How to remove standing water from GRP flat roof

[Fishyboy]

Hi all,
Our new-to-us house has an extension with a GRP flat roof, which was built 12 years ago. The roof probably had a decent fall when built and has two scuppers with drain down pipes. However, the central parts of the roof have gently sagged and water ponds after any sort of moderate to heavy rain. The puddles are about 10mm deep and don't reach the scuppers.

I am thinking of semi-permanently putting a manually operated puddle pump (https://www.henrypumps.co.uk/puddle-buddy-100-automatic-puddle-pump-2523-p.asp - ), which should be capable of reducing the puddle down to 1mm. I was thinking of attaching 25mm pipe and running it through the existing scuppers to the down pipes. The plan is to leave the pump up on the roof during the winter.

Does this make any sort of sense or are there some more practical solutions?

Thanks in advance.


Phil

 

[voipio]

There's no mention of the Puddle Buddy 100 being self-priming, so I'm guessing it will need to be submerged to at least the depth of the impeller compartment for it to prime properly. This would involve making a shallow sump in the roof, for the pump to sit in.

 

[Mark 5]

Hi all,
Our new-to-us house has an extension with a GRP flat roof, which was built 12 years ago. The roof probably had a decent fall when built and has two scuppers with drain down pipes. However, the central parts of the roof have gently sagged and water ponds after any sort of moderate to heavy rain. The puddles are about 10mm deep and don't reach the scuppers.

I am thinking of semi-permanently putting a manually operated puddle pump (https://www.henrypumps.co.uk/puddle-buddy-100-automatic-puddle-pump-2523-p.asp - ), which should be capable of reducing the puddle down to 1mm. I was thinking of attaching 25mm pipe and running it through the existing scuppers to the down pipes. The plan is to leave the pump up on the roof during the winter.

Does this make any sort of sense or are there some more practical solutions?

Thanks in advance.


Phil

Hi, a pump will help, as large as the puddle is is it deep enough for a pump to cope?

I am a fan GRP roofs, the roof is only 12 years old, I'd be wanting to know why the sag.

I have come across this before, be it the fall isn't correct or the sub-decking used wasn't a minimum of 18mm WP ply or both.

 

[Bullet2012]

leaf blower !

 

[gaz1]

the sag does depend on what the owners have done inside of the property

what beams have been used

is there a leak on that grp roof ...

as goes for the weight of the water its not important at 10mm

do you need to remove the water nope as it all depends on if it freezes badly whilst teh answer is you wont get much freezing where you are compared to more northern propertys

do i think your waisting your money and time in doing so to be honest yes

depends on what you have but it would need to have a full pic of the roof or take a few pics to show the whole roof on what you have before even i can suggest your best aproach to curing what you have

as goes for the insides is it full length and width between the walls

remember not all wood is dried properly alot of it is still wet when delivered

 

[DAPPH]

My mate had as similar problem . He made up a five inch at the ends and almost 6 inch in the middle ( like a humpback bridge) hollow box braced joist from Stirling board , galv nails , super grab contact adhesive out of a cartridge gun and some CLS giving it a 20 mm bow in the middle vertically , keeping the base level , then ACRO jacked it into the internal ceiling to lift it by say 20 mm inside the room then put strong wooden buttresses in at each end and boxed the lot in with plaster board ..
IIRC the span was in excess of nine feet
A different chain of thought .... perhaps the acidic condensate electric pump from a dead central heating boiler .
I can't recall how little depth was required or if it was on a timed supply that ran whilst the boiler was in operation . Mine outlasted the 10 yr old boiler

 

[brightspark]

its a pain in the a,rse but just live with it sweep it off every so often so it dont go green otherwise its re board it on a slope and a new fiberglass skin . id just l;eave it

 

[Bullet2012]

if it bugs you that much, just drill a few holes, the problem of water collecting on the roof will soon pale into insignificance with the issue of the wet floor in the room below.

 

[8ob]

Does this make any sort of sense or are there some more practical solutions?

Thanks in advance.


Phil

Get someone in to overlay with proper asphalt ( hot bitumen and sharp sand), goes down like a screed so you can re establish falls.

Bob

 

[roofman]

Form 1m long box gutters going into the low spots and out through the outlets, only need to be 100mm wide. Easy job which we do as an alternative regularly instead of taking all the boards off and laying on fairings to form a fall across the whole roof.

 

[voipio]

A wet vac (Vax or similar) would pick the water up, no bother, apart from having to climb up a ladder, unless the roof is immediately outside an upstairs window.

 

[CompoSimmonite]

I used a cheap automatic boat bilge pump when I had similar problem

 

[Agroshield]

Get someone in to overlay with proper asphalt...

If the roof is sagging, the weight of the asphalt will make it sag more. That makes it a practical problem to apply enough fall so that the water still runs away after the extra sag has taken place.

When you design roof joists, the roof covering material affects the self-weight imposed load you use in the calculations. It would be prudent to see if the roof construction is suitable for an asphalt overlay. That is the theoretical/engineering problem.

---

Knock a course of bricks from the perimeter walls as that will lower the outlets.

Do they make a wet version of those robot vacuum cleaners?

 

[cheb]

Strips of cotton held vertically so the bottom edge is in contact with the roof. The water will wick up the cotton and evaporate away. 100 or 150mm high should do it

 

[roofman]

If the roof is sagging, the weight of the asphalt will make it sag more. That makes it a practical problem to apply enough fall so that the water still runs away after the extra sag has taken place.

When you design roof joists, the roof covering material affects the self-weight imposed load you use in the calculations. It would be prudent to see if the roof construction is suitable for an asphalt overlay. That is the theoretical/engineering problem.

---

Knock a course of bricks from the perimeter walls as that will lower the outlets.

Do they make a wet version of those robot vacuum cleaners?

The water is not reaching the outlets.

 

[Bullet2012]

or keep the roof temperature at 100 degrees centigrade and the water will evaporate.

 

[iNf]

What about laying a rope in the water and down the outlet and see if capillary action will take the water away, cheap and easy to try.

 

[ajlelectronics]

If you can get the roof completely dry, lay up some fbreglass mat to level the dip?