Exterior Insulation for an Ugly Brick Building

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Exterior Insulation for an Ugly Brick Building

The best way to insulate an old brick building is with a continuous exterior layer of rigid foam

Posted on Apr 13 2018 by Martin Holladay

How do you insulate an old building with exterior walls made of structural brick? The best approach, according to building science professor John Straube, is to install a continuous layer of exterior insulation. Straube told me, “It’s a great solution for ugly buildings.”

This approach was used a few years ago in a rehabilitation project in Brandon, Vermont, by a nonprofit developer of affordable housing, the Housing Trust of Rutland County. The developers converted a remarkably ugly three-story brick office building into attractive, energy-efficient apartments for low-income Vermonters. To insulate the walls, the project team decided to install 4 inches of polyisocyanurate on the exterior side of the existing brick walls. They also transformed the existing flat roof by installing new roof trusses with generous roof overhangs.

The building had been abandoned

The building acquired by the Housing Trust was the former administration building at the long-closed Brandon Training School, which operated for years as an institution for developmentally disabled Vermonters. When the rehab project began, the administration building had been empty and unused for over ten years.

Using a variety of funding sources — including funds from the federal low-income housing tax credit program, the Vermont Housing and Conservation Board, Vermont Housing Finance Agency, Department of Housing and Urban Development, and USDA Rural Development — the Housing Trust converted the building in 2013 to 18 apartments.

The project architect, Laz Scangas of Arnold and Scangas Architects in St. Albans, Vermont, shared details of the rehab project at a presentation he gave at the Better Buildings By Design conference in Burlington, Vermont, on February 8, 2018.

The existing building was nothing special

The existing 24,393-square-foot brick building was built in 1956. “It was a a basic box with a flat membrane roof,” Scangas told attendees at the Burlington conference. “It was used for offices. There was nothing historic about the building.”

The three-story building had concrete slab floors bearing on the exterior masonry walls. “The concrete floors created a thermal bridge, making interior insulation difficult,” said Scangas. “So we figured, maybe we can insulate on the exterior.”

A comprehensive energy retrofit project

Scangas and the project consultants performed a deep energy retrofit on the old administration building. Their plan allowed them to create create an excellent 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., and to install continuous exterior insulation around the entire building.

Here’s what they did:

  • Foundation insulation: 3 inches (R-15) of continuous XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. was added to the exterior of the foundation walls from the footings to the top of floor slab.
  • Wall insulation: 4 inches (R-24) of continuous foil-faced polyisocyanurate was added to the exterior of the existing brick walls.
  • Roof framing: New roof trusses were installed on the existing flat roof, which had no parapets. The existing membrane roofing was left in place to act as an air barrier.
  • Attic insulation: 18 inches (settled depth) of blown-in cellulose (R-64) was installed above the existing membrane roofing.
  • Windows: New aluminum-clad wood windows (a mixture of awning windows and fixed windows) were installed in wooden window bucks that extended out to the depth of the new wall insulation. The windows had low-e2 triple glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill..
  • Space heating: A new hydronic heating system was installed. The main boiler is an OkeFen wood-pellet boiler, aided by a Buderus oil-fired boiler for backup. The large mechancical room includes a 12-ton pellet bin. Pellets are conveyed from the bin to the boiler with an automatic pneumatic conveyor.
  • Air conditioning: None.
  • Domestic hot water: A new solar thermal system (including roof-mounted flat-plate solar collectors) supplies 50% to 55% of the residents’ hot water needs; the backup system is the wood-pellet boiler.
  • Mechanical ventilation: A Lifebreath HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. serves the common areas; each apartment has a continuously operating Panasonic exhaust fan.
  • Blower door test results: 2,264 [email protected] pascals for the 24,393-square-foot building.

Laz Scangas describes the job

The foundation got new exterior XPS insulation, from the footings to the top of the slab.

“We decided to do two layers of 2-inch foil-faced polyiso on the exterior of the brick walls,” said Scangas. To prepare for new triple-glazed windows, installed in wood-framed bucks were installed. The wood bucks extended 4 inches (the depth of the polyiso) beyond the bricks.

“The workers used self-tapping brick screws — the fasteners were from Colorado — to attach the polyiso to bricks,” said Scangas.

Scangas continued, “They taped the joints of each layer of polyiso. Then they installed new OSB sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. over the polyiso, followed by Hardie clapboard and HardiePanel siding over the OSB.”

The existing flat roof had no parapets. “We wanted a sloped roof instead of the old flat roof, so we installed new roof trusses,” said Scangas.

“We ended up with good roof overhangs,” he said. “The existing roofing membrane was left in place as the air barrier. The roof had no leaks. We put the new trusses on, and then the insulation contractor installed new blown-in cellulose above the membrane.”

Scangas explained, “The building has a huge mechanical room. There’s room for a 12-ton pellet storage bin. We chose an OkeFen pellet boiler for this job because it was cheaper than a Frohling boiler. The hydronic system has Grundfos Magna 3 variable-flow circulators and a Honeywell Aquatrol AQ2000 control system which allows the owner to control the upper limit of thermostat settings and nighttime thermostat setbacks.”

Costs and results

Scangas shared fuel use data gathered over four years of opearation. “The average fuel use per year is 24.6 tons of wood pellets and 1,182 gallons of fuel oil,” said Scangas. “That’s $6,552 peryear for pellets, and $3,064 per year for fuel oil. The total fuel cost for heating and hot water at the 18 apartments is $9,617 per year. That’s $534 per year for each apartment, or $44.50 per month for heat and hot water.”

Ugly no more

The completed project provides safe housing with high levels of comfort and low energy bills. Equipped with a new name — the Shirley Farr House — the building is no longer ugly.

Martin Holladay’s previous blog: “Reports from Owners of High-Performance Homes.”

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Image Credits:

  1. Laz Scangas

Apr 13, 2018 11:16 AM ET

Nice project!
by Malcolm Taylor

In every respect. A quite simple renovation that has yielded a really welcoming, efficient building. I know it isn't the remit of this site, but I'd like to have seen floor plans of the units.

Apr 14, 2018 9:50 AM ET

Almost every respect
by Charlie Sullivan

It's a shame to see otherwise excellent projects using XPS insulation. Fortunately, if we stay on schedule for the phaseout of HFC blowing agents in XPS the outsized global warming impact of XPS will go away soon--it seems that that will happen sooner than we will succeed in persuading all "green" builders (much less all builders) to avoid it.

Apr 18, 2018 12:21 PM ET

by David Baerg

Charlie, what do you suggest as an alternative to XPS for below grade applications? I haven't done a lot of research on this, but here's an interesting blog post on the topic .

Apr 18, 2018 12:31 PM ET

by David Baerg

I'm wondering why the article expresses air leakage in [email protected] Pa. Whenever authors do this, it sends me reaching for my calculator. Why not just use ACH50?

I get an ACH50 of about 0.6. Have I misplaced a decimal point? That's impressive! Of course, it does benefit from a low surface area to volume. In that respect ELA per square foot of surface area might be useful too. But I don't think most of us have a good feel for that metric.

Apr 18, 2018 12:38 PM ET

Edited Apr 18, 2018 12:48 PM ET.

Response to David Baerg
by Martin Holladay

Green builders who install rigid foam below grade usually specify EPS.

Either XPS or EPS loses R-value when saturated, so good drainage details around a foundation are always essential (and code-mandated). You don't want your insulation to sit in a puddle. Good drainage details prevent that.

Check with the EPS manufacturer to determine whether a particular type of EPS is rated for ground contact. In general, you want to avoid EPS with very low density -- the denser types are better when used below grade.

If you want to convert cfm at 50 Pascals (cfm50) to air changes per hour at 50 Pascals (ach50), multiply cfm50 by 60 minutes per hour and divide the product by the building volume, including the basement, measured in cubic feet.

Apr 18, 2018 9:54 PM ET

by David Baerg

Right. I'm just wondering why so many authors use cfm50 when it's really meaningless if you don't have the volume. And, even if they do give you the volume, why not just use ACH50? In this case, I guessed at the ceiling heights and calculated a volume to come up with an ACH50 of 0.6. Is there a good reason why I see it so frequently? Am I just being crusty and contrarian? It wouldn't be the first time.

Apr 19, 2018 7:03 AM ET

Response to David Baerg
by Martin Holladay

If you are a blower-door operator, cfm50 is what you read on your digital manometer when conducting your test. So blower-door operators tend to think in terms of cfm50.

Passive house builders tend to think in terms of ach50, because they are aiming for a goal expressed in terms of ach50.

Both metrics (cfm50 and ach50) are imperfect, however. Many experts argue in favor of an entirely different metric -- for example, the Envelope Leakage Ratio, or ELR. To calculate the Enclosure Leakage Ratio, divide cfm50 by the surface area of the building enclosure.

For more information on these issues, see:

Air Leaks Happen at the Surface, Not in the Volume

Blower Door Basics

May 8, 2018 4:46 PM ET

Edited May 8, 2018 4:47 PM ET.

Exhaust only bath fans at 0.6ACH50?
by user-7041260

Not accounting for common areas, 2,264cfm divided by 18 apartments is 126cfm. If the bath exhaust fans are running at 60cfm, is there not a substantial negative pressure (approx. 24 Pa) forever being exerted on this nice retrofit?

PS The GBA website will not let me enter my name, John Rockwell.

May 8, 2018 5:00 PM ET

Response to John Rockwell (Comment #8)
by Martin Holladay

Continuously operating bathroom exhaust fans do, indeed, create negative pressures in the apartments. As long as the apartments don't have any atmospherically vented combustion appliances, however, and as long as there are enough cracks in the building and air pathways to provide makeup air, the depressurization is not necessarily problematic.

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