Durability of Timber Block’s Panelized Wall System
Hello, I am looking into Timber Block wall construction method.
Why Timber Block? Part 1: a close look at Timber Block’s panelized wall building system
It is described as a “modified SIP panel” with an alleged R-value R-30 to R-36. The insulation used is closed-cell polyurethane foam with a stud every 24 inches. The interior and exterior OSB sheeting are replaced by Eastern White Pine 7” tall sections (“blocks”) which are stacked and joined with adhesives and wood joinery, then pre-stressed under 5000 lbs. of pressure. The company provides a 15 year warranty but I wonder about the durability of such assembly. There is no rain screen/drying cavity or water barrier protecting the exterior white pine other than stain and paint. Also not sure how the wall can reach R30 with wood studs
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Mauro,
I visited the site to see if I could get clarity on the cladding, stud and foam assembly, but found the material presented very short on details. There was one video presenting the structural engineer during which a wall with studs appeared to be in a pre-foamed state. If indeed the wall in the video is representative, the similarity to a SIP wall is a bit more distant than I would think from the other video showing panel elements being craned in.
Without a cross section of the wall or more "how it's made" videos, I would guess that they are framing a pretty normal 2x4 wall with 24" stud spacing first. Then adding horizontal 2x4 members to the exterior (?) side of the stud wall to which the timberblock exterior cladding is attached. I cannot surmise when the foam is added. It could be foamed as an open faced assembly which then receives the interior "skin" or perhaps the inside skin is added after the wiring is placed then the foam injected between panels.
If I am correct about the horizontal elements supporting the exterior skin, then the thermal bridging normally present in a stud wall is shorted out to just the contact points between the horizontal 2x and the vertical studs. This greatly reduces the direct all wood thermal paths to the exterior skin and would make R-30 over much of the wall credible. Still, the ultimate whole wall R values of each panel will be determined by the framing factor just like any standard framed and clad construction. Only a true full exterior continuous insulation method can suppress framing factor losses in a meaningful manner.
The apparent framing factor for this particular panelized construction would fall close to SIP if the panel sizes are sufficiently large. The examples presented show many panels that would have to have pretty significant framing factors to be structurally stable and thus less than the R-30 promised. Of course this can be true of SIPs if you are chopping up the panel areas with lots of windows. Same for Timberlock. Plus windows in general degrade whole wall values sharply.
The Timberlock panels could prove to be a good bit more resilient to moisture damage of the exterior skin than true SIPs, as the internal framing is ultimately attached to both skins. Still the detailing needed to keep interior moisture from migrating into the skin edges would pose the same demand for skilled assembly. The solid wood skins could well prove to be less susceptible to the skin rot seen in poorly installed SIPs.
One detail that I can't glean any info on from the photos provided is flashing at wall and roof intersects. I just can't find any good views that show how they do it. Nor for how windows are set and flashed. The longevity of the exterior finishes is certainly concerning. How would one refresh what might be a very high tech coating?
It is an interesting variant form that looks to be fast setting up. I do wonder what happens to the interior finish if it rains before the structure is dried in. If you get more answers to present, I am pretty sure GBA readers would like to hear them.
oslow,
"The solid wood skins could well prove to be less susceptible to the skin rot seen in poorly installed SIPs."
I wonder h0w much of that advantage is negated by the skin of this "SIP" also being the cladding?
Onslow,
thank you for your detailed answer.
You can see a schematic of the wall in the patent
https://patents.google.com/patent/WO2005052273A1/en
Mauro,
Two thoughts:
- The weaknesses of new building systems are rarely apparent in the first few years of their use. We are really just guessing how the Timber Block will do until we see that over time. Being an early adopter has risks attached to it.
- Houses can have a lifespan measured in centuries, if they are maintained and certain of their component parts that deteriorate are replaced. As the difficulty of replacing them can be the determinant as to whether a house is salvageable or not, the fundamental elements of the house - the foundation and structure - are either made from something with a very long life, or protected by other element that gets that periodic replacement.
In North America, where wood framing is common, walls and roofs typically fall into that latter category. The framing is protected by what you could call sacrificial layers of WRBs, underlayments, cladding and coatings.
My worry is that (much like conventional SIPS), in combining these elements Timber Block has exposed the entire structure to the much more rapid deterioration that wood cladding experiences, and failure of the cladding may affect the structural integrity of the house.
Malcom, yes I totally agree with you on the sacrificial layer concept. I believe this system have been around for about 15 years now. So no one really knows what happens after that and - guess what - the warranty also stops after 15 years. Anyway I believe it is a nice system just not willing to bet all "my chips" on it at his point unless the wall can be protected by some sort of exterior cladding or there are data out there to support long term durability.
Mauro,
It does seem like a strange decision their part to lock the panels into one type of integral exterior cladding, which also puts limits on the architectural styles the system will work for.
Mauro and Malcolm,
WOW! Was I ever off-base on the design details. Just reviewed the patent filing and whatever I managed to see in the video had nothing whatever to do with the the product. I will need a whole carboy of coffee to go with my humble pie.
This system frankly seems quite insane. I misunderstood the "block" feature to be the skins of the panels being made up of blocks, or strips if you will, of relatively thick solid pine, which were then adhered to the internal framing (as I perceived) from the one video. Kind of like a wall of finger jointed jamb stock. Nope.
They are actually making long horizontal blocks resembling 7" high walls with bottom and top plates that are stacked, then glued between each course and pressure clamped vertically. Apparently finished with long tie rods from top to bottom. The wood content is quite high. How one could get R-30 from this assembly would need to be proven. I will be back for more humble pie once I manage to check all the details presented.
onslow,
Why the humble pie? You are still way ahead of me understanding what they are - and that's not our fault.
Not sure what you mean by "not your fault". I however, am chagrinned that the actual product is so not what I was making it into. Once I have had time to be sure of the internal details I will post again. Think wood lego logs and lots of glue. Trying to see where the foam goes and why the skins aren't more variable. All in all a very odd product.
onslow,
It's not our fault that the manufacturer decided not to release some simple descriptive drawings or videos which would remove the ambiguity about what their wall system is.
It seems like a main component of the system is the pretension rod system, which theoretically allows for a much narrower shear wall ( judging by the pictures I think the is the main reason to use this). It seems similar to the Simpson strong rod ATS system https://www.strongtie.com/products/lateral-systems/strong-rod-systems/ats/details-specifications/system-details
I assume this is why they have internal studs.