Ponding issue on roof - help !

[shd1970]

So today was the day for ripping off the old felt roof and boards, laying new OSB3 T&G over my new joists (where the DPM is at the top of the photo) and the originals before laying an EPDM rubber.
By the end of today, a brand new roof....or that was the plan !

A day or so ago, i took off the chippings off the old felt roof in readiness and this morning, but to my horror this morning, yesterdays rain has shown what appears to be ponding :



The garage is 7.3m long with the run off/guttering at the back (where photo is take from)

Does anyone have any ideas how i resolve this please as i don't think firring/furring strips will be possible as the roof is too long ?
Alternatively, will this cause an EPDM roof issues, or being rubber, will it deal with it and natural wind movement rid the water naturally ?

Totally gutted, as was all set and today, the confidence has gone before i start and the builders merchants are only open till midday !!

HELP !

Thanks in advance

 

[^woody^]

You'll need to either rip down some bespoke furrings or make-up pieces, or fix some timber to the sides of the existing joists.

First thing is get the deck off and run some lines across to assess what you are up against.

 

[GoodDIYjob]

Yes mmm. check the fall looks inadequate.

 

[Munroast]

we have a 20 year old garden pond with this as a liner. Some say it lasts better under water as there is less UV to deteriorate it.

 

[GoodDIYjob]

I like it. I had a builder tell me some commercial felt roofs have sprinklers!! Still if the decking starts to flex it becomes a bigger and bigger problem. I guess it depends on depth!

 

[bernardgreen]

Water pooled on a roof is not a problem provided the roof does not leak. The layer of water reduces the effect of the sun heating the roof and this can prolong the life of the roof.

For what it is worth....

A bitumen and felt roof that was designed to be permanently covered in a few inches of water lasted for 50 years without any signs of a leak.

This was on architect Walter Segal's temporary house https://www.theguardian.com/cities/...y-walter-segal-self-build-south-london-estate"]

Known as the Little House in the Garden, this temporary structure lasted over 50 years.

The layer of water prevents rapid changes of temperature which is the prime cause of failures in flat roof.

 

[^woody^]

Pending water can increase cover stresses due to more frequent freeze/ thaw moment, which in turn reduces lifespan. So it's not advantageous, and is different to constant submersion under a depth of water.

 

[bernardgreen]

. So it's not advantageous, and is different to constant submersion under a depth of water.

Well it worked on Segal's "The Little House" and it worked on the small flat roof we had on our utility room and porch ( 15 years )
.
As regards cover stresses.

quoting from http://e-shootershill.co.uk/2014/01/05/segal/

The roof in the standard Segal design is flat, though with some critical differences to other flat roofs to avoid some of their problems. The waterproof membrane is not fixed down but laid loose on the roof deck, with a generous amount of overhang, like a table cloth. This allows the membrane to accommodate any movements in the building frame and to expand and contract with temperature, so it doesn’t crack or tear like fixed membranes. On top of the membrane is a 40mm layer of 20mm diameter shingle, which weighs it down and shields the membrane from direct sunlight.

 

[shd1970]

All,

Thanks for the quick replies and apologies for the delay
Thanks have been registered !)

I've literally just come down off the roof (well, at 22:00 much to the annoyance of my neighbours)

So after drying the felt and then ripping it off, the evidence (photo1) and reason (photos 2 and 3) was clear

The roof has been extended twice

Recently by me (the furthest green woodwork from the camera in photo 2) and by someone else previously as shown in photo 2 also where the brown boards are covering still

Photo 3 shows where the previous extension meets the original roof timbers (they are notched straight into the brickwork) albeit, the joists are 10mm lower, hence, the obvious bump in the felt

So, as i see it, i have 3 options :

1. plane/cut off 10mm off the top of the 4 x original timbers
2. fit 10mm wooden strips to the 1st extension attempt woodwork and all my woodwork (joists and headers
   
3. fit 10mm boards across the whole of my work and the previous attempt to raise the level

I'm think option 2 or 3 are preferable and edging towards option 2 rather than having the weight of the extra boards in addition to my OSB3 18mm

So option 2....would most agree this is the best approach ?

Either way, for option 2 or 3...what type of wood should i be using to bump up the level under the OSB3 layers ?
If not wood, is there any other product that would be suitable and fit the bill ?

Thanks again all for the replies, much appreciated as always !