Impregnation is not needed in a birdhouse; the wood breathes well enough in the open construction that it doesn't rot very quickly.
Pressure-treated wood is not as toxic as rumored; copper salts are not particularly dangerous compared to arsenic and chromium, which were used in the past. If we can have pressure-treated wood in the floor of an outdoor grill area, a birdhouse can have it too. A birdhouse is well ventilated and not at all like having treated wood indoors. But what happens to the birdhouse afterward? Will it remain in the forest and leak copper into the soil when it falls down in 10 years? Or will someone make the effort to take it to the recycling center and sort it as treated wood?
If by any unlikely chance a white-backed woodpecker or another critically endangered species (lesser white-fronted goose?) were to move into the birdhouse, I might reconsider a bit, so please don't place the birdhouse in a rotten aspen. But I believe that any bird that moves in would benefit more from a birdhouse than be harmed by a deck floor.
Pressure-treated wood is not as toxic as rumored; copper salts are not particularly dangerous compared to arsenic and chromium, which were used in the past. If we can have pressure-treated wood in the floor of an outdoor grill area, a birdhouse can have it too. A birdhouse is well ventilated and not at all like having treated wood indoors. But what happens to the birdhouse afterward? Will it remain in the forest and leak copper into the soil when it falls down in 10 years? Or will someone make the effort to take it to the recycling center and sort it as treated wood?
If by any unlikely chance a white-backed woodpecker or another critically endangered species (lesser white-fronted goose?) were to move into the birdhouse, I might reconsider a bit, so please don't place the birdhouse in a rotten aspen. But I believe that any bird that moves in would benefit more from a birdhouse than be harmed by a deck floor.
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Does it really matter if the "bottom and roof" happen to be planed? But I would use untreated timber everywhere. It feels a bit overworked and unnecessary to have several different types of timber in a birdhouse.P Plutus said:
Pressure-treated wood should be fine, as long as it's modern boards without arsenic. Birds in nesting boxes have almost no sense of smell, so they don't mind.
As for planed/unplaned wood, it doesn't matter at all for small birds. They just hop up to the hole.
Perhaps pressure treatment is unnecessary. A nesting box lasts quite a long time without any treatment. I do paint mine with three or four layers of linseed oil paint on both the inside and outside, but that's mostly for my own sake. However, all my boxes are fully occupied, so the birds clearly don't mind nice boxes.
As for planed/unplaned wood, it doesn't matter at all for small birds. They just hop up to the hole.
Perhaps pressure treatment is unnecessary. A nesting box lasts quite a long time without any treatment. I do paint mine with three or four layers of linseed oil paint on both the inside and outside, but that's mostly for my own sake. However, all my boxes are fully occupied, so the birds clearly don't mind nice boxes.