MODIFIYED 20X30 cabin 1 1/2 Story in Northern Maine

[eighthdoctor]

We are building the 20 X 30 cabin. We are going to modify this to 22 X 40 and we have some questions that I hope someone can answer for us.

1) We are going with the post and beam foundation 3 beams supported with sona tube 3 rows 8' apart 8" dia x 4' down to frost line SHOULD WE HAVE FOOTINGS UNDER THE SONA TUBES TO SIT ON. IF SO WHAT PRODUCT?

2) If we change the width to 22' does this change the 12/12 pitch of the roof if so to what?.

3) With the cold winter I am going to close the underneath of the cabin with cement board and ridged insulation on the inside (any thoughts??)

4).  We met our neighbors who had their cabin "raised" this past month.  The contractor did this "new" footing.  We are interested in hearing anyone's thoughts or experiences regarding this new procedure.  Here it is.... the hole is dug 2 feet down x 2 feet wide round.  Stone is poured into the bottom of the hole then a preformed cement round disc is placed over the stone, then the bracket is drilled into cement disc then the 6x6 post is adhered.  The other option was just the stone was piled and the cement disc was placed on top !!! how do you keep the stone from "spreading" out ?  We did not see this for ourselves but the contractor told our neighbors that this procedure ( the first one I explained ) will last 50 years. 

Thanks .... look forward to reading what you all have to share. 

[hhbartlett]

In Northern Maine (close to where I am), you might want to look at these:
http://www.bigfootsystems.com/

I'm no expert, but going to 22' shouldn't mean changing the pitch of your roof, just longer rafters. However, that will make it more difficult to get standard lumber for the rafters; because the roof is 11' tall over 22' wide, using regular math for right angle triangles that tells me the long (rafter) side is 15.5' not leaving any room for cutting out angles on the ridge board or fascia. When you have a 20' wide roof on a 12/12 pitch, you can use off-the-shelf 16' long rafters I believe (other experts here can correct me if I'm wrong) and it should fit perfectly.

As far as the other foundation you mentioned; northern Maine should probably have 4' deep footings, not 2' to avoid frost heaving.

We are building the 20 X 30 cabin. We are going to modify this to 22 X 40 and we have some questions that I hope someone can answer for us.

1) We are going with the post and beam foundation 3 beams supported with sona tube 3 rows 8' apart 8" dia x 4' down to frost line SHOULD WE HAVE FOOTINGS UNDER THE SONA TUBES TO SIT ON. IF SO WHAT PRODUCT?

2) If we change the width to 22' does this change the 12/12 pitch of the roof if so to what?.

3) With the cold winter I am going to close the underneath of the cabin with cement board and ridged insulation on the inside (any thoughts??)

4).  We met our neighbors who had their cabin "raised" this past month.  The contractor did this "new" footing.  We are interested in hearing anyone's thoughts or experiences regarding this new procedure.  Here it is.... the hole is dug 2 feet down x 2 feet wide round.  Stone is poured into the bottom of the hole then a preformed cement round disc is placed over the stone, then the bracket is drilled into cement disc then the 6x6 post is adhered.  The other option was just the stone was piled and the cement disc was placed on top !!! how do you keep the stone from "spreading" out ?  We did not see this for ourselves but the contractor told our neighbors that this procedure ( the first one I explained ) will last 50 years. 

Thanks .... look forward to reading what you all have to share.

[Don_P]

The contractor is assuming the 6x6 will last 50 years, quite probable. He is avoiding having multiple hinges up the support piers, what one engineer friend called built in collapse mechanisms. I bury deck piers to the footing for this reason.

Look at Bigfoot's tech data and write them asking about the appropriateness of using these for a house. Their well installed and very compact backfilled piers with I believe 8" above grade using their largest forms gave an impressive 8,200 lbs lateral resistance before failure. The piers had tipped over more than a foot at that point. I guess it depends on what one considers a failure. That wasn't an 8" tube on gravel. IIRC it was a 36" base form on a 15" tube with mechanically compacted fill in 6" lifts.

You desire to skirt the foundation. Real foundation walls provide real lateral resistance... which is why they are standard construction.

So much of these discussions is akin to the difference between pop riveting the frame of your jeep together and welding it. For whatever reason on construction forums the pop riveters sing loudest and on jeep forums it's kind of the opposite. Run what ya brung, just remember when it gets stuck in the mud you can't even attach a strap to pull it out.

[eighthdoctor]

Thank you for your input.  Our plans for our cabin do call for either A). Sonotubing, or B) using a PT post foundation, which entails digging a 4' hole using concrete or crushed stone for a footing with a 2x12 plate on top and then the 6x6  post sits on top of the 2x12 footing.  Then back fill the hole with either compact gravel, sand mix, or soil cement.  Ofcourse the normal foundation would be optimum, but money wise we are trying to do it right as well as save some money.  In talking with alot of people up their about their "camps"...we hear alot more about these type of different footings vs cement foundation.   

[hhbartlett]

You could also do a perimeter rubble trench, depending on your location. There's at least one member here that did that. Then you're only pouring a concrete beam, but still get the benefits of a perimeter foundation. Just another option if it's feasible at your location.

[Don_P]

Actually from a rubble trench a treated plywood and framing "permanent wood foundation" does a good job. It would provide the skirting and the wall is strong and stable from overturning. In the same lifespan range as the wooden pier. In good soil a weekend playing with a rented mini excavator and a load of gravel.

[Squirl]

Other foundation options are the same if not cheaper in cost as a post and beam, they just take more labor, but tend to last longer and add more value.

8 ft is a long span for posts.  My recollection was the plans john has drawn up has spacing closer than that, but I don't have them in front of me.  With the ground snow load in your location when running that little amount of piers on a wide house with 2 floors you are getting into possible soil bearing capacity problems, and larger more expensive beams.  I would consider more piers.

The footings question is easy.  Yes. Poured concrete.  How large is dependent on the building and soil capacity.  An 8" circle is a very small footprint.  Soil bearing capacities are usually measured in pounds per square foot from 1500-5000.  An 8" circle (pi*r^2 = 3.14*4^2) So it is 50 square inches or 1/3 sq. ft.  Northern Maine has high snow loads too. You are building a large building with very few points of contact with the soil. 

So quick and dirty math on how buildings are designed.  They are calculated in pounds per square foot.  The average used is 40 lbs per floor.  Sleeping areas are sometimes lowered to 30 lbs.   Many people consider half stories a sleeping area, but for framing and girder sizing 30 is so close to 40, people use the charts to treat it as a full floor of a building.  I am in central NY and have a ground snow load for roof calculations of 50 lbs per square foot.  My recollection is Northern Maine has a ground snow load of 70 lbs per square foot.  So with 22x40 you have 880 square ft per floor.  Now you just multiply and add it up (880X40 = 35200) (880x30 = 26400 ) (880 X 70 = 61600) = 123,200 pounds distributed over 18 piers or around 7000 lbs per pier if all the loads have been evenly distributed in the design, which center piers tend to hold half the weight of the floor while outside piers tend to hold half the weight of the roof.  This is just part of the math that goes into building design for a pier foundation.  I believe johns plans state that they can be extend length without any problems, but when you add width, the calculations and lumber sizing has to be redone. Most people go with 20 ft or 24 ft because lumber is normally sold in even lengths of 10 ft or 12 ft.

[alex trent]

I am not sure if you 8 feet refers to how far apart the beams will be or the spacing of the piers along the beams.  Eight feet is pretty far for this build...as has been pointed out, you have a lot of weight to support.  Not to mention the need to brace laterally...here it is the weight we deal with.

I did not run all the numbers again, but they look right.  If they are you need to stop and rethink.

You might get by with that spacing if your piers have more footing area. Again, as been pointed out, you have 7,000 lbs. per pier and it is 1/3 a sq. ft pier a very high load per sq, ft, and I think one which is way over what you should do in any soil.

If you do 18"x 18" footing on the piers you will have 2.25 sq. foot per pier. This makes your load 3,100 lbs. per sq. ft and a lot more reasonable...in my opinion still a bit on the short side.

At a 2x2 foot footing you have 4 sq. ft and 1,750 per sq. ft.  Decent and some room for error and variable bearing weights on the various piers (not all get the same load, so some may have almost 40% more and some less, but you should figure for the high ones).

If you increase the number of piers...say do them at six feet..you will have 24 piers and all the calculations based on how big the piers are can be redone to suit that.  Here for instance, at 18"x18" footings you would have  2,277 psi on the piers... not too bad.

Note that your piers do not have to be 2x2 or 18'x18" all the way up tp the beam...just the footing for each pier...about one foot thick...soil on the bottom and pier on the top. Footing need to be done right..... with rebar, concrete mixed right and tied to the piers in a single pour. None of that is real tough to do.

[CjAl]

the bigfoots are nice but they get pricey fast. i was going to use them but decided against it. the story and a half plans do have posts at or just under 8' apart with a trippled 2x12 beam. it also only has two beams but at 20' wide you need 2x12 select for floor joists. you cant go 22' with that so putting the third beam down the middle is needed. i am at 20' and am using a third beam. i can run smaller floor joists and i have more piers to distribute the weight since i am building on pure sand. i am using three foot long 8" sono tubes sitting on a 18" round, one foot thick footing. with rebar laid in a tic tack toe pattern. then four foot rebar pounded into the ground althru the footing and up the sono tube.

btw, i am in south east tx and have no snow loads to worry about so you may need bigger footing or more piers. i would be more inclined to do 6' spacing

[Squirl]

On #4. The "new" procedure.  Digging down 2 ft in a 4ft frost depth area without special provisions for drainage or insulation, is normally just being lazy.  I don't know how he expects to defy the laws of physics and thermodynamics.  There are scientific ways that have been developed to put foundations shallower in deep frost zones (FPSF), but just digging half the depth isn't one that I ever heard of.

The 2 ft round disc, I can't comment on.  I don't have enough information.  It would be a good footing depending upon depth and rebar reinforcement.  Concrete has great compressive strength, but poor tensile and shear strength.  They would be placing a very heavy load in the center of the disk.  It depends on how deep and how reinforced the concrete disc is whether it can distribute that load to the bottom of the disc.

[Squirl]

Thanks al, I didn't have them in front of me.  Triple 2x12s  works with a 70 lb snow load with two center bearing floors.  If clear spanning with that snow load, they are a little light.  Sorry, I believe you have one of the highest snow loads in the country to account for. 

Here is the beam sizing charts and guide how to read them.  If you are widening the building, they will be important.
http://countryplans.com/smf/index.php?topic=10511.0

I think alex made a good point about the footings.  Normal thickness for a full perimeter foundation would be 7-8".  Since your loads are higher and more concentrated, I think a thicker footing wouldn't hurt.

From the first post, the sonotubes don't have to be to the frost line, the bottom of the footing does.  Then you can set the sonotubes on that.

[alex trent]

1. I agree on depth with frost. I cannot see where digging another 2 feet or so deep in a frost zone is a big thing, so that needs to be addressed as well as the area of the pier footings.

2. I meant 2'x2', not round...as you know 2' round is about 3 sq. ft, not 4.  # sq. fwwt could be OK, but close IMO, unless you really know what is under there .

Can someone enlighten me on why Sonotubes are such a big deal if they cost as lot.  Digging the hole, if the soil is decently stable and just pouring the piers in it without tubes works fine.  I guess not in sandy stuff, but in lost of soil it is fine. Maine??  You can build a little form where they come out above grade.

[CjAl]

the sono tubes are cheap, its the bigfoot forms that i feel are expensive. cant remember but i think i was looking at $500 for the 15 i needed. of course then there is a good $300-$350 for simpson brackets. i know that cause i bought them yesterday but i got the more expensive ones with the bolt so i have a little adjustment. was $375 for 10 for 6" and 5 at 4".

when i dug my holes i just bell shaped them at the bottom and will pour the footing directlyinto them. i also mixed up some very watery cement mix and poured it in the bottom to soak into the sand and hopefully firm it up some. if its not raining the sand holes just colapse back onto themselves.

i just used the tubes to actually limit the amount of concrete used and make it look nice above grade. a 16" hole four feet deep uses a LOT of.concrete if you just fill it up. mabey not an issue if you have a cement truck coming but i am hand mixing it

[alex trent]

The Simpson's with the bolts are worth it for the adjustment factor.

That is the way I poured my footings and piers.  But I have clay so it did not collapse and we could carve out the pier holes to almost exactly 12 inches...went to 18" in the bottom just by carving out wit a post hole digger and a steel bar.  I bent the bottom of the rebar for the piers to make a footer to go across the bigger base.

We just made a little box form on top to make it neat.

[eighthdoctor]

THANK YOU TO EVERYONE FOR THERE COMMENTS WE ARE GOING TO STICK WITH THE WIDTH AT 20'

BUT I HAVE ANOTHER QUESTION WE ARE GOING TO USE T1-11 FOR THE SIDING THAT SAID CAN WE AND COULD WE USE A HOUSE WRAP          (TYVEK ECT) OVER THE STUDS IF I WAS DOING CLAPBOARDS I WOULD DO THE WRAP AFTER THE SHEATHING.

SO WHAT DO YOU THINK.

[CjAl]

i have seen many people put the house wrap over the studs then put the t1-11 on. i have wondered about this myself since i plan to use it but i plan for it to be temporary. i will eventually side over it. the bigger problem is windows. i see people attach them to tue studs then put the t1-11 over them. i would like to set them over the t1-11 and then trim around them but i dont know if that works or not. questions that still need answers. im not that far along

[MountainDon]

T1-11 over the studs may be allowed under code (if the panel is stamped as rated for structural use), but IMO is a case where the minimum is not the better solution. T1-11 is trying to do two jobs at once; the structural and the cosmetic. If the T1-11 deteriorates, as it always seems to because maintenance slips, then the structure loses strength. Personally I would not use it.  It also soaks up paint/stain like a sponge. Same can be said for rain if/when the finish fails.

[eighthdoctor]

I am going to do the same thing warp, t1-11 window and then trim seems like the right way to do it, Not to worried about the t1-11 holding up I will do the maintenance on it and can side later if needs be.

any good suggestions for raising the beam the roof rafter go to if I am on my own.

Thanks Again.

PS
there is talk of the adjustable simpson bolts is this for the beam to sit on and could someone give me a description or stock number.

[alex trent]

On the beam/post connectors..

What was being discussed was pier/post connectors.

On the post to beam lots of different options...some need a boost from Simpson and some do not....and depends on how you are building and how the beams rest on the posts.

You can go to their site and they have a ton of products.

Might help if you described how the beams (girders) will rest on the posts.

In my build, most of my connections were the girder resting on a notched post.  There I nailed through the girder into the post and that is all one needs.  I had a few connections were I did not have a notch to nail to and there I used "T" straps to secure the post to the girder.  There are other ways to do that but this worked for me. 

Nails, not bolts and plenty of them and good ones of the right size...Ardox type or ring shank,

[eighthdoctor]

I was thinking more of tying the 6x6 post to the concrete.

[alex trent]

Which is a lot different than post to beam.  Different structural components..

I used these and they work fine.

Be aware that this connection is a WEAK point in the pier to "house"  (posts and above).  They are strong, but will not keep the whole thing from bending over, so to speak.  These are mainly good for preventing uplift. Where the pier (and we assume it is well done) connects to the post is a critical place and this is not the be and end all in making the connection.  A 6' post does no  good if it twists on the pier! You need to brace well to counter some of this.  And you can do that, so keep on finding out how.

[UK4X4]

These were about the strongest I could find on the internet, I think the sheet steel ones just don't really do whats required

But I guess depends on the size of your piers

http://www.permacolumn.com/SW66-for-6-x-6-Post_p_8.html

[Don_P]

Guys, the moment capacity of these connectors is measured in inch pounds, you all are into problems of hundreds or thousands of foot pounds in lateral at these connections doing it this way. The post /pier connector is not the brace.

[alex trent]

Here are some Simpson connectors, These are the ones I used...there are many more on the site. If you study them a bot you will find the one you want/need.

http://www.strongtie.com/products/connectors/ab-aba-abe-abu.asp

Note that there are NOT for preventing the post from rotating on the pier. They are to prevent uplift and keep the post in position on the pier (so it does not slide off).  With a house, There are very big forces pushing on the house laterally...and thus "bending" the house on the post/pier connection (and in other places too, but this is the main one). "Racking", I believe is the term. Wind is the main culprit, but other things, like the relative position of Venus to Jupiter and the phase of the moon, also contribute.  You cannot depend on the connectors to resist that and without post to post bracing the house will be in jeopardy of being pushed over as the piers ho;d vertical and the post tilt.

The greater the post to beam distance from the pier connection, the greater the force on the connection. You can eliminate this by putting the beams directly on the piers and using no posts which have to be connected, losing the connection weak point. This may or may not be workable, depending on how far above ground the house sets, or the slope off the land it is built on.

There are tons of sites with info on this...and a lot on this site. I'd do a bit of looking to help better explain all this as it is of critical importance.