Question Box: What are Post Tension Cables?

Calgary Condominiums

There are over 200 units on the market today in condominiums that were built between 1970 and 1985 and of concrete construction (as opposed to wood frame.) Something that condo buyers should be aware of is the possibility of post tension cables in those condominiums and what it entails.

The following article is reprinted with permission.  Special thanks to Phyllis Fyckes, President of Condo Diagnostics

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Are Post-tension Buildings Too Scary?

When you learn that the building you are considering buying a condominium unit in is a post-tension building, don’t be frightened away until you learn the facts about that particular building. Most buildings constructed with a post-tensioning system are in reasonable to excellent condition – you just need to discover if the one you are considering is one of those.

What is post-tension anyway?

Particularly in the 1970s and 1980s, many buildings in Calgary were built with post-tension cable construction in one or more of the horizontal concrete slabs. Builders have been especially fond of using a post-tension system over a parkade. Some buildings being constructed today use this method as well.

This construction method uses steel strands inside a plastic tubing with grease or oil as a corrosion retardant. There are many strands in both directions cast within a concrete slab, with the strands tensioned against the concrete at the ends of the slab. Sometimes you can see the plugs on the end of a slab that conceal the tensioned end of a cable. The purpose is to create a slab that can support more weight without additional columns that consume space, and also to minimize cracking in the slab.

The concern about a post-tension system relates to the potential for corrosion and deterioration of the steel cables if water and oxygen has entered through a crack. If sufficient cables have deteriorated and lost tension, they may have reduced the slab’s ability to support weight, and may require costly replacement. Post-tensioned slabs also require a certain amount of preventative maintenance in the form of waterproofing any portions of the slab that are exposed to the elements. The waterproofing is another maintenance expense to the Corporation.

If the Corporation has been regularly having their post-tension system monitored by an engineering firm, and have been performing the maintenance as recommended by that firm, the building is no riskier than any other form of construction. However, the Corporation does need to set aside some funds in their reserve account to accommodate the possibility of a future expense.

Check your documents for a recent post-tension report.

The document package you receive from the seller of the unit should include a recent post-tension report if the building has used that construction method. The engineer’s comments will give you some insight into the condition of the system, and the likelihood of future problems. Many engineering firms also give a recommendation for what funding the Corporation may require in the future.

The financials will show whether the Corporation is setting aside money for post-tension work.

The operating budget shows if they are allotting an amount for annual post-tension inspections. You may find mention of post-tension work having been done recently in the audited financial statements. Their reserve fund study will reveal if any funding for post-tension work was recommended to the Corporation. And their reserve fund study plan will state if some of the funding is earmarked for possible post-tension work.

So post-tension is not necessarily bad?

You could be depriving yourself of an attractive home to live in if you immediately steer clear of post-tension buildings. In some buildings that post-tension system may be the only system that has some potential of large expense to the Corporation sometime down the road, but the building itself may otherwise be in top shape. In some other buildings without a post-tension system they may be encountering some other problems that are equally expensive.

As an example there is an apartment building that has been directed by the City to correct its heating and ventilation system; the most recent cost estimate they had was in the neighborhood of $100,000 (an expense to be shared by all the owners in the building, of course). Some townhouse complexes have been built with untreated pine shake roofs which have been suffering fungus problems and are failing much sooner than regular asphalt shingle roofs would. Shake roofs tend to be costlier than asphalt shingle.

The purpose of these examples is just to illustrate that many complexes have their own type of problem, which will require additional funding from the owners. If the prospect of having to provide additional funds for your new home daunts you, you need to remember that most home ownership of any kind requires extra dollars at some time or another – it’s a fact of life.

Be prepared, do your homework, and understand the future possibilities in the place you hope to call home.

Phyllis L. Fyckes, President
Condo Diagnostics Ltd.

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For more information on Post Tension Cables, including some Calgary specific information, click here

3 responses to “Question Box: What are Post Tension Cables?

  1. Mike but not mike F

    A Post Tension Cable System is simular to a tension cable bridge system. Cables under pressure each share a load, the crux is if 1 or more of the tension cables snap or break, that load now goes to the other cables causing them to fail (or fail sooner), thus the entire structure can come crashing down within minutes. Also the concrete wall is under stress from the cable to “hold it together” constantly.

    Water is a tension cables worst enemy as it can find its way into even the tighest of structures. (Google Hover Dam leaking) and see how even water can pass through the mightly Hover Dam concrete over time.

  2. how much tension does a post tension cable in a 5 story building normally have?

  3. Condominium Maintenance

    Thank you for your very interesting post. I have high regard for the valuable information you offer in your Articles i like it.

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