18x34 1 story + loft(s) in the Cariboo

Charlie A · February 07, 2011, 02:41:31 AM

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Charlie A · February 07, 2011, 03:11:19 AM

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February 07, 2011, 07:13:22 AM

Look forward to your build as it progresses. From the pictures it appears that this started in summer/late summer of last year. Can you work at the site now or is it snow covered?

Charlie A · February 07, 2011, 12:04:49 PM

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Charlie A · February 07, 2011, 12:21:24 PM

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February 07, 2011, 12:59:15 PM

Is it me, or do your built up beams split between the posts?

Also, may I ask the size of the beams. They look like 3 built up 2x8's spanning a 10 ft? span. I am only going off of this because the beams look as tall as the posts are wide. Also you said it was a 34ft long, and I only see four posts.

Also the center posts look they are poured at ground level and the side posts are sunk below the frost depth?

I'm sorry if I'm misinterpreting any of this, but I'm trying to get a bearing from the pictures.

BTW

Charlie A · February 07, 2011, 01:20:24 PM

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Squirl · February 07, 2011, 02:08:38 PM

I'm a little surprised that John's plans called for this.
Normally the conventional wisdom that I have learned from people on this site is that all joints on beams should split above a post. They become much weaker if not. I have seen this in real world situations were a beam breaks and collapses.

Also the girder sizing for a 10 ft span seams dangerously undersized. A 3ft 6 in. frost line is close to what I am dealing with in upstate NY, so I use the NY state building codes for girder/header sizing. I found them here:
http://publicecodes.citation.com/st/ny/st/b400v07/st_ny_st_b400v07_5_sec002_par013.htm
The maximum span for 3-2x8's is 6ft 5in. for a girder with a center bearing floor at 50lb snow load. I am using 50lbs, because that is what it is in my location with a similar frost depth. If you don't get much snow, you could probably go with 30lbs. That is without a break in the beam. Because you are adding a loft I would calculate it at 2 center bearing floors to be on the safe side with load, but that is just me. Technically, at that load 4-2x12's don't even seem to be rated to span 10 ft. I would add more posts.

Also with the center posts, I believe the fact that the side ones are sunk below the frost line, this could create a problem if they are not and there is frost. Even a few inches shift can easily crack mortar and drywall. I have had to fix this in many houses.

I am a not an expert myself. I have just had to fix certain problems over the years. Someone with more experience can easily jump in and correct any of my suggestions.

Charlie A · February 07, 2011, 03:41:56 PM

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February 07, 2011, 05:13:38 PM

Hi Charlie A,
I like the pictures!
I do however have a question,
what is you spacing between piers?

Charlie A · February 07, 2011, 05:16:47 PM

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Charlie A · February 07, 2011, 05:20:47 PM

Quote from: astidham on February 07, 2011, 05:13:38 PM
Hi Charlie A,
I like the pictures!
I do however have a question,
what is you spacing between piers?

I aimed for 10' (This was when I had planned a pole barn mind you). After digging there were rocks so big I did not attempt to remove them. So I believe the spacing between one set of piers is about 11'.

Charlie A · February 07, 2011, 05:30:54 PM

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Charlie A · February 07, 2011, 05:50:17 PM

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February 07, 2011, 05:51:28 PM

I know it is a little late for adding more piers to your build,
You might consider making PTWF panels, and putting them between your existing piers.
below is a link example of what Im talking about.

http://countryplans.com/smf/index.php?topic=4640.0

Charlie A · February 07, 2011, 06:02:54 PM

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Charlie A · February 07, 2011, 06:07:00 PM

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MountainDon · February 07, 2011, 07:12:26 PM

I see there has been some more added here since I started this post. I'll read it all later. For now...

That's a big undertaking for a solo build. It is very satisfying to look back and see what you've accomplished though. I've been lucky in haveing some help from our son on some of the parts of our build, not to forget my wife.

I like those five foot deep piers. They should not frost heave. They do remind me of the deep holes I dug back home in Manitoba when I was much younger. They also serve as a reminder to myself to not complain this summer when our plans call for digging some more pier holes here. At only three feet I should remember to not complain so much.

I sometimes tend to get wordy so please bear with me.

Not that it will help with this project, but perhaps some reader may benefit. I've built similar pier and girder foundations and have found assembling the girder 2x's right on the piers to work well. Some bar clamps help. It eliminates the task of having to move the very heavy girder as a one piece unit.

I'm guessing that you scaled this up from the Little House plans. There are some concerns when doing that. Squirl addressed some. Here are my concerns and ideas.

It is not clear whether or not the piers for the center girder are also dug down below frost level. They do appear to be at ground level. This might be of future concern as there may be differential frost movement between the deep piers and the surface blocks.

I'm guessing a little now. With an overall length 34 feet there appears to be maybe a one foot overhang at each end of the beam, sometimes called a girder. I prefer the term girder for beams that hold up structures. That would place the piers at ten feet apart, more or less.

As Squirl pondered, that is a long span for a triple 2x8 built up girder. Squirl referenced the NY state building code. It is based on the IRC by the looks of it. Many states use it and may make adjustments in some detailing but basically the structural portions are valid almost everywhere. I do not know what Canadian codes are based on but they are likely similar as this part of the codes are based more on structural engineering rather than being influenced by companies who want to see their products used. For reference anyone can view codes in a few places on the internet. They are normally available at any good public library. Click HERE for an online source. There is likely some Canadian specific site but I am not aware of where right off hand.

The tables in section 5 pertain to floors. Table 502.5(1) is for sizing girders and headers. A one story structure with a loft will have more load on the girders than a structure with no load, but less than a two story. I'm sort of like Squirl in that I tend to be a conservative designer and would lean more towards the 2 story sizing than the one story.

Using the 50 lb.sq ft snow load from where I used to live the one story floor with center support indicates that piers for a girder made from three 2x8's should be spaced no more than 6'5" apart, just as Squirl stated. The two floor with center supports section indicates a maximum span of 5'9". So I believe it would be highly advisable to install more piers in between the existing piers; all with the deep footers.

However, I believe there is another area of concern and I'm not certain how best to handle it. The outboard ends of the floor joists appear to be cantilevered about 2 feet, much like the Little House plans. The big difference here is that the Little House ios designed using one piece joists, no joints in the center. With a cantilever of around two feet there will be uplift forces on those joist hangers. I'm not sure how they will perform in that mode. Best practice here would have been to place the girders directly under the side walls. Maximum cantilever without engineering is limited to the the depth of the joist. That is a 2x8, actually 7 ¼ inches deep, should be cantilevered no more than 7 ¼ inches. A 2x12, would be cantilevered no more than 11 ¼ inches.

I'm not a licensed engineer so maybe there is something I've missed and perhaps this is not as worrisome as it appears to me.

One more point; before getting any further along it would be good to install diagonal bracing between the piers and the girders and joists, in the "north-south" and "east-west" directions.

John Raabe · February 07, 2011, 07:50:28 PM

It looks to me like the joists were trimmed back to be just about the joist depth on the cantilever. Which should be fine.

Charlie A · February 07, 2011, 08:01:17 PM

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February 07, 2011, 08:02:34 PM

Oh that's good. Looking at the first set of photos of the joists themselves and the T&G going down it appeared there was greater overhang. Sorry Charlie, I missed that, but let's leave the commentary as a reminder to anyone else reading. ok?

Sorry I missed on that.

MountainDon · February 07, 2011, 08:05:45 PM

On the rodent proofing under the floor...

The US National Forest Service has an excellent rodent exclusion manual available online. Link here.

http://countryplans.com/smf/index.php?topic=2919.0

Aluminum screen will not keep out rodents. Even small deer mice chew through in no time if they feel like it. It would be better to use something solid like 3/8 CDX plywood or steel hardware cloth with ¼ inch mesh.

Charlie A · February 07, 2011, 08:14:03 PM

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Charlie A · February 07, 2011, 08:38:59 PM

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MountainDon · February 07, 2011, 08:44:07 PM

Quote from: Charlie A on February 07, 2011, 08:14:03 PM

I was going to consider ply under the structure but i wanted the batts to breathe if need be. 1/4" steel cloth was a thought,

FWIW, I was concerned about 'breathing' too. We used mostly 3/8 plywood with a strip of the hardware cloth along each side, inboard of the girders.