primarily thermal bridging and loss of insulation with the 2 x 4 sleepers.

Sometimes you have to make a "ladder extension" to make gable end overhangs. Martin Holladay wrote about it in a Green Building Advisor. These ladder extensions are built on the ground and installed on the roof sheathing. I hope to avoid ladder extensions because I think they would be heavy and awkward to get up on the roof.

Martin Holliday's drawing on Green Building Advisor drawing of a "Ladder extension" to make overhangs on the roof. 

After the 2 x 4 sleepers are installed then you add the polyiso between the sleepers. In the CLAM Blue House they used one layer of 3.5" polyiso, but I would prefer to use 2 layers because polyiso can shrink. Seams between the polyiso would be foamed and taped to provide a continuous air-sealed layer. Then sheathing on top, then roofing felt followed by the metal roof. 

Another good article is "Retrofitting an Insulated Cold Roof" from the November 2008 Journal of  Light Construction written by Dan Perkins, a builder in Michigan. He used a similar design except that he used a different foam, XPS, as a solid layer on the roof abutted against one or two layers of 2 x 4 nailer(s) on the edge of the roof. 

Layer of XPS installed on roof sheathing covered by a synthetic roof underlayment in Nov. 2008 JLC article "Retrofitting an Insulated Cold Roof" by Dan Perkins. Please note the double 2 x 4 nailer on the edge of the roof. I cannot tell if the author taped the sheets of XPS together or not.  

XPS has higher compressive strength than does polyiso, so if you are going to install 2 x 4s directly over it, it will compress less. 

Installing purlins on the first layer of XPS in the JLC article "Retrofitting an Insulated Cold Roof"

The 2 x 4 sleepers which the author calls purlins were then attached on top of the first layer of XPS perpendicular to the slope of the roof. The areas between the purlins are filled in the another layer of 1.5" XPS.  The author uses the 2 x 4 purlins to so he can attach a 2 x4 perpendicular to them to provide the venting for the roof. 

This form of roof provides a more continuous layer of insulation and avoids the thermal bridging with the 2 x 4 sleepers shown on the CLAM Blue House. Also it looks like it is a little easier to install. I don't know if you can use polyiso under the 2 x4s or if you have to use more dense foam (which we are trying to avoid because of increased global warming potential in the blowing agents of these foams.)

I also like the way he retrofits this roof as a vented roof with a perforated metal edging. He uses this method because one of the major roofing concerns in Michigan is ice dams which is not an issue in South Carolina. Download the article, it is a great article with a elegant design. 

Here is a drawing from Green Building Advisor which shows the nailers on the edge before the foam is applied.

From Green Building Advisor article on "How to Build an Unvented Cathedral Ceiling"

Another way to insulate a roof with foam is to use a product called nailbase which is similar to SIPs (Structural Insulated Panels) only with the OSB on only one side. I think you would have to use a crane to get the nailbase on the roof though. I'm not really interested in renting a crane.

How will I decide the exact insulation strategy on the roof? I've got to over the details with Randy and Carlton and John and the people at Shelter Kit. These guys know the practical aspects, not just from reading about it which is all I know. I'll keep you informed.

References:

Global Warming Potential of Foam Insulation http://www.greenbuildingadvisor.com/blogs/dept/musings/calculating-global-warming-impact-insulation

Don't Forget the Science in Building Science http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/28440/Don-t-Forget-the-Science-in-Building-Science

Foam Shrinks, and Other Lessons by Joseph Lstiburek in Feb/March 2012 Fine Homebuilding

http://www.buildingscience.com/documents/published-articles/pa-foam-shrinks/view

Foam Shrinks, and Other Lessons: Correction by Joseph Lstiburek in Building Science 2012

http://www.buildingscience.com/documents/published-articles/pa-foam-shrinks-correction.pdf

CLAM Blue House Blog http://clam-bluehouseblog.blogspot.com/search?updated-max=2010-06-17T19:04:00-07:00&max-results=7

Ideal Roof Overhang Length? Question on the Green Building Advisor QA section

Retrofitting an Insulated Cold Roof by Dan Perkins in the November 2008 Journal of Light Construction

Retrofitting an Insulated Cold Roof PDF version found on Dan Perkins Construction website

How to Build an Insulated Cathedral Ceiling by Martin Holladay on Green Building Advisor Nov. 18, 2011

Challenges in Designing an Energy Efficient Home - Roof Details

I am trying to visualize the details for applying exterior insulation on the roof in my head all the time. Sometimes I have an Aha! moment and think I have it solved. And then realize what a pain it would be to execute while you are on a roof or scaffolding 20 feet in the air.

First a little bit about roof anatomy. This photo is borrowed from www.hometips.com.

This diagram shows several different kinds of roofs - a hip roof,  a regular gable roof with a doghouse dormer on it. We will have a simpler roof than the example above.

Simpler gable roof from a different website - Container Home Consultants

Ok, so the terms we need to know to talk about a gable roof for the purposes of this discussion are eaves, rakes, rafters, and rafter tails.

The eaves are the part of the gable roof that are horizontal. They are lowest part of the roof and serve to allow water to run off the roof without draining directly on the siding.

The gable end or rake end is the sloped end of the roof over the wall. It is usually extended to prevent rain from running down the siding as well. In heavy snow load areas, eaves and rakes do not usually extend as much as they do in the south because the snow can be so heavy and can mass on these areas causing ice dams, etc. Not a problem here. We need eave and rake overhangs to block the rain and the summer sun.

The eaves are usually formed from rafter tails, extensions of the rafters themselves.

The problem with the eaves and gable overhangs in the design of John's house is that there is no attic in John's house so the rafters themselves form the base of ceiling inside the house. The area between the rafters will be filled with dense pack cellulose just like the walls. Thermal bridging raises its ugly head once again. If the rafter tails protrude outside the thermal envelope they will conduct heat out of the house (or in summer heat INTO the house). So the issue is how to make overhangs that will not violate the thermal envelope. It's not easy.

The other issue about the rafter tails is that it is difficult to air seal around them. If your house is a simple gable shape as shown below, you can much more easily air seal around the exterior of the house than if you have rafter tails protruding.

Drawing borrowed from 2009 Solar Decathlon Gable House designed by students from the University of Illinois

One of the guys at Shelter Kit where we are buying the house kit from, suggested that this would not be a big issue in our part of the country since we are in a cooling dominated environment. I know that is true, but I still think it is important to consider these details and try to minimize the thermal bridging as much as possible.

Here is the latest drawing. (Please note: It is hard for me to draw overlapping wood 2 x 4s in 2-D). The top drawing shows the roof with plywood sheathing with parallel 2 x 4s that form the overhangs on the eave side of the roof. The bottom drawing shows a cross-section of the layers of the roof.

The roof itself is a simple rectangle covered with 1 inch of foam that has 2 x 4s standing up forming the rafter tails. 2 x 4s are nailed to the rafters below, but are separated by an inch of foam. The only penetration of the thermal envelope is the nails or screws holding the 2 x 4s in place. The area between the 2 x4s is covered with either foam insulation or Roxul mineral wool insulation. If you want to get really fancy (and you have a lot of money) you can add another layer of insulation over the 2 x 4s, before you add the last layer of sheathing, then the metal roof.

The rafter tails along the eaves can be covered with siding underneath when the siding is applied.

To make gable end overhangs, a ladder-like extension could be attached to the 2 x 4 near the gable edge of the roof and could extend past the roof-wall intersection by 8-12 inches. We don't need a wide overhang because of the porches around 3 sides of the house.

This design is complicated, but less so than some of the ones have seen on my favorite websites - Green Building Advisor, Fine Homebuilding and Journal of Light Construction. I do have to run it by some real builders though. I'll let you know.