Rough lumber shrinkage – green to cure
Hi all & I figure frenchy oughta have plenty of experience too…..
I’m still working to decide what to do with a bunch of nasty sweet gum trees that I recently cut….too much trouble to cut for wood working…..too smelly to burn……
So, I’m gonna use it as framing for a picnic shelter. It’ll be a very rustic unit so I’m not overly concerned with perfection in this case, as a matter of fact, perfection will be that it looks 100 years old when I’m finished.
Question: Against better judgement I’m going to build it this fall…only 3 months for it to season. I want to over compensate a bit to plan for expected shrinkage as it continues to dry…..any idea how much it’ll shrink over the next couple of years?
I’m thinking the longest piece will be 20′ and 8″ in diameter.
Pedro the Mule – Rustic on the cheap
Replies
Pedro,
I am guessing that you will see about 3/8" shrinkage in 8".
On my log home, we figured 1/2" per foot of wall height and that seems to have worked out pretty well. My log guy has been doing this for 20+ years and told me that the species of wood doesn't seem to make much difference.
Steve
Thanks PolarBear,
Is that for diameter only or is it about the same for the length too?
Pedro the Mule - Jest chekin'
The diameter only. The length won't change appreciably. If you are using those as columns, I would guess that you probably don't need to do much fudging.
When we built, we had to leave slip joints in the window framing to allow the logs to slide down around them. I generally left about 3 inches above each window and that gap has pretty well closed over the last 5 years or so. We also left gaps above the doors and interior walls that have closed up in a similar fashion.
We do have a bump out where we used the logs as columns and just framed right to them (2X6, OSB, spray foam, etc). Most of those logs are about 12 - 14" diameter and I haven't seen any gaps in that framing in this time (we built in 2003).
Mike Pielorz (Husky Log Work in Wasilla AK) built the shell and has the house on his web-site (http://huskylogwork.com/harmon.shtml) if you want to peruse the pictures. You will have to scroll down to the pics with the back deck to see the bump-out. There are also a couple of pictures of interior walls showing the slip joints with the belly band.
Hi PolarBear,
That is really Sweeeeeet!
I noticed you have green trim around the windows. Are they special order vinyl, painted....etc. ..... & are they the same color inside?
It sounds like I won't have much trouble with shrinkage......I'm actually using some discarded full length 4" pvc pipes filled with concrete and scrap metal for the posts, then wrap them in cord wood to make rustic columns and I'll have threaded rod out the top of the concrete to thru bolt the sweet gum to.....they'll be the roof framing and then I'll cover it in some sort of metal to handle stray sparks as this is going up next to my outdoor woodfired cook center.
Pedro the Mule - Rustic is as rustic does
Sounds like your plan should work. The shrinkage should be uniform, and in the roof, should disappear. Sounds like a great project - love to see some pics when it is all assembled.
The windows on the house are actually a MillGuard fiberglass unit that is wood clad in the interior. They were originally white, but I pulled them into the shop and shot a couple coats of auto-paint and clear coat onto them before we installed them on the house. It cost a bit to do it that way, but I figure that is about as close to maintenance free as you are going to get. I haven't had any issues with the windows, but might look for other options if I had it to do over again. If I had to change the color, I would probably still spray the automotive paint.
Steve
Hi Steve,
Thanks for the paint info.....we're planning to use casement style windows on the next house. The cupola on the roof will have bottom tilt out casements to draw air up and out during the summer without letting in sudden rain storms.
Pedro the Mule - Enjoying summer breezes
we're planning to use casement style windows on the next house. The cupola on the roof will have bottom tilt out casements to draw air up and out during the summer without letting in sudden rain storms.
They are called awning windows, and you may want to take a closer look at using a cupola for ventilation.
When DW and I had our house designed, one of the first iterations was awning windows in a a clerestory between the north and south roofs.After running the simulations with and without that design feature we discovered that it actually increased the house cooling load during the summer and during the winter the passive solar gains and the wood burning stove heat spilled into the area, negating some of it's usefulness.
E-mail me if you would like to see a copy of our energy performance summary. It was run with 6 different design and building methods, and although not as detailed as the final load analysis it is really an eye opener.
Hi Dave,
I'd love to have a copy of your load analysis.
I was planning for the walk up cupola to incorporate a thermal break and have a sealed door going into it. That way it isn't a part of the heating and cooling load when we choose not to use it. It would also be the highest portion of the home creating the greatest draw when in use but I'm always open to improvements and corrections before it's too late.
I tried emailing you from the BT system but it came back undeliverable.
I'm at [email protected]
Pedro the Mule - Always welcoming the free
Edited 7/16/2009 12:47 pm ET by PedroTheMule
Sent you an e-mail with my work address
I'll add it here ;
[email protected]
should to get me.
Pedro,
The length won't change, but the width will change differently radially (like quartersawn) and tangentially (like flatsawn).
In Bruce Hoadley's book "Understanding Wood" he has a table of shrinkage from "green" to "oven dry." You are already drier than green, and may never get to oven dry, so you can reduce these numbers. Can't tell how much though unless you want to use a deep-probe moisture meter. Or you could cut off a piece and weigh it before and after baking it in an oven.
Sweetgum is listed with tangential shrinkage at 10.2% (15/16" for 8" material), and radial shrinkage at 5.3% (7/16" for 8" material).
If you're planning to use these logs in the round, the difference between radial and tangential shrinkage means that you will have moderate checking on the surface.
Hi Mike_Maines,
Sure appreciate the detail! I can work with that......5/8" through bolts into the posts and hidden T's held with spikes.
Pedro the Mule - Always grateful
It won't shrink at all (well not noticably) in length. It will only shrink in width. If left round it most likely will check badly (split) because the outside will shrink while the inside remains the same size..
Hi frenchy,
Thanks .....I can deal with checking in this situation since I'm going for that woodsy aged look. It's nice to know that the length won't change.....now I don't have to attempt to compensate for it pulling the posts out of level.
Pedro the Mule - Making something good with something cheap