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Base board question for the exterior of the house

Dear Old House staff
I recently inquired about painting the exterior of our house. The painter suggested that I place a baseboard for all the perimeter of the house with the intent to decrease the moisture in the base of the exterior. The exterior wood lining is vertical and the baseboard would be horizontal.

Is this really necessary?

Please let me know what you think.


Re: Base board question for the exterior of the house

It's not really necessary, but there are some considerations here. First is to know that the end grain at the bottom of vertical wood is susceptible to absorbing moisture and is really tough to seal as all rainwater will run down there and 'hang' from that edge till it evaporates after the rain has stopped. This is why you usually find rot with vertical siding happening at the bottom. If there's no rot now you can just repaint, but pay extra attention to getting the bottom edge well painted.

If it doesn't look out-of-place you could install a horizontal trim at the bottom like the painter suggests, but the bottom edge should be at least 1/4" lower than the siding so that surface water does not get back to the siding, and the top edge should be slightly beveled (at least 7 degrees but not more than 22 1/2 degrees) so that water doesn't stand there but runs off the face instead. Wouldn't hurt for the bottom to be similarly beveled too. If you do this be sure the painter primes and seals the siding under the new wood first, then back-primes and end-seals the new trim before installing. I'd like to see that back-caulked too for better sealing, but at the least caulk the top after installing.

What that should accomplish is to help prevent future rot from water hanging on the end grain like I described earlier and if any rot ever does occur down there it should only be the trim piece which can be easily replaced.


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