Scott Young

there is a set of commercial hog barns on some property i hunt that i have taken an interest in. the barns have stood the test of time and are now no longer being use as hog barns as the owners have retired. i have been looking at the construction of them and other buildings and have come to question some of our residential building practices.

the barn has fink trusses on 8 foot centers. there are 2x4 purlins on 2 foot centers standing upright. there is an insulation board that is 1 inch thick and then the metal for the roofing.

this is similar to the chicken houses that have been designed to have metal trusses that carry the 2x4 purlins that span 8+ feet.

is 2x6 rafters, 16 inch oc, plus really neccessary for residential? i understand codes and such and will continue to build for the inspectors approval. but, i am just questioning the seemingly large contrast between accepted residental building and barn building.

Scott Young

I forgot to add the wall detail. the wall detail is post and beam with purlins spanning 8 foot. the sheating is fastened to the top beam and the bottom plate. the bottom plate is fastened to the slab. where the wall is only a half wall, the sheathing is fastened to the horizontal purlin and the the bottom plate.

i have seen this type of construction on many exterior non residential building and the top beam is what carrys the wall load and keep everything from sagging.

i under stand the need for vertical walls in houses and i really am not questioning the residential methods there because in residential the walls are in compression and not in suspension as in the post and beam of a barn.

Same Old

I think you need to relearn your framing engineering principles. You can build a house with the same method as the barn. A 2x4 will span 8' for a roof rafter. It's all the same engineering dude.

Scott Young

i wasn't questioning the veracity of the barn construction. i don't need to relearn the framing engineering principles dude. maybe i wasn't clear in my original post. i was questioning why such a contrast between barn building methods and house building. i haven't seen a house yet built like that. material cost the barn method is much cheaper.

joasis

I have built a few spec homes with engineered trusses on 8 foot centers, with 2X purlin on edge, solar gaurd, then metal for the roof. 2X on edge between the bottom chords for ceiling joists......it meets code as long as the trusses are engineered for the top load and the bottom load both.

Now what I have discovered is it is more labor intensive (man hours) to do this, it negates the savings over using standard trusses on 2 foot centers. Since I build primarily plain vanilla specs, very low budget, I am always looking for ways to save...and this was not one of them. I did beat a building inspector though, that tried to tag my construction as unacceptable....but he wasn't an engineer.

There is a book out by a guy name Ruiz, about value engineering a home...and the tricks and practices he describes will lead you in the right direction to cost effective building.

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Scott Young

joasis, there are a lot of houses being built here in south mississippi that are using metal for thier first roof. the are skipping the sheathing and going with 1x4 or 2x4 lath depending on builder on trusses set on 2 foot centers. i was wondering why they just didn't go with the 8' span and 2x4 vertical purlins instead.

interesting the man hours was more for you. i would have guessed it would have been about the same. what do you attribute the extra time to?

joasis

Unless you planned it out carefully, dimensionally, you will cut every purlin and joist...studs are too short and 8's have to be trimmed for length....also, the 2X6 or 2X8 trusses are twice as high, engineered for the added load for sheetrock and insulation plus safety factoring. If you did not allow for the bottom loading, and used standard "barn" trusses, you would need intersecting walls under every truss to "carry" or bridge loads...and you will not win an argyument with a building inspector without trusses engineered....

I prefer open floor plans and vaulted ceilings....and at $100 or so a truss on scissor 30's, much cheaper. As too the roof getting steel on strapping, check out the pictures I have posted under ICF home...I do this on all my specs, and a few custom homes I am getting bids on will be the same. Tradition dies hard.

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Kgmz

Think about it. How long does it take to roll trusses compared to installing a whole bunch of 2x4's in between trusses. Then compare the labor to intall all those 2x4's to the cost of the trusses. And remember that the trusses on 2' centers are a lot cheaper than trusses on 8' centers. The 8' center trusses will be a lot heavier built and may be doubled depending on the design and if the 2x4 pulins are on top of the truss or not. Also if the 2x4 roof purlins are in between the trusses then you have to deal with a whole bunch of hangers, the ceiling joists will be in between.

This is also why I won't build pole barn style buildings for shops, garages, etc. Up here in the NW eventually everyone wants it insulated and sheet rocked. Try and insulate a pole building and rock a pole building as well as you can with a stick built. It will end up costing you more and be kind of micky moused. Then try and get adequate insulation in the ceiling with a cathedral beween the trusses. And by adequate I mean R-30 not some 2" plastic faced roll insulation like is typical of most pole buildings. Stick built wins every time.

Scott Young

thanks guys.

i just couldn't get my brain around the issues. sometimes getting another's perspective as a sounding board, really helps.

joasis

There are times post and beam construction will work out, but it certainly wouldn't be a cost saving measure....I was just thinking about all those cool timber framed homes I have been in....and they do have thier own set of tricks, but not for low budget homes.

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