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My friend said yesterday that houses that are built with birch don't need to be chemically treated.

The wood what is now 50 years old has dark dots on the surface, but it seems to be strong. The wood is exposed to a litte water, since it is used only for those parts under the roof.

I have thought before that the wood would rot inside during such long periods of time. There may however be some fungi on the material, since the dark dots are very evident on the surface of the wood. Is it dangerous to build houses without chemically treated wood?

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most houses are built with non-treated wood for a majority of it. You only need treated wood when it's potentially in contact with moisture. – DA01 May 13 '13 at 2:01
How much can the food be in contact with moisture? Is sometimes raining enough? - Is there any negative sides of having little black dots on the surface of the lumber which however seems to be strong? – Masi May 13 '13 at 10:34

No it is not dangerous to build houses with treated wood. However treated wood will need different braces and fasteners to prevent rust. Also treated wood has a lower load rating than non treated.

Wood is chemically treated for moisture resistance or for fire prevention. If your house doesn't have excessive moisture or fire issues it probably does not have chemically treated lumber.

Also the black dots you describe seems like Artillery fungus to me. This is a very very slow moving fungus that makes its way through wood. I don't think it matters if the wood was chemically treated or not. If it were my house I would scrape the fungus off and clean the area.

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