Can You Use Green Wood In Timber Framing? - Part 1

hello my name is pat hennen i'm one of the hennans that teaches people how to design and build homes at the shelter institute should we use green wood in building timber frames this is a question that comes up all the time and of course you should never use green wood to build timber frames but it's all we do is use green wood to build timber frames so what you want to do is think through what really is going on here the problem with green wood is not really that it's green but that is full of water and so the cell structure of the uh wooden cells is loaded with trapped water so we have here a cell that's all bloated and about 45 years from now it will look like this so what you have to do is get your trees cut them down put them in a dry shed and wait 45 years and then build your timber frame it's very simple right so obviously most of us are not going to live long enough to do it that way so we're going to have to compromise somehow life is all full of compromises so what do we do first we look at the species of wood if we have wood that looks like this with a few very enlarged cells as opposed to wood that looks like this with lots of little tiny cells we can think about this for a few minutes and try to picture what the difference is on this tree we're going to have glues tying the cells together looking like this and over here we have glues tying all of these cells looking like this which of these two is stronger well obviously this one here is glued so much more often and so much denser that it is stronger and as water leaves this scenario leaving many many different sites the effect is going to be much greater so a drying piece of oak is going to twist and turn and crack with much more power than a piece of eastern white pine so picking your species would be quite a difference here at shelter and stew we have our classroom made of white pine and we have our store made of douglas fir and there's no question that the douglas fir expresses drying quite a bit more than the uh than the uh pine does so the first thing would be uh species next is when do you cut the wood in the in the chronology of building your timber frame well i have often cut a tree down or or maybe 20 trees down in one day and the next day mill it on my sawmill and then the day after that cut all the mortise and tenon joints and put them together 50 years ago when i did that with hemlock i built the house and it wasn't the first winter that windows started to crack a hemlock tends to grow like this and it shrinks as it dries in the reverse order so i learned very quickly that hemlock ends had to be tied down in a way that they could not rotate so that meant that the tendons and mortises had to be housed as opposed to simply budding it also helps to consider steel in those situations how could you put a threaded rod through with washers and bolts to lock ends of timbers to make them not twist now i know that that's the sacrilege among true timber framers so you want to create joints that lock the ends of the timbers in the other thing is time how long is the timber going to have to dry up if you put a uh a wood-burning stove in a fresh new timber frame home and bring the temperature in that home up to 80 degrees that will drive the moisture out of the wood in record time that means that all of this shrinkage of all the cells picture the cells around knots shrinking you have a branch going this way sideways out of a timber like this so since it's sideways it's going to cause the timber to to twist and all of our timbers of course are full of knots so if you give the timber too little time then of course you're going to be getting all kinds of twisting and and checking so what we want to do is control the length of time and that's done by preventing surprisingly preventing the timber from drying here's a cross-section of our timber and most of the timber framing situations we're getting one timber out of one tree if you're extremely wealthy or congressman something like that then you would be cutting down redwoods and getting a timber out of the side of a tree but most of us are stuck with this so what happens here is that all of these cells around the outside of the timber are losing their moisture and so they're all shrinking so if you picture all of these guys here shrinking around a bunch of cells that are not shrinking what has to happen well all these it's like a tug of war all these cells are pulling this way all these cells are pulling that way and pretty soon you get this big split here so that happens on all four sides now usually these splits are not all that deep so they don't affect the strength of the timber all that much but what if we were to somehow seal the timber with a material that prevents the moisture from leaving fast so now we have these cells on the outside losing moisture and that gives the moisture deeper in the timber time by capillary action to work its way out to the outside so now the entire timber is shrinking at the same rate and you don't get the uh the cracking so we started of course uh sealing all of our timbers years ago and we've had great success i haven't had a cracked window in at least 30 years just by keeping the timbers from drying up too fast and also of course admonishing our clients about raising the temperature too fast in the house and allowing the relative humidity to get too low too quickly the an extremely dry house will result in very quick drying the other reason you don't want to dry your house up too quickly is that that results in moisture condensing in parts of your house where you really don't want that happening so the reality is that ideally we would have perfectly dry timbers that somebody has stored somewhere for 50 years and then offer it to us but our population of the world grew tremendously in the past 50 years so there is no such thing available and the irs has charges charges taxes for inventory so some of you may be aware that about 40 years ago all lumber yards had sheds out back three or four story tall sheds with racks and wood in those racks drying and that wood was air dried was not dried in a kiln and that allows the moisture to migrate this way from inside to out slowly in the shade well when the irs started to tax that wood every january of course everybody got out of that and today no wood is air dried so the last topic of course is kiln drying why not kiln dry these uh this wood well all of the stick framers use wood that is kiln dried and what that means is that in a matter of hours all of the moisture is driven out of the timber so imagine you being one cell pick any positions in your two by four and you're lying there in the cell all the moisture is driven out of you and you go like that and everybody else in the whole 2x4 is like this having been dried up really fast you can tell what happens when you go to lowe's or home depot you'll find that there's a big pile of twisted two by fours that have been pushed to the back and now you're going to buy the nice straight one that is in the middle of the pack the only reason it's straight is that it's in the middle of the pack and it has been tied with bands so you stick that thing on the top of your car you drive home by the time you get home it's like this so it was dried way too fast kiln drying is not a great way to have really high quality timber but it is the state of the art today all of these uh one and a half inch supposedly two inch two by fours two by six is two by eights are kiln dried so we could do the same thing with uh timbers but it's extremely costly to kiln dry all the way down to the middle of an eight by ten so once again you would have to be a congressman who has taken billions of dollars from the pharmaceutical industry and then you would be able to to do this but for the rest of us using green wood works out just fine now of course you always want to uh give your wood an opportunity to dry on its own you certainly don't ever want your wood to get wet in addition to the wetness of being green so we would like to always stack our timbers with plenty of air space between them so we would place them on top of logs then we would put a sticker what's known as a sticker in between them this would be a one by one or a two by two and then pile up other timbers on top so on and we can make these piles as much as four feet tall and air is able to flow through this down here on the ground we should start off with a sheet of polyethylene film heat is constantly leaving the ground and that heat pushes moisture up that moisture comes up and then condenses at night on the cold timber place that you can see that is your car look at the bottom of your car in the morning and you'll find all this glistening moisture there if you park your car over a piece of plastic there won't be any of that moisture rotting it out so we make this four feet tall and then on top we would lay a sheet of plastic or a piece of plywood something on there that will keep water from impregnating all of this wood then wherever you have this pile of stickers you should place your stickers six feet apart so every six feet you place a band with a ratchet and you ratchet that as tight as you can get it so that now all of the timbers are locked and unable to freely twist they'll still twist because all of those cells are the accumulation of all those cells is quite powerful but the straps with the come alongs or even chained with a chain binder will cut that down to a minimum you don't want plastic to go down the sides you want that air to flow freely through it and you'd like not to have the sun shining on this pile so if you could place this under trees shady uh but still where the wind is constantly blowing if you put it down in a swale where cold moist air sits that's not going to help get it better it's all just common sense you would like your timbers to dry slowly there are a number of oils that you can use to do this job any oil will do it to one degree or another presently we're using heritage natural oils and we're able to put into these oils other ingredients if the customer wants so we can put anti-fungal material uv resistant material there are all kinds of additives that can customize the oil for whatever purpose we found that we can have bare naked timber frame sitting out in the weather for over a year without turning gray you know maintaining that beautiful honey color uh and and without doing any of the cracking and uh and twisting so we're going to be covering all of the timbers with the oils and we actually use rollers to do that the ends of timbers are cells that have been cut through so the moisture is going to leave those cells way faster than along the length of the of the timbers so the ends really have to be sealed more thoroughly and on the ends we actually use a paste wax and we press that in with the trowel so that it's thoroughly sealed otherwise we will get lots of cracks all along the ends thank you for watching and we'll see you in another video hey there thank you for watching here at shelter institute in woolwich maine we teach a wide variety of house building and timber framing and carving classes we'd love to see you here but if you can't make it to maine to take one of our classes our online class is available at [Music] shelterinstitute.com [Music] you

Channel: Shelter Institute

Views: 253,408

Keywords: timberframe, homebuilding, how-to, designbuild, thinkbuildlive, timber frame construction, timber framing, timber frame house, timber frame, timber frame basics, timber frame class, timber frame school, timber frame course

Id: U39fun9Iwjc

Length: 14min 37sec (877 seconds)

Published: Wed Feb 17 2021