When preparing the design for a second storey addition to a cottage or a home, it is important to determine whether the building’s existing foundation walls and footings will be able to support the proposed increased load.
What Types of Loads Must the Foundation be Able to Support?
It is essential that the existing foundation walls/piers and footings are analyzed to determine their ability to carry the load of the proposed addition. The added weight of the second storey will consist of the anticipated live load (which includes the weight of the furniture and people) and the proposed dead load (which is comprised of the weight of the second storey floor and walls). It should be noted that if the roof design maintains its former style and geometry, its weight will not impact the proposed sub-structure. If however, a design modification is introduced, the difference between the existing and proposed roof weights must be included in the dead weight calculations.
How Can I Get Information About my Building’s Existing Sub-Structure?
To determine their physical type and size, it may be necessary to dig test holes to expose the foundation walls and footings. Foundation types typically include perimeter foundations made of poured concrete, concrete block and insulated concrete forms (ICF). Another type of commonly used foundations are pier foundations.
Footings are located beneath the foundations walls or piers. The function of a footing is to support the loads imposed upon it and to transfer the weight of the structure to the soil beneath it.
Can Soil Type Impact the Design of my Building’s Foundation and Footings?
The type of soil on your property will directly impact the design of your building’s foundation and footings. Soil is defined by its particle size; the three main categories are sand, silt and clay, where sand particles are the largest and clay particles are the finest. Typically, soil is made up of combinations of all three and the relative percentages of the three types of particles in a given sample are what gives soil its texture. It is important to understand that fine soils, such as silts and clays, have a lower bearing capacity than granular soils such as sand.
The entire load of the building is transmitted through the foundation wall to the footing, and ultimately to the soil beneath. If the bearing capacity of the soil is low, the existing footing may have to be widened. With an increased bearing capacity, the amount that the footing has to be widened may be reduced.
What is a Soil Report and Why is it Required?
Your municipal Building Department may request that an on-site inspection be made by a soil engineer to examine the existing foundation, footings and sub-grade. The soil engineer will report on the existing maximum allowable soil pressure (bearing capacity) and advise you on the requirements for the proposed sub-structure. When you apply for your building permit, this report must accompany your application to the Building Department.
If your municipal Building Department advises that a soil engineers report is not required, the architectural designer will be able to utilize the Ontario Building Code (OBC) to design enhanced foundation walls/piers and footings that will support both the existing building weight and the weight of the proposed structure.
We Can Help
Ensuring that the foundation walls and footings of your building will be able to support the proposed increased load is fundamental to the architectural design for your second storey addition. With over 30 years of Ontario Building Code and practical building experience, Homes 2B Design can help to make your project a success.