Do NOT buy a home with a Block Foundation, unless…

Why does the concrete block foundation of a 50 or 60 year old building, which was in perfect condition a few years ago, suddenly appear to be weakening, deformed or showing significant damage? Surprisingly, the source of such a problem may be a homeowner’s idea to reduce their energy consumption by insulating the foundation. Interior renovations, particularly in the area of insulation, are often the cause of damages that may not be noticed until years later. Frédérick Beaucage, civil engineer at CEP Forensic and Regional Manager of the Ottawa office, answers a few questions about concrete block foundations, which are quite common in older buildings and cottages. He explains why sometimes it’s best to just “leave old foundations alone”.

1. First, can you tell us why some foundations are built with concrete blocks while others are built with poured concrete, and what are the major differences between the two?

One of the major differences is the installation method of the foundation walls, which is reflected in the cost. For instance, when it comes to cottages, concrete blocks are easier to transport to a confined area than having a concrete truck mixer come on site. In addition, there is no formwork to set up with concrete blocks.

For the majority of handymen, it is easier to lay a concrete block foundation than it is to build sound formworks for poured concrete. Moreover, when you consider older foundation walls, there was also a cost issue, as labour was cheaper than today, while poured concrete was more expensive.

The other major difference between the two types of walls, concerns the structural resistance of the foundation wall in terms of lateral thrust (meaning the inward pressure of the soil against the foundation). Concrete blocks, with their many joints, are more sensitive to inward movement than cast-in-place concrete, which can be seen as one big block. In terms of vertical strength, there is no real difference between both foundations, they both do a very good job of supporting the building.

2. What types of damages associated with concrete block foundations do you encounter most often in your work?

If you eliminate the damages related to soil movement that can be observed on both types of foundations, we often find inwardly displaced blocks with concrete block walls. This type of damage can be caused by ground pressure, ground freezing, hydrostatic pressure or a combination of all three. It is also important to note that this type of damage is only present when there is a basement or crawl space deep enough for there to be a pressure difference between the exterior and interior. What I mean is, when there is a high enough ground level on the outside, in comparison to the basement floor, there is a pressure difference from the ground that pushes the wall inward. From the inside, there are no restrictions to the soil pressure, since there is only an empty space for people to walk. Over time, the joints between the blocks break and the blocks shift slowly inward. 

3. Can you explain why doing interior renovations, such as insulating concrete block foundation walls, may not be a good idea?

Foundation walls of this type, especially older ones, need to “breathe”. There needs to be a place where the moisture can escape. Moisture from the outside will pass through the blocks due to the porous nature of the block material. From the inside, the blocks use the interior heat to dry and evaporate the moisture contained within them. This process will increase the humidity level in the basement, but that’s a whole other topic!

So, insulating walls with urethane, extruded or expanded polystyrene, or fibreglass insulation with a vapour barrier, limits the amount of heat reaching the wall and traps moisture in the blocks. In addition, insulation also limits the heat loss that can be directed through the ground to the outside. The escaping heat was preventing or limiting the freezing of the soil around the foundation since construction. If there is no frost outside, there is usually no frost pressure, and the blocks can therefore survive for a very long time.

4. Are damages caused by adding insulation worse in cold, dry winters or in mild, rainy winters?

A cold, dry winter is often less harsh on the foundation, but this depends on the type of soil along the foundation. If you have frost-susceptible soil and poor drainage, most of the problems observed are related to soil expansion occurring when the heat loss from the interior has been eliminated. With gravel or sand backfill and a good foundation drain, wall insulation will usually not cause problems with a cold continuous winter and a good snow cover.

However, in a mild winter, and with winter rains, the water can stay on the surface longer because of the frozen ground and the reduced percolation. And, if there is a rapid drop in temperature after the rain, the water will freeze and push on the foundation walls. 

5. In conclusion, is there a way to insulate a concrete block foundation without fear of causing its long-term degradation?

It is possible, but it is expensive! First, you need to limit the amount of water on the outside along the foundation walls. Good drainage is therefore necessary, as well as the waterproofing of the wall from the outside that will limit the amount of water that can penetrate the blocks.

It is also necessary to have non-frost-susceptible soil along the foundation (the backfill) and a good foundation drain. Afterwards, it is possible to insulate from the inside, without the risk of long-term damages, since no more water can freeze during the winter. If there is no water in the soil, there is no expansion on the outer side of the foundation walls, so no lateral thrust on the blocks.

Therefore, to save the planet and your wallet, you will have to invest at the start to save on heating costs now and on new foundations further down the road. This is something to think about!

BUYER BEWARE – Reducing Caveat Emptor

Market forces and other factors can reduce the feasibility of caveat emptor in some cases. For example, with real estate, because a seller typically knows the condition of a property better than a buyer, legal decisions relating to quality issues have begun to favor the buyers. There are other ways that buyers can feel more assured of quality and that is to have the seller sign to a warranty as to the condition of the basement. Disclosure Laws – These laws have been enacted for the protection of consumers buying certain goods and services, especially in big ticket item such as Real Estate.

So, in summary should you buy a home with a Block Foundation?
In my experience, yes and NO.

These are the steps to take to protect your future when considering buying a home with a block foundation.

• 1) Ask why is the seller selling, this is really important to know especially if repair work was stated to have been recently completed. Which begs the question, was the repair work done by a qualified contractor or was the repair work done at all?
• 2) If there was recent repair work to the foundation, ask for a copy of the work order and call and talk to the contractor and ask about a warranty with the work and their opinion of future problems and why the problem happened in the first place.
• 3) Ask for a Seller Property Information Statement or SPIS is important to understand, as its purpose is to protect both the purchaser and the seller. A SPIS is a standard form document that allows the seller to convey the condition of the property by answering various outlined questions to the potential purchaser. These questions are answered solely on a knowledge basis so if the seller is not aware of the answers, they have the option to state that. The document is then signed and acknowledged by the purchasers to state they have received the disclosure. The SPIS is important because it can prevent future disagreements about what information was communicated regarding the condition of the property. From a purchaser’s perspective, the SPIS provides fundamental information regarding the property. This includes information about the structure, heating, electrical, plumbing, water and sewage. It will also include work that has been completed to the property and current specifications of equipment in the property such as the electrical panel, septic system, well or hot water tank. The work completed can be especially useful to a property inspector, as it can allow them to further investigate specific issues, such as if a basement leak was fixed in the years prior.
• 4) Get the Seller to warranty the condition of the basement in the offer to purchase, for example: “The Seller represents and Warrants that the foundation walls are in perfect condition and do not leak since the repair work has been completed and no issues remain with the foundation.” If the Seller removes your statement in a counter offer then walk away from the offer to purchase.
• 5) Get a home inspection and bring your own moisture meter. These meters can be bought for $30 from Home Depot and are easy to use. place against the bottom of the basement walls and the level of moisture will be on display on the meter.
• 6) Before you seal the deal tell your home insurance company that the house has block foundation and is there extra coverage needed for it.

When in doubt move on, old homes crumble over time, and if you don’t have a good foundation then you will have a empty bank account by doing repair after repair.
If the basement is dry, doesn’t smell musty and no repair work has ever been done then more that likely there is a good foundation there, just make sure you are covered with insurance in the event of extreme weather events.