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Old 08-27-10, 01:12 PM   #1
Daox
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Default Larsen truss design

I gotta say, if I was going to build new, I would do this without doubt.

Green Home Building: Article about A Cost Effective Larsen Truss Design


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Old 12-24-10, 09:37 PM   #2
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This caught my eye right off the bat as my last name used to be Larsen. I'd do it that way myself, if the town would let me build a multifamily on any of the available properties. I gotta say though. I would use plywood. That housewrap may be great for 10 yrs but in 60 I'd be kicking myself in the arse because it had turned to tatters and then I'd have to pull the siding down and put up plywood.

EDIT: Also relying on drywall is not a good plan. that stuff gets trashed in time. What if your plumber needs to get into the wall to fix something? What if time moves on and you need to augment you electrical environment? If my house had been built with no plywood I'd be screwed every time I needed to replace cotton romex. Screwed with a capital, 24 point font S. I would never buy the house. Cheap is good but plywood doesn't cost that much or take much labor to put up or even to put up and caulk real tight.
So I'll chalk that one up to "short gain, long payment".

Last edited by S-F; 12-24-10 at 09:43 PM..
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Old 12-24-10, 11:37 PM   #3
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I've personally seen tyvek last 20 years without siding over it, with that said I agree that you need wood sheathing for sheer to keep the building from racking.
The nice thing bout building walls in this style is that you can go as thick as you want and your only cost is more insulation.
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Old 12-25-10, 02:29 AM   #4
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I'd have enough trouble getting the design approved by the city even if it had plywood or some other sheeting. Without it it's not going to stand a chance.
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Old 12-25-10, 07:03 AM   #5
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@ Ryland, what part of the country are you in? I live right where this guy is building and I have seen Tyvek go to shreds with no siding in maybe 5 years. Most of the insulation people out here, the real serious ones that is, scoff at house wrap. None of them recommend using it. They all say that $300 of caulking will go a lot further than Tyvek ever will. Maybe that's why he insulates himself. It stands to reason. Imagine the difference between being out in the windy cold in both a Tyvek suit and a plywood box which has been well caulked at all of the seams.
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Old 12-25-10, 09:06 AM   #6
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I'm in Wisconsin and my parents house has tyvek on one addition, after about 20 years they put another layer on because it has some odd angles to side over that no one wants to do.

I like tyvek not because it acts to seal the house from air but because it helps seal the plywood sheathing from water, for air sealing I would rather caulk as well or use the expanding foam, or they even make an expanding construction adhesive that you can get for the gun foam guns, but also vapor barrier should be on the inside in most houses, not on the outside, that is why tyvek is used on the outside, it breaths.

They don't at any point that I saw say how they get fresh air in to the house, I suspect that the bath fans are the style that have heat exchangers built in to them (Panasonic makes a few like that bring in preheated make up air) but the trouble is the tiny heat exchangers in those bath fans freeze up easily so there is a bypass flap that closes off the heat exchanger at 20F.

The advantage of a house like that over building a 2x6 wall is that 2x4's are cheaper, last I looked they were 40% cheaper so even tho you use twice as many your cost only goes up by about 20%, most building inspectors should also be ok with that style of framing because it's basically a 2nd wall on the outside of the house.
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Old 12-28-10, 03:05 PM   #7
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A suggestion that would be easier and cheaper when building a house would be it use 2x6s for the outside of the frame and alternating 2X4s for the supports. The blue bar is the 2x6 and the red are the 2x4s.
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I was thinking of doing this when building a house for some of the interior walls to reduce the penetration ability of sound by removing direct transfer from drywall to 2X4 to drywall. Using it for the exterior would do the same and allow for extra insulation, it will not be as good as one foot of space but gives and extra 2".

Also, I would not use MDF in a home as it gases off toxic chemicals and if it gets wet it swells and falls apart.
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Old 12-28-10, 03:19 PM   #8
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That would eliminate thermal bridging quite well. However, it would limit the wall thickness to 5.5" thick. With the larsen truss you can go as thick as you want. Most super insulated houses are ~12" to get around R60 insulated walls.
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Old 04-13-11, 11:54 AM   #9
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Here is the reason given for using Tyvek (taken from their site)

A weather resistant barrier is a building's main protection against the damaging effects of the elements. A funtioning barrier must include four basic properties:

* It must have a high level of AIR RESISTANCE - to help prevent drafts, reduce energy bills and resist the flow of moisture laden air through wall cavities.
* It must have a high level of WATER RESISTANCE - to help protect the wall cavity from water that gets behind the cladding.
* It must have moderate to high VAPOUR PERMEABILITY - to promote drying in wall systems.
* It must be DURABLE - to withstand the rigors of the construction site and continue to perform once construction is completed.

DuPont™ Tyvek® HomeWrap® is a non-woven, nonperforated sheet made by spinning extremely fine continuous high-density polyethylene (HDPE) fibres that are fused together to form a strong uniform web. DuPont™ Tyvek® is a unique brand and the only product manufactured this way. This tough, durable and unique structure is not susceptible to the compromises of a perforated material. The fibrous structure is engineered to create millions of extremely small pores that resist bulk water and air penetration while allowing moisture vapour to pass through. DuPont™ Tyvek® HomeWrap® achieves an excellent balance of weather resistance and vapour permeability.
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Old 04-18-11, 12:18 AM   #10
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I love this.

I'd do plywood over the outside as stated above but the fact that you can build as thick of walls as you want that is amazing.

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