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This article was published 14/6/2013 (1223 days ago), so information in it may no longer be current.
QUESTION: We have a 1929 two-storey house in Crescentwood. Sometime before we became the owners of it in 1962, a porch had been attached to the north wall of the living room. It's a 10-foot-by-10-foot interior porch, with a gable roof and a door cut through the living-room wall. It has plastered interior walls and an the exterior walls are painted lapped cedar. The porch foundation was done with concrete pads and posts.
For years, the porch did not move much and we had no winter mice. But over the past seven summers, the porch has started to move more and more each summer, and every winter we have mice to cope with. The house itself has never moved, to our knowledge, and we have had no basement cracks and no need for additional basement posts or the resizing of house doors.
Six years ago, we hired a well-known and reputable firm in Winnipeg. They suggested putting two east-west beams, each with two jacks, under the porch. But this seems to have been an inefficient expenditure.
After every recent summer, there are large, three-quarter-inch cracks in the southeast interior wall of the porch. This is, no doubt, the porch pulling away from the house. Granular insulation from the porch attic is falling into the porch. The exterior east side of the porch usually pulls away by about 11/2 inches from the exterior house siding. There are a few very small cracks on the east and west interior sides of the porch.
Every fall, we hire the same firm to go under the porch to adjust the jacks, which now only close the gaps in a minor way. No doubt the recent hot summers and the abundant Winnipeg clay are to blame for the increased porch movement.
We are thinking of selling the house in a few years. We are now both 80 and stairs are always a problem for the elderly. But first we want to fix up the porch foundation problem, if we can afford it. What are the reliable solutions? And how would they differ in reliability and cost?
Roy and Nancy Vincent
ANSWER: Movement of attached porches is a very common problem, especially in very old homes like yours. There are three main options for repairing a supporting structure, to prevent significant movement. We will look at the merits of the options you have not chosen and weigh them against those of your current system.
The two main methods for supporting any residential building with a crawl space are post and pads, like your home, or a grade-beam system. Grade beams are normally constructed of poured concrete and extend somewhat below grade to the underside of the floor joists. This short foundation is supported either on a footing or poured-concrete piers, commonly referred to as piles.
The difference between having a footing, normally less than a metre below grade, and piers is the depth of installation. Concrete piers are normally poured at least three metres deep and often up to six metres down. This provides excellent support and prevents movement due to frost, which can affect footings or concrete pads on grade.
Piers, then, are a superior option and should prevent any future movement of a porch. However, they're more expensive to install and can lead to differential house settlement, which can cause the same issue you are experiencing.
Grade beams are usually poured concrete, due to the durability and strength, but can also be constructed of pressure-treated wood and plywood. This is a less-costly option than concrete and will still provide good perimeter support and a barrier to pests and outside moisture from getting into the crawl space.
Poured-concrete piers are sometimes poured right up to the underside of the beams or joists and a treated-wood skirting is installed rather than a structural grade beam. Both of these options are similar and can be easily insulated and incorporated with summer vents and access panels if the crawl space is to be heated.
The other main option, posts and concrete pads, is often used because of the minimal cost relative to poured piers. I'm glad to hear your contractor installed adjustable posts to counteract the effects of frost and soil-moisture changes on this type of foundation.
As you've observed, frequent adjustments may be required to prevent movement relative to the home. However, I'm surprised at the size of the gaps you're seeing each year and the inability to close them with adjustments. Normally, these gaps will increase or change in size only slightly over the course of a year. It's possible the new beams may be poorly designed and not transferring the load of the building evenly. The most cost-effective option to prevent major annual movement and pest problems may be to modify the existing floor-and-beam structure. Hiring a professional structural engineer to evaluate the current system and design modifications should minimize the frequent problems. The repairs may include moving or increasing the size of the beams or footings. It may also include replacing the precast concrete blocks with poured-concrete footings on grade, to help stabilize the structure without major changes.
The final issue to discuss is differential movement between the foundation of your home and whichever system you choose for the porch repairs.
While you may think your house is stable and not moving, that may not be the case. Homes frequently are subject to the same forces that are causing your porch to shift. While the changes may be more subtle, you should be cautious when choosing a support structure like poured piers. While this is a superior system that should completely eliminate any movement in the porch, it will do nothing to prevent continued movement of the home. There could still be seasonal movement that creates gaps, but it would be the home moving instead of the porch.
For that reason, a better-designed beam system, with adjustable posts, may be the proper choice for your home.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and president of the Canadian Association of Home & Property Inspectors - Manitoba (www.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 www.trainedeye.ca.