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Wood as a Material for Window Work (notes)

Posted: November 18th, 2011, 4:36 pm
by johnleeke
Wood as a Material for Windows

(Following are some notes & ideas. When you see "..." that is an invitation to add more yourself. Click on "Post Reply" above to comment.)

Old-growth vs. new-growth…

Species and characteristics…

Peter Carroll offers these notes:
Could we describe the properties of the wood to be used for certain purposes? Such as, "straight grain, clear of knots/defects, hardwood or disease resistant species of soft wood milled to a similar dimension of the original sill" Maybe then give some suggestions of species to use, & not use for certain purposes.

Regional choices of wood species and quality: not all woods are available everywhere... What is available in your area?...

Salvaged wood & new wood…

include the use of salvaged window parts...

Consider the phrase "replace in kind to match existing if suitable", elaborate on its meaning, and determine if we can use this phrase as a catch all in many of the standards, with a complete definition of it here. (see this discussion on wood selection: viewtopic.php?p=533#p533)

Re: Introduction to Wood

Posted: February 1st, 2012, 2:19 pm
by Jim Derby
Hi Everyone;

I wanted to point out some differences between old wood vs new wood.

Old wood found in American historic buildings is often "old growth" wood which grew slowly for two main reasons: It grew up naturally in a mature forest with a limited amount of sunlight, and it grew when the climate was colder. This very slow growth means their is a higher ratio of latewood to earlywood which in turn makes the wood stiffer, stronger, more rot resistant and hold nails better.

Today, forestry practices are to grow wood as quickly as possible by thinning forests and the climate is warmer than 200+ years ago thus also accelerating growth. I do not know the exact science why dense, slow growth wood is more rot resistant, but I see it all the time in old buildings. Of course the species affects the rot resistance and other qualities too.

New slow growth wood is rare to find today so it may be fair to say all new wood will behave differently than the wood used in our historic buildings.

I know a preservation architect who strongly feels that reproduction windows should be made with naturally rot resistant wood, even if it is not historically correct such as being a tropical hardwood, so the wood windows will be durable. I agree with this deviation from preservation standards. I have seen replacement sash rot out in less than 20 years and this gives ammunition to the window replacement industry among other problems.

Salvaged wood is likely old growth wood. We need to be careful not to develop such a demand for old wood that it accelerates the rate of salvage (demolition) of old buildings, otherwise known as mining the urban forest. The study of American historic carpentry is still in it's childhood and we need as many buildings to survive as long as possible just from the aspect of studying them.

Thanks for doing so much to save old windows!

Jim Derby

Re: Introduction to Wood

Posted: February 1st, 2012, 5:11 pm
by johnleeke
Jim, welcome to the Window Standards collaborative. Thank you for your comments about wood.

That's an interesting point about the extensive use of salvaged wood promoting the destruction of old buildings. I wonder if the wood salvage companies have set up a certification program as has been developed for the sustainable harvest of rain forest hardwoods.

Re: Wood as a Material (rough draft)

Posted: March 8th, 2012, 2:09 pm
by peter_carroll
Jim's reply is right on. "the qualities of the wood" in old windows & sash should be referenced often.

If plantation wood is used we should think heavily on how to choose pieces (heartwood vs sapwood, quarter sawn vs plane sawn) & how best to protect them from rot. (especially those end grains) Lately, I've been given allot of thought to new building techniques of storm sash that minimize end grain exposure, like pocket mortise & tenon joinery or free M&T. Also new wood is lighter & sash counterbalancing will be affected.

I took a piece of old growth fir and compared it to a similar size piece of Ipe and felt from a purely subjective point of view for them to have similar qualities. (density, durability, grain) The cost between Doug Fir & Ipe locally was not as much as I though it was going to be. Everything else being the same (maybe have to sharpen the blades more often with Ipe) it might make sense to upgrade species for sash & repairs when historical accuracy is not prevailing.

Re: Wood as a Material (rough draft)

Posted: March 8th, 2012, 4:53 pm
by oculus
I have often wondered about upgrading species as well. My hesitation has always been about the different expansion/contraction between the two species when exposed to moisture. And how that would effect the repair. Might be an interesting experiment. I am also leery about where species like Ipe come from. As a tropical hardwood I would want to be very careful about who I am buying it from.
A question that comes up out here is whether to put a cedar piece in place of a rotted out Doug. Fir piece. A good example is a rotted out fir sill plate. Should another fir piece be put in (in-kind repair) or should a piece of cedar be used instead which gives a bit more rot resistance?
I don't have a good answer for it. We have much discussion with SHPO about it on a case by case basis.

Re: Wood Basics (rough draft)

Posted: August 22nd, 2012, 2:31 pm
by Bob Yapp
I tend to believe in using "In Kind" as a definition for replacing a wooden part or parts. To me this means the same species as well as similar age when first cut. I agree that we don't want to promote demolition for the sake of having old growth wood. However, I have two garages filled with old growth window sashes I have collected from window replacement contractors. The small amount of old growth wood I use to rehab historic structures and windows is only a recycling endeavor, not promoting demolition. I rarely have to replace window stiles and rails but when I do, it is important for similar contraction and expansion that I use "In Kind" wood to do so. I am opposed to using these exotic hardwoods from central and South America as most of this is causing the ruination of our rain forests as well as paint retention. Hardwoods do not, as a rule, hold paint well.

According to United States Department of Agriculture, Forest Service, Forest Products Laboratory, General Technical Report
FPL–GTR–190. Harwoods like walnut, oak etc are unsuitable for paint finishes. They list all cedars, white pines and true fir as the best woods to hold paint finishes for extended periods of time. Most sashe were made from eastern or western white pine. So, for durability and sustainability an in kind repair of an eastern white pine sash I would use either species of white pine of similar age (number of rings per inch).

Re: Wood Basics (rough draft)

Posted: January 4th, 2014, 9:03 pm
by hiles8500
I'm looking for wood sources in the DC suburbs for a storm window project. The big box stores and woodworking supply stores could not point me to sources of clear pine or doug fir. Old wood would be even better.

Before the recession, the Brass Knob Back Door had a great inventory of old windows that could have provided the stock. That was a great place. But they are gone now. Any pointers to good new and salvage sources would be much appreciated. I may try out Community Forklift in Hyattsville and Second Chance in Baltimore.