Your Cottage Roof Structure
The age of your cottage will most likely indicate whether it was built according to the Ontario Building Code requirements or was just hammered together by a local carpenter. Modern cottages are constructed to meet the Specified Snow Loads provided by the Ontario Building Code. Read the Code
Older cottages are also predominately built using rafters for roof construction. Many do not have collar ties or purlin supports installed to stop rafter spread and add stability to the roof. As you can see in the image to the right, having collar ties and supported purlins adds considerable support to the average cottage room. Unfortunately many older cottages only have the basic rafter structure.
The added collar ties and purlin bracing adds stability to the entire roof structure. Rafter spread is a common issue with older roofs and could even progress to the point of pushing out the exterior supporting walls leading to failure of roof and possible wall structure.
Many areas of Ontario have or had many individuals who made their living in the winter shovelings snow off cottage or even residential roofs. The Ontario government discourages people from going on their roofs and recommends people to hire “insured snow removal” companies to perform the work on the roof. Where the roof is accessible from the ground it says people can use a “snow rake” to reduce the load. If in doubt about any roof component get a Roof Inspection
Ice Dams on Roof
Causes of Ice Dams
Ice dams form at the eave section of roof, letting water penetrate and cause damage to the interior of walls and roofs. This only occurs when part of your roof warms to above 32 degrees F, warm enough to melt the snow, while the roof edge remains below freezing. When snow melts on a roof it runs down until it meets the unheated bottom edge of a roof and then freezes. This area of ice is called an ice dam, this process continues creating an ever increasing ice dam which will cause water to backup beneath shingles and Ice dams cause damage to walls and roof structures.
A lot of older homes have insufficient insulation, particularly at junctions where the roof and walls meet. This problem is most notable with low-sloped roofs and short overhangs. As heat is transferred through framing members it warms the roof deck and melts the snow; that water then runs down under the snow to the overhang where it is no longer heated by interior factors, and it freezes again.
Blocked soffit vents are another cause of Ice Dams. Blocked soffits allows heat to be trapped at wall and sheathing area of eave and causes the snow to melt which will then freeze at edges of roof causing an ice dam.
Air movement through ceilings and wall joints is another common problem as a lot of heat is transported by air. This warms the attic and causes that same melting to occur.
Prevention of Ice Dams
The secret to curing and preventing ice dams is to make sure the temperature of your roof stays consistent with the eaves. To do this, prevent inside air from reaching attic or roof space by sealing any leaks. You can also upgrade the insulation in your attic and add ventilation to the outside. This will ensure that warm air is quickly carried away from the roof. The ideal attic temperature would be the same as the outside air.
Cottage foundations run the full gamut from homes supported by masonry blocks sitting on the ground or on patio stones to full blown poured concrete foundations. The Ontario Building Code did not come into being until 1975, the National Building Code came into being in 1941. As many cottages are only 3 season and are winterized to prevent freezing pipes etc there is no protection from frost heaving, this leaves many cottagers always adding or removing shims as there cottages go up or down.
Modern cottages are typically 4 season homes and are built just the same as regular houses, these will typically have pour concrete foundations or masonry block foundations. Even moderately older 3 season homes are required to be supported on concrete piers which extend down below the frost line. Many cottages in the Honey Harbour area are supported on bedrock. ( the Canadian Shield ) They use rock anchors drilled into bedrock, either epoxy in or a Hilti rawl. If there is a covering of soil in the area then they excavate until they hit bedrock and use sauna tube with concrete for support pier.
Frost Heaving of Foundations
Frost heaving can occur when these three basic conditions are met: the soil must be frost-susceptible; water must be available in sufficient quantities; and cooling conditions must cause soil and water to freeze. If one of these conditions can be eliminated, frost heaving will not occur.
Frost-susceptibility is based on the coarseness of soil particles. In general, coarse-grained soils such as sands and gravels do not heave, whereas clays, silts and very fine sands will support the growth of ice lenses even when present in small proportions in coarse soils. If frost-susceptible soils located where they will affect foundations can be removed and replaced by coarser material, frost heaving will not occur.
Prevention of Frost Heaving
The accepted practice in the design of foundations to prevent frost damage is to place the foundation beyond the depth of expected maximum frost penetration so that the soil beneath the bearing surface will not freeze. This measure alone, however, does not necessarily prevent frost damage; if the excavation is backfilled with frost-susceptible soil it may lead to damage from adfreezing. Depths at which foundations should be placed are normally determined by local experience, as incorporated in building bylaws.
For more information on Cottage Foundations call Roger at 705-795-8255
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