Saggin Flat roof

[DrCrash]

If a flat roof is bad.
Like on a BenRoy.
Then whut is the fix.

No no no some one will say
difernt profile or dont make it flat.

Question is what is the
problem with a flat roof?

What is the fix?

[DrCrash]

25 Hits and not one reply
I am a thread killer

[DrCrash]

Was thinking aluminum channel with oak or
hardwood core to keep roofline from
sagging.

[DrCrash]

I am really boared !
Any one like my new pic?

[Mary K]

Pretty!!

The problem is that water catches on the top, IF you have Trim up there like I did. I did have a leak and had to fix it...or I hope I fixed it.

[starleen2]

After building two flat roofers – I have learned that they eventually sag due to gravity, rain, and/ or snow build up. The next build I put a slight bow and did not have a sagging problem – If your roof has excessive sagging due to warping of plywood and struts, then the only fix is a roof replacement. However a solution to the flat roof dilemma is to build it with a slight angle to the rear to Keep water from puddling – I usually just jacked up the front end a little bit to allow rain water to run off.

[DrCrash]

was thinking of putting a slight bend in the channel, to keep a
natural bow in the roof.

No Mary I wont have any trim on the top or sides to trap water
up there.

good tip on keeping in nose down for storage as not to
trap snow and water up there.

[Barry J]

I am building a BenRoy now i hope I don't have a problem with water.

[48Rob]

Nice picture...good smile...


The "problem" with a flat roof is that water stands on it.
A flat roof that sags is even worse, as it will hold more water.

Surface tension causes water to puddle, or bead.
The same as water beads and stands much taller than the surface of a waxed car.
Water on a trailer roof can stand much higher than one would think water on a "wet" surface would.

So, the problem comes in when the water stands on the flat roof and becomes tall/thick enough to reach the sealed roof to sidewall trim joint, screw heads, or sealed joints around the protrusions, like roof vents.
The slightest break in the seal will allow water to find its way in.
Once it has a path, capillary action will continue to draw water into the hole until the supply is exhausted.
Over a long winter, this is a very bad thing...

The fix?

Find a way to keep the roof pitched at a steep angle as has been suggested so the water is forced to run off before any appreciable thickness can develop (not practical during a thunderstorm while camping) or be darn sure you have everything sealed well, and recheck the seal every year.
Storing the trailer, if outside in a snow/freezing climate, at a steep angle is wise.
Snow, ice, or both can accumulate, thaw, freeze, thaw, refreeze, and over time accumulate to several inches thick.
Besides the extra weight the roof wasn't designed for, the melting snow or rain on top of the thick ice may now be high enough to seep in to the trailer through the roof vent, which is not designed to be waterproof like a submarine...

While there are a huge number of flat roofed trailers that are now firewood because of (poorly sealed/un maintained) flat roofs, there are also many survivors still in use, because the owners took a few minutes a year to maintain them...

If you take the time to understand a flat roof, there will be no need to fear them.

That said, flat roofs are not the best thing man ever invented...

Rob

[Miriam C.]

25 Hits and not one reply
I am a thread killer

Welcome threadkiller! Flat roof doesn't have to be completely flat and the flat part for the vent doesn't have to be on a level plane. Confused yet.

I have a beautiful lake on mine. Call it Aunti's fishing spot.

[DrCrash]

What do you think of the aluminum channel idea there Rob?

Or is it overkill?

[S. Heisley]

Sorry, DrCrash.

I suspect everyone is stunned by your new avatar picy!
It's pretty funny!

Are you serious? Do you really have a sagging flat roof?

[48Rob]

Doc,

Aluminum channel isn't a bad idea, especially with a stiffener in it.

I think If I was going to go to all the trouble though, I'd use steel.
Much less likely to bend/sag when someone gets on the roof.
Not that much more weight for the size, but a lot more strength.

I don't know if your trailer is already built, but a good builders trick is to hand pick the roof support lumber.
Most every one does, searching for perfectly straight pieces.

Normally this is a good thing, but for the roof supports, it is better to choose pieces that are bowed up to an inch in the middle of the span.
As you build the trailer, the bow is placed "up".
Over time, the bow will relax a little, and maintain a slight crown, or worst case, will end up flat.

If you start with perfectly straight, over time it will bow the other way...

I use Oak, stood on edge for roof supports.
While some (factory) builders used supports turned flat, it was, and still is a very bad idea.
There is almost no strength to the wood when laid flat, and it will without a doubt cause the roof to sag.

The size depends on the span, but for my 7 foot wide trailer, 3/4" x 2" pieces ripped from very straight grain stock, with no knots supports my 190 pounds while on the roof, which is no more than two 1/8" sheets of plywood.
I have "trim" on my roof also, but have cut small "channels" near the ends to allow water to escape.

On the 1948 travel trailer I did a few years ago, the roof was very flat, for about 10 feet.
It held water, even with upward bowed roof supports.
Nothing much could be done to make the flat roof anything but what it was.
So, the next obvious answer was to make sure that there was nothing that could leak.
I sealed everything well, and despite having standing water each time it rained or we had a heavy dew, there were no leaks.

Rob