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Renovation & Design

Structural engineer required to evaluate foundation

Carlos Munoz / AP files

Whether it’s a sprawling mansion or a tiny cabin in the woods, a solid foundation is critical.

Question: I wonder if you could provide some advice for a problem we are having with our lakefront family cottage. This small 28x24-foot cabin was moved onto a poorly constructed pony wall foundation 13 years ago. The four-foot high pony walls are constructed on cement footings in very sandy soil, which has been subject to lots of moisture over the past few years. The floor under the cabin is sand and there has never been a cement pad. The weeping tile was incorrectly installed on top of the footing, along the base of the wall. The walls have begun to shift, either the bottoms have moved in or the tops of the walls have moved outward. Whichever is the situation, they are no longer straight and we are seeing major issues inside the cabin.

We have been advised to dig out a foot or so of sand from the floor, lay a thick layer of plastic over the sand and pour either a cement pad or a cement grid that would anchor braces against the walls to prevent any further movement. The contractor we consulted felt this would give us another 15 years. We are seeking a second opinion and advice on what would be involved in fixing this issue properly and permanently.

Thanks, Pam Wassill. 

Answer: Repairs to damaged foundations, whether they are seasonal cottages or full-time homes, should be designed by professional structural engineers and constructed to those specifications by contractors very experienced in those type of repairs. There are many factors to take into consideration, to avoid a reoccurrence of the problems you are currently experiencing.

The moisture and movement issues you are having with your cottage appear to be due to a very complex situation, due to several factors in play at that location. It is unusual to have that much movement in a small building constructed on sandy soil, as that is one of the most forgiving types of substrates to build on. Many cottages and homes in our area that would not accommodate this type of foundation on clay-based soils work well in lake areas with sandy soil conditions. Weeping tile systems are rarely used in this type of footing-on-grade foundation, due to excellent drainage properties of the sandy base. Even on a lakefront property, like yours, this should not be a serious issue unless one or more major mistakes was made.

Even with sandy soil, grading and height of the foundation can be the most important consideration when locating a new building. If the area chosen for construction is marshy, has a high-water table, or is too low in relation to the surrounding lake, it may always have a moisture issue with any foundation built on grade or below. Ensuring the current location is suitable may be determined by a professional structural or geotechnical engineer. Taking soil samples and investigating local conditions should determine whether the spot chosen for the current footing foundation is suitable. If it is determined that it is not viable, relocating the building to higher ground, or replacing the grade beam with a more suitable foundation, like poured concrete piers, may be the only permanent solution you seek.

For a more temporary solution, improvements to the drainage tile system and soil height inside the crawlspace may minimize the issues. Installation of a proper sump pit and pump inside the crawlspace, with weeping tile properly sloping and draining downward to the sump, should provide a fair bit of relief from any standing water situations. This should help dry out the soil under the building, especially during and after the spring thaw. This water will have to be discharged well away from the cottage, but drainage should not be a problem with a lakefront property. As far as excavation of the crawlspace and installation of polyethylene sheathing and concrete, that will likely do nothing to improve the situation. In fact, lowering the soil inside that area will probably make the moisture issue worse and instead additional soil should be added, to raise that area above the surrounding grade.

The next item to address is the movement of the cottage, itself. Even with a perennially wet crawlspace, there should not be that much permanent movement if the foundation is properly constructed and anchored. As long as the footing has not moved significantly, it is likely that the knee-wall foundation was poorly constructed or secured. If the grade beam has significant cracking and obvious shifting, then that may indeed be the cause of the cottage damage. If not, the knee-wall is probably moving seasonally, because it is not properly secured to the footing or cottage floor. In either case, evaluation and major repairs are likely warranted to lift the existing structure, repair or replace the knee-wall, or relocate to a new foundation.

Determining the best course of action should be left up to an expert, in this case a professional structural engineer. These individuals are educated and trained to determine the suitability of building design elements for the intended purpose. Even with an experienced general contractor, any plans should be evaluated by the engineer before being submitted for the appropriate building permits. That should ensure that a repeat of the current situation does not occur, whatever the causes are now.

Your desire for a permanent solution to the moisture and movement issues seen with your cottage can not be achieved with speculation or trial and error attempts by contractors. Evaluation and a plan of proper remediation should be done by a professional engineer or geoscientist to properly address the problem.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.

trainedeye@iname.com

 

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