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dcrowley3
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# Posted: 18 Jan 2017 09:29am
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Hi everyone
I am new to cabin building, but do have some construction/carpentry experience. I have read alot from this site and learned alot already.
I am in the planning stages of building my retirement cabin in Trinidad, CO. I want to build a 20'X36" cabin and have some beam size/span length questions. The cabin is single story, 8' high walls, and using pre-fabricated trusses with (I think) a 4/12 pitch. I was told 30 psf snow load in this area.
I plan on using 12" dia concrete pier dug below frost line. I was planning on installing 3 rows with 4 piers per row (so 12' OC pier span). I was planning to use tripled 2x10's across the piers. Then install 2x8 floor joist 16" OC.
Is tripled 2x10's just right/to much/to little?
Is a 12' beam span just right/to much/to little?
Any and all advice desired.
Thanks for your help.
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neckless
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# Posted: 18 Jan 2017 10:00am
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its all ways better to start with a good foundation...... too late when u putin roof on..... when my joist i nailed a 1 x 2 on the side of joist 3 inches down from top and cut 2 1/2 in blue Styrofoam and droped it in then sheeting....it was a lot of work but in winters was worth the effort
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MtnDon
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# Posted: 18 Jan 2017 10:30am
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Have you checked with the city or county if outside the city limits as to whether or not they will approve a pier foundation? A quick Google indicates the city uses IRC 2013 and the surrounding county uses IRC 2009, which do not approve a pier foundation without an engineer's design.
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KinAlberta
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# Posted: 18 Jan 2017 01:26pm - Edited by: KinAlberta
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Approvals aside, I think piers get a undeserved bad reputation because of some inappropriate use. (Like hating concrete foundations because some crack and leak and cost a fortune to fix. ...but yes, a full foundation is the gold standard. But here were talking cabins.)
I've posted elsewhere about our two cabins. 24'x24' and 24'x30' build on concrete blocks in the 1950s. Drainage is good and both have been amazingly stable requiring very little jacking and shimming.
However, I sure wish they were slightly higher off the ground. 6" or so in some points really limits my ability to get under them to insulate or jack and shim. If only they'd (my dad & my uncle) had used another layer of blocks or better yet 2x12 or 2x14" beams. (Ironically my dad was a builder back then and used 3/4 plywood walls and roofing and heavy concrete on a rental he built for my grandfather.)
Also, the build on our cabins sounds very much like dcrowley3's plans. Our beams are mostly 3 boards laminated but supported 8' apart. Now here Is where I sure wish they'd overbuilt and added a couple more boards - or better yet deeper beams for far more strength to span a settling pier and enable easier jacking.
The added cost would have been minimal but 70 or so years later I'd love the ease of fixing up the places. Instead, it's a pain.
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dcrowley3
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# Posted: 18 Jan 2017 03:47pm
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MtnDon - Thank you very much for the information. Luckily I have not bought property yet, but very soon. After doing a quick Google searched, as you advised it looks like I will move a little west into Costilla county and buy there. They have very liberal building requirements. Just a recommendation to build per code (not a requirement) and then just an electrical and plumbing inspection from the state in order to get a Certificate of Occupancy.
KinAlberta - Good information, will keep that in mind.
So, back to my original question about foundation and beam.
Is tripled 2x10's just right/to much/to little?
Is a 12' beam span just right/to much/to little?
I put together a little sketch to help if I am not explaining very well.
Also, anyone heard of or use a product called "Form Footer" looks like a nice easy way to make strong piers.
Thanks again for everyone's help. Very excited to start building my cabin and get out of the city.
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MtnDon
Member
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# Posted: 18 Jan 2017 06:27pm
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One of the reasons piers do not meet code without an engineer is that each pier is independent of all the others, when built as your see most. Each pier is free to move down or up, free to rotate about some arbitrary axis or not. Notice the quote above, "...amazingly stable requiring very little jacking and shimming... My 32 year old house on a slab has required no such work, the house we owned before it was 55 years old and had never moved. Some folks may be luckier than others, some may fare much worse. Foundation work, after the fact, is an onerous and can be a dangerous task.
I suggest thinking carefully about foundation choices, the more so if there is any chance the "cabin" becomes a full time "home". In my life so far, 7 decades, we have encountered a few totally unseen changes.
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dcrowley3
Member
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# Posted: 20 Jan 2017 09:12am
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MtnDon - Thanks for all your advice and info.
We do plan on making this a full time home in the future and I definately do not want to build something that is not stable. I see alot of people on this site who build with pier foundation.
Is the pier style foundation an issue due to the size that I plan on?
What kind of foundation would someone suggest for a 20X36 cabin plan (see description above post)?
We are getting ready to buy some property this summer and I just want a plan before buying somewhere.
Any suggestion, advice, comments accepted, you will not hurt my feelings.
Thanks for your help in advance guys
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MtnDon
Member
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# Posted: 20 Jan 2017 10:24am
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Concrete slab or a crawl space with a full perimeter footing. Either a formed concrete wall or a concrete block wall are superior to piers. Methods have been developed to a prescriptive design. The IRC contains the details as to size of rebar, width, depths and have been time proven to be a very good foundation. Solid and not likely to have settling issues when done right. Soil testing or local knowledge determines some of the details as to how wide the footing should be. Some locations with lousy soil may need something more... and if that is the case piers are even worse.
Twelve individual piers are 12 separate points for failure. The perimeter footing with rebar is tied into one piece. If you search the Las Animas county website you can see what the county recommends for a modular home foundation. (I know you are not going modular but hang in there for a sec) They have a drawing online that shows piers being used to support the modular home. They have a steel reinforced concrete beam (formed concrete) in the ground at the frost depth. 36" I think. It runs the continuous length of the structure from one pier to the next. Then the masonry piers that will support the modular home are built on top of that. Rebar ties the beam to each pier. The concrete beam holds the bottom end of the piers in place. Independent piers can and do rotate; the bottom moves south lets say and the top tries to go north. The concrete beam also distributes the load evenly over the earth. Wood or concrete piers built the way all the piers you see here and on other sites do not have the shared load carrying provided by the beam, nor the lower ends locked in place. Each independent pier is free to move hither and yon on their own.
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bldginsp
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# Posted: 20 Jan 2017 10:29pm
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12 feet between piers for girders is too much. If you are going to design it all yourself, learn to do basic load calcs and use the span charts. It's pretty easy.
I agree, use a full spread footing, or slab with perimeter footing for a building that size. Makes it a real building.
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Mossbett
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# Posted: 2 Feb 2017 09:17am
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I always appreciate the advice given, and just wanted to add this idea.
We built our "cabin" in northern NH and struggled with slab vs. piers, cost etc. as money is ALWAYS an issue we wanted strong yet frugal foundation.
Piers do work, but remember it is opposite from your thought the ends are least loads, the piers in from the ends hold increasing loads all as said earlier independent so... Freeze..wind settle etc. slabs monothiclic are well established designs yes, but 6-9000.00 if all goes well.
We went with a PWF, not cutting any corners IE gravel base etc, and added the frost protected above frost designs as digging hard in granite to get down. Both are ACCEPTED by IRC, and approved by Amer Civil Engineers etc.
Cost was just 200.00 less than piers and Much more stable.
4 years in drywall not cracked doors open windows not sticking and Well works well.
Again just two cents and yes more work, follow ALL design rules and we shall see
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Jim in NB
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# Posted: 3 Feb 2017 05:52am
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I went with a 32x24 posts spaced 8' (5 of them) and beams spaced 10'. I went with 2'x2' 6" deep concrete pads on surface with PT laminated 2x6 posts and PT 2x10 trip laminated beams. Built my place in 2010 and not heated in winter. No problems with windows or doors at all and only a few spots where the drywall has acted up a bit - on the seams between sheets. This was to code. I would NEVER build a structure on a slab other than a garage. Every building I have ever seen on a slab has moved substantially. And any building that hasn't - well, just wait. My comments is based on my expereince for places that have significant frost.
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