Converesation with Elijah Pearce, architect.
- Sears house - that was legit
- Microhouses - can't sell that for money afterwards
- Selling this after you are done - that is a serious proposition.
- So going legit is a big deal.
- Katrina Cottage - https://www.mariannecusato.com/. Full set of docs for construction. Set of plans is step 1.
- But - regulatory - and the general contractor part of the enterprise. She delivered something for a contractor, not a person.
Catarina and Marcin,
Sorry for the lengthy email. This one little detail has a lot to it. I've put my thoughts below about the two options, as well as thrown out a possible third route.
Thoughts on Option 1 (offset sheathing): - I like getting a better connection between panels. Not only would you have the top plate of your double top plate tying the individual panels together, with this offset strategy you have the sheathing bridging two panels together. Aside from the structural benefits, I would imagine this would help with alignment of the individual panels and more uniform exterior plane. -Also, I like creating a more circuitous path for water, with the joint of the plywood now offset from the joint in the housewrap. -I see the major downside of this option being that it doesn't seem to allow you to tape that vertical lap in the housewrap. While the code only dictates a 6" lap, this is in regards to "No. 15 asphalt felt" (tar or building paper). Housewrap, which I agree is a superior material, is technically an "other approved water-resistive barrier". Housewrap, is of course, basically universally approved, but typically each manufacturer has an ICC report showing how their proprietary material meets/exceeds the performance of No 14. asphalt felt. The issue is that in their ICC reports, there is typically a statement that installation must meet manufacturer's written instructions. So in a slightly convoluted way, to meet code, you must meet the manufacturer's written installation instructions. Many will require a taped vertical seam, even with a 6" overlap. See Tyvek (https://www.dupont.com/content/dam/dupont/amer/us/en/performance-building-solutions/public/documents/en/K16282-Residential-WRB-Install.pdf) for example. I also took a look at Kimberly-Clark's Block-It, which is what I believe you are using now. They do not have a taping requirement :) ....but do require a 12" overlap at vertical joints :( .(https://www.kcprofessional.com/Umbraco/media/278855555/blockitinstructionsheetpdf.pdf). Would a code official really call you on that? Maybe/maybe not? Aside from the code issue, a taped joint really would be preferable.
Thoughts on Option 2 (double sided tape) - I like this as it seems to meet the letter, if not typical intent, of the code. This may make it an easier sell across different jurisdictions. - My main concern with this option is how to deal with the resulting flaps. Can you roll/fold the flaps neatly enough to lay the batten tightly against the exterior sheathing? Also, I would expect the batten's nails would have to penetrate the rolled/folded portion of the house wrap. One nail would make several holes through the stacked wrap. -One addition to this option would be to add a layer of self adhered waterproof (SAWP) membrane overtop the entire length of the joint. Most manufacturers have a "tape" version of SAWP membrane that comes in 4" or 6" rolls. If a layer of this was added over the roll/folds of the housewrap, it may help keep everything in place as well as provide extra protection for the batten nailing. Self adhered flashings have a self-sealing property that can close around nails/staples in a way that house wrap cannot do.
I also sent this conundrum out to a Tyvek rep that we've worked with before. He sent me their recommended installation for panelized walls (see attached). If you are willing to install the exterior sheathing after the walls are erected things get a bit simpler and mainstream details will apply. However, I understand that this may defeat the purpose of a fully pre-built solution.
Aside from your two options, I wanted to throw out a third route. Rather than treat the joints between the panels as typical wall and attempt to lay the WRB down in a typical code compliant fashion, what if you approached these as truly independent panels but sealed together? I was thinking about sliding glass doors. These have a gasket system at the door jambs and a weeped threshold at the sill. The attached options are all a play on that theme. While I think these options follow general principles of good flashing design -- have I ever used or seen a detail quite like this? -- no. These would be quite the experiment. In a typical architecture firm, you try pretty hard to avoid experiments. Generally you want to shoot for something that somebody else has tried and worked the kinks out over the years. That being said, what you are doing is much more exciting! I would just recommend testing out whatever route you choose as much and thoroughly as you possibly can. Codes and installation requirements are generally written by the pile of failures spanning decades. Buildings fail a lot. New ideas don't have the benefit of those years of trial and error. But if you can do mock ups, blower door tests, hose tests and anything else that makes sense - you might be able to preempt some of the worse potential problems.
Finally, a few thoughts on permitting/inspections. Anytime you stray from the standard code compliance path there is a risk of a zealous plan checker or inspector pushing back and causing some problems. I think any of these options run that risk, but a well researched argument can often win the day. I would just be prepared to have to do a bit of defending when presenting this building to any building department.
Ok well I hope this may help. Do let me know if there is anything else where I might be of assistance.
What if we use double-sided tap stuck on to the underlying panel?
--- If you can physically do this, this is probably the most straightforward solution. I was just imagining you needing to drop the panels down over the anchor bolts -- making taping that side awfully hard. But if you can get double sided tape on that side (tilt the panels in, or slot holes perpendicular to the foundation?)...I think this is a winner. Less complicated and it would be hard to say that it doesn't meet code.
Hmmm, maybe we need to go to Tyvek. But how do we find out exactly if we will pass? Does this mean talking to building officials in specific locations? Do they typically take that type of question, or do they brush you away and tell you to bring an architect/engineer stamp?
--- Unfortunately it really varies by jurisdiction. Some building officials are super helpful, some are less so. Some may want you to submit plans before they will get into details with you.
Hmm, interesting. Once again, how do we verify for sure that this would pass? Can an engineer/architect certify this as part of the permit package?
---Unfortunately, no guarantees. Plans with an architect's or engineer's stamp still have to go through the same plancheck process as everyone else.
Yes, it would, but this may potentially be a fall-back solution if the other ways can't pass.
---One area you may want to consider this (applying the exterior sheathing afterwards) is at the corners. You typically want to wrap the corners much more than 6". I think most housewrap manufacturers recommend 36". You could do this pretty easily, if you were willing to leave the exterior panels off 4 panels (one at each corner).
I like that. Are you suggesting that the same housewrap/taping rules are not operative, and different rules apply?
---That is exactly the argument you could make. Rather than not quite meet the typical housewrap requirements -- acknowledge you are doing something very different but doing it very well.
Right. Is this separate from the actual permitting - ie - an engineer would still have to stamp it?
--- My concern here is that whatever a building department approves, you obviously still want to make sure it works well and long term. While there are some building departments that can drill down, there are others that basically check that your fees are paid and wave you through. Testing would just be for your own benefit, it would not really affect the permit process.
Right. So I think the answer is that it will be tricky. In that case, is there a bulletproof solution - such as getting some engineer to sign off in order to trump any argument from building officials? And what would the associated cost be?
--Building officials give engineer's and architect's plenty of hassel too. I don't think you are necessarily going to achieve a universal bulletproof solution. I think more realistically you get a preferred solution that works in 95% of cases but then have a few alternative options for troublesome jurisdictions.
Option 1 - does that qualify for the 6" overlap of WRB?
--- I think it's probably better than a 6" overlap, but I doubt most code officials have seen anything like it. All of these versions I show come with the risk that a building department just won't buy it. If you cant get a more straight forward code compliant option to work, I think this gasket route is a strong option. But for instance, if you can get that double sided tape to work on your overlap option, that seems like the winner.
Also, in our original idea we were going to screw the 2x6s of adjacent panels together. Still the lack of the stabilization of the sheathing between panels - that really calls for the overlap solution.
--- With the top double plate tying things together, I wonder how much value you'd get from bolting the panels together or adding that 2x4 connector. This is a question for a structural engineer though. Any luck ever finding an interested structural engineer?
But once again - is there a bulletproof solution - and at what cost? Is there something we can get engineering that trumps building officials?
--Again, everything is unfortunately up to the interpretation of the authority having jurisdiction. But if you can meet the letter of the code, the likelihood of running into trouble seems slim.
As for structural engineers, I can ask a couple of people, I remember talking to a few, without any luck, after we first spoke a few years ago. I have a couple of other engineers that I know now. Just need to find an inventive outside the box thinker...with a structural engineering degree.
Waterproofing really falls into an architect's court. There are some agencies that specialize in "building science" (https://www.buildingscience.com/) and then there are waterproofing consultants (http://d7consulting.com/) that architects occasionally hire -- but typically for very complicated situations. They tend to be on the pricey side, but maybe you can charm some free advice out of them. I also saw you have a handful of architects among your advisors. Any practicing architect should have an idea or two about flashing and waterproofing.
I think your overall plan for a stamped set is good. I do think the liability issue will be a hurdle, but I would imagine some legal CYA language could be added to alleviate this. I will do some asking around to structural engineers though!
After more debate, we are leaning towards going with your option 1 and modifying it a bit like this on pages 3-5:
The main differences are: - We can't actually use tongue and groove (or shiplap), so the panels would just sit side by side - We'd cover the seam between the panels with SAWP tape - and then cover the tape with a (ripped plywood) board (a spin on board and batten finish) - We would add another top plate because the plywood is not connecting adjacent panels.
So, we wanted to ask you:
- What do you think? Can this work? - Is it ok that our panels are not tongue and groove (as long as we connect/lap them with a structural board)? - What kind of SAWP tape should we use? I'm sort of imagining something like Self-Adhesive Waterproof Flashing that we use on windows. But I'm not sure if that's the right stuff. - Will the SAWP tape work on rough sawn panels? I'm pretty sure the butyl-based window flashing stuff will stick to anything... But what do you think?
Thank you so much for all your help, you've been a rock star!
Marcin + Catarina
I do think it can work. A few comments/reservations:
-I think a strip of house wrap tape on the interior side is some cheap insurance
-The through wall flashing
- Is it ok that our panels are not tongue and groove (as long as we connect/lap them with a structural board)?
The T&G was nice aesthetics and a little water protection, but I don't think it's a make or break item. As for the structural board, I am not convinced such a short member would actually do much structurally. However, this is another question for the structural engineer. (I emailed a handful of structural engineers earlier this week. I'll let you know if I hear anything good back from them).
- What kind of SAWP tape should we use? I'm sort of imagining something like Self-Adhesive Waterproof Flashing that we use on windows. But I'm not sure if that's the right stuff.
Correct, that is what I had in mind (similar to self-adhered window flashing). This is a product we've specified before: https://gcpat.com/en/solutions/products/vycor-weather-barrier-flashing-tapes/vycor-pro
- Will the SAWP tape work on rough sawn panels? I'm pretty sure the butyl-based window flashing stuff will stick to anything... But what do you think?
So I would recommend going with Butyl rather than an asphaltic flashing. Butyl is more expensive, but it has much better temperature ranges, and sticks to just about everything. The Vycor product linked above says it can bond to plywood and OSB - so I would imagine the rough sawn panels should work as well. There also are primers that you can use for especially tricky substrates.