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Building Science: 101 Ventilation Best Practices

ventilation best practices

I am often asked what cold-weather planning the building committee should be considering. Surprise is expressed when I suggest the condominium’s attics and their venting. It is true an attic only needs one tenth the ventilation in the winter than in the summer to control moisture buildup and temperature, but the wintertime also has some unique issues.

  • First, if the building committee wants attics to be inspected by an engineer or contractor, it is a lot easier inspecting a cold attic than an attic on an August afternoon.
  • Secondly, if repairs are needed, it is better to prepare bid documents before the busy spring and summer construction season.
  • Finally, ice dams are caused by excessive heat loss through an inadequate attic insulation/vapor barrier. If the attic ventilation system cannot properly remove this hot air against the underside of the roof sheathing, a cycle of freezing and thawing of expanding roof ice may infiltrate through the roof surface, causing interior water damage.

There are a lot of myths about what makes good ventilation in an attic. One venting myth to dispel is the best natural ventilation is rising hot air venting solely through ridge or gable vents. This is sometimes called gravity ventilation. Tests have shown this chimney effect is negligible when compared to wind movement which has a much higher efficiency and allows for considerably smaller net venting area to be successful.

Maximizing Wind Movement

The difficulty with relying on wind movement is areas of high and low pressure will change with wind direction; thus, existing buildings are dependent on the structure’s design and orientation for determining the type and location of vents. The best designs have the outlet as high as possible, such as a ridge vent, and the inlet as low as possible such as the soffit area. To improve this airflow, air chutes are often installed during initial construction or later retrofitted. These chutes are formed plastic channels that are attached to the roof joists and are butted up to the soffit vents to act as a pathway conduit for air coming through the soffit vents. They also serve as a barrier to prevent the attic insulation from clogging the soffit vents.

Soffit vents are probably the most important of all vents as they can act as both an inlet and outlet for airflow. That is why it is imperative they be kept free of debris or other material that could clog the vents. For this reason, attic inspection should ensure the attic’s floor insulation is not currently blocking the soffit vent’s air pathway. This blockage can occur as early as the initial installation of the attic floor insulation or after the insulation is disturbed by recent attic work on the sprinkler or electrical systems found in the attic. Without soffit venting the ridge or high gable vents would draw make-up air through the ceiling instead of from outside. For this reason, the soffit vent should have at least 50 percent of the net free area (NFA). This NFA rating is stamped on vent products. A rule of thumb is that the summer ventilation requirement can be estimated by determining the volume of attic space and dividing by two, which will produce the needed cubic feet per minute (cfm) of ventilation. Local building codes often require one square foot of venting for every 300 square feet of ceiling space.

When selecting replacement vents always seek vents that will have low airflow resistance. They come in either perforated or slotted. The slotted has a reputation of resisting clogging by airborne debris. Some ridge vents come with baffles designed to draw air out due to the suction developed.

Areas of your complex with cathedral ceilings can be more difficult to inspect for proper ventilation. These areas typically do not have attics. Instead, the ceiling sheetrock and vapor barrier is installed directly to the underside of sloping cathedral roof rafters. In these cases, plastic pre-formed rafter baffles are installed between the rafters from the soffit vent all the way up to the ridge vent to form an unobstructed airway and not blocked by the insulation installed between the rafters.

Problem Indicators and Solution Alternatives

Other visible signs your attics’ ventilation is underperforming are the attic ceiling is hot to the touch; mold growth is visible on the underside of the roof sheathing; or moisture droplets are detected on the roof rafters. If attic ventilation problems persist and ridge/soffit venting cannot be improved, other ventilation options could include the installation of roof turbine vents and electric or solar powered vents. These steps will improve indoor air quality, reduce energy consumption, and extend the life of an overworked HVAC system.

In the summer, of course, the main problem from poor attic ventilation is heat. Ninety-degree weather can create temperature of over 150 degrees in an attic. Heat kills. It can kill your air conditioning budget and reduce the lifespan of an asphalt shingle roof by one half its rated life. So, if you start having cabin fever, make sure you vent.

Article written by Jack Carr, P.E., R.S., LEED-AP, Criterium Engineers
Published in Condo Media

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Liabilities and Risks of Ignoring Issues: An Engineer’s Perspective

Liabilities and Risks of Ignoring Issues: An Engineer’s Perspective

Repairs reserves

Question:

A recent reserve study identified a number of repairs/replacements that should be addressed in the community. However, while the reserve is being funded on a monthly basis, there isn’t enough in the current reserve fund for the repairs/replacements. With inflation and knowing that owners won’t be happy, the board decided not to increase condo fees or approve a special assessment and instead will wait to make the repairs/replacements when the money is available in the reserve fund.

Since the reserve study has indicated that these repairs/replacements should be addressed, how might the board’s decision impact our liability should one of these items fail and/or cause damage to the community or someone is injured by our failure to address the repair/replacement?

Answer:

Unfortunately, underfunded condo or Home Owners Association (HOA) reserves are a common occurrence in New England, especially in communities with buildings greater than 25 years old. Most New England states do not have specific requirements for the level of needed reserves nor even a requirement for a full reserve study. States’ HOA and condo statues do place an obligation of fiduciary duty on boards and their members. They must act in good faith and be prudent and faithful in furthering the association’s best interests. A current reserve study and a properly funded reserve fund are often key to protecting a community’s long term financial health and provide good risk management.

Commissioning a reserve study by the board is a good first step in planning for the future. Problems can arise when the reserve study reports underfunding the correction of current common asset deficiencies. In an ideal world, the board recognizes the importance of these reported deficiencies, initiates a plan to raise the needed funds, and orders repairs. But in reality, circumstances may occur when the board feels the community cannot afford an increase in assessments or will oppose a special assessment to fund the needed improvements. It is at this point the board should be aware it may be incurring significant known and unknown risks and liabilities.

Reputation and Building Risks

Some of these risks and liabilities fall in the “legal” category while others in the “quality of life” or “financial” category. That is, if a member of the community or visitor were to be harmed by tripping on an unrepaired sidewalk hazard or a broken deck component, litigation could ensue. Leaving aside the potential success of this type of litigation or the protection of board of directors by liability insurance, the long-term effect could be damage to the community’s reputation. One of the most important duties of the board is the protection of the owners’ net worth. If the community is seen by the real estate market as a dangerous or risky place to live, its future average unit sale value will be reduced. This situation will signal two red flags to potential buyers: First, it will raise doubts about the latent condition of other community assets; and second, it will underscore the significance of the underfunding and future need of special assessments or other emergency measures for future owners. These circumstances could impact the timing of future unit sales.

Most professional property managers will agree ignoring important repairs or putting off needed improvements typically will only increase the damage and costs over time. Not only will the community’s curb appeal be diminished but so will the desirability of banks providing unit loans or refinancing. Responsible communities recognize it is in their own best interests and will not kick the can down the road but face their current and future fiscal needs. Banks and real estate agents often review reserve studies to understand their investment risks. Having the need for future repairs and improvement projects is not the problem. The problem is not having a plan to carry out or fund the repairs and improvements.

Written by Jack Carr, P.E., R.S., LEED-AP, Senior Consultant Criterium Engineers
Published in Condo Media

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Moisture: The Root of all Maintenance

Moisture: The Root of all Maintenance

Moisture maintenance

One of the primary issues in building science is the study of how moisture damages buildings and reduces the quality of life of its inhabitants. Moisture penetration can cause mold, rot, and interior damage. Serious moisture problems and their cure are often hard to solve as the physics of air flow, dew points, and vapor transmission can be complicated even with invasive inspections and the introduction of modern tools such as infrared scanning and moisture meters. As these more difficult problems will need a longer article to fully explore, let us focus instead on the more common problems faced by homeowner association and condo boards.

Leaking Foundations

Foundations are usually constructed with poured concrete or concrete block. Modern foundations are protected with a waterproof coating on the exterior surface and a foundation drain around the foundation perimeter at the base of the footing, often with an under-slab drainage system with an associated sump pump. With these operating properly, basements should be dry. If a modern foundation (less than 30 years old) experiences water infiltration, something is not working right and the source is probably surface water. If someone tells you it is due to rising ground water, be skeptical. Keep in mind the water table is the depth in the earth that is permanently saturated with water. According to the building code, modern foundation basement slabs are built above the water table. If the water table is too high, then the building will not have a basement but rather it will be built on a slab on grade. If you have any question about where the water table is, the municipal code officer or a local foundation excavating contractor can help.

Two-Step Approach

If your foundation is leaking, you need a two-step action plan. First, fix the wall problem allowing water to infiltrate into the basement and second, minimize surface water reaching the exterior of your foundation wall. As it will prove difficult and expensive to re-apply waterproofing to the exterior wall, the typical repair is a pressure injection of polyurethane or other type of foam product into cracks in the wall. The second step is just as important.

Surface water comes from a variety of sources. It can be rain or snow melting on the roof, rain falling on the soil near the foundation, or water from nearby sloping land. Roof gutters are supposed to divert water away from the building, but often they are the primary source of water to the ground around the foundation. Gutters are often poorly designed – either they are undersized in handling the flow of water off the roof area, do not have enough downspouts to handle the quantity of run-off water, or the gutter/downspout is broken or incorrectly placed.

If gutters are installed too low at the roof edge, steep roofs will create a velocity in the laminar flow of water to overshoot the gutter during heavy rain events. Downspouts often discharge their water near the foundation rather than diverting it away from the wall. I recommend adding a minimum six-feet extension to the end of the downspout. Furthermore, you should treat the drip edge area along the foundation wall as a ‘secondary’ roof. By this I mean, you should seal the drip edge from allowing water from the roof or other source to enter the soil near the foundation.

Keep in mind the soil has been cultivated and it absorbs water readily. Newer homes also have the problem of the soil along the foundation being backfill soil that is not compacted well, allowing easy water passage, in effect creating a short circuit from the roof to your basement. This soft soil also is susceptible to settlement, creating a place for water to pool or cause erosion allowing even more water to enter the soil.

To prevent this problem, you must first create a positive slope on the surface away from the foundation. A good rule of thumb is to create a slope dropping three inches over six feet. Once the proper slope is in place, cover it with 6 mil poly plastic approximately 18 inches wide along the foundation perimeter. This is your “secondary’ roof preventing water from entering the soil. Cover this waterproof barrier with stone or other suitable material to prevent the poly sheet from moving.

You may also have to slope the land nearby to prevent your neighbor’s land from contributing to your surface water. This can be done with shallow surface ditches called swales or buried ditches called French drains. This type of drain is a trench at the foot of a slope shedding water toward your home designed to intercept surface water from reaching your foundation wall. Buried in the trench is a perforated pipe to divert water. Your landscaper or property manager can provide details on available options. With a logical plan, you can have the dry basement you deserve.

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