Deck scantlings/loading.

Ask questions before buying our plans or request a new design. Anybody can post here
jbo_c
Very Active Poster
Very Active Poster
Posts: 1046
Joined: Sat Jun 30, 2007 8:51 pm
Location: Gainesville, GA

Deck scantlings/loading.

Post by jbo_c »

This is probably a little like asking “How long is a rope?”

I don’t plan to occupy the cabin roof, but I can see where it might occasionally be handy, or maybe nice for lounging if we chose.

Area is 7’x6’. What “joist” spacing and surface thickness would I need? I know the requirements for a house, but that would be significantly overbuilt for a boat in my estimation.

Will be glassed outside and can be inside if needed.

Jbo

User avatar
Jaysen
* Bateau Builder *
* Bateau Builder *
Posts: 6497
Joined: Wed Aug 05, 2015 7:59 am
Location: St Helena Island, SC
Contact:

Re: Deck scantlings/loading.

Post by Jaysen »

This is going to be an odd comparison but might give you an idea.

I built a v12. Hull is 1/4" and has 12oz glass. The largest bottom span is a section about 28" long and 24" wide (I'll measure and update this size once the rain lets up). I can plop my 210lbs on that section and you can't "feel" it flex. It does flex a little you just can't feel it.

That is my way of saying that my experience is that a 24x28" section of 1/4" meranti gassed with 12oz on the outside of the arch can support a 210lb fat guy.

I would think 18" spans made of 3/8" ribs would give you a large margin for safety.
My already completed 'Lil Bit'. A Martens Goosen V12 set up to sail me to the fishing holes.
Currently working on making a Helms 24 our coastal cruiser.
“Mark Twain/Samuel Clemens” wrote:Eat a live frog first thing in the morning and nothing worse will happen to you the rest of the day.
Jaysen wrote: Mon Apr 29, 2019 3:44 pm I tried to say something but God thought I was wrong and filled my mouth with saltwater. I kept my pie hole shut after that.

jbo_c
Very Active Poster
Very Active Poster
Posts: 1046
Joined: Sat Jun 30, 2007 8:51 pm
Location: Gainesville, GA

Re: Deck scantlings/loading.

Post by jbo_c »

Guess I left out an important detail. Max “joist” span will be 6’ due to overhang.

And to make sure I’m clear - NOT a party deck in the least. Literally just to hop up and lay back or maybe if necessary to reach something for some reason(and don’t know what that might be). Would rather plan and not need it than punch through it one day in a pinch. :)

Jbo

jbo_c
Very Active Poster
Very Active Poster
Posts: 1046
Joined: Sat Jun 30, 2007 8:51 pm
Location: Gainesville, GA

Re: Deck scantlings/loading.

Post by jbo_c »

Thanks, Jaysen.

That’s a good reference point.

I was thinking maybe 18” would be sufficient, but wasn’t sure that would be enough with 1/4” skin. I’d prefer to keep the skin at 1/4” even if it meant more joists.

Jbo

User avatar
Jaysen
* Bateau Builder *
* Bateau Builder *
Posts: 6497
Joined: Wed Aug 05, 2015 7:59 am
Location: St Helena Island, SC
Contact:

Re: Deck scantlings/loading.

Post by Jaysen »

I honestly think you can go wider. Hopefully Jacques or Ried (he's really up on the materials) can provide a more official response.

My 1/4" feel solid with me on it. I'm not jumping on it mind you, but it doesn't need the water to feel strong.
My already completed 'Lil Bit'. A Martens Goosen V12 set up to sail me to the fishing holes.
Currently working on making a Helms 24 our coastal cruiser.
“Mark Twain/Samuel Clemens” wrote:Eat a live frog first thing in the morning and nothing worse will happen to you the rest of the day.
Jaysen wrote: Mon Apr 29, 2019 3:44 pm I tried to say something but God thought I was wrong and filled my mouth with saltwater. I kept my pie hole shut after that.

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: Deck scantlings/loading.

Post by fallguy1000 »

Point loading is the biggie. So, if you need the roof for maintenance; you can go on it and be super careful, if you send a couple gals up there and they start dancing; the loading becomes dynamic and worse than a point load.

I setup my roof to be able to handle snow loads. And it might be too heavy now..but I did.

My rooftop spans 8' by about 12'. The span changes everything. My beams are 1.5" deep and 2.5" wide and elliptical and on 11" centers.

For a 6' span; you can reduce the center spacing. An arch supports more than a flat. But an arch is hard to sun on.

Once you determine if the roof is arched or elliptical, you can determine better the beams. Perhaps you will jist slant it forward so rain heads forward and tanning is less uncomfortable.

I'd say for a lightweight plywood roof, glass skin on back of 12oz and beams on 16-20" centers. Most of this type of thing is self design. So you glass a piece of plywood and then put some beams up on 2x4s and then walk on it to decide. But probably on the order of 1.5"x1.5" would be close... for 7' of them maybe 4-5 beams or so by my gut

I did not glass my plywood skins on the bottom of my roof and punched a hole in one with my knee before the glasswork on top was done, for example. And I was being careful. So glass helps a lot..
My boat build is here -------->

viewtopic.php?f=12&t=62495

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: Deck scantlings/loading.

Post by fallguy1000 »

My ceiling is beams with 4mm ply above with 12mm foam core above that with 17oz glass above that. I think glassing the ply panels would have allowed me to use a wider span, but the panels had two seams...so I did not.
My boat build is here -------->

viewtopic.php?f=12&t=62495

jbo_c
Very Active Poster
Very Active Poster
Posts: 1046
Joined: Sat Jun 30, 2007 8:51 pm
Location: Gainesville, GA

Re: Deck scantlings/loading.

Post by jbo_c »

This will have some curvature. Undetermined at this point how much. That choice will be based on aesthetics(as much as my caveman brain allows). If it is too much for comfortable lounging and we end up using it much, I will make pads that compensate for the curvature to use when wanted.

Jbo

fallguy1000
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 10198
Joined: Tue Jan 12, 2010 12:25 am

Re: Deck scantlings/loading.

Post by fallguy1000 »

The way to make beams for curvature is to laminate them with thickened epoxy or sawcut them from hardwood if they are gonna show from below.
My boat build is here -------->

viewtopic.php?f=12&t=62495

JSHaley
Frequent Poster
Frequent Poster
Posts: 18
Joined: Mon Dec 13, 2021 8:13 am
Location: Rochester, NY

Re: Deck scantlings/loading.

Post by JSHaley »

Is your answer below you? Spacing that supports your deck?

Also, covering your beams in FG may stiffen them up a bit. What about FG's cousin Carbon Fiber tape?

Post Reply

Who is online

Users browsing this forum: Netpackrat and 2 guests