Tag Archives: insulation

Do-over dilemma

Project specific factors usually determine what insulation method would be suitable. For our roof those factors were a target R-value of 60 or more, the existing low slope roof with its ten inch roof joists, the spatial constraints of the south attic, and the need for some roof deck repair down the road.

We reconciled these sometimes conflicting factors with an insulation assembly that started with three layers (total of 10 1/2 inches) of rock wool batts (R-45), followed by four inches of XPS foam boards (R-20). That should give us an R-value of 65 anywhere between the roof joists.


It looked like we had the perfect roof insulation for our project. Yet, it was also risky, which suddenly made it a lot less perfect.

What I neglected to consider in my schedule and material driven decision making, was the building science – the issue of moisture management.

From cold to wet to rotten

The current insulation assembly is so effective that I created a cold roof deck. During winter time, its temperature will be close to the outside air temperature. In other words, it will be around or below freezing.

Any water vapor in the assembly is likely to condense at the cold roof deck – or, to be more precise, the water vapor will be absorbed by the boards and the upper (cooler) sections of the roof joists.

That could drive up the material moisture content. Once the moisture content rises above 28%, rot or biodegredation may set in. This could compromise the structural integrity of the roof deck and roof joists.

See also: BA-1308: Moisture Control for Dense-Packed Roof Assemblies in Cold Climates: Final Measure Guideline

We did fairly successfully airseal the 2nd floor, including the roof plane. That is, however no guarantee that the roof assembly is vapor tight. Plus the stack effect will constantly pound the insulation assembly with warm and moist air. Some of it will get into assembly. But I am not sure if it has an effective way to get out again.

The accumulation of moisture in the assembly would probably be a slow and gradual process. To get to and sustain a risky moisture content would probably take years. So should I lose sleep over it?

Yes. And I already lost a lot of sleep over it! We plan to be in this building for many years to come. The aspect of durability is very important to us. It makes economic sense and is sustainable. Plus we plan to put us a green roof. I don’t want to ignore the problem now only to risk costly structural roof issues 5, 10 or 15 years down the road.

The fix

Our current insulation assembly is upside down. If I move the XPS insulation on top of the roof deck, I should be able to keep it warm enough to reduce the sorption risk (often referred to as condensation).


The rock wool insulation can stay in place as is. It is vapor open and allows for seasonal drying of the now much warmer roof structure. With that, the moisture content of the roof deck and roof joists should remain in the safe zone, which would be below 20%. (Mold growth is likely to occur if the moisture content is in excess of 20%)

I don’t like doing things twice. But in this case it is the lesser evil. I will now spend a few days taking down our carefully installed XPS insulation. Reinstalling it atop the roof deck will happen sometimes down the road.


Trying to determine how to insulate or ventilate a roof isn’t easy. Here is a list of articles that guided me in the process:

Related posts:

Multi tasking

I’ve concluded the last post contemplating the real world issue of two different trades (carpenter and insulation installer) working on an insulation assembly at the same time.

How about bringing a third trade into the picture: The plumber.

The outdoor cooking concept

The last room to insulate is the 2nd floor kitchen. Back in the day, I had roughed-in the gas line for the stove, knowing that I need to fine tune this connection once we start framing and insulating.

To add resilience to our design, we plan on extending the gas line to the back porch, which would allow for outdoor cooking during the dog days of summer. Shifting the cooking onto the back porch keeps the unwanted cooking heat out of the conditioned and hopefully cooler building interior.

Task layering

Installing the the interior perimeter wall framing with the rock wool insulation has become almost routine. Integrating the gas line into the assembly would typically be the last step, similar to what we did on the 1st floor.

However, aligning and drilling the holes through the already installed studs filled with rock wool batts and then fitting in the gas line is like a puzzle you don’t really want to put together. I always wondered if there is an easier way. My friend Drew and I decided to give it a try and represent three trades at once: carpenter, insulation installer and plumber.

Rather than installing the gas line last, we drilled the holes into the studs and fitted sections of the gas line while we were assembling the framing with the insulation.

I am not sure if this was a faster method. But it was easier and more precise with less puzzling. Pre-drilling the studs while we put the framing together made a big difference because it allowed us to perfectly align the holes.

I’ve learned that you have to be on your toes and constantly think and rethink the task sequencing, because layering three trades into one task is, let’s say, unconventional.

The bump-out


The rethinking of sequencing was further complicated by the chimney bump out on the west facing wall. I did not want the framing to follow the bump out. That would make for complicated drywall installation and even more complicated kitchen cabinet fitting.

Instead, we opted to hide the bump out behind the framing. Yet we still had to fit the two layers of rock wool insulation.

Our solution was to frame the wall left and right of the bump-out with two by six lumber. That gave us the three and a half inches to fit the first rook wool layer between the framing and closed cell foam. We framed the chimney bump-out with regular two by four studs with one layer of rock wool. This gave us a continuous wall plane.

I would like to thank our friends Drew and Rubani for their help with the multi-tasking and for putting their minds into this job and keeping me out of trouble!

Related posts:

Framing, insulation, and the real world

Now that I have picked up my last load of rock wool, it’s time throw it into the wall.

We have the perimeter walls in the front (or north two-thirds) of the building already framed and insulated. The back (or south third) is a slightly different beast, because I have no ceiling joists to which I can attach the perimeter wall framing. I had removed the ceiling joists to have enough room to fit the attic insulation.


I worked around this problem by anchoring the top plate of the perimeter wall framing into the masonry wall, and in that process carefully minimized any thermal bridging.


Other than that, the process was similar to what we did in the front of the building: We offset the framing by 3 ½ inches to fit the first layer of rock wool between the back of the studs and closed cell foam. Once the rock wool was in place behind the studs, we set the framing plumb and anchored the top plate to the wall. Last but not least, we installed the second layer of rock wool in between the studs.

This gives us an uninterrupted layer of closed cell foam and rock wool insulation, which greatly improves the thermal envelope because we practically eliminated all thermal bridges.

A real world issue

This worked out really well, because I did the framing and rock wool installation myself. In the real world, however, you probably have contractors doing this work. And this is where it gets tricky.

A carpenter doesn’t necessarily want to deal with insulation, and an insulation installer may not know much about carpentry. Yet both trades are needed at the same time to put this kind of insulation assembly together.

This scenario, where an installation tasks spreads across trades, is not an exception in an energy retrofit. Nor is the fact that contractors find themselves in the situation where they have to think outside the box, such as with the pipe insulation.

There are plenty of contractors out there. But finding the one who brings the right level of attention to detail, who can think on the spot, who is willing to schedule with you and other trades, and who exhibits some level of coordination skills, is like finding a needle in a haystack.

If you are a contractor looking for a way to future-proof your business, turn renaissance and turn on your critical thinking skills. I am pretty sure you won’t run short on projects.

Related posts:

Last rock wool pick up

We had started to frame out the perimeter walls on the second floor, and at the same time insulate them with rock wool.

Well, the time had come to make one last trip to pick up the last batch of rock wool. If I measured and calculated correctly, this last batch should allow us to complete the 2nd floor insulation. I may need another bag for an odd job here or there. But the big task – the insulation of the building envelope – was about to be completed!


This felt like another milestone. The numbers are certainly impressive:

To insulate our building envelope I purchased 194 bundles (or bags) of rock wool.

That took care of the basement and 1st floor2nd floorand attic.






We unpacked, handled, fitted, and installed a total of 2,328 rock wool batts, each measuring 15 ¼ inches wide, 47 inches long and 3 ½ inches in depth (stud depth). At 4.975 square feet per batt, we installed a total of 11,581.80 square feet.

The total material cost added up to $6,348.37, including taxes. That translates into $0.55 per square foot of 3 ½ inch batts, or $0.16 per board foot (one board foot is one inch over one square foot).

That leaves us with a nice, comfortable, and quiet building interior. That’s right! The rock wool does not just provide thermal insulation, but also sound insulation.

Related posts:

Breeze hunting

When we give tours of our deep energy retrofit and I am asked about our insulation methods, I always point out that the insulation is only as good as the building is air tight. And I am only repeating what is being preached in the weatherization, energy retrofit and green building community.

Take a day like yesterday, with freezing temperatures and a wind chill factor as low as -20 degrees Fahrenheit. Imagine yourself all bundled up in a very warm down coat, except your front zipper doesn’t quite work for six inches and leaves a small gap. If you go and walk into the wind, you will be chilled by the cold air blowing through the faulty zipper. That little gap completely negates the warming factor you would expect from the coat.

It’s sort of the same with insulation. If I have air blowing through my insulation, I have spend a lot of money (on insulating), but won’t get the performance that would have justified the investment.

Needless to say that I was rather alarmed when I detected some drafts at our newly installed 1st floor windows. To make sure the drafts were real, I had our friend John Bergman help me trace them with a smoke pen, and mark them with a piece of blue tape.

It turns out that the idiom “The devil is in the details” is not just a saying.

A number of the leak locations coincided with the shims we used during the window installation. We were very careful to foam around the newly installed windows, but some of the shims were not foamed in.




Luckily, this took only a step ladder and a can of spray foam to correct.

I thought I was pedantic about the window installation and air sealing, but it looks like I haven’t been pedantic enough.

Related posts:

1st floor replacement windows

1st layer – closed cell insulation

Finishing the job

Larry Jackson liked this post

2nd floor perimeter framing

Its not just a framing job, like it was on the 1st floor. This is a framing and insulation job at the same time.

Let’s look back at the 2nd floor insulation strategy.

Because the 2nd floor exterior wall consists of two wyth, rather than the three, we have a little more room for insulation. We air sealed the building with two inches of closed cell foam. Following the foam, we planned on two layers of rock wool insulation, one layer behind the framing and the second layer between the studs.

This assembly gets us to a R-value of 40 at almost the same cost of the R-28 insulation assembly from the 1st floor.

Back to the job on hand. I decided that I should try to install the first layer of rock wool together with the framing, to keep things simple. The question was, how?

For once, it turned out to be simpler than expected. We put the framing together as usual and lifted the sections into place, making sure the bottom plate was in its final position. We tilted the top of the framing section into the room. That gave us enough space to start stacking the first layer of rock wool between the framing and the closed cell insulation.

Once all the rock wool was stacked behind the tilted framing section, we pushed it into a vertical position and attached the top plate.

The attic, the space between the ceiling joists and roof joist, was a little more complicated because it is a tight space. But we followed the same principles.

What is left now is to install the second layer of rock wool between the studs.

Once it is all done, this will be a very cozy apartment!

Related posts:

1st floor perimeter wall framing

Double duty

2nd floor closed cell installation

Blower door test – before insulation

2nd floor insulation strategy

2nd floor closed cell installation

3rd layer – rock wool insulation

Insulation preps – plugging the 3” gap

Insulation preps – 3” thermal break

Insulation update

The insulation riddle is back

Following the control layers

Insulation riddle resolved

Insulation – how much is needed

Insulation – which material cuts it

Insulation – starts with moisture management

Insulation – lots of conflicts

Insulation – how it started

Anne Alt, KA Washington liked this post

Utility room pipe insulation

We have diligently insulated the pipes in our plumbing system, including all hot and cold water pipes. If you want to know why, you can read up on the rationales in the blog post [LINK] “Plumbing – energy conservation (part 1)” and “Pipe insulation.” And, I shouldn’t say “we,” because Cathy did all the insulating.

We did the same thing for the PEX tubing feeding our hydronic heating system – or more simply put – the baseboard radiators.


This should help with our energy saving efforts and assures we get the precious hot water where we want and need it: At the point of use, such as the faucet or the radiator, instead of losing it along the way to the delivery point.

But one key area has not received any pipe insulation yet – the source of the hot water, the utility room. All of the piping running from our boiler to the hot water buffer tank, to the domestic hot water storage tank, and to the heating system manifolds, are still sitting there naked without their winter coats.

And this really matters, particularly when you have large hot water storage tanks like we do.

An argument against hot water storage tanks you may have come across is about “standby loss.” That’s the thermal energy that should arrive at your faucet or radiator, leaking from the storage tanks and heating up the utility room.

The hot water storage tanks come insulated, which reduces the standby loss. But the various plumbing connections to or from the tank (a minimum of four) are not. They effectively siphon the heat out of the tank along the metal plumbing lines. Just put your hand on one of those connections at your hot water tank – but be careful not to get burned!

Cathy came to the rescue to control that thermal energy bleeding. She put her skills to task and insulated the entire plumbing system in the utility room with closed cell pipe insulation.

Not an easy job, considering that some of the tubing was hidden behind the tanks and in very awkward corners. Plus, the connections at the storage tanks were rarely a uniform pipe size, but tend to step down, which required a lot of puzzling with the corresponding pipe insulation sizes.


Does this stop the heat bleeding? No. But it minimizes it and slows down the heat loss, whether through standby or the delivery process. That in turn allows for more hot water to be delivered where we need and want it – at the point of use.

Related posts:

Plumbing installation – pipe insulation

Pipe insulation

Plumbing – energy conservation (part 1)

Wrestling the unruly

Radiator déjà vu


Blower door test – after insulation

It was time to face the music – or better, the roar of the blower door fan.

Quick recap: We applied for an insulation rebate. To qualify for the rebate, we were required to demonstrate an energy savings of at least 30%. The energy savings are in part calculated on how leaky or air tight a building is.

John, from Chicago Home Performance, conducted a blower door test prior to any insulation and air sealing. That pre-improvement test is used as the baseline to calculate the energy savings. It turned out that our 2nd floor was pretty drafty at 4,763 cfm50 or 13.9 ach50.

The preparations

A lot of work has been completed since that first test:

Were we done with all the air sealing tasks? No – not yet. I still needed to install an insulated back door from the kitchen to the porch and replace the remaining double hung windows with new insulated glazing units (IGU’s).

But – with the insulation rebate deadline approaching, these items just had to wait. We needed to get the post-improvement blower door test done – quickly!

The test

John set up his blower door equipment, just like he did for the pre-improvement test. He fired up the fan – and he didn’t get a reading at first!

The blower door fan has two flow rings (A and B) and a lid that covers the center.


The building was so leaky during the pre-improvement test that John had all of the flow rings on the fan removed.


Fast forward to post-improvements: We had tightened up the building so much that, with all flow rings removed, there wasn’t enough airflow velocity through the fan to yield a valid reading. John increased the velocity by constricting the airflow with the flow ring A, and eventually with the flow ring B.


That finally gave us a valid reading:

720 cubic feet per minute at 50 pascal (720 cfm50) or 2.1 air exchanges at 50 pascal (2.1 ach50).

That is an 85% reduction compared to the 4,763 cfm50 or 13.9 ach50 of the pre-improvement test.

Needless to say that our air sealing and insulation work paid off. We were all surprised – pleasantly surprised!

The meaning of…

What does 85% reduction in air leakage or 2.1 ach50 mean? It would be more than enough to meet the energy rebate requirement of 30% energy savings. But how does it compare to other projects or standards?

The recently published International Energy Conservation Code (IECC 2012) requires buildings to meet 3 ach50 for climate zone 5 (Chicago is in climate zone 5).

The Canadian R-2000 program mandates 1.5 ach50, while the Passive House standard requires 0.6 ach50. The latter is a hard one to achieve, even in new construction.

The Green Building Advisor blog post “Blower Door Basics” by Martin Holladay mentions that “a 2002 study of 24 new Wisconsin homes showed a median air leakage of 3.9 ach50” and “new home builders in Minnesota routinely achieve 2.5 ach50.”

Mind you, these are results for new construction. Tightening up an existing building is considered to be notoriously more difficult. So I think we are doing pretty well with our 2.1 ach50 – although I would like to get it down to 1.5 ach50.

Maybe we will get there once we install the drywall, tape and mud it, once the new kitchen back door is in, and once we have all the new replacement windows installed.

To learn more about blower door tests, read the following:

GreenBuildingAdvisor.com – Blower Door Basics

Wikipedia.org – Blower door

Related posts:


Matthew Johnson liked this post

Double duty

The closed cell spray polyurethane foam (SPF) came in handy while solving a problem with the attic insulation.

We used salvaged four inch XPS boards under the roof joists in the attic. Because salvaged material is rarely perfect around the edges, I was left with gaps where the boards meet.

Edit: The described insulation assembly does not comply with important  building science principles. For more information read the following post: Do-over dilemma


These gaps needed sealing to prevent warm air and moisture from migrating into the insulation assembly. The associated energy loss — and even more so the wetting of the roof assembly — would be counterproductive or even dangerous.

Taping over those gaps didn’t seem feasible. I thought about using spray foam cans to fill the gaps. That would would be a big and expensive job.

Sealing the seams with closed cell SPF, however, is relatively straight forward, particularly with our installer and his attention to detail.


During the SPF installation, the installer “over sprayed” the top of the wall to properly seal the interface between the XPS boards and the masonry wall. From there he moved on to the ceiling, and sealed the joints between the boards with foam.

I got the gaps between the boards closed up. But it doesn’t entirely solve the problem of air or moisture from migrating into the roof assembly. There will always be some imperfections, leaving small pathways. My plan to manage that moisture is a good subject for another blog post.

Related posts:
Anne Alt liked this post

2nd floor closed cell installation

It is time to make nails with heads, screws with threads, and foam with no gaps!

I covered the technical aspect of the 2nd floor insulation strategy, why we decided on two inches of closed cell spray polyurethane foam (SPF), and the importance of ending up with the right vapor permeance rate. We also had some excitement with our first blower door test, a prerequisite for the insulation rebate we are after.

It was time to get started with the hands-on part — the actual closed cell foam installation.


This is a good time to talk about skills. Not mine – but the skills of the SPF installer.

I had three different installers on this project. One for the garden unit, another one for the 1st floor, and Kent’s Thermaseal for the 2nd floor. I now wish I would have known about Kent’s crew when I started this project, because he would have done all floors for us.

Take a look at the video below. The cured spray foam surface may look a little rough and wavy. But believe me, that is the smoothest, most even closed cell application I have seen. It is incredibly difficult and takes a lot of skill to keep the spray foam at a consistent depth.

This experienced installer first sprays lines 16 inches on center, which he uses as depth gauges, and then sprays out the space in between.

Attention to detail

I have written about the potential consequences if the attention to detail is deficient during a SPF installation.

I didn’t have any of those issues this time around. You can see in the video how the installer is pacing himself, allowing for the foam to expand and cure, before he continues with the next pass.

He “over-sprays” at the bottom of the wall, an important detail that eliminates weak spots at this transition and change in planes.

If you carefully watch the video, you can see the installer using a depth gauge – a needle set to two inches which he pokes into the foam to see if he has reached the specified spray depth. The use of that depth gauge is not that remarkable. But the fact that the installer goes back to where he poked into the foam and applies another pass to seal up the pin hole he created, is remarkable. And he did that consistently.

That kind of attention to detail tickles me!

Related posts:
Matthew Johnson liked this post