Friday, June 15, 2012

Learning from Swedish Home Building - Part 3

Its friday so it must be time to show the latest video in our Series about building high performance walls like the Swedes do. In our first video we explained why it makes sense to look to Sweden for a direction for our house building techniques. The second video we reviewed the Good/Better/Best model for easing builders into high performance wall building. Today we look at Swedish Platform Building, the best advancement in house building since the Western Platform Frame. Wow, is our house nerd showing here or what?

I've been trying to keep these videos short, and make them just an introduction to the ideas presented. But for the Swedish Platform Frame I was not able to do a short video. What happened was I ended up making a 3d model of the prototypical Swedish Platform Frame, and it was obvious that this was such a good way to explain this that I decided to just go ahead a make a detailed description of the framing system. So it is almost 20 minutes long - my apologies. Stop at the restroom, get a large popcorn, turn off your cell phones, note the exits, and prep yourself for the Director's Cut of the Swedish Platform Frame...


This video piece is about how Sweden has modified the Western Platform Framing method for better energy performance in residential construction. We call this modified framing method Swedish Platform Framing.

This video is quite long, and we apologize about that. If we figure out how to say all this in a shorter video we'll produce a new version. In this video we make a very breif review of the history of stud framing systems - Balloon Framing and Western Platform Framing. Then we proceed to look in detail at the differences between Western and Swedish Platform framing.

Swedish Platform Framing is explained in much more detail on our web site, and you can read that on this page:

http://blog.lamidesign.com/p/swedish-platform-framing-info.html

As with the USA New Wall, the walls shown in this video use Stone Wool insulation rather than fiberglass. We mention in the video that this is because Stone Wool offers higher insulation values - R23 for 2x6 stud spaces, and R30 for 2x8 stud spaces. We also mention that it allows for better installations. You can read a detailed article about why this is so on our blog:

http://blog.lamidesign.com/2012/01/what-you-don-know-about-mineral-wool.html

Not covered in detail in the video is the Vapor Retarder membrane. We prefer a Variable Permeability Vapor Retarder membrane. There are several sources for this unique vapor retarder, notably Certainteed's Membrane:

http://www.certainteed.com/products/insulation/mold-prevention/317391

And Intello Plus, and DB+ by ProClima:

http://foursevenfive.com/product-category/air-sealing-system/interior-membranes-air-vapor-control/

You can read the entire Letters from Sweden series by clicking on the respective link under the the above blog post's title's.

The USA New Wall, and Swedish Platform Framing are an outgrowth of our research into Swedish building practices. Again, you can find details of the USA New Wall here:

http://blog.lamidesign.com/p/usa-new-wall-info.html

And again Swedish Platform Framing here:

http://blog.lamidesign.com/p/swedish-platform-framing-info.html

If you need assistance implementing the USA New Wall or Swedish Platform Framing in your projects, we are here to help. Please contact us.

11 comments:

  1. Very informative. Thanks for doing it.

    What kind of increase in cost is there for the Swedish wall?

    Would you modify any of your stock plans to incorporate the New Wall or a Swedish Wall? Perhaps the Plat242?

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  2. I don't have a hard number on that, and since the USA New Wall is detailed in both 2x6 and 2x8 configurations there is no one answer. I would expect the 2x6 Best version to increase the cost at least 25%, maybe more. The 2x8 over a standard 2x6 wall maybe a 50% increase or more.

    I am already incorporating the USA New Wall and Swedish Platform Framing into my latest house plans. All variations of the Lagom House design come with documentation for both the 2x6 and 2x8 versions. And I can do a plan modification for these wall systems for the Plat House drawings, or any other of our plans if any customer requests it.

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  3. In your description of the typical platform framing you dismiss a single top plate as impractical (if I understand your comment) but then you do show a single top plate with the Swedish system. In that system, the joints and trusses would need to be aligned with the studs, wouldn't they?

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  4. No, that's not quite what I am saying.

    I am dismissing imposing a 24" grid as impractical because it impacts all of the window and door openings, particularly if you are adapting an existing design - which most builders in the US would be doing. Hence, they just won't do it.

    In Swedish Platform Framing I am indeed showing a single top plate at the top of the wall where the roof trusses bear. This is simple to achieve because its easy to line up roof framing with the wall studs. It does not have to carry down through the first floor wall since there is the equivalent of a double plate there because the single top plate of the first floor wall is immediately below the sole plate of the second floor wall. The floor joist ledger allows floor framing to be off module as well, loosening up the restrictions the grid imposes in Advanced Framing.

    I hope that clarifies.

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  5. Hi Greg,
    Great series. The first thing that comes to my mind is the same thing that happens with ICF walls. That is, when maximizing the square footage for joist length and plywood layout, you could now use the inside face of the wall, rather than the outside. This provides some palpable sf advantage to help offset the additional costs. Only problem is the way the plywood extends out over the first floor plate. Is there another way to tie things in to capture that s.f? In a 40x30 house, two story, we are talking about 140s.f. assuming just a 2x4 wall, more with a thicker wall system.

    The second thing is that it is clear that the vapor barrier is applied prior to the second floor deck going on, so that it is the framer installing the cavity insulation rather than an insulation contractor. I know we were talking a little about this (closed cavity vs open cavity) we we were at the panel plant. I guess my question becomes "is it ok for the framers to install insulation and then close it off from all eyes with the vapor barrier?" It doesn't seem to fall in line with the quality check system built in to our codes. Not as big a deal to fit everything tightly, I suppose, with the extra layers inside the electric chase and outside.

    It would be great to try to apply hard costs to these various assembly components, as well as energy use parameters, so that a true cost/benefit model can be developed.

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  6. Tom,

    The Swedes actually do what you say - they put a particle board layer on the inside, and have no sheathing on the outside. The particle board plus their heavy wood siding provides the bracing, and the interior particle board makes it easy to hang shelves and cabinets.

    But for us, I don't think it makes as much sense. First the overriding concern is that American builders are used to sheathing on the outside. This is such a fundamental practice that I think it would be very difficult to overcome. For model wall systems that we hope to spread widely, I think we have to carry exterior sheathing forward. Second, the exterior sheathing is beneficial in other ways. We almost always cool our houses, even in some of the coldest climate zones our houses have air conditioning. In this situation the sheathing is a great benefit, providing a back up to house wraps, or in the case of newer sheathing products like ZIP, a basis for keeping warm and moist ambient air out of the wall cavity in the summer when the vapor profile is reversed and there is potential for summer condensation.

    I'm not sure I understand your comment on plywood. What is the benefit of not extending the floor deck over the wall? This is standard practice in Western Platform Framing, and it is carried over here where it provides an important role to tie the floor diaphragm to the walls.

    Regarding the vapor retarder running behind the floor joists. The carpenters would have to install the membrand, just a band equal to the floor system depth with a tail for taping. The insulation can be installed up behind this - some trouble but not so bad. But all that happens after framing inspection. That said, this Swedish Platform Framing really begs to be done in factory as panels, but with some practice the slightly different sequence it demands will be not much different than conventional platform framing. Different, not harder.

    A true analysis would be great. I'd love to do that, and I will as soon as somebody is willing to fund it. This is not a shot in the dark however. It is based on practices that have been refined over 40years in Sweden. Will it cost more - surely it will. A better wall always does. It is very hard to get around putting more value into a wall system costing more.

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    1. I wasn't clear. When I design a house, I typically start with the outside edge of my envelope and work out 2' and 16" increments to maximize my lumber efficiency. Here, with the inside of the wall governing my joist layouts, I could add the wall space to the inside volume without increasing my costs to a great extent. For example, with a 6" wall, a 32' deep house, with 16' floor joists and a center bearing beam typically has 15-2 as the inside room dimension. This could now grow to 15-8 with no increase in cost in floor framing material. 6" may not seem like much, but it matters to some (ha ha).

      I don't think it will take too much to work up cost side. The material is easy. We need to develop some labor costs for the extra layers. The benefit side is a little more obtuse to me, but must be easy for someone with more HVAC background. The lower bridging and air infiltration numbers backing into Btuh and then some cost factors thrown in, resulting in a savings per month after you plug in your energy cost. I'm still waiting for someone to make up a drawing program that does all this on the fly. We enter our wall system, lat and long., shading conditions, and then as we design we have a readout on the bottom of the screen telling us our efficiency. Seems like all this technology is ready to go, but I've not seen it anywhere.

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  7. Often in platform framing, the walls are framed flat on the floor and then tipped up into place. Can that still be applied to the Swedish system?

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    1. Yes it could. You would have to take measures to ensure the ground floor joists were stable before relying on it as a working platform. But once the walls were tilted up, and the ribbon fastened to the wall, it would then be tied together.

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  8. Thanks again for your reply. Another question if you don't mind. In traditional platform framing, the floors are held up structurally by the wall framing itself, where as in the Swedish system, the floor are relying on the bolted connection between the ledger and the studs. Does this translate into a greater risk of catastrophic failure if, for example, some moisture leak into the wall led to unseen corrosion?

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    1. No Chris - first off, in any such situation conventional framing with smaller nails and screws would be much more vulnerable no matter where the joists are bearing. Second, the kind of deterioration you are describing would have to happen over a wide number of fasteners in order to have a "catastrophic" failure - so for a leak, no, it would not affect a wide area. If one or two ledger connections failed the whole floor would not collapse. The great thing about stud framing is redundancy.

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