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General => Owner-Builder Projects => Topic started by: retiredmarine on August 17, 2015, 07:03:32 AM

Title: 20X40 cabin - foundation plan
Post by: retiredmarine on August 17, 2015, 07:03:32 AM
Ok guys (and gals) I've moved to the next phase of the project - design.  I'm building a 20X40 - with a small attached mud room - in MO (frost line 23 in).  I've thought about post construction but a lot of the comments here have made me think otherwise - yes I lurked for a while.  I'm going with cinder block construction - 3 levels (24 inches) to bring me to grade and then 2 more to give me 16 inches ground clearance under the cabin.  That makes the columns 16X16 and 60 inches on center.  I'll fill the outside cavity with concrete and add a J bolt.  I'm spanning the columns with 4X6 (laying the 6 inch side down. I'll cut the 4X6's to keep the joints over the columns and stagger them across the build.  I'm using 2X12 joists 24 inches on center.  Thoughts?
Title: Re: 20X40 cabin - foundation plan
Post by: MountainDon on August 17, 2015, 04:46:40 PM
Let's see.... basically   questions in that.
1. Is using concrete block piers, 16 x 16" on 60 inch centers ok?
2. Are 4x6 timber across tops of those piers, running in the 40 foot direction, laid on the 6 inch side ok?
3. Are floor joists, 2x12 on 24 inch centers ok?


#1  Did I interpret your verbal plan correctly? A series of nine such piers down each 40 foot side?  That would be better than a series of 6x6 inch wood posts. However it still has one of the main shortcomings of a pier/post foundation. That is each pier is a unit by itself. It may be tied to the building structure above, but unless it sits on a continuous concrete footing that runs around the perimeter the bottom ends are free to move. The larger surface area of the 16x16 concrete pier will resist lateral movement better than a 6x6 post would. So in that respect your plan is superior to many simple wood post foundations. But if there were building inspections and the IRC was the handbook used, they would likely be asking for an engineers report before saying go ahead.

IMO, a building of this size should be constructed on a full perimeter foundation. The footing would be rebar reinforced. The bottom of the footing at the frost depth and about 8 inches thick IIRC. Concrete block or formed and poured concrete is solid and would pass virtually any codes in the country. You could also use those 16x16 concrete block piers on a poured footing. That would be what is called a raised floor in some areas. Google can find raised floor info. It looks just like what you have envisioned but the bottom ends of the piers are rebar tied to the footing and piers and footing act more like a monolith than a buch of separate parts. Making it a little higher off grade would make for a good crawl space.  See#3... floor joists

#3, No.
Not if they are only supported at each end.  Here is a link to a handy AWC joist and rafter calculator (http://www.awc.org/codes-standards/calculators-software/spancalc). Choose wood species, dimensions, grade, type of member, use deflection L/260 for a floor (unless you want to tile it), set the joist spacing, use LL of 40 psf and Dl of 10 (those are normal). When I use #2 Douglas Fir as the species that comes up with a 14'9" maximum span.

Twenty feet is a stretch for sawn lumber. If I use Select Doug Fir at 16 centers, it works. Those will be pricey. A beam down the center would reduce the span to where almost any 2x8 #2 would be a solid span. You could use manufactured joists, either floor trusses or I-joists can be designed to clear span that distance. I believe they are best suited to use when fully protected from weather. That is the space under the floor should be enclosed, as in a crawl space or a full basement. Hopefully Don_P or someone with more experience with manufactured trusses can check in on that. Floor trusses or I-joists can be sized and priced at the dealers who sell them. They could also advise on what protections they should have.


#2... 4x6 with 6 inch side down. No.
About the only place we use lumber or timbers laid "flat" like that would be when we use 2x's as bottom and top wall plates. Or when laying a length of lumber as a mud sill on top of a perimeter wall, fully supported along the enteire length. When we span an opening as in going from one pier to another the maximum resistance to bending happens when the timber/lumber is placed with the greater dimension vertical. That is that 4x6 would sit on a 4 inch face. Except a 4x6 is probably too small for spanning piers on 5 foot centers. I would have to check some tables and have a little more information, but I believe a 4x8, or 2 - 2x8's nailed together would be suitable.  Snow load for the area, whether it is a single story building or taller need to be factored in for a solid answer.

Hope that helps some.
Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on August 17, 2015, 05:35:30 PM
MountainDon, Thanks!  I had a feeling I'd hear the continuous footing suggestion.  If I understand right though your only suggesting the footing not that I continue the block all the way around the structure.  I'd still like to have the columns.  I'm going to hold off on this decision until I see the soil and what's under it.

As for the floor joists i left out there are three series of nine piers on in the middle, the widest joist span is 10 ft. and again if I read right your suggesting a 2X8 #2 would suffice vice the 2X12.  (good news that's a savings..)

and lastly it sounds like the 4X6 on it's side is out (truth be told I figured that was a bad idea I just didn't know why - makes sense now) So I'll change the design to 2 - 2X8's nailed together or a 4X8 which ever is cheaper. 

Thanks for the second set of eyes!  I'm working on the framing design next - hopefully by then I will have figured out how to post pictures so me explanations make a bit more sense.

Thanks again!
Title: Re: 20X40 cabin - foundation plan
Post by: Don_P on August 17, 2015, 09:54:38 PM
Quote from: retiredmarine on August 17, 2015, 05:35:30 PM
MountainDon, Thanks!  I had a feeling I'd hear the continuous footing suggestion.  If I understand right though your only suggesting the footing not that I continue the block all the way around the structure.  I'd still like to have the columns.  I'm going to hold off on this decision until I see the soil and what's under it.
Check the foundation chapter of the IRC for design and reinforcement.

Quote
As for the floor joists i left out there are three series of nine piers on in the middle, the widest joist span is 10 ft. and again if I read right your suggesting a 2X8 #2 would suffice vice the 2X12.  (good news that's a savings..)

and lastly it sounds like the 4X6 on it's side is out (truth be told I figured that was a bad idea I just didn't know why - makes sense now) So I'll change the design to 2 - 2X8's nailed together or a 4X8 which ever is cheaper.

These two revolve around each other. The center girder is supporting 1/2 to 5/8 of the floor load. Is there another floor load from above, a roof load? That wasn't girder sizing going on there yet. You probably won't find a 4x8 but that is not a bad thing, a built up girder helps to distribute the defects in the final beam better, this translates into a 10% increase in design strength for a 2 ply and 15% for a 3 ply assembly over a solid sawn timber.

Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on August 19, 2015, 05:28:04 PM
Thanks Don!  Yea I'm going with 2X8 sandwiched for girders on all three of the sets of columns (outside and down the middle) Then I'll use 2X8s for joists.  It's a one story cabin with a 1/4 loft for storage.    This page is great! Thanks for the advice!  Hey how do I add pictures here?  They are so much better than my descriptions.. lol
Title: Re: 20X40 cabin - foundation plan
Post by: MountainDon on August 19, 2015, 06:07:34 PM
Quote from: retiredmarine on August 19, 2015, 05:28:04 PM
Hey how do I add pictures here?  They are so much better than my descriptions.. lol

LINK (http://countryplans.com/smf/index.php?topic=11663.0)
Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on August 20, 2015, 07:54:20 AM
Thanks!  Pictures to follow!
Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on August 21, 2015, 01:19:46 PM
This should make my rambling more clear..

Here's my pier plan

(https://i851.photobucket.com/albums/ab76/retiredmarine/20X40%20blocks1.jpg) (https://s851.photobucket.com/user/retiredmarine/media/20X40%20blocks1.jpg.html)

and here's my girder plan

(https://i851.photobucket.com/albums/ab76/retiredmarine/20X40%20blocks.jpg) (https://s851.photobucket.com/user/retiredmarine/media/20X40%20blocks.jpg.html)

Thanks MountainDon!
Title: Re: 20X40 cabin - foundation plan
Post by: Don_P on August 21, 2015, 03:17:59 PM
It looks like from your description and pic you have 240 block in the main structure. By my count doing it conventionally would take about 400, you would pick up footing cost but lose the girders on the exterior. At that point it would be sitting on a far stronger foundation and the floors would be stiffer.
Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on August 22, 2015, 08:39:44 AM
Ok I went back and looked at my math and plan... For a concrete footer 24 in deep X 16 wide X 156 ft long I'd need about 17 yards of concrete add the rebar and then my block count would drop because I'd be on-grade already.  The block would be providing the height above grade I wanted (16 inches) new block count 264 (1.5 ft height). There's no doubt it would be stronger but I'm wondering why so many houses are still standing with dry rock foundations still in tact.. and yes the cost is a concern too.  I've got some time since I'm still in the planning phase when I finish the rest of the cabin design and cost it I'll have a better idea of what I can afford.  I need to look around here and see how many people pier built and how it's going. 
Title: Re: 20X40 cabin - foundation plan
Post by: MountainDon on August 22, 2015, 09:40:44 AM
Quote from: retiredmarine on August 22, 2015, 08:39:44 AM
... For a concrete footer 24 in deep X 16 wide X 156 ft long I'd need about 17 yards of concrete add the rebar ....

The footing should be a minimum of 6 inches thick, with 8 inches being better. Rebar supported in the middle of the thickness.


Quote... wondering why so many houses are still standing with dry rock foundations still ...
They are not all going to fall down. They may move enough to makes windows and doors bind, though.  A part of Don_P's construction career has been placing proper foundations under old homes built on such movable foundations. I remember him saying that many of those homes have windows that haven't opened in a long time by the time he is called upon.


Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on August 22, 2015, 10:59:47 AM
LOL well windows and doors that open are kinda important...
Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on August 23, 2015, 03:16:30 PM
Hey one more question for the Sub-floor.  I was watching a guy on youtube (thebossoftheswamp) as he was adding an addition to his cabin.  He lives in Maine and it gets KINDA cold there.  He swears by the rolled aluminium insulation on top of the joists before he nails down the sub-floor.  He says it does a great job retaining heat and the critters don't bother it.  Thoughts?
Title: Re: 20X40 cabin - foundation plan
Post by: MountainDon on August 23, 2015, 05:06:58 PM
Do an online search for "FTC reflective insulation" or "FTC radiant barriers".  Or if you want to leave the government out of it search "reflective insulation problems".  You will find there are many exaggerated claims for reflective insulation and radiant barriers. FTC has sued manufacturers for exaggerated claims about the products.


If the material in question is of the foil faced bubble wrap type there will be some R-value from the bubbles, but that is small. Generally no more than R-1 per foil bubble layer.

An article from the Reflective Insulation Manufactures Association International (http://www.rimainternational.org/index.php/myths/) dispells some myths about reflective insulation.

Many of the claims made by manufacturers of the foils are for the assembly. That's the foil, the air spaces, etc, etc. When someone installs it and changes one part the claims can easily fail.


And other references too, like this article fromgreenbuildingadvisor.com (http://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/30705/why-reflective-insulation-still-being-sold-hd)... Here's a quote from the article.... talking about a wall not a floor, but the principle remains the same......

"A copy of a thorough 2010 study by the Canadian National Institute for Research in Construction is also attached. Their conclusion: In a perfect state (with no dust on the surface), a radiant barrier with an air gap increased the efficiency of insulation in a wall by 10%. In other words, if the wall was already R6, adding 'miraculous' foil bubble wrap added .6, for a total of R6.6."


Lastly another reference work... 5 Things You Must Know Before Buying Radiant Barrier (http://www.energyattic.com/tx/wp-content/uploads/2012/05/radiant-barrier-answers.pdf) It's not all bad or a waste of money.

Get educated using more sources than youtube. Nobody is vetting anything posted to youtube, unless it's porn. Youtube has some good info and a lot of useless info, a lot of partially incorrect and totally bad info as well. Sometimes it is not easy to sort it all out.
Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on August 23, 2015, 05:35:26 PM
Another great reply!!  Thanks for the detail... wait they vet youtube porn?  Who knew?!?!
Title: Re: 20X40 cabin - foundation plan
Post by: Don_P on August 23, 2015, 09:34:35 PM
Are we talking like veterans, or veterenarians... that's just wrong  :-\
Title: Re: 20X40 cabin - foundation plan
Post by: MountainDon on August 23, 2015, 10:28:26 PM
We're talking like Canadians or Brits......  ::)

to vet something or someone is (from the Oxford English Dictionary)

(British) Investigate (someone) thoroughly, especially in order to ensure that they are suitable for a job requiring secrecy, loyalty, or trustworthiness




Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on September 01, 2015, 06:59:43 PM
Update!

Sub-floor insulation idea.  Before MountainDon accuses me of not listening... :-) I used the rolled foil insulation only because it seems the insects and vermen don't like it not for its insulation value.

(https://i851.photobucket.com/albums/ab76/retiredmarine/Mobile%20Uploads/subfloor%20insulation.jpg) (https://s851.photobucket.com/user/retiredmarine/media/Mobile%20Uploads/subfloor%20insulation.jpg.html)
Title: Re: 20X40 cabin - foundation plan
Post by: MountainDon on September 02, 2015, 07:46:48 PM
IF a rodent decided it really wanted to look at the other side it would have no problem chewing through. But the same could be said about the 3/8 plywood I used; it would just take longer. Install it tight, maybe use battens around the edges and over seams. Those little bu**ers get through the smallest of spaces. And do at least an annual inspection. The inspection gives me one of my excuses for owning an assortment of flashlights.   ;)
Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on September 02, 2015, 07:53:57 PM
Your a flashlight addict too?????   Lol
Title: Re: 20X40 cabin - foundation plan
Post by: MountainDon on September 02, 2015, 08:44:44 PM
 [noidea'Just got a TN31 Thrunite on a deal I could not pass up. I got the cells all charged and am waiting for it to get dark enough to see what throw it has.   ;D 
Title: Re: 20X40 cabin - foundation plan
Post by: nailit69 on September 03, 2015, 07:55:53 AM
 (Pax Prentiss) " I used to be an addict, but now i'm not"... 

I'm not a addict but do have a large assortment of flashlights...anything LED is my newest craze.  Recently converted all my older MagLites over and gave them to my kids (so I could buy new ones), I just put a 3600 Lumen LED bulb on my dirtbike, LED lightbar on the truck, looking for LED headlights for my truck... ok, I might be addicted.
Title: Re: 20X40 cabin - foundation plan
Post by: John Raabe on September 03, 2015, 10:05:49 AM
I've recently tried some motion detecting LED garden lights that are working out well. They light the path when a guest approaches or when I come out of the house. They sip power from a stack of C cells.

http://www.amazon.com/gp/product/B00OJOIWW6?psc=1&redirect=true&ref_=oh_aui_detailpage_o03_s00

They can some times be over sensitive, but they seem to adjust to wind and critters (deer for us).
Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on September 03, 2015, 05:10:05 PM
No question... just an update...  I'm moving right along in the planning..

(https://i851.photobucket.com/albums/ab76/retiredmarine/cross%20section.jpg) (https://s851.photobucket.com/user/retiredmarine/media/cross%20section.jpg.html)
Title: Re: 20X40 cabin - foundation plan
Post by: Don_P on September 03, 2015, 06:07:29 PM
Frost depth is 24" correct? If so eliminate the bottom course of block and pour an 8" thick footing 4" larger all around, 24x24x8" with 4@18" pcs of rebar 3" off the bottom in a # pattern. A footing is a snowshoe, it distributes the weight over a wider footprint and helps prevent overturning. Rebar hooked around the footing rebar and up into grouted cells in the block will help tie it all together. That rebar should tie to whatever is attached to the girders (developing a continuous load path).

If there is a deck hanging off the rim joist on those cantilevered floor joists there is a problem, the rim would need to be supported on the foundation, however you are correct in centering the load on a pier.
Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on September 03, 2015, 07:48:57 PM
Ok that makes sense..I get the snowshoe visual.  Nothing hanging off the floor joists the run across the cabin (2 - 2x10x10) 20 ft wide cabin.  I'm going to hang decks off either side of the 40 ft runs for a front and back porch.  Thought I'd hang those joists off the girders.
Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on September 17, 2015, 07:43:15 PM
Ok lets move to the top of this project... straight to the top - the roof.  I found this picture and it's the exact roof I want to use.  remember the cabin is 20X40 and there is a 8' covered porch on each side.  Anyone want to take a shot at the components of this roof? engineered truss?   Thanks in advance!

(https://i851.photobucket.com/albums/ab76/retiredmarine/roof%20idea.png) (https://s851.photobucket.com/user/retiredmarine/media/roof%20idea.png.html)
Title: Re: 20X40 cabin - foundation plan
Post by: garyc on September 17, 2015, 08:29:07 PM
Quote from: retiredmarine on September 17, 2015, 07:43:15 PM
Ok lets move to the top of this project... straight to the top - the roof.  I found this picture and it's the exact roof I want to use.  remember the cabin is 20X40 and there is a 8' covered porch on each side.  Anyone want to take a shot at the components of this roof? engineered truss?   Thanks in advance!

(https://i851.photobucket.com/albums/ab76/retiredmarine/roof%20idea.png) (https://s851.photobucket.com/user/retiredmarine/media/roof%20idea.png.html)

It looks like a standing seam metal roof. Big $$$$!It takes special tools and a crimping machine to install. The advantage to this roof is your fasteners are hidden and can be used in a low pitch roof.    They do make a snap on standing seam roof that is cheaper. menards does sells the snap on. https://www.menards.com/main/building-materials/pole-barn-post-frame-materials/steel-panels/premium-pro-snap-steel-panel/p-2044892-c-5717.htm?tid=732349041227881606
Title: Re: 20X40 cabin - foundation plan
Post by: Don_P on September 17, 2015, 09:40:48 PM
Certainly can be a truss. It can also be 10' sidewalls with a ridgebeam and stick framed rafters. The porch rafters rest on the same top plate then out to a post and beam support. It can also be ridgebeam and stick framed for the main roof and monochord trusses for the side porches.  All the beams should be properly sized and supported.
Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on September 18, 2015, 09:30:48 AM
Am I reading this right?

http://www.southernpine.com/app/uploads/SS_15-20L.pdf

Table 15-30 (30spf Ground snow load)
20' span of supported roof framing (width of structure)
Clear opening 24' (the max available on the table)
3 -1/2X16 ridge

if so then with a structure that is 40'long I would need to plan a support at the 24' point of the ridge and add the remaining 16 foot of ridge to complete.
Title: Re: 20X40 cabin - foundation plan
Post by: John Raabe on September 18, 2015, 10:44:42 AM
Here are some diagrams to explain how a load trace is done. You start at the peak of the roof and follow these loads as they accumulate ultimately to be carried by the foundation and supported by the earth of the site. At each step the beams, posts, joists and rafters will have certain limits to what they can carry.

You build from the ground up but design from the sky down.

One of the first subcontractors to get local help from is often a home designer or engineer. They can likely use local materials and design loads to help you make a practical support structure.

https://www.google.com/search?q=ridge+beam+load+tracing&rlz=1C1CHFX_enUS620US621&es_sm=122&tbm=isch&imgil=7_xQOX7g0HUQUM%253A%253BWRBlBCKvCsEVeM%253Bhttp%25253A%25252F%25252Fbct.eco.umass.edu%25252Fpublications%25252Fby-title%25252Fsizing-engineered-beams-and-headers%25252F&source=iu&pf=m&fir=7_xQOX7g0HUQUM%253A%252CWRBlBCKvCsEVeM%252C_&biw=1366&bih=643&usg=__j0r-7lwusYZJUkuwtuUn2LTDlgw%3D&ved=0CCkQyjdqFQoTCOey2_rxgMgCFYQDkgodzgcDPQ&ei=liz8VeePDISHyATOj4zoAw#imgrc=BGHU8baQMSlWKM%3A&usg=__j0r-7lwusYZJUkuwtuUn2LTDlgw%3D
Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on September 18, 2015, 10:50:08 AM
John thanks.. totally get the concept and the math of load transference..  now it's a matter of choosing material that doesn't take a giant to move and still gets the job done  .. oh yea and looks nice..
Title: Re: 20X40 cabin - foundation plan
Post by: Don_P on September 18, 2015, 01:37:49 PM
The looks nice part is a glulam. I rolled through your southern pine span tables quickly, it looks like the glulam they are using has a bending strength of 2400 psi and stiffness is 1.7. Off the top an LVL is going to come in around 2800 psi and 2.0E so may reduce size a bit... although the southern pine table took a load reduction I wouldn't, a pile of wet snow is heavy and it only has to happen once.
Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on September 19, 2015, 10:20:43 AM
A bit of figuring on the cost and weight of that construction has convinced me to go the truss route.  Here's what I'm thinking after looking at the truss tables.

(https://i851.photobucket.com/albums/ab76/retiredmarine/Slide1.jpg) (https://s851.photobucket.com/user/retiredmarine/media/Slide1.jpg.html)

(https://i851.photobucket.com/albums/ab76/retiredmarine/Slide2.jpg) (https://s851.photobucket.com/user/retiredmarine/media/Slide2.jpg.html)

Title: Re: 20X40 cabin - foundation plan
Post by: Don_P on September 19, 2015, 01:41:08 PM
The steeper the outside pitch and the shallower the inside the stronger a scissor truss gets. It looks like a 10/12 pitch in the photo above.

I would set the side roofs on the main roof to gain more pitch, it'll hold water and fail sooner at the pitch break at those pitches. Just let the scissor designer know what you are doing. I would try a sketch at 6/12 outside main roof, 2/12 interior,3/12 sidesheds and see how high they crawl up on the main roof visually.

Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on September 19, 2015, 01:56:14 PM
Don,

If I understand what your saying you're suggesting that I use a 6/12 pitch on the main roof and a 3/12 pitch on the side sheds. And then when I attach the side sheds attach them to the main trusses instead of setting them on the wall?

I don't quite understand what you mean about the interior pitch.  Is that the pitch of the interior members - the "scissors"?  and when you say it looks like a 10/12 pitch in the photo your talking about the real photo and not my sketches right?

I'd like to keep as much openness inside as I can so I'm trying to pick something that only has enough room for insulation and no more so I can keep the ceilings high.
Title: Re: 20X40 cabin - foundation plan
Post by: Don_P on September 19, 2015, 10:41:20 PM
Yes, what looks like a 10/12 to me is the original photo in the thread. If you want high ceilings inside start with a steeper pitch outside. The stresses on the members and the joints goes down as the pitch increases as well. The porch roofs will intercept the main roof faster if the main roof is steeper.  Steep roofs are not as much fun to work on.

Yes, the interior pitch is the "scissors", and yes the side sheds land on a ledger across the topside of the main roof
Title: Re: 20X40 cabin - foundation plan
Post by: retiredmarine on September 21, 2015, 04:13:40 PM
Don,

When your right your right... The pros are great to deal with... truss selection ...Done!
(https://i851.photobucket.com/albums/ab76/retiredmarine/roof%20truss.jpg) (https://s851.photobucket.com/user/retiredmarine/media/roof%20truss.jpg.html)