Hello All.
I have done some work on timber frames in other states, log cabins and new homes. I am a licensed GC in another state.

I was hired recently to assemble a kit and believe there are some structural problems but have not been able to locate anything to help. I am finding myself getting more and more into timber framing through all of this and am looking forward to my next project. Let me thank everyone in advance for any help.

Issues:
The timbers are all Hemlock cut here in Maine. These where all soaked upon arrival to the site. Everything is spaced four feet on center. My doubt is the floor system.Like I said foor feet on center, six by eight beams, eighteen feet long. We crowned everything and followed our plans and specs provided to the letter. We first noticed the bounce the floor has when installing the 1-1/2X6 tongue and groove flooring. Today I pulled a string and the floor has a deflection of a little over 1/2" in the eighteen feet.

My fear is that as it continues to dry out and people begin living in this home the floor will continue to sag and possibly become a safety concern. The original builder will probably end up in litigation over their performance and I am curious if these where infact undersized from the begining. We have had problems all along the way getting the materials that had been paid for delivered from this guy. I have always over built everything and there have been so many design flaws in this frame it is pathetic.

I guess I am asking more if you had an 18' span for a first floor system going over a basement what size joist would you use and how would you space it?

I plan on installing a carrying beam or girder under this floor tomorrow to remedy the situation and try and jack the floor up level. My thoughts where based on my experience the beams should have been larger for such a span and possibly closer together. The carrying beam was a disappointment to the customer as they where looking for a clear span in this area.

Here in ME, where we are building there are no inspections so it is up to me to build this and make it a safe structure and I would appreciate anyone's advice.

Without checking or calculating, if four foot centers are desired, I would start my calcs with No. 1 6 x 12 and see how that works out.

I'm not an engineer, but according to my calculations, in #2 hemlock, you'd need 6x14's to span 18' @ 4' o.c.

I'd be pretty concerned about working on a job like that. You are obviously and justifiably concerned, so if you haven't already, you should talk to the owner today and tell them your concerns. Recommend they hire an engineer to determine if the frame is safe.

Using the 6x8x18' hemlock, my math shows a deflection of 1.46 inches on a first floor 47.5 psf load. (0.6 inches max allowed at 1/360). Looks like you've got nearly that max allowed deflection without any more than dead load.

Assuming second floor loads of 30psf live and 10 psf dead:

Hemlock #2
E: 900000
Bending: 600 psi
Fc Perp: 550 psi
Fc Parallel: 400 psi

72 sq ft area = 2880 pounds per joist
Length of span = 216"

Beam Depth = 8"
Beam Width = 6"

Deflection 1.640"
L/D = 1/131.7
Bending Stress = 1215

(note, this is from a simple beam calc spreadsheet - you need to get a local PE fluent in timber frame involved as it sounds like something went awry during the design phase...)

We can improve a bit if we go to 2' OC, but they still fail.

Hemlock #2
E: 900000
Bending: 600 psi
Fc Perp: 550 psi
Fc Parallel: 400 psi

36 sq ft area = 1140 pounds per joist
Length of span = 216"

Beam Depth = 8"
Beam Width = 6"

Deflection .820"
L/D = 1/263.4
Bending Stress = 607.5


Even looking at a Hem #1 the 4' OC fails.
Moving to Douglas Fir #1 we still fail.

Assuming first floor loading of 35 live and 15 dead - it only gets worse.

Get a pro involved before you get too far along.

Numbers for 6x12

Assuming second floor loads of 30psf live and 10 psf dead:

Hemlock #2
E: 900000
Bending: 600 psi
Fc Perp: 550 psi
Fc Parallel: 400 psi

72 sq ft area = 2880 pounds per joist
Length of span = 216"

Beam Depth = 12"
Beam Width = 6"

Deflection .486"
L/D = 1/444.4
Bending Stress = 540



Assuming first floor loads of 35psf live and 10 psf dead: (the 6x12 now fails)

Hemlock #2
E: 900000
Bending: 600 psi
Fc Perp: 550 psi
Fc Parallel: 400 psi

72 sq ft area = 3960 pounds per joist
Length of span = 216"

Beam Depth = 12"
Beam Width = 6"

Deflection .668"
L/D = 1/323.2
Bending Stress = 742.5

You're very correct in your concerns. A 6x8 spanning 18' is much too small a member to handle the load.

Specs:
18' Span
Spacing: 4' o.c
Live Load = 40 psf (code stipulated)
Dead Load = 10 psf (pretty typical)
Timber Species and Grade: Eastern Hemlock, No. 2
Category: Posts & Timbers (6x8): Bending Strength: 600 psi
Category: Beams & Stringers (6x10 and 6x12): Bending Strength: 750 psi
Modulus of Elasticity (deflection) 900,000 psi
Deflection Limits: L/360 (code stipulated - floor loads)

For these specs, a 6x8 No. 2 Hemlock fails big time for bending. The max length of this timber under these conditions should be no more than 11'. So, yeah, way undersized.

A No. 2 Grade 6x12 Hemlock spaced 4' o.c will be Ok for both deflection and bending. In fact, it's perfectly suited for exactly 18' span for these loading conditions and 4' o.c. spacing.

You could use 6x10 members, but they would have to be spaced no more than 24" o.c.

You could also use 6x8 members, but they would have to be spaced no more than 12" o.c.

I think you are quite correct on installing a girder.

I'd be more than happy to provide you with exact calculations if you're interested. Send me an e-mail.

And how will these new larger timbers be joined to the cross sills?

It has been said that there are other faults with the frame, care to share what some of them are?

Tim

Other problems with the frame, This is a design that utilizes 3/8" lags instead of pegs. The only joints in it are lap joints.

The person who sold the kit claims the capability to cut 26' of timbers but I have walls that are 18' with 12' top and bottom plates, this basically means I have walls that want to pivot on this lap joint.

With all of the above joints if you followed there layout of 4' on center there are no posts or "studs" that fall under these lap joints to support them and carry the load down to the foundation.

We had to have numerous calls regarding inventory and site meetings because we had timber labeled on one end to go in one location and on the opposit end of the same timber they where labeled to go some where else.

The skin panels that arrived could have been used for rocking chair runners they where so warped. We installed one wall and it looked like a vertical view of the ocean it was so wavy.

And much more.