I’ve been following Wikihouse for a long time and always wanted to build a house with it. This year, it seems it might finally happen. I’m envisioning a 2-story barn-shaped building, where the upper floor has a glazed gable end wall that is recessed about one block deep. Below you see a mock-up using the simple design kit in Sketchup.
This raised some questions:
In the latest version of Skylark (v0.2.2), the verge block for the 42-degrees sloped roof has been retired. I don’t see how I can obtain the desired result except by not using end blocks altogether. This then introduces a problem on the ground floor: there is no end floor block to connect to the foundation. Nor can the ground floor end wall be connected to the floor blocks in the usual way.
Does anyone has suggestions of how to best approach this?
To the Wikihouse team: any chance the roof verge block can be brought back, since I think other people might want windows above the level of the eaves too?
For those who have some notions of structural engineering: do you think it’s even realistic to have a frame for the gable end windows on the upper floor that can transfer the load of the ridge beam? Looking at some of the Wikihouses in Almere, I’m optimistic it should be possible, but would like to get your take on it (gut feeling, later to be checked by structural engineer).
Somewhat unrelated to the questions above: does anyone have an idea wether it’s realistic to support this 2-story Wikihouse with a screw pile foundation? The site I’m looking at has a clay soil.
Thanks in advance for any feedback or pointers you might have for me. Happy building!
Elias
You asked for gut feeling so here is one - I don’t think it is going to work. The end where you have all glass, the ridge beam is not supported by anything. Imagine a load coming straight down on the roof. Without the support, it is going to spread sideways. I think you either need to support it vertically or tie it together horizontally. I think there is a video describing this situation on the youtube channel. Maybe this one: WikiHouse ridge beams explained I think the wikihouses in Almere have a different construction so the loads spread differently.
hi @zbynek.winkler , thanks a lot for your feedback! Indeed, in absence of a full fledged wall there is not much to support the ridge beam. But not nothing, I’m hoping the frame could transfer the loads downward and tie the structure together horizontally. I tried to show this by the red arrows in the picture attached.
I’m curious to hear from others if they agree this is probably a no go or not.
Hi @Elias,
great work on a such a concept design! Happy to provide some engineering ideas if helpful (But please be aware that I do not know the specifics of your project).
The combination large opening + recessed block is not trivial from an engineering point of view in my opinion. Let me try to sketch what I think it is happening:
The ridge beam is collecting essentially half of the roof weigh. At the support of the beam, you need to transfer the load into the foundation somehow. The trivial way is a single continuous gable wall below the support, i.e. the standard solution. If you remove it, then you need an equivalent structure doing that. Creating a frame like you suggest is possible to solve the upper floor, but the elements sizes might be larger than you have drawn. That’s because you will have the diagonal elements working in compression (and they might buckle → buckling capacity is dependent on the material as well as section size). Also the forces can not simply be transferred by pure contact, and you will need to solve the connection with fasteners (and probably a few), so again the size will be important (there are minimum spacing requirements when installing fasteners, hence might need larger sections). The other option could be looking into steel for reducing the size if that’s a concern. The next challenge is beam at the first floor, because it receives two rather large concentrate forces. That would be difficult to manage I think, because remember you have essentially 1/4 of the entire roof weight if I am not wrong over quite a decent span. Bending will be an issue.
About verges, I am afraid that they might not solve the problem either. Verges do not work in bending, so they need to be supported by the gable walls anyway. That was actually one of the reasons why we opted to simply absorb them in the gable walls.
One way perhaps to approach the problem would be to design specific custom blocks for this case. One possibility (but it might change your design) could be slightly change the position of the frame, and nest some glulam columns in the bottom floor blocks so that they are aligned with it. In this way you might be able to bypass the beam and transfer the load with columns directly into the foundations. I suspect also lateral load stability will require some thinking… on that glass facade there is not much stopping the lateral load deformation, which is normally provided by the wall. Probably there are ways of doing that, but it might require some analysis. Do you have the opportunity to work with a structural engineer on this specific project? It might be good to engage at concept stage as they might be able to spot all the critic aspects right away.
Hope that helps! Please see us updated on how it progresses as the idea is lovely!
Gabriele
hi @Gabriele , thanks a lot for the detailed feedback and constructive thoughts.
The increase of sections should be workeable! I believe a beefier frame will not hinder the overall aesthetic, as long as the frame does not interfere too much with the line of sight for the people standing or sitting in that upstairs room (which I envision to be the living room).
I had not thought at all about the concentration of forces at the bottom of the vertical frame pieces. That is a very good point. I like your idea of aligning the blocks below sensibly and reinforce them so that they transfer the load directly downwards. Definitely something to flush out once I start involving a structural engineer. Same for the concern you raised on lateral deformation.
When it comes to the verge block, I was mostly thinking about it because in my current design, the ground floor end block does not have a way to rest onto a foundation in the direction parallel to the gable end wall. My gut feeling tells me that’s not good. Or am I missing something here?
Nice to hear the screw pile foundations should work!
I will definitely keep you posted on my progress. My plan is to engage both an architect (which is legally required for structures >50 m2 here in Belgium) and a structural engineer. In the current ‘ideation phase’, I already want to foolproof my design ideas as much as possible in order to reduce the number of iterations I have to go through with them. Since those iterations drive up the cost for me
Thanks again to both of you for your ideas! -Elias
