Problems with insulation, and water, in Chicago masonry buildings

By William Decker, CMI - Decker Home Services

In the northern Illinois area, we have seen many problems with water leaks in newer brick and masonry buildings.  Some of these problems are the result of the recent "housing bubble" when many houses and condominium buildings were built in haste and by less-than-qualified builders and sub-contractors.  One additional cause is the construction details, either those that the Architect actually called for in the plans, or in how the builder "modified" the details.  Sometimes, these details are modified in an effort to save money, but many times it is because neither the builder, or the Architect, actually understands the proper way to construct a building envelope.

What is a building envelope?

One of the requirements of a house or a condominium building is the need to maintain the interior environment.  In technical jargon; " The "Building Envelope" is the area that separates conditioned space  from unconditioned space or the outdoors."  Simply put, the house's insides (the "conditioned space") must be separated from the outside.  Indoor temperatures, humidity levels, and indoor air quality must be kept relatively stable and constant.  Sometimes, the conditioned space of a house will not include the attic or the crawlspace, but in modern construction, more and more, building scientists are finding that extending the building envelope to include the attic and crawlspace in the "conditioned space" will help to maintain better indoor air quality, lower energy costs (for both heating and cooling) as well as increasing the life of the building's roof, electrical system, plumbing and structure.

The building envelope serves as a barrier and helps to control movement in the house.  The major design criteria for proper  building envelope performance are:

Structural integrity (in the case of masonry and brick homes, this means supporting the structure)


Moisture control (both liquid water and water vapor)


Temperature control


Control of air pressure boundaries

The design and materials of the building envelope are determined, in large part, by the local climate and weather conditions of the area where the house is being built.  Adobe exterior walls have been a good exterior wall material for centuries in the southwest United States, but adobe houses would not last long in the rainy northwest.  Likewise, the wooden frame and siding buildings of the New England coast would fail very quickly if they were built around the gulf coast.  Different climate conditions require different materials and different construction details that are specific to the requirements and needs of each climate area.  There is no "one best way" to build a house and, sometimes, what used to work in the past does not work when conditions change.

What has changed in the Chicago area?

The winters of 2006-07 and 2007-08 were much more warm than the averages of the past.  Temperatures would regularly be below zero for a week or two in February and most of the precipitation would be in the form of snow.  But during these two winters, the temperatures were much warmer (32 F, as opposed to the average of 26 F) and there was a lot of rainfall as opposed to snow.  The summer of 2008 gave us record rainfall readings.  The winter of 2008-09 and last winter had a record number of freeze / thaw cycles (where the temperatures swing, wildly, causing water to freeze and thaw many times).  This summer (2010), the Chicago area experienced 40+ days of temperatures over 80 F and the humidity levels have been oppressive.  All these factors have lead to some major problems with newer houses and buildings, especially in ones constructed of brick, stone and concrete blocks.

Chicago has a long history of building with masonry.  This is a local preference and is rooted in the cities' history of the Great Chicago Fire, a conflagration that burned for 3 days, killing hundreds and totally destroying 4 square miles of the city.  The large number of wooden frame buildings, as well as their close proximity and haphazard construction (during a building boom, with sub-standard contractors.  Déjà Vu all over again?) greatly contributed to the Chicago Fire's devastation.  As a result, the Chicago Building Codes are some of the most strict in the nation and greatly exceed the national electrical and fire safety codes.  People started building with brick and stone because these materials were not flammable and would resist the spread of fire.

But, contrary to popular belief, brick stone and masonry buildings are not waterproof.  All masonry is porous and will allow water to flow though it, and will even suck moisture into small cracks in mortar joints through capillary action.  Masonry is very sturdy, provides superior structural integrity and looks appealing, but it is not a sure guard against water intrusion. While masonry has a high thermal mass (resistance to temperature changes) it is not a good insulator for heat and is susceptible to air leaks.  Because of these factors, the details of the building envelope. especially of masonry buildings, are very important.

What are the factors or a good building envelope for a masonry building?

First, the basics of heat and water movement (thermodynamics) through the building envelope:

Heat moves from warm to cold.


Moisture moves from warm to cold.


Moisture moves from wet to less wet.


Air moves from high pressure to low pressure.

So, how does this work in houses?


Heat has to be retarded from moving and this is done by means of insulation.  We measure the retardation of heat movement by the R factor of the insulation, which is the reciprocal of the heat conductivity of a material.  So materials that do not conduct heat well are good insulators and have a higher R value.  But the R factor is not the only measure of a good insulator when the insulation is in place in the house.  Lab results and measurements do not always apply in the real world.  We have seen many new houses where R 38 fiberglass insulation was installed (but improperly) that, when actually measured, were only providing  R 10 insulation values.  The insulation of a house should be evaluated by its performance, not just its specification based upon ideal laboratory conditions.  Additionally, if the insulation is improperly installed (which is usually he case) it will not perform anywhere near what it was designed to do.

Also, as we see from the above movement dynamics, if we want to properly control the heat movement we must also control air and moisture movement.


To control the movement of moisture, which is not only liquid water but also water that has been dissolved in air (otherwise known as water vapor or humidity) an impermeable barrier is used.  But with humidity, we must also control air movement and not all liquid water barriers are also air barriers.  House wrap materials (Tyvek, Typar) will mostly stop the movement of liquid water, but not water vapor or air.  We also want to stop water from entering the house through the building envelope but not water that may be leaving, a house has to be able to breath and dry.  To do this, a water barrier must be able to stop water going in, but also allow water vapor to go out.


Air leakage can cause heat loss (or cold air infiltration) as well as water vapor movement.  How can we stop this air movement but still allow the house to breath as well as provide the proper amount of ventilation so that the houses inhabitants can also breath?  We don't want to stop all air movement but we do want to be selective and have better control over how much air moves through the envelope and what type of air it is (wet, hot, cold, etc).

How are masonry building envelopes being built now?

The typical modern Chicago area masonry building (as opposed to a wooden framed, brick veneer house) is constructed in one of two ways:

Double wythe masonry wall

Single wythe masonry building


Left: A double wythe masonry building.  Double wythe means that the wall is actually two walls with and air space between them.  The interior wall is structural and supports the floors and roof and the exterior (usually brick) wall provides protection from water and has a more pleasing appearance.  Please note the air gap between the walls which provides a channel for drainage of water that penetrates the brick.

Right: A single wythe wall, and how many of the urban houses and condominiums are now being built.  You will note that there is no air gap and the only detail keeping water from leaking through the masonry is the flashing.  If the flashing is not done properly, water will be absorbed through the masonry (concrete block) and wick into the wooden floor and roof trusses.  This will cause the trusses to rot and, eventually, lead to structural failure.  Unfortunately, we are seeing more and more of this happening.

When water, which can be from rainwater or humidity (and Chicago is well known for its humid summers) is absorbed through the concrete block and the flashing has not been properly installed, that is where the problems begin.  Our clients see water stains on their walls and baseboards, ceiling water leaks and increased heating costs (wet insulation does not insulate very well).  But water stains are, at worse, a cosmetic problem.  The larger concerns are mold formation on the walls (both visible and unseen mold growing on the back side of the drywall) and, in the long term, rotting wood floor and roof joists.  Both of these conditions can lead to long term problems, expensive repairs and lack of resale value for the house or condominium unit.

As seen in the diagram at the left, A single wythe masonry wall is not a good idea in the Chicagoland area.  The reasons for this are many:

bulletA single wythe wall does not allow for an air gap between the two walls.  Water cannot jump an air gap, but can (and does) wick through concrete block, especially when it has not been properly sealed or maintained.
bulletThen the required flashings in the wall (under the coping stone and at the joist pocket areas (compare to the diagram above) there is nothing to stop the water from migrating inward.
bulletThe stone roof parapet wall coping is almost always flat when it should be beveled or curved so as to drain rain water and snow melt outwards.  As a result, water pools on this stone and drains into the wall from above.  Most builders use an artificial type of stone (Renaissance Stone) that is even more porous than natural limestone.  The reason for this is usually cost, but also the preference of the homeowners ("It is easier to rest your beer can on.").
bulletWhen the floor and roof joists are not shimmed, so as to provide an air gap between the masonry and the wood, the wooden truss ends will also absorb moisture.  This will cause the joists to rot and / or the metal gussets that hold the truss together will rust.  Either process will, eventually, cause the trusses to fail and can lead to structural collapse.
bulletThe commonly required interior wall detail calls for foil faced rigid foam, covered with a plastic vapor barrier on the inside and drywall, is just not correct for this climate.  Many times, in an effort to save money, the builder substitutes non-faced fiberglass insulation instead of the more expensive rigid foam.  Combined with the plastic vapor barrier directly behind the drywall, this creates an aquifer where water can accumulate in great quantities.  Many Architects are ignorant of this "in the field" situation, having just done a "cut and paste" in their drawings from some commonly accepted national standards.  These "standards" just don't work in this area where there is only minor events of humidity entering the wall from the inside.  Remember, Chicago has 3 humid seasons and humidity is more likely to migrate into the house than out of it.  This detailing leads to long term moisture being trapped against the back side of the drywall and causes mold growth.  We have even seen, in extreme cases, water leaking out of exterior wall electrical receptacles and light switches where the plastic vapor barrier has been penetrated.  The proper detail for this type of wall is to use a closed-cell spray foam, sprayed directly on the masonry wall.  This provides not only insulation against heat loss, but also seals against air, water and vapor infiltration.


Flat roof problems:

When a building has a flat roof, there can be special problems.  The old model was to insulate (and, hopefully, provide a vapor barrier) on the ceiling of the top floor while ventilating the space between the insulation and the roof decking.  This still works, but it does not take into account the increased usage of recessed lighting fixtures.  This type of light fixture, which penetrates the insulation and the vapor barrier, allows humid air from inside the house to travel up into the attic area.  When this humid air comes in contact with the cold underside of the roof decking, it condenses into a liquid form.  We have seen extreme cases where the light fixtures are dripping water at a rate of 4 - 5 gallons per day!  To make matters worse, many of the newer flat roof buildings do not provide for ventilation of this space, preferring to have a wooden roof deck installed, directly, on the roofing membrane (and don't even get me started about the problems with wooden roof decks!).

This accumulated moisture will lead to mold formation, but more importantly the wet roof structural members will start to rot and will, eventually, loose their structural integrity and collapse.  The picture on the left illustrates this condition.  Note the black wood on the roof trusses and the roof decking, above.  This is water saturated wood.  When the moisture content of the wood exceed 19 - 20%, mold spores start to grow and eat the cellulose that provides the wood with its stiffness.  Wood rot mold (Cladosporium) is usually not harmful to humans, but other types of mold can be deadly.  Note the exotic mold that is growing on the underside of the roof at the upper right corner of the picture.  Another problem with this moisture is the rusting of the metal gussets that hold the wooden truss together.  Also note the pronounced sag in the roof decking.  It is a good thing that this condition was found when it was, otherwise this whole roof would have collapsed, possibly killing the inhabitants.  This was the ceiling area above the house's master bedroom.

The proper way to construct this type of house would have been to install open cell spray foam on the underside of the roof decking.  This foam would provide an air, water and vapor barrier as well as insulation and stopped the moisture, either from in the house in the winter or from out of the house in the summer, from accumulating in this space.

Rotted roof trussesAs it is, this homeowner had to have a complete gut and rebuild of the top floor of his house, including the roof structure..


Unfortunately, once the house o condo construction is completed, most of these problems have already been "built in".  There are, however, steps that can be taken to correct the problems even after construction is completed.

bulletFirst, and foremost, when these buildings are condominiums, the main problem is getting all the unit owners informed and on-board with the situation and what it will take to correct them.  Most smaller condominium buildings have very little cash repair reserves.  Sometimes this is because the owners have no idea of what it takes to maintain a large building, but more often it is because the  builder took the association's reserve funds when he handed the building over to the association.  When buying into a condominium association, it is vital that you, or your real estate lawyer, performs the necessary due diligence and verify that all association funds are in an escrow account that the builder does not control.  It is also important for the association to have a transition and reserve study inspection done BEFORE the builder hands over the building's common areas.  These inspections will not only inform the owners of the building's condition but also help to set the assessments at a level so that the money will be there when maintenance and repairs are required.
bulletMake sure to hire a professional and certified home inspector, one who also also trained in thermal imaging and is experienced with the problems of newer concrete block buildings and houses, to do your pre-purchase inspection.  He will use thermal imaging, deep probing moisture meters and masonry absorption testing to determine the initial condition of the house or building.  Forewarned is forearmed!
bulletIf there are large mortar cracks on the exterior of the building, they should be ground out and re-pointed.  It is important that the proper mortar type is used, that all the cracked mortar is ground out and that the new mortar joint is properly tooled to a concave finish.  The new "European" style of flat pointing is NOT an acceptable technique for a mixed humid / wet climate like Chicago and, usually, is only a thin parge coating over the old mortar.
bulletHave single wythe masonry buildings sealed.  The old "best practice" was to have the exterior block sealed with a silicone-based penetrating and pigmented siloxane sealer.  This will stop water intrusion for a 3 - 5 year timeframe, but it is equally important that the sealing contractor applies the product properly, in accordance with the manufacturer's instructions.  The newer, and longer lasting solution is to seal the exterior surface of the block with an elastomeric "plugger" type paint.  This paint goes on very thick and is like enclosing the building in a rubber coating.  Sealing with an elastomeric paint will also work to close the hairline mortar cracks that are commonly seen in these type of buildings and houses.  DO NOT use a sealer paint over brick.  Brick must be allowed to breath.
bulletMake sure that the parapet wall coping is properly flashed.  The flashing should be installed under the coping and extend out both sides.  A good quality job will display stainless steel drip edges where the flashing protrudes from the wall.  Stainless steel drip edges will resists wear and will not corrode.
bulletOnce the exterior has been sealed and the coping flashed, there will still be a lot of water that has been sequestered in the block walls.  A small 3 unit, duplex down condominium building can contain some 3,000 gallons of water in the block.  If the exterior of the block has been sealed, this water has also been sealed in, with no where to go but inwards.  Once the block has been sealed, it is important that each floor be equipped with a commercial sized de-humidifier and that these de-humidifiers be run for 2 - 3 weeks.  This will suck all the moisture out of the masonry.
bulletAs a last step, once the masonry has been sealed, flashed and dried, is to properly detail the insulation.  The drywall, plastic and wet insulation should be removed and a closed-cell type spray foam applied directly on the masonry.  This will stop air, water, water vapor and heat from penetrating the wall cavity and will stop this movement from both the outside and the inside.  Once this insulation is in, the drywall can be reinstalled and painted.
bulletThe owner should enter into a maintenance agreement with a reputable masonry contractor, one who has experience with water intrusion problems, so that the building's condition can be monitored.  The contractor should come out and inspect the building for problems every year.  It is always better to find a small problem, and correct it, before it has a chance to become a big (and expensive!) problem.