Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Building & Construction

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 07-02-2013, 07:13 PM   #1
Newbie
 
Join Date: Jul 2013
Posts: 17
Share |
Default

spanning 20 feet on a deck


Hi everyone, first off my apologies if this is in the wrong forum. I have just a quick question.

What I have is a 20 feet by 12 feet deck attached to my cabin. I have the floring and everything in place my question is on my corner posts as well as my posts on the floor are 4X4 on 4 foot by 4 foot spacing.

I know a little over kill, I want to know if I can use a 2x8 laminated beam to span 20 feet from corner to corner to maximize my view of the lake, or do I need to go 2x10 or perhaps 2x12? Any thoughts and thanks in advance and once again sorry if this is in the wrong forum.

Bartk is offline   Reply With Quote
Old 07-02-2013, 09:01 PM   #2
Member
 
GBrackins's Avatar
 
Join Date: Apr 2012
Location: Fairhaven, Massachusetts
Posts: 2,807
Default

spanning 20 feet on a deck


Bartk, Welcome to the Forum!

I'd suggest reviewing this document: http://www.awc.org/publications/DCA/DCA6/DCA6-09.pdf

this is the American Wood Council's "Prescriptive Residential Wood Deck Construction Guide." span of framing members is not only based upon the span length, but the grade and species of the wood members.

this guide will allow you to determine the size of beams and joists based upon their length as well as the species of wood.

Hope this helps!

Post back with any questions.

__________________
Gary

"You get what you pay for, and sometimes free costs more!"
GBrackins is offline   Reply With Quote
Old 07-02-2013, 10:12 PM   #3
Newbie
 
Join Date: Jul 2013
Posts: 17
Default

spanning 20 feet on a deck


thanks for the reply, after looking at it I don't even think it will be possible to do, even with bracing. bummer. I wonder if I sandwich a piece of 1/4 or 3/8 steel between the beams if it would support it or not. Any thoughts on that. Thanks
Bartk is offline   Reply With Quote
Old 07-02-2013, 11:02 PM   #4
Remodel and New Build GC
 
MTN REMODEL LLC's Avatar
 
Join Date: Sep 2010
Location: Colorado @ 7651'
Posts: 2,567
Default

spanning 20 feet on a deck


Quote:
Originally Posted by Bartk View Post
thanks for the reply, after looking at it I don't even think it will be possible to do, even with bracing. bummer. I wonder if I sandwich a piece of 1/4 or 3/8 steel between the beams if it would support it or not. Any thoughts on that. Thanks
Maybe an engineer can calculate.... or how about a steal beam?
__________________
Never stop learning (xcep fer speling en typeing)
MTN REMODEL LLC is offline   Reply With Quote
Old 07-02-2013, 11:08 PM   #5
Member
 
GBrackins's Avatar
 
Join Date: Apr 2012
Location: Fairhaven, Massachusetts
Posts: 2,807
Default

spanning 20 feet on a deck


got a sketch of your deck you can post?
__________________
Gary

"You get what you pay for, and sometimes free costs more!"
GBrackins is offline   Reply With Quote
Old 07-02-2013, 11:31 PM   #6
Newbie
 
Join Date: Jul 2013
Posts: 17
Default

spanning 20 feet on a deck


No sketch but what I have is a 12 foot by 20 foot deck. On 4 foot by 4 foot centers I have 4x4 posts supporting the deck.

I am wanting to go across the front of the deck spanning 20 feet so I can have an unobstructed view. I know that I could span 12 feet but I have not heard of spanning 20 feet.

I am thinking what I am going to have to do is either use 2x8 or 2x10 and have to sandwich some metal in between the boards.

Thanks once again for all the replies.
Bartk is offline   Reply With Quote
Old 07-02-2013, 11:50 PM   #7
General Contractor
 
CENTERLINE MV's Avatar
 
Join Date: Jun 2013
Location: Martha's Vineyard, MA
Posts: 51
Default

spanning 20 feet on a deck


A picture, sketch, or drawing would really help. I'm not understanding the 4' x 4' centers you have a post? Not following the logic.
CENTERLINE MV is offline   Reply With Quote
Old 07-03-2013, 01:14 AM   #8
Newbie
 
Join Date: Jul 2013
Posts: 17
Default

spanning 20 feet on a deck


Ok. So you will have to forgive my crude sketch. Please let me know if you have any questions about it.
Attached Files
File Type: pdf deck sketch.pdf (55.0 KB, 50 views)
Bartk is offline   Reply With Quote
Old 07-03-2013, 05:12 AM   #9
Member
 
Join Date: Apr 2012
Location: UK
Posts: 710
Default

spanning 20 feet on a deck


Sketch is fine, though it looks like a forest beneath that deck!

Seriously; assuming your beam would be supporting one-half the load up to the next row of columns back, the deck area supported by the beam would be 40 sq ft, say about 2000 lbs live load plus dead load.

Even with a couple of 2x12s, with that load you might find that deflection (sag) is an issue. Also, there would be considerable eccentricity of the load on the end 4x4s, which might overstress them.

You can sandwich a steel plate between the timbers (that's a 'flitched' beam) but you would need an SE to detail this for you.

Last edited by tony.g; 07-03-2013 at 07:36 AM. Reason: pour speling
tony.g is offline   Reply With Quote
Old 07-03-2013, 08:56 AM   #10
AHH, SPANS!!!
 
Join Date: Apr 2012
Location: Durham NC
Posts: 1,641
Default

spanning 20 feet on a deck


call your local lumber supply give them your dimensions and have them spec out an exterior engineered beam and possible attachment specs as well.
hand drive is offline   Reply With Quote
Old 07-03-2013, 09:07 AM   #11
Residential Designer
 
AndyGump's Avatar
 
Join Date: Sep 2010
Location: Orange County CA.
Posts: 1,258
Send a message via Skype™ to AndyGump
Default

spanning 20 feet on a deck


On your sketch, if the lower horizontal line is the deck what do the upper horizontal/hatched lines represent? A cover?
How would taking out one row of the 4x4s help with the view at all? Would there not still be all the other rows of 4x4s to be in the way?

What is your location and why do you want to embed the posts in to concrete?

Andy.
__________________
Residential Drafter/Designer
www.draftinginoc.com
AndyGump is online now   Reply With Quote
Old 07-03-2013, 06:18 PM   #12
Newbie
 
Join Date: Jul 2013
Posts: 17
Default

spanning 20 feet on a deck


Thanks for the replies, there are no 4x4's continuing up to the roof, minus the ones on the left side and the right side of the deck (top view). Currently there are the ones across the front of the deck, bottom side (top view also). we would just like to remove the ones across the front so there would be an unobstructed view.

Also pertaining to the live load and dead load. We are planning on putting a metal/tin roof on the top of it to reflect the sun. The only live load on the roof would be maybe a porch swing back close to the cabin, so I'm thinking there isn't much of a load for the roof at all.

We do plan on using 2x6's for the roof and then along the outside of the deck 2x6 possibly 2x8. Me and dad always "over engineer", just didn't know if a 2x8 flitched beam would suffice.

Thanks once again and now I know what a flitched beam is.
Bartk is offline   Reply With Quote
Old 07-03-2013, 07:47 PM   #13
Member
 
robertcdf's Avatar
 
Join Date: Nov 2005
Location: Colorado Springs, Colorado
Posts: 655
Default

spanning 20 feet on a deck


So you're wanting to span the opening of 20' with a ROOF not a deck... Just use trusses you can span some great distances with that, this is a 20' span I think.
robertcdf is offline   Reply With Quote
Old 07-03-2013, 07:58 PM   #14
Remodel and New Build GC
 
MTN REMODEL LLC's Avatar
 
Join Date: Sep 2010
Location: Colorado @ 7651'
Posts: 2,567
Default

spanning 20 feet on a deck


Quote:
Originally Posted by robertcdf View Post
So you're wanting to span the opening of 20' with a ROOF not a deck... Just use trusses you can span some great distances with that, this is a 20' span I think.
Robert... What kind of truss is that....?????

I can't see a scissor and no inverted hip involved.... just wondering.... looks cool.

TIA

Best
__________________
Never stop learning (xcep fer speling en typeing)
MTN REMODEL LLC is offline   Reply With Quote
Old 07-03-2013, 08:22 PM   #15
General Contractor
 
CENTERLINE MV's Avatar
 
Join Date: Jun 2013
Location: Martha's Vineyard, MA
Posts: 51
Default

spanning 20 feet on a deck


I've used these a bunch of times.

http://woodbywy.com/document/tj-7102/

The grid of 4x4 posts has me baffled though.

CENTERLINE MV is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Cedar deck help mickbiv Painting 11 08-08-2013 09:21 PM
Miscellaneous deck questions NewHomeDIYGuy Building & Construction 38 09-17-2012 02:41 PM
Deck Staining thread but I am desperate- please help mickbiv Painting 3 09-08-2010 12:28 AM
Leveling a deck denemante Building & Construction 10 08-24-2010 08:11 AM
Sagging concrete pool deck Immolate General DIY Discussions 1 06-11-2008 09:16 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.