Wood expansion and contraction in Seattle & Portland

[Greg Magone]

How much of a problem is wood expansion and contraction due to seasonal humidity changes in Seattle?

I am working on building a fine piece of furniture. It'll be used in Seattle and I'm curious to know how much the wood will expand and contract over the years so I can plan accordingly in my design.

[Kent A Bathurst]

I use this tool. You just need to get historical humidity range for Seattle - I'm guessing it ranges from a low of 90% to a hi of 100%? :)

http://woodbin.com/calcs/shrinkulator.htm

[Bob Smalser]

How much of a problem is wood expansion and contraction due to seasonal humidity changes in Seattle?

I am working on building a fine piece of furniture. It'll be used in Seattle and I'm curious to know how much the wood will expand and contract over the years so I can plan accordingly in my design.

The Seattle metropolitan area only gets 30" of rain a year. Some coastal areas with 150" of rain are different stories. I'm less than 50 miles away as the crow flies and I get 60". And almost all of Seattle rain falls between 1 November and 30 May. Summers are very dry. But centrally-heated structures tend to negate excessive winter humidity and the usual rule of thumb of 8% for furniture stock and 6% for flooring stock works fine.

In general, when I moved back here from the Northeast I only had trouble with tools made there like wooden handscrews that swelled to the point they had to be recut, along with two or three shop-made interior drawers that required planing out of dozens. So if I was building a piece in Rhode Island destined for Seattle, I'd allow another hair of clearance for drawers and door stiles. If I was in Georgia, it would be a wash, as would a piece buillt in Seattle and destined for Seattle. If I was building in Arizona, I'd allow a whole lot.

[Brad Wood]

I'm south of you a bit, but I'm in the Cascade foothills and get much more rain than the Vancouver/Portland area (usually about double). I've recorded as much as 96" and as low as 64" in the last three seasons I've been here.

The humidity in my house varies about 10% in the 40% to 50% range. My shop/garage is a different story and can flux between below 30% to 90+%. I run a dehumidifier set to 50% to keep it under control. I put the dehumidifier in before I started using it as a woodworking shop. The boxes I had stashed out there our first winter, just after moving in, were nearly wet to the touch and I knew I needed to have something out there just to keep everything from molding.. slightly off topic I suppose, sorry.

[Peter Aeschliman]

I use this tool. You just need to get historical humidity range for Seattle - I'm guessing it ranges from a low of 90% to a hi of 100%? :)

http://woodbin.com/calcs/shrinkulator.htm

I just learned something new. My initial response to your post was that our humidity is not NEARLY that high.

But I did a quick search and found that it is in the 80% range... I was surprised by that because the south, midwest, and east coast all feel drastically more muggy and humid than Seattle does. But apparently it's because Seattle's dew point is much lower than those areas... the water in the air turns from vapor to liquid at a lower temp here... so it doesn't hang in the air like it does in other areas.

Interesting. That explains why my cast iron tables rust over a few times a year if I don't do anything about it, even though it doesn't feel muggy!

[Kent A Bathurst]

[QUOTE=Peter Aeschliman;1220862]I just learned something new. My initial response to your post was that our humidity is not NEARLY that high.
QUOTE]

You saw the smiley face - I was gently ribbing you about your climate. I live in Atlanta, where the July-August over/under is 165. That's the sum of temp + humidity.

The issue IMO is not what the avg humidity is, the issue is the range min to max - that tells you how much the cross-grain movement will be. If your humidity is 80% and always stays at 80%, then you don't have an issue once the wood is climatized in your shop. Notice that the shrinkulator gives you both radial and tangential. Very helpful to determine what is going to happen, by species, with flatsawn v qtrsawn.

[Josiah Bartlett]

This information is simple to get... just go to www.weather.gov, type in your zip code, and get the local observations history.

Heres what mine looks like for Hillsboro (about 20 miles from PDX):
http://www.wrh.noaa.gov/mesowest/getobext.php?wfo=pqr&sid=KHIO&num=168&raw=0&dbn=m

You can see that the RH varies from 10% to 90% in the course of 24 hours. Now, the real issue is how much it changes inside a building, averaged out over a longer period. My porch floorboards go from having basically no gap in the winter to a good 1/8" gap between each board in the dry part of summer. I live fairly far from any body of water. Close to Puget Sound means less variation. The thing about the PNW is that it is full of local microclimates, so you have to assume that there will be a very large variation.

[Dan Mitchell]

That explains why my cast iron tables rust over a few times a year if I don't do anything about it...

That's interesting Peter, I don't have that trouble at all, and if anything, I'm a bit lax with the wax.

My gut feeling would have been that, compared to when I lived in Columbus, Ohio, where the drying effect of winter heating tends to mimic the Sahara, and the oppressive, words can't express how much I hated it, abysmal summer humidity rivaled that of equatorial New Guinea (I exaggerate only slightly... ), furniture would be much happier in the PNW. As Kent said, it's the swing in humidity that causes difficulty.

It is a fact that many US cities not thought of as rainy get more annual precipitation than does Seattle. New York City; Buffalo; Providence, RI; Philadelphia; Atlantic City, NJ; Hartford, CT; Boston; Indianapolis; and yes, even Klummus, Uhia! :D.

[Peter Aeschliman]

That's interesting Peter, I don't have that trouble at all, and if anything, I'm a bit lax with the wax.

Huh... My shop is in Woodinville in a converted horse barn. It has a slab concrete floor in about half of it and a plywood/cinderblock/pressure treated 2x4 floor in the rest.

It was built with standard 2x4 studs, with basically a plywood siding. No attention was paid to gaps in doors/windows/etc. I have gone through and weather-proofed the place, and I'm about 75% done drywalling and insulating. So we'll see if that ends up solving the problem. If it doesn't, I'm going to start looking into dehumidifiers.

It's actually really hard on my tools. I live downtown, so I only make it out to my shop once/week or so. there have been times in the past when life got busy and I didn't make it to the shop for a month. One of those times, I came back and found that it was really tough to get my planer table to move up and down with the crank. It was nearly stuck completely... My mortiser wouldn't plunge at all and I had to take it apart, clean it and oil it.

Not good! It's especially strange that you don't have these issues!

Sorry for the hijack.

[John Michaels]

When we get cold spells like that one last winter the RH can really plunge. I had some lumber that was stored inside my house and it warped pretty good, when the cold spell ended it went back to how it was before.

[Dan Mitchell]

Huh... My shop is in Woodinville in a converted horse barn...

Yeah, I don't have anything like the issues you describe. My shop occupies about 1.5 cars of a 3.5 car garage, in Edmonds, ~3/4 mile from the Sound. It's not heated at the moment (plan to address that... ) but even with 2 wet cars coming in and out during the rainy winters of low shop use, I haven't noticed even light surface rust on the TS & jointer tables, etc. I did put a coat of Johnson's paste wax on the tools initially, but I certainly haven't been religious about maintaining it. That is odd, I hope you get it sorted out.

Dan

[Joe Pelonio]

I think rust comes more from hot humidity. In other words, if you get summer rain the heat vaporizes the moisture and it causes more rust than cool rainy weather.

OK, so we get 30+ inches of rain a year. When it's raining it's 100% humidity, but in the usually brief summer there is none, even at 85-100 it's very comfortable compared to some other areas and cools off at night. This year we had the driest spring, summer, and so far fall since we've been here (16 years). I worked with another company on a large steel sign for a condo development that went up in March. It was left sanded but unfinished because they wanted it to get rusty for effect. I pass it every day on the way to work, and it's just now starting to show a few signs of orange.

The only moisture issue we have ever had here is the patio French door sill plate. When it rains hard at an angle it gets wet and swells, making the door harder to open for a week or so. Most of the year it's fine. We never have problems with doors or furniture.