Flat roof problems

Firstly, that sounds like a decent size so do it up and enjoy :-)

Sound like the problem is the way the under parts of the balcony have been constructed - wrong slope for drainage etc.

It may well be that the fibreglass has been a desperate attempt to fix a hopeless roof.

Anyway, I would go for fibreglass but applied correctly to a properly constructed roof/balcony.

At out last house we had a fibreglass balcony (somewhat bigger) at the back over a sun room and that was fine, but it did have proper joists, insulation, and a professionally applied deck.

Construction for something you walk and sit on should be much the same as for an internal floor with regard to joist thickness and spacing. Someone will be along with a calculator shortly :-)

If it has been leaking for some time you need to take the covering off anyway to confirm that there is no rot underneath.

Straightforward to DIY - our pet builders have just done three recently with no previous experience of fibreglass. One was a massive balcony, the other two were flat roofs to sun rooms.

The main trick is getting the roof itself properly constructed and insulated.

You can buy the fibreglass roofing kits off the Internet.

Cheers

Dave R

So you'd put the slope into the parapet wall? I think the OP wants to sit out there not have a goldfish pond. B-)

Looking at the pictures the slope is right as, as it quite common, the drainage point from the roof is between the end of the parapet wall and the main house wall.

If the newer looking darker grey stuff is the recently applied flashband that has nearly cured the problem I'd hazard a guess that the upstand has fallen away and or failed in some way. Perhaps along where it changes from horizontal to vertical. Have a good look around and up the outside edge where the water drains out, gales can blow considerable quanties of water through tiny holes.

The point loads from chair legs on almost any unprotected flat roof material worries me. I'd be tempted to cover it with 300 mm slabs spaced 1/2" or so apart to spread the loads, making sure there was nothing underneath them to puncture the covering.

Missed the pictures.

IMHO any design which slopes back to the house is ripe for problems - any issues with drainage at the edges and you end up with a swimming pool with the deep end by the house wall.

Joints between the wall and the deck are most likely to fail so it seems sensible to have the water drain away from the house, not towards it.

However in this case that could be a major re-design.

With regards to point loads - I know you get shouted at if you wear stilettos on a Yot but I don't recall any sailing or motor boat with flags on the deck to protect the fibreglass.

We certainly didn't have any problems with garden furniture on our fibreglass balcony.

Cheers

Dave R

No but heavy traffic areas there will be duck boards and you wear soft soled flat shoes...

Fibre glass bonded directly onto the decking is probably one of the more substantial coverings but I wouldn't like to say you won't induce micro cracks that will let the frost in and degrade it over time.

On Tuesday 20 August 2013 21:11 Dave Liquorice wrote in uk.d-i-y:

My roofer was less impressed by GRP - said he had to felt over one that cracked.

He had more time for butyl rubber but was still suspicous of how much it was liable to tearing.

If you are going to be walking and putting chairs on a flat roof you need to lay ?Promenade Tiles, over a waterproof base

Thanks for that link. I've seen these tiles elsewhere and like the rubber ones. Because of the point loading I was thinking I could build a very shallow wooden deck on top of the roof to help spread the load.

I've still to decide on the best (easiest) method of getting a good seal all over the roof. This site

I'm tempted to take everything up, lay waterproof ply on a continuous slope with a 1" drop over the 4m width of roof, cover the whole lot in hot bitumen (how many coats?) and put some sort of tiles (possibly these rubber ones) on top. Good idea?

Kit Jackson

The supporting "joists" will give linear "point loading", they would also have to be along any fall so as not to obstruct drainage.

Lots of what looks like good design information but as far as I could see only refers to bitumen based coverings. Nothing about GRP or butyl sheet.

I'm not overly keen on felt/bitumen based roofs, just had ours GRP'd. Time will tell... Flat roofs are just a pain, full stop.

Essential

That's only a 1:200 slope - I'd rather have a bit more if possible. It shouldn't be essential to have the ply waterproof - it should be dry under the top coat.

I think I'd be tempted to use butyl rubber as the waterproof layer rather than hot bitumen. I've had some on the shed (under the green roof) for about four years now, and it seems fine so far.

You certainly need something over the bitumen/rubber. Tiles, decking, *something*

Roofers generally neither understand nor like fibreglass, mainly because if properly done it lasts for many decades without needing repair. Using felt on a flat roof a roofer is not only establishing a job for life but one he can hand over to his son in due course confident it will be a good earner for many years of leaking.

On Thursday 22 August 2013 17:37 Peter Parry wrote in uk.d-i-y:

Possibly.

I will reinvestigate that in 15 years or so.

At least now it has the correct decking (OSB, not chip) and the soffits/edges are correctly profiled and vented. That was half the job.

GRP is ok if it has been laid properly on a very solid base and is a reasonable thickness otherwise it Will crack eventually and almost immediately if you walk on it once its aged over 10 years