Platform Decks - We want to deck a flat roof; but the water is collecting in the middle. Need expert decking advice!?

We want to deck a flat roof; but the water is collecting in the middle. Need expert decking advice!?

we have a flat kitchen roof which we want to deck. Problem is water collects in the middle. What kind/style/method/mannar of decking do we need to ensure the decking drains to the side (rather than water collecting in the middle of the decking). Please make your answer as detailed as possible!! Many thanks everyone!! We also recentled had the flat roof re-tarred so no water is leaking into the room below. Basically a puddle forms in the same place each time it rains.

Public Comments

Sounds like the roof needs sorting before you put anything on top of it.
Let's see. Maybe you could put drainpipes that would go from the middle to the sides, and are tilted a bit. Basically, they run right through the roof. The ends that would direct the water are the same level with the roof, and the ends that spit water out are on a lower level; they go under the roof.
John H says that if the water is collecting in the middle the surface under the roofing felt has failed and will need to be checked out before you add more weight, try to avoid walking on it till it has been checked by a good roofer, sorry but it will not get batter by avoiding the problem or patching it and covering it with decking. If the roof is more than 10 years old it will be past its best and could fail in a heavy storm and cost you thousands if you take shortcuts
The style and decking is not the issue . The flat roof is the problem because it has either sunk in the middle on the joists or wasn't laid properly in the first place. Flat roofing is the easiest form of roofing there is but that doesn't help you. If I were you I would renew the roof or a cheaper option is to get a pre moulded fibre glass "cover" for the roof which will direct the water to where its required. I have tried to find a mouldings company for you but without knowing where abouts you are its pointless. To deck the roof after you will have to fix it to the exterior walls first as any pressure on the roof ie nails or fixings will puncture the roof and then "slat" the holding timbers from the exterior uprights and then deck from there.
get the experts in
Build up the low area with Insulated Sheeting, they make it for that purpose-and even comes tapered , draw a String line across the roof, see how deep the low spot is, then use Sheeting to even it out- its not heavy so weight should not be a problem. You should look below in the Kitchen and make sure there is no sag in the cieling- if so you need Framing support.
All decking should bbe laid with a slight fall so that rainwater doesn't collect but flows off.(e.g. 1 side is25mm higher over 3 metres). If the decking is already laid, you can drill a few small holes(3mm) where the water is pooling, these holes will be so small that you'd have to look for them to see them, but will be effective for drainage.
Careful !! you already have a serious problem with your roof because there is insufficient fall to keep the rain from puddling. Secondly the roof joists will have been sized to support the roof structure and not pedestrians. Better go back to square one and have a structural engineer run his eye over it and advise you
why decking,tile it with quarry tiles and create a run off at the same time.check the joist size,6*2" will be OK for a 3m span,8*2" for up to 4.2m span.
If your flat roof was leaking, the felt should have been stripped, the decking below (boards) checked and if additional weight is to be loaded- in the form of modern timber decking, planters etc, the joists should be strengthened/ increased. If the fall was not sufficient to shed rainwater into the gutters, firring pieces (long wedges) should first be fixed onto the joists before boarding over with either 18mm Sterling OSB3 of plywood boards. 3 layers of fully cross bonded high tensile felt, should then be applied, preferably with hot blown bitumen, solar reflective paint should be applied to cut UV breakdown of the bitumen. If the flat roof is to be used as a recreation area, promenade tiles should be applied for weathering/ fire safety along with balcony rails to sides for fall arrest.