We recently purchased a forty-plus year old cottage on a Lake in Ontario. It has evolved from a single cabin to include additions and is now 24 by 30. It sits on large beams that are resting on the ground. Only half the area under the floor has ventilation, as the ground drops to the lake. From what we can see through the trap door in the floor, there is little or no rot. The dirt floor in the crawlspace, which we can see from the trap door, is littered with Porcupine feces so we know there has been some damage from that.
Our quandary is the old musty smell that permeates the building, especially when the wind comes in off the lake and can get in under the floor and blow the earthy scents up into the cabin. We are leaning toward keeping the structure, levelling it, and taking care to fix it up.
Can we get rid of the smell through a new floor that is insulated and in effect sealed with new plywood and vapour barrier, etc? This cabin would likely be shut down in late fall.
Overall, is there a rule of thumb to consider when evaluating whether or not to just take a structure down or rebuild it? The insurance company says that it would take at least $30,000 to rebuild the structure. Are we just kidding ourselves in trying to restore the existing vs. simply going with a new shell and working from there with new materials and technology.
There is, unfortunately, no magic formula to evaluate when renovations of an older building is not practical. There are always many variables, some of which are sentimental. Many people go to great lengths to preserve old cottages, when demolition and complete replacement would be considerably easier and less expensive. We will look at some of the more practical issues you should investigate before making your decision.
The first item to consider, you already have partially addressed. Before beginning any work, the condition of the current structure should be evaluated by a home inspector, structural engineer, or reputable general contractor. The crawlspace or spaces should be entered, with adequate breathing protection, and the floor system probed to check the extent of moisture damage or rot. This will be of primary concern because of the construction of the floor beams on grade. There will undoubtedly be rot in these beams, and they may have to be replaced or reinforced if the cottage is to be lifted and levelled. If the dampness under the cottage has caused significant rot in the floor joists, lifting and levelling the structure may not be practical or even possible.
The next thing to consider, which is normally the largest concern, is what type of foundation will be used in the renewed building. Currently, the foundation consists of wooden beams sitting on what I am assuming is exposed bedrock and soil. This is not a proper foundation and the renovations should certainly include proper footings, posts, and beams or a poured concrete footing and grade beam or knee-wall. A proper foundation will also allow for raising of the cottage, to allow access to all areas under the floor structure and proper ventilation of the area under the cottage. This will help remove the damp, musty smell, which is mostly due to poor ventilation in a damp area. Insulating and sealing the underside of the floor may have little effect on the smell unless the source of moisture is dealt with.
Having more than one addition on the original structure may also factor into your decision. Most older cottage additions were slapped on the side of the existing building without attachment to the roof structure. They have a tendency to move independently from the original building and often pull away when attempts are made to lift and level the entire structure. The addition roof or roofs may have different pitches and may increase the chance of leaks from rain and snow accumulation.
The final consideration is always an economic one. New construction is normally less expensive than major renovations to existing buildings. This is only true if the building is to be altered significantly or is in very deteriorated or damaged condition. As previously mentioned, the character of the original cottage will be completely lost if it is torn down, but this may be not be an issue if it was poorly built, in the first place. Building new will certainly improve the performance of the dwelling in relation to improved systems. You will have to take all these issues into consideration before making your decision whether to renovate or tear the old place down.