Flat roof leak

[trevorbayliss]

I have a leak on my flat roof. It doesn't seem to be on the roof itself, but the way water is running off and down the wall. So we are getting a leak around the window area in the kitchen. I don't have a photo of the roof holding the water, but it seems it is holding a lot of water over this edge of the building (not running away to the other side where the gutter is).

Her are some photos to help show what i mean.

Any ideas ? It may be a case of taking everything up and putting a better slope on the roof.

 

[Brigade77]

My old man used to say that their are 3 things certain in life, "you were born, you will die & flat roofs leak".

I wish to add a 4th.

You can help stupid people all you want, but they just go off & do something else that's stupid.

 

[trevorbayliss]

What was the point in posting that info ? How did that help me work out what i can do to solve this issue.

Anyway, i have been watching some videos and have seen the GRP system. This looks pretty easy to me. I just need to strip off what i have and then relay the roof on a decent slope because i doubt it has one at the moment.

So does anyone know how i can engineer a slope onto the roof joists ? Can i buy some pre made chamfer pieces of wood to fasten to the current joists ?

 

[^woody^]

Those are parapet capping stones. Are you saying that your flat roof is at the height of those stones? If it is, that's your problem.

 

[^woody^]

My old man used to say that their are 3 things certain in life, "you were born, you will die & flat roofs leak".

Two out of three ain't bad I suppose.

 

[trevorbayliss]

No the roof is lower down. They are 20-30cm above the level of the roof. But the water is holding next to these edging stones and i think coming in to the kitchen somehow, under these stones.

 

[^woody^]

You can't have 300mm of standing water on a flat roof, so that it overflows over a raised parapet.

 

[trevorbayliss]

The water is only mm's deep because on the other side is a gutter and so i imagine the roof must drain off to that dose, but it is holding water around this parapet edge. I will try get a photo to show what is happening.

 

[chappers]

just a photo of the roof from the inside of the parapet will do

 

[trevorbayliss]

This is the roof. The roof is completely flat as had my level on it today. The section which collects water has a fall into that area, so away from the gutter side

I think i am just going to redo the whole roof in fibreglass and do it myself. Had a roofer have a look today as he was outside having a coffee and he said he could rejig the holding water section for about £200, but i reckon i can redo it all in fibreglass for about £800 (23 sq/m). If i don't need to buy new ply wood i can save about £200. So maybe £600

 

[vinn]

Your first post on saturday had the right idea to "take everything up and put in a better roof slope". You should also lift and do away with the parapet. You should then repair all damage and construct a warm roof to falls. At the moment you seem to have penetrating water going into the roof and the parapet walls which could mean possibilities of wood decay and electrical danger.
There can be no short cuts with roofing and the idea that a quick patching and repair fix that will give the roof local falls and can be made for £200 is make believe.

By the way, the rotting bedroom window frame has fillets of crumbling sand and cement used as caulking.

 

[trevorbayliss]

I think i will do this properly. On eBay the fibreglass kits are cheaper than what i was quoted today, so all looking good for me.

The internal roof is coming down tomorrow as i am doing a full rewire and we need access. The current insulation is looking like cotton wool. So needs some kingspan in there as well.

On these flat roofs, do you need to leave an air gap between the plyboard on the outside and the insulation underneath or can you just fill it all up ?

Windows are coming out as well.

 

[chappers]

If you are going to replace then do as Vinn says strip the whole lot back to the rafters, ditch the parapet. run firring pieces along the rafters to create a fall then ply and a VCL, then insulate above to create a warm roof no need to ventilate. Fit fascia along the wall where the parapet was with an arris rail curb or fibre glass profiles if you prefer.

 

[trevorbayliss]

any links on how a warm flat roof is made ?

Not sure where the insulation sits. IS it on top of the ply boarding ? How do you fix the insulation to the boarding ? Does the fibreglass go on top of the insulation ? Sorry a bit confused

 

[chappers]

now there's a question. traditionally plywood deck then insulation then a secondary plywood deckfixed through with long screws.
Nowadays there are loads of new products available some don't require the lower ply deck but may require a top plywood deck others need the lower ply deck but don't need the top deck others have a ply deck already bonded to the insulation.
For a fibre glass roof I would go with a make up as follows, you want it pretty ridged as fibre glass could otherwise crack if walked on

flat roof joist
firing pieces to obtain fall
18mm OSB or ply deck
VCL, either self adhesive or butyl taped along joist lines (self seals when screwed through)
insulation
18mm osb (takes fibreglass well) ideally tongue and grooved, but again not essential.Screwed through to joists, though there seems to be a movement towards gluing layers down
weatherproof covering.

Don't forget to infill open joists ends with insulation tight packed and any gaps sealed with foam and lap VCL up over the edges of the insulation too and ideally down over the joist infill insulation too(though this is really belt and braces)