What would be the condition of a wood cottage that has been abandoned for ~20 years?

Question

Suppose a two-storey timber cottage has been left unoccupied for 15 to 20 years. The entire structure is wooden, including all beams and supports, with a rammed earth foundation. It's situated within a small stoney clearing in the outer skirts of a broadleaf temperate forest, with alternating cool/dry and wet/warm seasons and relatively high periods of humidity - think temperate forests in central China. The clearing is surrounded by tall trees which allow in patches of sunlight, but there is little undergrowth in the area beyond ground cover shrubbery. There are streams that run through the forest, but they are seldom prone to flooding.

Regarding the structure itself, it is rather small and dingy. Windows are paper-paned and shut tight. The roof is built from clay tiles, and from straw for a porch. The floors and walls are all wooden, and so are all furniture and appliances, with some iron and bronze present. Upholstery comprises rough woven textiles such as hemp and bamboo, and some cotton and fur. The house was well-maintained prior to abandonment, and has not been broken into by humans or animals over the stated period (bugs and small scavengers notwithstanding).

Given the above, what would be the condition of the cottage, externally and internally, following the period of vacancy, in terms of structural integrity, takeover by vegetation & critters, degradation, etc.?

EDIT - A few more details: The geography/climate of this setting draws heavily on temperate Eurasian forest ecosystems, with yearly temperatures averaging from 3 to 16 degrees Celsius. Snowfall is unlikely at this particular altitude as the climate is generally mild to humid, and winters would be dry.

The cottage's design combines elements of Zhou- to Han-dynasty housing styles for the lower classes (thus the heavy reliance on wood and the rammed earth slab foundation, even though a crawlspace might be expected instead).

I understand that break-ins are practically unavoidable IRL, so I should clarify that there would be Plot Reasons(TM) justifying the lack of interruptions.

Answer 1

I used to work as a forester in Canada, where we do have temperate climate (although somewhat on the colder side of the spectrum, I must admit). I've seen several habitations and other abandoned things through my days in the bushes, so I have some range through my assessment.

First, was it build to last? It seems so from your description, yet most of the materials you mentioned won't last very long after the maintenance stopped. Still, 15-20 years isn't that much, so you should be all right. The wood will have turned grey outside the house and inside near every opening. Where water infiltrated you'll see that the wood texture is not the same as elsewhere. If there was rain lately, it may even be still wet. You may find puddles if the degradation is that bad.

Second, is the cottage anywhere near civilization? If so, people will at some point find it - and by "people" I mean "kids or teens". This means that the furniture inside the house will be broken, the windows smashed, the tableware broken (often outside the house). Kids aren't gentle to what they find.

Vegetation will grow. 20 years is not much in a forest's cycle, but plants look for light all the time and will try and colonize the clearing. Raspberries and other thorny colonizer-type plants will have taken over parts of the clearing, while light seeking trees like poplars or... bamboo I guess? - will have small representatives growing around. Some of these will be hugging the walls, yet this isn't a forest yet (trees height will vary between "mini-groot" for the youngest ones to "human size" for those less than 10 years old and "bush size" for the oldest colonizers (which aren't technically old, just the first to colonize in this case). It's the forest starting to attack the clearing. Another 20 years will see the place overrun with those light-seeking species, which won't really look like the forest around them because they are part of a cycle and in less than 100 years they will start being replaces by other variety of vegetation.

Animals will explore the place. Rodents like squirrels and such will have nested in the roof and will have shit everywhere. If some of the furniture is stuffed, like a sofa or a mattress, you will see some stuffing rotting on the ground (also they often will be damp) and that the rodents have dug around making nests inside them. Most nests like that are ancient things, though, abandonnes for a while. Bigger animals like bears and stuff won't play around the place unless they smelled food, which might have happened right when it was abandoned but never later.

How cold is the winter? If the winter is cold enough, the house will have a floor, and underneath it there will be some space that animals will want to colonize too. This one might still have something living in there. Skunks, raccoons and other small yet unpleasant animals can have made their den under the house, especially if the access there is not that easy. They would be disturbed bu somebody exploring the house. Also, if there's a floor and water problems, the planks might be rotten enough to bend under the weight of somebody exploring the house, and ever break underneath him.

You might notice some things which will seems "out-of-place", but only because this place is straight from the past. 15-20 years isn't much in this regard, but I've seen really surprising stuff from older abandoned places, or places abandoned by natives.

EDIT: Also: wasps. There will be at least one wasp nest, probably an empty one as they die during winter. There may be live ones, too. They often nest near the wall just under the roof, outside the house - rarely inside, but they can. Other insects can and will colonize the place, but they are more subtle.

Answer 2

It will be pretty run down, especially if it is made of wood. Vegetation will have taken possession of the surroundings.

I have seen such places during my vacations in some remote areas of rural Japan, they have their sinister appeal.

Here is what can be found online:

Fascinating footage shows an explorer uncovering an abandoned Japanese village that has lay empty for more than two decades.

Houses, shrines and temples that had been knocked down by overgrown trees which took root in the remains of Nagatani Village.

Explorer Kei Oumawatari discovered houses, shrines and temples that had been knocked down by overgrown trees which took root in the remains.

Old ropes, brooms and brushes and other household appliances are strewn across the floor after being left more than 20 years ago

Answer 3

Based on your rather unreasonable requirements that it hasn't been broken into. The cottage will look almost pristine.... on the outside.

The wall boards will have shrunk. There will be gaps in the walls. This will allow free air flow, keeping the structure somewhat dry.

The roof will sag a bit because those tiles will leak. If it has never gotten any snow, then it should still be fine.

The floor will be ruined. You will probably fall through the floor when stepping on it.

The location where the foundation meets the ground will be extremely rotten. It was probably rotten a few years after it was built. A common thing to do for those old cottages was to use beams made of giant trees that sit on exposed or pilled up rocks. This keeps the rot surprisingly low. You could go 60 years and still be fine with this set up. I would need to know the exact foundation to give a better estimate between 3 years and 60 years.

The weird one though, chances are the building is leaning, or may have even fallen over. A house is heavy (citation needed) and sinks into the ground. Often at different speeds around it's foundation.

And the scary one. The insides of the house will be coated with old black mold. The underside of the floor will be covered in mold. The top of the floor will be covered in mouse poop. This house is extremely disease ridden and deadly to even breath it's air. Do not go inside it, do not sleep in it, you can't even safely light it on fire.

Answer 4

It will be destroyed. There are two factors you mention that will do it:

1. Trees - they will not only add the possibility of falling on the house but each fall they add weight to the roof with leaves. Those leaves also rise the floor level around the house that is rotting. So any fauna that could benefit from wet, warm environment and like to eat wood would flourish there.
2. Closed windows and doors. In combination with better insulation on the roof (leaves) your house become a greenhouse. Rising the moisture and temperature in the house. Making it better not only for mushrooms but also speeding up rotting process of furs and textiles

After 20 years the cottage could still be recognised as one but the roof would collapse on it's own (you have weight from outside and weakened support on the inside). Iron would rust. Materials could still look like usable but would crumble when touched. The place would be heaven for all small things that like to munch on pre-processed wood, fibers and leather. And animals that like to feast on those critters.