I have owned a 50 year old summer cottage in northern Ontario (Sault Ste Marie) and it is approximately 24 ft by 30 ft, and is sitting on a very gradual slope with the rear of the cottage sitting on the ground or rocks and the front section on concrete blocks and 4×4 posts. Due to the winter snow fall and the wet springs the cottage always seems to be moving and the supports underneath are mostly on an angle or have been pushed into the ground, which obviously creates problems closing and opening doors and windows. I would like to dig and pour some concrete pads to level and stabilize this situation.
Can you give me some advice? How deep do I have to dig them? What size pads should I pour? Should they be round or square pads? What distance should I space these pads apart? Do I need to put steel re-bar in the cement forms for re-enforcement?
Thank you for any advice that you can share with me.
Many older cottages are still in use that rest on foundation blocks and posts or other footings of questionable integrity. These will allow minor to major seasonal movement, and in the worst case cause the building to fall of the posts and collapse, to rest on the ground below. I have seen this happen as recently as a few years ago in the area near my own cottage. You are to be commended for taking the initiative to improve the situation, but care must be taken to do it correctly.
Sizing of the new concrete footings and correct spacing is dependent on many factors. The first item to take into consideration is type and condition of the soil in the area where your cottage is located. The area of the Canadian Shield you are in may have exposed rock near the surface that may be very stable, or may be covered with a substantial amount of poor quality soil and be highly susceptible to seasonal movements. I have seen cottages in North West Ontario that are constructed with wooden posts sitting directly on the exposed bedrock that remain very stable, while others appear to be on solid footing and move considerably. The size and type of footings or piers you use for support are largely dependent on this issue.
The quality of construction of your cottage will also determine proper spacing of posts and footings. Many older cottages and homes had undersized joists and beams that allow a substantial amount of deflection in the floor structure. Extra beams or floor joists may be required to increase the stability of the older building. This will be an ideal time to reinforce the floor structure and improve the stability of the older floor. This may even reduce the number of footings and posts required when levelling the cottage.
Your questions are all very relevant, but the inquiry is directed to the wrong individual. To properly determine the footing requirements, a licensed structural engineer, familiar with the area, should be consulted. For a moderate cost, you should be able to obtain a report detailing the proper specifications for your building. A site visit will likely be required, so travel costs may also be involved. The Professional Engineer will be able to inspect the cottage structure, measure the size of floor joists, beams, etc. and will provide a schedule of proper footing and post spacing and size requirements.
To obtain a building permit from the local municipality, you may be required to provide a rough sketch or more detailed drawing of the cottage, before approval. A stamp from an engineer may also be necessary on a foundation drawing or plan before a permit is issued. This should all be obtainable after the visit from the structural engineer to your cottage site.
You should also consider raising the cottage, at the time of proper footing construction, to minimize rot in the floor structure and ensure easy access underneath. You stated that the rear of the cottage was sitting on or near grade and this will not only make access underneath difficult, but will promote moisture damage and pest intrusion. You will have to build new stairs for entry to the raised building, but this is a small price to pay compared to replacement of rotten joists and beams.
The National Building Code has specific recommendations for minimum and maximum floor joist, beam and footing spans that you can research, for more information. You may even use this reference to draw a proposed foundation plan for your cottage. This will help in your knowledge when attempting the repairs, and may cut down on your overall costs. Nonetheless, I can’t stress enough that you need professional help when dealing with major structural issues like this. I have seen far too many amateurish repairs, especially in cottages and summer homes, that can have disastrous consequences over time.