Houseboat roof

I am building a 34' pontoon houseboat with a 20' by 8' cabin. I have 1 and 3/4" light steel square tubing, on 16" centers for the roof. What light but strong enought, to support at least 4 people, products do I need to cover and waterproof it? I was thinking of 3/8" plywood with a one piese rubber type roofing. I need to keep the weight down. Any ideas?

 

Your materials are way too weak to support 4 people on an 8 foot span with 3/8 flooring on 16 inch centers. Not to mention that on an 8 foot wide boat 4 200 pound people on the roof may capsize the boat. Your light square steel tubing may work if you put a slight crown (curve) in it and reinforce with a straight piece attached to the ends. Your floor really needs to be 5/8 minimum and 3/4 is better. You don't want a foot coming through the ceiling.

 

Jonathan is correct that bit of roof "crown" will add a great deal of additional strength to the structure. This is a curve running outward toward the sides of the roof. An 8' span would be well served with a 4 to 6 inch crown (6" taller down the centerline, sloping to the sides) which will also shed water quickly, rather then let it pool. I think your roof beam size and spacing is adequate, but again, the substrate is thin. Would you walk four of your big bellied buddies around a house with 3/8" plywood floors? Me neither. Some stringers running fore and aft (front to back) tying these roof beams together would help a bunch too. Some 1" angle stock, welded to the beams on 16" centers would be nice (more weight) or some 1" flat stock laid on top to save weight.

If your roof beams don't have a crown, cut a piece of 2 x 6 to the curve and lag it from the inside of the boat, through the roof beams. This becomes your nailer, with built in crown.

If the rest of the structure shows this type of engineering, your wise trying to keep the weight down. A laminated roof of three layers of 5 ply 1/4" plywood, in concert with the roof crown, may be strong enough for light traffic, but no dancing or parties (Lowes/Depot 1/4 ply can't hack it). 4 layers will be better, but the weight will be higher. This will need be glued and screwed in place (each layer) making a sandwich of plywood, molded to shape. The glue should be at least a type 1 structural adhesive (liquid nails doesn't cut it) preferably epoxy. Stagger the butt joints as much as possable, from one layer to the next.

A roof, generally doesn't need this level of reinforcement, but if it will have foot traffic, then it's a floor too, needing be built like one. The covering could be a rubber roof membrane, but they aren't designed for foot traffic either. Fiberglass, set in epoxy and painted is a good choice here, maybe "cool deck" could work, if there wasn't much movement in the substrate. Whatever you use, it will need to tolerate UV (sunlight) and foot traffic, so plan material selections around this. There are higher tech ways to make a very light, strong roof, but the cost and difficulty can sky rocket.

 

weight, not roof height mentioned. on open roof beams you may hit your head so often you requet having kept the cost down

 

The roof on my house boat is 1/2 Ply. It is a stressed meber with a substantial crown. The whole things is of course covered with heavy fiberglass about 1/4 thick. Then has textured paint for grip. You can see the crown a bit in the first photo.
http://www.houseboatingworld.com/forum/forum_posts.asp?TID=1900&PN=1

 

I agree with the crown effect - but why wouldn't chequer plate aluminum do the trick better? (i.e lighter and stronger)?

Just an idea!

Cheers!

 

Have you ever walked on any type of diamond type of plate when it is wet and crowned? We are settling out of court because of how slippery it becomes. Add open water gusts of wind? Metals are slippery when wet. Keep the floor flat just like the main deck of the boat. You will have the same pounds per square foot as the main deck. People go where they want to on houseboats. 2nd floor is no different.

 

All the time, most casting decks on alloy fly fishing boats downunder are crowned to shed the water, and the chequer plate forms a nice grip - lots of alloy recreational boats use the material for it's wet grip properties.

Anything wet can slip - some slip better than others...wet fibreglass ain't so non skid, I'd back the chequerplate alloy against anything else mentioned in this thread so far.

Maybe if your in a place where hot sun heats the roof to uncomfortable temps it might be a P.I.A. - but otherwise I'm betting it's at least worthy of consideration (or I wouldn't have mentioned it!).

Cheers!

 

Standard roof construction for houses in the US uses 1/2" plywood on 24" centers, and can support 4 people, though obviously aren't meant for constant usage. Your 16" centers should be pleanty adequate for 1/2" ply, especially with a crown. Use a higher grade of plywood with more plies - makes a huge difference in strength.

Forget about the single-ply membrane. It can't take the traffic. Epoxy/glass is the way to go.

If you go with aluminum (that's what my boat has), you might consider smooth plate and add a nonslip surface. Likewise on GRP.

A pontoon boat (catamaran design) of the size you're considering should be plenty stable for 4 people on the roof. My 28' cat has had 6 people on the roof, all leaning over one side to watch whales and the heeling has been minimal.

 

I have converted to snap in place, marine carpet, as a great no slip floor surface. For the expence of the snaps put in the floor and any UV carpet, it is the safest, even with wet Mayonase? on it. Just make sure all the snaps holes are sealed correctly. A fall on it does no damage to skin.

 

Thanks for the help.

I believe we are going to use 1/2" 4 ply treated plywood with an one piece,aluminum .040 thick. We will put a white non skid surface on it. No crown because, you cannot bend 2" square steel tubing accurately without a high dollar jig bender. The roof will have several inside wall supports in the cabin. Just adding wood on top would add no extra support. We have been thinking about the Rhino type spray on rubber for the non skid surface. It seems to be tough in the pick-up truck beds. We will also use a biscuits joints on the plywood to prevent warpage. Thank for your ideas.

 

Check with the manufacturer regarding surface prep. What sticks to a pickup bed might not stick to aluminum. You might need to treat the surface and/or use some type of primer.

 

i've been 'noodling' building a housboat for a while. in my research,
i found this site: http://www.lockdry.com/features.htm
which may answer your need for a watertight loadbearing roof that is simple to install. http://www.lockdry.com/lockdrydemo.htm
tested to 240psf live load , about 1# per sqft (i weighed a sample on a certified scale),
costs $7us per square foot as of Feb 2005, and comes in four colors.

the only drawback: the product is aluminum and your 'rafters' are steel.

 

Deering, Is alaska still part of the US? Standard roof construction on 2' centers is 5/8 t&g or 5/8 square edge ply with clips.

 

Last time I checked Alaska was part of the US, but maybe that's changed...?

In fact that may have already happened since we base our house building codes on the INTERNATIONAL Residential Code. Yoe are correct - my statement of roof sheathing being 1/2" on 24" centers was incorrect. Actual code calls for 15/32" plywood. That's LESS than 1/2" here in Alaska.

Might you be thinking of commercial construction?