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Planning a Retrofit in the Pacific Northwest

The owner of a drafty, poorly insulated house looks for advice

Posted on Nov 13 2017 by Scott Gibson

Brad Steeg's Seattle home was built in 1915, and from the description he provides in this post at GBA's Q&A forum, it's not hard to understand why Steeg is so uncomfortable during the winter: not much insulation, single-pane windows, and lots of air leaks.

"During the winter, my thermostat reads 70° but it still feel cold because the cold walls and ceiling suck the heat out of my body," Steeg writes.

Exterior walls on the single-story, 900-square-foot house are framed with 2x4s. Steeg says some fiberglass batt insulationInsulation, usually of fiberglass or mineral wool and often faced with paper, typically installed between studs in walls and between joists in ceiling cavities. Correct installation is crucial to performance. has been "stuffed in nooks and crannies" as previous owners opened up walls in the past. But the insulation is apparently spotty, and what's there is dirty, indicating plenty of air gaps.

His plan is to add Tyvek housewrap, two layers of 2-inch-thick Roxul ComfortBoard 80 mineral wool insulation, 2x4 furring strips to create a rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. gap, and, finally, fiber-cement siding. Ceiling insulation will have to wait until an electrical upgrade in the future.

Steeg's single goal is "comfort." The question for this Q&A Spotlight is whether he's on the right track.

Air-sealing before insulation

A continuous layer of insulation on the outside of the wall is typically a good idea, but adding insulation to a wall with lots of air leaks is putting the cart before the horse, suggests Dana Dorsett.

"Adding insulation over an air-leaky wall isn't the best investment, since the air leaks can be anywhere," Dorsett says. "Whether you add insulating sheathing or not, fixing the air leaks is the first order of business."

One option would be to drill holes through the siding and sheathing (or removing a clapboard) and blowing in either cellulose or fiberglass from the outside of the house. That, Dorsett says, would "tighten things up a lot" and give Steeg a whole-wall R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of about 10, even before any exterior insulation was added. Even a single 2-inch layer of ComfortBoard would cut the heat loss through the walls nearly in half.

"An old 102-year-old house like the one you describe is a good candidate for blower-door-directed air sealing," adds GBA senior editor Martin Holladay. "Hire a home performance contractor or a weatherization contractor equipped with a blower door and focus on air sealing."

Steeg plans on removing all of the existing siding, he replies, so it will be easy to drill holes through the sheathing and blow in some insulation. However, he wonders whether it would be safer to remove the drywall inside the house to insulate the wall cavities because in that case he would be able to check the wiring.

"That way I could remove all existing bat insulation (most likely incorrectly installed, just like it is incorrectly installed in the attic) and I can inspect the wiring," Steeg writes. "With an old house like this I don't want to do anything without seeing it first."

He adds that when he removes the siding, he will be able to seal cracks and seams in the sheathing and install housewrap.

"I could place a membrane over the sheathing to completely air seal the walls," he says, "but in an old house like this I'd be nervous. Rainscreen over 4 inches of Roxul over taped Tyvek over my sheathing seems like the least risky approach to insulating the walls of my home."

New windows will make a big difference

One reason the house feels so cold may be the single-pane windows and clear glass storm windows, or clear double-pane windows, do not have a low-e coatingVery thin metallic coating on glass or plastic window glazing that reduces heat loss through the window; the coating emits less radiant energy (heat radiation), which makes it, in effect, reflective to that heat; boosts a window’s R-value and reduces its U-factor. , Dorsett says.

"Weatherstripping the windows and replacing the storms with tight, low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor. storms can also make a huge difference in comfort," he says. "The low-e storm on the exterior raises the temperature of the interior side glass, reducing the convection drafts and raising the radiant temperature slightly. That might make the most economic sense if you don't have to pull the windows when adding the exterior insulation.

"If you're pulling the windows and replacing them, a U-0.25-ish double-pane with low-e coatings on surface #2 (the usual low-e glass unit) and surface #4 (the inside facing surface glass) can make a major uptick in comfort," Dorsett continues. "The low-e on #4 lowers the surface temperature of the window a bit, but it reflects body-heat and room heat back toward the source, improving the mean radiant temperatureMean radiant temperature (MRT) is roughly the average temperature of all the objects or surfaces that a person "sees" inside a building, with the surface temperatures being weighted by their area. A surface or object's contribution to MRT is also based on its temperature in comparison to the person (temperature difference or differential) and the viewing angle between the person and the surface. (the primary source of comfort) by quite a bit."

In fact, he says, the comfort shortcomings in the house can best be explained by single-pane window sash.

"The U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. of wood sash single-panes is usually about U-1.0, aluminum sash single panes run about U-1.2. That is about 10 times the heat loss of a cedar-clad 2x4/R-11 wall per square foot, about 4 times the heat loss of an uninsulated 2x4 wall, and the windows are likely to dominate the current heat load numbers, while dragging down the mean radiant temperatures."

Unless Steeg is shooting for Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. performance, triple-glazed windows would be overkill. Yet replacing older units with low-e glass would make a dramatic difference in the mean radiant temperature of the room, and thus just how comfortable the house will be.

What's the best exterior insulation?

Steeg clearly has mineral wool in mind for exterior insulation, in part because of the horrific fire in London earlier this year at a high-rise apartment building clad in a product containing polyethylene foam insulation.

Holladay, however, tells him that a foam insulation exterior will not increase the risk of fire.

"But if rigid foam makes you nervous, you can certainly use semi-rigid mineral wool instead if that's what you want to do," he says. "Just be aware that installing semi-rigid mineral wool isn't as easy as installing rigid foam, because mineral wool is squishier. That makes fastening the furring strips a little trickier — it's harder to get the furring strips co-planar with mineral wool than it is with rigid foam."

Yet there's another reason Steeg might prefer mineral wool over rigid foam insulation — ants.

Carpenter ants are a particular problem in the Pacific Northwest, he says. Citing an article by Paul Fisette, Steeg notes that carpenter ants like wet wood because it's easy to chew. And they like foam insulation.

Our expert's opinion

Here's what Peter Yost, GBA's technical director, added:

Even if it’s all about thermal comfort, you still need to honor the physics embedded in hygrothermalA term used to characterize the temperature (thermal) and moisture (hygro) conditions particularly with respect to climate, both indoors and out. management.

Here is a document I use with all my clients on what we have to manage and why in older buildings.

Hygothermal Analysis Summary.pdf.

The order of priority is always the same:

  1. Bulk management.

  2. Air leakage (convective) control.

  3. Dedicated directional drying potential.

  4. Thermal (conductive) control.

Can you detail housewrap as a key element of your continuous air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both.? Sure, just make sure that it connects/extends to overlap with below-grade wall and roof air barrier components. But where is the control of air leakage most important? Low and high (from stack effectAlso referred to as the chimney effect, this is one of three primary forces that drives air leakage in buildings. When warm air is in a column (such as a building), its buoyancy pulls colder air in low in buildings as the buoyant air exerts pressure to escape out the top. The pressure of stack effect is proportional to the height of the column of air and the temperature difference between the air in the column and ambient air. Stack effect is much stronger in cold climates during the heating season than in hot climates during the cooling season. in cold climates, Climate Zone 4 and above), so rim joists and attic should receive the greatest initial attention in terms of air sealing. You should strongly consider redoing your wiring before you address the #2 priority, air leakage.

Windows absolutely are key to thermal comfort, from both a convective and conductive perspective. You can keep your existing windows and increase thermal comfort, and if you choose that route try using this tool to learn more about your options. If you are considering a window replacement, use this tool for guidance.


Tags: , ,

1.
Nov 13, 2017 9:27 AM ET

Air temperature is the
by Jon R

Air temperature is the primary determinant of thermal comfort, but it's far more complex than that. Here is a tool to help:

http://www.healthyheating.com/solutions.htm

Ideally you would find someone who can present all of the upgrade options along with the cost effectiveness - including simply turning up the heat on colder days.


2.
Nov 15, 2017 11:10 AM ET

Sealed insulating sheathing
by Walt Suman

Wouldn't rigid foam sheathing with weather barrier and air sealing attention (either on structure, or on rigid insulation) address both the infiltration and thermal issues? An empty stud cavity represents no thermal disadvantage with enough outboard Rs and even as proposed, state code would have an interior vapor retarder optional.

Rigid foams (XPS or ISO) offer superior insulation, moisture resistance and, as stated, constructability.


3.
Nov 15, 2017 7:35 PM ET

RE Planning a Retrofit in the NW
by Dennis Heidner

From the story: "However, he wonders whether it would be safer to remove the drywall inside the house to insulate the wall cavities because in that case he would be able to check the wiring.
"That way I could remove all existing bat insulation (most likely incorrectly installed, just like it is incorrectly installed in the attic) and I can inspect the wiring," Steeg writes. "With an old house like this I don't want to do anything without seeing it first."

I live in the Seattle area, east side of Lake Washington. Houses that were built in Seattle during the era described were often knob and wire in the attic... sometimes upgraded by owners or DIY'ers over the years. Pulling the sheet rock off provides a far greater flexibility in making the house resilient and perhaps able to with stand for another 102 years.

First, The 1915's houses probably are not sheet rock, but are lathe and plaster. And you might find some rats inside the walls. If it is plaster, that may have been added on top of the lathe and plaster.. or it had been remodeled previously. Check with the city to see what permits had been previously pulled for the house. If it had been remodeled in the 70's and later then permits and inspections are probably in the city records and they may be able to help guide your priorities.

1. Checking the wiring is just one of the reason... (even if it had been upgraded in the 50's or early 60's) Occasionally in older houses in this area you can run across outlets that are ungrounded -- or a three prong outlet on a two wire system. There was a time in the 60's and 70's in which aluminum wire was pulled in houses... this gives a great opportunity to check for and correct that if necessary.

2, Old houses can have dead legs of water pipe that still attached to the active water lines - but capable of brewing bacteria... good time to spot those and remove with the sheet rock off.

3. Removing the sheet rock also allows better inspection of the structure from inside the house... addressing any dry rot that might have occurred over the years.

4. Earthquake hardening... yup we are in one of those areas that can have significantly stronger earthquakes than even some areas of southern California. With the sheet rock off - the structure can be attached to the foundation, made more rigid and able to handle the forces on it. In the area there are a number of companies that can handle the engineering of the house... having that sheet rock off speeds up the process and lowers the cost.

5. While the sheet rock is off - you can also look at the placement of switches and outlets adding new locations and removing old switches/outlets that just don't work for the house.

6. A 1915 built house is likely to have lots of lead paint, ceilings with "pop corn" texturing could contain asbestos.. so be prepared for additional work.

7 If you open up the walls - you may also discover some artifacts of historical value... like old Seattle Pilots banners, Olympia & Rainier beer bottles. Old newspaper from a century ago...

I prefer the Roxul comfort board to the other suggestions - but that's because I know that in some areas of Puget Sound the rain is driven pretty hard at times by the wind.. and it can swirl around. The mineral wool solution can take a soaking and not support mold... I've seen most of the foam products that get wet here support mold over time.

There was some mention of carpenter ants and foam... that could be managed in general with keeping the area around the house clean and landscaping away from the house. And if you've seen carpenter ants in the neighborhood its probably more important to look inside the walls to make sure that there hadn't been any structural compromise in years gone by.

Even though we live in the Seattle area (marine climate zone 4).. the area is actually reasonably dry. We saw that last summer with months without rain. Seattle area homes normally don't have a big problem with condensation on the outside walls (seldom drops much below freezing for any amount of time... and dew point isn't reached as often - unless the house has had bathrooms and kitchens venting into the walls. I've seen that done MULTIPLE times. You won't necessarily notice the problem and be able to fix it unless you have the inside wall cladding off.

I'd guess the big issue is do you have the time and the money to gut the house and fix problems that might be discovered?


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