Timber frame with 8-in. XPS wrap-and-strap assembly: What have I gotten myself into?
24-foot square timber frame with “REMOTE / PERSIST” envelope, from inside to out: timber-frame post; drywall; horizontal or vertical 2×4 ‘studs’ 16 in. on center without insulation; staggered sheathing; peel & stick; 8 in. XPS; 1″ or 1-3/4″ furring attached through XPS to 2×4 framing with 11 in. SIP screws, (fastened at an angle) 24 in. on center, and a mix of clapboard, board and batten and shingle siding.
I will be attempting this build asap in intermittently seismic NH. I have already purchased the class-cut TF and the recycled 4 in. 2×8′ XPS sheets to achieve R-40 throughout, so I’m really in a pickle now.
1) I’m concerned about racking resistance in bringing the sheathing away from the timber frame, ie on the outside of the 2×4 stud wall which is outside of the timber frame.
2) I became concerned about the strength of 11 in. Oly/Timberlok screws in their holding capacity of the furring and siding, cantilevered out through 8 in. of XPS after reading Martin Holladay’s recommendation to consult an engineer with more than 4″ of foam between siding and framing.
3) Being a timber frame, I do not have the option of insulating the attic with blown cellulose as in the REMOTE system from Alaska. Although more expensive, the PERSIST system seems to be what I need to do, (ie 2nd roof assembly) but I’ve had trouble finding a good description and relating it to the timber frame.
I’ve gotten as many different answers as engineers I’ve sat down with, and I don’t know what to think or who to consult, so I’m asking you guys for any thing you might have to say….
By the way, thank God for this site!
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What roof overhang are you looking to achieve?
Also, what is the roof pitch?
Is this a 1 or 2 floor TF~ sorry about multiple posts
Well, you asked for "anything", so this is my suggestion:
Give away the XPS, frame a floor assembly that extends out beyond the timber frame by 18" and wrap the frame with straw bales, with #30 felt air-fin gaskets outside each framing member, then coat with 1½" of earthen plaster inside and out with a lime/sand/manure finish coat.
Frabricate parallel-chord trusses to overlay a T&G pine roof deck, create broad overhangs (min. 2') and fill with dense-pack cellulose under sheathing and roofing of your choice.
Why would anyone take a beautiful wooden timber frame and wrap it with plastic?
Hi Roy,
No problem. The overhang will be a good 2-3' horizontally I hope, and the roof pitch is 12/12.
The TF is a "1 storey", not including the full basement. It's assembled on top of a poured foundation and conventionally framed deck, with squash blocks or posts continuous beneath all TF posts. It's a very simple design with 9 posts including a center post, supporting an attic floor. The posts along the length of the building continue above the attic floor and terminate at the horizontal tie beams that tie the three girts together, giving the attic space a 2' kneewall. These horizontal tie beams in turn support the roof rafters.
Robert,
I knew you'd chime in and tell me to be done with the XPS! Unfortunately, as much as I wholly appreciate your approach, (and wish I could afford to camp at Austin Brook and attend Yestermorrow and swim at Warren Falls every afternoon:-) I didn't learn about the Larsen truss until after I had made several less informed decisions that my wife delicately terms "hurdles". So now, since I'm stuck with an upside down mortgage on my 1st home purchase and a meager income and a 50-60 hour per week job on top of 8-10 hours of commuting, I'm simply looking to get out of, as quickly and gracefully as possible, the rather "cute" cape my wife loved at first sight that some guy named Jack built... The existing house is unhealthy to say the least and far beyond fixable (fieldstone foundation one half and cracking block on the other- don't ask) I learned the former a few months after moving in, and a while after that I assumed the latter after having read that renovation, however green, is typically more expensive than a new build. I would love to do cellulose, but the 4" XPS I got from Insulation Depot was more R value than I could afford to purchase new in any type of insulation. So, I settled on the Remote system, thinking "hey, then I can have a wall I can puncture at will and run utilities etc down the line", and I can keep the structural timber frame well away from the dew point, and hopefully have a reinforced foundation and TF that will last a couple of hundred years, with the proper ventilation and site drainage. The entire budget to build a house is astronomical and still something I've a hard time wrapping my head around. Although many gba subscribers might not like my approach, the plain fact is that I can't afford to hire someone like you, Robert, to build my house, and yet I can't afford to throw my money away by hiring the sort of contractors I might possibly be able to afford to hire... I should probably have stated before that, due to finances, I intend to do every bit of this build by myself or with the help of friends if i can manage it. I can hear you all laughing- heck, half the time I'm laughing to, (a little insanely) but now... I'm committed. Can't get a loan in this economy, so for the sake of my wife's health and my own I'm struggling to... get the hell out my cute house!
Rather than angle the screws, I would build some kind of angled support base that extends out from the foundation at 45° to carry the siding/window loads to the ground. This can be frabricated from PT lumber.
I'm no structural engineer but couldn't you simplify your proposed wall assembly by framing your 2x4 walls between your timber posts instead of outside of them. Then your exterior sheathing would attach into the posts directly. Yes you lose some of the interior exposure of the attractive TF post but sounds like your in a pickle here.
The shear issue needs to be addressed in terms of how your timber frame is configured. When I got in to building timber frames (1988) exterior wall assemblies were completely discounted for strength: the frame took up all of the loads, through braces, primarily. So, if your frame is well braced, adding wall build for shear strength may not be necessary (even in a mild seismic zone such as NH).
Your concerns about screw cantilever is warranted, IMHO. Little to do but reconfigure the wall to provide wood for siding fixing and/or support from below if you're stuck on the other components.
You could extend a mud sill out to carry this, but it would need to be well engineered and constructed.
How far along in the build process are you?
Chris, I don' t think Ryan is worried about shear in the timber frame, but rather the shear in the 11" screws cantilevered through 8" of foam and supporting siding and probably windows.
J, The posts are 12' oc, so require additional framing to support the sheathing.
Ryan, I believe you mean that the posts terminate at the rafter plates which tie the three bents together. The tie beams connect the three posts in each bent. Girts are intermediate horizontal members between posts, typically to attach sheathing or siding. Purlins are intermediate horizontal members between principle rafters to support the roof deck or roofing.
Ryan,
The REMOTE builders in Alaska definitely use 6 inches of foam routinely, and I suspect that someone has done a REMOTE wall with 8 inches of foam. You might want to contact the Cold Climate Housing Research Center with your questions about engineering the screws.
I assume you have seen these two useful resources:
http://www.cchrc.org/docs/best_practices/REMOTE_Manual.pdf
http://www.insulfoam.com/images/stories/docs/JLC-finalfeature.pdf
When in doubt, you could always hire an engineer -- that might be your cheapest solution.
Ryan..... And you plan to build this yourself in your "spare time"?
It does sound like you are going about this "backwards"
I think your headaches are only beginning.
Help us understand what you have already "done" and purchased....
Have you started the foundation?
What does "class-cut" mean?
Do you already own the frame? Are you storing the parts?
How much XPS do you own? if it was such a bargain why not re-sale?
Or pay a restocking penalty?
hey Ryan, having just wrapped our Timberframe with REMOTE, you're on the right track. I would defenitely contact a PEng to go over your project to make sure you got all the details correct. You can find a list of the ones familiar with TF on the Guild's website @ https://connect.computility.com/directory/index.php?id=ab5fa89df128343f89e79e690876203a
In our case I was dealing with 5.5" of foil faced polyiso for walls and 8" of reclaimed xps for the roof. The material is super easy to work with solo, and about 1/.4 of the cost of sips. Funny, reading your story is like reading my own... lol People will laugh and point fingers, but if you're commited you can do it. Like you I put in 40-50 hr in my full time job with a 10hr commute, building our house was a part time gig and I'm a walking example (like many others out there) that if you're commited...sky's the limit.
The "wrapnstrap" has been used on TF's for a long time, we're not reinventing the wheel here. The guys at CCHRC made things much easier with the publication, and are very helpful if you're stuck on something.
Here is how I built the enclosure:
-2x4 curtain walls, screwed to the frame with 6" panel screws,
-layer of 3.5" IKO Enerfoil (seams acoustisealed and taped) nailed with 5" roofing nails (two nails per panel),
-second layer of 2" IKO Enerfoil (seams taped) temp. supported with 7" panel screws and plywood plates,
-horizontal 1x4 rough cut pine strapping secured with 8" panels screws 16" OC
-siding.
The roof
-random 1x pine roof decking,
-two 4" layers of Dow Deckmate (seams taped) edges, peaks and valleys foamed,
-typar,
-vertical layer of 2x4's 16" OC (on flat) screwed into 4x10 dougfir rafters with 12" panel screws, ran out to form eave overhang
-horizontal layer of 2x4's 16" OC (on flat) toenailed to first layer and screwed around perimiter with 14" panel screws,
-steel roof.
your can view it here:
http://www.tfguild.org/forums/ubbthreads.php?ubb=showflat&Number=22170&an=
and the project here:
http://www.tfguild.org/forums/ubbthreads.php?ubb=showthreaded&Number=24698#Post24698
my blog needs updating, but now that we're moved in and I have some time, I'll be updating it more often:
http://crookedhemlocks.blogspot.com/
If you provide me with your email addy, I can send you some detailed drawings in sketchup of the curtain wall attachment, bottom termination and the wall/roof intersection....all very important spots if aiming for "airtight"...
Hello gents,
I was typing a reply when my computer lost power, so I'm going to make this one a little shorter, I hope. Thanks for the recommendation J, but I'd really like to avoid burying the TF braces, which are set to the outside of the frame, in an infill 2x4 wall. Out of the three engineers I've spoken to, one advised this and the others weren't concerned, I don't know why. That's the reason why I'm asking all of you for help- I've had conflicting recommendations from the three engineers I've talked with, and although I'm sure they are all perfectly good engineers, none of them design TFs.
Thanks Robert, I'll think about how to implement a support base for the siding and windows, and Thank You for calling attention to my terminology mistakes: I meant bents when I said girts and rafter plates when I said tie beams... Not much help am I!
Thanks, Chris, the TF is fully braced and designed to carry the loads- the sheathing is a concern only in that it helps the TF avoid twisting, I believe. I hate the idea of a thermal bridge but if I need to extend the mudsill or a support base out, so be it. As far as the build process, I have the luxury of planning a build on my existing property, in a separate location from the existing house. I haven't broken ground yet, haven't even finished designing the plans obviously until I get these pesky details squared away with, but as I said I'm committed to this build simply because I have 1) purchased and stored the TF, which was discounted due to being cut by amateurs in a timber framing class, 2) purchased and stored 8800 sq ft of recycled 4" XPS which is non-returnable. There are other materials we've gotten as well, but those two are the big ones.
Martin, thanks for the links- not sure if I've seen the 2nd. I should definitely contact the CCHRC as you said. As for the engineer, I would be much obliged if someone might recommend one, preferably licensed in NH.
John, I think I answered most of your questions above. If by having the time to purchase materials in advance I am indeed going about this backwards, I see no other way for us to achieve our goal with our budget. If I am in the midst of building I will have no time to purchase the necessary big ticket items on time and in a financially savvy manner, so this has been my approach. As for returning or reselling, I'm not about to give up on my plans. It's my only option. I'm one of those citizens who, out of pride or conscience, refuses to foreclose and add my box of trash to the heap, and add one more burden to all of those who pay taxes in this land. However unfair the "buyer beware" aspect of real estate, I accept full responsibility for the decision made in buying this house I live in. Doesn't mean I want to continue living in it though.
hi Raff,
THANKS! I'm not sure how to privately message you my email, so I'll just write it out here: wrshanahan at gmail dot com
Again, thank you so much!!
nothing backwards about your methods my friend... I have friends who spend more $$$ on kitchen remodels than what I've got in this entire build. You buy then it's available NOT when you're desperate for it....lol Concept hard to grasp for some, but it can slash the budget by 2/3...ask me how I know..lol
your mud sill concern can be addressed by bringing the wall outsulation below the mudsill and bringing the frost wall outsulation up to meet the wall insulation...Remember, you're hanging the curtain wall onto the TF, you're not relying on the mudsill to carry any loads it's just there to rest the curtain wall while you're screwing it to the frame...
Raff!
Wow! Very nice spread there in Ontario. Btw, looking at your links, I think the 3rd TF guild link might not be right? http://www.tfguild.org/forums/ubbthreads.php?ubb=showthreaded&Number=246
Links to a "drawboring screwup" thread, couldn't find your project.
My goodness, though, that's one heck of a job you did- that mailbox is a gem! All the thanks in the world for providing me with a glimmer of hope...
Ryan & Raff,
My "backwards" comment was about having a plan... not when to buy materials.
I get the impression that Ryan has not really thought thru how all of this is going to fit together.
I also get the impression that Raff did considerable planning FIRST.
hi Raff,
Scratch that about the link, I got it!
Hi John,
I'm doing everything I can to think all of this through, I promise you. Could be worse, couldn't it? I could have a foundation and an erected TF, with no clue how to wrap it. I originally was planning a stick build, OVE frame, but then I saw the TF deal and thought, "hey, the structure and some aesthetic appeal all in one, and at a good price!" I won't deny that I'm in over my head with multiple aspects of this project. The TF certainly solved the problems I was having designing the structural frame itself. As for the plans, I have the foundation and TF plans from the TF builder, but they assume I'll go with SIPs. With SIPs my problem would be solved, excepting the cost and the question of long term durability, ie delamination. I suppose SIPs have their place, but if I can achieve a very respectable R40 with cheap recycled XPS instead of having more expensive new SIPs built with less R value, why would I not attempt it? I appreciate your input and the various past posts of yours that I've read that contained good info, but please take no offense when I say that I've yet to read a critically constructive post from you pertaining to my issues.
Ryan,
I am not trying to offer deconstructive advice....
You seemed to be asking for help and I was trying to see what your "givens" are.
Sounds like the Timber Frame is the big Given.
Now I have timber frame envy ;--)
It is fortunate that you have not started the foundation yet and...
It is fortunate that Raff has come along.
I am not familiar with Recycled XPS?
Does it come from deconstruction?
Ryan,
Sorry to go a bit tangential on your thread...
I am also curious where you got recycled XPS from? Did the opportunity just pop up in some kind of inventory list?
I am currently searching for as much recycled material as possible for my own upcoming project...
Hello Ryan,
I've put your shoes on, wandered around in them a bit trying to understand the build while learning from the other great suggestions.
I vote for the Riversong approach, but understand the situation that you have shared.
While I'm sure of the weight of the panels, I can't imagine that they would be that much.
Perhaps you could create a detail at the top of the outside of the TF, and the point at which the remote roof framing overhangs the TF that would allow you to hang these panels first, and then fasten to the frame.
This would allow an opportunity to install gasket material at all points of contact that could be a little thicker for a better conform to the TF.
Much of the concern about shear of the long screws would be eliminated, as their purpose would be to hold back, rather than hold up.
I use a simple and inexpensive 2 piece hanging system that allows very heavy kitchen cabinets to be hung very tight to the wall by its design. It consists of ripping a 45 degree angle down the middle of whatever width stock deemed appropriate, installing one piece in the "hang" position to the inside top of panels and the other piece to the top of TF.
Most of this work could be done easily by 1 person and the hanging would be really easy. Same technique would work at top of gable ends by starting at the low end first~ bumping a section of the side panel that would extend to meet at th corner.
After the panels are secured, and before window and door loads are installed the suggestion of installing a 45 degree shelf angle tightly under the panels into the foundation would be important.
I'm kind of new to writing about this stuff~ hope something may be gained from my wording.
Hi John,
Thank you for not being offended. I'm having a bit of TF envy as well, after seeing Raff's cruck frame. Wood is a gift from God, for sure. The 4" XPS is from Insulation Depot, I believe what I purchased was probably from a commercial deconstruction. It's in great shape compared to any of the other material I've seen them advertise, and at about 33% of new retail, I couldn't beat it. David Volpe over there is a good salesman- he got me to jump! Pita to unload and store a tractor trailer's worth, but now I have enough foam on hand for the foundation, slab and TF. Someday when I'm cozy and content I'll attempt an addition using Robert's truss system and cellulose, but here and now I'm focusing on not heating the stratosphere with my gas... And I expect the TF to go up in a day or two at most, so that much less time to get the roof on and those timbers out from under the weather. Happy trails!
Not sure of the weight of the panels...correction
Hi Lucas,
Insulation Depot.com? Is I believe the URL. The good material goes quick, though, and the price for the good stuff is significantly more than the stuff they have on hand all the time. Best bet is to contact them, express your interest and be ready to put a downpayment on the good stuff when they get wind of it coming down the pike. Then be patient and ready to take delivery at a moment's notice. Not the easiest process I'll admit.
Roy,
Thanks for the suggestion! I'll have to think a bit about how to implement such a strategy, but that's where the fun is, at least for now!
I dislike wrap and strap systems precisely for these reasons. But I wonder: can you install studs @ 2' o.c. (such that the foam fits between)? Depending on how thick your foam billets are, I can imagine either a single, deeper stud, or two shallower ones, off-set to minimize thermal bridging. This allows for good fixing of siding, windows, GWB, etc. If the deeper stud is the better scenario, I can imagine a thin, continuous layer of foam and vapour barrier directly behind the GWB and room-side of the studs. Top and bottom plates are continuous: the thickness of the wall. Thermal bridging is not a big issue in the plates, as the wood has ~ R1 per inch.
Your initial query 1) concerns racking; hence my shear comments. Shear in the fasteners in deep insulation is a difficult one to overcome without supporting the weight from below. This is one reason why SIPs are so popular to enclose timber frames: all of these issues go away.
GWB? Global Warming Barrier? Now that's what new homes really need.
[OK, gypsum wall board, but most of us call that drywall.]
Let's be more precise. It may be the most common track for modern timber frames and the quickest and easiest, but that doesn't make it "right". "Right" depends on the entire spectrum of goals that we SHOULD include in our shelter designs if we wish to help build a healthy, sustainable world.
That's certainly not an engineer talking. Every element of a structure has to be "grounded", since it is the earth below that must support all gravity loads. If a significant element, and one that determines the weather resistance of the structure, is not grounded directly down onto the foundation, then forces become much more complex and problematic (like cantilevered decks).
As one who teaches engineering to builders and architects (though not a professional engineer), I would never rely on long screws alone to support a building's exterior cladding assembly. Even my Riversong Truss wall, though gusseted to the primary frame 24" oc vertically and horizontally, is supported both on the foundation and hung from the rafter tails or outlookers.
Hence my suggestion to use a beveled support structure below, similar to the braces on the timber frame.
Ryan,
Since you haven't yet built the foundation, you might consider extending the floor deck out beyond the frame sufficiently to carry the outsulation and cladding assemblies. The thermal bridging through the joists is measureable but not that significant in the whole scheme of things.
I did something similar for a straw-bale wrapped timber frame (though it was only a woodshop and not a house) for the Yestermorrow Natural Building Intensive 2008. I poured a concrete grade beam over a rubble trench foundation, capped it with roughsawn cedar sills which supported the timber posts, and then built a roughsawn 2x12 deck around the posts extending 21" outside the frame to support straw bales and plaster. The floor assembly was filled with dense-pack cellulose.
Pictures of some of the Yestermorrow Natural Building projects can be seen at http://picasaweb.google.com/yestermorrowschool/NaturalBuildingIntensive#, though this past year's magnificent TF home project is not yet there. The pictures from #81 onward are of the project I was involved in. The whole set of photos shows the many methods of doing natural walls and finishes, which are the perfect complement to one of the finest natural methods of house framing.
There are a few pictures and a description of the Natural Building 2010 timber-frame house project at:
http://yestermorrowschool.blogspot.com/2010/08/natural-building-intensive-2010.html
I should add that, in the Picasaweb photo set for NBI 2008, pictures 120, 121 and 122 show what was done to "hide" the overhanging deck with drylaid stone masonry, simulating a fieldstone foundation at the outside perimeter.
[also, pictures #107 and #109 are me on rope, helping the timber framers set up a safety anchor for working on the roof.]
Thank you very much, Robert- that buildout sounds doable. You've been most helpful, and the links to Yestermorrow's albums are truly amazing!
Ryan,
The extended floor assembly is one option, or an extended mudsill. But if you want to avoid the thermal bridging, then pour the foundation high enough out of the ground to build that triangular support base for the outsulation system and tie it to the foundation wall. You could even have a PT ledger poured into the side of the foundation (to avoid having to drill in concrete anchors) as an anchor point for the beveled support base. Or attach angle iron as a support for the extended wall and butt the foundation insulation up to that to maintain continuity of the outer wall plane.
Robert, you're correct, I'm only assuming that after screwing the curtain wall to the frame @ 16" OC @ all posts and beams with structural fasteners, the loads on the mudsill would be marginal. The plans were approved and stamped, so I'm confident in this assembly.
Would've loved to get into more natural enclosure on my project, but it's not something I would attempt at learning how to do on my house. With everyone on the "green" kick these days, to farm this out would cost a small fortune...a lot of these guys cater to the elite... and are more concerned about sustaining their bank accounts rather than help people build sustainable homes.
Given that Ryan already has the XPS I still think he's on the right track...JMHO... your milage may vary...
Sorry, yes GWB = gypsum wall board. I've been working on a set of architect drawn plans with the abbreviation.. and it's shorter to type than "drywall.."
Chris, nothing wrong with "GWB." It's standard terminology.
To revive a (not too) old thread...
Raff, a question for you as winter is winding down. Do you have any ice dam issues with your roof? Might seem like a silly question with a ventilated sealed roof (those words don't sound right together, but looking at your details, I think that's the best way to describe it), but I came across this article by Joe Lstiburek at BSE noting problems with uninsulated overhangs and thermal plumes at the exterior siding.
http://www.buildingscience.com/documents/insights/bsi-046-dam-ice-dam/?searchterm=roof
Not sure how many winters you've been through with this house, but I wondered if you had any proctical experience with this issue?
sorry for the late reply Drat. Our first winter has left me very impressed with the REMOTE system.
I worked in the unheated portion of the house all winter long in a thin sweater and a big smile on my face. With breaking record temps this winter (a few days of -40deg.C days) and nothing but leaked heat from the basement to keep me warm upstairs, this is shaping up to be one cozy house :)
There were no ice dam issues to report, but we also do not have the siding on yet, so hard to comment on the " thermal plumes at the exterior siding"...will update next spring ;)