Going wider

[RIjake]

Good morning all. 

I'm sure that this question has been raised before and I know that the reason most keep the width of their cabin to under 20' is for ease of building, but my vision of what my cabin will be necessitates the extra 4 feet in width.

I'd like to alter the 20' 1.5 story plans to 24' wide.  The foundation will be post and pier.  Other than additional piers down the middle and maybe larger floor joists what other factors are going to play into extending the width?  Am I missing something else? 

Will I be able to still use the plans for the 1 1/2 story?   

Right now I'm thinking 24' x 32' with a partial loft.  I'm hoping to have some aspects of a traditional timber frame using wood from my property.

I'd especially like to hear from others that have gone wider than 20' with the drawings.

Thanks!

[MountainDon]

Anything is possible. Some things just take more materials/money/time.

You could use a beam down the center to help in supporting the floor joists. Or you could order engineered floor beams that would not require that.

If you use a center beam then you could also use a load bearing wall or beam down the center to support the upper floor. Or use the engineered wood solution.

The roof could be the usual rafters or another engineered solution; roof trusses.

The sizes for the engineered products would be determined by the engineer at the truss/joist manufacturer.

If you need to submit drawings for building permit approval you will have to do some alterations to the basic plan sheets. Drawings for the engineered wood products would be supplied to you by the truss manufacturer once you paid them.

Going wider also means more load on the ground. Going wider might be the time to switch to a full perimeter footing and foundation. although the raised floor people use piers on a continuous footing. That depends in part on what your soil is like and again, maybe if there is a building permit process you have to work with.

[johnky]

I think I can summarize it.  The 20x30 plans are sized to use full span joists for the floor joists and the loft joists.  It also calls for rafters that only need a ridge board, not a ridge beam and the piers for the foundation are only on the perimeter, there is no center row of piers.  

Once you go to 24' wide, you are going to need to change all of that...  you'll need three rows of beefier piers instead of two or use two beefier rows of piers and engineered joists, you'll have to support your loft with a pillar or load bearing wall, and you'll have to use a ridge beam to support the roof or use engineered trusses.  If you stay with the 12/12 pitch roof, you are going to have to work on a roof that is a few feet taller than the 20' wide cabin and your rafters will need to be over 18' long, which may be hard to find.

I've worked out the costs both ways.  The beauty of John's 20x30 plan is that it's the most bang for the buck, so to speak.  Once you go beyond the 20' it adds a lot of cost per square foot.

Do you think you can do what you need to do by just having an extension stick out in one area, instead of the entire cabin width being widened?  Or maybe you can build a separate room addition that has it's own framing members and separate rafters - an L shaped cabin if you will?

[HoustonDave]

I'm no expert but have been digging through this forum many hours (and others). In addition to the pros and cons raised by the previous two folks, also consider the longer term. If (god forbid) you get settling down the road, it is much easier to relevel a foundation consistig of two beams and two rows of piers. When you add a middle beam and row of piers, you have more complexity in how the foundation could settle and more complexity in re-leveling it.

[glenn kangiser]

I think the short answer is that you can not use the 20 wide plans for a 24 wide building.  Everything changes.  Loads per lineal foot of house change as mentioned above.   Weight on each pier increases requiring different load calculations to the footings. 

Increasing length is easy.  Loads per footing remain the same as length increases.  Depending on your reason for and size of needing the extra width, perhaps the extra 4 feet could be handled with a popout and an appropriate sized header supporting the open area at the sidewall.  Then you could use the same plan, and even have custom designed trusses over the entire area or simply use a shed roof.  Then you may want to be sure to raise the sidewalls for sufficient slope on the extra roof area.

[Don_P]

I'd especially like to hear from others that have gone wider than 20' with the drawings.

As others have pointed out you cannot go wider with the drawings.
With a popout or some addition, even a porch, you are loading the girders higher.
There is nothing wrong with the concept at all but it probably needs looking at from the ground up... not a big hill to climb if you want to.

Floor trusses can span 24' as can attic trusses that have the loft floor built into them neither would require center support.

As an aside;
That is a good graphic in MD's link showing a prescriptive continuous footing and an engineered pier arrangement. Look carefully at the corner pier height's and widths. I suspect that design had 4 hooked vertical bars at the corners and 2 in each of the intermediate piers.

[bayview]

   Oops . . .    I thought this post was about over eating during the holidays!

       

/.

[RIjake]

Thanks for the replies. 

I've got some estimating to do, looks like it'll come down to cost. 

I do like the "ell" idea.  I did some rough floor plans using one back in the early planning stages.  Perhaps I'll revisit that route.

[rwanders]

In my experience (certainly less than many here), once you get past the need for drawing and spec changes, the actual building for 24 versus 20 wide doesn't seem to be much harder. There are obviously some $$ differentials but, the benefits of that extra 4' of width are many and become very obvious in the final product---especially in a 1 1/2 or 2 story where you need to fit a staircase in your floor plan. I have also found that an extra 2' in depth for porches or decks  (10' vs 8') pays great dividends in return for really minimal extra material expense.

An important factor in the 24 vs 20 width decision is how your wife will feel about the resulting floor plan and available spaces----we all know what happens when "momma ain't happy"-------"ain't nobody happy".