[GSBN] Prefab hoe-down
rene.dalmeijer at hetnet.nl
Thu Feb 25 11:21:26 CST 2016
As you might know I am a strong advocate of pre-fab. To me pre-fab is the way to make sustainable building competitive with conventional building. An important effect of pre-fab is that it forces you to do much more detail engineering before hand. This saves a huge amount of cost during the building phase.
Recently I ran into a project that was originally envisaged as a pre-fab straw bale project. The main contractor involved, Strabag needed an affordable alternative to the chosen source of the prefab SB elements, they turned out to be far too expensive. I offered to look into the project to see if I could come up with a building method and structure that would fit the available budget. My first choice was pre-fab but I rapidly ruled this out due to the constraints of the project.
The main problem was that the SB wall sections are roughly 7.5m high. To make manageable SB elements the walls were split into 3 vertical sections in the design. The architect wanted continuos earth plaster from floor to ceiling. The approach with 3 separate stacked pre-fab elements would create a risk for cracking at the horizontal seams between the elements. Due to this the pre-fab elements would require a complicated interface structure to allow tolerances but at the same time movement free connections to the surrounding main structure. Basically there would be to many wood members involved. I decided that it would be much easier to frame it out on-site. Utilizing pre-cut TJI posts and design in such a way that a minimum of custom bales were required. I hope to find some time to write an article giving more details about the onsite straw bale build which came in 35% under budget.
What this project taught me is that some times pre-fab off site is not the cheapest solution.
Besides this I definitely prefer on site owner built SB. Its simply much more fun and gives time to think about options while you build. It might not be the cheapest method but it gives a much more enjoyable experience.
Rene Dalmeijer Proces Advies
Thomas Hoodstraat 2
1086 WE Amsterdam
On Feb 24, 2016, at 14:23, Chris Magwood wrote:
> Hi John,
> We've approached building panels in every conceivable way... on-site tilt-up plastered horizontal, on-site tilt-up plastered vertical; built off-site unplastered, built off-site preplastered; built off-site with mag-board finish; and currently we're working on built off site system with no plaster, using wood fiber board sheathing on both sides. We've framed them with lumber, with Durisol sheets, with TJIs, with Tectum... I feel like there aren't very many versions we haven't built with. In total, we've been involved with about 35 prefab bale buildings now.
> I made the tilt-up suggestion for the fire victims because we have found that to be the fastest and least expensive approach (by far), and so for bringing the most affordable form of straw bale construction to people, I think this can't be beat, whether it's done by a professional crew or the home owners, or some hybrid of the two. I'm sure this could be adapted to California requirements (do the interior coat of plaster horizontal, stand the panels up and apply full mesh wrap to the exterior and plaster vertical?). Built on site in tilt-up form, the walls can also be built as continuous panels between door and window openings, so there needn't be seams other than the openings. This is one advantage of this approach... the panels don't have to be sized for transportation or handling.
> However the prefabrication is done, we have found that it beat site bale construction times and costs hands down. We use the tilt up version when cost is the driving factor and when the off-site shop space isn't available or affordable. A reasonably sized one story house can be panelized in this form in two to three days, fully plastered, so it's not much of slow-down for the construction timeline. However, there are lots of advantages to building off site in advance... We have found that two people and a boom truck or small crane can install the pre-plastered panels so quickly that the cost for the equipment is negligible or less than having more bodies on site. Essentially, we've found that there's a prefab strategy for every scenario!
> It would be amazing to have a prefab summit at the CASBA meeting. We've done so much work we'd be glad to share with everybody.
> Chris Magwood
> Director, Endeavour Centre
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