Roof Guttering For Rainwater

[tutsiwarrior]

we had a flash rainstorm tonight and I went to see how the drainage for my magnificent new terrace was holding up...the first opportunity. There are 3 shophouses in a row and 2 drained well as I supervised the design for them. The third was built independently and accumulated water at an alarming rate...the angle of the concrete floor was not sufficient. The back end of these houses is not designed to carry the steel and concrete load for the terrace and lots of non draining water after a storm worries me.

you be the engineer...is it better to layer the offending concrete so that the drainage is better or to put up a roof gutter across the 3 houses? The gutter will require a discharge pipe that would be unsightly and would have to be supported in 'sky hook' fashion but would take less work and effort than to raise the required angle on the concrete floor to get proper drainage.

Does roof guttering require expertise or could I get the crew to buy the materials and simply put the mother up?

anyone?

[Crossy]

What's under the terrace??

Typical Thai fix would be to locate the lowest point where water accumulates and core a drain through, water gushes away and becomes an SEP (Someone Else's Problem).

[Farma]

The last guttering I had installed was done by the village plumber. I supplied the tin sheeting.

He bent the tin into shape and installed it in 1 day. That was the front and rear of a large house and included downpipes into large water pots at the back of the house.

It was a fair while ago so I don't have up to date costs.

[chownah]

The guttering needs to be big enough to handle the water flow developed and it needs to be sloped so that the water runs off fast enough. The structure needs to be strong enough to hold the weight of the gutter system WHEN IT IS FULL OF WATER TO THE BRIM because it is entirely likely that at some point in the future it will plug up and it WILL fill up to the brim. It sounds like your situation is a typical one so the local expertise is hopefully adequate to handle the situation....but you never know when someone claims to know how to do it and really they don't.

You say you are worried that the weight of the standing water will overload the structure....how deep does it get at its worst? If you know the surface area of the standing water and its maximum depth then you can calculate the weight....like this theoretic scenerio: If a 2 metre by 4 metre terrace floor has a 5 cm maximum depth of water then you convert all the measurements in to the same units first (either cm or metres) and then multiply them together...I'll use cm.....200 x 400 x 5 = 400,000. What does this weigh?......well, one cubic cm of water weights one gram so you have 400,000 grams which is 400 kg.

400 kg is the weight of about 8 adult people....if 8 people were on this theoretic terrace would the owner worry that it would collapse? If this theoretic terrace was flooded with 5 cm of water it is unlikly that there would be anyone out there on it so it is unlikly that you would have both the weight of 8 people AND the weight of the water.....etc.

I hope you get the idea...

Chownah

[lopburi3]

The local tin shop normally handles this project as there is a lot of cutting/shaping and soldering involved - as well as attachment to roof. They should know how to do and not be the local ditch digging crew.

Galvanized steel does not last long in our experience. SS is much more expensive but in the 10-15 years we have had it there have been no issues.

But if land drain can not take the amount of water/keep it off your terrace, you are back to needing a flood barrier to keep it out of shop/house anyway.

Those storms can drop a whole lot of water in a very short time! We have a good slope (for Bangkok) but in extreme rain can have several inches of water making a mad rush down the drive.

[tutsiwarrior]

The guttering needs to be big enough to handle the water flow developed and it needs to be sloped so that the water runs off fast enough. The structure needs to be strong enough to hold the weight of the gutter system WHEN IT IS FULL OF WATER TO THE BRIM because it is entirely likely that at some point in the future it will plug up and it WILL fill up to the brim. It sounds like your situation is a typical one so the local expertise is hopefully adequate to handle the situation....but you never know when someone claims to know how to do it and really they don't.

You say you are worried that the weight of the standing water will overload the structure....how deep does it get at its worst? If you know the surface area of the standing water and its maximum depth then you can calculate the weight....like this theoretic scenerio: If a 2 metre by 4 metre terrace floor has a 5 cm maximum depth of water then you convert all the measurements in to the same units first (either cm or metres) and then multiply them together...I'll use cm.....200 x 400 x 5 = 400,000. What does this weigh?......well, one cubic cm of water weights one gram so you have 400,000 grams which is 400 kg.

400 kg is the weight of about 8 adult people....if 8 people were on this theoretic terrace would the owner worry that it would collapse? If this theoretic terrace was flooded with 5 cm of water it is unlikly that there would be anyone out there on it so it is unlikly that you would have both the weight of 8 people AND the weight of the water.....etc.

I hope you get the idea...

Chownah

yeah, I get the idea...last night's rain was moderate and not the usual deluge you get during the rainy season where in a badly drained area the accumulation could add a load of over 1000kg to the structure (using your same volume calculation) very quickly...

however, I think that my concern regarding last night's example is premature...the area where we had the accumulation was in the new shophouse area that is better designed to take the load. The area for the two existing shophouses drained nicely and that was where I had the worry. The terrace there was built over the two kitchens the columns for which previously only supported the roof...now we got steel, concrete slabs and finishing concrete on the existing support structure which probably overloads it already...

however, I will look into a gutter along the roofline above the terrace...can't cost too much to build...

thanks for your advice, folks!

[chownah]

yeah, I get the idea...last night's rain was moderate and not the usual deluge you get during the rainy season where in a badly drained area the accumulation could add a load of over 1000kg to the structure (using your same volume calculation) very quickly...

So this is equivalent to about 20 adults on your terrace.....would you feel insecure with that many people on your terrace? What was the maximum depth you used in your calculations?

Chownah

[tutsiwarrior]

yeah, I get the idea...last night's rain was moderate and not the usual deluge you get during the rainy season where in a badly drained area the accumulation could add a load of over 1000kg to the structure (using your same volume calculation) very quickly...

So this is equivalent to about 20 adults on your terrace.....would you feel insecure with that many people on your terrace? What was the maximum depth you used in your calculations?

Chownah

the terrace is trapezoidal but roughly 3 x 10m and using a 2 - 3 cm rainwater depth results in a volume that would give roughly 1000kgs undrained rainwater load...but I ain't running a partyhouse here and would never expect 20 adults at one time...undrained rainwater is the hazard. As I explained the existing two shop houses' support for the terrace is dodgy...I'm not sure that the kitchen columns we ever piled as the roof was the only anticipated load. But that area drained OK from last night's observation.

We shall see when the rains come next year...on the terrace sipping my vodka and then a horrible creaking sound then 'geronimooooh'...

[The Skipper]

Sure, a gutter will help but the real problem is the contractor that does not know that water runs downhill, or the person that approved and paid for the work.

[tutsiwarrior]

Sure, a gutter will help but the real problem is the contractor that does not know that water runs downhill, or the person that approved and paid for the work.

yeah...and shit floats to the top...the area where the problem is was not designed for proper drainage, it got away from me...when we extended the terrace across all three houses I made sure that the drainage was suitable and this was demonstrated with the rainstorm.

not to worry...I'll get one of the family retainers to push the accumulation out the drain holes in the wall when the time comes...or one of the nieces...

tutsiwarrior hungover and vicious... 'grab that broom, goddamit...sweep that fuggin' water out dem fuggin' holes, goddamit...DO IT NOW or I'll paddle yer ass goddamit...'...'but uncle tutsi, it's 3 am and I have school tomorrow', JUST DO AS I TELL YA, goddamit...

whadda demon...rainwater problems and family drama...

[chownah]

Concerning your question about layering the concrete to improve drainage....I'm assuming by "layering" you mean to put another layer of concrete on top of the existing floor to give it more slope.

General rule of thumb for engineering is that 2% slope is good for these types of drainage situations. This means that with a 3m wide terrace that is flat to start with you will have 6 cm of concrete/mortar at the thick edge and 0 cm (zero cm) thickness at the thin edge. Usually you don't go to zero cm but we'll assume this best case scenerio. This means that the average depth of the concret overlay is 3 cm which is the same thickness of water that you were using in your estimate for the depth of the pool during a downpour. Since concrete is roughly 2.4 times as heavy as water then clearly the concrete will give you 2.4 times the weight of the water so it is obviously not a good solution if you are trying to minimize the load on the terrace floor.

Chownah

[tutsiwarrior]

Concerning your question about layering the concrete to improve drainage....I'm assuming by "layering" you mean to put another layer of concrete on top of the existing floor to give it more slope.

General rule of thumb for engineering is that 2% slope is good for these types of drainage situations. This means that with a 3m wide terrace that is flat to start with you will have 6 cm of concrete/mortar at the thick edge and 0 cm (zero cm) thickness at the thin edge. Usually you don't go to zero cm but we'll assume this best case scenerio. This means that the average depth of the concret overlay is 3 cm which is the same thickness of water that you were using in your estimate for the depth of the pool during a downpour. Since concrete is roughly 2.4 times as heavy as water then clearly the concrete will give you 2.4 times the weight of the water so it is obviously not a good solution if you are trying to minimize the load on the terrace floor.

Chownah

yeah, but the problem is localised to a 3 x 3m area of the 3 x 10 total area plus the builder has finished the concrete and another layer would be a big mess. Most of the accumulation comes from the roof so some guttering might do the trick plus bullying whomever is around to sluice off the water after a deluge. I'll put up a sign DO YOU LIKE YOUR TERRACE??? BE CAREFUL THAT THE RAINWATER DOES NOT DESTROY IT sort of like the public garden signs that the drunken protagonist in Malcolm Lawry's Under the Volcano would hallucinate about in delirium tremens...

a nice touch, tutsi's drunken literary terrace...maybe I'll invite Gertrude Stein, Ernie Hems and some of the other pals from the salon over for iced tea...

Edited December 10, 2006 by tutsiwarrior

[chownah]

yeah, but the problem is localised to a 3 x 3m area of the 3 x 10 total area

The same analysis applies to the smaller area...meaning that the concrete will be about 2.4 times heavier than your estimated flood. Sounds like you've decided on either the do nothing option or the gutter option. I usually advise people to keep their minds out of the gutter but in your case I'll make an exception....so....why don't you forget inviting those poseur people you're considering and go immediately to the gutter level ........like Sid Vicious and friends.

Chownah

[tutsiwarrior]

yeah, but the problem is localised to a 3 x 3m area of the 3 x 10 total area

The same analysis applies to the smaller area...meaning that the concrete will be about 2.4 times heavier than your estimated flood. Sounds like you've decided on either the do nothing option or the gutter option. I usually advise people to keep their minds out of the gutter but in your case I'll make an exception....so....why don't you forget inviting those poseur people you're considering and go immediately to the gutter level ........like Sid Vicious and friends.

Chownah

are we havin' a bad day clownnah?...if my pal, the 'ol Nobel Laureate Ernie heard you callin' him a poseur he would box yer ears...

Sid?, nah... no good for the terrace...he'd disturb the neighbors...

[chownah]

are we havin' a bad day clownnah?...if my pal, the 'ol Nobel Laureate Ernie heard you callin' him a poseur he would box yer ears...

Sid?, nah... no good for the terrace...he'd disturb the neighbors...

I'm having/had a great day!!! Absolutely!!! Well, your laureate Ernie might TRY to box my ears but then my gutter scum Mr. V might just intercede with some projectile.........vomit of course.

Chownah

[tutsiwarrior]

are we havin' a bad day clownnah?...if my pal, the 'ol Nobel Laureate Ernie heard you callin' him a poseur he would box yer ears...

Sid?, nah... no good for the terrace...he'd disturb the neighbors...

I'm having/had a great day!!! Absolutely!!! Well, your laureate Ernie might TRY to box my ears but then my gutter scum Mr. V might just intercede with some projectile.........vomit of course.

Chownah

there shall be no disreputable behavior on my new magnificent terrace...

[chownah]

I can just hear tutsiwarrior now as he greets the guests arriving at his party...."We have canopees in the carport, disrespecful behavior in the bedrooms, and waterpolo on the terrace!"

Chownah

[tutsiwarrior]

I can just hear tutsiwarrior now as he greets the guests arriving at his party...."We have canopees in the carport, disrespecful behavior in the bedrooms, and waterpolo on the terrace!"

Chownah

look out clownnah...the wife is gonna bring in the monks from the local wat to bless the new shop house and if you don't cool it I'm gonna have to tell them that there is a falang that is evil and wishes ill intentions on the magnificent new terrace...they may then have to do sumpin' that may damage your karma...

mods, shut this thread down before clownnah does any more damage to his wicked soul...