Most of the 243 National Register homes in Old Nampa's 18-block grid still wear painted wood lap siding from 1900 to 1940 — not vinyl, not hardie. That siding takes a soft wash at low pressure, because the paint on a hundred-year-old clapboard wall is the only thing keeping water out of the wood.
Drive the grid between 4th Avenue South and 11th Avenue South and you are looking at clapboard and wood lap on nearly every block, with brick foundations and the occasional stucco porch column on the later 1920s and 30s bungalows. Wood lap has a horizontal seam every six or eight inches, and every one of those seams is an opening if you push water uphill into it. A pressure washer at siding-cleaning pressure will find the seam, get behind the board, and sit there for a week. So we run a soft wash — cleaning solution at low pressure, dwell time, then a rinse — and we always work down the wall, never up into the laps. The chemistry does the work. The wand is just there to move water.
On these older lots the sprinkler heads sit close to the house and throw straight at it, and Nampa's water is hard — tested as high as 7.08 grains per gallon on the city side, worse on ditch rights off the canal. What that leaves is a band along the bottom two or three feet of siding: chalky white mineral crust, and on ditch-fed yards an orange-brown iron tint that follows the spray arc. It comes off, but not with pressure alone. Mineral scale needs the right solution and dwell time to release from the paint, and iron staining is a separate chemistry from algae. We treat that lower band as its own step rather than assuming one pass down the wall handles it. Moving or capping the offending head is usually the permanent fix, and we will say so.
The old grid is shaded by mature silver maple, elm, and sycamore, and that canopy is why the north and east walls of these houses grow algae while the south side looks fine. Shade plus overnight moisture plus airflow blocked by a hedge or a detached garage sitting eight feet off the property line — that is the recipe. The growth reads as a gray-green film first, then black streaking in the shadow line under the eave. It is biological, so it needs a solution with contact time, not force. Blasting it off a painted wall takes the top layer of paint with it and it comes back in a season anyway, because the roots are still in the surface. Killed properly, a north wall in this district stays clean twelve to eighteen months.
The honest note: if the paint on your sun-side wall is already chalking heavily — you rub a hand across it and come away white — a house wash will clean it, but it will not restore it. Chalking is the binder breaking down from UV, and the fix is paint, not cleaning. Worse, if paint is actively curling or flaking, even low-pressure rinsing can pull loose chips off. On a pre-1978 home, and nearly every house in this district is, that means paint debris in your beds. We do not strip, sand, or blast paint. When we walk a wall and see failing paint rather than dirt, we tell you the wash will disappoint you and let you decide. It is a shorter conversation than the one after.
House washing is $0.18 per square foot of wall surface — the actual siding we clean, not the home's floor square footage — and it is safe for painted wood, brick, stucco, hardie, and vinyl alike. Most single-story bungalows in this district land in a tight range because the footprints are similar; two-story foursquares with wraparound porches run higher. We carry Monthly and Quarterly memberships with no contract and a 7-Day Rain Guarantee, and same-day or next-day slots are usually open. Because the historic district is a compact grid just off downtown, we can often batch several houses on one street in a morning. Call and we will walk the walls before quoting, including the north side you probably have not looked at since spring.
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Not the way we do it. Soft washing uses cleaning solution and dwell time at low pressure — closer to a garden hose than a pressure washer — and we always rinse downward so water never gets driven up under the laps. What damages old siding is high pressure aimed at a horizontal seam. If your paint is already flaking, we will tell you before we start rather than take chips off your wall.
Sprinkler overspray. Nampa water runs hard, and heads set close to the house throw minerals onto the same two or three feet of siding every cycle until it builds into scale. On ditch-fed yards it picks up an orange-brown iron tint too. It removes with the right solution and dwell time, not pressure. The lasting fix is moving or capping that head so it stops repainting your wall every morning.
Shade and moisture. The mature maple and elm canopy over the old grid keeps north and east walls damp overnight and slow to dry, which is exactly what algae wants. South walls get enough sun to stay clear. It is biological growth, so it needs a solution that kills it rather than force that scrapes the surface off. Treated properly, a north wall here holds clean twelve to eighteen months.
We do not strip, sand, blast, or otherwise disturb paint — soft washing at low pressure is meant to clean the surface, not remove coatings. That said, if paint is already curling or flaking on a wall, any rinse can dislodge loose chips. On homes this age we look at the paint first, and if it is failing, we recommend paint work before a wash rather than pretending cleaning will fix it.
By wall surface area at $0.18 per square foot, not by the home's floor square footage. That matters on a house with a wraparound porch, dormers, or a two-story back addition, because those add wall without adding much footprint. We measure what we actually clean. Brick foundations, stucco porch details, and painted wood all price the same, so there is no penalty for a mixed-material elevation.
Yes, and they are usually part of the same job. The brick foundation courses on these homes catch the same sprinkler minerals and soil splash the siding does, and shaded porch columns pick up the same growth as a north wall. Brick and stucco tolerate the process fine at soft-wash pressure. Concrete steps and walks are a different service, but we can quote them at the same visit.
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