exterior and interior insulation of heavy masonry buildings in … · 2016. 10. 24. · this...

Exterior and Interior Insulation of Heavy Masonry Buildings

In North America and Norway

– A comparison

Figure 1: Bygningsdetaljer 723.312 (SINTEF)

Victoria Nordhagen ARCH 4672 March 8th 2012

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Introduction and background

To meet rising modern demands for thermal comfort and government regulations, it

has become increasingly popular to apply additional thermal insulation to existing buildings.

This article will discuss problems associated with insulating heavy masonry walls, pros and

cons using different approaches and compare the methods used in North America and

Norway.

Heavy masonry walls are something other than what is normally being built today,

which often is a steel frame or skeleton in which all the forces are distributed, and clad with a

building envelope, which protects the indoor climate from the outdoors. However, heavy

masonry walls have two purposes; distribute loads into the ground and also protect the

interior against the outdoor climate. They are therefore very thick at the lower floors to

manage the loads, while reducing in thickness upwards. Later heavy masonry walls were

built with an integrated, supporting steel structure. Figure 1 and 2 shows heavy masonry

buildings from respectively Norway and Canada.

Figure 2: A typical Oslo apartment building from 1890-19101

Figure 3: Customs Examining Warehouse in Winnipeg 2

1 http://pub.tv2.no/multimedia/na/archive/00783/sverdrupsgt5-4-3_7830154x3.jpg 2 http://www.nrc-‐cnrc.gc.ca/eng/ibp/irc/ci/volume-‐4-‐n2-‐15.html


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Building physics

The transport of moisture, air and heat is intimately connected. All will take the line

of least resistance from the location with a great concentration to a location of low

concentration to achieve balance. Heat is transported in different ways; trough conduction,

convection and radiation. Conduction is the kind of thermal transport that occur in a thermal

bridge, no movement of air is necessary. Atoms with a high energy will excite adjacent atoms

and in this way the thermal energy will travel from where the temperature is high, to a place

of lower temperature. Heat and water will both move through convection. This is a mixing of

air as a batch of air (containing heat energy and vapor) moves to a place of lower pressure,

temperature and heat. Thermal radiation is electromagnetic emission from an object caused

by the thermal motion of charged particles. At temperatures below absolute zero (0°K = -

273°C = -460°K), no radiation is being emitted. Moisture also moves independent of air

movement, this is called diffusion, and is the motion of water in the direction of decreasing

concentration.

The thermal resistance of a material (or across a wall) is measured by what is called

thermal resistance, R [Watt/m2]. The content of moisture in the air is measured by relative

humidity (%RH). This value tells how much vapor the air contains in relation to maximum

capacity at a given temperature. When RH reaches 100%, the water vapor will condensate to

liquid and clings to surfaces or accumulates inside the wall assembly. The temperature at

which water vapor condensates is called the dew point temperature.

Types of insulation:

Insulation is a barrier that hinders the transfer of heat. A wide variety of insulation

materials with different properties exist on the market. Mineral wool is made out of thin

glass, stone or ceramic fibers pressed loosely together. It is fire resistant up to 230-250 °C


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(glass wool) and 700-850°C (stone wool). Mineral wool is a hygroscopic material. This type

of insulation material binds moisture in its pore system, so it is important to be certain that

the water transport away from the wall is sufficient. This is achieved by installing a vapor

barrier on the interior side of the insulation. Extruded polystyrene (XPS) is a compact

insulation of extruded polystyrene foam. The material is homogenous with a closed cell

structure, which gives the product a high compressive strength and good heat insulating

ability. The closed cell structure gives the XPS non-hygroscopic attributes, which makes it

performs well under humid conditions. This product is to be found in flat boards of different

sizes. Polyurethane foam is a product that is applied by spraying it onto the wall. A product

like this with good air barrier characteristics provides several advantages: (1) airtightness, (2)

continuity at junctions, (3) applicability over irregular surfaces and (4) good control over

total thickness3.

Vapor and wind barriers:

A vapor barrier is added to keep water vapor from entering the insulation and the

brick wall from the interior of the building. When dealing with old masonry buildings in a

cold climate this is crucial to the longevity of the building. If water vapor is allowed to

condense on the cold masonry wall it can cause massive damage to the bricks during freeze

and thaw cycles4. If the vapor condenses in the insulation material, it severely reduces the

materials ability to insulate properly, simultaneously allowing fungi to grow. A liquid spray-

on vapor barrier is often used in combination with polyurethane foam. The greatest advantage

with this kind of product is that the risk of puncturing it during construction is very small,

compared to other kinds of vapor barriers like plastic (polyethylene - PE), fabric or metal

sheets1. If a fabric/plastic with aluminum lining is used, the aluminum works as a barrier for

3 Gonçalves, M., page 3 4 Straube, J., p. 19, 2011


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heat radiation, in that way, even more energy can be saved. The main problem with sheet/roll

products is to make the joints tight. A wind barrier can either be a roll product or its like

applied on the cold side of the insulation, or the outer parts of the wall itself. The main

objective of a wind barrier is to prevent wind from blowing into the wall assembly. Since

water molecules are larger than air molecules, the wind barrier will also prevent water from

penetrating.

Insulating an existing wall:

There are two ways of insulating an existing wall, exterior, or interior insulation.

When placing insulating the exterior side of the wall the brick is protected against the cold

winter temperatures and moisture from the outside, in addition to being heated from the

inside. You also mostly avoid thermal bridges, which are a major cause of thermal discomfort

and heat loss in a building. However, it is extremely difficult, if not impossible, to keep the

historical appearance of the building when using this approach. With this said, this method is

in most cases out of the question in cases where the exterior preservation aspect of the project

is a priority. Therefore interior insulation often is the preferred approach, even though there

are several problems associated to this method. First of all the brick wall itself will no longer

receive heat from the interior of the building, which makes it more susceptible to damage

from freeze-thaw cycles during the cold season1. The lack of heat from the interior causes a

prolonged drying time and also lowers the temperature in the wall5. Another problem is that

the temperature gradients (the difference between indoor and outdoor temperature) will

increase in magnitude, which makes the thermal bridge issue to a significant problem.

Insulating the interior walls also “eats up” some of the space inside, shrinking the area of the

room.

5 A. H. P. Maurenbrecher et al 1998


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In Canada, an old warehouse built in 1908-1911 in 1993 went through a retrofit

makeover to become offices and laboratories3. A part of the wall assembly was left

uninsulated for comparison. In the study of this building a number of different parameters

were recorded over four years. These parameters were thermal and pressure differences

(interior/exterior), thermal bridging at floor level, thermal resistance of wall components,

wetting by rain of the exterior wall, moisture changes in the wall and surface condensation.

The results of the observations show that renovation of the wall resulted in an increase of the

thermal resistance by 47 to 67% compared to the uninsulated wall. At the same time, the

exterior temperatures of both insulated and uninsulated walls were approximately equal

(range of 63°C), whereas the temperature of the interior surface of the brick in the insulated

wall sunk drastically. The temperature at the interior of the brick wall by in the insulated wall

could be 25°C below that of the corresponding in the uninsulated wall, and well below

freezing point for several months during winter. The research team expected a thermal bridge

at the intersection of the insulated wall and floor. It was found that the temperature of the

wall in this location was fluctuating around 10-12°C, which was 9-11°C lower than the

temperature at mid-height. This temperature does not satisfy the American Standard (from

1992) on thermal comfort, and there is a risk of vapor condensation but due to low RH inside,

the dew point temperature was as low as 4°C. The report concluded that moisture within the

wall assembly would not be a problem as a result of the retrofit approach, so freeze-thaw

damages would not be a problem.

Another more recent Canadian survey explores ten masonry buildings that were

subject to different kinds of retrofit approaches (though all had insulation added to their

interior) by computer simulation, visual, non-destructive examination and by looking through

construction documents. The results suggest that increasing the thermal resistance on the

interior side of the masonry would theoretically produce favorable conditions for an


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increased rate of condensation in six out of eight measurable cases. The other two cases had

opposite results; there was a decrease in the rate of condensation. This difference between the

two groups is explained with the fact that the latter wall assemblies had an air gap in the

masonry on the cold side of the air barrier, allowing drying6.

SINTEF Byggforsk (SINTEF Building and Infrastructure, Norway’s leading

disseminator of research-based knowledge to the construction industry) explored the

consequences of excessive interior insulation of a concrete (and wooden) wall in a typical

Oslo climate through one-dimensional simulation. 150, 250 and 400mm of thermal insulation

(glass wool) were added to a wall along with a vapor barrier. Their calculations indicate that

the risk of mold growth in the outer parts of the construction increased along with the

thickness of insulation. This is when RH exceeds 80% and the temperature is between 0 and

5°C7. Even though the temperature on the interior face of the concrete wall went below

freezing point during the coldest periods, the RH never exceeded 100%, so there was no

condensation. It is possible to compare these findings to a masonry wall, as a massive

masonry wall has the same thermal resistance as a concrete wall8 , even though the

hygroscopic properties could be different, depending on material properties such as porosity,

capillarity and composition.

Advices:

In both North America and Norway, putting insulation on the wall is not the number one

alternative, as it is an expensive and invasive method in order to save energy and improve the

indoor thermal conditions. Both U.S. and Norwegian agencies advise to go through with an

energy audit, to “evaluate the current energy use of the building and identify deficiencies in

6 Gonçalves M., 2007 7 Geving & Holme, p.24 8 Kvande, T., table 5, 2003


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the building envelope or mechanical systems”9. Further, both countries also advise that

before considering insulating either interior or exterior of walls, any air

infiltration/exfiltration (possibly discovered during energy audit) should be limited to a

minimum. Other measures of choice are insulating attic and floor above basement and

improve (not change) the windows.

Exterior insulation is not discussed a lot in U.S. and Canadian articles, but many

different of different interior insulation methods are discussed. The option of putting up a

drywall on a steel stud wall filled with batt insulation is argued against, mainly because of the

risk of condensation and mold growth in the wall10. This is also the reason used when

recommend against using biodegradable materials such as wood inside the wall. Both Straube

and Gonçalves argue that spraying airtight insulating foam directly onto the interior side of

the existing masonry is the best alternative. They argue that air leakage is prohibited and that

the foam also protects the masonry against water vapor from the interior. Research by

Straube (2009) supports adding interior insulation to a masonry wall; findings show a low

risk of water vapor condensing in the wall assembly in cold climates, mainly because of the

low RH in the air. A general concern is corrosion of embedded steel beams in the masonry

wall, as the insulated walls contains more moisture11.

Norwegian authorities still argue what kind of retrofit approach would be the most

appropriate in the Norwegian climate, which can be both cold and humid during winter. As

previously discussed, this is not a favorable combination for interior insulation. Also, most of

the concerned buildings have embedded timber joists that support the floors. Water

condensation in the wall could lead to rotting12. However, the most common way to apply

interior insulation is by putting up a wood frame and filling it with glass wool insulation

9 Preservation brief 3, page 3 10 Straube, J., Ueno, K., & Schumacher, C. (2011, December 21) 11 Straube 2009 12 Eir Grytli, 2004


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before closing the wall with a vapor barrier and a wooden or plasterboard cladding. The

importance of using wood with water content below 20wt% is stressed13. As a rule of thumb,

the amount of interior insulation recommended is limited to 100mm ≈ 4”14. Buildings

protected by law rarely undergo retrofitting. Insulating with spray foam as insulation is barely

mentioned. The Norwegian buildings discussed have a relatively porous brick protected by a

lime based plaster and paint on the outside. This promotes easy wetting and drying of the

building. The walls can contain a large amount of water.

Conclusion:

It seems like the views on insulating buildings are quite similar in Norway and North

America. In order to save energy and improve occupant comfort both recommend that house

owners should try other, less invasive, approaches before deciding to add interior insulation.

However, the methods and materials used when insulating are very different. In the U.S. and

Canada, use of mineral wool as insulation is advised against, because of the materials

hygroscopic properties and difficulties sealing off the construction from the potential humid

indoor air. It is also advised against using wood because of the risk of deterioration in case of

water condensing in the wall assembly. In contrast, because of Norway’s long traditions of

using wood for construction and the high availability, the use of wood is common, also when

applying interior insulation, although only small amounts of insulation is advised (and even

using mineral wool). The general Norwegian resistance towards interior insulating historic

masonry buildings can be explained by the porosity of the brick and potential humid + cold

climate.

13 Einstabland, H., 2007 14 Dehlie, Camilla S. "Etterisolering av Murhus." Message to the author. 2 Mar. 2012


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Bibliography:

Dehlie, Camilla S. "Etterisolering av Murhus." Message to the author. 2 Mar. 2012. Web.

8 Mar. 2012.

Einstabland, H. (2007). Bindingsverk av Tre: Varmeisolering og Tetting. In SINTEF -‐

Byggforskserien. Retrieved March 5, 2012

Eir Grytli. (2004). Fiin Gammel Aargang -‐ Energisparing i Verneverdige Hus (Energy

Conservation in Historical Buildings). Retrieved March 1, 2012, from

www.sintef.no/upload/fiin_gammel_aargang.pdf

Geving, S., & Holme, J. (2010). Høyisolerte Konstruksjoner og Fukt (Highly Insulated

Constructions and Moisture). Retrieved March 1, 2012, from

http://www.sintef.no/upload/Byggforsk/Bibliotek/SB%20prrapp%2053.pdf

Gonçalves, M. D. (n.d.). Insulating Solid Masonry Walls. In Patenaude-‐Trempe. Retrieved

March 6, 2012, from http://www.patenaude-‐

trempe.com/PDF/NBEC_EN_Insulating_Solid_Masonry_Walls.pdf

Gonçalves, M. D., & Semple, B. (2007, March). Performance Evaluation of Retrofitted

Solid Masonry Exterior Walls. In Canada Mortgage and Housing Corporation.

Retrieved March 6, 2012, from http://www.cmhc-‐

schl.gc.ca/odpub/pdf/65033.pdf?lang=en

Kvande, T., & Waldum, A. M. (2003). Etterisolering av Betong-‐ og Murvegger (Post-‐

Insulation of Concrete and Masonry Walls). In SINTEF -‐ Byggforskserien.

Retrieved March 1, 2012

Hensley, J. E., & Aguilar, A. (2011, December). Improving Energy Efficiency in Historic

Buildings . In Preservation Briefs. Retrieved March 6, 2012, from

http://www.nps.gov/hps/tps/briefs/brief03.htm


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Maurenbrecher, A. P., Shirtliffe, C. J., Rosseau, M. Z., & Zaïd, M. A. (1998, September 10).

Monitoring the Hygrothermal Performance of a Masonry Wall With and Without

Thermal Insulation. Retrieved March 6, 2012, from http://www.nrc-‐

cnrc.gc.ca/obj/irc/doc/pubs/nrcc42462.pdf

Straube, J., Ueno, K., & Schumacher, C. (2011, December 21). Internal Insulation of

Masonry Walls: Final Measure Guideline. In Building Science. Retrieved March 3,

2012, from http://www.buildingscience.com/documents/reports/rr-‐1105-‐

internal-‐insulation-‐masonry-‐walls-‐final-‐measure-‐guideline

Wilkinson, J., De Rose, D., Straube, J. F., & Sullivan, B. (2009). Measuring the Impact of

Interior Insulation on Solid Masonry Walls in a Cold Climate. In Building Science.

Retrieved March 3, 2012, from

http://www.buildingscience.com/documents/reports/rr-‐0910-‐measuring-‐

impact-‐interior-‐insulation-‐masonry-‐walls-‐cold-‐climate

Ramstad, T., & Edvardsen, K. I. (2010). Trehus (Wooden houses) (pp. 1-‐333). N.p.:

SINTEF Byggforsk. Can be bought online:

http://www.sintef.no/Byggforsk/Publikasjoner/Handboker/Trehus/

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