Renovation & Design
Renovation & Design
ASK THE INSPECTOR: Soil moisture key to sinking basement floors
QUESTION: I have a 2800-square-foot, split-level home on the Assiniboine river in Westwood. Over the past few years, with dry summers and limited rain, the floor in one section of the lower level has dropped around two inches. There are no cracks in the walls or window frames. We were told when we purchased the home 20 years ago that it was on piles and the floor was not anchored into the foundation.
Is this normal for river property and, with rehydration of the soil, will the floor elevate to pre-existing level?
Thank you, Jim Thliveris
ANSWER: Unfortunately, it's quite normal for there to be significant swelling and shrinkage in the soil under basement floor slabs in our area. Being in close proximity to the river may be a contributing factor, but cracking and shifting of concrete floors can occur almost anywhere in the Red River Valley.
You may see some rebound in the sunken concrete once normal soil moisture levels return, but likely not enough to prevent the need for eventual repairs.
Basement concrete floor slabs primarily serve two functions in most homes. They prevent moisture, insects and dirt from entering our homes by providing a solid surface over the soil, and they provide lateral strength to prevent the bottom of the foundation from bowing inward due to soil pressure.
In most homes, these thick, non-reinforced concrete slabs are poured directly over a thin polyethylene sheet installed on top of a layer of pea gravel or round stone. Pea gravel is used because it lacks sharp edges and has good flexibility, which prevents damage to weeping tiles and plumbing pipes below this area.
The drawback of using this type of granular fill on top of the naturally occurring expansive clay soil underneath, is the lack compressive strength. Changes in soil moisture may occur in varying degrees in different areas of the hollowed-out basement excavation. This can create uneven areas of expansion and contraction, which creates different forces on different areas of the basement slab above. This uneven movement may also be partially due to different soil composition in various layers, especially if there is silt in some locations. That is more likely in areas near rivers, like your home.
The uneven movement of the soil beneath your basement floor can cause some areas of the concrete to heave upwards, while others may stay put or drop. Because this "floating slab" is not reinforced with steel or anchored into the foundation, these uneven forces will cause the cracks you are seeing.
In some cases, soil erosion underneath the slab occurs because of differing soil compositions, damaged weeping tiles or poor backfilling. That's what has likely caused your floor to sink in one area only. As the moisture in the soil outside your foundation drops because of hot, dry summer weather, major shrinkage can occur.
Uneven soil shrinkage can occur because many different variables can affect moisture levels, including direction of foundation walls, vegetation outside the area, grading, downspout termination locations, and proximity to the river.
South- and west-facing foundation walls have a tendency to have drier soil because of the warming effects of the sun. Also, erosion of the soil on the riverbank may not be visible to the naked eye, but may cause settling of your entire yard in that direction.
All of this could be causing a loss of soil underneath your foundation walls, which may be partially replaced by fill sliding in from under your basement floor. In that scenario, a small void could be created under the concrete, causing your slab to sink.
This is similar to the "sinkholes" we sometimes see on the nightly news, which occur under roadways and swallow up vehicles or large sections of pavement when they collapse. While a similar catastrophe is unlikely in your basement, taking some steps to prevent a worsening of the situation may be wise.
The first thing to do is to ensure that soil outside your foundation, particularly on the south side and river side is replaced if it is eroding or shrinking. Simply shovelling soil against the foundation and in low areas, covering it with sod or grass seed, should help prevent further shrinkage.
Regular watering of these areas and any nearby trees is critical to prevent loss of soil in dry weather. While it may not be possible to water enough for a replenishment of the soil underneath your foundation, keeping the upper layers of soil moist may prevent excessive drying and shrinking of the soil deep down. Keeping trees properly hydrated will not only prevent soil erosion, it will help stop deep roots from removing what little moisture is still in the clay near the bottom of your foundation.
Ultimately, the only real solution to your problem is to remove the concrete, replace the missing fill and re-pour new concrete to provide a more even surface. But since there's no guarantee that this type of repair will be permanent, it should only be done if the slab is seriously damaged.
Maintaining better soil moisture outside your home is a better alternative to a messy and costly concrete repair.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the President of the Canadian Association of Home & Property Inspectors - Manitoba (www.cahpi.mb.ca). Questions can be e-mailed to the address below. Ari can be reached at (204) 291-5358 or check out his website at www.trainedeye.ca.
trainedeye@iname.com
Renovation & Design
SOLUTIONS: Washing soda great for oven racks
QUESTION: How can I clean oven racks by soaking them in borax and water? I tried once and it worked fantastically but I have misplaced the information and don't know how much borax to use. Cathy (Killarney, MB)
ANSWER: An easy way to clean a non-self-cleaning oven is to sprinkle the bottom of the oven with baking soda. Pour white vinegar over the baking soda, let bubble and soak for 30 minutes. Wipe and rinse with water.
In the meantime, put an old towel on the bottom of your bathtub, fill it with hot water and one cup of washing soda (if you cannot find washing soda, borax is an alternative). Let oven racks soak overnight and in the morning (while wearing gloves) rinse the racks and wipe with vinegar. Caution: Never leave water in a bathtub overnight if young children are accessible.
You can also use borax to make an all-purpose cleaner for countertops, walls, backsplashes etc. In a spray bottle, combine 2 tsp. borax with four cups hot water. Add 1 tsp. dish soap and 4 tbsp. white vinegar. Shake, spray and wipe.
QUESTION: We have a two-storey, slab, on-grade home. The main living area is on the first floor where we have an open fireplace. On the ground floor we have a wood-burning stove. Both fires are served by a single exterior masonry chimney with a separate flue for each unit.
The problem is that in cool damp weather the flue for the wood-burner backdrafts and we end up with an acrid smell in the house. We have tried putting in a new stove, stuffing paper in the door and latching it ,and even tried putting bowls of kitty litter in the stove without success. Do you have any suggestions? Thanks. Anne and Dick, Winnipeg
ANSWER: Cozy up in front of a woodstove on a frigid day and you won't want to leave your home, but sometimes the unwelcome smell of a woodstove can send you running. You were smart to replace the older wood stove with an airtight model that will reduce harmful emissions because even if you wisely and thoroughly clean the stove box often, any traces of ashes will fill the room with odour.
Here are a few additional solutions to try: Close the damper whenever not in use. Add a top sealing damper and a tight fitting glass fireplace screen. Pouring vinegar into the box of the screen will not be strong enough to combat the odor which is coming from the pipe and sides and top of the box, proper sealing is your best solution.
QUESTION: I have a blue shirt that leaves my body blue. I've soaked it in vinegar and also a salt solution. I really love the shirt but hate having to shower every time I wear it. It was an expensive shirt and purchased in an airport so I can't return it. Michelle, Winnipeg
ANSWER: Sometimes textiles are not completely colorfast and soaking them in vinegar or salt helps. However, it sounds as though the dye used to make your shirt is faulty.
Check the manufacturer's label on the shirt and contact the company to explain the situation. Many companies will send you an offer to reimburse at least part of your cost. Another option is to head to a store that usually carries fabric dye because they often also sell dye treatments that set textile dye. If you cannot find a color set product, purchase dye remover and then re-dye the fabric.
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Renovation & Design
ASK THE INSPECTOR: Cap that sump pit to combat humidity, radon
QUESTION: I have an interesting question for you about our house, which is in the country and about eight years old.
Should a sump pit in a basement, next to a forced-air electric furnace, be capped to vent outside?
I ask this because I have just capped ours with a vent pipe leading outside the house. I have done this because it seemed to have a great capacity to push cool/damp air upwards and out onto the basement floor. I believe this is what is happening because the plastic vapour barrier that I covered it with seems to "dome up" with internal pressure.
I'm afraid that this may lead to excess moisture in the house during the cold winter months. Is it a good idea or not? We have two pumps, one being a back-up, battery-powered unit. Thank you, James Temple
ANSWER: Having a properly sealed sump pit in your newer home is important for a couple of reasons. While it should have been done when your home was built, it may be fairly easy to accomplish even now.
Initially, I was not clear what you meant by having your sump pit "capped". I originally thought you meant putting a cap on the discharge pipe outside, which would have been a major mistake. Upon further reading, I realize that you simply put a plastic over the pit in an attempt to properly seal it. Again, I'm not sure how you have installed a vent with the pit sealed in this way, but it's something that should not be necessary once you properly fit and seal the lid.
In fact, if you have a properly sealed sump, there should be no need to vent any gasses to the exterior of the home, as they should remain in the pit, and may even partially vent to the outside once the pump comes on.
There are two fundamental reasons why all sumps installed in new homes are required to be sealed. The first is a safety-related issue: to prevent soil gas, or radon, from entering the living space of the home.
Radon is a colourless, odourless gas that is naturally occurring due to the decay of uranium in the soil. Uranium is radioactive and radon gas is one of the bi-products that emanate from these mineral deposits. In some types of soil and areas it can be a serious issue and others it may hardly be a concern. The problem with radon gas in the living space is that it has been strongly linked to lung cancer.
For that reason, all homes built in Canada in the last few decades have required polyethylene sheathing to be installed under the basement floor slab, to prevent soil gas intrusion. While this can be quite effective if properly installed and sealed, there is still a problem with one other component, the sump.
The sump pit in most newer homes is installed simply as a location to collect the water from the terminal ends of the weeping tiles. To accomplish this, we must have the weeping tiles running through the soil beneath and around our home.
Research conducted over the last couple of decades has found that the majority or radon entering our homes is from beneath the concrete basement floor or sub-slab soil. Because modern weeping tiles are now plastic tubes running through this soil, they can be a main conduit not only for water drainage, but for radon gas. Since these terminate in the sump, it may be the number-one location where this dangerous gas seeps into our basements.
The simplest way to ensure this does not happen is to tightly seal the lid of the sump and caulk around the pit to ensure there is no communication between the air inside the pit and the home.
The second reason to seal the sump is the one you have cited. Because there may be a constant flow of fresh groundwater into the sump pit, and typically some standing water, it's a large potential source of moisture intrusion into our homes. When water is constantly present inside a living space, without adequate ventilation, relative humidity will increase inside the home.
Sealing the sump pit lid not only will prevent dangerous soil gasses from leaking into the home, but also water vapour. This is not only a concern in the heating season, as you suggest, but year-round. The air movement inside your plastic "dome" may be more noticeable in the winter, due to all the doors and windows being shut, but can occur even in warm weather.
Properly air-sealing a modern sump pit can be as simple as replacing or modifying the existing lid. Most newly installed pits have an integral weatherstripping, either on the underside of the lid or the top lip of the plastic sump. This, combined with metal bolts to secure the lid, is often enough to provide a proper seal except if there is something protruding through the lid.
Some homes have the ABS plastic discharge pipe sticking out through the top of the lid, while others wisely have this buried in the basement floor slab. If your pipes, and the wires for the sump pump power sources, enter the sump through this area they have to properly sealed, as well. Rubber gaskets or stoppers can be purchased that fit snugly into the holes of the lid while maintaining a tight fit around these pipes or wires.
If your current sump pit has a loose-fitting top or large openings around the discharge pipes or electrical cords, replacing the lid with a one that has the appropriate gaskets may be the simplest way to seal the area. And that's very important to prevent excessive humidity in the basement and protect against dangerous radon gas from the soil.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the President of the Canadian Association of Home & Property Inspectors - Manitoba (www.cahpi.mb.ca). Questions can be e-mailed to the address below. Ari can be reached at (204) 291-5358 or check out his website at www.trainedeye.ca.
trainedeye@iname.com